US Patent: 2,606,405
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| Polishing Means and Method
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Patentee:
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| Russell S. Ohl (exact or similar names) - Red Bank, Monmouth County, NJ |
| Manufacturer: |
| Not known to have been produced |
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Patent Dates:
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| Applied: |
Aug. 17, 1946 |
| Granted: |
Aug. 12, 1952 |
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Joel Havens
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Description: |
| Claim:
In an example of practice an approximately flat surface of a slab of silicon cut from an ingot of solidified fused silicon of high purity is polished to produce a substantially optically fiat surface. The method employed comprises producing relative movements 'of rotation and translation between a tin lap and the surface of the slab of silicon over a nonrepetitive path while the lap and slab are both immersed in water carrying an abrasive such as sapphirine and dioctyl sodium sulfosuccinate which is a water soluble chemically inactive detergent. The surface of the tin lap is provided with a spiral groove, the function of which is to cause a continual flow of abrasive charged water from the center of the lap toward the periphery to continually carry away the particles of silicon removed from the surface of the slab and bring in fresh abrasive. In carrying out the method a rotatable upright cup mounted on a vertical shaft is provided with a tin lap having a fiat ground surface which has a spiral groove concentric With the shaft. The tin lap is centrally positioned in the bottom of the cup with the ground surface facing upward. A metal disc with the slab of silicon cemented to one face thereof rests on the grooved surface of the tin lap with the exposed surface of the slab in contact with the lap. By means of a second ro tatab-le shaft, the lower end of which rests in a recess in the metal disc, the silicon slab is given a reciprocal motion of translation across the lap and a motion of rotation about a vertical axis. The cup is filled with a liquid to a depth sufficient to immerse both the silicon slab and the lap while the cup and lap are rotating during the polishing operation. The liquid bath comprises distilled water containing levigated sapphirine, 3 percent dioctyl sodium sulfosuccinate solution and 1/5 percent potassium bichromate. The pressure for polishing is about pounds per square centimeter, The polishing is accomplished by a true abrasive action which is effective because the sapphirine particles are of the Water extremely small and of the proper hardness to produce on silicon a highly polished substantially optically flat surface. The combination of the dioctyl sodium sulfosuccinate with the very fine polishing material reduces the surface tension and increases the effectiveness of the abrasive. |
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