In many integrated circuit manufacturing steps, wafers are completely coated wit
ID: 3369056 • Letter: I
Question
In many integrated circuit manufacturing steps, wafers are completely coated with a layer of material such as silicon dioxide or a metal. The unwanted material is then selectively removed by etching through a mask thereby creating circuit patterns, electrical interconnections, and areas in which diffusions or metal depositions are to be made. A plasma etching process is widely used for this operation, particularly in small geometry applications. Energy is supplied by a radio-frequency (RF) generator and causes plasma to be generated in the gap between electrodes. The chemical species in the plasma are determined by the particular gasses used. Fluorocarbons are often used in plasma etching
An engineer is interested in investigating the relationship between the RF power setting and the etch rate for a particular tool. The objective of an experiment is to learn about the relationship between the etch rate and the RF power rate and to specify the power setting that will give a desired target etch rate. The experimenter is interested in a particular gas (C2F6 ) and gap (.80 cm), and wants to test four levels of RF power: 160 W, 180 W, 200 W, and 220 W.
i) From the computer output the mean for 160 W is 551.20 which is different from the mean of 587.40 for 180 W, which is different from the mean of 625.40 for 200 W, which is different from the mean of 707.00 for 220 W. Thus, it can be concluded that the means for the different power levels are not the same. One-way ANOVA: Etch Rate versus RF Power MS Source RF Power 3 66871 22290 66.80 0.000 Error Total DF 334 16 5339 19 72210 S- 18.27 R-Sq 92.61% R-Sq (adj) -91.22% - Individual 95% CIs For Mean Based on Pooled StDev Level N 160 W 5 551.20 20.02(-*---) 180 W5 587.40 16.74 200 W 5 625.40 20.53 220 W 5 707.00 15.25 Mean StDeV ---+----+--+--+-- ? 550 600 650 700 Pooled StDev-18.27Explanation / Answer
iii) The p-value for testing the null hypothesis that the means are all the same is less than .05, consequently, the null hypothesis is rejected. The conclusion is that not all the means are the same.
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