Sub-wavelength Holographic Lithography: The Possibilities And Advantages. (NANOTECH SWHL, 6-1 Kazarmenny per., Moscow, Russia)

Transcription

1 Sub-wavelength Holographic Lithography: The Possibilities And Advantages Mikhail V. Borisov, Dmitriy A. Chelyubeev, Vitalij V. Chernik, Alexander A. Gavrikov, Dmitriy Yu. Knyazkov, Petr A. Mikheev, Vadim I. Rakhovsky, Alexey S. Shamaev (NANOTECH SWHL, 6-1 Kazarmenny per., Moscow, Russia)

2 What is proposed? 1) Replace traditional mask with a hologram (Sub-wavelength holographic mask - SWHM) 2) Completely remove projection system Exposure stage at conventional projective lithography 1 Exposure stage at sub-wavelength holographic lithography (SWHL) 1. Carl Zeiss Patent, US , 2004

3 Hologram pattern (SWHM) structure Desired topology in Si-wafer Corresponding SWHM Small part of SWHM The small part structure 300 nm 300 nm 300 nm 9 transmission clusters Pattern of one transmission cluster «Pixels» of transmission cluster (Transmission Areas)

4 Stability of aerial image to SWHM local defects (big square defect) SWHM without defects SWHM with big square defect 25% of right peak is closed Aerial images (bottom raw) created by the corresponding SWHMs (upper raw)

5 Stability of aerial image to SWHM local defects (random dust) 0% 44.8% 98.6% Aerial image reconstructed from SWHM changes as part of SWHM area is covered with random dust. Images were reconstructed from SWHM with 0%, 44.8% and 98.6% area dusted Conditions of computer simulation: High level of tolerance to local defects for SWHM is illustrated by images reconstructed from a SWHM for a test topology. Brightness is normalized for the all three images. Without this normalization brightness decreases in proportion to the area which is covered with dust.

6 Virtual Phase-Shift Object wave Reference wave Virtual object: green - 0º, red - 180º Optical scheme of hologram synthesis: object - O, hologram (SWHM) H, NA=0,53 Exists only in computation! SWHM transparency function for the test image consisting of 15 strips Desired topology Aerial image for 15 strips reconstructed from this SWHM with the shown transparency function

7 Applying Virtual Phase-Shift Virtual Strong Phase-Shift Minimal distance between elements is equal to about λ/2, where λ is a reconstructing radiation wave-length. This topology allows to get bicolor image in such a way that every two elements having a minimal distance between them are colored with different colors. Virtual Strong Phase-Shift is applied to memory cell topology Recovered contour (threshold level = 0.2) This topology structure doesn t allow the use of Strong Phase-Shift Virtual Weak Phase-Shift: red - 0º, green - 120º, blue - 240º Recovered aerial image Virtual Weak Phase-Shift This example of a topology doesn t allow 180 Phase-Shift technology implementation, but allows «Weak» Phase-Shift technology, where phase is being shifted by 120. Disregarding whether it is possible to create such a phase-shift by a traditional technology, we can create it for almost any topology.

8 Conventional OPC and Virtual HoloOPC Chris Mack, «Fundamental Principles of Optical Lithography:The Science of Microfabrication», 2007 John Wiley & Sons Desired topology Contours of aerial image without HoloOPC Virtual HoloOPC NANOTECH SWHL Contours of aerial image with HoloOPC NANOTECH SWHL

9 Phase-noise suppression If SWHM quartz substrate is not absolutely flat, local thickness variations result in phase changes and phase noise. Magnitude of phase noise is determined by maximum deviation of thickness. Thickness map of SWHM substrate Results of modeling of image recovery from SWHM created on substrates with various thickness irregularity 1,5λ λ λ/2 1,5λ. Noise suppression by calculation

10 Challenge 1: zero diffraction order Phase-shifting layer on the hologram suppresses the zero diffraction order. The reconstructed image is practically free from the zero diffraction order when transmission function average value for the whole synthesized SWHM is equal to zero. However in this case transmission function would be negative at certain SWHM s domains. During manufacturing such SWHM this negative values domains should be coated with a phase-shifting layer. The domains to be coated have smooth boarders that simplifies technological realization of the mentioned above coating After recovering an image from a hologram three images appear: 1 real image 2 conjugate image 3 0-order diffraction image Our method of SWHM production allows to get rid of parasitic illumination caused by 0-order while increasing intensity of real and conjugate images by 20%.

11 Challenge 2: Full-size chip calculations 1) HPC clusters are used for everyday calculations 2) A specially designed algorithm allowing to calculate SWHM for full-size IC topology layers on state-of-the-art HPC clusters was developed and implemented as a part of parallel software package. MIIT T4700 and MVS-100K supercomputers 3) A project of specially designed computational system (8 nodes: quad-core Opteron CPU + 8 GPUs) for calculation of real IC layer containing elementary pixels is under development. This computing system could perform SWHM synthesis for real IC layer in 8 hours. SWHM synthesis for elements The initial topology contains 150'944'944 elementary topology fragments situated periodically or about elementary pixels. Linear dimension of each pixel is equal to 0.65 of wavelength. Periodically repeated elementary topology fragment One of about 1500 SWHM transmission areas Fragment of reconstructed aerial image (threshold level is 0.2 from the maximum intensity)

12 SWHL Advantages Computer Generated Hologram (SWHM) Projection lens free optical scheme Simple hologram pattern structure Immunity to SWHM local defects Computer Generated Hologram (SWHM) Virtual Phase-Shift Virtual OPC Object wave Reference wave Aberrations compensation

13 Main features of SWHL CD = k λ NA NA up to 0.7 Immersion is possible (NA ~ 1.35) Multi-patterning is possible OPC & Phase-Shift (only computation!) Radiation sources are available (λ=212nm, 193nm) Immunity to SWHM local defects Projection lens free optical scheme