A method using V-grooves to monitor the thickness of silicon membrane with m resolution

Abstract

This article presents a method capable of easily identifying the membrane thickness of micro-sensors by a V-groove depth ruler that has been made in advance on silicon wafers before sensor fabrication. The proposed method not only provides a viable alternative to other etch-stop techniques, but can also be used as an in situ tool for depth or thickness monitoring with micrometer resolution. Without p+ diffusion or an n-epitaxial layer on silicon substrates, the batch processing capability of silicon piezoresisitve micro-sensors can be preserved with V-grooves. Furthermore, the method proposed herein could also calibrate the etching rate of anisotropic etching solutions, check the uniformity of pressure sensors and offer guidelines on how to further improve the batch process of silicon bulk micro-machining. Moreover, a revised shape of V-groove depth ruler with self-alignment capability is also proposed herein.

Foundry Service of CMOS MEMS Processes and the Case Study of the Flow Sensor

“…Figure 5a shows the CMOS standard process, which is composed of four kinds of different thin films including silicon nitride (Si3N4), silicon dioxide (SiO2), aluminum, and polysilicon on the silicon substrate. The arrangements of thin films in the order from bottom to top are silicon substrate, silicon dioxide, multiple metal layers with their inter-layer for bulk micromachining [91,165]; (c) acid etch metals (surface micromachining) [35,37]; (d) deep trench plasma etching the oxides to release the cantilever [130]; (e) acid is used to etch metals and TMAH used to etch the Si substrate [57]; (f) electroplating Ni in the process (c) [90,137]; (g) parylene or gelatin is coated on process (e) [87,88]; (h) anisotropic and isotropic etching with STI protection [96,97,102,166].…”

“…It also has good selectivity in metal preservation. The disadvantages are that it wastes the wafer area at the slope on the {111} [87,167] plane [161,165]; the backside photolithography needs to use a double-sided mask aligner; the wafer needs to be thinned and have an additional protective layer (PECVD nitride or sputtered oxide) [165].…”

“…The above drawbacks of the post-process Figure 5b are due to the backside V-groove etching [161,165]. When a metal layer is well-designed in advance and assigned to be the sacrificial layer in the post-process (Figure 5c), the sacrificial layer will be etched completely from the front side, and the silicon nitride layer will be released as a suspended structure in the micrometer scale.…”

In Situ Monitoring of Silicon Membrane Thickness during Wet Etching using a Surface Acoustic Wave Sensor

“…The advantages and disadvantages of wet and dry etching are well known. 2) A novel method, which differs from that of any previous work on etch-stop techniques, [5][6][7][8] develops a novel method in situ for monitoring the thickness of a silicon membrane from 50 mm to 80 mm with high accuracy, a simple setup and can be used for mass production. The principles of the method, detailed process flows, the set up for taking measurements and simulation and experimental results are discussed.…”

A process to control diaphragm thickness with a provision for back to front alignment in the fabrication of polysilicon piezoresistive pressure sensor

“…In the bulk micromachining, one of the important aspects is to control the diaphragm thickness during anisotropic etching of (100) silicon. A number of techniques are in practice for the control of diaphragm thickness during bulk micromachining (Chang and Yang, 1998;Kloeck et al, 1989;Kopystgeski and Obeiner, 1997). In all these cases, a separate process is introduced with limited applications owing to the factor of technological compatibility.…”