JP2003229407A - Semiconductor substrate and etching method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the smoothness of an etching surface by employing the water solution of KOH as etching solution upon effecting etching treatment, by immersing a semiconductor substrate into the etching solution. <P>SOLUTION: A silicon wafer 50 is employed as the semiconductor substrate and a silicon oxide film 70 is formed on the main surface 51 of the silicon wafer 50, then, the oxide film 70 is removed through etching employing the water solution of potassium hydroxide as the etching solution, and, subsequently, the silicon wafer 50 is processed through etching treatment from the side of the main surface 51 of the same. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor substrate etching method in which a semiconductor substrate is etched by immersing the semiconductor substrate in an etching solution, and more particularly to a pressure sensor, an acceleration sensor, a gas sensor, a flow sensor and the like. It is suitable for use in an etching method when forming a diaphragm as a thin portion on a semiconductor substrate.

[0002]

2. Description of the Related Art Conventionally, when a silicon diaphragm such as a semiconductor pressure sensor or a semiconductor acceleration sensor is formed,
The main surface of the silicon substrate is made of SiO which is an etching resistant material.
It is covered with an etching mask made of ₂ or SiN film, and in this state, wet etching is performed using an etching solution such as KOH (potassium hydroxide) aqueous solution.

As a result, a recess depressed from the main surface is formed in a portion of the main surface of the silicon substrate corresponding to the opening of the etching mask, the bottom of the recess becomes a thin portion, and this thin portion serves as a diaphragm. It is formed.

Here, the etching of silicon using a KOH aqueous solution is performed by adjusting the KOH concentration and the temperature, and in particular, from the viewpoint of the smoothness of the etching surface (the bottom of the recess) and the etching rate, the KOH concentration is 30. weight%
Those in the vicinity are generally adopted as the etching solution.

[0005]

However, for example, as a silicon substrate, the plane orientation index of its main surface is (110).
In the case of using the above-mentioned one, the shape of the etching surface becomes a characteristic concavo-convex shape, and it is difficult to form a smooth diaphragm. It is considered that this is due to the anisotropy of the etching rate near the (110) plane.

Incidentally, according to the study by the present inventors regarding the conventional etching method, the characteristic uneven shape of the etching surface, which is the (110) surface, is KOH of the etching solution.
It is known that streaks are formed at 38% by weight or less and pyramidal unevenness is formed at 40% by weight or more depending on the concentration.

The silicon diaphragm is formed to a desired thickness by etching most of the silicon diaphragm with respect to the thickness dimension of the silicon substrate. For example, in order to ensure the accuracy of the sensitivity characteristic with respect to pressure in the semiconductor pressure sensor, it is necessary to make the thickness of the diaphragm uniform, that is, to form the bottom surface of the recess, which is the etching surface, smooth and flat.

Besides the KOH aqueous solution, the wet etching method for finishing the etching surface to be a flat surface is as follows.
For example, JP-A-8-13165 and JP-A-2000.
The method described in Japanese Patent Laid-Open No. 91307 has been proposed.

The former is one in which a silicon substrate is immersed in an ammonium fluoride (NH ₄ F) solution and an etching process is performed while applying a potential to the silicon substrate, and the potential is controlled to be, for example, a rest potential or less. This is a technique for obtaining atomic level flatness. The latter uses an aqueous tetramethylammonium hydroxide (TMAH) solution as an etching solution, and performs etching while applying a potential to the silicon substrate.

However, the above-mentioned Japanese Patent Laid-Open No. 8-1316 is used.
In the methods described in Japanese Patent Laid-Open No. 5 and Japanese Patent Laid-Open No. 2000-91307, the flatness of the etching surface can be secured,
NH ₄ F solution and TM as etching solution to be used
Since the AH aqueous solution originally has a smaller etching rate than the KOH aqueous solution, the workability is not good in the semiconductor manufacturing process, and the former solution contains fluorine ions, which is unsafe.

In view of the above circumstances, the present invention has an object to improve the smoothness of the etching surface by using a KOH aqueous solution as the etching solution when the semiconductor substrate is immersed in the etching solution for the etching process. .

[0012]

In order to achieve the above object, according to the invention as set forth in claim 1, in a method for etching a semiconductor substrate in which the semiconductor substrate is etched by immersing the semiconductor substrate in an etching solution, silicon is used as the semiconductor substrate. After using the substrate (50) to form an oxide film (70) on the main surface (51) of this silicon substrate, the oxide film is removed by etching using an aqueous potassium hydroxide solution (20) as an etching solution. The silicon substrate is characterized by being etched from its main surface side.

According to this, the oxide film previously formed on the main surface which is the surface to be etched of the silicon substrate is removed by etching with the KOH aqueous solution, and the etching of the silicon substrate is started at the same time when the etching of the oxide film is completed.

Although a clear mechanism is not known, it is expected that the starting point of silicon etching will be a hydrophilic surface by etching the silicon substrate at the same time as the etching of the oxide film is completed. Then, it is considered that uniform silicon etching is started by the formation of the hydrophilic surface, and as a result, a smooth etching surface is obtained on the silicon substrate.

In fact, as a result of experiments and examinations, according to the etching method of the present invention, the etching surface (2a) is superior in smoothness to the etching method using the conventional KOH aqueous solution.
was gotten. For example, the surface roughness Rz of the etching surface is 0.
Good smoothness was obtained with a thickness of less than 8 μm.

As described above, according to the present invention, it is possible to provide an etching method in which the KOH aqueous solution is used as the etching solution and the smoothness of the etching surface can be improved more than ever before.

Here, as in the invention described in claim 2,
By adjusting the KOH concentration of the potassium hydroxide aqueous solution (20) to 39 wt% to 48 wt% and adjusting the liquid temperature to 90 ° C to 140 ° C, the oxide film (7
0) and the silicon substrate (50) are preferably etched.

Further, in the etching method according to claim 1 or 2, the silicon substrate (50) has a main surface (51) whose surface orientation index is (110) as in the invention according to claim 3. It is especially effective when using a thing.

Further, in the invention described in claim 4, the semiconductor substrate is etched by the etching method according to any one of claims 1 to 3, and the surface roughness Rz of the etching surface (2a) is Of less than 0.8 μm is provided.

The semiconductor substrate of the present invention is appropriately manufactured by the etching method according to any one of claims 1 to 3, and the effect is the same as above.

The reference numerals in parentheses for each means described above are examples showing the correspondence with the specific means described in the embodiments described later.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention shown in the drawings will be described. In addition, in each of the following embodiments, the same portions are denoted by the same reference numerals in the drawings.

(First Embodiment) FIG. 1 is a diagram showing a schematic sectional structure of a semiconductor pressure sensor S1 according to a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a silicon substrate as a semiconductor substrate. In this example, the silicon substrate 1 has a main surface 1a, 1b having a plane orientation index of (100).

One surface of the main surface of the silicon substrate 1 (see FIG.
On the lower surface (inner side) 1a, a recess 2 is formed by denting from the one surface 1a by KOH etching. Then, in the silicon substrate 1, the bottom surface 2a side of the concave portion 2 becomes a thin portion, and this thin portion is formed as a diaphragm 3 for pressure detection.

On the other surface 1b, which is the main surface opposite to the one surface 1a of the silicon substrate 1, a strain gauge 4 is formed in a region corresponding to the diaphragm 3. The strain gauge 4 is for outputting an electrical signal according to the stress generated when the diaphragm 3 is distorted by forming a bridge circuit, for example. The strain gauge 4 is configured as a diffusion resistance formed by ion implantation or diffusion.

In the semiconductor pressure sensor S1, when the diaphragm 3 receives pressure and is deformed, a signal is output from the strain gauge 4 according to the strain generated by the deformation of the diaphragm 3. The output signal from the strain gauge 4 is output to an external signal processing circuit or the like via a wiring section or a pad section (not shown). In this way, the pressure is detected.

Next, a method of manufacturing the semiconductor pressure sensor S1 will be described. The sensor S1 is formed by using a silicon substrate whose main surface has a plane orientation of (110) and subjecting it to a well-known semiconductor manufacturing technique. The method of etching the silicon substrate will be described.

FIG. 2 is a diagram showing a schematic structure of an etching apparatus 100 used in the present etching method. Reference numeral 10 denotes an etching tank made of, for example, Teflon (registered trademark), and the etching tank 10 contains an aqueous potassium hydroxide (KOH) solution 20 as an etching solution.
The KOH aqueous solution 20 is preferably adjusted to have a KOH concentration of 39% by weight or more and 48% by weight or less.

Further, the etching apparatus 100 is provided with a temperature controller 30 having a temperature sensor and a heater, and the temperature controller 30 allows the KOH aqueous solution 20 to be supplied.
Are heated and cooled and temperature controlled. KOH aqueous solution 20
The liquid temperature is preferably maintained in the range of 90 ° C. or higher and 140 ° C. or lower.

Further, a stirrer 40 is arranged at the bottom of the etching tank 10 inside the tank, and a KOH solution 20 is stirred at a stirring speed such that the temperature distribution of the KOH aqueous solution 20 becomes uniform by applying a rotating magnetic field. The aqueous solution 20 is agitated.

As the silicon substrate to be etched, a silicon wafer 50 whose main surface 51, 52 has a plane orientation index of (110) is used. The wafer 50 is immersed in the KOH aqueous solution 20 in the etching bath 10. The etching process is performed in this state. Although FIG. 2 is a schematic diagram showing only one silicon wafer 50, it is needless to say that a configuration for simultaneously processing a plurality of silicon wafers 50 can be adopted when used in the manufacturing process.

Here, FIG. 3 shows the silicon wafer 5 described above.
0 is a view showing a state where an etching mask 60 for forming a diaphragm is formed on a main surface 51 on one side of 0, (a)
Is a plan view seen from the main surface 51 on the one side, and (b) is a schematic sectional view. Silicon wafer 5 in the state shown in FIG.
Etching is performed while 0 is immersed in the KOH aqueous solution 20.

Main surface 51 on one side of silicon wafer 50
Is a surface corresponding to the one surface 1a of the silicon substrate 1 and is an etched surface on which the recess 2 is formed. First, as shown in FIG. 3, a silicon oxide film 70 is formed on the main surface 51 by thermal oxidation or the like. Then, the strain gauge 4 is formed on the other main surface 52 of the silicon wafer 50.

Then, the silicon wafer 50 (110)
The silicon oxide film 7 is formed on the main surface 51 on one side which is a surface.
An etching mask 60 is formed on top of 0. The mask 60 is formed by depositing a film made of a silicon nitride film, which is an etching resistant material, on the silicon oxide film 70 by plasma CVD or the like, and then opening a region to be etched in the deposited film by photolithography. Is formed by. In FIG. 3, the opening 61 of the mask 60 has a square shape in plan view, but its shape and size do not matter.

After the silicon oxide film 70 and the etching mask 60 are formed on the silicon wafer 50 in this manner, the etching process of the silicon wafer 50 is performed using the etching apparatus 100 shown in FIG. Although not shown, the main surface 52 and the side surface on the other side of the silicon wafer 50 are masked so as not to be exposed to the KOH aqueous solution 20.

FIG. 4 is an explanatory view showing the progress of etching of the silicon wafer 50. First, as shown in FIG. 4A, the silicon oxide film 70 exposed from the opening 61 of the mask 60 is etched and removed by the KOH aqueous solution 20. Simultaneously with the completion of the etching of the oxide film 70, the main surface 51 of the silicon wafer 50 appears and the etching of the silicon wafer 50 is started.

Although the clear mechanism is not known, by etching the silicon substrate at the same time as the etching of the oxide film, the main surface 51 on one side of the silicon wafer 50, which is the starting point of the silicon etching, becomes a hydrophilic surface, It is considered that uniform silicon etching is started by the formation of this hydrophilic surface.

Then, the silicon wafer 50 is etched from the one main surface 51 side, and finally, as shown in FIG.
As shown in (b), the recess 2 is formed. Actually, the bottom surface 2a of the recess 2, that is, the etching surface 2a has a high smoothness.

Thus, the diaphragm 3 is formed along with the formation of the concave portion 2, and further, the silicon oxide film 70 and the etching mask 60 are selectively removed from the silicon wafer 50 by etching or the like. The semiconductor pressure sensor S1 shown can be manufactured.

A specific example of improving the smoothness of the etching surface 2a is shown in FIG. In FIG. 5, the temperature of the KOH aqueous solution 20 is maintained at 110 ° C. by the temperature controller 30, and a silicon oxide film (thermal oxide film) 70 having a thickness of 0.12 μm is formed on the surface to be etched by thermal oxidation. It is a figure which shows the KOH density | concentration dependence of the surface roughness Rz of the etching surface 2a at the time of carrying out the etching process of the formed silicon wafer 50.

As shown in FIG. 5, the surface roughness Rz of the etching surface 2a depends on the KOH concentration of the KOH aqueous solution 20. In this example, the KOH concentration is 39 wt% or more and 48 wt% or more.
In the following range, the surface roughness Rz is less than 0.8 μm, and the smoothness of the etched surface 2a is at a level where there is no practical problem.

At this level, the plane orientation index of the main surface, which is relatively easy to secure the smoothness of the etched surface, is (10
In the silicon substrate of 0), it is a level that is realized when the recess and the diaphragm are formed, and there is no problem with the diaphragm characteristics.

Further, the same thickness as in FIG. 5 is 0.12 μm.
In etching the silicon wafer 50 on which the m silicon oxide film (thermal oxide film) 70 was formed, the effect of smoothing was examined when the etching conditions, that is, the KOH concentration of the KOH aqueous solution 20 and the liquid temperature were changed. The result is shown in FIG.

As shown in FIG. 6, an orthogonal coordinate system was set with the KOH concentration (% by weight) on the horizontal axis and the liquid temperature (° C.) on the vertical axis. In addition, the region R shown by hatching in FIG.
This is a range in which the surface roughness Rz of the etching surface 2a is less than 0.8 μm. Here, in the region R, the upper limit of the liquid temperature is the boiling point of the KOH aqueous solution 20. In other words, if the KOH concentration and the liquid temperature of the KOH aqueous solution 20 are within the range R, the surface roughness Rz of the etching surface 2a can be achieved at a level with no practical problem.

Therefore, in the etching method of the present embodiment, as shown in the region R in FIG.
In order to improve the smoothness of the etching surface, it is preferable to adjust the KOH concentration of the aqueous solution 20 in the range of 39% by weight or more and 48% by weight or less and the liquid temperature in the range of 90 ° C or more and 140 ° C or less.

As described above, according to the present embodiment, it is possible to provide the etching method which can improve the smoothness of the etching surface as compared with the conventional case by using the KOH aqueous solution as the etching solution.

Further, according to the present embodiment, the above-described etching method, that is, after forming the silicon oxide film 70 on the main surface 51 of the silicon wafer 50, the oxide film 70 is removed by etching using the KOH aqueous solution 20, and then the silicon oxide film 70 is removed. The silicon substrate 1 forming the semiconductor pressure sensor S1 is formed by the method of etching the wafer 50 from the main surface 51 side thereof.

In this silicon substrate 1, the main surface 51 which is the surface to be etched is the (110) surface, but the surface roughness Rz of the etching surface (the bottom surface 2a of the recess 2) is 0.8 μ.
It is less than m. That is, according to the silicon substrate (semiconductor substrate) 1 of the present embodiment, the (110) plane is KOH
When etching, it is possible to realize an etched surface having excellent smoothness, which was difficult to achieve in the past.

(Second Embodiment) FIG. 7 is a view showing a state in which an etching mask 60 for forming a diaphragm is formed on a main surface 51 on one side of a silicon wafer 50 according to a second embodiment of the present invention. , (A) is the main surface 51 on the one side.
A plan view seen from the view, (b) is a schematic sectional view. In the present embodiment, the silicon wafer 50 in the state shown in FIG.
The etching treatment is performed while being immersed in the OH aqueous solution 20.

In the first embodiment, the silicon wafer (silicon substrate) 50 having the silicon oxide film 70 formed under the etching mask 60 is used, but in the present embodiment,
As shown in FIG. 7, a similar etching method is performed using a silicon wafer (silicon substrate) 50 having a silicon oxide film 70 formed on an etching mask 60. Also in this case, the same effect as the first embodiment can be obtained.

Specifically, first, as shown in FIG. 7, the strain gauge 4 is formed on the other main surface 52 of the silicon wafer 50, and the above-mentioned strain gauge 4 is formed on the one main surface 51 of the silicon wafer 50. Etching mask 60 in the same manner as
Then, a silicon oxide film 70 is formed on the silicon wafer 50 in the mask 60 and the opening 61 by the CVD method or the like.

After the silicon oxide film 70 and the etching mask 60 are formed on the silicon wafer 50 in this manner, the etching apparatus 10 is used as in the first embodiment.
0 is used to etch the silicon wafer 50.

FIG. 8 is an explanatory diagram showing the progress of etching of the silicon wafer 50 in this embodiment. First, as shown in FIG. 8A, the silicon oxide film 70 is etched and removed by the KOH aqueous solution 20.
Simultaneously with the end of the etching of the oxide film 70, the mask 6
The main surface 51 of the silicon wafer 50 appears from the opening 61 of 0, and the etching of the silicon wafer 50 is started.

Also in this embodiment, by etching the silicon substrate at the same time as the etching of the oxide film, the main surface 51 on one side of the silicon wafer 50, which is the starting point of the silicon etching, becomes a hydrophilic surface. It is considered that uniform silicon etching is started by the formation of.

Then, the silicon wafer 50 is etched from the one main surface 51 side, and finally, as shown in FIG.
As shown in (b), a recess 2 having an etching surface (bottom surface) 2a having high smoothness is formed. As a result, the semiconductor pressure sensor S1 shown in FIG. 1 can be manufactured.

Thus, also in this embodiment, the first
Similar to the embodiment, a silicon substrate (semiconductor substrate) capable of improving the smoothness of an etching surface by using a KOH aqueous solution as an etching liquid when performing an etching process by immersing the semiconductor substrate in an etching liquid
1 and its etching method can be provided.

(Other Embodiments) In the above embodiment, after the oxide film 70 on the silicon wafer (silicon substrate) 50 is removed with a KOH etching solution, the silicon substrate is more positively etched. . For example,
The etching amount of silicon is 1 in terms of the depth of the recess 2.
It is made to be 00 μm or more.

In the silicon substrate used in the present invention, the plane orientation index of the main surface to be etched is (110).
It may be something other than.

The present invention is not limited to the pressure sensor, and it is needless to say that the present invention is effective when it is used for etching a silicon substrate with a KOH aqueous solution in an acceleration sensor, a gas sensor, a flow sensor or the like.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a semiconductor pressure sensor according to a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of an etching apparatus used in the etching method according to the first embodiment.

FIG. 3 is a configuration diagram showing a state in which an etching mask is formed on a silicon wafer as a silicon substrate used in the first embodiment.

FIG. 4 is an explanatory view showing a progress state of etching of the silicon wafer shown in FIG.

FIG. 5 is a diagram showing the KOH concentration dependence of the surface roughness Rz of the etched surface when the temperature of the KOH aqueous solution is kept at 110 ° C. and the silicon wafer is etched.

FIG. 6 is a diagram showing the results of examining the smoothing effect when the KOH concentration of the KOH aqueous solution and the liquid temperature are changed.

FIG. 7 is a configuration diagram showing a state in which an etching mask is formed on a silicon wafer as a silicon substrate used in the second embodiment of the present invention.

8 is an explanatory diagram showing a progress state of etching of the silicon wafer shown in FIG. 7. FIG.

[Explanation of symbols]

2a ... bottom surface (etching surface) of the concave portion, 20 ... potassium hydroxide aqueous solution, 50 ... silicon substrate, 51 ... main surface on one side of silicon substrate, 70 ... silicon oxide film.

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2F055 AA40 BB20 CC02 DD05 EE40                       FF11 GG15                 4M112 AA01 AA02 BA01 CA01 CA03                       CA05 CA08 DA04 DA06 DA10                       DA11 DA12 DA15 EA03 EA06                       EA07 FA20                 5F043 AA02 AA31 BB02 DD07 GG10

Claims (4)

[Claims] 1. A method for etching a semiconductor substrate in which an etching treatment is performed by immersing a semiconductor substrate in an etching solution, wherein a silicon substrate (50) is used as the semiconductor substrate, and an oxide film is formed on a main surface (51) of the silicon substrate. After forming (70), an aqueous potassium hydroxide solution (20) is used as the etching solution.
Is used to etch and remove the oxide film, and then the silicon substrate is etched from the main surface side. 2. K of the aqueous potassium hydroxide solution (20)
The OH concentration is in the range of 39% by weight to 48% by weight,
The oxide film (70) and the silicon substrate (50) are etched by adjusting the liquid temperature in the range of 90 ° C to 140 ° C.
The method for etching a semiconductor substrate according to. 3. The method for etching a semiconductor substrate according to claim 1, wherein the silicon substrate (50) has a main surface (51) having a plane orientation index of (110). 4. A semiconductor substrate etched by the etching method according to claim 1, wherein the etching surface (2a) has a surface roughness Rz of less than 0.8 μm. Characteristic semiconductor substrate.