Charles R. Szmanda

On The Dissolution Kinetics Of Positive Photoresists: The Secondary Structure Model

Dissolution kinetics of several model resins with well defined molecular structures were studied extensively. These include a pure m-cresol formaldehyde novolac resin and an alternating m,R-cresol novolac. Other phenolic materials, such as poly(4-hydroxy-styrene), were also examined. Secondary structures of these materials were predicted by molecular mechanics energy minimization techniques and corroborated by comparison with existing experimentally determined X-ray crystallographic data, where available. The excellent agreement between theory and experiment for simple systems lends credence to structural predictions for our model systems. The salient conformational features of these molecules are manifested in the variety of inter- and intramolecular hydrogen bonding interactions which influence strongly the dissolution properties of a given resin. Dissolution kinetics were studied as a function of cation type, developer ionic strength, normality and temperature. The results are explained in terms of the inter- and intramolecular interactions predicted for these resins. Finally we show results which indicate the utility of our model to the design of resist/developer systems.

Simple method for measuring acid generation quantum efficiency at 193 nm

Traditional methods of measuring the Dill C Parameter involve monitoring the absorbance of a resist as a function of exposure. In chemically amplified resist, absorbance changes with exposure are small and frequently have little correlation to the amount of photoacid generated.

Film quantum yields of EUV& ultra-high PAG photoresists

Base titration methods are used to determine C-parameters for three industrial EUV photoresist platforms (EUV- 2D, MET-2D, XP5496) and twenty academic EUV photoresist platforms. X-ray reflectometry is used to measure the density of these resists, and leads to the determination of absorbance and film quantum yields (FQY). Ultrahigh levels of PAG show divergent mechanisms for production of photoacids beyond PAG concentrations of 0.35 moles/liter. The FQY of sulfonium PAGs level off, whereas resists prepared with iodonium PAG show FQYs that increase beyond PAG concentrations of 0.35 moles/liter, reaching record highs of 8-13 acids generated/EUV photons absorbed.

Methacrylate resists and antireflective coatings for 193-nm lithography

Methacrylates were the first class of resist to be examined for use in 193nm lithography. They are still useful today, but have a very different molecular structure because of the requirements for development in 0.262N tetramethyl ammonium hydroxide and high etching resistance. A major driving force for their continued use is the availability of a wide variety of methacrylate monomers and the use of free racial polymerization which imparts a wide range of properties to the polymers and makes them very cost effective.

Resolution, Line-Edge Roughness, Sensitivity Tradeoff, and Quantum Yield of High Photo Acid Generator Resists for Extreme Ultraviolet Lithography

Ultrahigh loadings of photoacid generators (PAGs) in phenolic extreme ultraviolet (EUV) resists have generated the highest known film quantum yields (FQYs). We evaluate the performance of these resists in terms of resolution, line-edge roughness (LER), and sensitivity and collectively evaluate these three parameters (known as RLS) in terms of KLUP and Z-Parameter figures of merit. An analytical model describing the kinetics of photodecomposition was developed to explain the relationship between film quantum yield and PAG concentration. Resists were prepared using a broad range of concentrations of iodonium (DTBPI-PFBS), sulfonium (TPS-PFBS), and non-ionic (NDI-PFBS) PAGs. The model fits the experimental data (correlation coefficient R2 = 0.998, 0.994, and 0.995) and compares the rate at which electrons react with PAGs or recombine with holes. Resists prepared with 15–20 wt % of iodonium nonaflate PAG exhibit both high quantum yields and the best RLS performance as determined using both KLUP and Z-Parameter methodologies. The improvement in RLS performance correlates with the increase in FQY at higher PAG concentrations.

Organic antireflective coatings for 193-nm lithography

Organic anti-reflective coatings (ARCs) continue to play an important role in semiconductor manufacturing. These materials provide a convenient means of greatly reducing the resist photospeed swing and reflective notching. In this paper, we describe a novel class of ARC materials optimized for lithographic applications using 193 nm exposure tools. These ARCs are based upon polymers containing hydroxyl-alkyl methacrylate monomers for crosslinkable sites, styrene for a chromophore at 193 nm, and additional alkyl-methacrylate monomers as property modifiers. A glycouril crosslinker and a thermally-activated acidic catalyst provide a route to forming an impervious crosslinked film activate data high bake temperatures. ARC compositions can be adjusted to optimize the films real and imaginary refractive indices. Selection of optimal target indices for 193 nm lithographic processing through simulations is described. Potential chromophores for 193 nm were explored using ZNDO modeling. We show how these theoretical studies were combined with material selection criteria to yield a versatile organic anti-reflectant film, Shipley 193 G0 ARC. Lithographic process data indicates the materials is capable of supporting high resolution patterning, with the line features displaying a sharp resist/ARC interface with low line edge roughness. The resist Eo swing is successfully reduced from 43 percent to 6 percent.

Photoactive Compound Structure And Resist Function: The Influence Of Chromophore Proximity

In this study the influence of polyPAC structure was determined by examining the dissolution characteristics of various experimental photoresists. The PACs in these materials have structures in which the PAC chromophores are deployed at low and high density but otherwise have the same functionality, with three diazoquinone (DAQ) moieties per PAC molecule. Our studies indicate that the greatest degree of dissolution inhibition is obtained when the DAQ groups are spread broadly across the same molecule. Furthermore, those PACs which showed the strongest inhibition in unexposed and lightly exposed resists exhibited the least dissolution rate enhancement in exposed resists. Resists made with PACs whose DAQ moieties are widely separated exhibit an extraordinary supralinear relationship between the dissolution rate and the exposure energy. Energy reaction orders for these materials have values much greater than the expected value of three predicted by polyphotolysis theory. A possible mechanism for this phenomenon is proposed. In addition, the lithographic implications of the dissolution characteristics of these experimental resists are discussed as they relate to resist optimization.

Etch resistance : comparison and development of etch rate models

Etch resistance and post etch roughness of ArF photoresists still remain some of the critical issues during process integration for sub-100nm technology nodes. Compared to phenyl-containing KrF polymers, methacrylate polymers commonly used for ArF lithography show weak bulk etch resistance in addition to a highly damaged surface after standard etch processes. Counter to the photoresist, the etch rates of BARC are required to be very fast to prevent degradation of the photoresist before the image has been transferred to the substrate. There are a number of etch models in the literature which attempt to describe the correlation between polymer structure and blanket etch rates. Ohnishi Parameter and Ring Parameter are the most common etch models correlating atomic and structural trends in the resist polymer and etch rates. These etch models have been tested in two ways: systematically changing the composition of a terpolymer and using polymers with different functional groups. By comparing the etch rates of this large series of polymer structures it was found that these etch models were not sufficient in describing the relationship between the atomic or structural trends in polymer with etch rates. New etch models that describe the structure property relationship and etch rate trends have been developed. These new models show a better correlation with the observed experimental results. Finally, new polymers have been developed, for both ArF and BARC applications. These materials show a significant improvement in term of etch properties.

Simulations of bar printing over a MOSFET device using i-line and deep-UV resists

Numerical simulations of printing of a bar in photoresist over a MOSFET gate using positive and negative, i-line and deep-UV resists are presented. The masks were chosen to produce the same nominal structure. The resist process was simulated in three separate phases: exposure, post-exposure bake, and development. Three-dimensional relief images of the printed bar are given for these cases.

Resist Dissolution Kinetics And Submicron Process Control

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.