The quality of vertical roughness produced by the etching of Si in aqueous KOH has been studied by varying several experimental parameters such as molarity, time of etching, temperature, and stirring. We note that at room temperature, unstirred etching is smoother at low and high molarities, and etch rate and roughness both peak near 5–6 M. With no stirring, roughness increases as a function of etch time, then levels off. With stirring, roughness decreases, especially around the peak etch rate near 5–6 M. For a fixed molarity like 5 M, unstirred etching becomes smoother with increasing temperature even as the etch rate increases rapidly. Such results suggest that masking by hydrogen bubbles or silicate etch products is the principle origin of vertical roughness. Bubble properties as a function of molarity and stirring (as determined from electrolysis experiments) are used to suggest a pseudo‐masking model to explain some roughness properties.

Etching roughness for (100) silicon surfaces in aqueous KOH

The understanding of deflection, stress and strain of thin diaphragms with clamped edges under various loads including when the diaphragm touches the substrate is of great importance for designing and fabricating sensors and actuators. This article reports the finite element analysis (FEA) of these diaphragms for computer-aided design of touch mode capacitive pressure sensors. The advantages of the touch mode operation are good linearity in touched range, mechanically robust and large overload protection. These simulation results predict the change of the performance when the device parameters are varied and can be served as a design tool to arrive at a set of desired performance. The results also are useful for designing actuators with diaphragms.

Modeling of touch mode capacitive sensors and diaphragms

A method and system for calibrating temperature measurement devices, such as pyrometers, in thermal processing chambers are disclosed. According to the present invention, the system includes a calibrating light source that emits light energy onto a substrate contained in the thermal processing chamber. A light detector then detects the amount of light that is being transmitted through the substrate. The amount of detected light energy is then used to calibrate a temperature measurement device that is used in the system.

System and process for calibrating pyrometers in thermal processing chambers

The pressure sensitivity of boron-doped silicon membranes has been characterized as a function of diaphragm dimensions and internal membrane stress. Using an electrostatic technique based on silicon microbridges, the internal stress for p/sup ++/ silicon (on glass), LPCVD silicon dioxide, and LPCVD silicon nitride was measured; typical values are 40, -300, and 950 MPa, respectively. Silicon membranes with several different edge lengths and deposited oxide and/or nitride coatings were characterized for sensitivity. While the pressure sensitivity can be reduced by more than a factor of twenty in the membranes due to boron-induced internal stress, the use of stress-compensating dielectrics can improve this sensitivity by a factor of six or more. Based on this theory and the measured material parameters, scaled experimental devices show typical sensitivities within 10-20% of the theoretical design targets. Pressure sensitivities as high as 2900 ppm/Pa have been achieved. >

Internal stress compensation and scaling in ultrasensitive silicon pressure sensors

Influences of residual stress on mechanical properties of boron-doped silicon diaphragms are analyzed Considering the residual stress, the total stress analytical solutions for square-shaped boron-doped silicon diaphragms with small deflection and large deflection are presented It is found that the residual stress should not be neglected in calculation of the total stress for diaphragms with large ratio of edge length to thickness The load limitation Pmax of the square-shaped boron-doped silicon diaphragms is calculated based on the total stress analytical solution and the Griffith fracture criterion The results agree well with the reported experiments Many micro-etch-holes were found on the surface of boron-doped silicon diaphragm made from wet etch process, and these holes cause great degradation of the load limitation Pmax compared with perfect crystal silicon diaphragms

E. D. Palik

Papers

Fabrication and Characterization of Si Membranes