> On 28/08/06, Takeshita K <marinerone at gmail.com> wrote: >> My understanding is that the current size is the one which produces >> the most yield under the current process using the stepper. >> It's not the choice by the camera makers or sensor makers etc. >> I used to have a link which explains this, but lost it. Will dig it
> I'm not familiar with the term "stepper:" in this context. Yield > factors make a big difference to sensor manufacture affordability over > other general semiconductors which don't often exceed 10x10mm. The > shear expanse of a sensor area means that due to the lower numbers of > chips per silicon wafer (for all intents a fixed cost) any wafer > contaminants will render a larger portion of the wafer to waste. And > since wafers are circular (Sony now produced 300mm diameter wafers) > the larger the sensor produced the more the waste. > The tech used to produce the sensor used in the Kodak 14MP FF meant > that there were only 11 full sensors per wafer (approx 125mm diameter) > assuming a 100% yield, no wonder they were expensive. Think how many > 24x16mm sensor could be shoehorned into a 300mm diameter wafer vs > 36x24mm sensors, it's not a linear correlation. My mail on this subject bounced, and that's probably because I inadvertently used a different address. If it's duplicated somehow, my apology. Anyway.... I have not dug into any specific site yet, but my memory goes like this. This is indeed a "stepper' issue, and not about the usual yield per wafer argument. APS-H size sensor is the maximum size that can be obtained by a one shot exposure in the lithography process using a stepper. i.e., it's a stepper-driven size limitation. Anything smaller than that indeed becomes a yield issue, i.e., max obtainable numbers per circular wafer. Incidentally, Nikon is the world largest maker of the high performance stepper which Sony also uses. I thought I saw an article somewhere that Canon developed a process (or probably stepper) which can make a FF size sensor in one shot exposure, thus significantly reducing the cost of such sensor, hence 5D. Nevertheless, my understanding is that the cost of the FF size sensors is at least 10 times (or more) that of the APS sized one, and this gap is not going to narrow any time soon. I also saw some articles that both Nikon and Pentax, particularly Nikon, said that if the cost of FF sensors come down sufficiently to make any commercial sense, and if the lens/sensor performance could be reasonably conformed to such a sensor, there is no reason not to produce FF machines. But most of experts are predicting that APS size sensor has already become a de facto standard, and with the performance of APS sized sensor being rapidly increasing, they do not see any pressing need to rush the FF machines. We'll see. Cheers, Ken -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
