Gregory S. Doerk

Computational Aspects of Optical Lithography Extension by Directed Self-Assembly

EUV insertion timing for High Volume Manufacturing is still an uncertainty due to source power and EUV mask infrastructure limitations. Directed Self Assembly (DSA) processes offer the promise of providing alternative ways to extend optical lithography cost-effectively for use in the 10nm node and beyond. The goal of this paper is to look into the technical prospect of DSA technology, particularly in the computational and DFM area. We have developed a prototype computational patterning toolset in-house to enable an early Design –Technology Co-Optimization to study the feasibility of using DSA in patterning semiconductor devices and circuits. From this toolset we can identify the set of DSA specific design restrictions specific to a DSA process and plan to develop a novel full chip capable computational patterning solution with DSA. We discuss the DSA Computational Lithography (CL) infrastructure using the via and fin layers as examples. Early wafer data is collected from the DSA testmask that was built using these new toolsets. Finally we discuss the DSA ecosystem requirements for enabling DSA lithography and propose how EDA vendors can play a role in making DSA Lithography (DSAL) a full-chip viable technology for multiple process layers.

Deterministically isolated gratings through the directed self-assembly of block copolymers

Pattern customization is a necessary requirement to achieve circuit-relevant patterns using block copolymer directed self-assembly (DSA), but the edge-placement error associated with customization steps after DSA is anticipated to be at the scale of the pattern features, particularly as a result of overlay error. Here we present a new self-aligned approach to the customization of line-space patterns fabricated through chemical epitaxy. A partially inorganic chemical pattern contains a prepattern with pinning lines and non-guiding “blockout” features to which the block copolymer domains are aligned. Pattern transfer results in a line-space pattern with self-aligned customizations directly determined by the prepattern. In the transferred pattern, pinning lines determine the placement of single-line gaps while blockout features determine the placement and size of perpendicular trim across lines. By using designed two-dimensional chemical patterns, this self-aligned, bidirectional customization scheme enables the fabrication of high-resolution circuit-relevant patterns with fewer trim/exposure steps.

Computational lithography platform for 193i-guided directed self-assembly

We continue to study the feasibility of using Directed Self Assembly (DSA) in extending optical lithography for High Volume Manufacturing (HVM). We built test masks based on the mask datatprep flow we proposed in our prior year’s publication [1]. Experimental data on circuit-relevant fin and via patterns based on 193nm graphoepitaxial DSA are demonstrated on 300mm wafers. With this computational lithography (CL) flow we further investigate the basic requirements for full-field capable DSA lithography. The first issue is on DSA-specific defects which can be either random defects due to material properties or the systematic DSA defects that are mainly induced by the variations of the guiding patterns (GP) in 3 dimensions. We focus in studying the latter one. The second issue is the availability of fast DSA models to meet the full-chip capability requirements in different CL component’s need. We further developed different model formulations that constitute the whole spectrum of models in the DSA CL flow. In addition to the Molecular Dynamic/Monte Carlo (MD/MC) model and the compact models we discussed before [2], we implement a 2D phenomenological phase field model by solving the Cahn-Hilliard type of equation that provide a model that is more predictive than compact model but much faster then the physics-based MC model. However simplifying the model might lose the accuracy in prediction especially in the z direction so a critical question emerged: Can a 2D model be useful fro full field? Using 2D and 3D simulations on a few typical constructs we illustrate that a combination of 2D mode with pre-characterized 3D litho metrics might be able to approximate the prediction of 3D models to satisfy the full chip runtime requirement. Finally we conclude with the special attentions we have to pay in the implementation of 193nm based lithography process using DSA.

Customization and design of directed self-assembly using hybrid prepatterns

Diminishing error tolerance renders the customization of patterns created through directed self-assembly (DSA) extremely challenging at tighter pitch. A self-aligned customization scheme can be achieved using a hybrid prepattern comprising both organic and inorganic regions that serves as a guiding prepattern to direct the self-assembly of the block copolymers as well as a cut mask pattern for the DSA arrays aligned to it. In this paper, chemoepitaxy-based self-aligned customization is demonstrated using two types of organic-inorganic prepatterns. CHEETAH prepattern for “CHemoepitaxy Etch Trim using a self-Aligned Hardmask” of preferential hydrogen silsesquioxane (HSQ, inorganic resist), non-preferential organic underlayer is fabricated using electron beam lithography. Customized trench or hole arrays can be achieved through co-transfer of DSA-formed arrays and CHEETAH prepattern. Herein, we also introduce a tone-reversed version called reverse-CHEETAH (or rCHEETAH) in which customized line segments can be achieved through co-transfer of DSA-formed arrays formed on a prepattern wherein the inorganic HSQ regions are nonpreferential and the organic regions are PMMA preferential. Examples of two-dimensional self-aligned customization including 25nm pitch fin structures and an 8-bar “IBM” illustrate the versatility of this customization scheme using rCHEETAH.

Measurement of placement error between self-assembled polymer patterns and guiding chemical prepatterns

Extensive pattern customization will be necessary to realize viable circuit patterns from line-space arrays generated by block copolymer directed self assembly (DSA). In pattern customization with regard to chemical epitaxy of lamellar block copolymers, quantitative and precise knowledge of DSA-feature registration to the chemical prepattern is critical. Here we measure DSA pattern placement error for spatial frequency tripling and quadrupling indexed to specific lines in the chemical prepattern. A range of prepattern line widths where minimal DSA placement error can be expected is identified, and a positive correlation between DSA placement accuracy and prepattern uniformity is shown. Considering the experimental non-idealities present in the chemical prepatterns used in this work that arise from using electron-beam lithography, we anticipate that 3σ DSA placement errors will be at a minimal level if highly uniform chemical prepatterns produced by optical lithography are used.

Raman Spectroscopy for Characterization of Semiconducting Nanowires

Raman scattering behavior germane to semiconductor nanowires (NWs) and the application of Raman spectroscopy to characterize the structure, composition, strain, and temperature of individual semiconductor nanowires with submicron resolution are discussed.