Generic selectors
Exact matches only
Search in title
Search in content
Post Type Selectors
Filter by Categories
Case Studies

Amplifying Adhesion: HMDS Bake

Our client faced persistent issues with photoresist delamination during the photolithography process. To address this, we implemented a solution involving Hexamethyldisilazane (HMDS) priming using the Apogee® 200mm Bake Plate. This enhanced photoresist adhesion, improved yield, reduced defects, and lowered costs, ultimately streamlining project timelines. Additionally, a 75° contact angle was achieved within a 90-second process, showcasing the success of the solution.


Facing challenges with inconsistent adhesion of photoresist in the photolithography process, the client encountered persistent issues with photoresist delamination. Initial process optimizations included surface preparation, testing different photoresists, and modifying process parameters, with no positive outcomes. As a consequence, they continued to experience reduced throughput, increased expenses, rework, and delayed project timelines. In order to establish a durable bond between the substrate and the photoresist, the wafer surface was prepped with HMDS before the coating.


A review of the client’s existing process included an analysis of the following potential causes:

  • Surface Contamination
  • Inadequate Surface Activation
  • Surface Roughness
  • Incompatible Materials
  • Insufficient Bake
  • Improper Spin Coating
  • Contaminated Photoresist
  • Substrate Temperature
  • Chemical Incompatibility
  • Aging of Photoresist

The root cause of the poor adhesion was identified as inadequate bonding of the photoresist due to absorbed water in the silicon wafer from ambient humidity. A simple dehydration bake was inadequate to resolve the issue. The use of hexamethyldisilazane (HMDS) chemical vapor deposition (CVD) was proposed for use before the application of photoresist.


HMDS priming enhances the substrate surface for photoresist adhesion through the formation of a hydrophobic monolayer, reducing surface energy to ensure uniform coating. This layer also prevents air entrapment, enhancing photoresist wetting and minimizes defects during photolithography.

The Apogee® 200mm Bake Plate served as the ideal foundation to accommodate the client’s substrate sizes. The standard bake process model was modified to include the following and then installed into the X-Pro II Workstation:

• vacuum chamber hood with an HMDS inlet
• pressure can with HMDS bubbler for vaporization
• control box with specialized valves
• recipe-controlled process parameters via Datastream™ software

Operational Flow:
1. Set the bake plate to the desired temperature.
2. Initiate vacuum inside the chamber to commence the initial dehydration bake.
3. Nitrogen pre-purge to eliminate oxygen from the chamber.
4. Introduce HMDS vapor to the chamber, promoting the formation of a monolayer on the wafer.
5. Apply vacuum to the wafer to bake off residual HMDS and displace remaining water molecules.
6. Nitrogen post-purge, ensuring complete removal of HMDS from the chamber.



A contact angle measurement provides important insight into the HMDS process. For photoresist coating, a measurement between 60-90 degrees is typically desired for proper wetting and adhesion. Unfortunately, a standard silicon wafer is measured at only ~40 degrees. The application of HMDS, brings the contact angle into the acceptable range.

With this implementation, the customer was able to demonstrate a 75 degree contact angle which led to a marked improvement in:

• Photoresist Adhesion
• Throughput (90 second process)
• Minimized Defects
• Decreased Rework
• Yield

Project timelines were reduced, promoting efficiency and a reduction in costs.

Technical Details

Substrate Sizes







Technical Details

Vacuum Chamber: >24 inHg vacuum

HMDS canister with tube-controlled bubbler from 0-10 lpm

Rotameter-controlled pre/post inert (N2) gas purge, controlled from 0-5 lpm

Temperature range up to 180°C

Recipe controlled via Datastream™ software



silicon & silicon oxide wafers

Share It!
Share It!