Evaluation of the Electrical Properties, Piezoresistivity and Noise of poly-SiGe for MEMS-above-CMOS applications
- PDF / 426,405 Bytes
- 6 Pages / 595 x 842 pts (A4) Page_size
- 39 Downloads / 203 Views
1153-A19-04
Evaluation of the Electrical Properties, Piezoresistivity and Noise of poly-SiGe for MEMS-above-CMOS applications P. Gonzalez1, 2, S. Lenci1, L. Haspeslagh1, K. De Meyer1,2, and A. Witvrouw1 1 IMEC, Kapeldreef 75, 3001 Leuven (Belgium) 2 K.U. Leuven, Kasteelpark Arenberg 10, 3001 Leuven (Belgium) ABSTRACT In this work, the electrical properties of heavily doped poly-SiGe deposited at temperatures compatible with MEMS integration on top of standard CMOS are reported. The properties studied are resistivity, temperature coefficient of resistance, noise, piezoresistivity, Hall mobility and effective carrier concentration. The obtained results prove the potential of using poly-SiGe as a sensing layer for MEMS-aboveCMOS applications. INTRODUCTION The monolithic integration of the micro-electro-mechanical systems (MEMS) with the driving, controlling and signal processing electronics on the same CMOS substrate can improve performance, yield and reliability as well as lower the manufacturing, packaging and instrumentation costs [1]. The post-processing route (fabricating MEMS directly on top of CMOS) is the most promising approach for CMOS-MEMS monolithic integration as it enables integrating MEMS without introducing any changes in standard foundry CMOS processes. However postprocessing limits the maximum fabrication temperature of MEMS to 450ºC-520ºC [2], to avoid introducing any damage or degradation in the performance of the existing electronics or interconnects. This temperature constraint is quite restrictive for post-processing surface micromachined MEMS, as it might affect relevant physical properties such as crystallinity, growth rate, mechanical properties, doping activation, etc. Polycrystalline silicon germanium (poly-SiGe) has emerged as an attractive alternative to polycrystalline silicon (poly-Si) for MEMS-above-CMOS applications thanks to its lower electrical resistivity [3] and lower transition temperature from amorphous to polycrystalline [4,5], which can be as low as 400ºC (with the appropriate germanium content). The main objective of this work is to investigate the resistivity, temperature coefficient of resistance, piezoresistivity and noise of poly-SiGe deposited at temperatures compatible with MEMS post-processing on top of standard CMOS wafers with Al interconnects. For this study, boron in situ doped (with a chemical concentration of 3.6·1021cm-3) poly-Si24Ge76 was deposited at a wafer temperature of 450ºC using chemical vapor deposition (CVD). The resistivity is measured in the temperature range of -10 to 200ºC using a four point probe. The active carrier concentration and mobility are determined from Hall measurements. The piezoresistivity is estimated by measuring the resistance variation when a uniform and uniaxial stress provided by a four point bending fixture is applied to the films. To allow for comparison, boron-doped poly-Si layers were also deposited at 550ºC with an estimated chemical doping concentration of 1·1021cm-3. EXPERIMENTAL The samples were fabricated using a two mas
Data Loading...
