Tag Archives: COO

Lowering Cost of Ownership (COO) “Track” Tools in Back end of the Line (BEOL) Thick Resist Film processes

As it becomes apparent that the adoption of new process nodes has been significantly slowed down due to availability and cost of next generation FEOL lithography technologies, it becomes ever more important that the continuation of cost reductions and functionality improvements that have driven the growth of the Semiconductor industry over the last 40 years be sought elsewhere. Some of the investment heretofore focused on the FEOL “bleeding edge” technology should now be refocused more in BEOL Photo resist lithography for packing where the lower hanging fruit lies. This will require simplification of processes and reduction in material costs wherever possible while at the same time improving process control, yields and functionality and reducing photo resist processing tool costs.

One way to reduce costs is by substantially reducing waste in photolithographic processing technology. It has long been noted by just about anyone who performs spin processing on Photoresist Track equipment that there is an enormous amount of waste in the process as most of the Photoresist material consumed in the process is actually thrown off the wafer during the spin process and wasted. Textbooks in disusing the process point out the wastefulness of the process. The waste becomes especially meaningful in BEOL WLCSP, 2.5D and 3D processing where thicker resist films need to be cast. Multiple spins to achieve the film thickness required exacerbates the waste, while increasing Photoresist viscosity so that the thicker films can be cast adds substantially to equipment costs as the pumps required to pump the material can cost well into the 5 figures in US Dollars. Multiple spins also require more Photoresist track equipment for multiple trips through the equipment. The high viscosities also make elimination of bubbles a constant struggle further increasing costs. The film is formed during the spin process and then baked typically on a hot plate to remove additional solvent to render the film stable and photo definable. All of the foregoing tends to substantially increase photo resist processing costs in the Back End of the Line (BEOL) lithography for Wafer level Chip Scale Packaging (WLCSP). Another avenue is to use expensive chemically amplified resist (CAR) systems, which have the effect of improving CD control and aspect ratio’s in a single coat, however further increasing material cost substantially.

The engineers at S-Cubed™ have invented a new process…FastSpin™ that addresses all of these cost/complexity issues. In the new process (patents applied for) the film is not cast so much as wet formed by spinning the wafer under exquisite servo control for a very short time, subsequently processed to render the film stable and photo definable. The wet film is maintained in the wet state and is allowed to level, allowing for planar coatings over topography. The process not only substantially reduces photo resist consumption for both standard and CAR resists, it also substantially reduces the cost of the photo resist processing tools, Photo resist track, by reducing the number of spin processors required for a given spin processor tool throughput.

Please request further information regarding S-Cubed™ FastSpin™ click on the link:

https://www.s-cubed.com/contact-us/

System Granularity and Management of Change and Growth

A very important aspect of cost of ownership (COO) of tools that include spin coaters and developers (often referred to a photoresist track tools) in the back end of line (BEOL), MEMS, and patterned sapphire substrate (PSS) processing-type processing lines is one that does not appear on the COO software packages. Often referred to as “opportunity cost,” it is specifically defined as “the difference in return between an investment one makes and another that one chose not to make.” A high degree of system “granularity” enables appropriate investment as customer needs evolve. Ultimately this can substantially reduce opportunity cost. Granularity specifically relates to tools sized to the capacity need, as well as properly balanced for output in order to minimize waste. Lets look at how that works, in the context of opportunity cost.

Since opportunity cost is always a comparison of the path chosen to the path that was not chosen, we will compare two hypothetical systems whose COO on a per wafer output basis is identical, but its granularity is different. Granularity will tend to go up in integer values. Let us suppose a system whose out put is equal to one unit of capacity, (i.e., 2000 wafers per month) and another whose out put is equal to two units of capacity (i.e., 4000 wafers per month). If the need is for one unit of capacity, then if the COO is the same and the more granular system is the clear choice. If it is two units of capacity then the choices are equal. However what happens when it is three units of capacity; then four; then five? Capacity needs often develop in incremental steps over the long term instead of in immediate doublings. The investment in the “granular approach” is obviously the more appropriate forward-thinking plan. As needs eventuate, so that capacity can be adjusted to market needs at the lowest possible cost in capital spread over time.