Junction Depth Measurement

1. Junction Depth Measurement For Epi films and diffusion

2. Junction Depth Measurement Groove and Stain Bevel and Stain The wafer is subjected to a mechanical abrasion to expose the junction for viewing. The junction is delineated by utilizing the electrical differences between N-type and P-type materials

3. Groove and Stain A grooving machine ( Philtec ) is used to create a groove in the wafer � A wafer or section of wafer is loaded into the holder. A micro-abrasive paste is applied to the roller of the machine The sample holder is placed into the machine The roller is turned on (specific settings for diameter of wafer) The sample holder is held against the drum and a groove is ground into the wafer. The groove size is dependant on diameter of the roller

4. Philtec groove and stain

7. Bevel and stain A bevel is ground onto the edge of a sample � A small piece of the wafer is epoxied to the specimen holder overlapping the center of the bevel on the holder The specimen holder is attached to the body of the holder A small amount of micro-abrasive is placed on a specially prepared glass plate

8. Bevel and Stain The specimen holder is placed into the chuck and the entire assembly is carefully placed on the glass plate into the micro-abrasive The holder is moved on the glass plate in a figure 8 pattern to polish or grind a bevel onto the edge of the specimen The specimen is carefully washed in preparation for staining

9. Lapping chuck

10. Lapping chuck and specimen holder

11. Lapping plate prepared by rubbing 2 pieces of glass together with a 25 micron slurry Larger plate will be used for the lapping process

12. Specimen epoxied to specimen holder Note angle of holder

14. Micro abrasives for the lapping process

15. Lap specimen by a figure 8 motion No pressure is applied to holder, weight of holder is enough for process

16. Etching Technique Place drop of HF and water mixture over exposed junction Heat lamp is directed onto the exposed junction Heat and light cause holes or electrons to flow in each region As a result of the current flow, the etch rate of the HF-H2O mix is higher for the N-type region making it appear darker

18. Staining Technique mixture containing copper is dropped onto exposed junction heat lamp is directed onto junction a �battery� is formed by the poles of the junctions, with the copper solution being the electrolytic solution the current flow causes the copper in the solution to plate onto the N-type side of the junction

19. Once specimen is lapped and washed, surface is stained to delineate junction

21. Delineation observations After delineation optical interference fringes are created by shining a monochromatic light source onto a glass slide over the delineation � Each optical interference fringe represents a specific depth, adding them up gives you the junction depth. � In our lab we will use the microscope as a reference to calculate the junction depth It is simple geometry to determine the actual junction depth.

24. Stained section from project W2002 Note drain and source diffusions as dark areas on right side of image --- the brown area being the lapped part of wafer

25. Spreading Resistance Probe Another method to determine junction depth is to use the Spreading Resistance probe � a taper is ground onto the edge of a sample (same method as above) very fine probes are used to measure the resistance value along the taper the measurements are fed into a computer to calculate the doping profile the measurements are graphed and the junction depth is determined

27. ENDJunction Depth Measurement For Epi films and diffusion