JP2000049133A - Method of cleaning semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove microscopic damages caused by processing a semiconductor substrate, satisfactorily removing fine particles adhered to the surface of the semiconductor substrate, using the reduced number of processes and remove metallic impurity adhered to the surface of the semiconductor substrate. SOLUTION: After impregnating a semiconductor substrate in a mixture of hydrogen peroxide and ammonium hydroxide and then in dissolved ozone water, the semiconductor substrate is impregnated in a liquid containing hydrofluoric acid at 0.005-0.25 weight%. After this, it is preferably soaked in oxidizing liquid. Organic acid or organic salt at 0.0001 weight% or more is further preferably added to hydrofluoric acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for cleaning a surface of a semiconductor substrate such as a silicon wafer.

[0002]

2. Description of the Related Art Metal impurities, fine particles having a particle diameter of 1 μm or less, organic substances, and the like adhere to the surface of a semiconductor substrate of this type during the manufacturing process, and processing damage is formed. As semiconductor devices become more highly integrated and more sophisticated, it is increasingly required that the surface of the semiconductor substrate is not contaminated with these metallic impurities, fine particles, and organic substances, and that there is no processing damage. Cleaning technology has become extremely important in the overall semiconductor device technology.

As a conventional semiconductor substrate cleaning method, an RCA cleaning method using an SC1 solution of hydrogen peroxide and ammonium hydroxide and an SC2 solution of hydrogen peroxide and dilute hydrochloric acid is known. In this RCA cleaning method, first, a semiconductor substrate is SC
The substrate is immersed in one solution to remove fine particles and organic substances from the substrate due to the oxidizing and alkaline properties of the solution. That is, in this SC1 solution, both oxidation and reduction reactions are performed simultaneously, and reduction with ammonia and oxidation with hydrogen peroxide compete in the same tank. At the same time, fine particles and organic substances are removed from the substrate by the etching action of the ammonium hydroxide solution. Remove by lifting off from surface. Also, mechanical minute damage caused by processing of the semiconductor substrate is removed. Next, the semiconductor substrate is immersed in a hydrofluoric acid aqueous solution to remove a natural oxide film on the substrate surface.
It is immersed in two acidic solutions to remove alkali ions and metal impurities insoluble in the SC1 solution. Therefore, RCA
In the cleaning, the substrate surface cleaned by the etching action of the ammonium hydroxide solution is re-cleaned by cleaning with an acidic solution.

[0004]

As a method for increasing the efficiency of removing metal impurities in RCA cleaning, a method of adding a complexing agent for trapping a metal in an ammonium hydroxide solution has been disclosed (Japanese Patent Laid-Open No. 10-12584). ). However, in this method, when hydrogen peroxide solution is added to the ammonium hydroxide solution to which the complexing agent has been added, the complexing agent itself is decomposed by the oxidizing power of the hydrogen peroxide solution, and the effect is reduced. is there. An object of the present invention is to provide a method for cleaning a semiconductor substrate, which removes minute damage caused by processing of the semiconductor substrate and removes fine particles adhering to the surface of the semiconductor substrate satisfactorily in a small number of steps. Another object of the present invention is to provide a method for cleaning a semiconductor substrate, which satisfactorily removes metal impurities attached to the surface of the semiconductor substrate.

[0005]

The invention according to claim 1 is
As shown in FIG. 1, a step (a) of immersing a semiconductor substrate in a mixed solution of hydrogen peroxide and ammonium hydroxide, and a step (b) of immersing a semiconductor substrate immersed in the mixed solution in dissolved ozone water (C) immersing the semiconductor substrate immersed in the dissolved ozone water in a solution containing 0.005 to 0.25% by weight of hydrofluoric acid. When fine particles, organic substances and metal impurities are attached to the surface of the semiconductor substrate and processing damage is formed, when the semiconductor substrate is immersed in a mixed solution of hydrogen peroxide and ammonium hydroxide, both oxidation and reduction reactions occur simultaneously. Done,
The reduction by ammonia and the oxidation by hydrogen peroxide compete in the same tank, and at the same time, the fine particles and organic substances are removed from the substrate surface by the etching action of the ammonium hydroxide solution, and the minute damage caused by the processing of the semiconductor substrate is removed. You. Subsequently, by immersing the substrate in dissolved ozone water, the substrate is oxidized, and the subsequent reduction treatment with hydrofluoric acid can be performed effectively. That is, when the semiconductor substrate is immersed in a solution containing hydrofluoric acid, the natural oxide film formed on the surface of the substrate is removed, and the fine particles and metal impurities on the natural oxide film and the metal contained in the natural oxide film are removed. The impurities migrate into the liquid containing hydrofluoric acid. However, if the substrate is sufficiently oxidized with dissolved ozone water, the fine particles are easily separated from the substrate surface. In addition to removing the natural oxide film with hydrofluoric acid, it is also possible to clean metal impurities in the natural oxide film.

A second aspect of the present invention is the method according to the first aspect, further comprising a step (d) of immersing the semiconductor substrate in an oxidizing solution after the step (c). When a semiconductor substrate is immersed in an oxidizing solution, an oxide film is formed on the substrate surface,
The formation of the oxide film prevents adhesion of fine particles in the air to the surface of the substrate taken out of the oxidizing solution. When the liquid in step (c) contains an organic acid or an organic acid salt, the organic acid or organic substance attached to the substrate surface is decomposed and removed without complexing metal impurities. The invention according to claim 3 is the invention according to claim 1 or 2
The method according to claim 1, wherein the liquid in step (c) further contains 0.0001% by weight or more of an organic acid or an organic acid salt in addition to hydrofluoric acid. When a semiconductor substrate is immersed in a solution containing an organic acid or an organic acid salt in addition to hydrofluoric acid, the surface of the substrate, the peripheral surface of the metal impurities, and the peripheral surface of the fine particles are each negatively charged because this solution is an acidic solution. Since the surface potential of the substrate and the respective surface potentials of the metal impurities and the fine particles are the same, the metal impurities and the fine particles have an action of repelling the substrate, and migrate from the substrate into the liquid. The metal impurities transferred into the liquid form a complex with the molecules of the organic acid. The complex ion of this metal complex salt is also the same minus the surface potential of the substrate. As a result, the negatively charged fine particles and the metal complex, which have moved into the liquid, respectively, do not adhere again to the substrate having the negative surface potential, and both the metal impurities and the fine particles that have adhered to the semiconductor substrate surface are removed. Removed well.

The invention according to claim 4 is the invention according to claim 3, wherein the organic acid or organic acid salt in step (c) is oxalic acid, citric acid, succinic acid, ethylenediaminetetraacetic acid, tartaric acid, salicylic acid, Formic acid, acetic acid, propionic acid, butyric acid,
Valeric acid, caproic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachinic acid, benzoic acid, acrylic acid, adipic acid, malonic acid, malic acid, glycolic acid, phthalic acid, terephthalic acid, pimelic acid And one or more organic acids or salts thereof selected from the group consisting of fumaric acid. The above-listed organic acids or organic acid salts have a function of complexing metal ions of impurities that contaminate the substrate. The invention according to claim 5 is the invention according to claim 2.
4. The cleaning method according to any one of the above items (4) to (4), wherein the oxidizing solution in the step (d) is a dissolved ozone aqueous solution, a hydrogen peroxide solution or nitric acid. The oxidizing liquids listed above have an action of forming an oxide film on the substrate surface and decomposing and removing organic acids or organic substances attached to the substrate.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A cleaning method according to a preferred embodiment of the present invention comprises a step (a) of immersing a semiconductor substrate in a mixed solution of hydrogen peroxide and ammonium hydroxide as shown in FIG. (B) rinsing the semiconductor substrate immersed in the mixed solution with dissolved ozone water, and immersing the semiconductor substrate rinsed with the dissolved ozone water in a solution containing 0.005 to 0.25% by weight of hydrofluoric acid ( c) and a step (d) of immersing the semiconductor substrate immersed in the solution containing hydrofluoric acid in an oxidizing solution. The mixed solution used in the above step (a) is composed of hydrogen peroxide (H ₂ O ₂ ) and ammonium hydroxide (NH ₄ O ₂ ).
H), which is used in the RCA cleaning method.
This is a solution corresponding to the C1 solution. As described above, this mixed liquid has an action of removing fine particles, organic matter, and minute damage caused by processing of the semiconductor substrate. The ozone concentration of the dissolved ozone aqueous solution used in the above step (b) is 0.5 pp
m or more. When the amount is less than 0.5 ppm, the oxidation of the substrate is insufficient, and the fine particles are less likely to be separated from the substrate surface in the step (c). Since the solubility limit of ozone in pure water is about 25 ppm, the ozone concentration of the dissolved ozone aqueous solution is more preferably 2 to 25 ppm, and 2 to 1 ppm.
0 ppm is more preferred.

The concentration of hydrofluoric acid in the liquid used in the step (c) is 0.005 to 0.25% by weight. Especially 0.
005 to 0.10% by weight, preferably 0.05 to 0.1% by weight.
0% by weight is more preferred. If it is less than 0.005% by weight,
If the natural oxide film on the surface of the semiconductor substrate is poorly stripped, and if it exceeds 0.25% by weight, this solution becomes a strong acid, the surface potential of the fine particles becomes positive, and the fine particles adhere again to the substrate surface. Further, when an organic acid or an organic acid salt is added, dissociation of the organic acid in the liquid is suppressed, and the complexing action is reduced.

The type and concentration of the organic acid or organic acid salt to be added to the solution used in the step (c) are determined according to the type of the metal impurity to be removed. The concentration of organic acid or organic acid salt in the liquid in this step is 0.0001% by weight.
That is all. Preferably it is 0.003 to 10% by weight. If it is less than 0.0001% by weight, there is a problem that the complexing action of metal impurity ions released from the substrate surface is not sufficient. Examples of the organic acid or organic acid salt include oxalic acid, citric acid, succinic acid, ethylenediaminetetraacetic acid (EDT
A), tartaric acid, salicylic acid, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachiic acid, benzoic acid, acrylic acid, adipic acid, malon Organic acids such as acid, malic acid, glycolic acid, phthalic acid, terephthalic acid, pimelic acid, and fumaric acid, and salts thereof. The above-mentioned organic acid or its salt is appropriately selected according to the metal element constituting the metal impurity. Examples of the oxidizing solution in the step (d) include a dissolved ozone aqueous solution, a hydrogen peroxide solution, and nitric acid. Among them, a dissolved ozone aqueous solution is preferable because it has high purity, low concentration, high oxidizing power, and easy availability. The dissolved ozone aqueous solution has an ozone concentration of 0.5 p
pm or more. If it is less than 0.5 ppm, it is difficult to form a hydrophilic oxide film on the substrate surface, and the action of decomposing and removing organic acids and organic substances attached to the substrate surface is reduced. Since the solubility limit of ozone in pure water is about 25 ppm, the dissolved ozone aqueous solution preferably has an ozone concentration of 2 to 25 ppm.

[0011]

Next, examples of the present invention will be described together with comparative examples. <Example 1> An uncleaned silicon wafer having undergone a normal polishing step was subjected to a cleaning treatment under the following conditions. In the step (a), the above silicon wafer is subjected to SC1 solution (H ₂ O: H ₂ O).
₂ (30%): NH ₄ OH (29%) = 5: 1: 0.5) and treated at 80 ° C. for 10 minutes. Then, step (b)
The silicon wafer has an ozone concentration of 5 ppm
For 10 minutes in dissolved ozone water at room temperature. Next, as a step (c), a solution prepared by adding 0.06% by weight of citric acid as an organic acid to a solution in which 0.05% by weight of hydrofluoric acid is added to pure water is prepared. The silicon wafer immersed in ozone water was immersed for 5 minutes. Next, as a step (d), the silicon wafer is treated with an ozone concentration of 5%.
It was immersed in a dissolved ozone aqueous solution at room temperature for 10 minutes for 10 minutes.

Comparative Example 1 A conventional RCA cleaning method was employed as the cleaning method of Comparative Example 1. That is, an uncleaned silicon wafer that has been subjected to a normal polishing process in the same manner as in Example 1 is SC1.
Solution (H ₂ O: H ₂ O ₂ (30%): NH ₄ OH (29%) = 5: 1:
0.5 mixed solution) and treated at 80 ° C. for 10 minutes, and then the silicon wafer was rinsed with ultrapure water for 10 minutes. Next, this silicon wafer was subjected to H ₂ O: HF (49%) = 5.
It was immersed in a 0: 1 mixture for 15 seconds, and rinsed with ultrapure water. Subsequently, the rinsed silicon wafer was immersed in an SC2 solution (mixture of H ₂ O: H ₂ O ₂ (30%): HCl (37%) = 6: 1: 1), heated to 80 ° C., and heated at 80 ° C. Treated for 10 minutes. Thereafter, the silicon wafer was rinsed with ultrapure water for 10 minutes.

<Comparative Test and Evaluation> The number of fine particles having a particle size of 0.12 μm or more remaining on the silicon wafer surface after cleaning in Example 1 and Comparative Example 1 was counted by a particle counter. The number of fine particles remaining on the wafer was calculated. The result is shown in FIG. As is clear from FIG. 2, the number of fine particles remaining on the wafer cleaned by the method of Example 1 was as small as 29. On the other hand, the number of fine particles remaining on the wafer cleaned by the method of Comparative Example 1 was extremely large at 420. From this, it was found that the cleaning method of Example 1 cleans fine particles better than the cleaning method of Comparative Example 1.

[0014]

As described above, in the cleaning method of the present invention, the semiconductor substrate is immersed in a mixed solution of hydrogen peroxide and ammonium hydroxide, further immersed in dissolved ozone water, and then immersed in a solution containing hydrofluoric acid. By immersion, processing damage can be removed from the semiconductor substrate, and fine particles adhering to the surface of the semiconductor substrate can be satisfactorily removed. In particular, by adding an organic acid or an organic acid salt to a solution containing hydrofluoric acid, metal impurities adhering to the substrate surface can also be satisfactorily removed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cleaning step according to an embodiment of the present invention.

FIG. 2 is a view showing the number of fine particles remaining on the surface of a silicon wafer after cleaning in Example 1 and Comparative Example 1.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C11D 7/60 C11D 7/60 (72) Inventor Shigenari Yanagi 1-5-1 Otemachi, Chiyoda-ku, Tokyo Material Co., Ltd. F term (reference) 3B201 AA03 AB01 BB01 BB92 BB96 4H003 BA12 DA15 DC02 EA05 EA23 EA31 EB07 EB08 ED02 EE03 EE04

Claims (5)

[Claims] A step of immersing the semiconductor substrate in a mixed solution of hydrogen peroxide and ammonium hydroxide (a); and a step of immersing the semiconductor substrate in the mixed solution in dissolved ozone water (b). (C) immersing the semiconductor substrate immersed in the dissolved ozone water in a solution containing 0.005 to 0.25% by weight of hydrofluoric acid. 2. The method according to claim 1, further comprising a step (d) of dipping the semiconductor substrate in an oxidizing solution after the step (c). 3. The solution of step (c) is further added to hydrofluoric acid in addition to 0.1%.
3. The method according to claim 1, comprising at least 0001% by weight of an organic acid or an organic acid salt. 4. The method according to claim 1, wherein the organic acid or organic acid salt of step (c) is oxalic acid, citric acid, succinic acid, ethylenediaminetetraacetic acid, tartaric acid, salicylic acid, formic acid, acetic acid, propionic acid, butyric acid,
Valeric acid, caproic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachinic acid, benzoic acid, acrylic acid, adipic acid, malonic acid, malic acid, glycolic acid, phthalic acid, terephthalic acid, pimelic acid 4. The method according to claim 3, which is one or more organic acids or salts thereof selected from the group consisting of: and fumaric acid. 5. The method according to claim 1, wherein the oxidizing solution in step (d) is a dissolved ozone aqueous solution,
The method according to any one of claims 2 to 4, wherein the method is hydrogen peroxide or nitric acid.