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An In Situ Etch Rate Monitor Controller

IP.com Disclosure Number: IPCOM000088974D
Original Publication Date: 1977-Aug-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 3 page(s) / 44K

Publishing Venue

IBM

Related People

Bassous, E: AUTHOR [+2]

Abstract

This article describes a device for measuring the etch rate of material while it is immersed and etching inside a chemical solution. The method is particularly applicable to the etching of silicon wafers. The device is termed an Etch Rate Monitor (ERM) which is suitable for the determination of the etch rate of silicon while the silicon sample is immersed in the etching solution. Its major advantages are: (a) in-situ measurements can be made and (b) continuous readings are possible without disturbing any part of the system. The ERM is particularly useful in the fabrication of silicon nozzles and in the study of the etching behavior of Si and similar materials.

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An In Situ Etch Rate Monitor Controller

This article describes a device for measuring the etch rate of material while it is immersed and etching inside a chemical solution. The method is particularly applicable to the etching of silicon wafers. The device is termed an Etch Rate Monitor (ERM) which is suitable for the determination of the etch rate of silicon while the silicon sample is immersed in the etching solution. Its major advantages are: (a) in-situ measurements can be made and (b) continuous readings are possible without disturbing any part of the system. The ERM is particularly useful in the fabrication of silicon nozzles and in the study of the etching behavior of Si and similar materials.

The principle employed here for determination of etch rates is based upon measurements of the electrical resistance of a silicon wafer while it is immersed in the etchant. Four-point probe or Van der Pauw techniques are two well known measurement methods used in semiconductor technology. For example, in the four-point probe method the measured sheet resistivity R(s) is given by the resistivity R = thickness x of the wafer. Assuming R = 1 ohm cm and x = 0.02 cm, a change in thickness Delta x = 1 Mu m produces a change Delta R(s) given by:

(Image Omitted)

The initial change in sheet resistivity is 0.25 ohm/sq. for a change in thickness of 1 Mu m. Such a change in R(s) can readily be measured, and, therefore, the etch rate can easily be computed by monitoring R(s) while the wafer is in the etching solution. The sensitivity of this technique can be increased significantly by using thin, high resistivity wafers. For example, a wafer
0.01-cm thick and 20-ohm cm resistivity will change initially by 20 ohm/sq. per Mu m of etched Si. Since a change of 0.2ohm/sq. is readily measurable, it is possible to detect changes in thickness of 100 Angstroms.

A representative sketch of an ERM 2 is shown in the figure. The ERM is comprised of sections 4 and 6 which are made of an inert material, such as TEFLON*. A silicon wafer 8, which is to be etched, is secured against 0-rings 10 by a TEFLON nut 12. Sections 4 and 6 are secured together by screws (not shown) in screw holes 14, with 0-rings 16 providing a fluid-tight seal. Four probes 18, 20, 22 and 24 are mounted in section 6 such that they just touch the back surface of silicon wafer 8 when sections 4 and 6 are secured together. Four wires 26, 28, 30 and 32 are connected to probes 18, 20, 22 and 2~, respectively. Wires 26 and 32 are connected to a constant curre...