A TiW layer is deposited on a substrate using a sputtering tool. Table 6E.14 contains layer thickness measurements (in angstroms) on 20 subgroups of four substrates.

(a) Setup x and R control charts on this process. Is the process in control? Revise the control limits as necessary.
(b) Estimate the mean and standard deviation of the process.
(c) Is the layer thickness normally distributed?
(d) f The specifications are at 450 + €“ 30, estimate the process capability.

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sTABLE 6E.14 Laver Thickness Data for Exercise 6.34 subgroup x, x2 x, x. 459 449 435 450 443 440 442 442 457 444 44 444 469 463 453 438 443 457 445 454 444 456 456 457 45 449 450 445 46 455 449 452 44 452 457 440 432 463 463 443 445 452 453 438 456 457 436 457 459 445 44 447 441 465 438 450 460 453 457 438 453 444 451 435 451 460 450 457 422 431 437 429 444 446 448 467 450 450 454 454 12. 13 14 15 16 17 18 19 20