Sensors and Actuators A, 37-38 (1993) 123-726 723 Stress in low pressure chemical vapour deposition polycrystalline silicon thin films deposited below 0.1 Torr zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM A. Bemtez zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Depariament Electrhca, Umversztat Authoma de Barcelona, 08193 Bellaterra, Barcelona (Spam) J Bausells, E CabruJa and J Esteve Centro Nacronal de Macroelectromca (CSIC), Campus UnrversrtatAuthoma & Barcelona, 08193 Bellaterra, Barcelona (Spam) J Samher LCMM, Facultat de F&a, Umversrtat de Barcelona, Daagonal 645, 08028 Barcelona (@ am) zyxwvutsrqponmlkjihgfedcbaZYXWVUT Abstract Stress control m low pressure chenucal vapour deposItion (LPCVD) polysd~con IS mqortant for mxromechamcal processes mvolvmg surface maxomachnung Residual stress 111 polynbcon thm films has been studled for a number of years for deposition temperatures m the range 570 to 650 “C, and m the 200 to 500mTorr range of deposition pressures The stress m such as-deposited undoped polysihcon thm fihns IS usually compresswe, but very low stress values or even tensde stress can be obtamed m some cases by doping and/or anneahng the films The stress m thm films 1s greatly Influenced by the film structure, and this depends on both the temperature and pressure of deposition In this work the stress m polyslhcon thm 6lms deposited at lower pressures (80 mTorr) IS studxd and related to the film structure Deposition temperatures between 580 and 630 “C are used Some wafers are doped by ion Implantation, and some wafers are annealed under vanous con&tions Stress values are obtamed by usmg polysticon nucromechamcal structures, such as cantilevers and doubly-supported beams, fabncated by surface nucromachmmg Compressive stress 1sobtuned m all cases, and processmg condmons that produce very low stress values are reported zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA IIltRldUCtIOll S&con rmcromachmmg has become an important techmque for the fabncation of rmcromechamcal devices and, specmlly, of sensors and actuators In particular, the technology of surface nucromachmmg 1s playmg an mcreasmgly important role Its advantages, when compared wth bulk rmcromachmmg, are that it allows the fabncation of devxes mth smaller dnnen- slons and it can be integrated m an easier way v&h mtegrated cxrcmtry [l] As the polycrystalhne &con (polys~con) 1s a standard matenal m IC technology, its use as a structural matenal on a surface-nucromachm- mg sacnficlal layer technology 1s advantageous for the fabncation of integrated nucromechamcal sensors and actuators Successful fabrrcation of polyslltcon nucro- mechamcal devxes, however, depends on the stress control m polytuhcon thm 6lms [2] Polyslllcon thm films are usually deposited by low pressure chenxal vapour deposItion (LPCVD), by usmg the pyrohttlc decomposition of Dane (M-I.,) [3] The residual stress m LPCVD poly&con has been studied for a number of years The deposltlon tempera- tures used have been m the range from 570 to 650 “C Although earher stumes did not state the deposltlon pressure used [4,5], most results have been obtamed between 200 and 500 mTorr of dane pressure [6- 131 Withm these ranges of deposItIon parameters, the stress m as-deposited undoped polysficon thm films 1s usually compresswe, but it can be changed to tensde m some cases or reduced to very low values by dopmg and/or anneahng the fihns [8,9, 11-131 The stress m thm films depends on the fihn structure [ 141 The structure of LPCVD s&on thm films depends on both the temperature and the pressure of deposition [ 1S- 17] The structure dependence on pressure 1s spe- cially nnportant m the temperature range of mterest for polyshcon deposition [ 171 In tlus work the stress m polysticon thin films deposited at a pressure lower than 100 mTorr (13 3 Pa) 1sstud& The am of the work 1sto determme processing conditions that produce low stress values smtable for rmcromechamcal devxe fabncatlon The effect of deposition condltlons 1s studied, and some of the films are doped and/or annealed The stress 1s obtamcd from measurements on rmcromechamcal struc- tures fabncated by surface nucromachmmg, and also from wafer curvature In the followmg sections the structure of polysticon thm tis IS bnefly reviewed, the 0924-4241/93/$6 00 @ 1993 - Elmer Sequoia All nghts reserved