JP2808843B2 - Manufacturing method of semiconductor pressure sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a semiconductor pressure sensor, and more particularly to a method for forming a diaphragm thereof and a method for forming a metal layer for mounting the sensor itself to a base. .

[Conventional technology]

The semiconductor pressure sensor has a gauge resistor on one surface of a thin portion as a diaphragm. This gauge resistor changes its resistance value when strain is generated by pressure (piezoresistance effect). The pressure is measured by detecting this resistance change as an electric signal.

The thin portion, which is a diaphragm, was obtained by etching the back surface of the semiconductor substrate to form a recess,
A mounting metal layer is formed on the back surface of the thick portion that is the non-etched portion. The mounting metal layer is formed to be fixed to the base by brazing or the like.

A conventional method for manufacturing a semiconductor pressure sensor will be described with reference to FIG.

As shown in FIG. 2 (a), the substrate used for the semiconductor pressure sensor has a multi-layered semiconductor layer, and includes an n ⁺ type silicon substrate 1 and a p-type epitaxial silicon layer formed on one side thereof. 2 and an n-type epitaxial silicon layer 3 formed on this surface. On the surface of the n-type epitaxial silicon layer 3, a bridge circuit including a gauge resistor 10 which is a p-type semiconductor is formed. Further, an amplifier circuit 11 for an electric signal detected from this circuit is also formed.

First, a silicon oxide film 21 and a silicon nitride film 22 are formed on the surface of the n ⁺ -type silicon substrate 1 except for a region 4 where an electrolytic etching terminal to be described later is to be formed (hereinafter, referred to as an electrolytic etching terminal forming region 4). Are sequentially formed. Next, an aluminum layer 23 is formed on the surface of the silicon nitride film 22 and on the surface of the n ⁺ -type silicon substrate 1 in the region 4 where the terminal for electrolytic etching is to be formed. The surface of this aluminum layer 23
The mask 24 is masked by the photoresist 24 so that the window 5 is formed in the recess forming region 5. Aluminum layer 23 of the region 5, the silicon nitride film 22 and silicon oxide film 21 is removed through a plurality of etching processes, as shown in the final Fig. 2 (b), n ⁺ -type silicon substrate 1 is opened windows It will be in the state that was done.

FIG. 2C shows a dry etching step. The n ⁺ type silicon substrate 1 is dry-etched with an SF ₆ -based gas while being masked by the aluminum layer 23. Thereby, the concave portion 5a is formed. This dry etching is stopped before the bottom surface 5b of the concave portion 5a reaches the pn junction surface 12 of the n ⁺ type silicon substrate 1 and the p type epitaxial silicon layer 2.

Thereafter, in the electrolytic etching terminal forming step of FIG. 2 (d), the aluminum layer 23 in the electrolytic etching terminal forming region 4 is left as the electrolytic etching terminal 23a, and other portions are removed.

2E and 2F show an electrolytic etching step.
First, the n ⁺ type silicon substrate 1 is masked with a photoresist 24a in a state where the concave portion 5a formed in the dry etching step and the terminal 23a for electrolytic etching are opened. Next, the semiconductor substrate is immersed in a hydrofluoric acid-based aqueous solution, and the electrolytic etching terminal 23a is connected to the anode to perform an electrolytic etching process. Here, since the pn junction surface 12 serves as an etching stopper, the bottom surface 5b of the concave portion 5a, which is the etching progress surface, is used for this electrolytic etching.
n ⁺ type silicon substrate 1 and p type epitaxial silicon layer 2
Stops when it reaches the pn junction surface 12. By forming the concave portion 5a, the diaphragm 25 as a thin portion is obtained.

Next, FIGS. 2 (g) and 2 (h) show a mounting metal layer forming step for mounting the semiconductor pressure sensor on the base. A Cr-Au layer 26 is formed on the entire surface of the n ⁺ type silicon substrate 1, and a mask of a photoresist 24b is formed on the surface of the Cr-Au layer 26 excluding the concave portion 5a. Then, the Cr-Au layer deposited in the concave portion 5a is removed by wet etching, and the Cr-Au layer 26a on the thick portion 1a is
Remains as 6a.

[Problems to be Solved by the Invention] As shown in FIG. 2 (f), the Cr-Au layer 26 excluding the recess 5a is formed.
In the step of forming a photoresist mask 24b on the substrate, the photoresist residue 24c may adhere to the inside of the concave portion 5a, particularly to the bottom surface 5b. When wet etching is performed in this state, photoresist residue 24
c The metal piece 26b of the lower Cr-Au layer 26 may remain.

Further, in the wet etching step of removing the Cr-Au layer 26 adhered to the inner surface of the concave portion 5a, the etching solution hardly enters the inside of the concave portion 5a, and further, the dissolved metal stays in the concave portion. , The dissolution rate of the Cr—Au layer 26 varies, and as shown in FIG.
-The metal piece 26b of the Au layer 26 may remain.

The finished product of the semiconductor pressure sensor in which such a metal piece 26b remains has a poor appearance, and therefore, the yield of the semiconductor pressure sensor has been reduced.

In order to prevent the Cr-Au pieces 26b from remaining inside the concave portion 5a, the wet etching time is extended and the Cr-Au
Although it is possible to completely etch the Au layer, if the wet etching time is carelessly extended, this time, n ⁺
C sandwiched between the silicon substrate 1 and the photoresist 24b
Side etch 30 occurs at the end of the r-Au layer 26a,
This side etch causes another appearance defect.

Therefore, in any case, there has been a demand for a method for improving the yield reduction due to poor appearance.

In view of the above problems, an object of the present invention is to prevent the metal pieces used for the mounting metal layer from remaining or the like by performing the etching step of the mounting metal layer before the recess forming step. An object of the present invention is to provide a method for manufacturing a semiconductor pressure sensor that can realize cost reduction and improvement in yield.

[Means for solving the problem]

In order to solve the above problems, in a method of manufacturing a semiconductor pressure sensor having a gauge resistor on one surface side of a semiconductor substrate and a concave portion opened on the other surface side, the means taken by the present invention is as follows. A step of coating a metal layer for attachment on the other side of the substrate to attach the semiconductor pressure sensor to the substrate;
Next, a step of coating at least one lower mask material layer of a lower mask to be used in a subsequent etching step on the mounting metal layer in advance, and an upper layer in which a region where the concave portion is to be formed is opened. A step of coating a mask on the lower mask material layer, and then etching from the window opening of the upper mask to the mounting metal layer through the lower mask material layer to form a shallow recess. 1 etching process;
Thereafter, a second etching step of forming the concave portion in the semiconductor substrate by etching from a window opening of the lower layer mask obtained in the first etching step is provided.

When the region where the concave portion is to be formed is mainly an n-type semiconductor layer, first, a p-type semiconductor layer is formed on the other surface of the n-type semiconductor layer, and then the semiconductor pressure sensor is attached to the base. After the mounting metal layer to be formed is formed on the surface of the p-type semiconductor layer, a mask having a window formed in the area where the concave portion is to be formed is covered on the mounting metal layer.
The concave portion is formed by etching the metal layer, the p-type semiconductor layer, and the n-type semiconductor layer from a window opening of the mask.

Further specifically, after the step of forming the p-type semiconductor layer, the method further includes a step of removing a part of the p-type semiconductor layer to expose a part of the surface of the n-type semiconductor layer, An electrolytic etching terminal to be electrically connected only to the n-type semiconductor layer is formed on the exposed region with the help of a forming step of the mounting metal layer, and power is supplied through the electrolytic etching terminal in the etching step. It is desirable to use an electrolytic etching process that causes

[Action]

According to the above means, after forming a metal layer for mounting the semiconductor pressure sensor on the substrate on the other surface side of the semiconductor substrate on which the gauge resistance is formed on one surface side, a region where a concave portion is to be formed thereon When the mask which covers the window is opened and etching is performed to form a concave portion constituting the diaphragm, the metal layer for attachment can be left on the surface around the thick portion of the concave portion.

Therefore, since it is not necessary to form the mounting metal layer after forming the concave portion, the metal pieces used for the mounting metal layer do not remain inside the concave portion. Therefore, appearance defects due to the remaining metal pieces can be prevented, and the yield can be improved. Moreover, when the concave portion is formed by etching, the mounting metal layer can be formed on the surface around the thick portion of the concave portion at the same time. Therefore, it is not necessary to form the concave portion and the mounting metal layer in a separate step, and the number of steps can be reduced. And cost reduction can be realized.

In particular, the present invention provides a method in which at least one lower mask material layer of a lower mask to be used in a subsequent etching step is coated on a mounting metal layer in advance, and then the upper mask in which a region where a concave portion is to be formed is opened is opened. Covering the mask material layer, etching from the window opening of the upper mask to the mounting metal layer through the lower mask material layer to form a shallow recess, and the lower mask of the lower mask obtained by this etching process is formed. This is an etching method in which a concave portion is formed in a semiconductor substrate by etching from a window opening portion, and a concave portion is further dug by using the lower layer mask while forming a lower layer mask in a self-aligned manner. Therefore, a dedicated process for forming the lower layer mask is not required, and cost reduction can be realized. Further, since no mask shift occurs, it is possible to suppress a variation in the opening area of the concave portion, and to improve the yield.

Further, when a p-type semiconductor layer is formed on the surface of the n-type semiconductor layer, a mounting metal layer is formed on the surface, and then a concave portion is formed by using an electrolytic etching process, the p-type semiconductor layer and the mounting metal layer are formed. Is insulated and separated from the n-type semiconductor layer by the pn junction surface, the p-type semiconductor layer and the mounting metal layer are not electrolytically etched and remain on the surface around the thick portion of the concave portion.

Therefore, an electrolytic etching step can be used as an etching step after forming the mounting metal layer.

In addition, since the terminal for electrolytic etching that is conducted only to the n-type semiconductor layer is formed with the help of the step of forming the mounting metal layer, the number of steps can be reduced.

〔Example〕

Next, a method for manufacturing a semiconductor pressure sensor according to an embodiment of the present invention will be described below.

In the manufacturing process of this example, a process for forming a mounting metal layer for mounting a semiconductor pressure sensor on a substrate and forming a terminal for electrolytic etching with the aid of the mounting metal layer (metal layer forming process), It is composed of a step of covering the mask with the window opened over the mounting metal layer (mask forming step), a dry etching step to form a concave portion in a region where the concave portion is to be formed, and an electrolytic etching step to make the thickness of the diaphragm constant. Have been.

 FIGS. 1A to 1E show sectional views of these steps.

First, as shown in FIG. 1 (a), the substrate used in the semiconductor pressure sensor of this example is a substrate having a multi-layer semiconductor conventional example having the same structure as, n ⁺ -type silicon substrate 1, p
And an n-type epitaxial silicon layer 2. On the surface of the n-type epitaxial silicon layer 3, a bridge circuit including a gauge resistor 10 which is a p-type semiconductor and an amplifier circuit 11 for an electric signal detected from this circuit are also formed.

First, as the metal layer forming step, the entire surface of the n ⁺ -type silicon substrate 1, p-type silicon layer 6 is formed by the epitaxial growth method, the p-type silicon layer 6, the n ⁺ type silicon substrate 1 and the pn junction plane 13 Is formed. Next, the p-type silicon layer 6 in the region 4 for forming the terminal for electrolytic etching and the surface layer of the n ⁺ -type silicon substrate 1 thereunder are removed by etching, and a part of the surface of the n ⁺ -type silicon substrate 1 is exposed. . A Cr-Au layer 7 is formed on the exposed surface of the n ⁺ type silicon substrate 1 and on the surface of the p type silicon layer 6. As shown in FIG. 1A, the Cr-Au layer 7 is insulated from a Cr-Au layer 7a on the surface of the p-type silicon layer 6 and a Cr-Au layer 7b on the surface of the n ⁺ -type silicon substrate 1. Separated.

Next, in a mask forming step, a plurality of mask layers used in a subsequent etching step are sequentially formed. First,
On the surface of the Cr-Au layer 7, a polyimide layer 8 and an aluminum layer 9 are formed. The surface of the aluminum layer 9 is masked by the photoresist 24c so that the region 5 where the concave portion is to be formed is opened. Next, the aluminum layer 9, the polyimide layer 8 and the Cr-Au layer 7a in this region 5 are sequentially removed by an etching process, and the n ⁺ type silicon substrate 1 is removed.
Is opened as shown in FIG. 1 (b). The Cr-Au layer 7a left in this state is used as a metal layer for mounting the semiconductor pressure sensor on the base.

Next, FIG. 1 (c) shows a dry etching step.
After the photoresist 24c is removed, the p-type silicon layer 6 is removed.
The n ⁺ -type silicon substrate 1 is dry-etched with an SF ₆ -based gas while being masked by the aluminum layer 9 to form a concave portion 5a. This dry etching is performed in the recess 5a.
Is stopped before reaching the pn junction surface 12 of the n ⁺ type silicon substrate 1 and the p type epitaxial silicon layer 2.
The Cr-Au layer 7a as a mounting metal layer remains on the surface around the thick portion 1a in the concave portion 5a.

Next, FIGS. 1D and 1E show an electrolytic etching step. After the aluminum layer 9 and the polyimide layer 8 are removed by etching, the semiconductor substrate is immersed in a hydrofluoric acid-based etching solution, and the Cr-Au layer 7b is connected to the electrolytic etching terminal 7b.
And an electrolytic etching process is performed. Here, since the pn junction surface 12 serves as an etching stopper, the bottom surface 5b of the concave portion 5a which is the etching progress surface is formed.
Stops when it reaches the pn junction surface 12 of the n ⁺ type silicon substrate 1 and the p type epitaxial silicon layer 2. By forming the concave portion 5a, the diaphragm 25 which is a thin portion of the concave portion 5a is obtained.

Here, on the surface side around the thick portion 1a in the concave portion 5a, the p-type silicon layer 6 and the Cr-Au layer 7a left on this surface are connected to the n ⁺ type silicon substrate 1 by the pn junction 13.
Is in an insulated state, and no electrolytic etching current flows through the p-type silicon layer 6 and the Cr-Au layer 7a.
The p-type silicon layer 6 and the Cr-Au layer 7a are not electrolytically etched.

As described above, in the manufacturing method of the semiconductor pressure sensor of the present example, the Cr-Au layer 7 is formed on the surface of the n ⁺ type semiconductor layer,
After performing masking in a state where the region 5 where the concave portion 5a is to be formed is opened, a plurality of etching steps are sequentially performed to form the concave portion 5a, and at the same time, the thick portion in the concave portion 5a.
The Cr-Au layer 7a, which is a mounting metal layer, can be left on the surface around 1a.

Therefore, it is not necessary to form the mounting metal layer after forming the thin portion of the concave portion serving as the diaphragm, so that the mounting metal piece does not remain inside the concave portion. As a result, appearance defects can be prevented, and the yield can be improved.

In particular, in this example, an etching method in which after forming a plurality of mask layers used in the etching step in advance, a lower layer mask is formed in a self-aligning manner, and a concave portion is further dug using the lower layer mask. Therefore, a dedicated process for forming the lower layer mask is not required, and the cost can be reduced. Further, since no mask shift occurs, it is possible to suppress a variation in the opening area of the concave portion, and to improve the yield.

In addition, the Cr-Au layer 77b conducting only to the n ⁺ -type semiconductor layer 1 is formed with the help of the step of forming the Cr-Au layer 7, and the Cr-Au layer 77b is used as the electrolytic etching terminal 7b. Since it is not formed in the process, the number of processes can be reduced,
Cost reduction can be realized.

〔The invention's effect〕

In the method for manufacturing a semiconductor pressure sensor according to the present invention, after the step of forming a metal layer for mounting the semiconductor pressure sensor to the substrate on the other surface side of the semiconductor substrate,
The method is characterized in that the metal layer and the semiconductor substrate are etched from a window opening portion of the mask to form a concave portion forming a diaphragm, so that after the concave portion is formed, the mounting metal layer is formed. Is not formed, the metal piece used for the mounting metal layer does not remain inside the concave portion forming the diaphragm, and the appearance defect is reduced, as a result,
The yield can be improved.

In particular, the present invention provides a method in which at least one lower mask material layer of a lower mask to be used in a subsequent etching step is coated on a mounting metal layer in advance, and then the upper mask in which a region where a concave portion is to be formed is opened is opened. Covering the mask material layer, etching from the window opening of the upper mask to the mounting metal layer through the lower mask material layer to form a shallow recess, and the lower mask of the lower mask obtained by this etching process is formed. This is an etching method in which a concave portion is formed in a semiconductor substrate by etching from a window opening portion, and a concave portion is further dug by using the lower layer mask while forming a lower layer mask in a self-aligned manner. Therefore, a dedicated process for forming the lower layer mask is not required, and the cost can be reduced.
Further, since no mask shift occurs, it is possible to suppress a variation in the opening area of the concave portion, and to improve the yield.

When the concave portion is formed by etching the area where the diaphragm of the mounting metal layer is to be formed, the mounting metal layer remains on the surface around the thick portion of the concave portion, so that the number of manufacturing steps can be reduced and the cost can be reduced. .

In the electrolytic etching step, a part of the mounting metal layer is separated and used as an electrolytic etching terminal, so that the number of manufacturing steps can be reduced and the cost can be reduced.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... n ⁺ type silicon substrate (n-type semiconductor layer) 2 ... p-type epitaxial silicon layer 3 ... n-type epitaxial silicon layer 4 ... Planned area for forming a terminal for electrolytic etching 5 ... Planned area 5a for forming a concave portion ... recess 6 ... p-type silicon layer (p-type semiconductor layer) 7 ... Cr-Au layer (mounting metal layer) 7a ... Cr-Au layer (mounting metal layer) 7b ... Cr-Au layer (electrolysis) (Etching terminal) 10 ... Gauge resistor 12,13 ... pn junction surface 24,24a, 24b, 24c ... photoresist 25 ... diaphragm.

Claims (3)

(57) [Claims] In a method of manufacturing a semiconductor pressure sensor having a gauge resistor on one side of a semiconductor substrate and a concave portion opened on the other side, the semiconductor pressure sensor should be attached to the base on the other side of the semiconductor substrate. A step of coating the mounting metal layer, and a step of previously coating the mounting metal layer with at least one lower mask material layer of a lower mask to be used in a subsequent etching step; Covering the lower mask material layer with an upper mask in which a region where a concave portion is to be formed is opened, and then, from the window opening of the upper mask to the mounting metal layer through the lower mask material layer. A first etching step of forming a shallow concave portion by etching the semiconductor substrate, and thereafter, etching the semiconductor substrate through a window opening of the lower layer mask obtained in the first etching step. The method of manufacturing a semiconductor pressure sensor, characterized by a second etching step of forming a section. 2. A method of manufacturing a semiconductor pressure sensor having a gauge resistor on one side of an n-type semiconductor layer and a recess opened on the other side, wherein a p-type semiconductor layer is provided on the other side of the n-type semiconductor layer. Forming a metal layer for mounting a semiconductor pressure sensor on a substrate on the surface of the p-type semiconductor layer; and Covering the mounting metal layer, and thereafter, etching the metal layer, the p-type semiconductor layer and the n-type semiconductor layer from a window opening of the mask to form the concave portion. A method for manufacturing a semiconductor pressure sensor, comprising: 3. The method according to claim 2, further comprising, after the step of forming the p-type semiconductor layer, removing a part of the p-type semiconductor layer to expose a part of the surface of the n-type semiconductor layer. And
Forming an electrolytic etching terminal to be conducted only to the n-type semiconductor layer on the exposed region with the help of the forming step of the mounting metal layer, and the etching step includes supplying an electric power through the electrolytic etching terminal. A method for manufacturing a semiconductor pressure sensor, comprising an etching step.