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Chapter 8. The Multi-Vari Analysis: Homi... > Workshop Exercise 1: Semiconductor W...

Workshop Exercise 1: Semiconductor Wafer Multi-Vari Plan

On a semiconductor wafer (containing several hundred chips or dies), thickness measurements were made to determine which families of variation contributed the most to thickness differences in a multi-vari study. The Green Y is variation in thickness. Assume that the accuracy of the measuring instrument is more than six times the specified thickness tolerance. Design a multi-vari plan to address the following questions from aspects of the plan listed below.

  1. Identify the major families of variation (i.e., time-to-time, unit-to-unit, within-unit) for each of the following eight aspects of the plan.

    1.On each wafer, five dice were measured (north, south, east, west, and center)___________________________
    2.Three wafers were sampled from each batch exiting the deposition process.___________________________
    3.Wafers were selected from three locations in the batch process: left, center, and right locations in the chamber.___________________________
    4.Two deposition chambers were used.___________________________
    5.Each batch took two hours, with four batches per shift.___________________________
    6.Samples were taken from two consecutive batches on shift 1 and shift 2.___________________________
    7.Sampling was done on Monday, Tuesday, and Wednesday.___________________________
    8.Wafers were sampled over the three consecutive weeks.___________________________

    Table 8-1. Multi-Vari Preparation Table: Printed Circuit Board Drilling

    (The answers to each workshop exercise are given immediately following the exercise throughout the text.)

  2. Draw a family tree.

  3. How many wafers should the total multi-vari run include?

  4. What reductions could be made in the total samples of wafers required if previous history indicates few significant variations occurred from week to week, day to day, or shift to shift.


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