Nicholas K. Eib

Design of a bottom antireflective layer for optical lithography

The advent of deep-UV(DUV), chemically amplified, acid catalyzed photoresists as successors to positive diazoquinones photoresists has brought about a new set of process environment concerns directed towards all materials in contact or absorbed by the photoresists. In addition to the application of DUV bottom anti-reflective coatings (BARCs) to suppress optical reflection and subsequent linewidth distortion, we must consider the properties and interaction of the BARC layer with the labile photoacid of the latent image. In this regard, we have examined the physico-chemical aspects of the DUV BARC with regards to acting as a barrier layer to substrate poisoning, and as an optical absorbing layer that does not interact and/or distort the deep-UV profile. Various single component polymeric BARCs were synthesized and examined. Considerations will be discussed of the optical absorbance, the coating quality, dry etch rate, and the impermeability of the BARC layer to photoacid diffusion to fulfill the performance requirements of BARCs for DUV lithography.

Characterization and simulation of acid-catalyzed DUV positive photoresist

An investigation of the dissolution behavior of an acid catalyzed deep ultraviolet (DUV) positive resist has been completed. The immersion develop dissolution rate as a function of dose and post exposure bake temperature was measured by Perkin Elmer Dissolution Rate Monitor (DRM) for single layer resist on a silicon substrate. A reaction-diffusion model has been built to describe the dependence of development rate on exposure dose and post exposure bake (PEB) time/temperature. A mixed diffusion model has been built to account for catalyst diffusion and quenching. Developed images have been compared with simulated image quality, line width, and process window.

Novel DNQ PACs for high-resolution i-line lithography

The use of i-line lithography for the 16 to 64 Mbit DRAM device generations calls for increased performance of i-line resists. This paper reports on investigations on novel sensitizers for advanced i-line lithography, starting out with a discussion of general design criteria, then discussing methodology and results of a screening phase, and examining in greater detail a small number of selected candidates for which resolution, exposure latitude, and depth-of-focus data were obtained. Finally, a new advanced resist for i-line lithography, AZR 7500, is presented, and its performance is evaluated in terms of the above criteria as well as thermal flow resistance.

Strong phase-shifting optical maskless lithography for the 65 nm node and beyond

Ever-increasing reticle cost makes optical maskless lithography an attractive alternative to mask-based technologies, particularly for low-volume runs such as prototypes, ASIC personalization, and engineering short loops. If the resolution and imaging performance of the optical maskless exposure tool can match or exceed standard reticle based scanners, then one can seamlessly integrate mix-and-match strategies into the manufacturing flow or even go to an all maskless strategy since resists and film stacks are unchanged. We have developed optical maskless analogs for a majority of the reticle based strong phase shifting techniques. These include analogs to binary, attenuated PSM, alternating PSM, CPL + assist features, and vortex reticles. We will present simulation of maskless vs. reticle based lithography of all these techniques, demonstrating how to move off grid, change CD, OPC correct through pitch, and present common feature process windows and CD / image placement error sensitivities that suggest that for certain applications, optical maskless will be superior to reticle based lithography.

Progressions in deep-ultraviolet bottom antireflective coatings

Deep ultraviolet (DUV) bottom anti-reflective coating (BARC)- to-resist compatibility is a key component in process optimization. In addition to the reduction of optical interference effects, BARCs also improve CD uniformity by preventing substrate contamination. However, if the BARC is not compatible with the resist, it can create adverse affects. If the acidity level of the BARC is not tuned to the resist for example, the profiles will foot or undercut, or if the BARC-to-resist developer interactions are not considered, high levels of post-develop defects will most likely occur. Etch selectivity, topography conformality and bowl/drain compatibility are other factors to consider when selecting a BARC. This paper follows the progressions of the leading DUV BARCs for Acetal-based resist systems and addresses the problems that could be encountered with implementing a BARC process. From DUV32 to the topography-conforming DUV42 and finally to the profile-enhancing DUV44, the 248 nm BARCs are continually evolving to resolve the BARC-to-resist compatibility issues.

Achieving sub-half-micron I-line manufacturability through automated OPC

We present results of a verification study of totally automated optical proximity correction (OPC) for mask redesign to enhance process capability. OPC was performed on an aggressive 0.35 micrometer i-line LSI logic SRAM design using the automated OPC generation code Eoptimask, employing the aerial image simulation code FAIM, both from Vector Technologies, Inc. Three different tests were performed, varying in the aggressiveness and type of corrections made. The key issues addressed in this work are the predictive capability of the aerial image simulation and, particularly, the ability of automatically generated OPC to significantly improve the fidelity of the final printed resist image for different geometries. The results of our study clearly demonstrate the utility of automated OPC based on aerial image simulation. Key experimental results include: two-fold increase of depth of focus latitude; demonstration of the feasibility of full off-axis illumination on the stepper; successful resolution of different feature types (posts, lines and spaces) on the wafer to correct CD at a single common exposure and focus condition. Future research will address detailed issues in reticle manufacture and inspection which are critical for cost-effective large-scale OPC.

TAR processing for CD control in I-line and 248-nm lithography

The combination of dyed photoresist and top antireflection (TAR) coatings was applied to I- line and deep-UV lithography on polysilicon. Optimization of the resist layers absorption and application of the TAR process significantly improves CD control of submicron gate level lithography.

Formulation and modeling of dyed positive i-line resist for control of the reflective notching and CD variation

This study evaluates the effect of dyes, including photosensitive dyes, on resist performance such as: swing curve reduction, resist dissolution rate, resolution, dose and focus latitude, scumming, etc. The paper demonstrates good correlation between modeling of the dyed resist performance and experimental results.

Characterization Enhancements in Resist Photospeed

Current photospeed testing methods are based on dose to clear (E 0 ) or resist contrast (γ 10 ). Either method is inadequate for controlling sensitivity to within ±1.5%. We investigated various methods for improving these photospeed tests. Ranked in order of decreasing importance are: (i) controlling standing waves (reflectivity); (ii) choice of developer, (iii) develop time; and (iv) exposure pattern. Reflectiuty can be controlled by careful attention to resist thickness, addition of a bottom antireflective layer, addition of a low refractive index layer (AquaTar), or by using a thick photoresist. Moreover, we can utilize the whole dissolution curve rather than the one-point determination of the E 0 test

Efficient numerical simulation of high-NA i-line lithography processes

Numerical algorithms employing the ID imaging model and the 2D wave-guide scattering model were implemented to achieve high speed in simulating high NA i-line processes. The CPU consumption and the range of validity of the models used were discussed. The simulator was applied to study the possibility of imaging 0.35/mi lines and spaces(L/S) utilizing lenses of NA=0.55, 0.60 and 0.65 and single layer resist (SLR) processes.