Nyberg (1999) has shown that silicon nitride (SiNx) grown by Plasma En-

hanced Chemical Vapor Deposition (PECVD) is a promising candidate for an antire ection coating (ARC) on commercial crystalline silicon solar cells.

Silicon nitride was grown on polished (100)-oriented 4A silicon wafers using a parallel plate Plasma Technology PECVD reactor. The diameter of the electrodes of the PECVD is 24 cm and the diameter of the shower head

(through which the gases enter) is 2A. The RF frequency was 13.56 MHz.

The thickness of the silicon nitride was one-quarter of the wavelength of light in the nitride, the wavelength being 640 nm. This wavelength is ex-

pected to be close to optimal for silicon solar cell purposes. The process gases were ammonia and a mixture of 3% silane in argon. The experiments were carried out according to a 25 factorial design. The results are shown in the table on the next page.

(a) Fit the factorial model to the response y1 including all interactions up to the 5-way.

(b) Make a normal plot of the eects or regression coecients to determine which main eects and interactions are signicant.

(c) Drop insignicant terms from the model and make residual plots to check the assumptions of the model t.

(d) Use your model to determine the conditions (i.e., factor levels that will minimize the refractive index).