Browse Prior Art Database

Metal Etch Monitor

IP.com Disclosure Number: IPCOM000076317D
Original Publication Date: 1972-Feb-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Hoekstra, JP: AUTHOR

Abstract

In the metal etching of a large batch of samples, the total etch time is generally determined by the testing of one sample. The completion of the etch cycle is determined by the total time required to delineate the etch pattern. Because of variations in the metal distribution per sample and per batch, a certain amount of overetching is necessary to insure that all of the samples are clean etched. In addition, the temperature of the etchant which is employed also affects the total etch time. When a batch of samples is inserted in the etchant, it causes a temperature change that affects the etch rate. Because of these variables, a visual inspection is also necessary to insure that each sample is properly etched.

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Metal Etch Monitor

In the metal etching of a large batch of samples, the total etch time is generally determined by the testing of one sample.

The completion of the etch cycle is determined by the total time required to delineate the etch pattern. Because of variations in the metal distribution per sample and per batch, a certain amount of overetching is necessary to insure that all of the samples are clean etched. In addition, the temperature of the etchant which is employed also affects the total etch time. When a batch of samples is inserted in the etchant, it causes a temperature change that affects the etch rate. Because of these variables, a visual inspection is also necessary to insure that each sample is properly etched.

There is described herein a technique which enable the determination of the completion of the etch cycle and wherein the dimensions of the etch pattern are inspected. in the technique, the metallized sample is examined as to its transparency to infrared light. The transmitted light intensity is a function of the degree of completion of the metal pattern to be etched. Because each sample is monitored individually, the final results are not adversely affected by metal thickness variations or by changes in temperature of the etchant. The technique is, therefore, advantageously adaptable to automatic procedures.

In the carrying out of the technique, it is to be realized that an element such as of silicon is transparent to infrared light. However, the metal covering the silicon is not. Accordingly, there is enabled the examination of the etch pattern at the moment that the etchant causes a break through the metal. In this connection, reference is made to Fig. 1 wherein the sample 10, i.e., silicon covered with metal 11, is immersed in a temperature controlled etch bath 12. The light from a source 14, which may suitably be a tungsten light source powered by DC current, is directed in a path against the sample.

The other structures in Fig. 1 are essentially optical devices.

Thus, structure 16 is a microscope objective. The light focused by objective 16 is directed to a beam splitter 18. One beam from beam splitter 18 proceeds to an infrared photomultiplier 20, the output of photomultiplier 20 suitably being made use of in some electronic instrumentation equipment, not shown. The other beam from beam splitter 18 is provided to a device such as an infrared snooperscope 22 which enables visual inspection. It is seen in the operation of the apparatus that, as soon as the metal 11 covering the silicon in sample 10 is broken through by the etchant in bath 12, light will be transmitted through sample 10 to the optical apparatus and observation will be enabled. The point of breakthrough of the metal and the point of completion of the etch are very close together as compared to the total etch time. Thus, it may be sufficient to merely mo...