While much work has been done in the design of photo resist for EUV lithography, these materials have typically been
optimized for so called "standard developer" i.e., 2.38% tetra methyl ammonium hydroxide. However we felt that it
would be reasonable to consider specifically the developer as opposed to the resist design. Indeed it has been suggested
that the polarity and cation size in developer are important positive tone resist performance. It is our hypothesis that a
base that could wet and penetrate faster into partially deprotected resist could result in a faster photo speed, and thus
make more process margin available for resist design; for example a slower system incorporating higher quencher
loadings. Additionally, we sought to probe the effects of solvent polarity with varying amounts of non-aqueous solvent
additive. By reorganization of the nascent solvent shell with the non aqueous additives, we sought to perturb the
development kinetics and thus change the resist's performance envelope by accelerating photo speed and potentially
increasing contrast. This approach has been applied to non chemically amplified resist to good effect. In the three
positive tones EUV and a 193nm photo resist was evaluated with the prototype developers we found that the
performance was profoundly impacted by these two probes (i.e. solvent polarity and cation hydrophobicity).
Concentration gradients of photoacid generator through the thickness of the photoresist film can profoundly affect the
material's performance. To engineer the acid concentration through resist thickness, we have developed a new type of
resist adhesion promoting layer that incorporates photo acid generator chemistry. These adhesion promoting photo acid
generators, called as a class "APPAG" enhance acid concentration at interface between the resist and the substrate. We
will provide an overview on the preparation and characterization of two siloxane based APPAG materials along with a
performance comparison of commercial DUV, EUV and E-beam photoresists on APPAG.
Nonaflate analog (APPAG 6) with shorter acid diffusion length was found to have a mild impact on 250nm node DUV
lithography. However the triflate analog (APPAG 9), owing to the larger acid diffusion length, was shown to provide a
greater influence. APPAG 9 was found to give nearly a 50% improvement in depth of focus.
For EUV lithography, both APPAG 6 and APPAG 9 will be shown to substantially improve performance envelope for
100nm dense lines and spaces and at reduced post exposure bake (PEB) temperatures. This indicates that this approach
can be used to gain margin at reduced PEB which is desirable to minimize thermally driven diffusion effects. Thus the
materials represent an important new approach to extending photoresist performance margins.
Pixelated photoresists, i.e. resists that compartmentalize photochemistry into discrete imaging elements are an emerging
design for improved resolution. A pixelated design seeks to overcome chaotic organization in complex resist
formulations through application of small regular or symmetric imaging species, and/or through the application of
preorganization of resist components. 
Another approach, backbone scission, has also emerged as a powerful method to improve resist performance.  In this
approach, the parts of the resist structure that have undergone radiation driven chemistry are disconnected from the
unaffected material. This enhances contrast and also confers an additional mechanism: structural disruption.
Bile acids have been used recently as building blocks to enable host-guest chemistry  and have been incorporated as
additives in photoresists  and structural elements . They as a class are fairly large (mw ~400) highly
functionalized molecules possessing a hydrophobic face, alcohol groups and a carboxylic acid group.
We describe here a scissionable pixelated resist architecture based on bile acids bound by acid-sensitive tertiary ester
linkages into dendrimeric arrays. This design seeks to employ structural disintegration and catalyst pre-organization in
addition to solubility switching as contrast mechanisms. Preliminary EUV and ebeam studies have shown G0 and G1
materials capable of sub-micron imaging.
We developed an atomic force microscopy (AFM)-based technique to measure intrinsic material roughness after base development. This method involves performing an interrupted development of the resist film and measuring the resulting film roughness after a certain fixed film loss. Employing this technique, we have deconstructed the resist into component materials and established that the photoacid generator (PAG) is a major material contributor of film roughness and that PAG segregation in the resist is likely responsible for nanoscale dissolution inhomogeneities. Small differences in PAG concentration as a result of standing waves in the resist can lead to large changes in surface roughness due to PAG or PAG-photoproduct segregation and the resultant nonlinear change in nanoscale dissolution rates. The temperature dependence of the PAG segregation suggests that increased mobility of the PAG that occurs may be due to a lowering of the film Tg during the deprotection process.
A method has been developed to probe the Innate Material Roughness (IMR) of resist materials. We have applied this to EUV and 248 nm resists to deconvolute the material contributions to roughness: 1) the polymer alone, 2) interaction between the polymer, photoacid generator (PAG), base quencher, and photolysis byproducts, 3) the effects of exposure, and 4) development. We studied ESCAP based resists (with more limited data on APEX polymers), an iodonium nonaflate PAG, a tetabutyl ammonium hydroxide (TBAH) base quencher, and standard tetramethylammonium hydroxide (TMAH) development.
We have developed an AFM-based technique to measure intrinsic material roughness after base development. This method involves performing an interrupted development of the resist film and measuring the resulting film roughness after a certain fixed film loss. Employing this technique, we have deconstructed the resist into component materials and established that the PAG is a major material contributor of film roughness and that PAG segregation in the resist is likely responsible for nano-scale dissolution inhomogeneities. Small differences in PAG concentration as a result of standing waves in the resist can lead to large changes in surface roughness due to PAG or PAG-photoproduct segregation and the resultant non-linear change in nano-scale dissolution rates. The temperature dependence of the PAG segregation suggests that increased mobility of the PAG occurs due to a lowering of the film Tg during the deprotection process.
To fulfill industry requirements for EUV resists, the development of entirely new polymer platforms is needed. In order to address transparency issues, we have been studying low absorbance materials, specifically silicon based resist platforms. In this approach, we have synthesized and studied resist materials based on polysilanes, polycarbosilane, and polysilsesquiazanes. Poly(methylphenylsilane) was chemically modified to incorporate polar groups to enhance solubility in polar solvents and developer solution. Copolymerization of the modified polysilane with an acid sensitive monomer has been used to produce chemically amplified copolymers. Preliminary studies have shown promising behavior. Polysilsesquiazanes-based resist were synthesized and tested using a 248 nm stepper. They showed excellent lithographic performance but some issues, including long term stability, are presently unknown. Our strategy to produce silicon-based resist together with outgassing and lithography issues will be discussed.
Performance requirements for EUV resists may require the development of entirely new polymer platforms. In the first approach, we have synthesized norbornene-based copolymers using ring-opening metathesis polymerization (ROMP). Silicon containing norbornenes were synthesized and copolymerized with a series of monomers having acid sensitive and polar groups, including nitrile, carboxylic acid, hydroxyl, and anhydride functions to achieve random copolymers with suitable properties to be applied as resist materials. Using well-characterized metal alkylidene complexes, we could prepared polymers having controlled molecular weights and low polydispersities. From initial exposure studies using an EUV interferometer, we were able to pattern 150 nm pitchs without additional optimization. In the second approach, polysilane has been copolymerized with acid sensitive monomers (acrylate and styrene derivatives) to produced chemically amplified polysilane-copolymers.
Intel’s recent 157nm fluoropolymer photoresist development is described, including the benchmarking of photoresist patterning and the suitability of resists in typical Intel etch processes. The imaging results show that the new ultra-low absorbance resists (absorbance <1/μm) show great promise for meeting the 65nm-node ITRS targets. The materials also show good etch resistance when exposed to SiO2, Si3N4 and SixOyNz dry etch chemistries.
Line width roughness (LWR), transferred from a patterned photoresist to a gate during the etch process, may have a significant effect on the device performance beginning with the 65 nm technology node. Two factors that make LWR a greater concern for this node than for previous technology nodes are: 1) LWR does not scale in proportion to the critical dimensions (CDs), and 2) LWR has been shown to increase as film thickness decreases. A significant challenge for this technology node is the development of a resist process with sufficiently low LWR. In this paper, we investigate the effect that changing processing conditions has on LWR. We begin by reviewing the literature to determine which processing parameters have been shown to impact LWR. We then present experimental results that show how variations in processing parameters affect LWR. We conclude with molecular data showing the relation between resist surface roughness and LWR.
The success of extreme ultraviolet (EUV) lithography depends upon developing resists that meet the patterning requirements for the technology node in which EUV is inserted. This paper presents Intel’s patterning requirements and development strategies for EUV resists. Two of the primary problems for EUV resists are meeting the linewidth roughness (LWR) requirement, and reducing resist absorbance to obtain good sidewall profiles. Benchmarking data shows that none of the current EUV photoresists meet LWR targets. Modeling results for EUV resists show the impact of resist absorbance on sidewall angle and resolution.
We describe a cyclopolymerization approach to novel cyclic materials incorporating a) etch-stable adamantyl esters and b) t-butyl esters as functionalities suitable for chemical amplification. The synthesis of the monomers follows a highly convergent approach from the readily synthesized 1- adamantyl malonate ester. Two polymerizable side chains are then added, incorporating either a(t-butyl acrylate esters, or b) a terminal olefin functionality. These bifunctional, carbon-rich monomers undergo smooth and efficient free radical ring-closing cyclopolymerization to afford soluble, processable polymers that do not contain residual olefinic signals. In order to optimize the lithographic performance of the materials, these crystalline monomers can also be copolymerized with maleic anhydride, or other desirable monomers. These resists show excellent transparency at 193 nm and outstanding etch resistance. When used in combination with a photoacid generator, they ca be used to formulate deep UV, chemically amplified photoresists. Preliminary imaging experiments conducted with a 193 nm ArF laser stepper exposure unit demonstrate features below 0.18 (mu) .
We introduce here a novel approach to highly EUV transparent, carbon dense polymers for application as photoresist materials. The backbone of the prototype polymer consists of bicyclic hydrocarbons spiro-fused to cyclohexane moieties decorated with pendant t-butyl esters. This high polymer is formed through the free radical cyclopolymerization of functionalized norbornane derivatives. Imaging experiments conducted at 193 nm demonstrate features below 0.15 microns.