METHOD OF MAKING MULTIPLE SENSING AND/OR ACTUATING ARRAYS ON A SINGLE SUBSTRATE
Original Publication Date: 1997-Mar-01
Included in the Prior Art Database: 2002-May-14
This document describes a method of making multiple sensing and/or actuating arrays on a single substrate (i.e. silicon). The sensing array is fabricat- ed using a combination of electrochemical etching (ECE), electrical isolation, and timed etching to form diaphragms of varying thickness, which col- lectively make up the sensing array. In ECE, it is typical to use an n-type layer deposited on (i.e. through epitaxial grow) or diffused into a p-type sil- icon substrate. In many sensor applications, the n- type layer is used as a diaphragm for pressure or acceleration transduction, or thermal isolation for chemical sensors. The described method of making is not limited to sensing arrays, but can be extended as a method of making actuating or a combination of sensing and actuating devices. Figure 1 shows, as an example, an array of three pressure sensors fabri- cated using the disclosed method of making. The fabrication process involves using an electrochemi- cal etch stop (with each diaphragm biased at Vs) to form uniform diaphragm thickness across the wafer (Figure 1A). ECE eliminates the effect of any non- uniformity in wafer thickness or etch rate. Each diaphragm is electrically isolated from each other, which is typically accomplished through a p-type isolation diffusion. Upon completion of ECE, the bias to two of the diaphragms is opened and a timed etch is performed (Figure 1B). When the desired diaphragm thickness is reached, the bias is turned back on to that diaphragm to create etch stop (Figure 1C). Finally, when the last desired diaphragm thickness is achieved, the bias is turned back on to that diaphragm. As a result, diaphragms with varying thickness are fabricated on a single substrate for the purpose of measuring different pressure ranges. This method can be used to fabri- cate different types of sensors or actuators on a wafer which require different diaphragm thickness for optimized performance (e.g. a pressure sensor and a chemical sensor). It is noted that specific areas of the wafer can be purposely etched through by keeping the power turned off to those areas, if the application calls for it.