Adam R. Pawloski

Measuring acid generation efficiency in chemically amplified resists with all three beams

A method for measuring acid generation efficiency is presented and utilized to determine the relative efficiency of four photoacid generators (PAGs) upon radiation with photon, electron, and ion beams. In this method, chemically amplified resists are prepared with varying amounts of base, coated into thin films (1000 A), and exposed. Linear plots of the base concentration against the threshold exposure dose for each resist yield the threshold acid concentration and the acid generation rate constant for each PAG. The acid-generating efficiency of the four PAGs (ND-Tf, TPS-Tf, TBI-PFOS, and TBI-Tf) upon irradiation with DUV (248 nm), EUV (13.4 nm), x-ray (1 nm), e beam (30 and 50 keV), and He+ ions is evaluated.

Photolithographic synthesis of high-density DNA probe arrays: Challenges and opportunities

The continual need for increased manufacturing capacity in the production of GeneChip™ DNA probe arrays, and the expanding use of these arrays into new areas of application such as molecular medicine, has stimulated the development of new chemistries and production methods with higher efficiency and resolution. For current production methods based on contact photolithography, modifications in substrate materials and photoactivated synthesis reagents have provided significant improvements in array performance and information content (≥4×106 sequences∕cm2). An alternative next-generation manufacturing process is also in development, which utilizes photoacid generating polymer films, and automated projection lithography systems. This process has the ability to fabricate arrays with 1 micron feature pitch and smaller, providing an unprecedented sequence density of 108∕cm2 and greater.

Evaluation of the standard addition method to determine rate constants for acid generation in chemically amplified photoresist at 157 nm

The rate constants for acid generation (C parameter) in chemically amplified photoresist are determined for four photoacid generators (norbornene dicarboximidyl triflate, triphenyl sulfonium triflate, bis-4-t-butylphenyl iodonium perfluorooctane sulfonate, and bis-4-t-butylphenyl iodonium triflate) under exposure to 157nm radiation using a standard addition technique. The technique utilizes an in film neutralization of photogenerated acid by base quencher to determine the increase in exposure energy necessary to produce an equivalent fee acid concentration at each loading of base. We present a general model to interpret the data that also accounts for the strong absorption of radiation by the resist film. An average absorption coefficient of 13.2micrometers -1 (base e) has been measured at 157nm for these resist films. Results from 157nm irradiation are compared to deep ultraviolet and ionizing radiation, indicating that resist photochemistry at 157nm includes processes important to both energy regimes.

Applications of molecular modeling in nanolithography

The design of resist materials capable of resolution below 100 nm requires a fundamental understanding of the chemical and physical processes that occur at length scales comparable to the dimensions of individual molecules. At these length scales, the thermophysical properties of photoresist films are different from those of the bulk; molecular simulations provide a useful tool to study the behavior of these materials at the molecular level, thereby providing much needed insights into phenomena that are difficult to characterize experimentally. In our group we have developed and implemented molecular based simulations to study materials for nanolithography at various levels of detail. At the chemically detailed, atomistic level, molecular dynamics techniques are used to determine specific effects arising from the molecular architecture of the resist components. In these systems, we explore the intra- and intermolecular structure of the resist resin polymer. The chemical architecture of the resin influence...

Effect of photoacid generator concentration on sensitivity, photoacid generation, and deprotection of chemically amplified resists

The dependence of resist processes (sensitivity, efficiency of photoacid generation, polymer deprotection) on the concentration of the photoacid generator (PAG) in formulations of chemically amplified photoresist was investigated as a function of the concentration of photoacid that was generated upon exposure. Although the sensitivity of a photoresist formulation improved by increasing the concentration of PAG in the resist formulation, the concentration of photoacid required to achieve an appropriate extent of deprotection to render development also increased. Using a standard addition technique, the efficiency of photoacid generation was quantified for resist systems consisting of triphenylsulfonium triflate as the PAG in an environmentally stable chemically amplified photoresist-type polymer primarily composed of 4-hydroxystyrene and tert-butyl acrylate monomers. Determination of the apparent efficiency of photoacid generation (the resist C parameter) allowed the concentration of photoacid within the r...

Micromolar concentrations of base quenchers impact the apparent efficiency of photoacid generation in chemically amplified resists

The chemical composition of the base quencher added to chemically amplified photoresist formulations was found to influence the apparent efficiency of processes that lead to photoacid generation upon exposure to ionizing radiation. Resists formulated with the base quencher 1-piperidineethanol (1PE) required lower exposure doses to render development than resists containing 3-piperidino-1,2-propanediol (3P12PD) as the base. A standard addition technique was employed to determine the efficiency of photoacid generation in resist formulations consisting of one of the two base quenchers, the photoacid generator triphenylsulfonium triflate, and a matrix polymer composed of primarily p-hydroxystyrene and tert-butylacrylate monomers (environmentally stable chemically amplified photoresist type). The resist containing 1PE exhibited an apparently greater efficiency for photoacid generation than the formulation containing 3P12PD. Analysis of development processes showed that resists containing these bases exhibited identical dissolution behavior to that of a system without base quencher, verifying that resist dissolution could not explain the difference in exposure dose required for development of the 1PE and 3P12PD resists. Furthermore, the action of photoacid to deprotect the polymer, as interpreted from infrared spectroscopy, and the concentration of photoacid required to render development were the same for both resists. These results suggest that the small concentration of base in the resist may participate in the complicated chemical processes that produce photoacid from the decomposition of PAG upon exposure to ionizing radiation.

Useful protocol for evaluating subtle and important differences between photoresist formulations

A useful protocol is presented for evaluation of the lithographic performance of chemically amplified photoresists that differ by formulation. A standard addition technique, infrared spectroscopy, and a development rate monitor were used, respectively, to measure the efficiency of photoacid generation upon exposure, the extent of polymer deprotection after the postexposure bake (PEB), and the dissolution rate of the resist in aqueous base developer. The combination of these experimental methods enabled the determination of (1) the concentration of photoacid that was generated in the resists as a function of exposure dose, (2) the extent of polymer deprotection that was achieved after the PEB as a function of the concentration of photoacid, and (3) the dissolution rate of the resist as a function of the extent of polymer deprotection. Photoresists may be compared using these three key relationships to evaluate the effects of formulation on resist performance. These methods were applied to investigate the i...