Tag Archives: spin process tools

The Argument for New Vs Refurbished Used Photoresist Process Equipment

In an earlier BLOG we discussed “Lowering the Cost of Ownership (COO) of Spin Process Tools.” we did not discuss the fact that the customer does have an option to purchase a used, “used and refurbished” or “as is” version of a tool built at some point in the past as another means of lowering cost.

There are some obvious and immediate COO issues that come to mind when used equipment, sometimes more respectfully referred to as “legacy” equipment is purchased as opposed to new equipment. They include:

  • Very short warranty. Used or legacy equipment typically has a 30 to 90 day warranty, whereas today’s new equipment will often have a two-year warranty on components and one year on labor.
  • Availability of spares. Used equipment, some of which was built up to 30 years ago, is becoming more and more difficult to support as the electronic control means are often no longer in production. While this issue is mitigated when new controls are implemented on old platforms, however this adds to the overall cost.
  • Foot print issues. Equipment made before the advent of process stacking, typically done on the thermal modules, occupies more than twice the space as modern tools with Stacking. Used equipment that has stacking capability is often more expensive than new tools with stacking.
  • Installation Costs. Frequently it can cost as much to install a used tool as it cost to buy it. That is not the case with new equipment, where installation costs and facility costs are low.

In addition to the direct cost factors noted above, there are more subtle factors that come into play. Including:

  • Process support. New tools come with factory process support not typically available in used tools.
  • Software support. New tools can be “tweaked” to meet specific customer requirements, whereas used tools typically are not available with ANY software support or modification.
  • Capability to meet new process requirements that did not exist at the time of the design and manufacture of the used tool. Such factors as multiple movable dispenses, high reliability robots, hot plates designed to handle thicker photoresist films typically used in special purpose photolithography.
  • A great deal of the used “track” equipment was built before the advent of Semi Safety Standards and is difficult, if not impossible, to render safe.

The photoresist process equipment available today is low in cost and high in functionality and reliability. It can be tailored to the specific needs of the very specific customer who buys new and not used.

Why Back End of Line (BEOL) Photoresist “Track” Tools are and must be Different from Front End of Line (FEOL) Photoresist Processors

In earlier writings we have discussed cost of ownership issues (COO) related to photoresist processing tools. In this entry, we will discuss the important functional differences between tools generally intended for the FEOL, and those more adaptable to the needs of BEOL wafer fabrication.

As the semiconductor industry has packed more and more functionality and speed into ever smaller chips (here one almost always must refer to Moore’s Law well know to those in the industry), the size and cost of the packaging of the chip has made necessary the creation of new types of wafer processing, which is needed to do wafer-level chip scale packaging. In this specific technology, photolithographic processing is used so chip outputs and inputs can be repositioned, so as to adapt to interconnect circuitry directly without the intervention of a typical pin out type package. In this case the chip is “rewired” and “bumped” so that it can be “flipped and bonded” directly to the chip interconnect circuitry. Such rewiring and wafer bumping is accomplished on the finished device wafer prior to singulation of the wafer into chips.

While the patterning concept is identical to that required to make the chip itself in practice, the geometries are far larger and the need for organic insulating film more prevalent than in the creation of the chip. This means that the spin cast films are much thicker and there is far more effluent of material leaving the wafer during the required “bakes” done in the thermal modules of the requisite tools. These thicker films require the following considerations in the design and implementation of the tool.

  • The cost of the process must be kept low, thus requiring tools with a low COO.
  • The spin cup must be designed to handle thicker films and capable of modulating spin exhaust conditions on a step-by-step basis throughout the process recipe.
  • The higher viscosity resists that are used to spin the thicker films means pumps must be geared to accomodate those viscosities.
  • The higher viscosity resist requires that the dispense height be preferably programmable rather than adjustable so that it can be varied during the dispense.
  • The much thicker films evolve far more solvent and other effluent requiring that the effluent be directed away from cold surfaces where it can condense and require frequent bake module cleaning, or create defective films owing to effluent reflux.

While FEOL tools may be utilized in BEOL, their high cost can be prohibitive, and their performance while tuned to the FEOL is not appropriate to the BEOL provider.