Argon ion implantation has been investigated as a means of achieving resist stabilization, such that a
second resist layer may be patterned without attacking the 1st layer. The viability of such an
approach has been investigated for double printing. Potential benefits include resist feature shrinkage
and Line Width Roughness (LWR) improvements. Line shrinkage benefits the lithographic process
window as features can be printed larger, while improvements in LWR, is a further valuable
attribute. We report on the role played by ion implant dose, its impact on both lateral and vertical
resist shrinkage, LWR as well as its impact on organic BARC reflectivity. The performance of such
masks during dry etching of a gate layer has been additionally evaluated.
A two-year study on the feasibility of High-n Immersion Lithography shows very promising results. This
paper reports the findings of the study.
The evaluation shows the tremendous progress made in the development of second-generation
immersion fluid technology. Candidate fluids from several suppliers have been evaluated. All the
commercial fluids evaluated are viable, so there are a number of options. Life tests have been conducted on
bench top fluid-handling systems and the results referenced to full-scale systems. Parameters such as Dose
per Laser Pulse, Pulse Rate, Fluid Flow Rate, and Fluid Absorbency at 193nm, and Oxygen/Air
Contamination Levels were explored. A detailed evaluation of phenomena such as Last Lens Element
(LLE) contamination has been conducted. Lens cleaning has been evaluated.
A comparison of High-n fluid-based technology and water-based immersion technology shows
interesting advantages of High-n fluid in the areas of Defect and Resist Interaction. Droplet Drying tests,
Resist Staining evaluations, and Resist Contrast impact studies have all been run. Defect-generating
mechanisms have been identified and are being eliminated. The lower evaporation rate of the High-n fluids
compared with water shows the advantages of High-n Immersion.
The core issue for the technology, the availability of High-n optical material for use as the final
lens element, is updated. Samples of LuAG material have been received from development partners and
have been evaluated. The latest status of optical materials and the technology timelines are reported.
The potential impact of the availability of the technology is discussed. Synergy with technologies
such as Double Patterning is discussed. The prospects for <22nm (hp) are evaluated.
DPL (Double Patterning Lithography) has been in public as one of candidates for 45nm or 32nm HP since
ITRS2006update disclosed. A lot of report of the performances and issues regarding to DPL were published.
The current main concerns are evaluation of the infrastructures such as decomposition software, advanced
photomasks, higher-NA exposure tool and leading-edge hard-mask process. If there is simpler procedure to
evaluate DPL using a conventional environment without hard-mask process, the development of DPL will be
accelerated. Here, the simple evaluation procedure for DPL using actual photomasks combining double
exposure technique was proposed. The pseudo DPL result in terms of mask CD uniformity, image placement
and overlay were demonstrated. In this evaluation procedure, decomposition restriction, mask latitude and
fabrication load were also discussed
In this paper we report the status of our feasibility work on high index immersion. The development of high
index fluids (n>1.64) and high index glass materials (n>1.9) is reported. Questions answered are related to
the design of a high NA optics immersion system for fluid containment and fluid handling, and to the
compatibility of the fluid with ArF resist processes.
Optical design and manufacturing challenges are related to the use of high index glass materials
such as crystalline LuAG or ceramic Spinel. Progress on the material development will be reviewed.
Progress on immersion fluids development has been sustained. Second-generation fluids are
available from many suppliers. For the practical use of second-generation fluids in immersion scanners, we
have evaluated and tested fluid recycling concepts in combination with ArF radiation of the fluids. Results
on the stability of the fluid and the fluid glass interface will be reported. Fluid containment with immersion
hood structures under the lens has been evaluated and tested for several scan speeds and various fluids.
Experimental results on scan speed limitations will be presented.
The application part of the feasibility study includes the imaging of 29nm L/S structures on a 2-beam interference printer, fluid/resist interaction testing with pre- and post-soak testing. Immersion defect
testing using a fluid misting setup was also carried out. Results of these application-related experiments
will be presented and discussed.
As gate dimensions continue to shrink, improving CD control is a major challenge for sub-0.25 micron DUV lithography. One concern is line edge roughness which takes the form of both high and low frequency effects. In this paper, high frequency line edge roughness refers to high frequency small amplitude CD variations noted along the edge of a wet developed resist feature. Low frequency line edge roughness (LFLER) refers to the higher amplitude waviness observed along the edge of developed features. BOth these roughness parameters could lead to significant variations in device characteristics. Several factor such as the resist formation, quality of the aerial image and process conditions have in the past been attributed as possible sources of roughness. In this study, a quantitative characterization of wet developed feature roughness was conducted and attempts were made to determine the sources of its origin, along with the impact of plasma etch. High and low frequency LER was characterized using a Dektak SXM atomic force microscope and a Hitachi 7800 scanning electron microscope. Nominal 0.20, 0.18, and 0.16 micrometers isolated lines were studied following photolithography and the gate etch. Additional variables in this study included substrate type, resists composition, develop time, focus and the impact of aerial image.
Deep UV lithography is widely used to print contacts and vias for the 0.25 micrometers process technology and beyond. Although significant improvements in the depth of focus and exposure latitude of the resist systems have been made using optimized resist formulations, their integrity against plasma etch conditions has to be addressed for the successful implementation in deep submicron process flows. In this paper, the first part of the discussion focuses on quantifying the etch rate differences and the impact of resist profile on the etched profile of different commercial DUV resists, using a Magnetically Enhanced Reactive Ion Etch tool with CF<SUB>4</SUB>:CHF<SUB>3</SUB> and C<SUB>4</SUB>F<SUB>8</SUB>:CHF<SUB>3</SUB> fluorocarbon etch chemistries. In the second part, sources of critical dimension variations such as iso vs dense contacts, wafer temperature effects during contact etch as well as etch issues related to the integration of BARC at the contact level are discussed.
The continued push towards smaller feature sizes has placed increasingly stringent demands upon CD control. Several techniques have been used in the past to improve the CD control over topography, starting with dyed resist and progressing through top anti-reflective coating, spin on- organic BARC and more recently inorganic dielectric ARC. The increased use of DUV lithography has limited the use of the TAR coating, as it fails to prevent true reflective notching. Organic BARC has therefore been the method of choice. Recently however, the use of inorganic dielectric anti-reflective materials has become more widespread due to potentially improved performance, particularly over high topography. We report on the relative performance of both types of materials as applicable to MOS gates. Practical factors such as resist footing, relative defectivity after polysilicon patterning, CD bias after etch, problems in removal of the ARC during etch and strip and the impact on process integration are discussed. The overall aim is to provide a production viewpoint as to the usefulness of each approach and to highlight their individual strengths and weaknesses.
New I-line resists are claimed to be usable at 0.35 micrometers design rules. We have examined the suitability of several such materials (JSR IX750, Sumitomo PFi-38a, OCG RX64I) for this purpose and compared them with our production 0.5 micrometers resist, JSR IX700. A variety of criteria have been used, including the measured focus exposure windows at e-min and e-max, DOF vs. CD for grouped and isolated lines as well as contacts, linearity, and proximity response as a function of pitch. A limited study has been done on the impact of embedded phase shift reticles on printing small geometry contacts. We report upon the process improvements observed with two different reticle transmissions, their impact on isofocal bias, as well as the issue of sidelobe formation. Proponents of DUV claim that modern DUV materials exhibit significant advantages in terms of process window and more over are applicable to smaller geometries without the need for supplementary techniques such as phase shifting or modified illumination. In this study, we have examined the performance of a number of DUV materials (BASF ST3.5, OCG ARCH, JSR KRFL2 and an as yet experimental JSR resists) on ASM-L and Nikon excimer laser steppers. Limited results were also obtained using Shipley 2408 and dyed XP-9444 (0.8) on the SVG Micrascan II. Our studies conclude with a comparison of the CD swing observed over a variety of chemically mechanically planarized steps. This has been done for selected I-line and DUV resists with the aid of a TAR or BARC or as in the case of the broad band SVG system either a BARC or a dyed resist.
For deep submicron lithography, reduction of linewidth variation due to topography is critical. While advanced resists are available which demonstrate wide process latitude on flat substrates, their performance on realistic topography is not adequate. A new method of predicting performance over topography using data taken from flat substrates is described. The method uses data from both maximum and minimum incoupling resist thicknesses to determine the overlapping depth of focus (ODOF). The usefulness of the ODOF approach in predicting process latitude for substrates with topography is shown.
Results for both I-line and deep UV imaging on poly gate level topography are presented. Results obtained with 2 top anti-reflection (TAR) layers (Hoechst Aquatar and a non-commercial TAR material) are compared to those from a dyed resist, an anti-reflection coating (ARC) and a contrast enhancement material (CEM). Methods of determining the optimal TAR thickness experimentally are presented. TAR materials give the best results for I-line.
Shipley XP-89131 is a wet developable negative tone DUV resist, capable of resolving features down to 0.3 micrometers when used in conjunction with the ASM- L PAS 5000/70 stepper (NA equals 0.42). Practical implementation of this material at the limit, however, is marred by several problems, notably, poor C.D. (critical dimension) control over steps, inadequate adhesion and the formation of various types of residue between features. The authors have endeavored to find means by which these effects may be reduced. Methods investigated for tackling the residue problem have included the use of metal ion free and metal ion containing developers, a comparison of puddle, immersion and spray develop processes, changes in the percentage overdevelopment employed, as well as the effect of developer temperature. Additional work has been directed towards examining the effect of post-exposure baking time. The high transparency of such resists, coupled to the high reflectivity of substrates at 248 nm, gives rise to severe C.D. control problems over topography. We examine the effectiveness and tradeoffs of two alternative approaches potentially capable of effecting an improvement. Spin coatable DUV ARC materials have been found to significantly improve C.D. control over polysilicon and aluminum topography, although the more retrograde profiles observed, in conjunction with optical proximity effects, can impose other limitations. Several beneficial side effects have been noted, however, including improved adhesion on aluminum substrates, a wider exposure window and easier stripping of the resist following dry etching. Potential yield reducing factors such as the presence of resist residues or bridges between features, are also significantly reduced during the dry development of the ARC. The alternative method of employing dyed resists has also been evaluated using both Shipley XP-90166 and XP-90174 resists. While the latter version does offer some improvements over the undyed XP-89131 material, it is not as effective as the ARC approach in controlling C.D.s over topography. It is apparent too that the resolution limit of such materials has been blunted. Finally the focus and exposure latitude has been determined for features printed on silicon, both with and without ARC. In a similar way the focus/exposure window has been determined for etched contacts.
DUV lithography is an emerging technology which promises excellent resolution coupled with an
improved depth of focus. Whilst the hardware connected with this technology is rapidly maturing, there
remain question marks over the suitablilty of present DUV resists in the fabrication of actual circuits.
Two widely differing approaches are typified by Plasmask (DESIRE) which involves surface imaging and
dry development and by the wet developable Shipley Megaposit SNR 248-1.0, which utilises acid
catalysed chemistry. We have studied both materials using a contact printing system and the ASM-L PAS
5000110 DUV stepper (both at 248 nm wavelength). In particular we have compared the lithographic
performance of both resists on a variety of substrates and topographical features, commonly encountered
during processing. Practical issues such as the intrinsic adhesion, photospeed, exposure latitude, focus
latitude, linearity, thermal resistance and etch resistance are presented.
For the Shipley material we have compared its performance under various development conditions, with
respect to resolution, photospeed, profile and residues. On the Plasmask material we have investigated the
degree of silicon incorporation for various silylation conditions and for various Plasmask formulations.
Significant differences have been noted for exposures made with this wavelength (248 nm) and those
commonly reported with g and i-line exposure. Finally, the feasibility of using TMDS (1,1,3,3
Tetramethyldisilazane) as a silylating agent is presented.
The use of evolutionary resist processing techniques designed to improve profiles and extend process latitude, is of general
interest to lithographers. The more commonly known methods (HARD, LENOS) utilise the phenomenon of alkali catalysed
crosslinking, to create additional surface inhibition during development. Such techniques whilst undoubtedly useful, are by
their very nature limited to improving only the very top of the resist profile. Additionally under certain process conditions the
formation of a top hat profile can be observed, this is particularly noticeable on smaller features. The use of an interrupted
development cycle, or of multiple interrupted development cycles (PRISM) has also been reported to exert a beneficial effect
on profiles. However our own tests, utilising a single interrupted development cycle, are unable to support such claims, and
have in fact demonstrated degraded profiles, in comparison with a standard double puddle process.
We report here on an alternative technique, the so called intermediate development bake or 1DB, whereby a short low
temperature baking step is introduced midway during the development cycle. The distributed nature of this technique
discourages the formation of top hat profiles, whilst improving the upper part of the developed profile.
Previously reported work concentrated on the use of infra red baking. The present paper investigates this further, whilst
additionally covering the use of warm air and warm water treatments. The use of warm water in particular is potentially very
attractive, and we demonstrate its effectiveness on a range of i-line specific, g-line and multiwavelength resists, exposed
using i-line. A particularly close study has been made of Olin's HiPR 6512 resist using both metal ion and metal ion free
Based on a number of observations including the use of FTIR and XPS, we advance a mechanism to explain our results.