Generally, processor manufactuers don't use different quality silicon.
The vast majority of modern processors use p-type doped silicon (which is silicon with added boron, which changes the silicons electrical properties).
The main factor between quality of processors isn't the quality of the silicon, it's the quality/precision of the cuts made during the photolithography of the IC's on the wafer, which determines the CPU's max clock speed while remaining stable (and hence, what it's PR rating will be, and what price it will be marketed at).