A novel photoresist capable of dual-tone imaging, and a self-aligning two-level lithographic process which demonstrates its unique properties are described. This resist, composed of a positive and a negative photosensitizer in a phenolic matrix resin, can be imaged in either tone depending on the wavelength of exposure. In the self-aligned process, two distinct latent images, one in positive and one in negative tone, are generated simultaneously during a single exposure using a special mask. The latent images can be developed separately and independently. The alignment between these patterns is defined by the mask and is identical from wafer to wafer. The two patterns can be transferred to the substrate sequentially and with zero alignment error.

A novel, positive working, silicon-containing resist was developed for use in multilayer resist technology. The complexity of multilayer systems could successfully be reduced due to the dry development behaviour of the resist. Besides, the resist shows very high sensitivity on exposure to deep-UV radiation. Using appropriate sensitizers, the resist is also highly sensitive to g-, h- and i-line exposure, thus making the application in todays optical lithography possible. Submicron resolution could easily be achieved. Thanks to the high silicon content, resist structures were truly transferred into a planarizer resin by reactive ion etching in an oxygen plasma.

Polymers containing pyridinium-ylide units were prepared as water soluble MID UV resist materials. The absorption maxima of the N-iminopyridinium ylides are centered around 320 nm. Upon exposure the ylide sensitizer bleaches cleanly and undergoes two competing reactions, leading via a singlet state to 1,2-diazepines and via a triplet state to pyridine and nitrenes. Both reactions are accompanied by a change in polarity and can be used in the application as photoresists. This pronounced polarity change renders the polymers hydrophobic and water repellant. Therefore negative images can be obtained by development with pure water. Due to a quantum yield below 0.1 the sensitivity is low, but can be enhanced by addition of sensitizers.

The design and preparation of a mid-UV negative bleaching photoresist (BLEST) are described. This two-component resist system is composed of a cresol novolac resin and 4,4'-diazido-3,3'-dimethoxybiphenyl. BLEST is a negative working resist which has the advantage of alleviating optical interference effects caused by reflection from the topograhic features on the substrate surface. The resist is characterized by its photobleaching controllability which helps incident UV light to penetrate more deeply, thus realizing a high aspect ratio. BLEST was exposed to mid-UV light and developed in a tetramethylammoniumhydroxide aqueous solution. The sensitivity of the resist was about 150 mJ/cm2 and contrast was 1.7. A good resist profile was obtained by printing on a Perkin-Elmer Micralign 500 system.

Certain "onium salt" photochemical acid generators such as triphenylsulfonium and diphenyliodonium metal halides work as dissolution inhibitors for novolac resins in a fashion similar to diazonaphthoquinone. The two-component deep UV positive resists can be imaged in an aqueous base at 25 m.1/cm2 of 254 nm radiation. The system allows addition of a third component. For example, polyphthalaldehyde, a novel and efficient dissolution inhibitor miscible with novolac resins, is completely reverted to the starting monomer in the novolac matrix upon postbake. The design is based on removal of the polymeric dissolution inhibitor from the exposed areas through acid-catalyzed depolymerization to volatile monomer. Such three-component resist systems offer high deep UV sensitivity (2 mJ/cmh), high contrast (4.2), and wide formulation and process latitudes.

This paper describes the development of mid-UV photoresist materials based on the combined principles of chemical amplification and dissolution inhibition. These resists are composed of a novolac resin, a dissolution inhibitor containing an acid labile blocking group, and a photosensitive onium salt. A positive image is obtained by exposure to mid-UV irradiation, which generates a strong Bronsted acid from the onium salt, heating the resist so that the acid can catalyze deblocking of the acid labile groups on the dissolution inhibitor, and finally development with aqueous base. Interestingly, this system works well despite the fact that novolacs have previously been shown to become insolubilized by heating them in the presence of onium salt photoproducts.

The title compounds have been examined as photoactive components of two-part deep UV photoresists. All of the materials synthesized were soluble in typical photoresist solvents. Some were completely retained in photoresist layers baked at 95°C. The dependence of diazo compound retention on structure is discussed. Typical UV spectra of these photoresists are shown as well as the changes that occur on deep UV irradiation. Examples of typical development curves and PROSIM resist profiles are shown.

This paper describes the results obtained from studies of deep-UV lithographic properties of resists which utilize chemical amplification in novolac resins. These studies have shown that three-component novolac-based systems are surprisingly effective as deep-UV resists despite the high opacity of novolac at 254 nm. Analytical results are described which have measured the amount of Bronsted acid produced in chemical amplification resist films. The minimum acid concentration necessary for acceptable dissolution rates is far less than the corresponding active species content necessary for the proper functioning of diazoketone-novolac deep-UV resists.

Chemical amplification processes have been reported to be useful in the development of sensitive, high resolution photoresists. Acids, photochemically generated from onium salt precursors, catalytically remove a protective group from substituted hydroxystyrene polymers. Nonionic, acid precursors based on 2-nitrobenzyl ester photochemistry have been developed that have utility in resist applications. Several resist systems capable of imaging via chemical amplification processes have been evaluated in terms of their materials and lithographic properties. Resist with sensitivities ranging from ~15 to 150 mJ/cm2 in the deep-UV region have been prepared and 0.5 μm resolution has been demonstrated.

The use of nitrones as contrast enhancement materials has been extended to the mid-UV region. Diarylnitrones, which function effectively as near-UV contrast enhancement materials, have been found to be less suitable for mid-UV printing because of secondary photochemical reactions. α-Aryl-N-alkylnitrones, however, can be designed to absorb efficiently and photobleach cleanly over a wavelength range of about 280 to 350 nm. Arylalkylnitrones are much more resistant to hydrolysis than are their diaryl counterparts and have been successfully formulated as aqueous solutions. Submicron resist patterns have been printed with a scanning projection aligner operating in the mid-UV through the use of a contrast enhancement material based upon an arylalkylnitrone.

A contrast enhancement layer (CEL) process was developed with a commercially available contrast enhancement material on top of a novalac-based resist for use on a 5X i-line stepper. This process extends the resolution capabilities to the 0.5μm range while maintaining vertical resist profiles at all measured dimensions up to 2μm. In comparison to an image reversal process capable of achieving submicron resolution, the CEL process technique has increased resolution, improved control of linewidth bias and exposure latitude, and has an exposure time of one half that of the image reversal process, increasing the throughput in the exposure tool. The CEL process was developed for both submicron CMOS and bipolar circuits. It was used at the emitter level of the bipolar process to pattern emitters of varying sizes down to 0.6μm by 4μm with the required vertical resist profile. The poly level of the submicron CMOS work was patterned using the CEL process with poly gates as small as 0.5μm. It has also been used at the contact hole level of the CMOS work, replacing a two layer resist system. An analysis of optical linewidth measurements from both the CMOS and bipolar circuits will be given.

I-line lithography using contrast enhanced lithography (CEL) has been developed. With this technology, we used a newly-developed water-soluble contrast enhancing material. This material consists of p-morpholinobenzene diazonium chloride zinc chloride salt, poly(p-styrene sulfonic acid) and water. P-morpholinobenzene diazonium chloride zinc chloride salt's absorption peak is at around 365 nm. It also has high solubility in water and has excellent photobleaching characteristics. The poly(p-styrene sulfonic acid) as a matrix polymer prevents degradation of the diazonium salt in water, so it makes possible the long-term stability of the water-soluble contrast enhancing material. This lithography is capable of 0.5-μm pattern fabrication and it is convinced to be the major lithographic technology for 16 mega-bits DRAM production.

This article describes a new negative two-layer photoresist system formed by a simple, successive spin-coating method. An aqueous acetic acid solution of diazonium salt and poly(N-vinylpyrrolidone) is deposited so as to contact a phenolic resin film spin-coated on a silicon wafer. The diazonium salt diffuses into the phenolic resin layer after standing for several minutes. The residual solution on the phenolic resin film doped with diazonium salt is spun to form the diazonium salt-poly(N-vinylpyrrolidone) top layer. This forms a uniform two-layer resist without phase separation or striation. Upon UV exposure, the diazonium salt in the top layer bleaches to act as a CEL dye, while the diazonium salt in the bottom layer decomposes to cause insolubilization. Half μm line-and-space patterns are obtained with an i-line stepper using 4-diazo-N,N-dimethylaniline chloride zinc chloride double salt as the diazonium salt and a cresol novolac resin for the bottom polymer layer. The resist formation processes, insolubilization mechanism, and the resolution capability of the new two-layer resist are discussed.

The relative roles of ion bombardment and oxygen radicals have been examined for oxygen plasma etching of common photoresists and silicon containing resists. The degree of oxygen dissociation in the plasma has been measured as a function of power and pressure in the reactor. Etch rates for hydrocarbon resists increase with pressure over the range studied, although the ion bombardment energy and the flux of oxygen radicals decrease. This indicates that the supply of neutral oxygen molecules is the limiting factor in the range of operating conditions (20 to 80 mtorr) typically found in reactive ion etching (RIE). The role of ion induced damage is small for standard resist etching but the damage aids in the formation of an oxide layer when etching silicon containing materials.

The DESIRE process is based on a selective silylation of the exposed areas of the resist. We demonstrated earlier that this selective silylation is caused by a selective differentiation in diffusion rate of the silylating agent into the exposed areas. The naphthoquinone diazide, which is a vital component of the resist, seems to block the diffusion of the silylating agent very efficiently as long as it is not exposed. The exposed diazoquinone on the other hand will enhance the diffusion, thus resulting in a high differentiation in diffusion rate in exposed versus unexposed areas. An earlier study carried out by researchers at Philips showed that polyfunctional diazoquinone esters were more efficient in creating high selectivity than the monofunctional analogs. This was explained in terms of hydrogen bridge formation in the unexposed areas. We now have found that part of the effect is probably due to thermal crosslinking of unexposed naphthoquinone diazide during the baking time that proceeds the actual silylation. This silylation is typically carried out at 120-160°C and it was found that the time and temperature of the presilylation bake have an important influence on the required silylation time and the obtained contrast. It was also found that, after prolonged baking before the silylation, the diffusion of the silylating agent into the resist becomes slower and better selectivity, profiles and process latitude are obtained.

Recently, three approaches to sub-micron imaging using negative working, aqueous developable, novolac resin or poly(hydroxystyrene)-based resists have been reported: (1) Image reversal of positive working photoresists (2) Acid hardenable resist with post-bake process, and (3) Contrast enhanced-resist with deep uv flood exposure. Negative working resists with high resolution are important for fabrication of advanced devices. In the present study we examine a simple two component system consisting of a chlorinated novolac resin and an aromatic bisazide suitable for uv, electron and x-ray exposure. The resist is conventionally processed in aqueous developer, and provides negative working resist images with 0.25 μm space and line resolution without swelling or scum.

Two new concepts,"masking effect" and "internal CEL", are proposed to design a high resolution quinonediazide-novolak type photoresist. On the basis of these two design concepts, we optimized the composition of the resist, and succeeded in developing a high resolution resist, which is composed of m-cresol/p-cresol/xylenol/formaldehyde novolak resin and 2 ,3 ,4 , 4' -tetrahydroxybenzophenone 1 , 2 -naphtoquinonediaz ide-5 -sulfonate. This resist can resolve as small as 0.6 um lines & spaces with aspect ratio of 2.7 (NA.0.42) and has the gamma value of 2.0.

Fluorescence techniques were used to study the effects of casting solvent and film thickness on spin cast novolac films. A fluorescent probe, pyrene, was covalently bonded to the novolac backbone, and changes in its fluorescence were used to monitor the effects of casting on the films. The amount of excimer fluorescence depends on casting solvent and rises dramatically for very thin films (<2000 A), perhaps indicating an increase in ordering. Novolac polymers with various levels of pyrene tagging were used to measure the extent of pyrene aggregation. The tagged and free probes had similar responses at low concentrations (<= 5 mol% probe) but at high probe concentrations (20 mol% probe) the free probe aggregates to a greater extent than the tagged probe. The extent of aggregation is also affected by the casting solvent.

This work evaluates the performance of an Image Reversal (Im.Re.) resist with dye added (0-1% by weight) in order to minimize reflectivity effects over aluminum topographies. Planarization over 1-1.5 μm. aluminum steps is studied as a function of viscosity using Im.Re. dyed resist. It is shown that Im.Re. process performance is not only influenced by dye concentration and exposure energies, but it is also significantly affected by the resist composition. High plasma selectivity and sidewall profiles of 85 degrees or higher are obtained with 1.2 μm. coating thickness, resolving 1 μm. 1/s geometries and lower, with limiting resolution, over topography, of Im.Re. dyed resist established in the 0.7-0.9 μm. region.

The role of surfactants and agitation in improving the performance of diazo type positive photoresist is explored through dissolution measurements, quantitative models for process simulation with SAM-PLE and SEM profile comparison. In-situ dissolution measurements of a commercial resist, Shipley 1400-31 in MF312, 314 and 319 developers were made on a Perkin Elmer development rate monitor (DRM) with and without moderate agitation. The quality of the measurement data was improved by using a nitride-oxide-nitride thin-film coating to reduce standing wave effects within the resist. Both developers with surfactants, MF314 and 319, show improved contrast over MF312 in plots of thickness remaining versus exposure dose. Although contrast was improved in all three cases by agitation, the effect was most pronounced with MF314. R(M) plots, obtained from combining dissolution rate data with exposure state, distinguish surface retardation effects from bulk effects and suggest that the improvement in contrast for MF314 is due to enhanced surface rate retardation. Using the rate parameters extracted from the R(M) plots, resist profiles were simulated and compared to SEM profiles of fine-lines.

An organosilicon resist was investigated for use in deep UV laser lithography. The resist was based on 0-trimethylsilyl poly(vinylphenol) resin. It was found to exhibit transparency at 248nm comparable to the transparency of g-line light in conventional novolak resists, making single-layer resist processing possible. The results of single-layer and bi-layer patterning on an excimer laser contact printer are presented. The bi-layer processing uses oxygen reactive ion etching (RIE) for transfer of a top layer pattern into a thick underlying novolak layer.

A new positive working photoresist which is applicable to the bi-layer resist system using a current g-line stepper has been developed. This resist consists of a naphthoquinone diazide photoactive compound and a silicon containing novolak resin, which is synthesised from phenols with siloxane groups(-Si-O-), and formaldehyde by condensation reaction. The Si-containing resist has a resolution capability of 0.5μm L/S with a g-line sensitivity about 250 mJ/cm2, and a high resistance to oxygen plasma, with an etching rate ratio of 61:1(photoresist/Si resist). 0.5μm L/S pattern was precisely transferred to the bottom layer by 02 RIE with vertical side walls.

The aim of this work was to determine the effect of aging on absorption, thickness and dissolution characteristics of precoated photoresist blanks. Experimental results indicate that the aging of photoresist involves bleaching and darkening reactions. The temperature dependency of these reactions follow the Arrhenius Law.

In this paper, dissolution rate characteristics for high resolution positive photoresists are studied. The dissolution mechanism investigated by changing the concentration of photoactive compound, PAC, in the photoresist is also presented. Based on these dissolution rate characteristics, a new dissolution model and an analytic rate function are proposed. Dissolution rate, R, was measured as a function of relative PAC concentration, M, by changing exposure dose. It is found that R(M) is divided into three regions, depending on M values. These characteristics are commonly observed in high resolution positive photoresists which can resolve 0.5μm L/S with a high NA (0.45) g-line steppiere These behaviors cannot be explained by conventional dissolution model proposed so far.I To investigate this dissolution mechanism, dissolution rates, RI(M), of non-exposed resist (PAC+novolak) and ,RE(P), of fully-exposed resist (PPA+novolak) were measured. Log RE is almost proportional to PPA concentration, P. On the other hand , log RI shows a drastic change at the medium PAC concentration. R(M) expressed as a product of RI(M) and RE(P), agreed with measured dissolution rate. From these results,it is considered that the distinctive dissolution behavior of high resolution positive photoresist is mainly attributed to the PAC inhibitation effect. Based on these dissolultion rate behaviors, a new analytic dissolution rate function is proposed. SAMPLE simulation results show good agreement with the experimental pattern profiles.

A novel ladder structure silicone resist, silylated polyvinylsilsesquioxane (PVSS), was developed as a negative bi-level electron-beam or UV resist, showing high sensitivity, half micron resolution and an excellent oxygen reactive-ion etching (02-RIE) resistance. PVSS was prepared by hydrolyzing vinyltrichlorosilane and subsequent polycondensation and silylating active silanol groups. PVSS has vinyl functional groups as a side chain, making it highly-sensitive to electron beams. High resolution PVSS resist with a narrow molecular weight distribution was prepared by fractional precipitation. PVSS patterns are not etched and softened during the 02-RIE due to the large amount of silicon atoms and. high melting temperature. The 02-RIE etching rate of PVSS is about 100 times smaller than that of the planarizing layer and PVSS melting temperature after electron-beam exposure is above 2001. A 0.5 μm line-and-space pattern can be delineated at a dose of 7.6μC/cm using PVSS bi-level resist with molecular weight of 1.1 X 104 and dispersivity of 1.5. Also due to vinyl functional groups, PVSS resist to which adequate photoinitiator has been added is sensitive to UV light. PVSS resist is sensitive to the Ng lamp i-line(365.nm) when 2.6- bis-(4-azidobenzal)-4-methylcyclohexanone is added. It is sensitive to deep UV light when 2,2- dimethoxy-2-phenylacetophenone is added. PVSS UV resist has a 0.5 μm pattern resolution at a 1:1 contact exposure. Synthesis, molecular weight precipitation, and lithographic characteristics of PVSS are discussed in the sections that follow.

The mechanism of the post exposure bake effect, PEB, was studied in detail on several model photoresist compositions containing well defined PAC structures and novolak resins. Under standard processing conditions, reduction of standing waves was found to be dependent on the PAC functionality, PAC molecular size, resin glass transition temperature and on the solvent retained in the photoresist film. These results are all consistent with diffusion as the dominant mechanism of the PEB effect. PAC size was varied from 366 to over 1800 Daltons and resins were selected with glass transition temperatures, Tg, below and above the PEB temperature. Above the resin Tg, the PEB effect was found to be strongly relates to PAC size, with very large PAC molecules showing miniml standing wave reduction. When the PEB temperature is below the resin Tg, standing waves are eliminated only in photoresists containing the smaller PACs. Solvent retention enhances the PEB effect. PAC thermal decomposition, with or without indenecarboxylic acids, was found to be an insignificant contributor to standing wave reduction in normal PEB processing. Furthermore, experimental and simulation results indicate that the initial size of standing waves depends on the PAC functionality and the dissolution selectivity of the resist system. The dependence of diffusion on PAC size has important implications for lithographic modeling, particularly for resist compositions containing mixtures of PAC's of different sizes and degree of esterification. Resist compositions with very large PAC's or very high Tg resins may show limitations with respect to the range of practical PEB processes.

A novel dry develop method of photoresist - "unzipping development" by flood UV irradiation is described. Evaluated resist consisted of poly-methyl methacrylate (PMMA) and unzipping inhibitors such as p-benzoquinone (p-BQ) and 4,4'-diazide diphenylmethane(4,4'-DDM). As a preliminary experiment has shown that 4,4'-DDM was superior to p-BQ as an unzipping inhibitor, a resist : PMMA added with 40 wt% was mainly evaluated. At patterning exposure (600 ~ 1200 mJ/m2 at 210 ~ 280 nm), 4,4'-DDM in the exposed area fixed into polymer. Then, 4,4'-DDM in the unexposed area was removed in vacuo (0.4 mmHg at 120°C for 1 hr). Finally, negative resist pattern of 1.6 μm was developed by flood UV irradiation (24 J/cm2 at 254 nm) at 90 ~ 130°C without using any solvent. Mechanistic studies were carried out by using IR and UV analyses.

A kinetic approach to thermal processing of labile resist materials is proposed which compensates for non-isothermal heat treatments, run to run thermal variations and batch loading effects. This technique was used to control ammonia catalyzed image reversal processing and allowed consistent definition of 0.5μm and 0.6μm linear features using a g-line stepper equipped with 0.42 and 0.35 NA lenses respectively.

Material for Contrast Enhanced Lithography ( MCEL ) containing diazonium salt as a photobleachable material was developed for submicron optical lithography. New MCEL offers the following advantages. 1. Good thermal stability in solution and in film. 2. High A value ( A value : max 12 μm-1 ). 3. Good solubility to alkaline solution. 4. Excellent wettability. 5. No intermixing layer between MCEL and photoresist. In this study, we investigated the effect of MCEL on the characteristics of photoresist, such as sensitivity, gamma value, resolution, development time, exposure latitude and focus latitude, using a g-line wafer stepper with 0.35 NA lens and commercially available photoresist A as bottom layer. Key results are: 1. Incident dose was about 3 times larger than that of photoresist A. 2. Gamma value, resolution was remarkably improved and 0.7 μm line and space pattern with vertical wall was obtained and also the resolution of 0.6 μm line and space pattern was possible. 3. The focus tolerance was wider, however, the exposure tolerance was not improved. It is confirmed that newly developed MCEL had excellent properties for achieving the submicron fine patterns and wide process tolerance which assured high yields of the integrated circuits production.

The performance benefits of multilayer resist processes are well known, but because of the additional processing complexity their use has been restricted mainly to lab scale or pilot line environments. More recently a surface sensitive scheme [1], the so-called DESIRE process, has been developed. It has the potential of reaping the benefits of multilayer resist processes without their process complexity. In this paper a preliminary characterization of the lithographic performance of this process is described. In particular the issues of resolution, focus latitude, exposure latitude and uniformity are examined. When the appropriate silylation and development conditions are used, the data clearly show that a significant improvement in the working stepper resolution can be achieved while maintaining the uniformity across the wafer. In a 0.28 numerical aperture lens stepper, the exposure latitude first becomes the resolution limitation. Using the DESIRE process a five-fold increase in the exposure latitude is achieved as compared to an optimized process using conventional development. As the stepper numerical aperture increases, the focus latitude becomes the limiting factor to resolution. Using the DESIRE process the focus latitude increases nearly two-fold in a 0.35 numerical aperture stepper as compared to conventional processing. This preliminary characterization study shows that the DESIRE process has the potential of extending the useful life of optical projection printers.

A multilayer resist structure is typically composed of at least two materials, an oxygen plasma resistant layer and a planarising layer which is eroded in an oxygen based plasma. This structure is then subjected to a variety of excited and ground state species generated in the plasma. To understand the final etched profile produced by such a system, it is necessary to characterise both the chemical nature of the plasma, and its impact upon the structure subjected to the etching process. This paper will discuss the effect of the intrinsic plasma properties such as composition, density, potential and electron energy distribution upon the processes which produce etching of both the planarising and etch resistant layers. The effect of the chemical composition of organometallic etch barriers based on silicon, germanium and iron and the process by which they resist these plasmas will also be presented and compared with the properties of the planarising layers. The etching properties of the planarising layer will be shown to depend strongly upon the plasma excitation frequency.

A steady-state model has been proposed to predict the oxygen reactive-ion-etching resistance of organosilicon polymers. This model is based on a Silicon material balance and the assumption that a protective Si02 film forms and reaches a steady-state thickness on the surface of the polymer. At steady-state, the rate determining step is sputtering of the SiO2 film. This model predicts that the steady-state etching rate is proportional to the sputtering rate of Si02 and inversely proportional to the mass density of silicon in the polymer. It also predicts that the etching rate is independent of other chemical or physical properties of the material. This model accurately predicts the etching behavior of a silyl novolac polymer over a wide range of etching conditions. Two silyl methacrylates etch at the predicted rate under conditions typical of trilevel processing, but exceed the predicted rate under conditions where the average bombardment energy is lower. Surface analysis shows that the steady-state approximation is not valid for the methacrylates under these etching conditions; the oxide thickness continues to increase with time, even though a constant etching rate is achieved. Polymers with very low silicon content do not etch according to the model but form highly porous oxides that continuously accumulate on the surface of the polymer.

A new silylated resist process has been developed that provides the advantages of trilayer photoresist processing in a simpler bilayer format. In this new process, silicon for oxygen plasma etch resistance is added to a conventional photoresist layer after it has been exposed and developed. This silylated resist image provides an etch mask for 02 RIE etching of an underlying organic planarizing layer with 15:1 selectivity, vertical profiles, and high resolution. The process is positive-working, uses conventional materials, and improves the thermal stability of the resist image.

A new alkali-developable organosilicon positive photoresist for a bi-layer resist system has been developed. Novel alkali-soluble organosilicon polymers, polysilsesquioxane, polysiloxane, and polysil-methylene, were prepared as the matrix polymers. Among these polymers, poly(p-hydroxybenzylsilsesquioxane) ( I) exhibited the highest 09RIE resistance. A composite (OSPR-1334)prepared from I and naphEho-quinone diazide becomes an alkali-developable positive photoresist which is sensitive to i - g line light. The sensitivity and the resolution of OSPR-1334 are almost the same as those of conventional novolac-based resists when aqueous tetra(2-hydroxyethyl)ammonium hydroxide is used as the developer. Also, OSPR-1334 has excellent resistance to O2RIE. The etch rate is 3.6 nm/min, while that of polyimide or novolac-based resists is 100 nm/min. Thus, OSPR-1334 is suitable for use as the top layer of a bi-layer resist system. Submicron patterns with high aspect ratio can be easily obtained with this new bi-layer resist system.

Polysilanes are high Si-content polymers containing backbone Si-Si bonds. Their high Si content makes them very resistant to removal by 02 reactive ion etching (RIE) while their Si-Si bonding results in strong transitions in the mid- and deep-UV regions. Mid-UV photolysis causes chain scission, a process used by IBM workers in two lithographic applications: as imaging layers in organometallic bilevel, 02-RIE-developed resistsl and as contrast enhancement materials for imaging with positive photoresists.

A new silicone-based positive photoresist(SPP), composed of an alkali-soluble silicone polymer with diazonaphthoquinone, is developed. The sensitivity of SPP to near-uv light is almost the same as that of conventional photoresist(OFPR). SPP shows high dry-etching durability to 02 RIE. The etching rate ratio of SPP to OFPR is over 20. This high dry-etching durability allows the fabrication of thick OFPR resist patterns using an SPP pattern mask. A 0.6 μm line and space is clearly resolved in an SPP/OFPR resist system when exposed to a GCA stepper (NA=0.38)

This paper describes problems encountered in VLSI imaging and pattern transfer, via dry develop, over topography steps up to 1.5 μ in height. The dry develop method studied in this paper involves a vapor-phase silylation process, with consideration being given relative to overall production needs. Specifically, the following issues are considered: a. The choice of the resist to be used in the silylation process: for example, it was noted that the rate/degree of silylation varies with spectral sensitivity of the photoresist (see Table I), i.e. I-line/mid UV systems have shown to be more successful than conventional G-line photoresists. Specifically, positive photoresists that contain coupled, 2-1-4 diazoquinone/novolak esters as sensi-tizers, appear less prone to residual "grass" formation. This being unwanted SiO, formation in the unexposed areas which are then transferred to the wafer surface. b. The type of silylating equipment, the silylating agent, silylating conditions relative to time, temperature, and pressure were evaluated. For this study, the incorporation of hexamethyldisilizane was utilized in a piece of equipment modified to heat the "HMDS", thereby increasing its vapor pressure. c. Processing conditions required for dry developing in Reactive Ion Etch (RIE) vs Magnetron Ion Etch (MIE) were evaluated such as power, pressure, gases, flow and time. d. The potential effects of other variables were also addressed, such as the "HMDS" vapor time and exposure energy requirements needed for adequate silicon/oxide formation. The effects of such variables were studied relative to their impact on the dry development/etch conditions needed.

The leveling of 100 - 500 μm wide, 1 pm deep isolated holes and trenches by 1 - 3 μm thick silicone oil films was observed by measuring film thickness changes at the centers of the features using a non-contact, interferometric technique. The dependence of the leveling time t on feature width w, film viscosity n and the initial film thickness h0 was investigated and compared to theoretical predictions. Experimental data were obtained for various values of w, n and ho. Except when the film thickness was about 1 μm the data for each different type of geometry fell on a single curve when the degree of leveling or planarization was plotted against T E tyh03/nw4 where y is the surface tension of the film. At the same value of T, the degree of planarization of isolated holes was about twice that of isolated trenches. The planarization vs. T curves should apply to all Newtonian liquids and may be used to predict the degree of planarization that will be achieved at specified leveling times by materials having specified values of n, h0 and Y. Thus, the curves may be useful in selecting planarizing materials for semiconductor fabrication steps that require substrate topography leveling. Simulations of the leveling process based on capillarity-driven flow were performed and agreed well with the experimental data. The simulations predicted some interesting and unexpected behavior that was observed experimentally. At short times the planarization worsened before improving at longer times, and "humps" appeared in the film profiles that apparently are a first step in minimizing surface energy. Such simulations may prove to be useful in predicting the difficulty of planarizing various types of topographic geometries.

The details of photoresist dissolution kinetics play a major role in image quality and process control, especially at sub-micron geometries. Kinetic parameters for photoresist dissolution are obtained using methods familiar to most lithography engineers. For example, activation energies can be extracted from the temperature dependence of dissolution rate while chemical reaction orders are obtained from the variation of dissolution rate with developer concentration. Taken together, these data provide valuable insight, not only about the mechanism of dissolution but also about the details of resist performance. Large chemical reaction orders and negative activation energies are observed at low to medium exposure doses, which prevail at the edges of lithographic features. The decrease in exposure selectivity at lower temperatures might suggest that higher resolution can be obtained at higher developer temperatures. Furthermore, a resist-developer combination which exhibits a strong dependence of reaction order on exposure energy is expected to show higher selectivity than a system with a lower reaction order-exposure dependence. Other desirable lithographic properties such as sidewall angle, latitude and resolution will follow the same trend. In this paper, the results of experiments in dissolution kinetics are tied to submicron lithography through semiempirical Prosim modeling. Activation energies are measured for various exposures and developer concentrations. Dissolution reaction orders are obtained for various developer temperatures and exposure energies. The computer modeling program, Prosim, is then used to model resist characteristics under various conditions. These include exposure, focus and mask-matching latitudes as well as resist profiles. Prosim calculations are verified by selected applications results which illustrate the influence of kinetic parameters on lithographic performance.

Novolacs which alternate p-cresol monomer units with polyhydroxyphenyl monomer units have been synthesized by acid catalyzed condensation of 2,6-bis(hydroxymethyl)-p-cresol with polyhydroxybenzenes such as resorcinol or 4-chlororesorcinol. These novolacs are highly alkaline soluble and exhibit improved glass transition temperatures relative to conventional novolacs. Unexpected developer cation effects have been observed on the dissolution times of some of these novolacs. The effect of molecular weight on these effects will be discussed for one system. The dissolution discrimination and inhibition of a 4- chlororesorcinol containing novolac was examined relative to a standard m-,p-cresol novolac and polyvinyl phenol. Images produced from a resist using a p-cresol/ 4-chlororesorcinol novolac showed no significant image degradation at 200 degrees C.

The relationship between the molecular weight distribution(Mw/Mn) of novolak resins and performance of positive photoresists was investigated from the standpoint of the image formation process. Dissolution rates were measured on photoresists containing cresol-novolak resins having various Mw/Mn values. It was found that there is an optimum Mw/Mn value to exhibit high resolution capabilities. On the basis of experimental results, we discuss the roles of high molecular weight components and low molecular weight components of novolak resins in resist performance. Finally, we propose a new model for positive photoresist development---"Stone wall model", which is consistent with our azocoupling model for the dissolution inhibition mechanism. This model is applicable to design novolak resins for high resolution positive photoresists.

A design of g-line positive photoresists has been conducted by using SAMPLE simulation for the purpose of providing higher resolution and more vertical profile. By varying resist parameters in the simulation and knowing their influences on the physical properties of resists, some useful guiding principles for the design of submicron resists have been obtained. It was found that an increase in the amount of photobleachble component (A) was effective for the improvement in resolution, and an increase in dissolution rate of unexposed part (R2) was also found to be effective for the improvement. However, the same factors were found to give rather negative effect to the steepness of the profile. Thus a trade off relationship between resolution and profile was suggested from the same simulation. The trade off relationship was also confirmed in experimental observations. Based on the above, a new positive photoresist was designed, however, which in use, exhibited not only higher resolution but also better profile than the conventional resist used as a reference. The simulated profiles of the new resist on submicron imaging were not consistent with the actually observed images. A modification of the resist development modelling was made for more precise simulation of the new resist. A revised model incorporating "proximity effects in the development" into the parameter definitions, yielded results which were consistent with the actual images.

Thermally induced and base catalyzed reactions of a phenol ester of 1,2-naphthoquinone-diazide-5-sulfonic acid (DAM) with p-cresol were investigated. In total seven reaction products were obtained for the thermally induced reaction. The three major products, TR--F4, TR-F6 and TR-F7, were isolated and their structures were determined by means of several advanced spectroscopic techniques like Fourier transform nuclear magnetic resonance (FTNMR) and field desorption mass spectroscopy (FD-MS). Besides a cresol ester of indenecarboxylic acid (TR-F6) and an azo compound which contains two DAM originated moieties and cresol (TR-F7), the formation of a novel compound was found; a phenol ester of 2-cresyl-l-naphthol-5-sulfonic acid. On the other hand, four reaction products were found in the base (a 2.38wt% tetramethylammonium hydroxide aq. solution) catalyzed reaction products of DAM with p-cresol, and two major products, BC-Fl and BC-F3, which appeared at the initial stage of the reaction were isolated. The structure determination of the two major products was carried out in the same manner as described above. It was discovered that BC-Fl was a cresol ester of 1-naphthol while BC-F3 was an azoxy compound. Brief discussions will be made on those reactions of naphthoquinone diazides with a matrix novolak resin with reference to the results obtained by the present study.

X-ray exposure of selected novolac resins and commercial novolac-based resists show more varied end products and more crosslinking reactions than observed in the UV exposure. E-beam and x-ray induced reactions are somewhat similar. Novolac resin without the photoactive component (PAC) was shown to crosslink suggesting that x-ray and e-beam mechanisms must take this into account. Difference FTIR spectra were indicative of the structural changes. Mass spectrometry was less effective because of the volatility of PAC, although novolac resin without PAC was shown to contribute to the gaseous byproducts of exposure. The role of crosslinking of the novolac resin in process latitude and image reversal is discussed.

A resist dissolution data analysis tool (PARMEX) has been developed for automatically determining quantitative resist models for use with simulators such as SAMPLE and Prolith. In this software tool, models for both optical and electron beam exposure are supported. Dissolution rate is first related to fundamental exposure state descriptions, such as the normalized fraction of photo-active compound (PAC) exposed or the e-beam deposited energy. The use of rate versus exposure state plots cleanly distinguishes phenomena such as surface rate retardation from resist contrast. An optimizing routine is then used to best fit user specified models to the data. The software is capable of analyzing data for optical exposures on both reflecting and matched substrates. The concept of a "current working set" is introduced to facilitate the use of multiple wafer data sets in the analysis. The raw data can be input in the form of reflectivity versus time, thickness versus time or rate versus depth. The capabilities and utility of the software tool are demonstrated through analyses of Perkin-Elmer DRM measurements for optical exposure of Shipley Microposit 1400-31 on reflecting and non-reflecting substrates, and electron-beam exposure of Hitachi RD2000N using the Perkin-Elmer AEBLE-150. The software allows differences in resist performance, such as those due to surface rate retardation or thermal heating at high electron-beam current to be easily distinguished.

Characterizing the effects of the many variables that are a part of photolithography is not an easy task. As more sophisticated patterning techniques, such as contrast enhancement lithography (CEL), are introduced the number of variables increases. Two tools are commonly used to deal with the complex task of understanding the interrelationships of these many variables: experimentation and computer simulation. While experimentation, and in particular statistically designed experiments, can give a great deal of insight into a particular system, it is often difficult to extrapolate trends outside of the experimental conditions (e.g., to other lithographic systems). Computer modeling, on the other hand, is rather poor at predicting exact outcomes of specific conditions, but is at its best when predicting trends which may exist over a broad or narrow range of conditions. There exists, however, an uncertainty as to how accurately the model reflects conditions of the real world.

A new method of monitoring a photoresist process is described, in which the changes in the physical and chemical properties of the photoresist act as the monitor for each process step. This method provides unique insights into the photo process by independently monitoring each step and substantially improving the quantitative accuracy at each step. Examples of the potential of this method for process monitoring and process control improvements are given.

The advantages of minimizing polymer resist thickness to the macromolecular dimensions are manifold. In optical lithography, ultrathin resists can improve exposure and focus latitude and alleviate the problem of absorption in conventional resists for deep ultra-violet (UV) exposure. In electron beam lithography it is desirable to reduce the resist thickness to minimize forward electron scattering in the resist, and to allow penetration when using the scanning tunneling microscope (STM) as a very low voltage exposure source. Moreover, we can better understand many phenomena such as the nature of the pinholes and etching resistance, which are still puzzles for the thicker films. Here we describe the preparation and characterization of resists of ultrathin polymer films (10 nm to 200 nm) formed by both the Langmuir-Blodgett (LB) and spin-cast techniques. The characterization techniques include fluorescence spectroscopy, electron beam exposure and development, and etch resistance. The fluorescence spectroscopy results of spin cast polystyrene films suggest a dramatic increase in the ordering of the molecular structure as the film thickness is reduced below 0.2 μm; this increase is most marked for materials of large molecular weights. This suggested that the lithographic properties and the defect (pinhole) density of such films might be significantly different from the results expected by extrapolation from thicker (>200 nm) films. Ultrathin poly(methylmethacrylate) (PMMA) films (thinner than 20 nm) prepared by LB and spin-cast techniques and novolac resists prepared by the spin-cast technique were explored as electron beam resists, using a Perkin Elmer MEBES I pattern generation system for exposure. The results have demonstrated the resolution and etch resistance capabilities of such films for patterning 0.1 μm features in 50 nm of chromium film. The most surprising result has been that the pinhole density in these films has been far lower than previously expected levels.

The lithographic requirements for half-micron and sub-half-micron design rules are discussed in terms of the resolution capability of 436 nm, 365 nm and 248 nm reduction steppers, the depth of focus, bulk and reflection effects and the impact of using advanced single-layer resist systems instead of conventional positive photoresists. Using the simulation model SLIM (Simulation of Latent Image Manipulations) the distribution of the product of photolysis in the latent image is calculated as resulting from patternwise exposures and resolution enhancing procedures as Image Reversal (ImRe) and Built In Mask (BIM). On the basis of the concentrations and gradients arising from patterning with 365 nm in a 1.5 μm thick resist layer it is shown that, using an i-line lens with 0.42 NA, the patterning of 0.5 μm lines and spaces will be possible. For sub-half-micron dimensions a shorter wavelength (e.g. 248 nm) is required to ensure a sufficient image contrast. A difficulty that arises at this wavelength is that novolak-based photoresists exhibit a very low transparency, thus hampering the penetration of UV-light in the resist layer. It is shown that, in order to image these resists in the positive mode either the absorptivity of the resin or the thickness of the resist layer has to be reduced considerably. Alternatively a 'top-imaging' procedure, as for instance BIM and DESIRE could be used. In this case a penetration depth of the imaging UV-light of 0.3 μm may be sufficient. An additional advantage of these procedures is that both the problem of limited focus depth and the detrimental effects caused by reflection of UV-light at the substrate are alleviated.

The linewidth fluctuation which is caused by interference effect is a very serious problem for critical dimension (CD) control. Three simple resist linewidth fluctuation reduction methods are investigated. These methods are high-contrast resists, dyed resists, and contrast enhancement material (CEM). One-micron line and space patterns of various resist thicknesses are formed on silicide by exposing with a g-line stepper and the degree of linewidth fluctuation is measured. As a r result of the investigation, the high-contrast resist is the most effective method and the degree of linewidth fluctuation of the high-contrast resist is suppressed to about 60% of that of a conventional resist. The degree of linewidth fluctuation of the dyed resist and CEM used with the conventional resist is about 65 and 80% of that of the conventional resist, respectively. Therefore it is considered that high-contrast resist is the most effective method for tight CD control which is needed for 4MDRAM-level devices.

PCM-, trilevel-RIE- and singlelevel-RIE-resist systems are investigated for application in submicron technology. Simulation results of the PCM-technique are compared with experimental results using the K809/PMMA system. Gate and sub-micron contact hole etch results are presented for the Shipley PCM system using PMGI as the planarizing layer. For the trilevel technique using SOG or a-Si as intermediate layer, the loss of linewidth during bottom resist 02-RIE was of main interest. Finally, a dry developing technique, the DESIRE process using the PLASMASK resist, was studied and tested on device wafers.