PSG layers for surface micromachining

✍ Scribed by D. Poenar; P.J. French; R. Mallée; P.M. Sarro; R.F. Wolffenbuttel

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 550 KB
• Volume: 41
• Category: Article
• ISSN: 0924-4247
• DOI: 10.1016/0924-4247(94)80128-2

✦ Synopsis

The effect of both the deposItton parameters and subsequent thermal processmg upon LPCVD phosphosdlcate glass (PSG) IS cxperunentally mvestlgated w&h an emphasis on estabhshmg the effect of phosphorus content and PSG processing on the essentml charactenstlcs of PSG, such as etch rate, shnnkage, etch rate reduction and drstnbuhon of phosphorus after annealmg The effect of PSG upon the stress m overlymg mlcromachmed polysdlcon layers IS also mvestigated The entire processmg was camed out at a maxnnum temperature of 850 "C m order to avoid a slgmticant mcrease m the thermal budget and to mamtam fabncation compatlbdlty with already Integrated standard bipolar devices The shrinkage of the PSG IS shown to Increase hnearly wA phosphorus content, whde both the vertlcal-etch rate (as-deposlted and after annealing) and the under-etch rate demonstrated an exponential Increase wth phosphorus content The large value of the etch rate reduction after anneal (which can be as high as 70%) and its inverse proportionahty urlth shnnkage (w&h IS up to 8%) show that dens&atlon cannot be the only cause of the large vanations m etch rates after anneahng The chenucal meta-stab&y of the deposited PSG IS Identied m this research as a mayor cause of etch rate reduction after anneal, rather than the dens&z&on Stabduatlon IS obtamed wlthm 20 mm after a 850 "C anneal Increasing the phosphorus content of PSG from 2 to 6 at % results m a reduction m sheet res&vlty of the subsequently deposIted and doped polysdlcon from 14 to 0 9 ki?&l, both with and Hrlthout anneal of the PSG The phosphorus content and the anneal of the PSG have neghglble effect on stram In the overlymg polysdlcon