We would like to use your SOD as a source for dopants, we are currently interested in sources for B, P and As, and have some questions regarding that process:
1. Being a research facility, using the same tools for various processes we are cautious when introducing new materials in the clean-room. Therefore I would like to verify it is OK to use your SODs in the same spinner used for photoresists (with metal chuck and PP drain tubes). Particularly:
a. What (solvent?) can be used for spinner cleaning (IPA? we can’t use diluted HF). If utilized quickly, IPA or denatured alcohol can clean off SOG materials. Once dry however, dilute HF can be used but attacks metal surfaces and is not recommended.
b. Is that process a source of particulates. SOG is formed in an alkoxide reaction that occurs faster at higher temperatures or when exposed to air. For research purposed we utilize one dropper for each wafer. If dropper is used repeatedly for multiple wafers, particles will form on the sidewalls of the dropper which will get into the SOG material. As long as dispensing equipment is kept clean, particulates are not a problem.
2. How sensitive is the process to temperature, humidity and time variations between applying the SOD and starting the spin? If SOG is refrigerated when not in use, most materials will last over 1 year. For best coating consistancy, allow the SOG to come up to room temperature before dipensing. The heavier doped SOG materials are more sensitive to humidity and we recommend low humidity conditions for these materials. If moisture is absorbed onto the SOG film and fogs the film, this can translate to damage during the diffusion process. We generally flood the wafer 80% with SOG and then immediately spin at high acceleration for best film results.
3. Can you provide a reference process for each dopant, which is robust, repeatable and with proved uniformity (within wafer and wafer-to-wafer)?
Including all the parameters (Spin RPM, time bake temperature, predep time and Temp. and so on) for a shallow (deep) layer, from which we can start in order to achieve the profile we need. Yes, we have a process outline for each of our SOG materials.
4. Is the final distribution is Gaussian? It can be depending upon the diffusion conditions. There is a process modeling program that can be of immense use to you. The modeling link is: Fabweb.ece.uiuc.edu This will come up as ECEIllinois-ece444: Theory and Fabrication of Integrated………….Click on this to enter the modeling site, then click on the sub category “Calculators”. This will then give you several modeling options.
5. Do you have experience using RTP for predep? Our customers utilize both open tube diffusion and RTP processing. We would be happy to assist you with either process.
6. What material is used for masking, when want to apply SOD only to defined areas (is SiO2 / Si3N4 suitable for all dopants)? Typically thermal oxide is used for masking oxide for most semiconductor applications. However some designs/processes can utilize other masking materials including undoped SOG, PECVD or LPCVD materials.
7. Do you recommend PECVD SiO2 / Si3N4 layer to prevent out diffusion? (assuming the mask layer is thermal – LPCVD) If you are reffering to a capping layer over the SOG, it is not generally required. If you are referring to backside pretection to prevent a heavily doped backside outdiffusion or prevent SOG dopant outgassing to and affecting the back side, then a capping layer such as undoped SOG on the backside may be utilized.
8. Can you please send MSDS for your SODs (P/B/As)? Yes, a Desert Silicon representative will send the new SDS formatted guides to you today.