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Radial Temperature Gradient Detector

IP.com Disclosure Number: IPCOM000081134D
Original Publication Date: 1974-Apr-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 4 page(s) / 67K

Publishing Venue

IBM

Related People

Bratter, RL: AUTHOR [+2]

Abstract

Structural defects, or slip, in thin films deposited by the Chemical Vapor Deposition (CVD) method are directly related to product failure in integrated circuit manufacturing.

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Radial Temperature Gradient Detector

Structural defects, or slip, in thin films deposited by the Chemical Vapor Deposition (CVD) method are directly related to product failure in integrated circuit manufacturing.

The major contributor during CVD processing has been attributed to and defined as excessive temperature gradients, J. Bloom et al., Journal of Applied Physics, Volume 43, No. 3, March 1972.

Experience and the literature indicates that radial (or tangential) temperature gradients on the product (disk or wafer) are most critical during steady high temperatures (>1000 degrees C), at the beginning of the deposition cycle (neucleation period) and immediately afterward. This period is typically 30 seconds to 1 minute. This fact excludes purely manual means of tracking events meaningfully in this period, T. Kamis et al., Thin Solid Films, 16(1973), pp. 147- 165.

Slip occurs at steady temperatures above 1000 degrees C and propagates through the thin films deposited on the substrate, when a disk (wafer) undergoes a deflection beyond the plastic limits of the material or buckles. All materials exhibit deflections (stress relieving) when heated. During these deflections, if the surfaces (outside fibers) are stressed beyond the plastic limit of the material, permanent dislocations in the structural pattern of the material will take place.

In thin circular disks (wafers), uniform deflections cause diaphragm stresses, and nonuniform deflections cause buckling. Both of these stresses are nonlinear, and the circumferential compression may cause the buckling.

It is known that, at 1200 degrees C uniform temperature, a 10 degree C/cm thermal gradient across a 2" diameter silicon wafer will cause excessive slip and, under identical conditions, the diameter of the wafer and the permissible thermal gradient has a direct relationship.

The mechanical bending (Equation No. 1) and the stress relations (Equations Nos. 2 and 3) are expressed by J. Prescott, "Applied Elasticity", Longman, Green & Co., 1924:

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The radial stress for a parabolic temperature distribution is expressed by P. Penning, Philips Research Report 13, 79(1958) (Equations 4 and 5): 4) Sigma(r) = Sigma(o) (r/2/ over R/2/ -1)

5) Sigma(Phi) = Sigma(o) (3r/2/ over R/2/ -1)

Where:

E = Modulus of elasticity

a = Radius of wafer

W = Unit load

y = Maximum deflection

s(b) = Bending stress

1

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s = Total stress

v = Poisson's ratio (1/m)

t = Thickness

R = Radius of wafer

o(r) = Radial stress

o(Phi) = Tangential stress.

The parabolic radial temperature distribution is expressed by Huff et al., Journal of Electrochemical Society, 118, 143(A71).

The radial temperature gradient detector was developed to provide a practical in situ measurement means (output) during the CVD process, where the radial temperature gradients exposed on the...