JP2890220B2 - Etching method and etching solution - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a silicon wafer etching solution.

[0002]

2. Description of the Related Art Conventionally, HF / HNO ₃ / CH ₃ COOH /
An acidic etching solution consisting of H ₂ O = 1: 15: 3: 1,
An alkaline etching solution composed of NH ₄ OH / H ₂ O ₂ / H ₂ O = 1: 1: 5 is known.

Of the above-mentioned etching solutions, an acidic etching solution can be adjusted to some extent by dilution, but generally has a high etching rate (about 1 μm / min), and is delicate in etching required in a highly integrated circuit. Control is difficult. In addition, since there is selectivity of the crystal plane in the progress of etching, surface roughness is likely to occur. On the other hand, the alkaline etchant has a feature that it does not cause surface roughness, but the conventional etchant has an extremely low etching rate (less than 10 angstroms / min) as compared with the acidic etchant, so that it takes much time for etching. There was a problem. For this reason, an etchant having an intermediate etch rate (several tens of angstroms / min) between the above two types of etchants and having excellent etching characteristics has been demanded.

As one of the attempts to solve such a problem, efforts have been made to increase the etching rate of an alkaline etching solution. Since the only component having an etching action in the alkaline etching solution is NH ₄ OH, it is necessary to increase the NH ₄ OH concentration, or
Attempts have been made to replace H ₄ OH with other alkalis.
However, although an increase in the NH ₄ OH concentration has the effect of improving the etching rate almost proportionally in a low concentration region, the effect is saturated when the concentration exceeds this region, and to achieve the expected etching speed. I can't. On the other hand, N
Alkali for etching silicon wafers instead of H ₄ OH is still under investigation.

[0005]

[Knowledge to Solve the Problem] The present inventors have studied means for overcoming the saturation of the effect of NH ₄ OH in order to solve the above problem. And, surprisingly, it has been conventionally thought that the same amount (weight% concentration) of H ₂ as NH ₄ OH is required.
The O ₂ concentration can be limited without impairing the etching effect. Due to the limitation of the H ₂ O ₂ concentration, (N
H ₄ OH) The etching rate does not saturate to a relatively high concentration, and several tens of Angstroms / mi, which has been difficult
It has been found that stable etching of about n is possible.

[0006]

That is, the present invention provides the following etching method and etching solution. (1) A method for etching a silicon wafer using an alkaline etching solution containing NH ₄ OH, H ₂ O ₂ and H ₂ O, wherein the H ₂ O ₂ concentration is 0.6% by weight or less, and the H ₂ O ₂ / NH ₄ OH concentration ratio is 1/10 or less and NH ₄ OH is used in an excess amount that is equal to or higher than the concentration at which the etching rate is saturated when H ₂ O ₂ is set to a constant amount, so that etching is performed at a constant rate. A method for etching a silicon wafer. (2) The etching method according to the above item 1, wherein the saturation etching rate is controlled by adjusting the concentration of H ₂ O ₂ . (3) H ₂ O ₂ concentration of 0.6% by weight or less, H ₂ O ₂ / N
NH ₄ OH, H ₂ O ₂ and H having an H ₄ OH concentration ratio of 1/10 or less and an NH ₄ OH concentration of 10% by weight or more
Silicon wafer etching solution containing _{2 O.}

In the present invention, it is necessary to limit the H ₂ O ₂ concentration both in relation to the total amount of the liquid and in relation to the NH ₄ OH amount.

In relation to the total amount of the liquid, the H ₂ O ₂ concentration is set to 0.6% by weight or less. Above this range, the etching with NH ₄ OH does not proceed quickly because the absolute amount of H ₂ O _{2 on} the wafer surface is large.

In relation to the weight of NH ₄ OH, H ₂
The O ₂ concentration is set to 1/10 or less. If the concentration ratio exceeds 1/10, the etching rate will be 1 even if the NH ₄ OH concentration is increased.
The saturation occurs at about 0 Å / min.

[0010] The mechanism by which the attack of NH ₄ OH on the silicon wafer is inhibited by H ₂ O ₂ is not exactly clear, but H ₂ O ₂ molecules adhere to the silicon wafer surface, and this becomes NH ₄ OH. Is considered to hinder the action on the silicon wafer. By limiting the H ₂ O ₂ concentration according to the present invention, this disturbing effect can be substantially reduced, and the etching saturation rate (the highest value of the etching rate when the NH ₄ OH concentration is increased). Can be increased. Further, the saturation rate of the etching depends on the H ₂ O ₂ concentration. Therefore, H ₂ O ₂
By controlling the concentration, the etching rate can be controlled. In addition, since the H ₂ O ₂ concentration does not greatly change during the etching, an excessive amount of NH ₄ O
If H is used, etching can be stably performed at a constant speed (saturation speed).

Specifically, the concentrations of NH ₄ OH and H ₂ O ₂ can be determined in consideration of the etching speed and stability according to the purpose of the etching. According to the present invention, as described above, the etching rate is controlled by the H ₂ O ₂ concentration, and the NH ₄ OH concentration is used excessively within a range not exceeding the above limit . As shown in FIG.
_{4 The} OH concentration is saturated at 8% by weight or more.
Considering the consumption of NH ₄ OH during the process, 10% by weight
An etching solution having the above concentration is effective.

The NH ₄ OH and H ₂ O used in the present invention
_{As 2} , a material having a purity that has been conventionally used for an etching solution can be used. The remaining components of the etching solution are mainly pure water, but may contain other components as long as the effects of the alkaline etching solution and the effects of the present invention are not impaired. The production of the liquid can also be carried out according to custom.

[0013]

DETAILED DISCLOSURE OF THE INVENTION

Example 1 An alkaline etchant having a H ₂ O ₂ content of 0.29% by weight and an NH ₄ OH content of 20% by weight was prepared using purified NH ₄ OH, H ₂ O ₂ and H ₂ O. .
Using this etchant, the silicon wafer was etched at a liquid temperature of 80 ° C. for 30 minutes according to a conventional method, and the etching depth was 1050 Å (average etching rate: 35 Å / m).
in).

[0014]

Example 2 A silicon wafer was etched at a liquid temperature of 80 ° C. for 30 minutes under the same conditions as in Example 1 except that the NH ₄ OH content was changed to 15% by weight and 25% by weight. The etching depth was 1050 angstroms, which is the same as that in Example 1, and it can be seen that the etching rate does not depend on the NH ₄ OH concentration.

[0015]

Example 3 H ₂ O ₂ content of 0.58 wt%, NH ₄ O
The etching of the silicon wafer was performed at a liquid temperature of 80 under the same conditions as in Example 1 except that the H content was changed to 8, 11, and 17% by weight.
C. for 30 minutes. Etching depth is 60
0 Å (average etching rate: 20 Å / min) and the etching rate is NH ₄
It can be seen that it depends on the H ₂ O ₂ concentration without depending on the OH concentration.

[0016]

Comparative Example 1 A silicon wafer was etched at a liquid temperature of 80 ° C. for 30 minutes under the same conditions as in Examples 1 and 3, except that the NH ₄ OH content was changed to 1.7% by weight. The etching depths are 630 and 450 Å, respectively.
It can be seen that the etching rate does not reach saturation but changes depending on the NH ₄ OH concentration.

[0017]

Comparative Example 2 The content of H ₂ O ₂ was 2.9% by weight and the content of NH ₄ OH
The etching of the silicon wafer was performed at a liquid temperature of 80 ° C. under the same conditions as in Example 1 except that the content was set to 8, 11, and 17% by weight.
For 30 minutes. Etching depth is 300
Angstroms (average etching rate: 10 angstroms / min), and the etching rate is not sufficient.

In order to more clearly show the effects of the present invention, NH ₄ OH in the cleaning solution was used under various conditions in addition to the above examples.
The relationship between the concentration and the etching rate was examined. The results are shown in FIG. 1 together with the results of the above examples.

[0019]

According to the present invention, the effect of an alkaline etching solution containing NH ₄ OH as an etching component can be greatly improved. In addition, stable etching can be performed by performing etching at a saturation rate. Further, by controlling the above-mentioned saturation speed by the H ₂ O ₂ concentration, etching can be performed at a desired speed. Since the present etching solution has an effect of removing impurities and particles, it is not necessary to perform finish cleaning.

[0020]

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between an NH ₄ OH concentration in a cleaning liquid and an etching rate.

Continuing from the front page (72) Inventor Jiro Tatsuta 1-297 Kitabukurocho, Omiya-shi, Saitama Prefecture Mitsui Materials Corporation Central Research Laboratory (72) Inventor Yasushi Shimanuki 1-297 Kitabukurocho, Omiya-shi, Saitama Mitsui Materials Co., Ltd. (56) References JP-A-60-233824 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 21/308 H01L 21/306-21/3063 C23F 1 / 00-3/06

Claims (3)

(57) [Claims] 1. A NH _{4 OH,} a method of etching an alkaline etchant silicon wafer utilized which contains H 2 _{O 2} and _{H 2 O,} H 2 _{O 2} concentration 0.6 wt% or less, _{H 2} By using an O ₂ / NH ₄ OH concentration ratio of 1/10 or less and using an excess amount of NH ₄ OH that is equal to or higher than the concentration at which the etching rate saturates when H ₂ O ₂ is a constant amount, the etching is kept constant. A silicon wafer etching method characterized by proceeding at a speed of: _2. The etching method according to claim 1, wherein the saturation etching rate is controlled by adjusting the H ₂ O ₂ concentration. Wherein the concentration of H ₂ O ₂ 0.6 wt% or less, _{H 2}
O ₂ / NH ₄ OH concentration ratio is 1/10 or less, and NH ₄
NH ₄ OH, H ₂ O ₂ having an OH concentration of 10% by weight or more
And a silicon wafer etching solution containing H ₂ O.