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Photoresist Adhesion

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YIELD Engineering Systems Inc.

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PHOTORESIST ADHESION 

YES introduced a process now commonly known in the semiconductor industry as vacuum bake/vapor prime, a key step in the front end processing of silicon chips. The process dramatically improves the application of hexamethyldisilizane (HMDS) as a surface priming treatment, which is used to enhance adhesion of photoresist on a wafer surface.
Early application of HMDS used immersion or spraying of liquid chemical onto the surface of the wafer in a room atmosphere, but wet HMDS application processes have limited surface longevity. Process engineers must apply photoresist within a few hours of HMDS treatment or the surface modification affects of the HMDS are degraded or lost.
Investigation into the limited surface longevity revealed the culprit was water vapor, which is always entrained on surfaces exposed to atmosphere. Effectively, the HMDS was bonding to a microscopic water layer rather than to the wafer surface.
In order to extend the lifespan, first, wafers must be completely dehydratedónot only surface moisture, but chemically bound water molecules as well. To achieve this, Yield Engineering Systems developed a process combining high temperature with low pressure. The YES-1224 removes the moisture that is chemically bound to the surface so the silane/substrate bond isnít impaired.
Then, when chemical is applied, a superior bond is formed that is stable even after exposure to atmospheric moisture. Wafers properly treated will last for weeks with no change to surface adhesion.

BENEFITS 

Yield Engineering Systemís YES 450PB Series

The Vacuum Bake/Vapor Prime process offers several process advantages over liquid HMDS application:

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Chemical Deposition Uniformity

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Contact Angle Control Within +/- 3 Degrees

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Moisture Resistant Surface Modification

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Increased Time Available Between Process Steps

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Angstrom-Level Thickness Control

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Reduced Chemical Costs

Equipment such as the YES-450PB Series, YES-PBV300, and YES-1224 continue to reduce costs while increasing yield for chip manufacturers.

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Last modified: 2016-08-22