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Please use this identifier to cite or link to this item: http://eprint.iitd.ac.in/handle/2074/769

Title: Strain studies in LPCVD polysilicon for surface micromachined devices
Authors: Singh, Janak
Chandra, Sudhir
Chand, Ami
Keywords: Polysilicon
Residual strain
Surface micromachining
Furnace annealing
Spiral structure
Issue Date: 1999
Citation: Sensors and Actuators, 77(2), 133–138
Abstract: Polycrystalline silicon polysilicon has emerged as a preferred material for surface micromachined MEMS applications because of its compatibility with standard CMOS process. The important parameters of polysilicon films for sensor–actuator devices are the residual stress and stress gradient. For free standing microstructures, it is important to reduce the stress in the film. In order to exploit the advantage of polysilicon for MEMS applications, it is essential to develop a process to obtain low-stress polysilicon films. In the present work, we have investigated the effect of deposition parameters on 2–4 mm thick LPCVD polysilicon films using a specially designed spiral structure for strain measurements. The films were deposited in the temperature range of 580–6308C at pressures 180 to 320 mTorr.The role of post-deposition annealing at 10008C in N ambient on strain reduction has been investigated using conventional furnace 2 annealing and rapid thermal annealing RTA . The as-deposited films show significant strain under all the deposition conditions investigated. The strain is reduced to insignificant values after 100 min of furnace annealing. In case of RTA, similar strain values are achieved in only 30 s of annealing. The overwhelming superiority of RTA over furnace annealing in terms of the thermal budget of the process has been clearly demonstrated. The effect of polysilicon doping with boron or phosphorus has also been studied for applications in electrically conducting microstructures. The final strain values after annealing are about 1=10y4, which is the limit of resolution of the strain measurement scheme used in the present investigations.
URI: http://eprint.iitd.ac.in/dspace/handle/2074/769
Appears in Collections:Applied Research in Electronics [CARE]

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