JP3669419B2 - Semiconductor substrate cleaning method - Google Patents

Description

【００２１】
表１より明らかなように、比較例２では粒径の小さい粒子の抑制に適していることが判ったが、粒径が大きいＰＳＬ粒子ではあまり効果がなかった。また比較例３では粒径による抑制効果に違いはなかったが、それぞれ抑制する効果は十分とは言えなかった。これら比較例２、３に対し実施例３，４では１つの工程で洗浄を行うよりも抑制効果が高く、各粒径のＰＳＬ粒子の付着を抑制する効果が見られた。
【００２２】
【発明の効果】
以上述べたように、本発明によれば、有機酸又は有機酸塩を含む洗浄液で半導体基板を洗浄する工程を２つ以上含むことにより以下の効果を有する。２つ以上の洗浄工程のそれぞれの洗浄液に含まれる有機酸又は有機酸塩が互いに異なる種類であり、かつ特定の洗浄液により洗浄を行うと、半導体基板表面より付着する微粒子を良好に除去することができる。
【図面の簡単な説明】
【図１】 本発明の洗浄方法で洗浄したときの洗浄機構を示す図。
【図２】 本発明の予備工程で洗浄したときの洗浄機構を示す図。
【図３】 実施例１における洗浄後のウェーハ表面の微粒子付着指数を示す図。
【図４】 実施例２における洗浄後のウェーハ表面の微粒子付着指数を示す図。
【符号の説明】
１１ 半導体基板
１２ 微粒子
１３ 有機酸を含む洗浄液
１４ 第１洗浄槽
１６ 有機酸を含む洗浄液
１７ 第２洗浄槽
１８ フッ酸と有機酸を含む洗浄液
１８ａ フッ酸[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for cleaning the surface of a semiconductor substrate such as a silicon wafer.
[0002]
[Prior art]
Metal impurities and fine particles adhere to the surface of this type of semiconductor substrate during the manufacturing process. As semiconductor devices are highly integrated and highly functional, it is increasingly required that the surface of the semiconductor substrate is not contaminated with these fine particles, and the cleaning technology for the semiconductor substrate for that purpose is extremely high in the entire semiconductor device technology. It has become important. As a conventional semiconductor substrate cleaning method, an RCA cleaning method using an SC-1 solution of hydrogen peroxide and ammonium hydroxide and an SC-2 solution of hydrogen peroxide and dilute hydrochloric acid is known. In this RCA cleaning method, a semiconductor substrate is first immersed in an SC-1 solution, and fine particles and organic residues are removed from the substrate due to the oxidizing and alkaline properties of this solution. That is, in the SC-1 solution, both oxidation and reduction reactions occur simultaneously, and ammonia reduction and hydrogen peroxide oxidation compete in the same tank, and at the same time, from the substrate surface by the etching action of the ammonium hydroxide solution. Remove by lifting off. Next, the semiconductor substrate is immersed in a hydrofluoric acid aqueous solution to remove the natural oxide film on the surface of the substrate, and then the semiconductor substrate is immersed in an acidic solution of the SC-2 solution so that alkali ions and metal impurities insoluble in the SC-1 solution are obtained. Remove. For this reason, in the RCA cleaning, the substrate surface cleaned by the etching action of the ammonium hydroxide solution is recleaned by cleaning the acidic solution.
[0003]
However, the wafer cleaned with the SC-1 solution of the RCA cleaning method has a problem that many COPs appear due to the etching action of the ammonium hydroxide solution. Here, COP (crystal-originated particles) refers to a shallow bottom etch pit that appears on the wafer surface. This COP is a kind of defect caused by a crystal grown by pulling up from a silicon melt, and is detected by counting with a commercially available laser particle counter. There is also a problem that fine particles made of oxide or the like cannot be sufficiently removed.
[0004]
Therefore, the present applicant has proposed a semiconductor substrate cleaning method in which COP is less likely to appear after cleaning, and both metal impurities and fine particles adhering to the surface of the semiconductor substrate are well removed (Japanese Patent Laid-Open No. 11-274128). In this method, a semiconductor substrate is cleaned using a cleaning solution containing 0.0001% by weight or more of an organic acid or organic acid salt or further 0.005 to 0.25% by weight of hydrofluoric acid. According to this cleaning method, when the substrate is immersed in the cleaning liquid, the substrate surface, the metal impurity peripheral surface, and the fine particle peripheral surface are each negatively charged. Since the surface potential of the substrate and the surface potentials of the metal impurities and fine particles are the same, the metal impurities and fine particles move into the cleaning liquid. The metal impurities that have migrated into the cleaning liquid form a metal complex salt, and this metal complex salt is also negatively charged, so that reattachment of the fine particles and the metal complex salt to the substrate is prevented. Therefore, when the substrate is pulled up from the cleaning liquid, both metal impurities and fine particles can be removed well, and a cleaned substrate can be obtained.
[0005]
[Problems to be solved by the invention]
However, in the cleaning method disclosed in Japanese Patent Application Laid-Open No. 11-274128, the organic acid or the organic acid salt has a limited particle size range that can be removed depending on the type, so the fine particles outside the particle size range that can be removed. Remains on the substrate surface.
It is an object of the present invention to provide a method for cleaning a semiconductor substrate that satisfactorily removes fine particles adhering to the surface of the semiconductor substrate.
[0006]
[Means for Solving the Problems]
The invention according to claim 1 includes a citric acid, ethylenediaminetetraacetic acid or a salt thereof in a semiconductor substrate cleaning method including two or more steps of successively cleaning a semiconductor substrate with a cleaning liquid containing an organic acid or an organic acid salt. When the cleaning liquid is the first cleaning liquid and the cleaning liquid containing oxalic acid or a salt thereof is the second cleaning liquid, the semiconductor substrate is separately cleaned with the first cleaning liquid and the second cleaning liquid, and each cleaning is performed one or more times . A method for cleaning a semiconductor substrate is provided.
In the invention according to claim 1, by the two or more respective organic acid or organic acid salt contained in the cleaning liquid in the cleaning step to the different kinds each other physician, the fine particles to be removed with an organic acid or an organic acid salt The particle size range is expanded, and fine particles having a wide particle size range can be removed. In particular, a high removal effect can be obtained by washing with the first washing liquid and the second washing liquid containing organic acids or organic acid salts having different particle size ranges of the fine particles to be removed. In the above method, fine particles having a large particle diameter are removed by using a first cleaning liquid containing citric acid, ethylenediaminetetraacetic acid or a salt thereof, and small fine particles are removed by using a second cleaning liquid containing oxalic acid or a salt thereof.
[0007]
The invention according to claim 2 is the invention according to claim 1, wherein the total molar concentration of the organic acid or the organic acid salt contained in each of the two or more cleaning steps is from 1 × 10 ⁻⁶ to 1 ×. This is a method for cleaning a semiconductor substrate at 10 ⁻³ mol / l.
In the invention which concerns on Claim 2, in order to prevent the reattachment of microparticles | fine-particles to the board | substrate, the organic acid or organic acid salt of the said density | concentration range is preferable.
[0008]
The invention according to claim 3 is the invention according to claim 1 or 2 , and includes one or more of hydrofluoric acid and organic acid or organic acid salt before cleaning the semiconductor substrate in the first cleaning step. The semiconductor substrate cleaning method further includes a preliminary cleaning step of cleaning the semiconductor substrate with a cleaning liquid.
In the invention according to claim 3 , the natural oxide film formed on the surface of the semiconductor substrate can be removed by the hydrofluoric acid contained in the cleaning liquid in the preliminary process, and the fine particles on the natural oxide film can be transferred into the cleaning liquid.
[0009]
Invention is the invention according to claim 3, the first washing step and a method of cleaning a semi conductor substrate organic acid or an organic acid salt Ru allogeneic der contained in the cleaning liquid used in the preliminary washing process according to claim 4 It is.
In the invention according to claim 4 , the organic acid or the organic acid salt contained in the cleaning liquid used in the first cleaning process and the preliminary cleaning process is made the same type, so that the fine particles on the natural oxide film released in the cleaning liquid in the preliminary process. Can be prevented from reattaching to the substrate surface.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The method for cleaning a semiconductor substrate of the present invention is a cleaning method including two or more steps of successively cleaning a semiconductor substrate with a cleaning liquid containing an organic acid or an organic acid salt. In the cleaning liquid used in two or more cleaning steps, the type and concentration of the organic acid or organic acid salt are determined according to the particle size of the fine particles to be removed. The concentration of the organic acid or organic acid salt in the cleaning liquid is 1 × 10 ⁻⁶ to 1 × 10 ⁻³ mol / l. Preferably, it is 1 × 10 ^{−5 to} 5 × 10 ⁻⁴ mol / l. If it is less than 1 × 10 ⁻⁶ mol / l, the substrate surface and the peripheral surface of the fine particles are not sufficiently negatively charged, and if it exceeds 1 × 10 ⁻³ mol / l, the amount of fine particles attached to the substrate increases. . As the organic acid or organic acid salt of the present invention, citric acid, ethylenediaminetetraacetic acid or a salt thereof is used for the first cleaning liquid in two or more cleaning steps, and oxalic acid or a salt thereof is used for the second cleaning liquid. . One or more acids are appropriately selected from the above organic acids according to the particle size of the fine particles.
[0011]
In the method for cleaning a semiconductor substrate of the present invention, it is preferable to perform a preliminary cleaning step before the first cleaning step . In this preliminary cleaning step, the substrate is cleaned with a cleaning solution containing one or more of hydrofluoric acid and organic acid or organic acid salt. The concentration of hydrofluoric acid used for the cleaning liquid in the preliminary cleaning step is 2.5 × 10 ^{−3 to} 1.25 × 10 ⁻¹ mol / l. In particular, 2.5 × 10 ^{−3 to} 5 × 10 ⁻² mol / l is preferable, and 2.5 × 10 ^{−2 to} 5 × 10 ⁻² mol / l is more preferable. If it is less than 2.5 × 10 ⁻³ mol / l, the peeling action of the natural oxide film on the surface of the semiconductor substrate is poor, and if it exceeds 1.25 × 10 ⁻¹ mol / l, the cleaning liquid becomes a strong acid and the organic acid in the cleaning liquid or The dissociation of the organic acid salt is suppressed, the surface potential of the fine particles becomes positive, and the oxide film on the substrate surface is completely removed, so that the fine particles are reattached to the substrate surface. Examples of the organic acid or organic acid salt contained in the cleaning liquid in the preliminary cleaning step include organic acids such as formic acid, acetic acid, butyric acid, oxalic acid, malonic acid, succinic acid, citric acid, and ethylenediaminetetraacetic acid, or salts thereof. .
[0012]
The cleaning method according to claim 1 is the first step when fine particles 12 are attached to the surface of the semiconductor substrate 11 (FIG. 1A) as shown in FIGS. When the semiconductor substrate 11 is immersed in the first cleaning tank 14 in which the first cleaning liquid 13 containing citric acid, ethylenediaminetetraacetic acid or a salt thereof is stored (FIG. 1B), the first cleaning liquid 13 is an acidic solution. The surface and the fine particle peripheral surface are each negatively charged. Since the surface potential of the substrate 11 and each surface potential of the fine particles 12 are the same, the fine particles 12 repel the substrate 11 and move from the substrate 11 into the cleaning liquid 13. As a result, the surface potential of the fine particles 12 becomes the same minus as the surface potential of the substrate 11, so that the adhesion or reattachment to the substrate 11 is prevented. By using the first cleaning liquid 14, fine particles having a large particle diameter are removed. When the semiconductor substrate 11 is pulled up from the first cleaning tank 14 storing the first cleaning liquid 13 (FIG. 1C), fine particles 12 that could not be removed by the cleaning liquid 13 remain on the surface of the substrate 11. Then, the semiconductor substrate 11 is subsequently immersed in the second cleaning tank 17 in which the second cleaning liquid 16 containing oxalic acid or a salt thereof is stored (FIG. 1D). Here, the behavior of the fine particles in the cleaning liquid in the second cleaning tank is the same as the behavior in the cleaning in FIG. In the second cleaning tank 17, the fine particles 12 are released from the surface of the substrate 11 as in the first cleaning tank 14. By using the second cleaning liquid 16, fine particles having a small particle diameter are removed. When the semiconductor substrate 11 is pulled up from the second cleaning tank 17 in which the second cleaning liquid 16 is stored, the fine substrate 12 is removed and the cleaned substrate 11 is obtained (FIG. 1E).
[0013]
In the cleaning method according to the fifth aspect, as shown in FIGS. 2A to 2D, when the fine particles 12 are attached to the surface of the semiconductor substrate 11 (FIG. 2A), the first cleaning step is performed. When the semiconductor substrate 11 is immersed in a cleaning solution 18 containing hydrofluoric acid and an organic acid before cleaning (FIG. 2B), the natural oxide film 11a formed on the surface of the semiconductor substrate 11 is removed by the hydrofluoric acid 18a. The fine particles 12 on the natural oxide film 11 a move into the cleaning liquid 18. In other words, the natural oxide film 11a can be removed and the fine particles 12 on the natural oxide film 11a can be cleaned by a preliminary process in which hydrofluoric acid is added. Since the surface potential of the fine particles 12 becomes the same minus as the surface potential of the substrate 11, adhesion or reattachment to the substrate 11 is prevented (FIG. 2C). Subsequent to this preliminary step, the substrate is cleaned by the cleaning method according to the first aspect, whereby the fine particles are removed and a further cleaned substrate is obtained (FIG. 2D).
[0014]
【Example】
Next, examples of the present invention will be described.
<Example 1>
Formic acid, acetic acid, oxalic acid, malonic acid, succinic acid and citric acid were prepared as organic acids. Formic acid is 3 × 10 ⁻⁷ mol / l, 3 × 10 ⁻⁶ mol / l, 3 × 10 ⁻⁵ mol / l, 3 × 10 ⁻⁴ mol / l and 3 × 10 ⁻³ mol / l with respect to pure water. l Each was mixed to prepare a cleaning solution. Also, acetic acid is 3 × 10 ⁻⁷ mol / l, 3 × 10 ⁻⁶ mol / l, 3 × 10 ⁻⁵ mol / l, 3 × 10 ⁻⁴ mol / l and 3 × 10 ^{−3 with} respect to pure water. A cleaning solution was prepared by mixing each mol / l. Also, oxalic acid was added to pure water at 3 × 10 ⁻⁷ mol / l, 3 × 10 ⁻⁶ mol / l, 3 × 10 ⁻⁵ mol / l, 3 × 10 ⁻⁴ mol / l and 3 × 10 ^{− A} cleaning solution was prepared by mixing ³ mol / l each. Further, malonic acid was added to pure water at 3 × 10 ⁻⁷ mol / l, 3 × 10 ⁻⁶ mol / l, 3 × 10 ⁻⁵ mol / l, 3 × 10 ⁻⁴ mol / l and 3 × 10 ^{− A} cleaning solution was prepared by mixing ³ mol / l each. In addition, succinic acid was added to pure water at 3 × 10 ⁻⁷ mol / l, 3 × 10 ⁻⁶ mol / l, 3 × 10 ⁻⁵ mol / l, 3 × 10 ⁻⁴ mol / l and 3 × 10 ^{− A} cleaning solution was prepared by mixing ³ mol / l each. Furthermore, citric acid was added to pure water at 3 × 10 ⁻⁷ mol / l, 3 × 10 ⁻⁶ mol / l, 3 × 10 ⁻⁵ mol / l, 3 × 10 ⁻⁴ mol / l and 3 × 10 ^{− A} cleaning solution was prepared by mixing ³ mol / l each. Further, polystyrene latex particles having a particle size of 0.1 μm (hereinafter referred to as PSL particles) were forcibly added to these cleaning liquids at a rate of 8 × 10 ⁻¹¹ wt% with respect to 1 liter of the cleaning liquid. Next, a clean silicon wafer was prepared, and the wafer was immersed in the cleaning solution for 10 minutes, rinsed with ultrapure water for 1 minute, and the droplets on the wafer surface were removed by centrifugal force and dried. The adhesion amount of PSL particles on each wafer after each cleaning was measured by a particle counter (SP1 manufactured by KLA-Tencor). FIG. 3 shows the adhesion index in cleaning with each cleaning solution. The adhesion index indicates the relative amount of adhesion of the PSL particles, with the adhesion amount when the wafer is cleaned using pure water to which PSL particles are forcibly added as the cleaning liquid. As can be seen from FIG. 3, the adhesion suppressing effect can be obtained in the concentration range of 1 × 10 ⁻⁶ to 1 × 10 ⁻³ mol / l regardless of the type of organic acid.
[0015]
<Example 2>
As organic acids, oxalic acid, malonic acid, succinic acid and citric acid were prepared, and 3 × 10 ⁻⁵ mol / l of each organic acid was mixed with pure water to prepare a cleaning solution. Further, PSL particles having particle diameters of 0.1 μm, 0.178 μm, and 0.294 μm were forcibly added at a rate of 8 × 10 ⁻¹¹ wt% with respect to 1 liter of the cleaning liquid. Next, a clean silicon wafer was prepared, and the wafer was immersed in the cleaning solution for 10 minutes, rinsed with ultrapure water for 1 minute, and the droplets on the wafer surface were removed by centrifugal force and dried. The amount of PSL particles adhering to each wafer after being cleaned was measured using the same particle counter as in Example 1. FIG. 4 shows the adhesion index in cleaning with each cleaning solution. As apparent from FIG. 4, it can be seen that there is a difference in organic acid species having a high adhesion suppressing effect depending on the particle size of the PSL particles. It can be seen that oxalic acid is most effective for PSL particles having a particle size of about 0.1 μm, but the adhesion suppressing effect is reduced as the particle size is increased.
[0016]
<Example 3 >
Citric acid cleaning solution prepared by mixing 3 × 10 ⁻⁵ mol / l citric acid with pure water, and oxalic acid cleaning solution prepared by mixing 3 × 10 ⁻⁵ mol / l oxalic acid with pure water They were respectively prepared. A citric acid cleaning solution is stored in the first tank and an oxalic acid cleaning liquid is stored in the second tank, and PSL particles having particle diameters of 0.1 μm and 0.294 μm are stored in the first tank at 8 × 10 ⁻¹¹ for each liter of the cleaning liquid. It was forcibly added at a ratio by weight. Next, a clean silicon wafer was prepared, and this wafer was immersed in the first tank for 5 minutes and then immersed in the second tank for 5 minutes. Subsequently, the cleaned wafer was rinsed with ultrapure water for 1 minute, and the droplets on the wafer surface were removed by a centrifugal force and dried. The amount of PSL particles adhering to each wafer after being cleaned was measured using the same particle counter as in Example 1.
[0017]
<Example 4 >
Citric acid cleaning solution prepared by mixing 3 × 10 ⁻⁵ mol / l citric acid with pure water, and oxalic acid cleaning solution prepared by mixing 3 × 10 ⁻⁵ mol / l oxalic acid with pure water They were respectively prepared. Oxalic acid cleaning liquid is stored in the first tank and citric acid cleaning liquid is stored in the second tank, respectively, and PSL particles having particle diameters of 0.1 μm and 0.294 μm are stored in the first tank at 8 × 10 ⁻¹¹ weight per 1 liter of cleaning liquid, respectively. % Was forcibly added. A clean silicon wafer was prepared, this wafer was cleaned in the same manner as in Example 3, and the amount of PSL particles adhered was measured using the same particle counter as in Example 1 .
[0018]
<Comparative Example 1>
Pure water as a cleaning liquid, first tank, second tank stored respectively pure water, the first vessel respectively 8 × 10 particle size of the PSL particles 0.1μm and 0.294μm against washing liquid 1 liter ^{- It} was forcibly added at a rate of ¹¹ % by weight. A clean silicon wafer was prepared, this wafer was cleaned in the same manner as in Example 3, and the amount of PSL particles adhered was measured using the same particle counter as in Example 1.
<Comparative example 2>
A cleaning solution was prepared by mixing 3 × 10 ⁻⁵ mol / l oxalic acid with pure water. Oxalic acid was stored in the first tank, and PSL particles having a particle size of 0.1 μm and 0.294 μm were forcibly added to the first tank at a rate of 8 × 10 ⁻¹¹ wt% with respect to 1 liter of the cleaning liquid. A clean silicon wafer was prepared, this wafer was immersed in the first tank for 10 minutes, rinsed with ultrapure water for 1 minute, and the droplets on the wafer surface were removed by centrifugal force and dried. The adhesion amount of PSL particles after washing was measured using the same particle counter as in Example 1.
[0019]
<Comparative Example 3>
A washing solution was prepared by mixing pure water with 3 × 10 ⁻⁵ mol / l citric acid. Citric acid was stored in the first tank, and PSL particles having a particle size of 0.1 μm and 0.294 μm were forcibly added to the first tank at a rate of 8 × 10 ⁻¹¹ wt% with respect to 1 liter of the cleaning liquid. A clean silicon wafer was prepared, this wafer was cleaned in the same manner as in Comparative Example 2, and the amount of PSL particles adhered was measured using the same particle counter as in Example 1.
<Comparison evaluation>
Table 1 shows the adhesion index in Examples 3 and 4 and Comparative Examples 2 and 3 when the adhesion amount of each PSL particle in Comparative Example 1 is 1.
[0020]
[Table 1]

[0021]
As is apparent from Table 1, it was found that Comparative Example 2 was suitable for suppressing particles having a small particle size, but PSL particles having a large particle size were not very effective. Further, in Comparative Example 3, there was no difference in the suppression effect due to the particle size, but the suppression effect was not sufficient. Compared to these Comparative Examples 2 and 3 , Examples 3 and 4 showed a higher suppression effect than cleaning in one step, and an effect of suppressing the adhesion of PSL particles of each particle size was observed .
[0022]
【The invention's effect】
As described above, according to the present invention, the following effects can be obtained by including two or more steps of cleaning a semiconductor substrate with a cleaning liquid containing an organic acid or an organic acid salt . The organic acid or organic acid salt contained in each of the cleaning liquids of two or more cleaning steps is different from each other , and fine particles adhering from the surface of the semiconductor substrate can be satisfactorily removed by cleaning with a specific cleaning liquid. it can.
[Brief description of the drawings]
FIG. 1 is a view showing a cleaning mechanism when cleaning is performed by the cleaning method of the present invention.
FIG. 2 is a view showing a cleaning mechanism when cleaning is performed in a preliminary process of the present invention.
3 is a graph showing a particle adhesion index on the wafer surface after cleaning in Example 1. FIG.
4 is a graph showing a particle adhesion index on a wafer surface after cleaning in Example 2. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Semiconductor substrate 12 Fine particle 13 Cleaning liquid containing organic acid 14 First cleaning tank 16 Cleaning liquid containing organic acid 17 Second cleaning tank 18 Cleaning liquid containing hydrofluoric acid and organic acid 18a Hydrofluoric acid

Claims (4)

In a method for cleaning a semiconductor substrate comprising two or more steps of successively cleaning a semiconductor substrate with a cleaning liquid containing an organic acid or an organic acid salt,
When a cleaning liquid containing citric acid, ethylenediaminetetraacetic acid or a salt thereof is used as the first cleaning liquid, and a cleaning liquid containing oxalic acid or a salt thereof is used as the second cleaning liquid,
A method of cleaning a semiconductor substrate, wherein the semiconductor substrate is separately cleaned with the first cleaning liquid and the second cleaning liquid, and each cleaning is performed one or more times . The method for cleaning a semiconductor substrate according to claim 1, wherein the total molar concentration of the organic acid or the organic acid salt contained in each of the cleaning liquids in two or more cleaning steps is 1 × 10 ⁻⁶ to 1 × 10 ⁻³ mol / l. . The first washing step further comprises claim 1 or 2, wherein the pre-cleaning step of cleaning the semiconductor substrate with the cleaning liquid containing one or more of hydrofluoric acid and an organic acid or an organic acid salt before washing the semiconductor substrate with A method for cleaning a semiconductor substrate. The method for cleaning a semiconductor substrate according to claim 3 , wherein the organic acid or the organic acid salt contained in the cleaning liquid used in the first cleaning step and the preliminary cleaning step is the same.

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