Alexander Friz

Directed self-assembly of topcoat-free, integration-friendly high- x block copolymers

To extend scaling beyond poly(styrene-b-methyl methacrylate) (PS-b-PMMA) for directed self-assembly (DSA), high quality organic high-x block copolymers (HC series) were developed and applied to implementation of sub-10 nm L/S DSA. Lamellae-forming block copolymers (BCPs) of the HC series showed the ability to form vertically oriented polymer domains conveniently with the in-house PS-r-PMMA underlayers (AZEMBLY EXP NLD series) without the use of an additional topcoat. The orientation control was achieved with low bake temperatures (≤200 °C) and short bake times (≤5 min). Also, these process-friendly materials are compatible with existing 193i-based graphoepitaxy and chemoepitaxy DSA schemes. In addition, it is notable that 8.5 nm organic lamellae domains were amenable to pattern development by simple dry etch techniques. These successful demonstrations of high-x L/S DSA on 193i-defined guiding patterns and pattern development can offer a feasible route to access sub-10 nm node patterning technology.

A method to characterize pattern density effects: chemical flare and develop loading

Many recent publications have highlighted pattern density effects as a problem in both electron-beam and optical lithography. These effects are manifested as a systematic variation in critical dimension as a function of position on the wafer. It is becoming an increasing problem as the pattern density and diminishing critical dimensions are needed for production nodes 32nm and beyond. One potential source of pattern density effects is acid volatility, where acid is presumed to redeposit during exposure or bake; here we refer to this effect as chemical flare. Another source of density effects is develop loading which refers to the impact of local depletion of developer in highly exposed regions. Both develop loading and chemical flare can cause deviations in feature size that may be difficult to correct for by adjustment of the exposure process. Here we describe a method that allows the detrimental effects of chemical flare and develop loading to be separately characterized. The method makes use of arrays of 248 nm exposure sites and a controlled develop process within a custom liquid flowcell; this combination enables a systematic study of these effects.

Two complementary methods to characterize long range proximity effects due to develop loading

Variations in critical dimension (CD) as a function of the proximity of an individual feature to other exposed areas are a continuing problem both in mask fabrication and in optical lithography. For example, the CD uniformity (CDU) may degrade significantly depending on the proximity to densely or sparsely exposed areas. These pattern density effects will continue to worsen as feature sizes decrease to 22 nm and below. Pattern density effects in electron beam lithography using chemically amplified resists are believed to arise from several sources. One such source, fogging, refers to the backscattering of secondary electrons onto the resist to cause deviations from the nominal pattern size. A second contributor is acid volatility, where photogenerated acid is presumed to redeposit on the wafer or mask during exposure or bake; here we refer to this effect as chemical flare. A third source of pattern density effects is develop loading, which results in local depletion of developer in highly exposed regions. All three of these may simultaneously contribute to a net observed CD variation. In this report we describe the application of two different techniques for evaluating these proximity effects. The first is based on electron-beam lithography patterning, and compares CD values of test patterns which are exposed under brightfield and dark-field conditions. The second uses a series of different test patterns formed by DUV (248nm) exposure and a custom liquid flow cell to separately characterize resist related density effects.

Visualization of the develop process

Variations in critical dimension (CD) as a function of the proximity of an individual feature to other exposed areas are continuing to be a problem in the lithography process. For example, the CD uniformity (CDU) may degrade significantly depending on the proximity to densely or sparsely exposed areas. These pattern density effects will continue to get worse and become more complex as feature sizes decrease. Pattern density effects are believed to arise from several sources and may simultaneously contribute to a net observed CD variation [1]. One such source, develop loading, results in local depletion of developer in highly exposed regions, reducing the dissolution rate and thereby locally affecting CD. In this report we describe our results in visualizing develop loading by using pH sensitive dyes. Two different types of dyes are explored: acid/base pH indicators and a fluorescent dye bound to the resist polymer.

A silicon-containing resist for immersion lithography

We have developed a new silicon-containing resist for 193-nm immersion lithography. This resist is compatible with topcoats used in the industry today for immersion lithography. Most of the current topcoats contain 4-methyl-2- pentanol as a solvent. Our evaluations indicated that the previously developed silicon-containing resists are not compatible with the current topcoats because of their solubility in 4-methyl-2-pentanol. In the new resist polymers, we have incorporated high percentage (> 60 mol%) of lactone monomers to prevent them from dissolving in this solvent. In order to increase the lactone content in a silicon polymer, we have incorporated lactone containing acidlabile functionalities in addition to widely used acid-inert lactone monomers. Utilizing these polymers, we have demonstrated a functional silicon-containing photoresist for immersion lithography.