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Low-Stress Tungsten Films

IP.com Disclosure Number: IPCOM000038493D
Original Publication Date: 1987-Jan-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Ahn, KY: AUTHOR [+2]

Abstract

This article describes a technique wherein the high internal stress in sputtered tungsten films is reduced to a very low level, solving many problems associated with high stress. Tungsten films prepared by high-rate magnetron sputtering are considered to be used in VLSI technology for bipolar and FET devices because of low resistivity, and ability to withstand high-temperature processing. However, one problem with this material is the ever-present high stress in these films. The stress level can be adjusted by varying one of the deposition parameters, such as the Ar pressure, during sputtering, as shown in the figure. However, the cross-over pressure varies from day to day depending upon the background pressure and other plasma conditions, and it is not easy to reproduce.

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Low-Stress Tungsten Films

This article describes a technique wherein the high internal stress in sputtered tungsten films is reduced to a very low level, solving many problems associated with high stress. Tungsten films prepared by high-rate magnetron sputtering are considered to be used in VLSI technology for bipolar and FET devices because of low resistivity, and ability to withstand high-temperature processing. However, one problem with this material is the ever-present high stress in these films. The stress level can be adjusted by varying one of the deposition parameters, such as the Ar pressure, during sputtering, as shown in the figure. However, the cross-over pressure varies from day to day depending upon the background pressure and other plasma conditions, and it is not easy to reproduce. A technique has been developed wherein the total thickness of the desired film is divided into two, whereby the first half of the film is deposited at a lower pressure so the stress is compressive, while the second half of the film is deposited at a higher Ar pressure to produce tensile stress. Thus, the net stress will be either zero, or very small, as compared with a single-layer film. Extensive measurements of stress by X-ray technique revealed the operability of this technique, as observed in the figire, which shows stress as a function of sputtering gas pressure, Ar as measured by X-ray parallel and perpendicular to the scan direction during film growth. Stressgaug...