| 摘要 |
A flat vacuum chuck for restraining semiconductor wafer substrates and the like during processing applies a vacuum through holes in the chuck in a timed sequence. The localized areas of the wafer adjacent to each of the holes adhere to the chuck in a pattern that is controlled in such a way so as to minimize any residual gaps therebetween. In one application, the vacuum sequencing pattern is analogous to smoothing a curled sheet of paper on a flat surface with both hands by starting at or near the center of the sheet and moving both hands outward along the surface until the sheet is flat. The vacuum may be applied to substrates to overcome all types of distortions, including symmetrical, asymmetrical, and multi-plane distortions, depending upon the orientation of the net internal stresses resulting from the layers deposited on the wafer. The sequenced application of the vacuum through the chuck holes can be timed by installing a solenoid valve on each of the vacuum tubes connected to the ports. Alternatively, the vacuum applied through the chuck holes can be controlled by a single valve via different length tubes between the valve and the surface of the chuck. The holes with the shorter tubes reach nominal vacuum pressure sooner than those with longer tubes.
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