JPH08104988A - Etching solution - Google Patents

Abstract

PURPOSE: To obtain a 45 deg. mirror having superior surface roughness by using an etching soln. having a specified compsn. contg. potassium hydroxide at a prescribed concn. when a single crystalline Si wafer having (100) face orientation is subjected to anisotropic etching to produce a 45 deg. mirror. CONSTITUTION: Potassium hydroxide is added to isopropanol and water by 1.5-5wt.% of the total amt. to obtain the objective safe etching soln. easy to handle and used for forming a 45 deg. mirror excellent in surface roughness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching solution used for chemical etching when producing a 45 ° mirror by a Si micromachining technique.

[0002]

2. Description of the Related Art Conventionally, the following three methods are known as a method of manufacturing a 45 ° mirror using a Si substrate.

First, the first method will be described with reference to FIG. As shown in FIG. 4A, a single crystal S having a plane orientation (100) and an orientation flat <110>.
Prepare i-wafer 1. Subsequently, as shown in FIG. 4B, thermal oxide films 2 are formed on both surfaces of the Si wafer 1. Next, as shown in FIG. 4C, one thermal oxide film 2
A photoresist 3 is formed on the above by coating or the like. The photoresist 3 is omitted from the etching portions to be performed later. Then, as shown by 11 (off-alignment 0 °) in FIG.
The alignment is performed vertically or horizontally with respect to the orientation flat 13 of 0>.
<11 as shown in 2 (45 ° off-alignment)
Alignment is performed by inclining the orientation flat 13 of 0> by 45 °. Next, as shown in FIG. 4D, a mask pattern 4 for Si etching is opened in the thermal oxide film 2 by RIE (reactive ion etching) using the photoresist 3 as a mask. Next, FIG. 4 (e)
The photoresist 3 is removed as shown in FIG. Subsequently, the Si wafer 1 is placed in the chamber 20 of the etching apparatus shown in FIG. 6 and is etched using EDP (ethylenediamine pyrocatechol) as an etching solution.

Incidentally, a typical 45 using the first method.
° The mirror is manufactured by the publicly known document "OPTICAL PLANES AND REF".
LECTORS, ANISOTROPICALLY ETCHED IN SILICON "(The 7
th International Conference on Solid-State Sensor
and Actuators).

The second method will be described below. Figure 4 above
As shown in (a), a single crystal Si wafer 1 having a plane orientation (100) and an orientation flat <110> is prepared. Next, as shown in FIG.
Thermal oxide films 2 are formed on both sides of the i-wafer 1. Next, FIG.
As shown in (c), the photoresist 3 is formed by coating or the like. The photoresist 3 is omitted from the etching portions to be performed later. continue,
Normally, as shown in FIG. 5 at 11 (off-alignment 0 °), FIG. 5 shows at 12 (off-alignment 45 °) where alignment is performed vertically or horizontally with respect to the <110> orientation flat 13. As described above, the alignment is performed by inclining the orientation flat 13 of <110> by 45 °. Next, FIG.
As shown in (d), RIE (reactive ion etching) is performed on the thermal oxide film 2 using the photoresist 3 as a mask.
Then, the mask pattern 4 for Si etching is opened. Next, as shown in FIG. 4E, the photoresist 3 is removed. Then, the Si wafer 1 is treated with KOH (potassium hydroxide): IPA (isopropyl alcohol): H.
₂ O (water) = 20-21: 13-14: 63-64 wt
Etching is performed by using a solution of 10% as an etching solution.

A representative 45 using the second method is used.
° The mirror is manufactured by the publicly known document "OPTICAL PLANES AND REF".
LECTORS, ANISOTROPICALLY ETCHED IN SILICON "(The 7
th International Conference on Solid-State Sensor
and Actuators).

The third method will be described below. FIG. 7 (a)
, The crystal plane orientation 32 is (100), and
110> orientation flat 31 single crystal S
Slice the i ingot 30. Normally, this slice is performed by inclining by 90 ° with respect to the orientation flat 31 of <110> as shown by the broken line 33.
As shown by the broken line 34, the tilt is performed at an angle of 9.7 ° with respect to the 90 ° plane. At this time, the plane orientation of the sliced single crystal Si wafer 35 is, as shown in FIG. 7B, a plane orientation tilted by 9.7 ° with the orientation flat 31 of <110> with respect to (100) as an axis. Become. Next, as shown in FIG. 4C, the thermal oxide film 3 is formed on both surfaces of the single crystal Si wafer 35.
6 is formed. Next, as shown in FIG. 7D, a photoresist 37 is formed by coating or the like. The photoresist 37 is omitted from the etching locations to be performed later. Then, as shown by 11 in FIG. 5, alignment is performed horizontally or vertically with respect to the orientation flat <110>. Next, as shown in FIG. 7E, the thermal oxidation film 36 is subjected to RIE (reactive ion etching) by Si using the photoresist 37 as a mask.
The mask pattern 38 for etching is opened. Next, as shown in FIG. 7F, the photoresist 37 is removed. Then, KOH (potassium hydroxide): H ₂ O (water)
= Si is etched with a liquid of 4: 6 weight ratio. As a result, a surface 39 of 64.4 ° is formed on the surface opposite to the orientation flat 31 and a 45 ° surface 40 is obtained on the surface of the orientation flat 31 side.

A representative 45 using the third method is used.
° The mirror is manufactured by the publicly known document "FABLICATION OF EXTREME
LY SMOOTH MIRROR SURFACES IN SILICON FOR APPLICATI
ON IN AN INTEGRATED SPECTROMETER "(The 7th Intern
ational Conference on Solid-State Sensor and Actua
tors).

[0009]

However, in the case of the above-mentioned first, second and third conventional methods, there are the following problems. First, in the first method, there is a problem in safety of EDP (ethylenediaminepyrocatechol) which is an etching solution, and in order to prevent deterioration of the solution due to mixing of oxygen during etching, an inert gas purge as shown in FIG. 6 is performed. Special etching equipment that can be used is required.

Regarding the second method, there is no particular problem in safety and etching equipment, but there is a problem that the surface roughness R _{MAX of} the finished 45 ° surface is as bad as 15 μm.

The third method is excellent in surface roughness, but requires a special wafer inclined by 9.7 ° with respect to the (100) plane, and it is generally difficult to obtain such a wafer. Even if it can be obtained, the wafer is not a perfect circle, and therefore there is a drawback that it is inconvenient to handle in a later step, for example, when processing with an etching apparatus.

The present invention has been made to solve the above problems of the prior art, and provides an etching solution which is safe and easy to handle and which can provide a 45 ° mirror having excellent surface roughness. The purpose is to provide.

[0013]

The etching solution of the present invention is an etching solution used for producing a 45 ° mirror by anisotropically etching a single crystal Si wafer having a (100) plane orientation. Having potassium, isopropyl alcohol and water, the potassium hydroxide is 1.5 to 5 wt.
%, Which achieves the above object.

[0014]

In the present invention, KOH (potassium hydroxide) and I which are the same components as the etching solution used in the second method are used.
An etching solution composed of PA (isopropyl alcohol) and H ₂ O (water) is used.

The etching solution used in the second method is a condition that the etching rate in the vertical direction is relatively higher than the etching rate in the horizontal direction in order to obtain a surface as smooth as possible, that is, a condition that the vertical / horizontal selection ratio is high. The condition that the concentration of KOH (potassium hydroxide) with respect to the total amount of the etching solution is KOH = 20 wt% is used. On the other hand, the etching solution of the present invention is said to attack the 45 ° plane of single crystal Si having the (100) plane orientation.
The concentration of H (potassium hydroxide) is lowered to 30% or less of the etching solution used in the second method, and KOH (potassium hydroxide): IPA (isopropyl alcohol): H ₂ O
The ratio of (water) is such that KOH is 1.5 to 5 wt%.

When the single-crystal Si is etched by the etching solution having such a constitution, the vertical etching rate shown by a white circle in FIG. 2 is greatly reduced, that is, it takes an extra time to etch a certain amount. become. On the other hand, it is considered that the attack on the 45 ° surface by KOH is reduced, so that the surface roughness is greatly improved.

The etching solution may be placed in an open type beaker or an etching tank for etching. However, for the reasons described below, a method of etching using an etching apparatus in which the evaporation of the solution is prevented is particularly preferable. Is effective. Further, the etching apparatus is preferably a semi-sealed type or a sealed type equipped with a safety valve in order to prevent evaporation of the liquid and explosion of the apparatus due to increase in internal pressure.

[0018]

EXAMPLE An example of producing a 45 ° mirror surface using the etching solution according to the present invention will be described below with reference to the drawings.

FIG. 1 is a front view showing an implementation state of this embodiment. In this embodiment, a semi-sealed type etching device is used. This etching apparatus is provided with an etching tank 51 made of glass, Teflon, or stainless steel.
And an etching solution 52 in the etching tank 51.
Can be inserted. The etching solution 52 is heated by a hot plate (not shown) provided below the etching bath 51. The temperature of the etching solution 52 is monitored by a thermometer 53 provided in the etching tank 51, and is controlled to a constant temperature by heating and stopping the hot plate. Further, the etching liquid 52 is stirred by a magnetic stirrer 56 made of Teflon so that the temperature of the etching liquid 52 is constant in each part of the etching tank 51 and the etching liquid 52 is uniform. In order to accurately control the temperature of the etching liquid 52,
It is preferable that the hot plate perform feedback control based on the temperature signal from the thermometer 53. As the heating means for the etching liquid 52, the hot plate is used in the above, but a constant temperature bath or a throw-in heater may be used.

On the etching bath 51, a watch glass 59 is placed as a lid. The watch glass 59 has an etching liquid 52 which is formed by evaporation of the etching liquid 52 due to heating.
It is provided in order to prevent the etching rate from decreasing due to the composition variation of Further, even if the internal pressure rises when the etching liquid 52 is heated, the rise of the pressure can be avoided, and the watch glass 59 is placed in order to prevent an accidental explosion.

Inside the etching tank 51, there are provided a Teflon sludge 57 and a carrier 54 similar to the one which is not corroded by the etching solution 52. The carrier 54 holds a single crystal Si wafer 55 that is an object to be etched, and is set on the drainboard 57.

In this embodiment, etching was carried out in the following manner by using the etching apparatus of this structure. As the single-crystal Si wafer 55 to be etched, the same structure as the samples shown in the first and second methods, which was off-aligned by 45 ° with respect to the orientation flat <110> direction, was used. As the etching solution 52, KOH (potassium hydroxide), IPA (isopropyl alcohol), and H ₂ O (water), which were mixed in the following composition, were used.

KOH (xwt%) + IPA (250 ml) + H ₂ O (1000 ml) However, x = 1.5 to 5 In addition, the temperature of the etching solution 52 is heated to 60 ° C., and the etching solution 52 is stirred. The rotation of the magnetic stirrer 56 was set to 100 to 900 rpm. Furthermore, adjustment was made so that the etching amount in the depth direction was the same.

FIG. 2 shows the KOH concentration of 1.5 to 5 wt%.
FIG. 5 is a diagram showing a vertical etching rate (white circles), a horizontal etching rate (black circles) and surface roughness (squares) of the obtained 45 ° mirror surface when etching is performed in accordance with the above. The horizontal axis is the KOH concentration (wt%), the ordinate left etching rate (μm / h), the right side surface roughness R _{MA X}
(Μm). Note that FIG. 2 also shows the case where the concentration range of KOH exceeds 5 wt%.

As can be understood from this figure, the lateral etching rate and the surface roughness (R _MAX ) decrease almost linearly as the KOH concentration is lowered, but the surface roughness is more than the lowering of the lateral etching rate. Is reduced.

Table 1 shows that KOH = 5 wt% according to this embodiment.
The following shows the surface roughness of a 45 ° mirror surface when etching is performed in the vertical direction with a thickness of 200 μm using the above etching solution. Table 1 also shows the case of the conventional example by the above-mentioned first, second and third methods.

[0027]

[Table 1]

As can be seen from this table, by using the etching solution having the composition of the present invention, KO, which is the third method of the prior art as compared with the conventional etching solution, is used.
A smooth surface comparable to that of the H (40 wt%) liquid was obtained.

In the etching liquid of the present invention, KO
H (potassium hydroxide) concentration of 1.5 wt% to 5 wt%
The reason is limited to the following reasons. KOH concentration is 1.
When it is lower than 5 wt%, the single crystal Si is hardly etched, so the lower limit was made 1.5 wt%. On the other hand, the upper limit is 5
The reason why it is set to wt% is that if it exceeds that, a very good mirror surface cannot be obtained.

Since the mirror obtained by the etching solution of the present invention has a very good mirror surface, the known document "FABL
ICATION OF EXTREMELY SMOOTH MIRROR SURFACES IN SIL
ICONFOR APPLICATION IN AN INTEGRATED SPECTROMETE
R ”(The 7th International Conference on Solid-Stat
e Sensors and Actuators) can be applied to the reflection mirrors of optical fibers and surface emitting lasers.

In the above embodiment, the etching solution is heated to about 60 °, water and IPA (isopropyl alcohol) evaporate, the composition of the solution changes during etching, and the etching rate and the like decrease. In order to prevent it or to completely seal it, there is a danger of explosion due to an increase in internal pressure. Therefore, the semi-sealed etching apparatus shown in FIG. 1 is used, but the present invention is not limited to the etching apparatus shown in FIG. ,
Others can be used. For example, as shown in FIG. 3, a safety valve 60 is provided so as to automatically prevent the pressure rise when the internal pressure rises to prevent the explosion and prevent the etching liquid 52.
It is possible to use an etching device that prevents evaporation of In addition,
Since the safety valve 60 is provided, it is possible to use the sealing lid 61 in place of the watch glass 59 used in FIG. FIG.
2, the same parts as those in FIG. 1 are denoted by the same reference numerals.

[0032]

As described above in detail, when the etching solution of the present invention is used, it is safe and easy to handle,
Moreover, a 45 ° mirror surface having excellent surface roughness can be obtained by using a commercially available Si wafer.

[Brief description of drawings]

FIG. 1 is a front view showing a semi-hermetic etching apparatus suitable for use in the present invention.

FIG. 2 is a graph showing the relationship between KOH concentration, etching rate, and surface roughness when using the etching solution of the present invention.

FIG. 3 is a front view showing another etching apparatus suitable for use in the present invention, which is provided with a safety valve.

FIG. 4 is a process sectional view in the case of using first and second methods which are conventional techniques.

FIG. 5 is a diagram for explaining the alignment direction with respect to the <110> orientation flat in the case of using the respective etching solutions of the first, second and third methods of the related art.

FIG. 6 is a front view showing an etching apparatus used in a first method which is a conventional technique.

FIG. 7 is a process cross-sectional view of a process when a third method which is a conventional technique is used.

[Explanation of symbols]

 1 Single-crystal Si wafer 5 45 ° surface 11 Off-alignment 0 ° 12 Off-linement 45 ° 51 Etching bath 52 Etching solution 54 Carrier 55 Single-crystal Si wafer 56 Magnetic stirrer 57 Sunoko 59 Watch glass 60 Safety valve 61 Sealing lid

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Hirata 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture Sharp Co., Ltd. Incorporated (72) Inventor Shigeo Terashima 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka

Claims (1)

[Claims] 1. An etching solution used for anisotropically etching a single crystal Si wafer having a (100) plane orientation to form a 45 ° mirror, which contains potassium hydroxide, isopropyl alcohol and water. An etching solution containing 1.5 to 5 wt% of potassium hydroxide.