JP2013093632A - Gaas semiconductor substrate and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a GaAs semiconductor substrate having a surface clean enough to remove impurities and oxides on the surface by at least thermal cleaning of a substrate.SOLUTION: In a GaAs semiconductor substrate 10, the constituent atom ratio Ga/As of all Ga atoms to all As atoms in the surface layer 10a of a GaAs semiconductor substrate 10, calculated by X-ray photoelectron spectroscopy by using the 3d electron spectrum of a Ga atom and an As atom measured under conditions that the photoelectron extraction angle θ is 10°, is 0.5-0.9, the ratio of As atoms bonded to O atoms to all Ga atoms and all As atoms (As-O)/{(Ga)+(As)} in the surface layer 10a is 0.15-0.35, and the ratio of Ga atoms bonded to O atoms to all Ga atoms and all As atoms (Ga-O)/{(Ga)+(As)} in the surface layer 10a is 0.15-0.35.

Description

  The present invention relates to a GaAs semiconductor substrate having a clean surface, which is suitably used as a substrate for various semiconductor devices such as light emitting devices, electronic devices, and semiconductor sensors, and a method for manufacturing the same.

  A GaAs semiconductor substrate suitably used as a substrate for various semiconductor devices such as light-emitting devices, electronic devices, and semiconductor sensors has dangling bonds on its surface, so that impurities may adhere to the surface or oxidation may occur. An object is formed and its surface is altered. When a semiconductor device is fabricated by growing a semiconductor layer on a GaAs semiconductor substrate having impurities attached or oxides formed on the surface, the impurity or oxide is taken into the semiconductor device, and the device Degrading properties.

Therefore, before the semiconductor layer is grown on the GaAs semiconductor substrate, the GaAs semiconductor substrate is formed on the surface of the GaAs semiconductor substrate in order to remove impurities adhering to the surface of the GaAs semiconductor substrate and the formed oxide. Heating to about ˜600 ° C. (thermal cleaning of the surface of the GaAs semiconductor substrate (thermal cleaning)) is performed. However, the surface of the GaAs semiconductor substrate is very easily oxidized, and an oxide that cannot be removed by thermal cleaning of the surface can be formed. In particular, Ga ₂ O _3, which is an oxide of Ga, has an extremely high melting point of 1795 ° C. and cannot be removed by ordinary thermal cleaning at about 500 to 600 ° C.

  Attempts have therefore been made to provide a GaAs semiconductor substrate having a clean surface free of impurities and oxide formation. For example, Japanese Patent Application Laid-Open No. 07-201689 (hereinafter referred to as Patent Document 1) discloses a semiconductor wafer with a protective film in which a Langmuir / Projet film is formed on the surface of a GaAs wafer and a polymer film is coated thereon. However, since the semiconductor wafer with a protective film of Patent Document 1 uses a surfactant made of a high molecular weight hydrocarbon compound, the surface of the semiconductor wafer is not affected by thermal cleaning before the growth of the semiconductor layer. There is a problem that carbon atoms and / or oxygen atoms derived from the surfactant remain, and the characteristics of the semiconductor device are reduced.

Japanese Laid-Open Patent Publication No. 04-048074 (hereinafter referred to as Patent Document 2) describes the atomic ratio (Ga / As) of gallium and arsenic within 10 nm from the substrate surface and the gallium and arsenic atoms on the (110) cleavage plane. A final polished GaAs compound semiconductor substrate having a difference from the number ratio (Ga / As) _C of ± 0.2 or less is disclosed. However, even if (Ga / As) is brought close to (Ga / As) 2 _C, that is, the stoichiometric composition ratio, if a large amount of Ga is present on the surface of the substrate, the oxidation causes Ga ₂ O ₃ ( The melting point is 1795 ° C.) and cannot be removed by ordinary thermal cleaning at about 500 to 600 ° C.

Japanese Patent Application Laid-Open No. 07-201689 Japanese Patent Laid-Open No. 04-048074

  An object of the present invention is to provide a GaAs semiconductor substrate having a clean surface to the extent that impurities and oxides on the surface can be removed at least by thermal cleaning of the substrate.

  The present invention relates to all As atoms in the surface layer of a GaAs semiconductor substrate, calculated by X-ray photoelectron spectroscopy using a 3d electron spectrum of Ga atoms and As atoms measured at a photoelectron extraction angle of 10 °. The constituent atomic ratio (Ga) / (As) of all Ga atoms is 0.5 or more and 0.9 or less, and the ratio of As atoms bonded to O atoms to all Ga atoms and all As atoms in the surface layer (As -O) / {(Ga) + (As)} is 0.15 or more and 0.35 or less, and the ratio of Ga atoms bonded to O atoms to all Ga atoms and all As atoms in the surface layer (Ga--) O) / {(Ga) + (As)} is 0.15 or more and 0.35 or less.

In the GaAs semiconductor substrate according to the present invention, the surface roughness RMS can be 0.3 nm or less. Further, the concentration of the alkaline substance adhering to the surface can be set to 0.4 ng / cm ² or less.

  The present invention also includes a step of polishing the surface of a GaAs semiconductor wafer, at least one alkali cleaning step of cleaning the polished surface with an alkali cleaning liquid, and 0.3 ppm to 0.5 mass of the alkali cleaned surface. And an acid cleaning step of cleaning with an acid cleaning solution containing 1% acid.

  In the method for manufacturing a GaAs semiconductor substrate according to the present invention, the alkali cleaning liquid may contain an organic alkali compound. Moreover, the acid cleaning liquid can contain at least one selected from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid, and carbonic acid. Further, after the acid cleaning step, a drying step of drying the acid cleaned surface is further included, and the drying step can be performed by scattering the acid cleaning liquid remaining on the surface by rotating the GaAs semiconductor wafer. it can. Further, after the acid cleaning step, a pure water cleaning step of cleaning the acid cleaned surface with pure water having a dissolved oxygen concentration of 100 ppb or less can be further included. Furthermore, after the pure water cleaning step, the method further includes a drying step of drying the surface that has been cleaned with pure water, and the drying step scatters the pure water remaining on the surface by rotating the GaAs semiconductor wafer in the atmosphere. This can be done.

  According to the present invention, it is possible to provide a GaAs semiconductor substrate having a clean surface to the extent that impurities and oxides on the surface can be removed at least by thermal cleaning of the substrate.

It is a schematic sectional drawing explaining the X-ray photoelectron spectroscopy applied to a GaAs semiconductor substrate. It is the schematic which shows an example of the 3d electron spectrum of As atom in the surface layer of the GaAs semiconductor substrate measured by X-ray photoelectron spectroscopy. It is the schematic which shows an example of the 3d electron spectrum of Ga atom in the surface layer of the GaAs semiconductor substrate measured by X-ray photoelectron spectroscopy. It is a flowchart which shows one Embodiment of the manufacturing method of the GaAs semiconductor substrate concerning this invention. It is the schematic which shows other embodiment of the manufacturing method of the GaAs semiconductor substrate concerning this invention. Here, (a) shows an alkali cleaning step, (b) shows a first pure water cleaning step, (c) shows an acid cleaning step, (d) shows a second cleaning step, ( e) shows a drying process. It is the schematic which shows the relationship between Ga / As ratio in the surface layer of a board | substrate, and the haze intensity | strength after epitaxial layer growth. It is the schematic which shows the relationship between Ga / As ratio in the surface layer of a board | substrate, and the interface oxygen concentration between a board | substrate and an epitaxial layer. It is the schematic which shows the relationship between the surface ammonia density | concentration immediately after washing | cleaning of a board | substrate, and the interface oxygen density | concentration between a board | substrate and an epitaxial layer.

(Embodiment 1)
One embodiment of a GaAs semiconductor substrate according to the present invention is described with reference to FIGS. 1 to 3. Ga atoms and As measured by X-ray photoelectron spectroscopy (XPS) with a photoelectron extraction angle θ of 10 °. The constituent atomic ratio (Ga) / (As) (hereinafter referred to as (Ga) / (As) ratio of all Ga atoms to all As atoms in the surface layer 10a of the GaAs semiconductor substrate 10 calculated using the 3d electron spectrum of atoms. The ratio of As atoms bonded to O atoms with respect to all Ga atoms and all As atoms in the surface layer 10a (As-O) / {(Ga) + ( As)} (hereinafter also referred to as As-O) / {(Ga) + (As)} ratio) is 0.15 or more and 0.35 or less, and O atoms relative to all Ga atoms and all As atoms in surface layer 10a Ga bonded to The atomic ratio (Ga-O) / {(Ga) + (As)} (hereinafter also referred to as (Ga-O) / {(Ga) + (As)} ratio) is 0.15 or more and 0.35 or less. It is characterized by being.

By making the (Ga) / (As) ratio smaller than its stoichiometric composition ratio (ie, (Ga) / (As) = 1/1), it is usually about 500 to 600 ° C. on the substrate surface. It is possible to prevent the formation of oxides that cannot be removed by thermal cleaning. When the (Ga) / (As) ratio is less than 0.5, excess arsenic on the surface of the substrate is deposited, and arsenic oxide or metal arsenic is formed. Here, metal arsenic is more difficult to sublimate than arsenic oxide and is more difficult to remove by thermal cleaning. On the other hand, when the Ga) / (As) ratio is larger than 0.9, an oxide of Ga (high melting point oxide such as Ga ₂ O ₃ ) is easily formed. Further, when the (As-O) / {(Ga) + (As)} ratio is smaller than 0.15, As atoms and impurities are easily bonded, and when it is larger than 0.35, arsenic oxide is easily formed. Become. Further, it is difficult to manufacture a substrate having a (Ga—O) / {(Ga) + (As)} ratio smaller than 0.15, and if it is larger than 0.35, a gallium oxide (for example, Ga ₂ O ₃ or the like). Refractory oxide) is easily formed.

  Therefore, in the surface layer 10a of the GaAs semiconductor substrate, the (Ga) / (As) ratio is 0.5 or more and 0.9 or less, and the (As-O) / {(Ga) + (As)} ratio is 0.15 or more. When the ratio is 0.35 or less and the (Ga—O) / {(Ga) + (As)} ratio is 0.15 or more and 0.35 or less, impurities attached to the surface and the surface are formed. A GaAs semiconductor substrate having a small amount of oxide and having a surface clean enough to remove such impurities and oxides by general thermal cleaning at about 500 to 600 ° C. can be obtained.

  Here, the (Ga) / (As) ratio, (As-O) / {(Ga) + (As)} ratio, and (Ga-O) / {(Ga) + (As)} ratio described above are Is also calculated by X-ray photoelectron spectroscopy using the 3d electron spectra of Ga atoms and As atoms measured under conditions where the photoelectron take-off angle θ is 10 °. Hereinafter, X-ray photoelectron spectroscopy and (Ga) / (As) ratio, (As-O) / {(Ga) + (As)} ratio and (Ga-O) / {(Ga) + (As)} ratio The calculation method of will be described.

  Referring to FIG. 1, X-ray photoelectron spectroscopy (XPS) is a method in which atoms 10 excited by X-ray 1 are irradiated when X-ray 1 is irradiated on surface 10 s of a solid sample (GaAs semiconductor substrate 10). A method of analyzing the type and bonding state of atoms in the surface layer 10a of the solid sample (GaAs semiconductor substrate 10) using the phenomenon that shell electrons are emitted as photoelectrons 5.

  Here, referring to FIG. 1, in the X-ray photoelectron spectroscopy, when the surface 10 s of the GaAs semiconductor substrate 10 is irradiated with the X-ray 1, the Ga constituting the GaAs semiconductor substrate 10 excited by the X-ray 1 is formed. Inner-shell electrons of atoms and As atoms, for example, 3d electrons, are emitted as photoelectrons 5 from the surface 10s of the substrate. Accordingly, the depth d from the surface 10s of the surface layer 10a that can be analyzed in the X-ray photoelectron spectroscopy is determined by the depth until the excited 3d electrons are subjected to inelastic scattering and lose energy. This depth d is also called an electron escape depth d, and is defined as a distance in a solid (GaAs semiconductor substrate 10) in which an electron having a certain energy can travel without losing the energy. That is, Ga atoms and As atoms in the inner layer 10b inside the surface layer 10a in the GaAs semiconductor substrate 10 cannot be analyzed because their photoelectrons are not emitted from the surface even when excited by X-rays. The X-ray source in the X-ray photoelectron spectroscopy is not particularly limited, but Kα rays of Al atoms and Kα rays of Mg atoms are generally used.

It can be considered that photoelectrons are emitted from the surface almost isotropically, but the electron escape depth d differs depending on the photoelectron take-off angle θ. Referring to FIG. 1, the electron escape depth d is expressed by the following equation (1) using the electron mean free path λ and the photoelectron extraction angle θ.
d = λ × sin θ (1)
It is represented by

  3d electron spectra of As atoms and Ga atoms in the surface layer 10a of the GaAs semiconductor substrate 10 measured using a Kα ray of Al atoms as an X-ray source and a photoelectron extraction angle θ of 10 ° are shown in FIGS. 2 and 3, respectively. Shown in

  Referring to FIG. 2, a broad 3d electron peak P (As) having two peaks appeared in the 3d electron spectrum of the As atom. This 3d electron peak P (As) is divided into three peaks of P (As-O), P (As-1) and P (As-2) in order from the higher photoelectron binding energy. Here, the difference in the binding energy of the photoelectrons of the three peaks indicates the difference in the bonding state of As atoms. Of the three peaks, the P (As-O) peak is considered to be the 3d electron peak of the As atom bonded to the O atom. In addition, each peak area of P (As), P (As-O), P (As-1), and P (As-2) is proportional to the amount of As atoms in each bonded state.

  Referring to FIG. 3, a wide 3d electron peak P (Ga) appeared in the 3d electron spectrum of Ga atoms. This 3d electron peak P (Ga) is divided into two peaks of P (Ga-O) and P (Ga-1) in order from the higher photoelectron binding energy. Here, the difference in the binding energy of the photoelectrons at the two peaks indicates the difference in the bonding state of As atoms. Of the two peaks, the P (Ga—O) peak is considered to be a 3d electron peak of a Ga atom bonded to an O atom. In addition, each peak area of P (Ga), P (Ga—O), and P (Ga−1) is proportional to the amount of Ga atoms in each bonded state.

Here, in the X-ray photoelectron spectroscopy, the peak of each atom to be measured has a different relative intensity between the atoms, and the measurement sensitivity in each measurement can be different. For this reason, in order to quantitatively compare each peak area between different atoms, each peak area obtained from the measurement chart is expressed by the following equation (2).
(Peak area of P (M)) = (P (M) determined from the chart)
Peak area) × s (M) / f (M) (2)
The peak area corrected by is used. In formula (2), P (M) is the peak of the M atom, f (M) is the relative intensity of the electron peak of the M atom, and s (M) is the measurement sensitivity when measuring the peak of the M atom. Indicates. Here, the relative intensity f (Ga) of the Ga atom 3d electron peak is 0.42, and the As atom 3d electron peak f (As) is 0.48. The measurement sensitivity s (M) is read from the operation panel of the apparatus at each measurement. In the present application, each peak area of each atom means a value obtained by correcting each peak area obtained from the measurement chart of each atom by the equation (2).

1 to 3, the constituent atomic ratio ((Ga) / (As) ratio) of all Ga atoms to all As atoms in the surface layer 10a of the GaAs semiconductor substrate 10 is expressed by the following equation (3).
(Ga) / (As) = (P (Ga) peak area)
/ (P (As) peak area) (3)
Is calculated by

1 and 2, the ratio of As atoms bonded to O atoms to all Ga atoms and all As atoms in surface layer 10a of GaAs semiconductor substrate 10 (As-O) / {(Ga ) + (As)} ratio) is given by the following formula (4)
(As-O) / {(Ga) + (As)} = (P (As-O) peak area)
/ {(P (Ga) peak area) + (P (As) peak area)}
... (4)
Is calculated by

1 and 3, the ratio of Ga atoms bonded to O atoms with respect to all Ga atoms and all As atoms in the surface layer 10a of the GaAs semiconductor substrate 10 ((Ga-O) / {(Ga ) + (As)} ratio) is given by the following formula (5)
(Ga-O) / {(Ga) + (As)} = (P (Ga-O) peak area)
/ {(P (Ga) peak area) + (P (As) peak area)}
... (5)
Is calculated by

  Referring to FIG. 1, in the GaAs semiconductor substrate 10 of the present embodiment, the surface roughness RMS of the surface 10s is preferably 0.3 nm or less. When the surface roughness RMS of the surface of the GaAs semiconductor substrate is larger than 0.3 nm, the surface area in contact with the air becomes large and the air is easily contaminated. Here, the surface roughness RMS means the root mean square roughness, and is expressed by the square root of the value obtained by averaging the squares of the distances from the average surface to the measurement surface. The surface roughness RMS is measured by an atomic force microscope (AFM) or the like.

Referring to FIG. 1, in the GaAs semiconductor substrate 10 of the present embodiment, the concentration of the alkaline substance adhering to the surface 10 is preferably 0.4 ng / cm ² or less. When the amount of the alkaline substance adhering to the surface is more than 0.4 ng / cm ² , the oxidation of the surface is promoted, the number of O atoms at the interface between the substrate and the epitaxial layer grown on the substrate increases, and the characteristics of the semiconductor device Decreases.

(Embodiment 2)
Referring to FIG. 4, one embodiment of a method for manufacturing a GaAs semiconductor substrate according to the present invention is a polishing step S1 for polishing the surface of a GaAs semiconductor wafer, and at least one time for cleaning the polished surface with an alkaline cleaning liquid. It includes an alkali cleaning step S2 and an acid cleaning step S3 for cleaning the alkali cleaned surface with an acid cleaning solution containing 0.3 ppm to 0.5% by mass of acid.

  Foreign matters and / or impurities in the polishing agent adhering to the surface of the semiconductor wafer by polishing can be removed by at least one alkali cleaning. In addition, impurities in the alkali cleaning agent attached to the surface of the semiconductor wafer by alkali cleaning can be removed by acid cleaning. An appropriate concentration of acid in the acid cleaning solution optimizes the ratio of Ga atoms to As atoms on the surface, and suppresses the formation of excess gallium oxide.

  Hereinafter, with reference to FIG. 4, each process is demonstrated more concretely. The polishing step S1 is a step for polishing the surface of the GaAs semiconductor wafer. By the polishing step S1, the surface of the GaAs semiconductor wafer is mirror-finished. The polishing method in the polishing step S1 is not particularly limited, and various polishing methods such as mechanical polishing and chemical mechanical polishing are used.

  The alkali cleaning step S2 is a step of cleaning the polished surface of the GaAs semiconductor wafer at least once using an alkali cleaning liquid. By the alkali cleaning step S2, foreign matters and / or impurities attached to the surface of the GaAs semiconductor wafer by the polishing step S1 are removed. Here, the alkali cleaning agent is not particularly limited, but is an organic alkali compound that does not contain a metal element that affects electrical characteristics, such as quaternary ammonium hydroxides such as choline and tetramethylammonium hydroxide (TMAH). An aqueous solution containing 0.1 to 10% by mass of quaternary pyridinium hydroxide or the like is preferably used.

  The acid cleaning step S3 is a step for cleaning the alkali-cleaned surface of the GaAs semiconductor wafer using an acid cleaning liquid. By the acid cleaning step S3, impurities attached to the surface of the semiconductor wafer by the alkali cleaning step are removed. In the acid cleaning step 3S, by using an acid cleaning solution containing 0.3 ppm to 0.5% by mass of acid, the (Ga) / (As) ratio in the surface layer is 0.5 or more and 0.9 or less, (As -O) / {(Ga) + (As)} ratio is 0.15 or more and 0.35 or less, and (Ga-O) / {(Ga) + (As)} ratio is 0.15 or more and 0.35 or less. A GaAs semiconductor substrate is obtained.

Here, if the acid concentration in the acid cleaning solution is less than 0.3 ppm, the wafer surface modification action is reduced, and the influence of carbon dioxide (CO ₂ ) gas dissolved in the acid cleaning solution from the atmospheric atmosphere is increased, resulting in a finished wafer. It causes the chemical composition of the surface to vary. On the other hand, if the acid concentration of the acid cleaning liquid is greater than 0.5% by mass, the stoichiometry of the wafer surface is greatly increased by the acid and becomes As rich. However, when rinsing with pure water, drying or transporting, In the portion where a small amount of pure water adheres, the stoichiometry of that portion changes to the Ga-rich side due to the presence of a small amount of carbon dioxide gas dissolved in the pure water, and as a result, due to variations in conditions during rinsing with pure water, the wafer Variation in chemical composition increases in-plane and between wafers. In particular, it is significantly affected when performing wafer drying in the atmosphere. Further, in the case of excessive As rich, Ga—As bonds are reduced, resulting in an adverse effect of increasing oxygen on the wafer surface.

The acid cleaning liquid is not particularly limited. However, the acid cleaning liquid does not contain elements that have high cleaning power and affect electrical characteristics (for example, metal elements, sulfur, etc.), and when liquid droplets are scattered in the equipment, the acid cleaning liquid contains acid. From the point of view that it is difficult to cause serious secondary pollution and equipment deterioration by evaporating components, from the group consisting of hydrofluoric acid (HF), hydrochloric acid (HCl), nitric acid (HNO ₃ ) and nitrous acid (HNO ₂ ). It is preferable to include at least one selected. It is also preferable to include an organic acid such as acetic acid.

Further, the acid cleaning liquid from a high detergency standpoint, more preferably contains 0.3ppm~0.3 mass% of hydrogen peroxide (H ₂ O _2). If the concentration of hydrogen peroxide (H ₂ O ₂ ) in the acid cleaning solution is less than 0.3 ppm, the effect of dissolved oxygen in the acid cleaning solution increases and the effect of promoting the removal of impurities on the wafer surface decreases. On the other hand, if the concentration of H ₂ O ₂ in the acid cleaning solution is larger than 0.3% by mass, the etching rate on the wafer surface becomes too high and an etching step is generated on the wafer surface, which is not suitable for cleaning. From such a viewpoint, the concentration of H ₂ O ₂ is preferably 0.3 ppm to 0.3% by mass.

  Referring to FIG. 4, in the method for manufacturing a GaAs semiconductor substrate of the present embodiment, the acid cleaning step S <b> 3 holds the GaAs semiconductor wafer so that its main surface is horizontal and rotates it at 100 to 800 rpm. It is preferable to carry out by supplying an acid cleaning liquid to the surface of the GaAs semiconductor wafer. By supplying the acid cleaning solution to the surface of the GaAs semiconductor wafer while rotating it, the surface of the surface can be efficiently cleaned with acid while forming a film of the acid cleaning solution on the surface and suppressing oxidation of the surface. If the rotational speed of the GaAs semiconductor wafer is lower than 100 rpm, the cleaning efficiency cannot be increased, and if it is higher than 800 rpm, the cleaning liquid film cannot be formed on the surface and the surface may be in contact with the atmosphere and oxidized. .

  Referring to FIG. 4, in the method for manufacturing a GaAs semiconductor substrate of the present embodiment, the acid-cleaned surface of the GaAs semiconductor wafer is treated with pure water after the acid cleaning step S3, preferably immediately after the acid cleaning step S3. It is preferable to include the pure water washing | cleaning process S4 wash | cleaned using. The cleaning method in the pure water cleaning step S4 is not particularly limited, but the acid-cleaned surface of the GaAs semiconductor wafer may be cleaned with pure water having a dissolved oxygen concentration (DO) of 100 ppb or less for 5 minutes or less. preferable. Oxidation of the surface can be suppressed by washing with pure water having a low dissolved oxygen concentration of 100 ppb or less in a short time of 5 minutes or less. Here, the dissolved oxygen concentration of pure water is more preferably 50 ppb or less from the viewpoint of lower oxidizability. From the viewpoint of few impurities, the total organic carbon (TOC) of pure water is preferably 40 ppb or less.

  Referring to FIG. 4, in the method for manufacturing a GaAs semiconductor substrate according to this embodiment, the pure water cleaning step S4 holds the GaAs semiconductor wafer so that its main surface is horizontal and rotates at 100 to 800 rpm. However, it is preferable to carry out by supplying pure water to the surface of the GaAs semiconductor wafer. By supplying pure water to the surface of the GaAs semiconductor wafer while rotating it, the surface can be efficiently cleaned with acid while forming a pure water film on the surface and suppressing surface oxidation. If the rotational speed of the GaAs semiconductor wafer is lower than 100 rpm, the cleaning efficiency cannot be increased. If the rotational speed is higher than 800 rpm, a pure water film cannot be formed on the surface, and the contact between the surface and the atmosphere becomes direct and intense. , Oxidation is promoted.

Further, referring to FIG. 4, in the manufacturing method of the GaAs semiconductor substrate of the present embodiment, after the acid washing step S3 or pure water washing step S 4, preferably immediately after the acid washing step S3 or pure water cleaning step S4 The method further includes a drying step S5 for drying the surface of the GaAs semiconductor wafer, and the drying step S5 is performed by scattering the acid cleaning solution or pure water remaining on the surface by rotating the GaAs semiconductor wafer at 2000 rpm or more. Is preferred. The wafer surface can be uniformly and efficiently dried by rotating the GaAs semiconductor wafer at a high speed of 2000 rpm or more to disperse the acid cleaning solution or pure water on the surface.

(Embodiment 3)
In another embodiment of the method for manufacturing a GaAs semiconductor substrate according to the present invention, referring to FIG. 5, the polished surface of the GaAs semiconductor wafer 11 is first cleaned with an organic solvent such as alcohol and then washed with an alkaline cleaning solution 21. At least one alkali cleaning step (FIG. 5A) for cleaning, and an acid cleaning step for cleaning the alkali cleaned surface with an acid cleaning solution 23 containing 0.3 ppm to 0.5% by mass of acid (FIG. 5 ( c)). The present embodiment is a mode in which the GaAs semiconductor wafer 11 is cleaned in a batch manner, and a first pure water cleaning step (in which the surface cleaned with alkali between the alkali cleaning step and the acid cleaning step is cleaned with pure water 25 ( 5 (b)), a second pure water cleaning step (FIG. 5 (d)) for cleaning the acid cleaned surface after the acid cleaning step with pure water, and pure water cleaning after the second pure water cleaning step. And a step of drying pure water remaining on the formed surface (FIG. 5E).

  Here, in the drying step (FIG. 5E), the pure water remaining on the surface of the GaAs semiconductor wafer is scattered by fixing the GaAs semiconductor wafer 11 to the wafer holder 31 in the centrifuge 30 and rotating it at a high speed. It is preferable to carry out by carrying out. Further, the alkali cleaning liquid used for the alkali cleaning, the acid cleaning liquid used for the acid cleaning, and the pure water used for the pure water cleaning are the same as in the second embodiment.

  Here, as the acid of the acid cleaning solution, an inorganic acid such as hydrofluoric acid, hydrochloric acid, nitric acid, nitrous acid, etc. from the viewpoint of having a high detergency and not including an element (for example, metal element, sulfur, etc.) that affects electrical characteristics Organic acids such as acetic acid, citric acid and malic acid are preferably used. A combination of two or more of these acids, for example, a combination of hydrochloric acid and nitric acid is preferably used. Moreover, it is preferable that these acid concentrations are 0.3 ppm-0.5 mass% similarly to the case of Embodiment 2.

In addition to the method of diluting a high-concentration acid aqueous solution, these acid addition methods include acidic gases such as hydrogen chloride (HCl) gas, carbon dioxide (CO ₂ ) gas, and nitrogen oxide (NO _x ) gas. Can be carried out by a method of dissolving in water.

(Example A)
1. Production of GaAs semiconductor substrate (1) Production of GaAs semiconductor wafer (wafer production process)
Three GaAs semiconductor wafers were fabricated by slicing a GaAs semiconductor crystal grown by the vertical Bridgman (VB) method with a wire saw and grinding its edge to adjust its outer shape. Further, in order to remove the saw mark generated by the wire saw, the main surface of the wafer was ground with a surface grinder, and the outer peripheral chamfered portion was polished with a rubber grindstone.

(2) Polishing of GaAs semiconductor wafer surface (polishing process)
Next, in a clean room, the surface of each GaAs semiconductor wafer was polished with a hard polishing cloth with a mixture of a chlorine-based abrasive and silica powder. Next, the surface of each GaAs semiconductor wafer was polished with INSEC NIB abrasive (manufactured by Fujimi Abrasive Co., Ltd.) to make a mirror surface. On the surface of each mirror-finished GaAs semiconductor wafer, polishing cloth waste, foreign matter in the abrasive, and the like were attached.

(3) GaAs semiconductor wafer surface alkali cleaning (alkali cleaning process)
Next, each GaAs semiconductor wafer having foreign matter attached to the surface is immersed in a 0.1 to 10% by mass choline aqueous solution, and an ultrasonic wave of 0.9 to 1.5 MHz is applied to the aqueous solution for 3 to 12 minutes. The surface was washed with alkali. Next, the surface of each GaAs semiconductor wafer was washed with pure water and then dried with a spin dryer. The surface roughness RMS of the surface of the obtained GaAS semiconductor wafer was 0.08 to 0.15 nm as measured by AFM within a range of 0.5 μm × 0.5 μm.

(4) Acid cleaning of GaAs semiconductor wafer surface (acid cleaning process)
Next, each GaAs semiconductor wafer was placed in a cleaning apparatus having a mechanism capable of rotating and holding so that its main surface is horizontal. At this time, each GaAs semiconductor wafer was held by a centrifugal chuck disposed in the cleaning apparatus. The centrifugal chuck is formed of a low dust generation resin such as polyamide resin or polyether ether ketone resin.

While rotating each GaAs semiconductor wafer at 300 to 600 rpm, an aqueous solution containing 0.1 to 0.6% by mass of HF and 0.05 to 0.3% by mass of H ₂ O ₂ as an acid cleaning solution is formed on the surface thereof. Feed and acid wash for 6-20 seconds.

(5) Pure water cleaning of GaAs semiconductor wafer surface (pure water cleaning process)
Next, while rotating the respective GaAs semiconductor wafer in 300～600Rp m, on its surface, by supplying pure water total organic carbon 1~40ppb in dissolved oxygen concentration 0.1～50Ppb, 15 to 30 seconds pure water Washed. Next, the pure water to which an ultrasonic wave of 0.5 to 2.5 MHz is applied is removed from the pure water nozzle whose tip is at a distance of 0.5 to 2.5 cm from the wafer and swings in the radial direction of the wafer. The wafer was supplied to the wafer, and the surface was ultrasonically cleaned with the pure water for 8 to 20 seconds.

(6) Drying of GaAs semiconductor wafer surface (drying process)
Next, the supply of pure water was stopped, and the surface of the GaAs semiconductor wafer was dried by rotating the GaAs semiconductor wafer at 2500 rpm for 15 to 30 seconds to obtain three GaAs semiconductor substrates.

2. 1. Analysis of surface layer of GaAs semiconductor substrate Referring to FIG. 1, an X-ray photoelectron spectrometer (PHI ESCA5400MC) is used, an Al atom Kα ray is used as an X-ray source, and a photoelectron extraction angle θ is set to 10 °. Then, the spectrum of 3d electrons of As atoms and Ga atoms in the surface layer 10a of each obtained GaAs semiconductor substrate 10 was measured.

  2 and 3, peaks P (As) and P (As-O) appearing in the 3d electron spectrum of As atoms in each GaAs semiconductor substrate, and peak P (appearing in the 3d electron spectrum of Ga atoms, Based on Ga) and P (Ga—O), using the above formulas (2) to (5), the Ga / As ratio in each GaAs semiconductor substrate, (As—O) / {(Ga) + (As) } Ratio and (Ga-O) / {(Ga) + (As)} ratio were calculated. For each of the GaAs semiconductor substrates, the Ga / As ratio is 0.5 to 0.9, the (As—O) / {(Ga) + (As)} ratio is 0.15 to 0.35, (Ga− The O) / {(Ga) + (As)} ratio was in the range of 0.15 to 0.35.

3. Growth of Epitaxial Layer on GaAs Semiconductor Substrate On each of the above three GaAs semiconductor substrates, Al _x Ga _1-x N (x = 0.2) Three semiconductor layers were grown to obtain three epitaxial layer-attached GaAs semiconductor substrates.

4). Evaluation of physical properties of GaAs semiconductor substrate with epitaxial layer Referring to FIG. 6, the surface of each GaAs semiconductor substrate with an epitaxial layer (three points of Example A in FIG. 6) was irradiated with Ar laser after the growth of the epitaxial layer. The haze strength (haze strength after growth of the epitaxial layer) obtained by condensing the light obtained by irregular reflection was as very low as 1.1 to 4.0 ppm, and a good plane was obtained. That is, it was found that the surface of the epitaxial layer formed on the GaAs semiconductor substrate having a Ga / As ratio of 0.9 or less was good.

Further, referring to FIG. 7, for each GaAs semiconductor substrate with an epitaxial layer (three points of Example A in FIG. 7), the oxygen concentration (interface oxygen concentration) at the interface portion between the GaAs semiconductor substrate and the epitaxial layer is 2 When measured by secondary ion mass spectrometry (SIMS), the concentration was as low as 1 × 10 ¹⁸ cm ⁻³ or less. That is, it was found that the interface oxygen concentration between the GaAs semiconductor substrate having a Ga / As ratio of 0.9 or less and the epitaxial layer formed thereon was very low.

Further, the ammonia concentration on the surface was adjusted in the same manner as in Example A except that an aqueous solution containing 0.05% by mass of HF and 0.1% by mass of H ₂ O ₂ was used as the acid cleaning solution in the acid cleaning step. Three GaAs semiconductor substrates of four types of 0.2 ng / cm ² , 0.4 ng / cm ² , 0.5 ng / cm ² and 1 ng / cm ² were obtained. One of them was used for quantitative determination of the ammonia concentration on the surface. Here, the ammonia concentration on the surface of the substrate was quantified by immersing the substrate in pure water and then measuring the ammonia concentration of the pure water by ion chromatography. In one sheet, an epitaxial layer was grown on the substrate in the same manner as in Example A immediately after the acid cleaning step, the pure water cleaning step, and the drying step. One sheet was left for 2 hours at 22-25 ° C. in an ammonia atmosphere of 20 μg / m ³ after the acid cleaning step, the pure water cleaning step and the drying step, and then an epitaxial layer was formed on the substrate in the same manner as in Example A. Grown up.

  Referring to FIG. 8, even when the surface ammonia concentration immediately after the cleaning of the substrate is low, the substrate and the epitaxial layer formed after the substrate are left by being left in an atmosphere containing ammonia (for example, in the air). The interfacial oxygen concentration between the substrates was higher than the interfacial oxygen concentration between the substrate and the epitaxial layer formed immediately after cleaning. This is presumably because an alkaline substance such as ammonia in the atmosphere reacts with F atoms on the substrate surface to generate a salt and promotes oxidation of the substrate surface.

Further, considering FIG. 8, if the initial surface ammonia concentration of the substrate is 0.4 ng / cm ² or less, even if the substrate is left to stand for 2 hours and the epitaxial layer is formed, It has been found that the interfacial oxygen concentration can be suppressed to a low concentration of 1.0 × 10 ¹⁸ cm ⁻³ or less. This shows that the concentration of the alkaline substance adhering to the surface of the GaAs semiconductor substrate is preferably 0.4 ng / cm ⁻² or less.

(Comparative Example RA)
1. Production of GaAs semiconductor substrates Four GaAs semiconductor substrates were produced in the same manner as in Example A except that the acid cleaning step was not performed.

2. Analysis of surface layer of GaAs semiconductor substrate Ga / As ratio, (As-O) / {(Ga) + (As)} ratio and (Ga-O) / {(Ga) + (As)} in each GaAs semiconductor substrate The ratio was calculated as in Example A. For each of the GaAs semiconductor substrates, the Ga / As ratio is 0.90 to 1.52, the (As—O) / {(Ga) + (As)} ratio is 0.40 to 0.65, (Ga− The O) / {(Ga) + (As)} ratio was in the range of 0.30 to 0.70.

3. Growth of Epitaxial Layer on GaAs Semiconductor Substrate An epitaxial layer was grown on each of the four GaAs semiconductor substrates in the same manner as in Example A to obtain four GaAs semiconductor substrates with epitaxial layers.

4). Evaluation of Physical Properties of GaAs Semiconductor Substrate with Epitaxial Layer Referring to FIG. 6, after the growth of the epitaxial layer obtained in the same manner as Example A for each of the GaAs semiconductor substrates with an epitaxial layer (four points of comparative example RA in FIG. 6) Haze strength of 21 to 1870 ppm was higher than that of Example A, and a good flat surface was not obtained.

Referring to FIG. 7, the interface oxygen concentration measured for each GaAs semiconductor substrate with an epitaxial layer (four points of comparative example RA in FIG. 7) in the same manner as in Example A is 1 × 10 ¹⁸ cm ^−. Concentration higher than ³ .

(Example B1)
1. Production of GaAs semiconductor substrate In the same manner as in Example A, a GaAs semiconductor wafer was produced and its surface was polished. Next, referring to FIG. 5A, the polished GaAs semiconductor wafer is immersed in an aqueous solution of 0.5% by mass of tetramethylammonium hydroxide (TMAH), and an ultrasonic wave of 950 kHz is applied to the aqueous solution. The surface was washed with alkali for a minute. Next, referring to FIG. 5B, the surface of the GaAs semiconductor wafer was washed with pure water in the same manner as in Example A. Next, referring to FIG. 5C, a GaAs semiconductor wafer is immersed in a 0.3 ppm hydrochloric acid (HCl) aqueous solution, and 950 kHz ultrasonic waves are applied to the aqueous solution for 2 minutes to acid-clean the surface. did. Next, referring to FIG. 5D, the surface of the GaAs semiconductor wafer was washed with pure water in the same manner as in Example A. Next, referring to FIG. 5E, the GaAs semiconductor wafer 11 is fixed to the wafer holder 31 in the centrifuge 30 and is rotated at a high speed of 2500 rpm for 30 seconds, whereby the residual GaAs semiconductor wafer 11 remains on the surface of the GaAs semiconductor wafer. The surface of the wafer was dried by scattering water to obtain a GaAs semiconductor substrate.

2. Analysis of surface layer of GaAs semiconductor substrate In the same manner as in Example A, the spectrum of 3d electrons of As atoms and Ga atoms in the surface layer of the obtained GaAs semiconductor substrate was measured. For the GaAs semiconductor substrate of Example B1, the Ga / As ratio was 0.80, the (As—O) / {(Ga) + (As)} ratio was 0.27, and (Ga—O) / {(Ga) + The (As)} ratio was 0.15.

3. Growth of Epitaxial Layer on GaAs Semiconductor Substrate An epitaxial layer was grown on the GaAs semiconductor substrate in the same manner as in Example A to obtain a GaAs semiconductor substrate with an epitaxial layer. With respect to this GaAs semiconductor substrate with an epitaxial layer, the haze strength after epitaxial layer growth obtained in the same manner as in Example A was 2.1 ppm, which was as small as Example A and a good flat surface was obtained. The haze strength was measured with Surfscan 6220 manufactured by KLA-Tencor.

(Example B2)
A GaAs semiconductor substrate was obtained in the same manner as in Example B1, except that a 0.6 ppm nitric acid (HNO ₃ ) aqueous solution was used as the acid cleaning aqueous solution. About the obtained GaAs semiconductor substrate, Ga / As ratio is 0.85, (As-O) / {(Ga) + (As)} ratio is 0.28, (Ga-O) / {(Ga) + ( As)} ratio was 0.22. Further, in the same manner as in Example B1, an epitaxial layer was grown on the GaN semiconductor substrate to obtain a GaAs semiconductor substrate with an epitaxial layer. The haze strength after the growth of the epitaxial layer was 1.5 ppm, which was as small as Example B1, and a good flat surface was obtained.

(Example B3)
A GaAs semiconductor substrate was obtained in the same manner as in Example B1, except that an aqueous solution containing 0.3 ppm hydrochloric acid and 1.2 ppm nitric acid was used as the acid cleaning aqueous solution. In this aqueous solution, about 0.6 ppm of nitrous acid was produced from nitric acid by the reaction of hydrochloric acid and nitric acid. About the obtained GaAs semiconductor substrate, Ga / As ratio is 0.84, (As-O) / {(Ga) + (As)} ratio is 0.29, (Ga-O) / {(Ga) + ( As)} ratio was 0.21. Further, in the same manner as in Example B1, an epitaxial layer was grown on the GaN semiconductor substrate to obtain a GaAs semiconductor substrate with an epitaxial layer. The haze strength after the epitaxial layer growth was 2.2 ppm, which was as small as Example B1 and a good flat surface was obtained.

(Comparative Example RB1)
A GaAs semiconductor substrate was obtained in the same manner as in Example B1, except that the GaAs semiconductor wafer was not subjected to acid cleaning. About the obtained GaAs semiconductor substrate, Ga / As ratio is 1.03, (As-O) / {(Ga) + (As)} ratio is 0.17, (Ga-O) / {(Ga) + ( As)} ratio was 0.19. Further, in the same manner as in Example B1, an epitaxial layer was grown on the GaN semiconductor substrate to obtain a GaAs semiconductor substrate with an epitaxial layer. The haze strength after the growth of the epitaxial layer was 140.0 ppm, which was very large as compared with Example A and Examples B1 to B3, and a good plane was not obtained.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 X-ray, 5 photoelectrons, 10 GaAs semiconductor substrate, 10a surface layer, 10b inner layer, 10s surface, 11 GaAs semiconductor wafer, 21 alkaline cleaning solution, 23 acid cleaning solution, 25 pure water, 30 centrifuge, 31 wafer holder.

The present invention relates to all As atoms in the surface layer of a GaAs semiconductor substrate, calculated by X-ray photoelectron spectroscopy using a 3d electron spectrum of Ga atoms and As atoms measured at a photoelectron extraction angle of 10 °. The constituent atomic ratio (Ga) / (As) of all Ga atoms is 0.5 or more and 0.9 or less, and the ratio of As atoms bonded to O atoms to all Ga atoms and all As atoms in the surface layer (As -O) / {(Ga) + (As)} is 0.15 or more and 0.35 or less, and the ratio of Ga atoms bonded to O atoms to all Ga atoms and all As atoms in the surface layer (Ga--) O) / {(Ga) + (as)} is Ri der 0.15 or 0.35 or less, a GaAs semiconductor substrate surface roughness RMS of the surface, characterized in der Rukoto below 0.3 nm.

In the GaAs semiconductor substrate according to the present invention, the concentration of the alkaline substance (ammonia) adhering to the surface can be 0.4 ng / cm ² or less.

Claims (9)

  All Ga atoms relative to all As atoms in the surface layer of the GaAs semiconductor substrate, calculated by X-ray photoelectron spectroscopy, using a 3d electron spectrum of Ga atoms and As atoms measured at a photoelectron extraction angle θ of 10 ° The atomic ratio (Ga) / (As) of A is 0.5 or more and 0.9 or less, and the ratio of As atoms bonded to O atoms with respect to all Ga atoms and all As atoms in the surface layer (As-O ) / {(Ga) + (As)} is 0.15 or more and 0.35 or less, and the ratio of Ga atoms bonded to O atoms with respect to all Ga atoms and all As atoms in the surface layer (Ga-O) ) / {(Ga) + (As)} is 0.15 or more and 0.35 or less.   2. The GaAs semiconductor substrate according to claim 1, wherein the surface roughness RMS is 0.3 nm or less. 3. The GaAs semiconductor substrate according to claim 1, wherein the concentration of the alkaline substance adhering to the surface is 0.4 ng / cm ² or less.   A step of polishing the surface of the GaAs semiconductor wafer, at least one alkali cleaning step of cleaning the polished surface with an alkali cleaning solution, and an acid of 0.3 ppm to 0.5 mass% on the alkali cleaned surface. A method of manufacturing a GaAs semiconductor substrate, comprising: an acid cleaning step of cleaning with an acid cleaning solution.   The method for manufacturing a GaAs semiconductor substrate according to claim 4, wherein the alkali cleaning liquid contains an organic alkali compound.   5. The method of manufacturing a GaAs semiconductor substrate according to claim 4, wherein the acid cleaning liquid includes at least one selected from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid, and nitrous acid as the acid. After the acid cleaning step, further comprising a drying step of drying the acid cleaned surface,
5. The method of manufacturing a GaAs semiconductor substrate according to claim 4, wherein the drying step is performed by scattering the acid cleaning liquid remaining on the surface by rotating the GaAs semiconductor wafer.   The method for producing a GaAs semiconductor substrate according to claim 4, further comprising a pure water cleaning step of cleaning the acid cleaned surface with pure water having a dissolved oxygen concentration of 100 ppb or less after the acid cleaning step.   After the pure water cleaning step, the method further includes a drying step of drying the surface that has been cleaned with pure water, and the drying step includes the pure water remaining on the surface by rotating a GaAs semiconductor wafer in the atmosphere. The method for producing a GaAs semiconductor substrate according to claim 8, wherein the method is carried out by scattering.

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