JP3046807B1 - Recycling method of silicon wafer with metal film - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To minimize a decrease in substrate thickness during reproduction,
Provided is a method for regenerating a silicon wafer with a metal film, which is capable of remarkably regenerating a large number of times as compared with the conventional method. A silicon test wafer to be regenerated has an oxide film of 3000 Å or more formed under the metal film, and at the time of regeneration, the entire metal film is chemically etched with an alkaline solution or an acidic solution. Remove the minimum oxide film part,
Metallic contaminants on the oxide film surface are removed by chemical etching with an acidic solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for regenerating a silicon test wafer having a metal film formed on the outermost layer after it has been used for a process check in order to confirm whether a manufacturing apparatus / process is in a normal state. About the method.

[0002]

2. Description of the Related Art Conventionally, a prime wafer used in the manufacture of semiconductors has been directly used as a test wafer. However, since the price is high, the quality of the test wafer is now equivalent to that of a prime wafer. Different inexpensive monitor wafers or dummy wafers are mainly used.

[0003] This test wafer has a film thickness value, a resistance value,
Reflectance is measured as an evaluation item, and the soundness of the process is investigated. On the surface layer of the test wafer used for this process check, a diffusion layer made of a metal such as Al, Ti, W, Cu or the like, a nitride thereof, a silicide, an ion implantation layer, various films, etc. are formed. If the film on the surface including the edge is peeled off, it can be reused.

[0004] The reusable state means that the thickness of the substrate is maintained as a standard substrate and there is no contamination on the surface. For example, the standard substrate thickness of an 8-inch test wafer is 725 ± 25 μm, and the minimum usable thickness is generally said to be 600 to 650 μm. Therefore, the smaller the thickness is reduced after the completion of the recycling operation for reuse, the more the substrate can be recycled and reused.

[0005] The recycling of the silicon wafer with the metal film for testing is described in Japanese Patent Application Laid-Open Nos. 7-122532 and 9-1.
As described in Japanese Patent No. 7833, Japanese Patent Application Laid-Open No. 9-171981, etc., rough polishing is performed by holding a wafer inside a metal surface plate that rotates oppositely while supplying loose abrasive particles. After removing the film, and then lapping method of chemical etching and polishing, or after removing the surface layer using an acid or alkali solution,
A method by chemical etching for performing polishing is known.

[0006]

However, in the case of the former lapping method, the thickness of the substrate is generally reduced by about 50 μm at the completion of the regenerating process, so that the regenerating can be performed only about twice. In the case of the latter chemical etching, the thickness of the substrate is reduced by about 20 μm. Further, depending on the type of the solution, there is a problem that the substrate is not uniformly etched and the surface becomes uneven.

The problem to be solved by the present invention is to minimize the reduction in substrate thickness when removing a metal film for regenerating a test wafer in a metal film formation process, thereby reducing the number of reuses. The aim is to find a way to make it possible to achieve a dramatic increase.

[0008]

Means for Solving the Problems] The present invention, to test wafers lower layer oxide film is formed of gold Shokumaku, removing the metal film by a first chemical etching alkaline solution or acid solution And then rinse, then
The second chemical etching with an alkaline solution
The metal film remaining after the first chemical etching
Wherein removing a portion of the oxide film and, further, by acid solution
The method is characterized in that metal contaminants on the oxide film surface are removed by a third chemical etching.

In the silicon test wafer to be reproduced in the present invention, an oxide film is formed below a metal film.
The type and thickness are not limited, and the number of times of reproduction can be secured as the thickness of the initial oxide film is increased.

A solution for chemical etching for removing the entire metal film and a minimum part of the oxide film differs depending on the type of the film. For example, Al, Ti, W, Cu metals ,
In the case of a silicide film, TiN , or a multilayer film of a combination thereof, an alkaline solution of 1 to 20% by weight of KOH or NaOH and 1 to 20% by weight of H ₂ O ₂ , or 1 to 20% by weight NH ₄ OH and 1-20
Removable by wt% _H 2 _{O 2} but, Al-C
In the case of an Al-based metal film such as u, 1 to 20% by weight of KOH or Na in which insoluble reaction products are hardly generated.
Using some form of OH and 1 to 20 wt% of _H 2 _{O 2} is effective without adhesion of product to the surface. Further, in the case of a Cu metal film, the oxide film is hardly chemically etched.
Wt% of HCl and 1 to 20% by weight of the acid solution of _H 2 _{O 2} is valid, further 1 to 20% by weight of KOH or NaOH or _NH 4 OH and 20 wt.% _H 2 _{O 2}
The oxide film is partially removed using an alkaline solution of In order to completely remove the metal film, it is more effective to perform the chemical etching twice or more. These metal film removal methods are based on the recently used T film.
It can be applied to new metal films including a and Co.

The removal of the metal film is possible even with the above-mentioned alkaline solution, acid solution or concentration range, but the etching rate of the metal film, the etching selectivity between the metal film and the oxide film, the reaction It is disadvantageous in terms of product adhesion and economy. Further, the processing temperature needs to be determined according to the thickness of the metal film and the oxide film.

As a method for removing metal contaminants on the surface such as Al, Fe and Zn, generally, HCl, HF, H
Although an acidic solution such as NO ₃ is used alone or as a mixed solution, in the case of the present invention, in order to prevent the oxide film on the test wafer surface from being removed, 1 to 20 is used.
It preferred to use weight% HCl and 1 to 20% by weight of the acid-based solution such as H ₂ O _2.

When the number of particles on the surface of the oxide film needs to be ensured in order to expand the use of recycling, for example, for checking dust generation in a metal film forming apparatus, a method such as SC-1 cleaning is used. Known techniques can be added and applied.
In addition, the present invention can be applied not only to a test wafer but also to a prime wafer as a reproduction target.

[0014]

Embodiments of the present invention will be described below with reference to examples.

Example 1 An oxide film having an average thickness of 3005 Å was formed on 25 test wafers having a thickness of 725 ± 10 μm by an oxidation furnace, and the surface including the edges thereof was formed by sputtering to an average thickness of 10054 Å. A film on which an Al film was formed was prepared for reproduction.

As a first step of removing the outermost metal film,
The wafer to be reclaimed is immersed in a first tank for film removal, at a temperature of 50 ° C. and a weight ratio of KOH: H ₂ O ₂ : H ₂ O.
= 1: 1:18 immersed in a first tank of a Teflon bath filled with a solution for 5 minutes, stripped the metal film, and then placed a second tank containing ultrapure water.
Rinsing was performed in the bath.

Next, as a second step, at a temperature of 50 ° C., K
After immersion for 5 minutes in a third tank of a Teflon bath filled with a solution of OH: H ₂ O ₂ : H ₂ O = 1: 1: 18 (weight ratio), rinsing was performed in a fourth tank. The reason why the removal of the metal film is performed in two steps is to remove the metal film in the first step and to remove the metal film and a part of the oxide film that are partially left in the second step.

After removing the metal film, contaminants on the surface were removed. The wafer to be reclaimed from which the metal film has been removed is subsequently heated at a temperature of 80 ° C. and in a weight ratio of HCl: H ₂ O ₂ : H ₂ O = 1:
After immersion for 5 minutes in a Teflon-made fifth tank filled with a 1: 8 solution, rinsing was performed in the sixth tank, and then dried by a spinner dryer. The reduction in thickness due to this metal film and decontamination process was only 234 Å.

Next, even after the Al film was formed under the same conditions and the regenerating process was repeated ten times, the amount of reduction in thickness was finally only 2483 angstroms.

Here, since the remaining thickness of the oxide film became approximately 500 angstroms, the oxide film was removed by HF, and the oxide film was formed again to 3000 angstroms. In the case of an Al film, an oxide film having a thickness of 3000 angstroms enables reproduction 10 times. The average thickness reduction under these conditions was only 250 Å.

On the other hand, the metal contamination level of the reclaimed wafer was determined to be 5E10 at
oms / cm ² or less, which is a level sufficient for use in a metal film forming apparatus and an oxidation furnace.

Example 2 Twenty test wafers each having a thickness of 725 μm ± 10 μm
An oxide film having an average thickness of 3003 angstroms was formed in an oxidation furnace, and a W film having an average thickness of 10071 angstroms was formed on the surface including the edge thereof, and was prepared as a reproduction target. As a first step of removing the surface metal film of the wafer, KOH: H is used at a temperature of 50 ° C. and a weight ratio of KOH: H.
_It was immersed in a first tank of a Teflon bath filled with a solution of ₂ O ₂ : H ₂ O = 1: 1: 18 for 5 minutes, and rinsed in the second tank as in Example 1.

Further, at a temperature of 50 ° C., KOH:
It was immersed in a third tank of a Teflon bath filled with a solution of H ₂ O ₂ : H ₂ O = 1: 1: 18 for 5 minutes, and rinsed in a fourth tank.

Next, at a temperature of 80 ° C., HCl: H ₂ O ₂ :
After immersion in a fifth tank of a Teflon bath filled with a solution of H ₂ O = 1: 1: 8 (weight ratio) for 5 minutes, rinsing in a sixth tank, and then drying with a spinner drier to contaminate metal on the surface Was removed. This treatment resulted in a thickness reduction of 243 Å. Next, after forming a W film under the same conditions, it is necessary to perform a regeneration process.
Repeated times. Finally, the amount of reduction in thickness was 2497 angstroms, and the remaining thickness of the oxide film was only about 500 angstroms.

The average thickness reduction under these conditions was 250 Å, and it was found that, in the case of a W film, an oxide film having a thickness of 3000 Å can be reused 10 times or more. On the other hand, the metal contamination level of the reclaimed wafer was 5E10 atoms / cm ² , which was sufficient for use in a metal film forming apparatus and an oxidation furnace.

Example 3 An average of 30 sheets of 725 ± 10 μm thick was placed in an oxidation furnace.
An oxide film having a thickness of 08 angstroms was formed, and an Al film having an average thickness of 10023 angstroms was formed on the surface including the edge thereof, and was prepared as a reproduction target.

The wafer was subjected to a first stage of film removal at a temperature of 45 ° C. and a weight ratio of NaOH: H ₂ O ₂ : H ₂ O =
After immersion in a first tank of a Teflon bath filled with a 1: 1: 18 solution for 5 minutes to remove the metal film, rinsing was performed in a second tank. Next, as a second step of removing the outermost metal film, a temperature of 45 ° C.
NaOH: H ₂ O ₂ : H ₂ O = 1: 1: 1
The solution of No. 8 was immersed in the third tank of the Teflon bath for 5 minutes, and rinsed in the fourth tank.

Further, at a temperature of 80 ° C., a weight ratio of HCl:
The metal contaminants on the surface were removed by immersion in a fifth tank of a Teflon bath filled with a solution of H ₂ O ₂ : H ₂ O = 1: 1: 8 for 5 minutes, rinsed in a sixth tank, and then a spinner dryer. Dried.

The thickness loss from this process was only 224 Å. Next, after forming an Al film under the same conditions, a regenerating process was repeated 10 times. Finally, the amount of reduction in thickness was 2276 Å, and the remaining thickness of the oxide film was almost 700 Å.

From this, it can be seen that the average thickness reduction amount is only 230 angstroms, and in the case of an Al film, an oxide film having a thickness of 3000 angstroms can be reused 10 times or more.

On the other hand, the metal contamination level of the reclaimed wafer was 5E10 atoms / cm ² or less, which was sufficient for use in a metal film forming apparatus and an oxidation furnace. Example 4 An oxide film having an average thickness of 2998 angstroms was formed on 25 test wafers having a thickness of 725 ± 10 μm in an oxidation furnace, and a Ti film having an average thickness of 1,068 angstroms was formed on the surface including the edge thereof. A film was prepared and used as a wafer to be regenerated.

This wafer is immersed in the first tank,
At 5 ° C., weight ratio, NH ₄ OH: H ₂ O ₂ : H ₂ O = 1: 1:
After immersing in a Teflon bath filled with the solution of No. 18 for 5 minutes,
Rinsing treatment was performed in the second tank. Next, as a second step of removing the outermost metal film, KOH:
After immersing in a Teflon bath as a third tank filled with a solution of H ₂ O ₂ : H ₂ O = 1: 1: 18 for 5 minutes, rinsing was performed in a fourth tank. Next, in a fifth tank for removing metal contamination on the surface, at a temperature of 80 ° C. and a weight ratio of HCl: H ₂
After immersion for 5 minutes in a Teflon bath filled with a solution of O ₂ : H ₂ O = 1: 1: 8, rinsing was performed in a sixth tank. Then, it dried with the spinner dryer. The reduction in thickness due to this treatment was 131 Å.

Next, after forming a Ti film under the same conditions,
The reproduction process was repeated 20 times. Finally, the amount of reduction in thickness was 2,453 angstroms, and the remaining thickness of the oxide film was approximately 500 angstroms.

With a Ti film substrate, an oxide film having a thickness of 3000 Å can be reproduced 20 times, and the average thickness reduction under this condition was 120 Å. On the other hand, the metal contamination level of the reclaimed wafer is 5
E10 atoms / cm ² , which was a sufficient level for use in a metal film forming apparatus and an oxidation furnace.

Example 5 An oxide film having an average thickness of 3004 angstroms was formed on 10 test wafers having a thickness of 725 ± 10 μm by an oxidation furnace, and a TiN film having an average thickness of 10016 angstroms was formed on the surface including the edges thereof. Was prepared as a wafer to be regenerated.

As a first step of removing the film from the wafer,
At a temperature of 75 ° C., the weight ratio is NH ₄ OH: H ₂ O ₂ : H ₂ O =
The sample was immersed in a first tank of a Teflon bath filled with a 1: 1: 18 solution for 5 minutes and rinsed in a second tank. Then, as a second step of removing the film from the wafer, at a temperature of 60 ° C. and a weight ratio of K
_{OH: H 2 O 2: H} 2 O: = 1: 1: 18 After the solution was immersed 5 minutes in a third tank Teflon bath filled with the and rinsed with fourth tank.

Next, in order to remove metal contamination on the surface, at a temperature of 80 ° C., a weight ratio of HCl: H ₂ O ₂ : H ₂ O = 1:
After being immersed in a fifth Teflon bath filled with a 1: 8 solution for 5 minutes, rinsed in a sixth bath, and then dried with a spinner dryer.

With this treatment, the thickness reduction was 127 Å. Next, after a TiN film was formed under the same conditions, a regeneration process was repeated 20 times. Finally, the amount of reduction in thickness was 2398 angstroms, and the remaining thickness of the oxide film was almost 600 angstroms.

From the above, in the case of TiN film, 300
With an oxide film having a thickness of 0 angstroms, reproduction can be performed 20 times, and the average thickness reduction under these conditions was 120 angstroms.

On the other hand, the metal contamination level of the reclaimed wafer was 5E10 atoms / cm ² , which was a level sufficient for use in a metal film forming apparatus and an oxidation furnace.

Example 6 An oxide film having an average thickness of 3011 angstroms was formed on 25 test wafers having a thickness of 725 ± 10 μm in an oxidation furnace, and an average thickness of 29993 angstroms was formed on the dragon surface including the edge thereof. A Cu film was prepared as a reproduction target.

The wafer was subjected to HCl: H at a weight ratio of 30 ° C. as a first step of removing the outermost metal film.
After being immersed in a first tank of a Teflon bath filled with a solution of ₂ O ₂ : H ₂ O = 1: 1: 15 for 3 minutes, it was rinsed in a second tank. Next, as a second step of removing the outermost metal film, at a temperature of 75 ° C., a weight ratio of NH ₄ OH: H ₂ O ₂ : H ₂ O = 1:
After being immersed in a third tank of a Teflon bath filled with a 1:18 solution for 3 minutes, it was rinsed in a fourth tank.

Next, a weight ratio of HCl: H at a temperature of 80 ° C.
The metal contaminants on the surface were removed by immersion in a fifth tank of a Teflon bath filled with a solution of ₂ O ₂ : H ₂ O = 1: 1: 8 for 5 minutes, rinsed in a sixth tank, and dried with a spinner dryer. Dried.

With the above treatment, the thickness reduction was 15 Å. Next, after a Cu film was formed under the same conditions, a regeneration process was repeated 10 times.
Finally, the reduction in thickness was 162 Å and the remaining oxide film thickness was approximately 2850 Å.

From the above, in the case of a Cu film, 3000
It can be seen that an oxide film having a thickness of Angstrom enables reproduction more than 150 times. On the other hand, the metal contamination level of the reclaimed wafer was 5E10 atoms / cm ² , which was sufficient for use in a metal film forming apparatus and an oxidation furnace.

[0046]

According to the present invention, it is possible to: The thickness of the substrate is not reduced at all and the substrate can be used semi-permanently.

2. Since the removal amount of the oxide film per reproduction can be suppressed to a small value, if an oxide film having a thickness of 3000 Å is formed first, it can be used repeatedly at least ten times.

3. The cost related to the test wafer is also greatly reduced because the cost of the substrate, the cost of forming an oxide film, and the cost of recycling are reduced.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Iku Abe 272-8 Takao, Otsu-cho, Kikuchi-gun, Kumamoto Prefecture Hamada Heavy Industries, Ltd. Silicon Wafer Division Kumamoto Factory (72) Inventor Hisashi Taniguchi Takao, Otsu-cho, Kikuchi-gun, Kumamoto Prefecture 272-8 Hamada Heavy Industries Co., Ltd. Silicon Wafer Division Kumamoto Factory (JP, A) JP-A-1-235337 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21 / 306,21 / 308 H01L 21 / 02,21 / 66

Claims (6)

(57) [Claims] 1. A test wafer in which an oxide film is formed under a metal film, the metal film is removed by a first chemical etching using an alkali solution or an acid solution, followed by rinsing, The metal film and a part of the oxide film remaining in the first chemical etching are removed by a second chemical etching with an alkaline solution, and further oxidized by a third chemical etching with an acid solution. A method for regenerating a silicon wafer with a metal film for removing metal contaminants on the film surface. 2. The method for reclaiming a silicon wafer with a metal film according to claim 1, wherein the thickness of the oxide film to be formed is 3000 Å or more. 3. A solution of at least one of the first and second chemical etchings, wherein a metal film is a metal of Al, Ti, W, Cu, a silicide film thereof,
In the case of a multilayer film of TiN 2 or a combination thereof, 1 to 20% by weight of KOH or NaOH and 1 to 20% by weight are used.
20% by weight of an alkaline solution of H ₂ O ₂ or 1%
２０20% by weight of NH ₄ OH and 1-20% by weight of H ₂ O ₂
The method for reclaiming a silicon wafer with a metal film according to claim 1, wherein 4. The method according to claim 1, wherein the first and second chemical etching solutions are 1 to 20 when the metal film is an Al-based metal film.
Wt% KOH or NaOH and 1 to 20 wt% _{H 2}
The method of reproducing a silicon wafer with a metal film according to claim 1 is an alkali based solution of O _2. 5. The method according to claim 1, wherein the first metal film is a Cu-based metal film.
Of 1 to 20% by weight of HCl and 1
An acid-based solution of ２０20% by weight of H ₂ O ₂ , wherein the second chemical etching solution is 1-20% by weight of KOH or NaOH or NH ₄ OH and 1-20% by weight of H ₂ O ₂
2. The method for reclaiming a silicon wafer with a metal film according to claim 1, wherein the alkaline solution is an alkaline solution. 6. An oxide film is formed on the surface of a test wafer, a metal film is formed on the oxide film as a first step, and a chemical solution using an alkaline solution or an acid solution is formed as a second step. The metal film and a part of the oxide film are removed by etching, and HCl and H ₂ O _{2 are used} as a third step.
After removing metal contaminants on the surface of the oxide film by chemical etching of an acid-based solution of the above, after repeating the first to third steps a plurality of times, when the film thickness of the oxide film becomes a predetermined value or less, A method for reclaiming a silicon wafer with a metal film, comprising: removing an oxide film with HF; and providing an oxide film and a metal film on the test wafer from which the oxide film has been removed with the HF.