JP2576245B2 - Manufacturing method of semiconductor pressure sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor pressure sensor in which a semiconductor substrate is recessed by etching to form a diaphragm provided on a gauge resistor.

[Conventional technology]

Since the semiconductor pressure sensor detects pressure by a change in gauge resistance caused by deformation of the diaphragm due to the application of pressure, it must be recessed so that the thickness of the diaphragm becomes a predetermined thickness. For this purpose, electrolytic etching is performed, and so-called stop etching, which utilizes a change in etching characteristics at the interface between the p-layer and the n-layer, is performed. However, it takes a long time to process the entire concave portion by electrolytic etching. Therefore, rough processing is performed by dry etching. This concave processing is performed simultaneously on a large number of wafers, and then the wafer is divided into pressure sensor chips.

[Problems to be solved by the invention]

When roughing concave shape by dry etching method,
An Al mask is used. FIG. 2 shows a state after dry etching, in which a p layer 2 and an n layer 3 are formed on one surface side of an n ⁺ layer 1 on a silicon substrate. Above it via the oxide film 4
The Si ₃ N ₄ film 5 covers and protects the surface. On the other surface side, a mask 6 made of an Al vapor-deposited film is adhered, and a concave portion 71 is formed by dry etching using this mask. However, in this case, the burrs 61 of the Al mask may protrude to the side surfaces of the substrate as shown in FIG. Alternatively, there may be an impurity or a strain 21 that escapes from the n layer 3 to the n ⁺ layer 1 as shown in the figure. If such burr 61 or defect 21 is present, protected by a resist 8 and then removed Al mask as shown in FIG. 3, n ⁺ layer 1 to the etchant positive relative immersed cathode When a DC voltage is applied to perform electrolytic etching, a leakage current 22 flows, and a concave portion 72 formed by electrolytic etching is formed.
A non-stop phenomenon that does not stop at the interface between the n ⁺ layer 1 and the p layer occurs, and there is a problem that the thickness of the remaining diaphragm portion becomes smaller than the expected value by the dimension d, that is, the non-stop etch amount.

An object of the present invention is to solve the above-mentioned problems and to provide a method of manufacturing a semiconductor pressure sensor that prevents electrolytic etching from being stopped at a pn interface due to leakage current between an n-layer to be etched and an adjacent p-layer. To provide.

[Means for solving the problem]

In order to achieve the above object, according to the present invention, a concave portion is formed by electrolytic etching from the surface of an n layer on one surface side of a semiconductor substrate to an interface with an adjacent p layer to leave a diaphragm portion having a predetermined thickness. In the method for manufacturing a semiconductor pressure sensor including a step, a reverse voltage is applied to a pn junction between the two layers by using an electrode in contact with the n-layer and the p-layer before the electrolytic etching step, so that a Measure the leakage current,
Electrolytic etching is performed only when the value of the leakage current is smaller than a predetermined value.

[Action]

Before the electrolytic etching process, the semiconductor substrate with a large leakage current due to the flash of the Al mask or a defect penetrating the junction is measured by measuring the leakage current when the reverse voltage is applied to the pn junction to stop the etching. Can be
The occurrence of non-stop during stop etching is prevented.

〔Example〕

FIGS. 1 (a) to 1 (h) show a non-stop generation preventing step in one embodiment of the present invention, and the same reference numerals are given to the parts common to FIGS. 2 and 3. FIG. The silicon substrate shown in FIG. 1 (a), n ⁺ layer 1 as in the case of Figure 2,
The p layer 2 and the n layer 3 are formed, and the n layer 3 has ap ⁺ isolation diffusion layer 9 for separating a gauge resistor provided in the diaphragm portion from an attached circuit integrated in the outer peripheral portion. . n ⁺
Al film on the SiO ₂ film 4 covering the surface of the layer 1 and the exposed p ⁺ layer 9
10 is deposited. This Al film 10 is patterned using a resist film 81, leaving an Al electrode 11 on the p ⁺ layer 9 (FIG. B). Next, after depositing the Si ₃ N ₄ film 5 on the entire surface, the Si ₃ N ₄ film 5 on the Al electrode 11 is removed using the resist film 82 (FIG. C). On the other hand, the opposite SiO ₂ film 4 and Si ₃ N ₄ film 5 are
Patterning is performed using 3 to expose the n ⁺ layer 1 (FIG. D). Next, an Al film 10 is deposited on this surface for a dry etching mask and an electrode (FIG. E). Here, patterning of the Al film 10 using the resist film 84 is performed to remove the Al film in the portion where the concave portion is to be processed, but leave the Al electrode 12 in the portion facing the p ⁺ separation layer 9. (Figure f). Next, dry etching is performed in the same manner as in FIG. 2, and rough processing is performed up to the vicinity of the interface between the n ⁺ layer 1 and the p layer 2 to form a concave portion 71 (FIG. G). Thereafter, as schematically shown, a reverse voltage V is applied between the n ⁺ layer 1 and the p layer 2 using the electrodes 11 and 12.
Over the _R to measure the current I _R leakage. FIG. 4 shows the relationship between this I _R and the depth of etching beyond the interface between the n ⁺ layer 1 and the p layer 2 during electrolytic etching, ie, the non-stop etching amount d shown in FIG. There is a relationship as shown. The allowable range d ₀ of the nonstop etch amount is determined from the standard of the allowable range of the thickness of the diaphragm, and the leakage current I
_R0 can be determined in advance. I _R obtained by the measurement in FIG. 1 (g) is greater due to defects penetrating the burr or pn junction of the Al film, the silicon substrate is not advanced to the next step. Applying a protective plate 13 on the surface side non-defective silicon substrate in the next step, by performing electrolytic etching to cover the the Si ₃ N ₄ film 5 on the back surface side protective film 85, approximately n ⁺ layer 1 and p
Stop etching that stops at the interface with the layer 2 can be performed, and the concave portion 72 is formed (FIG. H).

〔The invention's effect〕

According to the present invention, before electrolytic etching,
The leakage current is measured even when a reverse voltage is applied to the pn junction, and the leakage current is measured during the concave processing for forming the pressure sensor diaphragm by electrolytic etching by not subjecting the semiconductor substrate with large leakage current to electrolytic etching. As a result, the etching depth was prevented from exceeding the pn junction, and the effect of efficiently performing stop etching for obtaining a pressure sensor chip having a diaphragm portion having a predetermined thickness was obtained.

[Brief description of the drawings]

FIG. 1 shows the concave processing step of one embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a dry etching step for concave processing, FIG. 3 is a cross-sectional view showing a conventional electrolytic etching step for concave processing, and FIG.
FIG. 4 is a relationship diagram between a leakage current of a junction and a non-stop etching amount. 1: n ⁺ layer, 2: p layer, 9: p ⁺ separation layer, 11, 12: Al electrode.

Claims (1)

(57) [Claims] 1. A method of manufacturing a semiconductor pressure sensor, comprising the step of electrolytically etching a surface of an n-layer on one surface side of a semiconductor substrate to an interface with an adjacent p-layer to form a concave portion leaving a diaphragm portion having a predetermined thickness. In the method, prior to the electrolytic etching step, a leakage current between the two layers is measured by applying a reverse voltage to a pn junction between the two layers using electrodes in contact with the n-layer and the p-layer, A method of manufacturing a semiconductor pressure sensor, wherein the electrolytic etching is performed only when the current value is equal to or less than a predetermined value.