JP2000124182A - Cleaning of semiconductor substrate and the semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor substrate which is manufactured by a method, wherein when the substrate is cleaned using an organic compound-added chemical, the organic compound itself is prevented from being adsorbed to the substrate and the yield of a device is not deteriorated. SOLUTION: A 5 to 100 angstrom oxide film consisting of a substrate material is made to form on the surface of a semiconductor substrate, and thereafter the substrate is cleaned with a chemical containing one weight ppm or higher to 10 wt.% or lower of an organic compound. Since the oxide film formed before hand acts as a protective film with respect the to adsorption of the organic compound to the substrate, the adsorption of the organic compound added to the chemical to the substrate, that is, the contamination on the substrate due to an organic substance can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning a semiconductor substrate and a semiconductor substrate cleaned by the method.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, it is widely known that particles (dust) and metal adhering to the surface of a semiconductor substrate cause wiring defects and deterioration of electrical characteristics. Therefore, chemical cleaning for removing these contaminants has been frequently used.

[0003] Representative chemicals include ammonia-hydrogen peroxide mixture (APM), hydrochloric acid-hydrogen peroxide mixture (HPM), sulfuric acid-hydrogen peroxide mixture (SPM), and dilute hydrofluoric acid solution (SPM). DHF) and the like. In recent years, new chemical solutions such as a mixed solution of hydrofluoric acid and hydrogen peroxide (FPM) and an aqueous solution of hydrofluoric acid and ozone have been used.

Further, an organic compound may be added for the purpose of improving the cleaning efficiency of the substrate with these chemicals. For example, a complexing agent is added to an APM cleaning solution (Japanese Patent No. 259).
No. 9021) and surfactants (K. Mori et al., 1993 Semi)
conductor Pure Water and Chemicals Conference, San
ta Clara, 1993, Chemical Proceedings, p. 122) or a method of adding a surfactant to FPM or hydrofluoric acid-ozone (S. Ojima et al., IEICE Technica).
l Report of IEICE, SDM95-86, p.105, 1995) has been proposed.

However, when an organic compound is added to a chemical solution as described above, the ability to remove particles or metals is improved, but the added organic compound itself is adsorbed on a semiconductor substrate, which induces crystal defects after heat treatment. Or may degrade the electrical characteristics of the device. Since crystal defects and deterioration of electrical characteristics lower the device yield, they become a major obstacle in application to mass production lines.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and prevents the organic compound itself from being adsorbed to the substrate in cleaning a semiconductor substrate using a chemical solution containing an organic compound, thereby improving the device yield. It is an object of the present invention to provide a semiconductor substrate which does not deteriorate.

[0007]

Means for Solving the Problems In view of the above problems, the present inventors have made intensive studies on the organic substance adsorption phenomenon. As a result, they have found that many organic compounds causing crystal defects and deterioration of electrical properties are easily adsorbed on the substrate material itself, but are hardly adsorbed on the oxide of the substrate, thereby completing the present invention.

The gist of the present invention is as follows.

(1) In a method for cleaning a semiconductor substrate having an oxide film having a thickness of less than 5 angstroms, after forming an oxide film of 5 to 100 angstroms on the surface of the semiconductor substrate, the substrate is added in an amount of 1 to 10 wt%. A method for cleaning a semiconductor substrate, comprising cleaning with a chemical containing the following organic compound.

(2) The cleaning method according to (1), wherein an oxide film is formed by a solution containing an oxidizing agent.

(3) The cleaning method according to (2), wherein the oxidizing agent is one or more oxidizing agents selected from hydrogen peroxide, nitric acid, and ozone.

(4) The cleaning method according to (1), wherein the oxide film is formed in an atmosphere containing an oxidizing gas.

(5) The cleaning method according to (4), wherein the oxidizing gas is one or two or more gases selected from nitrogen oxides, ozone, and oxygen.

(6) The cleaning method according to (1), wherein the organic compound is a surfactant and / or a complex forming agent.

(7) The chemical solution is an ammonia-hydrogen peroxide mixture (APM) or a hydrochloric acid-hydrogen peroxide mixture (HP
M), sulfuric acid-hydrogen peroxide mixture (SPM), dilute hydrofluoric acid solution (DHF), hydrofluoric acid-hydrogen peroxide mixture (FPM),
Alternatively, the cleaning method according to (1), wherein the cleaning method is an aqueous solution of hydrofluoric acid (HF) and ozone.

(8) The cleaning method according to (1), wherein the semiconductor substrate is a silicon wafer.

(9) A p-type semiconductor substrate which has been cleaned by the method described in (1) to (8), wherein the substrate is subjected to a heat treatment at 1100 ° C. for 120 minutes in a wet atmosphere to induce an oxide induced on the substrate surface. A semiconductor substrate having a stacking fault of 50 defects / cm ² or less.

(10) An n-type semiconductor substrate which has been cleaned by the method described in (1) to (8), wherein an oxide induced on the surface of the substrate is heat-treated at 1100 ° C. for 120 minutes in a wet atmosphere. A semiconductor substrate having a stacking fault of 500 defects / cm ² or less.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

In the present invention, it is necessary to use a semiconductor substrate having an oxide film thickness of less than 5 Å in order to easily control the thickness of the oxide film formed on the semiconductor substrate. For a semiconductor substrate having an oxide film thickness of 5 angstroms or more, it is preferable that an oxide film formed on the substrate be peeled in advance and a new oxide film be formed. As a means for removing the oxide film on the substrate, immersion in an HF aqueous solution can be exemplified.

Prior to the cleaning of the semiconductor substrate, an oxide film of 5 to 100 angstroms formed in advance functions as a protective film against the adsorption of the organic compound. As a result, it is possible to prevent the organic compound from remaining on the substrate surface after cleaning. If the thickness of the oxide film to be formed is less than 5 angstroms, the oxide film is too thin to allow organic compound molecules to pass through, so that it is impossible to sufficiently suppress the adhesion of the organic compound. On the other hand, if it exceeds 100 angstroms, the effect of suppressing adhesion is saturated, and an operation of removing an oxide film in a later step is required, which is not preferable in terms of productivity and cost.

As a means for forming an oxide film on a semiconductor substrate, there are a method of dipping in a solution containing an oxidizing agent and a method of exposing to an atmosphere containing an oxidizing gas. In the former case, hydrogen peroxide, nitric acid, and ozone are preferable as the oxidizing agent, and the solution containing these is APM, SPM,
Examples include nitric acid aqueous solution and ozone water. In the latter case, a nitrogen oxide gas such as NO ₂ , an ozone gas, or an oxygen gas is preferable as the oxidizing gas. Even if these gases are used alone, they are mixed with various gases such as air and an inert gas. It may be used after dilution. In the present invention, 5-1 to 1
As long as an oxide film having a thickness of 00 Å can be formed, the content of these oxidizing agents and oxidizing gases and the conditions for forming the oxide film are not particularly limited, but a method of immersing in 5 to 10 ppm ozone water at room temperature for about 5 minutes. Alternatively, a method of exposing to 200 ppm ozone gas at room temperature for about 10 minutes is preferable because a dense oxide film having a stoichiometric ratio can be formed, and the load of the waste liquid and the exhaust treatment after the treatment is small.

Then, the semiconductor substrate on which the oxide film is formed is washed with a chemical solution containing an organic compound to obtain a clean semiconductor substrate in which adhesion of metals, particles and organic substances is suppressed. Can be. Here, the concentration of the organic compound in the chemical solution used for cleaning needs to be 1 wt ppm to 10 wt%. When the content is less than 1 ppm by weight, the effect of the organic compound, that is, the suppression of the adhesion of metal and particles to the substrate, cannot be obtained. Is not preferred.

The organic compound to be contained in the chemical must be a substance capable of suppressing metal adsorption and removing particles from the substrate being washed. Complexing agents and surfactants are preferred. As complexing agents, catechol, tiron, tropolone, 8-hydroxyquinoline-5-sulfonic acid and the like, and as surfactants, sodium dodecylbenzenesulfonate, polyoxyethylene alkyl ether, Surflon S145 (trade name, manufactured by Asahi Glass Co., Ltd.), etc. Can be exemplified. Further, as the chemical solution, it is sufficient that the semiconductor substrate can be cleaned, and APM, HPM, SPM, DHF, FPM or HF-ozone aqueous solution is preferable.

By performing the above-described cleaning, a semiconductor substrate with few oxide stacking faults can be obtained. Specifically, the number of oxide-induced stacking faults generated on the substrate surface after heat treatment at 1100 ° C. for 120 minutes in a wet atmosphere is 50 defects / cm ² or less for a p-type semiconductor substrate and 500 defects / cm ^{2 for} an n-type semiconductor substrate.
cm ² or less.

[0026]

Embodiments of the present invention will be described below with reference to Tables 1 and 2 below.

[0027]

[Table 1]

[0028]

[Table 2]

Tables 1 and 2 show examples of the present invention and comparative examples. As the substrate, p-type 10Ωc pulled up by CZ method
m 6 inch silicon wafer was used. However, in Example J
For the group and R, an n-type wafer was used. For the group K and S, a 5 μm epitaxial layer (p-type 10 Ωcm) was used. An APM or FPM cleaning solution containing a surfactant or a complexing agent was used as the organic-containing cleaning solution.
The conditions of each process are shown below.

The starting substrate is one in which a silicon wafer is immersed in a DHF cleaning solution (1% by weight, room temperature) for 2 minutes, then overflow-rinsed with ultrapure water for 5 minutes, and then spin-dried. By this process, the natural oxide film on the surface of the silicon wafer is removed with hydrofluoric acid, and the bare silicon surface is exposed.

Here, the method for removing the natural oxide film of the starting substrate is not particularly limited. For example, a mixed solution of hydrofluoric acid and hydrochloric acid having an appropriate composition, a mixed solution of hydrofluoric acid and aqueous hydrogen peroxide, or the like may be used.

The starting substrate was immersed in a solution containing an oxidizing agent to form an oxide film on the surface. Specifically, 80
10 minutes by immersion in APM (29% ammonia water: 31% hydrogen peroxide solution: ultrapure water = 1: 1: 5 by volume) at 10 ° C.
Immersion in SPM (97% sulfuric acid: 31% hydrogen peroxide solution = 4: 1 by volume) at 120 ° C. for 5 minutes to 20 angstrom or room temperature nitric acid (68%
(Immersion in nitric acid: water = 1: 99) for 5 minutes to form an oxide film of 20 Å or 20 Å of room temperature ozone water (10 ppm) for 5 minutes to form an oxide film of 15 Å and overflow rinse with ultrapure water for 10 minutes. did.

Alternatively, an oxide film was formed on the surface of the starting substrate by using an oxidizing gas. Specifically, 50p
exposure to 20 Angstroms or 10 ppm ozone atmosphere for 10 minutes.
Exposure for 30 minutes or 30 Å or at room temperature in an air atmosphere, and the substrate was taken in and out of a horizontal oxidation furnace at 3 Å or 6 Å or at 600 ° C. in an air atmosphere to form an oxide film of 95 Å or 150 Å.

As a conventional material, a substrate not subjected to an oxide film forming process was prepared.

Subsequently, these substrates were washed with an APM cleaning solution containing an organic compound (29% ammonia water: 31% hydrogen peroxide solution: ultrapure water = 1: 1: 5 by volume, 80 ° C., 5 minutes).
Alternatively, cleaning was performed with an FPM cleaning liquid (50% hydrofluoric acid: 31% aqueous hydrogen peroxide: water = 0.04: 3: 7, room temperature, 5 minutes, 1 MHz ultrasonic wave application). Examples of the organic compound to be added include tropolone (hereinafter, TP) as a complexing agent, 8-hydroxyquinoline-5-sulfonic acid (hereinafter, HQ), and sodium dodecylbenzenesulfonate (hereinafter, DB) as a surfactant. And Surflon S145 (trade name of Asahi Glass Co., Ltd., hereinafter referred to as SF) were added at the concentrations shown in each table.

The following evaluation was performed on the obtained wafer.

(A) Measurement of Particles (Dust) Using a Laser Scattering Surface Contaminometer A SurfScan 6200 manufactured by Tencor Co., Ltd.
The number of particles having a size of 20 μm or more was measured. Evaluation of the measurement results is as follows: A: excellent (0 to 4 pieces / wafer), B:
Allowable (5 to 9 wafers / wafer), C: Acceptable lower limit (10
２９29 / wafer), D: failed (30 or more / wafer). Although the criteria for pass / fail regarding particles differ depending on the device to be manufactured, a typical reference value in a silicon wafer acceptance inspection by a device maker is said to be about 30 pieces / wafer. .

(B) Measurement of Heavy Metal Contamination by Total Reflection X-Ray Fluorescence Spectrometer C was measured by SYSTEM 3726 manufactured by Rigaku Corporation.
The r, Fe, Ni, Cu, and Zn concentrations were measured. Evaluation of the measurement results is as follows: A: excellent (less than 1 × ^{10 10} atoms / cm ² ), B: acceptable (1-2 × ^{10 10} atoms / cm ² ), C: acceptable lower limit ( ^2- 5 × ^{10 10} atoms / cm ² ), D: Rejected (5 × ^{10 10} atoms / cm ² or more). As in the case of particles, the pass / fail judgment criteria for metal differ depending on the device to be manufactured. However, a typical reference value in a silicon wafer acceptance inspection by a device manufacturer is said to be about 5 × ^{10 10} atoms / cm ^2. Determined according to this standard.

(C) Investigation of crystal defects after heat treatment Thermal oxidation was performed at 1100 ° C. for 120 minutes in a wet atmosphere, and the density of generated crystal defects was examined. This crystal defect induces a device wiring defect similarly to particles. If the density is low, it can be remedied by the redundant circuit of the device,
If the density exceeds a certain level, it will be impossible to remedy and will be rejected. The rejection criteria vary depending on the device to be made,
This time, the typical density set by the silicon wafer manufacturer as an internal management standard is 50 wafers / cm for p-type wafers.
² , 500 / cm ² n-type wafers were used as pass / fail judgment criteria.

(D) Measurement of average breakdown electric field of MOS diode After cleaning a normal CZ silicon wafer by the above-mentioned cleaning method, a polysilicon electrode MOS diode having a gate oxide film thickness of 250 Å was formed on the surface of the wafer.
The breakdown electric field was measured in μA. The organic compound is a so-called C mode (breakdown electric field of 11 MV /
cm) As the ratio worsens, calculate the C mode ratio,
Pass / fail was determined based on the case of washing with a washing solution containing no organic compound.

The results of these experiments are shown in Tables 1 and 2 above. Note that the column surrounded by a thick line regarding particle and heavy metal contamination indicates that the characteristics have been improved as compared with the ordinary method.
Further, shaded columns regarding the crystal defect density and the MOS diode C-mode pass rate indicate that the characteristics are deteriorated as compared with the ordinary method and the reject level is reached.

In the case of APM, when an oxide film is not formed, as shown in A1 to A4, J1, and K1 in Table 1,
While particle or heavy metal contamination is improved, crystal defects and the average breakdown field of the MOS diode are at reject levels. On the other hand, as shown in the examples of the present invention, when an oxide film of 5 to 100 Å is formed by any of the methods and the amount of the organic compound added is in the range of 1 ppm to 0.1 wt%, In addition, the generation of crystal defects was suppressed, and the average breakdown electric field of the MOS diode was improved. At this time, the capability of removing particles, which is an essential feature of APM, has not deteriorated. Furthermore, when a suitable amount of a chelating agent is added in the treatment with a chemical solution, heavy metal contamination is suppressed, and when a suitable amount of a surfactant is added, the particle removing power is improved.

Further, when ozone water or ozone gas is used as the oxide film forming means, generation of crystal defects and deterioration of the MOS diode breakdown electric field are more suppressed as compared with other means as seen in the groups E and G. I have. This is considered to be because the oxide film formed by the ozone water or the ozone gas is denser than the other cases, and has a high organic compound adhesion suppressing effect.

In the case of the FPM, when the oxide film is not formed, the crystal defects and the average breakdown electric field of the MOS diode become rejected levels as shown in L1 and L2.
On the other hand, as seen in the embodiment of the present invention, 5 to 1
An oxide film of 00 Å is formed by any of the methods, and the amount of the organic compound added is 1 ppm to 0.1 w
In the case of t%, the generation of crystal defects was suppressed, and the average breakdown electric field of the MOS diode was improved.
At this time, the metal removal capability, which is an essential feature of the FPM, has not deteriorated. Further, the improvement of the particle removing power when an appropriate amount of the surfactant is added is maintained even when the oxide film is formed in advance.

When ozone water or ozone gas is used as the oxide film forming means, the occurrence of crystal defects and the deterioration of the MOS diode breakdown electric field are further suppressed as compared with other means as seen in N and O. This is also the APM
It is considered that the oxide film formed by the ozone water or the ozone gas is denser than the other cases and has a high organic compound adhesion suppressing effect as in the case of the above.

The lower limit of the concentration of these added organic compounds is 1 ppm. The reason is that if it is less than 1 ppm, it is too thin and desired functions such as suppression of metal adsorption and improvement of particle removal ability are not exhibited (B1 and M).
1).

The upper limit of the concentration of the added organic compound is 10
%. The reason is that if the content exceeds 10 wt%, the concentration is too high to suppress the adsorption, and the organic compound remains, resulting in generation of crystal defects and deterioration of the average breakdown electric field of the MOS diode (for example, see B5 and M5). ). Addition of too high a concentration is disadvantageous in terms of cost.

The liquid composition, component concentration, processing time, and the like described above are merely examples, and it should be noted that they may be varied within a range where an oxide film of 5 to 100 angstroms can be formed.

When the thickness of the oxide film is less than 5 angstroms, it is impossible to sufficiently suppress the adhesion of the organic compound as seen in H1 and P1. This is presumably because the oxide film is too thin and the organic compound molecules slip through.

On the other hand, although the same effect can be obtained as shown by I2 and Q2 even if an oxide film of 100 Å or more is formed, the load for removing all the oxide film in a later step is large with this thickness. It is difficult to implement.

[0051]

The addition of an organic compound to a cleaning solution is effective as a means for compensating for the drawbacks of the cleaning solution, but the addition of the organic compound causes defects to be formed after heat treatment and a failure in oxide film breakdown voltage. Was difficult. However, according to the method of the present invention, side effects associated with the addition of the organic compound can be prevented. For this reason, a process in which a plurality of cleaning liquids are conventionally unavoidably combined can be shortened, so that space and cost can be saved as a whole of the cleaning process, and a semiconductor substrate having extremely excellent characteristics can be provided. it can.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Susumu Otsuka 3-35-1 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Nippon Steel Corporation Technology Development Division (72) Inventor Toshihiro Morimoto Ida, Nakahara-ku, Kawasaki-shi, Kanagawa 3-35-1 New Nippon Steel Corporation Technology Development Division

Claims (10)

[Claims] In a method for cleaning a semiconductor substrate having an oxide film having a thickness of less than 5 Å, after forming an oxide film having a thickness of 5 to 100 Å on the surface of the semiconductor substrate, the substrate is reduced to 1 wt% to 10 wt%. A method for cleaning a semiconductor substrate, comprising cleaning with a chemical solution containing an organic compound. 2. The cleaning method according to claim 1, wherein the oxide film is formed by a solution containing an oxidizing agent. 3. The cleaning method according to claim 2, wherein the oxidizing agent is one or more oxidizing agents selected from hydrogen peroxide, nitric acid, and ozone. 4. The cleaning method according to claim 1, wherein the oxide film is formed in an atmosphere containing an oxidizing gas. 5. The cleaning method according to claim 4, wherein the oxidizing gas is one or more gases selected from nitrogen oxides, ozone, and oxygen. 6. The cleaning method according to claim 1, wherein the organic compound is a surfactant and / or a complexing agent. 7. A chemical solution comprising an ammonia-hydrogen peroxide mixture, a hydrochloric acid-hydrogen peroxide mixture, a sulfuric acid-hydrogen peroxide mixture, a dilute hydrofluoric acid solution, a hydrofluoric acid-hydrogen peroxide mixture, The cleaning method according to claim 1, wherein the cleaning method is an aqueous solution of hydrofluoric acid and ozone. 8. The cleaning method according to claim 1, wherein the semiconductor substrate is a silicon wafer. 9. A p-type semiconductor substrate cleaned by the method according to claim 1, wherein the substrate is subjected to a heat treatment at 1100 ° C. for 120 minutes in a wet atmosphere, and an oxide-induced stacking fault generated on the substrate surface is reduced to 50%. Semiconductor substrate, wherein the number is not more than the number of pieces / cm ² . 10. An n-type semiconductor substrate cleaned by the method according to claim 1, wherein the substrate is subjected to a heat treatment at 1100 ° C. for 120 minutes in a wet atmosphere, and an oxide-induced stacking fault generated on the surface of the substrate is 500%. Semiconductor substrate, wherein the number is not more than the number of pieces / cm ² .