steppers spend most of their time aligning, focusing, stepping and exposing the wafer. The aligning part can be site by site (longest time) or global. The upgrade comment was within the stpper company manufacturing. I do not know if field retrofits of existing systems would be feasible.
The steppers are usually the bottlenecks of a manufacturing facility. From the number of steppers a company has, I can very accurately surmised their wafer manufacutirng capacity.
the number of steppers required to produce a given number of chips is independent of the wafer size. Yes, But also consider the size of the exposure field and the physical size of the device being stepped determine the amount of devices that can be produced per unit of time. That is why it is preferable to have the largest exposure field size. At 5x, you are almost always restricted to 1 device per exposure field and therefore the reticles have only one device. The larger the field size, the more likely it is to get possibly another die onto the reticle. Most of the time you do not. Therefore, you have not really optimized the use of the available exposure field relative to the device size. On the 1X systems that typical have a larger field size, you are able to optimize the number of devices exposed per exposure field by a combination of die array placement and field size.
This is very different in terms of sales than other equipment like etchers which act on the entire wafer at once. Absolutely correct. Steppers are concerned with consistency across a much smaller unit area which then needs to be repeated numerous times across the wafer depending on die size and field size wheras the etchers in question, require consistency across the entire wafer. There is a cost efficiency associated with full wafer processing in equipment like etchers. Give or take an insignificant amount of time, the etcher is transparent to the size of the wafer when it etches. It will take the same amount of time to etch a 200mm wafer as it would a 300mm if everything is sized correctly. Throughput per hour is very important here. When you say 50 WPH you have a good understanding what is going on and it is almost invisible to wafer size.
On the stepper, a 50 WPH throughput is meaningless if you do not know the field size being used (different for every 5X device run), diameter of the wafer, and whether it is global or site by site alignment being used. The more prefeered way is to talk about how much area per hour is processed. The larger the field size, the more area that is exposed so the higher the throughput will be.
Or will we see a new generation of stepper with larger field size,
shorter exposure periods, and faster stepping. All of these improvements (smaller feature size with larger field; larger and heavier wafer with faster and more precise stepping) sound challenging to me.
Over the course of the years, field sizes have grown. This is not easy when you consider this is optics, lens design, and lens construction. Think about simple camera lenses and how difficult it is to get real good telephoto lenses. Faster stepping is being addressed by step-and-scan, IMHO. Exposure times are measured in extremely small units of time which may add up over the course of the process, but they are extremely short in duration. As we change wavelengths of light used (436, 400, 365, 250, 193 nm) we improve resolution but sometimes the photosensitivity of the resists brought on line vary from company to company. More precise stepping will always be a challenge until it is perfectly stepped to the precise location desired to 3 sigma level of accuracy. This is probably the biggest challenge. Suffice to say, there is not enough room here to impart all the idiosyncrasies of the lithography process learned over the course of my 20 years in the business.
Steppers are the most expensive tools per unit sales in the entire semiconductor equipment arena. And they typically have the lowest overall throughput since wafers are processed through them many more times than any other piece of process equipment. I cannot think of any other type of equipment that costs as much, as an aggregate, for a manufacturing facility. Highest costs with the most number of units sold.
Andrew |
