*AV*--I would love to see a more definitive explanation of this article and other like it that have been circulating for the last few weeks. I have come to the conclusion that the key phrase is "semiconductor process". I have responded to this before with my opinion that the "manufacturing processes" basically consists of MLB (Material, Labor, Burden) with Burden including such costs as depreciation, utilities, and other fixed and variable costs. Burden is the largest component of wafer cost since it does include building and equipment depreciation. Material and Labor make up a small componet of MLB.
Therfore, I will be the first to theorize and agree that Dr. Ohmi can reduce the Materials cost of the semiconductor process to 10% of what it is today. I think this article is pointing out that a reduction of 90% of the chemicals, gases, acids, solvents , etal. can be achieved in the process. Many acids, gases, and chemicals can be replenished and recycled to reduce costs as well as more efficient uses of these same materials. You can also implement more advanced equipment that actually reduces the amount of materials used.
A few quick examples after some definitions.
1u=1 millionth of a meter
1 meter= 39.37 inches
1" = 2.54cm
1 cc = 1 cm3 = 1 cubic centimeter of volume but also defines length in 3 directions.
3785ml = 1 gallon
Volume = length * width * height
Area = length * width
Area of a circel = 3.14(pi) * radius * radius
Example #1 - Photoresist
In a perfect set of circumstances a gallon of DUV resist will cost roughly $5000 and contains close to 4000 ml of fluid. If 100% of the fluid is used in the container and only 5 cc of fluid is dispensed on each individual wafer, you could apply the light sensitive solution to 800 wafers. If you assume there are only 20 lithographic levels to manufacture the device, this means 40 fully processed wafers are produced per gallon of photoresist. This means the cost on a per processed wafer basis is $125. This is an absolutely perfect scenario with no waste in the dispense process.
Now let's talk about waste. You need the 5cc of resist to be dispensed on the wafer in order to get the resist to coat the wafer uniformly across the entire wafer surface to the specified final thickness. This needs to be tightly controlled since there is a direct corrrelation between thickness and proper critical dimension resolution of the device feature. Think of it as camera film with ASA 100, 200 or 400. The results are quite different if you use the same exposure time for each speed of film.
Given that and given that we want to coat a 1u film, the process and equipment are set up controllably obtain this thickness.
Now think about the amount of waster involved in this process. How much resist is in the 1u film. Well, the area of the wafer is:
3.14 * 4" * 4" * 2.54 * 2.54 = area of 8" wafer in metric units.(324cm2)
1u=0.0000001 meter or 0.00001cm, so the volume of resist actually on the wafer is 324*0.00001 or more than 99% of the resist is flung off the wafer into the waste drain.
Think about this. If you could recycle the resist by refiltering the resist into roughly 55 gallon drums and then retest and refine its sensistivity by adding a small amount of "concentrated stock resist" to re-establish the original incoming specifications, you have a tremendous savings.
Over the years we have moved away from the glass bottles and straight tubes (where you left more than 10% of the unused resist in the bottom of the bottle) to tilted bottles in tandem on scales with tilted reservoir tubes (still leaving some residual resist in the bottle) to NOWPAKs that are resist filled "IV bags" that use as close to 100% of the resist as you can get. Now that vapor prime has replaced liquid priming and if no priming can be done (you must process the wafers within a given time from the furnance operation to the coater to allow this), you eliminate all the chemical contamination in the resist dispense and waste collection process.
Now this is just theoretically possible since I have actually done it in a past life.
Example #2 - ACIDS
Both HF and Sulfuric Peroxide has been successfully recycled by major corporations in the US with great success. This type of reproecessing can eliminate another large cost since wafers are usually cleaned at least twice for every lithographic process they go through, sometimes even more. Reprocessing HF is much cheaper than buying new HF AND having to treat and neutralize the effluent HF.
Example #3 - CFMT cleaning or Cryogenic Cleaning
These technologies dramatically reduce the number of wet processes and associated chemicals that are used, thereby reducing materials costs as well as utilities and waste treatment costs.
Example #4 - Nitrogen
Nitrogen is used to a great extent to purge lines of gases in every etch process as well as to purge diffusion tubes in the furnances (also to provide an inert environment for subsequent temperature control and reactive gas distribution. Everytime you are able to cluster processes or combine/simplify processes, you are able to reduce the number of times and the huge volume of nitrogen that is used on a daily basis. I would venture a guess that any wafer fab worth its weight probably goes through the equivalent of 1 tanker (like those gasoline tankers you see delivering to the gas stations) of liquid nitrogen per day with the cost running into the 10 sof thousands of dollars per month.
I stopped at these 4 examples since #1 seemed to drone on. The advent of new process TOOLS (equipment) and new ways to do existing processes CAN result in the minimization of process costs like stated above. I still beleive that while process costs can go down, I do not necessarily beleive it comes at the expense of the processing equipment costs.
Until I see information to the contrary, I will still be of the opinion that these articles are not saying the cost of a wafer fab will be 10% of what it is today and that the cost of the equipment needed to process wafers will be 10% of what it is today. I still think they are talking about a small segment of the overall cost to deliver an IC to the marketplace.
Andrew |
