In the present work, we report a new technique for preparing phospho-silicste-glass (PSG) films using RF magnetron
sputtering process. For this, purpose, a 76 mm diameter target of phosphorus-doped silicon dioxide was prepared by
conventional solid-state reaction route using P<sub>2</sub>O<sub>5</sub> and SiO<sub>2</sub> powders. Since P<sub>2</sub>O<sub>5 </sub>is hygroscopic in nature, special care
was taken to prevent lump formation due to moisture incorporation during the target making process. The PSG films
were prepared in a RF (13.56 MHz) magnetron sputtering system at 200-300 watt RF power, 10-20 mTorr pressure and
45 mm target-to-substrate spacing without external substrate heating. The thickness, refractive index (n) and the
absorption coefficient (k) of the films were measured using a thin-film analyzer. To confirm the presence of phosphorus
in the deposited films, hot-probe test and the sheet resistance measurements were performed. As a final confirmatory
test, a p-n diode was fabricated in a p-type Si wafer using the deposited film as a source of phosphorus diffusion. The
phosphorus concentration in the target and the deposited film were analyzed using energy dispersive X-rays (EDAX)
tool. The etch rate of the PSG film in buffered HF was measured to be about 30 times higher as compared to that of
thermally grown SiO<sub>2</sub> films. The issues related to the use of RF sputtered PSG films as sacrificial layer in surface
micromachining technology have been addressed.
This paper reports a Ka-band microstrip patch antenna fabricated using post-CMOS compatible process technology. The antenna uses an air cavity underneath the patch radiator that is supported on thin membrane. To start with, a thin dielectric film of silicon dioxide is deposited on <100> single crystal silicon substrates by RF sputtering process. The membrane is then realized using bulk micromachining technology. The antenna structure was analyzed and optimized using the finite-element method (FEM) based Ansoft High Frequency Structure Simulator software (version 9). The antenna structure mounted on a test jig with K-connector was used for testing its performance. The measured results of the fabricated prototype antenna agree quite closely with the simulated results. The fabricated antenna resonated at 36 GHz with -10 dB return loss bandwidth of 1.2 GHz. In the absence of access to well-established MEMS foundry, the RF sputtering process reported here can be advantageously used for rapid prototyping of many antenna structures.
The influence of LPCVD process parameters on stress in polysilicon films has been investigated for surface micromachined structures. The as deposited films show a large strain which can be considerably reduced by post deposition annealing. The polycrystalline film deposited at 605 degree(s)C and 250 mTorr is found to have minimum residual stress. The rapid thermal annealing (RTA) at 1100 degree(s)C for 30 sec relieves the stress completely. Further, the RTA is shown to be a superior process compared to the conventional furnace annealing for obtaining stress free films.
The C-V measurement for MOS capacitor technique has been adapted to investigate the anisotropic electrochemical etching of silicon for bulk micromachining C-V characteristics of the etching cell have been obtained during the electrochemical etching process. The behavior of the characteristics has been explained on the basis of various layers at the etching interface.
A new approach has been proposed to realize suspended microstructures such as cantilevers, diaphragms, springs, spirals, etc. over pits of controlled depth in bulk silicon micromachining process using direct wafer bonding technology. The structures have been realized in heavily boron doped silicon and dielectric layers. The electrostatic actuation voltage of the cantilever beams have been computed as a function of physical parameters and compared with experimentally measured values. LPCVD polysilicon has been investigated with a view to obtain low stress films for use in surface micromachining technology. The effect of deposition parameters on stress in the polysilicon films has been studied. Post deposition annealing is shown to have profound effect on the stress properties of the polysilicon films. Rapid thermal annealing is found to be much more effective in reducing the stress compared to conventional furnace annealing. The advantage of direct wafer bonding technology for electrostatically actuated microstructures have been presented. The application of this technology for MEMS have been discussed.