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Control of Film Stress for Improved Device Performance

IP.com Disclosure Number: IPCOM000049238D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 4 page(s) / 102K

Publishing Venue

IBM

Related People

Brady, MJ: AUTHOR [+4]

Abstract

Contact metallurgies used in semiconductor device fabrication have large intrinsic stress values which are grown into the material due to the deposition process. This stress generates microcracks and other defects in the semiconductor devices (1). The defects reduce the carrier mobility and device lifetime with the consequence of reductions in device performance and reliability as well as manufacturing yields. One example of these problems is the dark line defect problem found in GaAs lasers. Extreme examples are microcleavages induced as materials due to contact metallurgy stress. These effects are shown in Figs. 1 and 2, and discussed in (2). Fig. 1 shows the microcleavage of a Si(3)N(4)-coated silicon substrate which was caused by the stress in the deposited niobium contact metallurgy. Fig.

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Control of Film Stress for Improved Device Performance

Contact metallurgies used in semiconductor device fabrication have large intrinsic stress values which are grown into the material due to the deposition process. This stress generates microcracks and other defects in the semiconductor devices (1). The defects reduce the carrier mobility and device lifetime with the consequence of reductions in device performance and reliability as well as manufacturing yields. One example of these problems is the dark line defect problem found in GaAs lasers. Extreme examples are microcleavages induced as materials due to contact metallurgy stress.

These effects are shown in Figs. 1 and 2, and discussed in (2).

Fig. 1 shows the microcleavage of a Si(3)N(4)-coated silicon substrate which was caused by the stress in the deposited niobium contact metallurgy. Fig. 2 shows the microcleavage in a GaAs substrate which was produced by the intrinsic stress of a deposited copper film.

In addition to the defects induced by a stress contact, metallurgical stress induces corrosion. The corrosion rate is increased by both macroscopic (total) stress and the localized stress at at grain boundaries and voids.

A further problem with stress in deposited films is the spontaneous spallation found when attempting to deposit thick films. Therefore, stress in deposits limits the thickness of films as well as the reliability of contacts.

The stress in the metallurgy is controlled by deposition conditions. By judicious selection of substrate temperature, deposition rate, bias (when appropriate), etc., the stress in these films may usually be reduced but not eliminated.

Recently, the variation of stress with high energy ion bombardment of a growing film has been reported (3). Ion energies of 1 to 10 KeV and higher were used. The use of high energy bombardment of depositing films has great disadvantages due to damage induced in the material as well as the enhanced resputtering of material which is attempted to be deposited. Therefore, a high energy process has less practical applications than a low energy process.

Stress-induced corrosion rates are usually reduced by trying to eliminate the chemical species responsible for corrosion. This is done by using contamination- free environments and handling. Also, the device is usually encapsulated with a protective layer.

A method of improving device characteristics by eliminating the stress in thin film metallurgy is described. This reduction and control of stress is achieved by bombarding the growing film with a controlled ion beam. Fig. 3 shows one configuration of the simultaneous bombardment and deposition process. In this figure, item 1 is the ion source, 2 is the ion beam, 3 is the evaporation source, 4 is the evaporated species, and 5 is the substrate platform with substrates. The ion beam source used is a wide-beam multiple aperture source where the ion current density and ion energy are varied independently.

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