INTERFERENCE MEASUREMENT OF THIN SURFACE LAYERS 1217 



shorter X would increase the resokition. However, a sodium lamp gives 

 enough light that one can easily work in daylight. 



The microscope is mounted above a micrometer cross-slide of the same 

 kind as used in the procedure for marking the p-n junctions. The stage 

 carries a special sample support. Fig. 5 gives a diagrammatic view of 

 the light path in the interferometer. A normal microscope is used with 

 an attachment carrying a semi-transparent mirror. Fig. 6 shows a photo 

 of the complete arrangement, and Fig. 7 gives the details of the sample 

 support. 



The prepared sample is waxed to a microscope slide and covered by 

 a half-silvered mirror. Both are placed on the adjustable lower jaw of 

 the sample support. The lower jaw is raised so that the upper jaw presses 

 against the mirror. In this position it is fixed by tightening the screw 

 in the back. Thus the mirror and sample are in contact, and the fringes 

 can be observed through the microscope. Three screws in the lower jaw 

 make it possible to change the relative position of mirror and sample. 

 Thus the fringe pattern can be adjusted to make it most suitable for the 

 particular case. 



THE MEASUREMENTS 



The measurement of a layer thickness was chosen to demonstrate the 

 principle of evaluating a fringe pattern. (See Fig. 8.) The first illustration 



Fig. 7 — Sample support. 



