JPH11233482A - Etching method of silicon wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain generation of micro-pyramids and make an etched surface more smooth, by adding Mg to alkaline solution, when a silicon wafer manufactured by a Czochralski method is etched by using etching solution composed of alkaline solution. SOLUTION: When Mg is added to etching solution, etching speed of the etching solution to which Mg is added is lower that that of etching solution to which Mg is not added. Progress of etching in the depth direction B approximately synchronizes with the progress of etching in the lateral direction A. By adding Mg, the etching speed in the depth direction B is much reduced, and reduction of the etching speed in the lateral direction A is very small as compared with the depth direction B. As a result, micro-pyramids formed by the progress of etching in the depth direction B are eliminated together with very small defects 13 by the progress of etching from the lateral direction A. Hence the micro-pyramids are not left on the etched surface 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for smoothing a processed surface of a structure obtained by three-dimensionally processing a silicon wafer, such as a diaphragm of a semiconductor pressure sensor and a sensing lever of a semiconductor acceleration sensor, or for processing a silicon wafer with high precision. The present invention relates to a method for etching a silicon wafer to be used.

[0002]

2. Description of the Related Art Conventionally, silicon wafers made of silicon single crystal, polycrystal silicon, etc.
It is regarded as an indispensable material for semiconductor integrated circuits typified by, for example, such as.

Further, in recent years, attention has been paid to the mechanical properties of silicon wafers, and silicon wafers have been applied to various devices as ideal elastic materials. Examples of this application include various semiconductor sensors (for example, a diaphragm of a semiconductor pressure sensor and a sensing lever of a semiconductor acceleration sensor) such as a valve, a nozzle, a printer head, a flow rate, a pressure, and an acceleration.

[0004] As a method of processing the silicon wafer,
Generally, an etching method has been frequently used. The above etching methods are roughly classified into dry etching and wet etching. Here, the wet etching is a processing method in which a silicon wafer is put into an etching bath filled with an etching solution, and an unnecessary portion of the silicon wafer is dissolved using a chemical reaction with the etching solution.

[0005] In this case, a commonly used etchant is an anisotropic etchant capable of performing anisotropic etching. Specifically, it is an alkaline solution such as an aqueous KOH solution, an aqueous NaOH solution, an EDP solution (a mixture of ethylenediamine and pyrocatechol), and hydrazine.

[0006]

However, the conventional method for etching a silicon wafer has the following problems. In other words, a silicon wafer manufactured by the CZ method has an intrinsic gettering action, which has an effective value of reducing a leak current and improving a lifetime. Such a silicon wafer may be subjected to a heat treatment in order to generate minute defects that getter heavy metals and the like.

However, when the silicon wafer 1 subjected to this heat treatment is etched with an alkaline solution, FIG.
As shown in (1), there is a problem that the micro pyramid 15 is generated on the etched surface 14 and the smoothness of the etched surface 14 is significantly impaired.

It is considered that the micro-pyramid 15 is generated by the following mechanism. In general, a silicon wafer 1 as described above is, as shown in FIG.
The defect-free layer 12 includes a high-density minute defect region 11 and a defect-free layer 12.

[0009] In the etching using an alkaline solution, silicon is hardly dissolved in the portion where the minute defect 13 exists, and the etching hardly proceeds. For this reason, when the silicon wafer 1 is immersed in an alkaline solution, as shown in FIG. 5, the minute defect 13 and a portion existing inside the minute defect 13 become a pyramid and remain on the etching surface 14. This remaining part is Micro Pyramid 1
5, which significantly impairs the smoothness of the etched surface 14.

Conventionally, there has been proposed a method of correcting the temperature and concentration of the etching solution to eliminate the occurrence of the micropyramid (see “Vacuum vol 29 (2) (1986) p.
85 "). However, in this method, a good etching surface is formed only when a specific etching solution is used and the temperature and concentration of the specific etching solution are adjusted so as to be within a specific value range, which is very troublesome. Was.

The present invention has been made in view of such a conventional problem, and proposes a silicon wafer etching method capable of suppressing the occurrence of micropyramids and making the etched surface smoother. .

[0012]

According to a first aspect of the present invention, a method for etching a silicon wafer manufactured by the Czochralski method (hereinafter abbreviated as CZ method) using an etching solution comprising an alkaline solution includes the steps of: M
g. The method for etching a silicon wafer is characterized by adding g.

The CZ method is a method of growing a silicon wafer by the Czochralski method, and the present invention is applied to a silicon wafer manufactured by this method. The above Mg is used in an etching solution of 10,000 to 10,000.
It is preferably contained at 00 ppb. 10,000ppb
If it is less than the above, the effect according to the present invention may not be obtained. On the other hand, if it is larger than 1,000,000 ppb, the etching rate becomes slow, and it may take an enormous amount of time for processing.

As the above-mentioned alkaline liquid, in addition to the liquid described below, an aqueous solution of NaOH, an EDP liquid (a mixture of ethylenediamine and pyrocatechol), hydrazine and the like can be used. In addition, as the alkaline liquid, Cu
Containing 100 to 100,000 ppb.

Next, the operation of the present invention will be described. The present invention is a method for etching a silicon wafer using an alkaline solution containing Mg. Incidentally, it is known that when etching is performed using an alkali solution to which Mg is added, the etching rate is reduced.

Here, an alkali solution prepared by appropriately adding Mg to a 32% KOH aqueous solution is prepared, and using the alkali solution at an etching temperature of 110.degree.
The surface was etched. With the etching rate at this time on the vertical axis and the amount of added Mg (Mg content) on the horizontal axis, the relationship between the two was measured and is shown in the diagram of FIG. From the figure, it was found that when the Mg content exceeded 10,000 ppb, the etching rate was reduced to 2/3 of the case where no Mg was contained.

As described in the prior art, Mg
When the silicon wafer is etched with an alkaline solution containing no, as shown in FIG. 5, the etching in the depth direction B progresses before the etching in the lateral direction A sufficiently progresses. For this reason, the micro defects 13 that hinder the etching serve as a mask, and the micro pyramids 15 are formed in these portions.

The above-mentioned minute defect is, for example, a lattice defect of a silicon crystal constituting a silicon wafer. In the case of a heat-treated silicon wafer, it is an oxygen atom precipitated by the heat treatment. Also, alcohol or the like adsorbed on the surface of the silicon wafer.

In the present invention, Mg is added to the etching solution, so that the etching rate of the etching solution used in the present invention is lower than that of the conventional product. Thus, as shown in FIG. 1, in the present invention, the progress of the etching in the depth direction B is substantially synchronized with the progress of the etching in the lateral direction A. This is because the addition of Mg greatly reduces the etching rate in the depth direction B, but the reduction in the etching rate in the lateral direction A is much smaller than in the depth direction B.

For this reason, as shown in FIG.
The micro pyramid formed by the progress of the etching is removed together with the minute defects by the etching from the lateral direction A that progresses. For this reason, the micro pyramid is less likely to remain on the etched surface.

Further, as described above, the present invention can be realized only by adding Mg to an alkaline solution serving as an etching solution, and therefore can be implemented very easily. Also, there is no need to adjust the etching conditions, etc.
The conventional equipment for the etching process and the control system of the equipment can be used as they are, and an increase in the cost for etching can be prevented.

As described above, according to the present invention, it is possible to obtain a silicon wafer etching method capable of suppressing the occurrence of micropyramids and making the etched surface smoother.

Next, it is preferable that the alkaline solution is one of an aqueous solution of potassium hydroxide (KOH) and an aqueous solution of tetramethylammonium hydroxide (TMAH). Thereby, anisotropic etching can be performed, and three-dimensional processing can be realized.

Next, as in the third aspect of the present invention, the silicon wafer has a high-density minute defect region inside, a defect-free layer outside the minute defect region, and It is preferable that the liquid etches the outside of the high-density micro-defect region and stops the etching by the etching liquid in the high-density micro-defect region.

As a result, the gettering action of the heavy metal can be given to the workpiece, and the warpage (deformation) of the workpiece can be reduced. The high-density minute defect area is defined as
For example, it is a region in which minute defects generated due to precipitation of oxygen in a silicon wafer exist at high density. The defect-free layer is a layer in which micro defects based on oxygen precipitation as described above hardly exist.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment An etching method according to an embodiment of the present invention will be described.
This will be described with reference to FIGS. In this example, when etching a silicon wafer manufactured by the CZ method using an etching solution composed of an alkaline solution, Mg is added to the alkaline solution.

Next, the etching method according to the present embodiment and the etched surface formed by the etching method will be described in comparison with a conventional example. The silicon wafer 1 processed by the etching method according to the present embodiment is, as shown in FIG.
A high-density minute defect region 11 is provided inside, and the outside thereof is covered with a defect-free layer 12. Reference numeral 120 denotes a silicon wafer surface, and etching proceeds from the surface 120 by immersing the silicon wafer 1 in an etchant.

The silicon wafer 1 is manufactured by a CZ method and has an intrinsic gettering function. Heat treatment has been applied.

Here, the high-density micro-defect region 11 is a region where micro-defects generated due to the precipitation of oxygen in the silicon wafer 1 exist at a high density. The defect-free layer 12 is a layer in which micro defects based on oxygen precipitation as described above hardly exist. In addition, high-density minute defect area 1
1, the density of the micro defects 13 is 10 ² to 10 ¹⁰ cm ^−3.
Degree, the density of minute defects in the defect-free layer 12 is 10 ² c
It is about less than m ^-3 . In FIG. 2, the description of the individual minute defects 13 is omitted for the high-density minute defect region 11.

The silicon wafer 1 having a size of 2 m
It was cut to a size of mx 2 mm x 0.3 mm (thickness), and was etched using a 32 wt% KOH aqueous solution containing 18.5 ppm (= 18,500 ppb) of Mg and 60 ppb of Cu.

The etching was performed by heating the etchant to 110 ° C., charging the silicon wafer 1 into the heated etchant, performing the process for 20 minutes, and then washing with water. The etching temperature at this time is 110 ° C.
Thus, the entire surface of the silicon wafer 1 was etched. This etching is performed on the silicon wafer surface 1
The process was terminated at the central portion of the silicon wafer within 20 to 300 μm.

In the manner described above, the three silicon wafers 1 are etched, and the number of micropyramids formed on each of the etched surfaces 14 is counted and measured while observing with an optical microscope. The results are shown in the diagram of FIG.

Further, in the same manner as described above, the amount of Mg added to the etching liquid for three silicon wafers 1 was 37.5.
Etching was performed with ppm. Further, for comparison, five silicon wafers 1 were etched using an etching solution to which Mg was not added. These results are also shown in the diagram of FIG.

According to the figure, compared with the case where Mg was not added, the amount of generated micropyramids was reduced to less than half by adding 18.5 ppm of Mg to 37.5.
It was confirmed that the amount of micropyramids generated was reduced to about 1/10 by adding ppm.

The operation and effect according to this embodiment will be described.
This example is a method for etching a silicon wafer 1 using an alkaline solution containing Mg.

It is known that when etching is performed using an alkali solution containing Mg, the etching rate is reduced. As described in the prior art, when a silicon wafer is etched with an alkaline solution containing no Mg, as shown in FIG.
Etching in the depth direction B progresses before etching to the surface proceeds sufficiently. For this reason, the minute defect 13 that hinders etching serves as a mask, and a portion inside the minute defect 13 remains without being etched, and a micropyramid 15 is formed in this portion.

In this embodiment, Mg is added to the etching solution, and therefore, the etching rate of the etching solution used in this embodiment is lower than that in the case where no Mg is added. Thereby, as shown in FIG. 1, in this example, the progress of the etching in the depth direction B is
Almost synchronously with the progress of the etching for. This is M
This is because the addition of g greatly reduces the etching rate in the depth direction B, and the reduction in the etching rate in the lateral direction A is much smaller than in the depth direction B.

For this reason, as shown in FIG.
The micro pyramid formed by the progress of the etching is removed together with the minute defect 13 by the etching from the lateral direction A that progresses. For this reason, the micro pyramid is less likely to remain on the etched surface 14.

As described above, according to the present embodiment, it is possible to provide a silicon wafer etching method capable of suppressing the occurrence of micropyramids and making the etched surface smoother.

As described above, this embodiment can be realized only by adding Mg to an alkaline solution serving as an etching solution, and therefore can be implemented very easily. Also, there is no need to adjust the etching conditions, etc.
The conventional equipment for the etching process and the control system of the equipment can be used as they are, and an increase in the cost for etching can be prevented.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an etching method according to an embodiment.

FIG. 2 is an explanatory diagram of a silicon wafer according to the embodiment.

FIG. 3 is a diagram showing a density of micropyramids in a silicon wafer etched by an etching solution to which Mg is added and an etching solution to which Mg is not added according to the embodiment;

FIG. 4 is a diagram showing a relationship between a content of Mg in an etching solution and an etching rate according to the embodiment.

FIG. 5 is an explanatory view showing a mechanism of generating a micropyramid in an etching method according to a conventional example.

[Explanation of symbols]

 1. . . 10. silicon wafer, . . 11. high-density micro defect area; . . 12. defect-free layer; . . Small defects,

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshiji Abe 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside DENSO CORPORATION (72) Inventor Kazuyuki Inoue 41st side street, Nagakute-cho, Nagakute-cho, Aichi-gun, Aichi Prefecture Ground 1 Inside Toyota Central Research Laboratory

Claims (3)

[Claims] 1. A method of etching a silicon wafer produced by the Czochralski method (hereinafter abbreviated as CZ method) using an etching solution composed of an alkaline solution, wherein Mg is added to the alkaline solution. Silicon wafer etching method. 2. The method for etching a silicon wafer according to claim 1, wherein the alkaline solution is one of an aqueous solution of potassium hydroxide (KOH) and an aqueous solution of tetramethylammonium hydroxide (TMAH). 3. The silicon wafer according to claim 1, wherein the silicon wafer has a high-density minute defect region inside, a defect-free layer outside the minute defect region, and the etching solution is high. A method of etching a silicon wafer, characterized by etching outside a high-density minute defect region and stopping etching by the etching solution in the high-density minute defect region.