Authors
Kevin Potcner
JMP
Objective
Analyze process variation and compare it to specifications using graphical tools, control charts, and capability analyses for a semiconductor manufacturing process.
Background
A semiconductor manufacturer is working on getting seven new etching lines up-and-running at a new facility to satisfy increased demand for chips. A critical step in producing integrated circuits is to etch select areas of an oxide layer from silicon wafers. One important quality metric is Etch Rate. This is the amount of oxide etched from areas of the wafer per unit time, measured in angstroms per minute.
Ideally, all wafers would be etched consistently to target and with variability within the process specifications. The target Etch Rate for these lines is 620, with lower and upper specification of 545 and 695 respectively (i.e., 620 +/- 75). Etching is done in sets of 20 wafers. A sampling plan has been established which will randomly sample 5 wafers from each run for 40 subsequent runs, resulting in 200 wafers sampled from each line. Etch Rate will be measured at 4 separate locations on each wafer.
This results in 5 x 40 x 4 = 800 Etch Rate values per etching line. Based upon this sampling strategy, three sources of variation can be examined for each line: 1) within wafer; 2) between wafer within run; 3) between runs.
Importantly, equipment recalibration was performed after the 20th run. This allows run variation to be separated into two other sources: 3a) between runs within calibration stage; 3b) between calibration stages.
In this case study, we will demonstrate a variety of analyses on one of the etching lines. The exercises will ask you to conduct similar analyses on the other six etching lines.
The Task
The primary objectives of the analyses are:
- Evaluate the performance of each etching line relative to the target of 620 +/- 75
- Examine the four sources of potential variation in Etch Rate for each line