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Method for Determination of Silicon-Silicon Dioxide Interface Stress in Thermally Grown Extra Thin Films

IP.com Disclosure Number: IPCOM000044637D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 3 page(s) / 35K

Publishing Venue

IBM

Related People

Pugacz-Muraszkiewicz, I: AUTHOR

Abstract

The method described provides an analytical tool for the investigation of the distribution of stress with respect to the thickness in silicon dioxide films. This in turn provides the potential for evaluation of oxidation processes. Other techniques have been used to measure stress in silicon dioxide films. However, they have inherent disadvantages. More particularly, the methods are useful with thicker oxides, i.e., 300 angstroms and above, and they require masking processes. In addition, the known techniques involve the use of considerable area of the sample to take advantage of etching-rate difference at room temperature or utilize an etching process which may take several days to etch silicon.

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Method for Determination of Silicon-Silicon Dioxide Interface Stress in Thermally Grown Extra Thin Films

The method described provides an analytical tool for the investigation of the distribution of stress with respect to the thickness in silicon dioxide films. This in turn provides the potential for evaluation of oxidation processes. Other techniques have been used to measure stress in silicon dioxide films. However, they have inherent disadvantages. More particularly, the methods are useful with thicker oxides, i.e., 300 angstroms and above, and they require masking processes. In addition, the known techniques involve the use of considerable area of the sample to take advantage of etching-rate difference at room temperature or utilize an etching process which may take several days to etch silicon. The method described herein consists of a series of silicon anisotropic etching and ultrasonic shaking steps which allow the formation of an oxide shelf at the perimeter of an opening. Once the underlying silicon is removed, the liberated silicon dioxide shelf deflects into sinusoidal undulations which can be mathematically analyzed to calculate the strain of the thin film. This method allows measurement of stress in oxides thinner than 100 angstroms. In addition, the method disclosed avoids the other limitations mentioned above. A new etchant, Na4SiO4, etches oxide at a relatively low rate at 50OEC, and etches the silicon at a fast rate at that temperature. The fast etching rate of silicon cuts the preparation time of the test site to a few minutes, while the slow silicon dioxide etching rate allows the technique to be practiced with very thin oxides. The step- by-step processing sequence is illustrated in Figs. 1-4 and is explained hereinafter. During the first step a discontinuity is revealed in the silicon dioxide layer which overlies the silicon, as shown in Fig. 1. The discontinuity can be a crack in the silicon dioxide, or it can be an opening formed in the silicon dioxide by conventional technique. In step 2, an aqueous one mole solution of Na4SiO4 is applied at 50OEC for about three minutes to etch the underlying silicon. This removes an area of silicon, as illustrated in Fig. 2, without enlarging the oxide opening substantially. Upon completion of the previous step, an ultrasonic water bath is applied to the opening to break off the liberated oxide along the perimeter of the pit formed i...