Why is APS-C still so popular? Manufacturing!

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magnetisch New Member • Posts: 1
Why is APS-C still so popular? Manufacturing!

I just stumbled across the article about the new Nikon Z50 and why it is APS-C again … .

One of the reasons why sensors larger than APS-C format are so expensive is the need for special equipment to manufacture them.

Semiconductor manufacturing consists out of a a group of steps that are run again and again to form the separate layers (about 20 to 40 or more depending on technology) on top of the silicon to manufacture a semiconductor chip or a CMOS sensor.

These steps for each layer are in a very generalized description:
1 deposition of a layer onto the silicon wafer (a siliconoxide, siliconnitride, polysilicon, metal or an isolating layer)
2. coating with photoresist
3. exposure with a photomask which contains the layout for this layer
4. developing of the photoresist
5. etching of the deposited layer
5b or implanting some ions to create differently conductive areas
6. cleaning.

Rinse and repeat for each layer. 20 to 40 times. Each step may include several single steps. It takes 4 to 8 weeks to manufacture a single wafer full of chips.

Steps 2 to 4 are called lithography. One of the most expensive piece of equipment for semiconductor manufacturing is a so called lithography stepper or scanner, it is the exposure tool in step 3. One of these tools will sell for about €5million up to €50million for a high end tool. A plant (a fab) will use dozens of them.

Lithography stepers or scanners are some kind of giant projector that demagnify the photomask onto the silicon surface that is coated with a photoresist. These tools use the most accurate mechanics and high end optics that are currently manufactured. Lenses of up to a meter in length consisting out of dozens of elements, several 10cm across.

And these optics are made to illuminate an area of roughly 33mm x 26mm. This is the largest chip size that can normally be manufactured and is a rough standard in semiconductor manufacturing. This area is illuminated step by step across the wafer surface to create a wafer full of chips.

APS-C is roughly 25mmx17mm. APS-H is 30mm x 17mm. Both will fit into this illuminated area of a standard stepper.

Canon created steppers in the early 2000s that can illuminate larger areas. That was the birth of full frame (well 35mm frame) sensors. But these tools are not as highly developed as the steppers and scanners that are used for high end semiconductor manufacturing with smaller illuminated areas.

So, nearly every fab that can do semiconductors can do APS-C sensors. But to do larger chips one needs different equipment.

This is one of the main reasosns that makes full frame sensors expensive.

I work in semiconductor manufacturing for 25 years now. Have done lithography, sensors, ASICs, manufacturing, technology development, circuit design and now failure analysis. I am always amazed that all this stuff works nearly all the time :-o

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