Stepper 3 (ASML DUV)

Stepper 3 (ASML DUV) Tool Type Lithography Location Bay 7 Supervisor Demis D. John Supervisor Phone (805) 893-5934 Supervisor E-Mail demis@ucsb.edu Description Deep-UV Stepper Photolithography Manufacturer ASML Model PAS 5500/300 Lithography Recipes Sign up for this tool

About

General Capabilities/Overview

The ASML 5500 stepper is a 248nm (KrF) DUV stepper for imaging dense features down to below 200nm and isolated line structures down to below 150nm (with effort). 300nm+ features are relatively "easy" to resolve. Layer-to-layer overlay accuracy is better than 30nm.

The system is configured for 4” wafers. The system is designed for high throughput, so shooting multiple 4" wafers is extremely fast, typically minutes per wafer, but any size other than 4-inch is difficult to work with (see below for more info). Additionally, exposure jobs are highly programmable, allowing for very flexible exposures of multiple aligned patterns from multiple masks/reticles in a single session, allowing for process optimization of large vs. small features in a single lithography.

The full field useable exposure area is limited to the intersection of a 31mm diameter circle and a rectangle of dimensions 22mm x 27mm. Users have stitched multiple photomasks together with success. See the Mask Making Guidelines page for more info on exposure field sizes and how to order your mask plates.

Tutorial: If you are not familiar with the differences between Contact Litho and Stepper Litho, please review this short tutorial: Demis D. John - Stepper_Reticle_Layout_vs_Wafer_Layout.pdf

• Explains how a Stepper mask can have many designs, and flexibly pattern the wafer with combos of designs.

Photoresists Available

See PhotoLith. Recipes for full process info & links to PR datasheets.

• UV210-0.3 - Positive: 300nm nominal thickness
• UV6-0.8 - Positive: 800nm nominal thickness
• UV26-2.5 - Positive: 2.5um nominal thickness
• UVN2300-0.5 - Negative: 500nm nominal thickness

• DUV42P-6/DS-K101 - Bottom Anti-Reflective Coatings “BARC”
• PMGI/LOL1000/LOL2000 - Underlayers

AZ300MIF Developer for all processes

Many of these DUV PR's are also able to be exposed with EBL.

Part Size Limits

With staff support, mounted pieces down to 14mm in size can be exposed using a 4” wafer as a carrier. Flatness will typically be worse in this situation, so small <<500nm features will usually have bad uniformity across the mounted part due to focus variations. Edge bead on irregular pieces (eg. quarter-wafers/squares) will significantly reduce yield/uniformity.

Multi-layer Alignment on mounted parts is particularly difficult, requiring either semi-permanent mounting to the carrier (eg. BCB, SU8 etc.) or significant difficulty/effort to re-align the part to the carrier wafer on each lithography (≤100µm re-mounting accuracy needed).

At this time the maximum wafer size is 4” (100mm) wafers with SEMI standard wafer flat (not Notch).

Service Provider

• ASML - ASML performs quarterly periodic maintenance and provides on-demand support.

Process Information

• Process Recipes Page > "Stepper 3" - Established recipes and corresponding linewidths, photoresists etc.
• Sample size: 100 mm wafers with SEMI std. major flat
  • Piece-parts process is possible but difficult - contact supervisor for info
• Alignment Accuracy: < 50 nm
• Minimum Feature Size: ≤150 nm isolated lines, ≤200 nm dense patterns
  • To achieve ≤200nm features with high uniformity, we recommend wafers with total thickness variation (TTV) ≤5µm, and designing your CAD with a smaller Image Size for the high-res. feature.
• Wafer Thickness: Minimum ≈ 200µm, Maximum ≈ 1.1 mm
• Maximum Dose: ~100mJ
  • Non-chemically amplified EBL resists are not permissible due to this limit.

Maximum Wafer Bow

Measured over 90mm on the Tencor Flexus

• Do not run wafers with bow values higher than the following values, contact supervisor for advice if needed.
• Silicon wafers (~550µm thick): 100 µm will likely fail.
• Sapphire (less pliable), ≥60µm bow will intermittently fail - DO NOT RUN
  • This applies especially for GaN-on-Sapphire, which often have high wafer bow.
• Near these values, and you may lose the wafer inside the machine due to wafer vacuum error - DO NOT RUN if unsure.
• Substrate material and substrate thickness affect this limit - please contact supervisor for advice.
• You can stress-compensate wafers to reduce the wafer bow, eg. via dep. on the back side of the wafer. If you wafer is concave down, then depositing a compressive film on the back will reduce its curvature. Coat the backside of the wafer with compressive PECVD SiO2 or IBD SiN, or other compressive films for concave-down bow.

Operating Procedures

All procedures are access-restricted only to authorized users with a UCSB NetID (YourNetID@ucsb.edu), by vendor request.
Please contact supervisor for access/training.

ASML Operating Procedures - access-restricted google drive folder of PAS 5500/300 operating procedures.

Stepper #3 Training Videos - these provide bookmarked quick-reference to various tool procedures & programming.

• To access, you must log in with your UCSB NetID, formatted like MyNetID@ucsb.edu - this is a Google login!
• Please contact the tool supervisor if you need access.
• Trouble accessing? Please click here for tips.

Training Procedure

To get access to this tool, please do the following:

1. Email the supervisor for access to the training materials. Please provide your UCSB NetID.
2. Study the training videos.
   1. If you are a technician and will never program jobs, only Part 1 is necessary.
3. "Shadow" someone in your group who uses the machine, until you are completely comfortable with (1) wafer cleaning (critical), (2) reticle load/unload and (3) running a pre-made job. When you are ready, do step 4:
4. Contact the supervisor for an short hands-on check-off, after which you'll get SignupMonkey access.

Design Tools

Mask Design and CAD files

• Stepper Mask-Making Guidelines - Generic info needed to design and order a reticle for any Stepper system. This is minimal unrestricted info that is viewable without additional paperwork.

• ASML-specific Mask Making Guidelines - All the detailed info you need to design and order a reticle for this specific ASML system.
  • Access is restricted to trained users only - please contact tool supervisor for access.
• Tutorial: Demis D. John - Stepper_Reticle_Layout_vs_Wafer_Layout.pdf

• See the Calculators + Utilities > CAD Files & Templates page for other useful CAD files, such as overlay verniers, vented fonts etc.

UCSB Photomasks Available

• UCSB DUV Reticles - Photomasks available with various Alignment Markers (contact, EBL), Resolution Testing etc.

Optical Proximity Correction (OPC): Going below resolution limit

• OPC General information and detailed investigation of lateral DBR patterns - Detailed info and investigation of OPC, use case examples, performance comparisons, how to order etc. By Gopikrishana G. Meena.
• UCSB Nanofab users have access to order photomask plates with OPC corrections applied to the patterns to enable accurate lithography on high-resolution structures, with a single photomask order.
• Model-based, "feed-forward" OPC - meaning you order only one photomask, no "feed-back", nor 2nd mask required.
• Photronics Inc. - OPC corrected mask plate provider for UCSB Nanofab users.
  • Contact Demis for quotes.
  • Photronics Inc. is collaborating with the Nanofab to develop + provide OPC correction to UCSB researchers.
  • Photronics' team has built a model-based OPC correction for our system, which appears to work for multiple photoresists (UV6-positive and UVN-negative tested so far).
  • Current OPC rules are for: Conventional (circular) Illumination / NA=0.57 / sigma=0.75

OPC Mask Correction	Positive Resist: UV6-0.8 - Lateral Waveguide Gratings with/without OPC on same photomask. Collaboration with photomask vendor Photronics Inc.
Rule-based OPC applies serifs to your patterns.	The Best exposure without OPC corrections; doesn't meet device criteria. Would require ordering a 2nd mask to correct.	With OPC applied to the patterns, the device criteria (length and spacing) are met on 1st mask rev, and process window is possibly wider.

Negative PR: UVN30. ASML DUV with and without same MB-OPC, on the same photomask, applied to a Meta-optic. Fabricated by Skyler Palatnik, Prof. Max Millar-Blanchaer's group in collaboration with photomask vendor Photronics Inc.
With OPC applied to mask pattern. Squares and circles with small gaps+small posts are resolved in one exposure.	Without OPC (standard photomask process). No combination of focus/dose can achieve desired results - "best" result shown here.

JobCreator: Python Scripting

• Create ASML Job files using python. Click the above link for more info.

Recipes

• Recipes > Lithography > Stepper Recipes > Stepper #3 - starting processes for various DUV photoresists, including Dose/Focus values.

To calibrate your own Litho processes, you will need to:

• Run your own Focus Exposure Matrix - this procedure shows how to do this on the ASML software
• Lithography Calibration - Analyzing a Focus-Exposure Matrix - how to analyze an FEM

Litho. recipes for all our photolith. tools can be found on the Photolithography Recipes page.

Process Control Data

• The Process Group regularly measures the lithography Critical Dimension ("CD") and Wafer-stage Particulate Contamination for this tool, using a sensitive lithography process that will reveal small changes in Dose repeatability and wafer flatness.
• Data Table for CD Uniformity and Particulate Contamination
• Plots of CD Repeatability

Example of Data Table with SEM's of 320nm features. Click for full data table.

Example SPC Chart - Measured Critical Dimension "CD" versus Date. Click for current charts.