摘要:

We have investigated the suppression of acid diffusion during postexposure baking (PEB) of chemical amplification resists in terms of the molecular control of base matrix polymers to control acid‐diffusion channels. According to a previously proposed model, acid diffuses along acid‐diffusion channels in chemical amplification resists. The acid‐diffusion channels are composed of OH groups outside the base matrix polymers (active OH groups) and vacancies in the matrices. The negative‐type chemical amplification resists used in this work consisted of cresol novolak with controlled molecular‐weight distributions as the base matrix polymers, an acid‐catalyzed crosslinker of melamine resin, and acid generators of onium salt. Measurements of the dependence of the pattern sizes of isolated lines on the PEB time made it clear that acid diffusion defines the resist pattern sizes based on Fick’s law. The densities of the active OH groups play a critical role in acid diffusion, and a base matrix polymer with fewer active OH groups is expected to result in less acid diffusion. Therefore, we can suppress acid diffusion by reducing the number of oligomers in the base matrix polymers by a precipitation method, since these oligomers stereochemically include many active OH groups. We have obtained high resolution by using a resist with an oligomer‐free resin. The acid‐diffusion model was also confirmed based on infrared absorption spectroscopy and thermal analysis. We conclude that acid diffusion can be suppressed by controlling the acid‐diffusion channels.

ISSN:0734-211X    

DOI:10.1116/1.588578

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Measurement and analysis of bake dependencies of resist profiles are used to establish the critical role of diffusion and acid loss in lithographic performance. Imaging experimentscarriedout with APEX‐E with postexposure bake temperatures above and below its glass transition temperature evidence widely dissimilar feature size dependencies attributable to different acid diffusion mechanisms in the glassy and the rubbery polymer, respectively. Examination of the mechanisms determining e‐beam exposed resist image stability show that, when an acid loss mechanism is present, the initial amount of acid generated the reaction rate, and the diffusion mechanisms are essential in predicting feature size dependence on postexposure bake conditions.

ISSN:0734-211X    

DOI:10.1116/1.588579

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Postexposure bake (PEB) dependence of photogenerated acid diffusion was investigated in a chemically amplified deep ultraviolet positive resist. The resist consisted of a tert‐butoxycarbonyl protected polystyrene as base resin and 2,4‐dimethylbenzenesulfonic acid derivative as photoacid generator. The diffusion length of photoacid increased with increasing PEB temperature or its time. Moreover, the activation energy of acid diffusion reaction within the resist film became smaller, with increased exposure dose. It is considered that hydrophilic OH sites of the base resin generated by the deprotection of hydrophobic protecting groups has a role as one of the diffusion paths in the polymer matrix. Furthermore, it was found that the diffusion coefficient under high PEB conditions was affected by the acid reduction. Based on the analysis of diffusion characteristics, clear correlation between acid diffusion in the resist film and PEB conditions was obtained. These results are useful for improving both resolution capability and pattern profiles.

ISSN:0734-211X    

DOI:10.1116/1.588580

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

We propose a novel technique for reducing substrate reflections in 248 nm deep ultraviolet (DUV) lithography. The method we have developed utilizes a multilayer scheme comprised of layers of silicon rich oxide. Deposition of the film stack is carried out on a production ready PE‐CVD tool in one continuous operation. The combining of multiple layers allows a gradual change in absorption thereby minimizing the reflection coefficient at the resist/ARC interface. The method of operation of these films is one of total absorption rather than the more common destructive interference method of a single layer film which relies on very tight thickness control. Absorption of the combined films is high enough to be effective on even the most highly reflective substrates such as aluminum. Furthermore, this technique does not require the ARC films to be tuned in their optical constants to accommodate the underlying substrate. We have successfully patterned wafers with feature sizes as small as 200 nm with no appreciable change in line width due to the underlying topography. The multilayer ARC system has been successfully integrated into the gate level of a 0.25 μm design rule device with excellent results. A description of the films used, their optical properties, and results from experimental data, as well as numerical simulations, will be reported.

ISSN:0734-211X    

DOI:10.1116/1.588581

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

The process of removing an overcoat (OC) on the tert‐butoxycarbonyl (t‐BOC) type chemically amplified positive resists has been studied, and it has been found that in the case of removing the OC after postexposure bake (PEB), or at development, the decrease in the dissolution rate at the exposed region results in the formation of the surface insoluble layer and scum. This reduction in the rate became larger with increasing the OC thickness and thet‐BOC ratio in the resist, and it was shown by Fourier transform infrared spectra that thet‐BOC group disappeared and a small amount of tert‐butoxy moiety appeared in the fully exposed region. When the OC layer remained on the resist film during PEB, isobutene generated by the deprotection oft‐BOC was prevented from permeating out of the resist film and then recombined with the OH group in the base polymer. Therefore, it was found and verified that by using the acidic OC material which exhibits a high permeability for gases, the resist performance was improved.

ISSN:0734-211X    

DOI:10.1116/1.588582

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Chemically amplified negative resist films of Shipley SAL 605 at 1.0 μm thickness show a statistically optimized sensitivity that is twice that observed with 0.5 μm films when exposed to x rays from an electron storage ring. Because of the large ‘‘depth of focus’’ of proximity x‐ray lithography, the differences between thick and thin films are due to resist chemical and physical effects and processing conditions, not to the exposure process. Using identical processing conditions, 1.0‐μm‐thick films showed 34% larger linewidths than 0.5 μm films for isolated lines from one mask with a target linewidth of 0.215 μm. Gel permeation chromatography results indicated that there was no dependence of resin or crosslinker concentration on thickness of the applied film. The photogenerated acid and residual solvent were quantified prior to postexposure bake, and neither was able to explain the apparent sensitivity dependence on thickness. The work suggests that some of the differences arises in the resist application process because of the ability of the thicker film to retain small molecular weight species which facilitate the linewidth production. This implies that thinner films should show better resolution purely because of chemical and physical factors in the resist film.

ISSN:0734-211X    

DOI:10.1116/1.588583

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Potential capabilities of a thinner resist process are verified from both points of view—lithography and etch processes. The experimental results for lines and spaces indicate that a larger gain in process window could absolutely go along with reduced resist thickness. It is found that the thinner resist process could successfully improve not only the optical proximity effect in lithography processes but also the microloading effect in etch processes. It is also demonstrated that an application of the thinner resist process would be useful to further extend advantages of higher numerical aperture exposure systems. The thinner resist process is found to be effective to improve the process window of contact holes. Moreover, a novel pattern transfer process could be demonstrated using the practical limit of resolution capability up tok1=0.4.

ISSN:0734-211X    

DOI:10.1116/1.588584

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

The method of single pixel exposures is applied for the determination of acid diffusion effects in negative chemically amplified resists. The wide range of crosslink density values contained in a single dot is used to determine nonlinear diffusion parameters. A reaction‐diffusion model is developed where the diffusion coefficientDis a function of the crosslink density Θ. This functionD(Θ) is evaluated for a given range of postexposure bake parameters in each case and the information obtained is used for proximity correction, also using the e‐beam lithography simulation toolLITHOS. In order to test the model under different circumstances, two resists are studied, namely, the commercially available SAL‐601 and the experimental epoxy novolac resist EPR. The diffusion coefficient is evaluated for each resist under the best processing conditions. The proximity correction procedure is fully demonstrated in the case of SAL‐601.

ISSN:0734-211X    

DOI:10.1116/1.588585

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

A pronounced feature of negative resist developed profiles is corner rounding. Almost all of the current resists are composed of polymeric materials and negative resists depend on cross‐linking during exposure for feature delineation after development. The envelope sphere polymer molecule modeling describes the creation of the rounded profile at corners of resist lines during dissolution. A cellular automata dissolution model incorporates the envelope model, simulates the mechanics of the etching process, and predicts the corner rounding. We used Shipley SNR‐248 negative resist for the experimental profiles. The experimental results confirm the dependence of the dissolution rateEri,jon the differential etch rate between exposed and unexposed regions (volumes) of the resist. High postexposure bake temperatures and higher development environment temperatures modify the profiles.

ISSN:0734-211X    

DOI:10.1116/1.588586

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

H2O vapor as the etching medium has been investigated for electron beam induced etching of an organic resist. The aim was the determination of the dependencies on the process parameters. The etch rate increases with decreasing beam energy and increasing H2O vapor flux (i.e., molecules per time and area). At 5 keV beam energy, the achieved etch rate is 55 nm/min. By lowering the beam energy to 1 keV (maximum of the secondary electron yield) and increasing the scan speed (approximately 1–5 MHz), a pronounced rise to the etch rate is expected.

ISSN:0734-211X    

DOI:10.1116/1.588587

出版商:American Vacuum Society    

年代:1996

数据来源: AIP