JP2014192353A - Method of processing substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of processing a substrate, with which it is possible to reduce an environmental load in waste liquid treatment.SOLUTION: A main surface of a substrate W1 is exposed to a mixture 21 containing ozone water and hydrochloric acid. In this method, the ozone water has a high oxidation reduction potential. By increasing a hydrogen ion concentration of the ozone water, it is possible to reduce an Fe concentration on the substrate surface without performing processing that uses a cleaning fluid that places a heavy load in waste liquid treatment. In a preferred embodiment, it is preferable that pH of the mixture 15 is two or less. The pH of the mixture, which is two or less, is preferable for the reduction of the Fe concentration. Also, in a more preferred embodiment, it is preferable that a concentration of hydrochloric acid (hydrogen chloride) in the mixture 15 is 6% or more. The concentration of the hydrochloric acid in the mixture, which is 6% or more, is preferable for the reduction of the Fe concentration.

Description

  The present invention relates to a method for processing a substrate.

  Patent Document 1 discloses a method for removing particles and metal impurities adhering to the surface of a silicon substrate. The silicon substrate is washed with ultrapure water containing ozone to form a silicon oxide film, and particles and metal impurities are taken into the inside and the surface of the silicon oxide film. Next, this silicon substrate is washed with dilute hydrofluoric acid aqueous solution, and the silicon oxide film is removed by etching.

JP-A-6-314679

  In compound semiconductor devices such as gallium nitride, with the miniaturization and high integration of elements, metal impurities mixed in the manufacturing process affect the element yield and device characteristics. Therefore, in the manufacturing process, the GaN substrate and the epitaxial substrate are cleaned to remove metal impurities. RCA cleaning is a typical cleaning method. In this method, since a large amount of high concentration chemicals is used, a large amount of ultrapure water is used for rinsing. Waste liquid treatment increases the environmental impact.

  In a silicon device, after covering the silicon surface with an oxide film, the silicon device can be washed with hydrofluoric acid to use the oxide film on the silicon surface as a sacrificial layer. That is, the metal impurities can be removed together with the oxide film. However, for compound semiconductors, no suitable oxide film has been found as a sacrificial layer that can be formed on the surface of the compound semiconductor substrate.

  Compound semiconductor wafer manufacturing and device manufacturing processes are subject to contamination by trace metals from the manufacturing line atmosphere and / or manufacturing equipment. In order to remove this contaminant, a total of 100 or more cleaning steps are performed. RCA cleaning, which is a typical cleaning method, uses a large amount of high concentration chemicals such as sulfuric acid / hydrogen peroxide mixture, hydrochloric acid / hydrogen peroxide mixture, and ammonia / hydrogen peroxide mixture. Therefore, a large cost is required for the waste liquid treatment after washing. Further, in order to remove chemicals contained in the cleaning liquid from the surface of the compound semiconductor, rinsing is performed with a large amount of ultrapure water. This is also a high environmental load.

  In silicon wafer manufacturing and device manufacturing processes, ozone-added ultrapure water is used instead of a sulfuric acid / hydrogen peroxide mixture to reduce environmental impact. By immersing silicon in ozone-added ultrapure water, a silicon oxide film is formed on the surface. It is practically carried out that the contaminated metal is taken into the oxide film and the contaminated metal is removed with hydrofluoric acid using the oxide film as a sacrificial layer. However, a nitride compound typified by gallium nitride is a stable substance that is not easily oxidized by a mixed solution of sulfuric acid / hydrogen peroxide and ultrapure water added with ozone. Therefore, the oxide film generated by these treatments is 1 nm or less, and an oxide film having this thickness cannot be used as a sacrificial layer. Therefore, at the present time, high-temperature and high-concentration chemicals represented by sulfuric acid / hydrogen peroxide are used for removing metal contamination on nitride compounds.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for processing a substrate capable of reducing the environmental load in waste liquid processing.

  The present invention relates to a method of processing a substrate. This method includes (a) a step of preparing a substrate having a main surface of a III-V compound semiconductor, and (b) a substrate containing ozone water and hydrochloric acid whose hydrogen ion concentration is adjusted to a predetermined pH or lower. Exposing the main surface. The group III-V compound semiconductor includes a group III-V nitride.

  According to this method (method for treating a substrate), ozone water has a high redox potential. By increasing the hydrogen ion concentration of the ozone water so as to be equal to or lower than a predetermined pH, the Fe concentration on the substrate can be reduced without performing a treatment using a cleaning liquid that causes a large burden on the waste liquid treatment.

  In the method according to the present invention, the pH of the mixture is preferably 2 or less. According to this method (method for treating a substrate), the pH of the mixture is preferable for reducing the Fe concentration on the substrate surface when the pH is 2 or less.

  In the method according to the present invention, the concentration of hydrochloric acid in the mixture is preferably 6% or more. According to this method (method for treating a substrate), when the hydrochloric acid concentration of the mixture is 6% or more, it is preferable for reducing the Fe concentration on the substrate surface. In the method according to the present invention, the hydrochloric acid concentration in the mixture is preferably 10% or more. According to this method (method for treating a substrate), it is preferable for reducing the Fe concentration on the substrate surface when the hydrochloric acid concentration of the mixture is 10% or more.

  The method according to the present invention further includes a step of generating ozone water from ultrapure water, a step of adding hydrochloric acid to the ozone water to generate hydrochloric acid-added ozone water, and preparing a mixed solution as the mixture. it can. The addition of the hydrochloric acid is performed so that the hydrogen ion concentration (pH) of the hydrochloric acid-added ozone water is located in the iron ionization region in the iron probe diagram.

In the method according to the present invention, the group III-V compound semiconductor _may be made of _{In X Al Y Ga 1-X} -Y N (0 ≦ X ≦ 1,0 ≦ Y ≦ 1).

  As described above, according to the present invention, it is possible to provide a method for processing a substrate capable of reducing the environmental load in waste liquid processing.

FIG. 1 is a diagram showing main apparatuses in the method according to the present embodiment. FIG. 2 is a drawing showing major steps in the method according to the present embodiment. FIG. 3 is a drawing showing an iron pool diagram. FIG. 4 is a view showing an effect relating to cleaning removal of copper (Cu). FIG. 5 is a diagram showing an effect relating to cleaning removal of nickel (Ni). FIG. 6 is a diagram showing an effect relating to cleaning removal of zinc (Zn). FIG. 7 is a view showing an effect relating to cleaning removal of iron (Fe). FIG. 8 is a drawing showing the effect of removing iron with respect to several cleaning solutions.

  Subsequently, embodiments of the present invention relating to a method for treating a substrate, a method for treating a surface of a group III-V compound semiconductor, and a method for cleaning a group III-V compound semiconductor will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

  FIG. 1 is a drawing showing main apparatuses in a method for treating a substrate, a method for treating a surface of a group III-V compound semiconductor, and a method for cleaning a group III-V compound semiconductor. In the system 11, the ultrapure water generator 13 generates ultrapure water UPW. The ultrapure water UPW is used for, for example, ozone water O3-UPW. The ozone water generator 15 generates ozone water O3-UPW. Ozone water O3-UPW can be generated, for example, by adding gaseous ozone to ultrapure water UPW by bubbling or the like. The ozone concentration in the ozone water can be, for example, 10 ppm or more, and can be 20 ppm or less. Next, the mixing device 19 adds the hydrochloric acid (or hydrogen chloride) from the hydrochloric acid (or hydrogen chloride) reservoir 17 to the ozone water O3-UPW to produce a mixture 21 of ozone water and hydrogen chloride. The mixture 21 is supplied to the first processing device 23. In the first processing apparatus 23, the substrate W1 is exposed to the mixture 21. The second treatment device 25 is supplied with ozone water O3-UPW. In the second processing apparatus 25, the substrate W1 is exposed to the ozone water O3-UPW. Pure water UPW is supplied to the third processing device 27. In the third processing apparatus 27, the substrate W1 is exposed to ultrapure water UPW. Waste water from the first treatment device 23, the second treatment device 25, and the third treatment device 27 is sent to the waste water treatment device 29. The wastewater treatment device 29 treats the supplies from the first treatment device 23, the second treatment device 25, and the third treatment device 27 to such an extent that they can be discarded.

FIG. 2 is a drawing showing main steps in a method for treating a substrate, a method for treating a surface of a III-V compound semiconductor, and a method for cleaning a III-V compound semiconductor. In step S101, a substrate W1 is prepared. The substrate W1 can have a main surface made of a III-V compound semiconductor, and in a preferred embodiment, the III-V compound semiconductor comprises III-V nitride. The substrate W1 is a group III-V nitride wafer, an epitaxial substrate in which a group III-V nitride is deposited on the wafer, an epitaxial substrate in which a group III-V nitride is deposited on a wafer different from the group III-V nitride. It can be a single crystal GaN substrate or the like. III-V nitrides can consist of _{In X Al Y Ga 1-X} -Y N (0 ≦ X ≦ 1,0 ≦ Y ≦ 1), as the group III-V nitride, for example GaN, It can be InGaN, AlGaN, AlN, or the like.

  In step S102, the main surface of the substrate W1 is exposed to the mixture 21 containing ozone water and hydrochloric acid. According to this method, ozone water has a high redox potential. By increasing the hydrogen ion concentration of the ozone water so as to be equal to or lower than a predetermined pH, the Fe concentration on the substrate can be reduced without performing a treatment using a cleaning liquid that causes a large burden on the waste liquid treatment. In a preferred embodiment, the pH of the mixture 15 is preferably 2 or less. Regarding the pH of this mixture, when the pH is 2 or less, it is preferable for reducing the Fe concentration. In a more preferred embodiment, the concentration of hydrochloric acid (hydrogen chloride) in the mixture 15 is preferably 6% or more. Regarding the hydrochloric acid concentration of this mixture, when it is 6% or more, the Fe concentration on the substrate surface can be suitably reduced. Alternatively, the concentration of hydrochloric acid (hydrogen chloride) in the mixture 15 is preferably 10% or more. When the concentration is 10% or more, it is particularly preferable for reducing the Fe concentration. This is because the higher the hydrochloric acid concentration, the lower the pH, and the lower the pH, the more the ionization of Fe is promoted. Here, the concentration of hydrochloric acid is a mass percent concentration.

  If necessary, after exposing the main surface of the substrate W1 to the mixture 21, in step S103, the substrate W1 can be exposed to pure water UPW. If necessary, after exposing the main surface of the substrate W1 to the mixture 21 or pure water UPW, the substrate W1 can be dried in step S104.

  Further, prior to the exposure step of step S102, the substrate W1 can be exposed to the pure water UPW using the apparatus 27. Independently of this, the substrate W1 can be exposed to the ozone water O3 + UPW using the apparatus 25 prior to the exposure step of step S102. Prior to the exposure step of step S102, the substrate W1 can be exposed to pure water UPW using the device 27, and the substrate W1 can be exposed to ozone water O3 + UPW using the device 25.

  Furthermore, the substrate W1 can be exposed to the pure water UPW using the apparatus 27 after the exposure step of the step S102. Independently of this, the substrate W1 can be exposed to the ozone water O3 + UPW by using the apparatus 25 after the exposing step S102. In addition, after the exposing step S102, the substrate W1 can be exposed to the pure water UPW using the apparatus 27, and the substrate W1 can be exposed to the ozone water O3 + UPW using the apparatus 25.

  Prior to processing on the substrate W1, in step S105, ozone water O3-UPW is generated from the ultrapure water UPW. Next, in step S106, hydrochloric acid or hydrogen chloride is added to the ozone water O3-UPW to generate hydrochloric acid-added ozone water, and a mixed solution is prepared as the mixture 21.

  Hydrochloric acid-added ozone water can be used as the mixture 21. The addition of hydrochloric acid or hydrogen chloride is performed so that the pH of the hydrochloric acid-added ozone water is located in the iron ionization region in the iron probe diagram.

This adjustment (adjustment of hydrochloric acid-added ozone water) is performed as follows, for example. FIG. 3 shows an iron pool diagram. The pool map is divided into three parts. In the first region, iron is inactive. In the second region, iron is passive. In the third region, iron can be ionized. In FIG. 3, the following symbols are used.
HCl: hydrochloric acid.
SPM: Sulfuric acid / hydrogen peroxide mixture, mixing weight ratio (sulfuric acid: hydrogen peroxide = 4: 1).
HPM: hydrochloric acid / hydrogen peroxide / pure water mixture, mixing weight ratio (hydrochloric acid: hydrogen peroxide: pure water = 1: 1: 6), liquid temperature is 70 degrees Celsius.
DHF: dilute hydrofluoric acid, concentration 0.5%.
UPW: Ultrapure water.
O3-UPW: Ozone-added ultrapure water (so-called ozone water), concentration 10-20 ppm.
HCl + O3 + UPW: Mixed solution of hydrochloric acid and ozone-added ultrapure water.
NH3: Ammonia water, concentration 29%.

  The oxidation-reduction potential of ozone water is about 1.2 volts, and this value is larger than the oxidation-reduction potential (about 1 volt) of hydrochloric acid having a concentration of 36%. The redox potential of the mixed liquid SPM and the mixed liquid HPM is greater than the redox potential of ozone water (about 1.2).

  Regarding the concentration of hydrochloric acid and the oxidation-reduction potential, as shown in FIG. 3, 6% hydrochloric acid is in the iron ionization region, and 10% hydrochloric acid is also in the iron ionization region. On the other hand, high concentration of 36% hydrochloric acid is in the iron ionization region. As indicated by the arrow A1, the ultrapure water UPW has a higher redox potential depending on the addition of hydrochloric acid. At a value lower than the redox potential of ultrapure water UPW, the redox potential of the iron ionization region increases at a substantially constant rate as the pH decreases. Therefore, pH 2 is exceeded for the first time at a certain concentration of hydrochloric acid. Therefore, in a dilute hydrochloric acid solution having a hydrochloric acid concentration of 6% and 10%, iron is in a passive region, and iron (Fe) cannot be removed from the main surface of the substrate W1.

  The redox potential of the mixture of HCl and ozone water does not change depending on the HCl concentration. For this reason, the oxidation-reduction potential of the mixture of HCl and ozone water is a substantially constant value as indicated by the arrow A2, although the pH of the mixture decreases as the HCl concentration increases. Since the hydrogen ion concentration of 4% HCl is slightly greater than 2 at the pH value, the iron in this mixed volume enters the passive region. On the other hand, in the mixture of HCl and ozone water (HCl concentrations 6% and 10%), the hydrogen ion concentration is less than 2 in terms of PH value, so iron in this mixed solution enters the ionization region. According to the inventors' estimation, the hydrogen ion concentration (pH) is approximately 2 in a mixture of HCl and ozone water (HCl concentration 4.2%). A mixture of HCl and ozone water is prepared so as to be higher than the hydrogen ion concentration (so that the pH is reduced). In order to avoid an environmental load in the waste liquid treatment in the present embodiment, the HCl concentration in the mixture of HCl and ozone water is preferably 20% or less in consideration of the effect of removing iron from the substrate surface.

  The removal of metal contamination in the wafer process is realized by ionizing the metal adhering to the wafer and dissolving it in the cleaning liquid, and detaching the metal from the wafer. Until now, in order to remove metal from the wafer surface, sulfuric acid / hydrogen peroxide mixture (SPM) or hydrochloric acid / hydrogen peroxide mixture (SC-2), concentrated hydrochloric acid with a concentration of 36%, ammonia with a concentration of 29% High concentration and high temperature chemicals such as water, dilute hydrofluoric acid having a concentration of 0.5%, and hydrofluoric acid / hydrogen peroxide mixture (FPM) have been used.

  In order to reduce the environmental burden, there is a demand for reducing the amount of these chemicals used. In a silicon device, an oxide film can be formed on the surface by immersing silicon in ozone-added ultrapure water. Utilizing this oxide film formation, contaminated metal can be taken in or on the oxide film, and the entire contaminated metal can be removed with hydrofluoric acid using this oxide film as a sacrificial layer. However, in a compound semiconductor device typified by gallium nitride, the generated oxide film (gallium oxide or the like) is thin. Therefore, it cannot function as a sacrificial layer. For this reason, III-V nitrides are still washed with high concentration and high temperature chemicals.

  In view of this problem, the present embodiment has found a method that enables cleaning to remove metal using, for example, a low environmental load cleaning liquid on gallium nitride. Functional water is used as a low environmental load cleaning solution. Functional water can be generated, for example, by adding ozone, hydrogen, ammonia gas, or the like to degassed ultrapure water at a concentration on the order of ppm, and the functional water itself can be discarded as normal water. For removing the metal, for example, ozone-added ultrapure water O3 + UPW having a concentration of 10 ppm is used.

  During the wafer process, copper (Cu) used for the electrode parts of the vapor deposition apparatus, iron (Fe) and nickel (Ni) contained in stainless steel that is the material of the vacuum chamber, and brass piping of the cooling apparatus In some cases, zinc (Zn) contained in the wafer adheres to the wafer due to wear of the apparatus or plasma damage. This becomes metal contamination. The removal of these metals was compared between ozone-added ultrapure water and a conventional high-concentration / high-temperature cleaning solution.

  FIG. 4 shows the effect on cleaning removal of copper (Cu). Referring to FIG. 4, ozone-added ultrapure water O3 + UPW (98%) is equivalent to other cleaning liquids (SPM (100%), NH3 (100%), DHF (96%), FPM (100%)). Have the ability. The numerical value in parentheses indicates the removal rate.

  FIG. 5 shows the effect on cleaning removal of nickel (Ni). Ozone-added ultrapure water O3 + UPW (80%) has the same cleaning ability as other cleaning liquids (SPM (97%), NH3 (98%), DHF (88%), FPM (97%)).

  FIG. 6 shows the effect on cleaning removal of zinc (Zn). Ozone-added ultrapure water O 3 + UPW (97%) has the same cleaning effect as other cleaning liquids (SPM (100%), NH 3 (99%), DHF (100%), FPM (100%)).

  FIG. 7 shows the effect on the cleaning removal of iron (Fe). The cleaning effect (99%) of SPM is remarkably superior to other cleaning liquids (NH3 (65%), DHF (69%), FPM (40%)) including ozone-added ultrapure water (35%).

  According to the inventor's knowledge, the iron removal effect can be understood based on the iron pool chart. Iron ionization is related to the redox potential of the cleaning solution and the hydrogen ion concentration (pH). Therefore, a cleaning solution that can be desorbed from the substrate or wafer by ionizing iron can be derived from the pool chart. FIG. 8 shows the iron removal effect for several cleaning solutions. When a mixture of 6% hydrochloric acid and ozone-added ultrapure water (86%), 10% hydrochloric acid and ozone-added ultrapure water (87%) was used, the removal rate of iron was determined by adding ozone-added ultrapure water (O3 + UPW) ( 35%), showing a cleaning ability close to SPM (99%). That is, iron is not ionized only with ozone-added ultrapure water (O3 + UPW). Therefore, iron is in a passive region, and iron (Fe) cannot be removed from the main surface of the substrate W1. However, iron can be ionized by adjusting the pH by adding hydrochloric acid (hydrogen chloride) to ultrapure water so that the pH value is 2 or less as the hydrogen ion concentration. In particular, the higher the hydrochloric acid concentration, the lower the pH value (the higher the hydrogen ion concentration), and the lower the pH value, the more the ionization of Fe is promoted. In the ionization of iron, iron as a contaminant is ionized and desorbed from the wafer. Therefore, by using a mixture of ultrapure water and hydrochloric acid to which ozone is added without using high-concentration and high-temperature SPM as in the past, contamination of metals such as iron, copper, nickel, and zinc adhering to the wafer process. It becomes possible to remove the substance. The use of a mixture of ultrapure water and hydrochloric acid to which ozone is added realizes a reduction in environmental burden, which has been a conventional problem.

  In this method, ozone water is generated from ultrapure water, and hydrochloric acid is added to the ozone water to generate hydrochloric acid-added ozone water to prepare a mixed solution as a mixture. The addition of hydrochloric acid is preferably performed such that the pH of the ozone-added ozone water is located in the iron ionization region in the iron probe diagram.

  In addition, the method for removing iron according to the present embodiment is a method that can also be applied to wafer manufacturing and device processes of other compound semiconductor materials, that is, gallium arsenide, indium phosphide, aluminum nitride, silicon carbide, and the like. In addition, since a sacrificial layer is not formed unlike silicon, fluctuations in the film thickness and surface roughness of the epitaxial layer can be suppressed.

  The present invention is not limited to the specific configuration disclosed in the present embodiment.

  As described above, according to the present embodiment, it is possible to provide a method for processing a substrate capable of reducing the environmental load in waste liquid processing.

DESCRIPTION OF SYMBOLS 11 ... System, 13 ... Ultrapure water generator, UPW ... Ultrapure water, O3-UPW ... Ozone water, 15 ... Ozone water generator, 17 ... Hydrochloric acid (or hydrogen chloride) reservoir, 19 ... Mixer, 21 ... Mixture, 23 ... first processing device, 25 ... second processing device, 27 ... third processing device.

Claims (6)

A method of processing a substrate, comprising:
Preparing a substrate having a principal surface of a III-V compound semiconductor;
Exposing the main surface of the substrate to a mixture containing ozone water and hydrochloric acid whose hydrogen ion concentration is adjusted to a predetermined pH or lower;
With
A method of processing a substrate, wherein the III-V compound semiconductor comprises III-V nitride.   The method of treating a substrate according to claim 1, wherein the pH of the mixture is 2 or less.   The method for processing a substrate according to claim 1, wherein the concentration of hydrochloric acid in the mixture is 6% or more.   The method for processing a substrate according to claim 1, wherein the hydrochloric acid concentration in the mixture is 10% or more. Producing ozone water from ultra pure water;
Adding hydrochloric acid to the ozone water to generate hydrochloric acid-added ozone water, and preparing a mixed solution as the mixture;
In addition,
The addition of the hydrochloric acid is performed such that the hydrogen ion concentration (pH) of the hydrochloric acid-added ozone water is located in an iron ionization region in an iron probe diagram. A method of processing the described substrate. The group III-V compound semiconductor _is composed of _{In X Al Y Ga 1-X} -Y N (0 ≦ X ≦ 1,0 ≦ Y ≦ 1), according to any one of claims 1 to 5 Of processing a processed substrate.

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