GaAs crystal ingot manufacturing method and GaAs crystal ingot

Abstract

The invention provides a GaAs crystal ingot manufacturing method and a GaAs crystal ingot, which can efficiently obtain a GaAs wafer with strictly controlled carrier concentration and low dislocation density. A method for producing a GaAs ingot, in which a seed crystal, an Si starting material as a dopant, a GaAs starting material, which is Si-doped GaAs having an Si concentration of 20-200 wt ppm with respect to GaAs, and boron oxide as a sealant are housed in a crucible, and crystal growth is performed by a vertical boat method, the loading amount of the Si starting material being 200-300 wt ppm with respect to GaAs, the boron oxide containing more than 5 mol% of SiO2 in terms of Si, and the thickness of the silicon starting material being 10-30 [mu] m. And melting the Si raw material, the GaAs raw material and the boron oxide by heating, and performing crystal growth while stirring the liquid boron oxide.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a GaAs crystal ingot and a GaAs crystal ingot. Background Art

[0002] As a manufacturing method of GaAs single crystal (hereinafter also referred to as GaAs ingot) for obtaining GaAs single crystal wafer (hereinafter also referred to as GaAs wafer), the Czochralski (LEC) method, the horizontal Bridgman (HB) method, the vertical temperature gradient (VGF) method and the vertical Bridgman (VB) method are known. A block having a straight body of a single crystal obtained by growing a crystal by these manufacturing methods starting from a single crystal seed is called an ingot, and a wafer is cut from the straight body of the ingot. A plurality of GaAs wafers are obtained from the same GaAs ingot, and the plurality of wafers are also referred to as a wafer group.

[0003] Here, vertical boat methods such as the vertical temperature gradient (VGF) method and the vertical Bridgman (VB) method are methods in which a seed crystal is placed at the bottom of a crucible, a single crystal raw material melt and a liquid sealant are arranged on the upper layer of the seed crystal, and the crucible is cooled from a specified temperature distribution so that the crystal grows from the bottom of the raw material melt to the top. In the case of the vertical temperature gradient method (VGF method), the temperature itself is lowered, and in the case of the vertical Bridgman method (VB method), the crucible is relatively moved within a specified temperature distribution. When manufacturing a Si-doped GaAs single crystal ingot, Si is added to the GaAs melt. In order to prevent the volatile component As from dissociating from the ingot, etc., boron oxide (B2O3) is generally used as a sealant. During crystal growth, it is known that an oxidation-reduction reaction based on the following reaction formula (1) occurs at the interface between the GaAs melt and liquid B2O3.

[0004] 3Si(in Melt)+2B2O3=3SiO2(in B2O3)+4B(in Melt)···(1)

[0005] In the vertical boat method, since the crystal grows from the bottom of the raw material melt to the top, the impurities not entrained by the crystal are concentrated in the melt. Here, if the amount of dopant Si (i.e., Si crystal added together with the GaAs raw material) added to the GaAs melt is increased in order to increase the carrier concentration, the equilibrium of the above reaction formula (1) moves to the right, and a large amount of boron (B) moves to the GaAs melt. Therefore, as the crystal grows and the impurities are concentrated, the production of boron arsenide is also promoted, and high crystallinity cannot be obtained. That is, in the GaAs single crystal obtained by this manufacturing method, the carrier concentration and the crystallinity are inversely related.

[0006] Patent Document 1 proposes a method for producing a GaAs single crystal having a high carrier concentration and high crystallinity by disposing a plate-shaped solid silicon dioxide at the interface between a GaAs melt and liquid B2O3 in a vertical boat method.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2012-246156 Summary of the invention

[0010] Problem that the invention aims to solve

[0011] In recent years, the effective use of surface-emitting lasers represented by VCSEL (vertical cavity surface-emitting laser) has been actively promoted in semiconductor lasers, and they are applied to optical communications, optical sensing, etc. In these applications, silicon (Si)-doped n-type GaAs wafers are used as element substrates. For GaAs wafers, the carrier concentration is strictly controlled and the dislocation density is low. Specifically, the carrier concentration is preferably set to 1.5×10 18 cm -3 Above and 2.9×10 18 cm -3 In addition, for low dislocation density, in wafers smaller than 6 inches (e.g., smaller than 4 inches), the maximum value of the etch pit density is preferably set to 1200 cm -2 For wafers larger than 6 inches, the maximum value of the etch pit density is preferably set to 1500 cm -2 the following.

[0012] From the GaAs ingot disclosed in Patent Document 1, only a limited number of wafers satisfying the conditions of the maximum values ​​of the carrier concentration and the etch pit density can be obtained, leaving a technical problem in terms of productivity.

[0013] Solutions for solving problems

[0014] During crystal growth, due to the segregation of Si, the Si concentration in the GaAs melt increases as crystallization proceeds, and the carrier concentration also increases from the seed side of the ingot to the tail side together with the Si concentration. In order to make the lower limit carrier concentration on the seed side of the straight body of the ingot to be 1.5×10 18 cm -3When the amount of Si raw material added as a dopant to the GaAs melt is increased as described above, polycrystallization sometimes occurs in the early stage of crystal growth and a single crystal ingot cannot be obtained. For example, when manufacturing a 4-inch GaAs ingot, if a GaAs raw material that does not contain Si is used and more than 300wtppm of Si raw material is added as a dopant, polycrystals are easily generated. Therefore, in order to achieve the above technical problem, the inventors conducted in-depth research and found that in a method for manufacturing a GaAs ingot in which a seed crystal, a Si raw material as a dopant, a GaAs raw material and boron oxide as a sealant are placed in a crucible and crystal growth is performed by a vertical boat method, in addition to using the Si raw material as a dopant, a predetermined amount of Si is doped into the raw GaAs raw material, and the boron oxide as a sealant contains a predetermined amount of SiO2, thereby controlling the Si concentration of the GaAs melt during crystal growth, even if the total amount of Si in the melt is greater than the amount that sometimes causes polycrystals to be produced when the GaAs raw material is not doped with the predetermined amount of Si (for example, 300 wtppm when used for 4 inches), the ingot will not be polycrystallized, and the carrier concentration and etching pit density in most of the straight body of the ingot can be within the desired range, thereby completing the present invention. Hereinafter, the sum of the Si amount of the Si raw material as a dopant and the Si amount in the GaAs raw material is recorded as the total amount of silicon loading.

[0015] The gist of the present invention is as follows.

[0016] [1] A method for manufacturing a GaAs ingot, comprising placing a seed crystal, a Si raw material as a dopant, a GaAs raw material, and boron oxide as a sealant in a crucible, and growing the crystal by a vertical boat method, wherein:

[0017] The GaAs raw material is Si-doped GaAs with a Si concentration of 20 to 200 wtppm relative to GaAs,

[0018] The loading amount of the Si raw material is 200-300 wtppm relative to GaAs.

[0019] The boron oxide contains more than 5 mol% SiO2 in terms of Si,

[0020] After the Si raw material, the GaAs raw material, and the boron oxide are melted by heating, crystal growth is performed while the liquid boron oxide is stirred.

[0021] [2] The method for manufacturing a GaAs ingot according to [1],

[0022] The present invention relates to a method for manufacturing a GaAs ingot having a straight body diameter of 140 mm or less, wherein the total amount of silicon loaded by adding Si in the GaAs raw material and the Si raw material is greater than 300 wtppm relative to GaAs, or,

[0023] The invention relates to a method for manufacturing a GaAs ingot having a straight body diameter greater than 140 mm, wherein the loading amount of the Si raw material is 200 to 250 wtppm relative to GaAs, and the total silicon loading amount obtained by adding the Si in the GaAs raw material and the Si raw material is greater than 250 wtppm relative to GaAs.

[0024] [3] A GaAs ingot,

[0025] The GaAs ingot has a straight body diameter of 140 mm or less, and the carrier concentration of the wafer obtained from more than 70% of the straight body is 1.5×10 18 ~2.9×10 18 cm -3 , and the maximum value of the corrosion pit density is 1200cm -2 The following, or

[0026] The GaAs ingot has a straight body portion with a diameter greater than 140 mm, and the carrier concentration of the wafer obtained from more than 70% of the straight body portion is 1.5×10 18 ~2.9×10 18 cm -3 , and the maximum value of the corrosion pit density is 1500cm -2 the following.

[0027] Effects of the Invention

[0028] According to the present invention, a GaAs ingot and a method for manufacturing the same are provided, which can efficiently obtain a GaAs wafer having a strictly controlled carrier concentration and a low dislocation density. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the GaAs ingot of the present invention.

[0030] Figure 2 This is a schematic diagram of an area with 69 points set on a 6-inch wafer for measuring etch pit density (EPD).

[0031] Figure 3 It is a schematic cross-sectional view of a manufacturing apparatus used for manufacturing a GaAs ingot according to the present invention.

[0032] Figure 4 It is a schematic cross-sectional view of the crucible 3 used for manufacturing the GaAs ingot of the present invention, and corresponds to a state filled with raw materials and the like before the start of crystal growth. DETAILED DESCRIPTION

[0033] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0034] <GaAs crystal ingot>

[0035] (Seed side, center and tail side of GaAs ingot)

[0036] Figure 1 The schematic diagram of the GaAs ingot of the present invention shows the positions 15 from the tapered portion to the straight portion, the position (middle) 16 of the half length from the position 15 to the position 17, and the position 17 where the straight portion ends. The GaAs ingot has a straight portion 18 of substantially the same diameter via a region 19 (also called a tapered portion) whose diameter increases from a seed crystal 6 (also called a seed crystal). The end from the position 17 where the straight portion ends to the end of the growth is called a tail portion. When the length from the position 15 from which the tapered portion changes to the straight portion to the position 17 where the straight portion for wafer processing ends is set to 100%, and the former position 15 is set to 0%, and the latter position 17 is set to 100%, the range of 0 to 5% is called the seed crystal side of the straight portion (hereinafter, also referred to as the seed crystal side), the range of 40 to 60% is called the central portion of the straight portion (hereinafter, also referred to as the central portion), and the range of 88 to 100% is called the tail side of the straight portion (hereinafter, also referred to as the tail side). The position 17 (the 100% position) where the straight body portion ends is the position of 90% of the volume (the position of 90% crystallization ratio) when the volume of the entire ingot is taken as 100%.

[0037] exist Figure 1 , a position 16 is shown which is the middle (50%) between the position 15 and the position 17. Hereinafter, the position 16 is also simply referred to as the middle.

[0038] The position of each wafer in the straight body portion is expressed as a percentage of the distance from the seed crystal end of the straight body portion. In the GaAs ingot, the solid-liquid interface moves from the seed crystal side 15 to the tail side 17, and crystal growth proceeds.

[0039] The average and maximum values ​​of the carrier concentration and the etch pit density (EPD) of the GaAs ingot according to the present invention can be obtained by measuring wafers obtained from the straight body portion 18 of the GaAs ingot.

[0040] The diameter of the GaAs ingot 18 is not particularly limited, and may be less than 140 mm or greater than 140 mm. The diameter of the GaAs ingot 18 may be, for example, greater than 50 mm and less than 140 mm, or greater than 140 mm and less than 162 mm.

[0041] The size of the wafer can be appropriately selected according to the diameter of the straight body 18 of the GaAs crystal ingot, for example, it can be 2 to 8 inches. When the diameter of the GaAs crystal ingot 18 is less than 140 mm, the size of the wafer is usually less than 6 inches, and when the diameter of the GaAs crystal ingot 18 is greater than 140 mm, the size of the wafer is usually greater than 6 inches.

[0042] <Method for producing GaAs ingot>

[0043] The manufacturing method of the GaAs ingot according to the present invention is a method of placing a seed crystal, a Si raw material as a dopant, a GaAs raw material and boron oxide as a sealant in a crucible and growing the crystal by a vertical boat method. As the vertical boat method, a vertical temperature gradient (VGF) method or a vertical Bridgman (VB) method can be optionally used.

[0044] Below, refer to Figure 3 and Figure 4 The present production method will be described in more detail.

[0045] (Manufacturing equipment and temperature control)

[0046] Figure 3 A cross-sectional view schematically shows an example of a manufacturing apparatus used in the method for manufacturing a GaAs crystal ingot according to the present invention.

[0047] Figure 3 The manufacturing device shown comprises: an airtight container 7 that can be vacuum-exhausted and filled with atmospheric gas from the outside, a crucible 3 arranged in the center of the airtight container 7, a crucible storage container (carrier) 2 that stores and holds the crucible 3, a mechanism 14 for lifting and / or rotating the crucible storage container (carrier) 2 (only the lifting / rotating rod is shown in the figure), and a heater 1 equipped in the airtight container 7 in a manner to surround the crucible storage container (carrier) 2.

[0048] An upper rod 21 having a stirring blade 20 mounted thereon which can rotate and move up and down is disposed above the crucible 3. The stirring blade 20 and the upper rod 21 form a stirring member, but the stirring blade 20 can be removed from the upper rod 21, and a sealing agent container or other components can be mounted on the upper rod 21.

[0049] The crucible 3 can be made of pyrolytic boron nitride (PBN). Figure 3 In the process, a seed crystal 6, a compound semiconductor raw material 5 (also referred to as a raw material melt), and boron oxide (B2O3) 4 as a sealant are filled in a crucible 3, and an airtight container 7 is filled with an inert gas 8 as an example.

[0050] Figure 4An example of a crucible used in the method for producing a GaAs ingot of the present invention is schematically shown in cross-sectional view, corresponding to a state filled with raw materials and the like before crystal growth begins. Figure 4 The crucible 3 shown is filled with a seed crystal 6, a GaAs raw material 9, a Si raw material 10 as a dopant, and boron oxide 4 as a sealant. Figure 4 In the present invention, in addition to the crushed GaAs polycrystals (9A), the GaAs raw material 9 also includes cylindrical GaAs polycrystals (9B) and disc-shaped GaAs polycrystals (9C), so that the Si raw material is arranged in a container made of cylindrical GaAs polycrystals (9B) and disc-shaped GaAs polycrystals (9C), but it is not limited to such a form, for example, only the crushed GaAs polycrystals can be filled.

[0051] After these fillings are completed, in a growth furnace filled with an inert gas, a temperature gradient is applied by a heater under PID control in such a way that the seed crystal 6 does not melt and the temperature on the seed crystal 6 side becomes lower, and the GaAs raw material 9 is heated to 1238°C or higher, which is the melting point of GaAs, so that the GaAs raw material 9 and the boron oxide 4 are melted, and the Si raw material 10 is dissolved in the GaAs raw material 9. Next, the temperature near the seed crystal 6 is raised, and after the upper part of the seed crystal 6 is melted, the overall temperature is slowly lowered while applying a temperature gradient, thereby obtaining a GaAs ingot. At this time, the cooling rate is preferably set to 10°C / hour or less.

[0052] (Stirring)

[0053] In the manufacturing method of GaAs according to the present invention, the liquid boron oxide 4 is stirred during crystal growth. Preferably, stirring is started from the time when crystal growth starts on the seed crystal side of the straight body portion to the middle (1 to 50% from the position of the straight body seed crystal). Stirring is preferably continued until the crystal growth on the tail side of the straight body portion is completed, and may be continued until the crystal growth is completed.

[0054] Stirring is preferably performed by placing a stirring member in the sealant (boron oxide 4) and rotating it. In the present invention, it is preferred that the Si concentration in the raw material melt is kept at a high state from the start of crystal growth to the start of stirring, and the sealant does not absorb Si as much as possible, and stirring is used to the minimum extent in order to suppress the extreme increase in Si concentration caused by segregation. Therefore, the rotation speed can be changed in a step-like manner from the seed crystal side of the straight body to the tail side, or it can be changed continuously, but the maximum rotation speed reached is preferably set to be less than 3 rpm.

[0055] The stirring member can be in a shape in which the stirring blade 20 is attached around the rotating shaft.

[0056] The shape of the stirring blade 20 is not particularly limited, and can be composed of a plate-like member of a predetermined shape, for example, a stirring blade composed of 2 to 8 substantially quadrilateral plate-like members can be cited, and the raw material can be carbon, BN, etc. The plate-like member is preferably installed at an inclination angle of 45° or more and 135° or less relative to the interface formed between the raw material melt and the boron oxide 4 in a stationary state.

[0057] The size of the area formed by the rotation track of the stirring blade 20 when the stirring member is rotated is preferably 30% or more of the area of ​​the interface formed between the raw material melt and the boron oxide 4 in a stationary state, and more preferably 70% or more.

[0058] The distance between the lower end of the stirring blade 20 and the interface formed by the raw material melt and the boron oxide 4 in a static state is preferably less than 2 mm, preferably less than 1 mm. However, it is preferred that the lower end of the stirring blade 20 does not contact the interface.

[0059] The stirring is preferably carried out at a speed of 0.5 rpm or more when the crystal growth is in the middle, and more preferably at a speed of 2.5 rpm or more. This is because the segregation of Si in the melt increases after the middle, and the carrier concentration exceeds 2.5×10 18 cm -3 Therefore, strong stirring is performed at this time to promote the absorption of Si in the melt into the sealant, suppress the rapid increase in Si concentration caused by segregation, and thus suppress the occurrence of dislocations and the rapid increase in carrier concentration.

[0060] (Seed)

[0061] The seed crystal 6 is not particularly limited, and a known seed crystal can be used. The size of the seed crystal 6 is not particularly limited, and can have a cross-sectional area of, for example, 1 to 20% of the cross-sectional area of ​​the inner diameter of the crucible 3, preferably 3 to 17%. When the diameter of the crystal to be grown exceeds 100 mm, the cross-sectional area of ​​the seed crystal 6 can be 2 to 10% of the cross-sectional area of ​​the inner diameter of the crucible.

[0062] (Crucible inner diameter and wafer size)

[0063] The inner diameter of the crucible 3 is preferably slightly larger than the target wafer size. The target wafer size can be, for example, 2 inches or more, preferably 3 inches or more. The upper limit of the wafer size is not particularly limited, for example, it can be 8 inches or less. For example, a wafer with a diameter of 2 inches to 4 inches is made from an ingot with a straight body diameter of 140 mm or less, and a wafer with a diameter of 6 inches to 8 inches is made from an ingot with a straight body diameter greater than 140 mm.

[0064] (GaAs raw material)

[0065] As a GaAs raw material, Si-doped GaAs having a Si concentration of 20 to 200 wtppm relative to GaAs is used. The GaAs raw material used may be polycrystalline or single crystal. The Si concentration in the GaAs raw material refers to the Si concentration calculated based on the carrier concentration measured by Hall measurement. If the Si concentration calculated based on the carrier concentration is within this range, even if the total amount of silicon loading relative to GaAs obtained by adding the Si raw material 10 described later is large, single crystalization will not be inhibited during crystal growth, and the carrier concentration in the obtained GaAs ingot can be easily controlled within the desired range. Since the GaAs raw material is used after melting, the average Si concentration of the entire GaAs raw material used can be within the above range, and GaAs raw materials with different Si concentrations can be used in combination.

[0066] Here, the Si concentration of Si-doped GaAs polycrystal calculated from the carrier concentration can be measured and calculated as follows. It should be noted that the same method can also be used to calculate in the case of a single crystal. It should be noted that the following conversion method from carrier concentration to Si concentration is a method for the case where the dopant of GaAs is Si and other p-type dopants and n-type dopants are not intentionally included.

[0067] <Carrier concentration based on Hall measurement>

[0068] Wafers with a thickness of about 1 mm were cut from the seed side and the tail side of the Si-doped GaAs polycrystal.

[0069] A scratch of □10 mm in size was made with a scriber at a grain boundary as large as possible on a polycrystalline wafer-like object, and a sample of □10 mm in size was cut out from the center of the wafer-like object.

[0070] Indium electrodes were placed at the four corners of the sample, heated to 330-360°C, and the carrier concentration was measured using the Van der Pauw method.

[0071] <Conversion of activation rate to Si concentration>

[0072] The Si atomic concentration (cm -3 ).

[0073] The volume density of GaAs (5.3161 g / cm 3 ), Avogadro constant, atomic weight of Si (28.1), convert the value of Si atomic concentration from unit (cm -3 ) is converted into units (wtppm).

[0074] [Mathematical formula 1]

[0075]

[0076] There is no limitation on the method for synthesizing Si-doped GaAs as a GaAs raw material. A method of synthesizing in a crucible by a vertical boat method, a method of synthesizing in a boat set in an ampoule by a horizontal Bridgman method, etc. can be used. During the synthesis, an amount of Si raw material that meets the desired Si concentration relative to GaAs is loaded.

[0077] When using the vertical boat method, for example, Si-doped GaAs polycrystals can be obtained by filling a crucible with high-purity Ga, high-purity As and Si raw materials (e.g., shot blasting of high-purity Si, crushed materials of high-purity Si substrate) and growing crystals. The crucible can be filled in the order of half high-purity As, all Si raw materials, the remaining half high-purity As, and high-purity Ga, but the filling order is not limited to this. In the synthesis of GaAs polycrystals, from the perspective of promoting Si doping and suppressing the amount of boron in the GaAs melt when used as a GaAs raw material, it is preferred not to use boron oxide as a sealant.

[0078] Si-doped GaAs as the GaAs raw material can also be used as a recycled product obtained by processing or crushing the parts other than the straight body part of other Si-doped GaAs single crystal ingots that have not been processed into wafers (the tapered part, the tail side of the straight body part and the area thereafter), and the unnecessary parts generated during wafer processing.

[0079] (Dopant)

[0080] As a dopant, a Si raw material 10 is used. The Si raw material 10 can be added to the GaAs raw material 9 by shot blasting of high-purity Si or crushing of a high-purity Si substrate.

[0081] The loading amount of the Si raw material 10 is set to 200 to 300 wtppm relative to GaAs in the GaAs raw material 9. It is more preferably set to 220 to 300 wtppm or more, and further preferably set to 240 to 290 wtppm.

[0082] For an ingot having a straight body diameter of 140 mm or less, the total amount of silicon loaded by adding the Si in the GaAs raw material and the Si raw material 10 is preferably greater than 300 wtppm relative to GaAs. In this case, it is more preferred that the loading amount of the Si raw material 10 is set to 220 to 300 wtppm or less relative to GaAs.

[0083] For a crystal ingot having a straight body diameter greater than 140 mm, the loading amount of Si raw material 10 is preferably set to 200-250wtppm relative to GaAs, and more preferably set to 220-250wtppm. The total silicon loading amount obtained by adding the Si in the above-mentioned GaAs raw material and the Si raw material 10 is preferably greater than 250wtppm relative to GaAs.

[0084] For example, in the manufacture of a 4-inch GaAs ingot, when a GaAs raw material containing no Si is used and more than 300 wtppm of Si raw material is added as a dopant, there is a tendency for polycrystallization. In addition, in the manufacture of a 6-inch GaAs ingot, when a GaAs raw material containing no Si is used and more than 250 wtppm of Si raw material is added as a dopant, there is a tendency for polycrystallization. However, when Si is included in the GaAs raw material in advance as in the present invention, even if the total amount of silicon loaded is set to such an amount, Si can be included in the GaAs melt without polycrystallization, and the carrier concentration of the entire body portion can be increased.

[0085] If the total amount of silicon loaded is controlled as described above, single crystallization will not be hindered during crystal growth, and the carrier concentration in the obtained GaAs ingot can be easily controlled within a desired range.

[0086] Here, the loading amount of the Si raw material 10 does not include the amount of silicon contained in the Si-doped GaAs raw material and the boron oxide. The total amount of silicon loaded does not include the amount of silicon contained in the boron oxide.

[0087] The Si raw material 10 is preferably arranged below (on the seed side) the center of the crucible (equivalent to the center of the ingot). The Si raw material 10 may also be placed in a GaAs container so that the dopant therein does not go out of the container until the temperature at which the GaAs container melts. Silicon has a lower density than GaAs, so there is a risk that the dopant (silicon) will float in the melt, the silicon concentration in the GaAs melt on the seed side will decrease, and thus the silicon concentration on the seed side of the GaAs ingot will decrease. The use of a GaAs container is effective in avoiding the above-mentioned situation. As a GaAs container, the GaAs raw material can be processed for use, Si-doped GaAs single crystals can be processed, and Si-doped GaAs polycrystals can be processed.

[0088] In addition to the Si raw material 10 , an amphoteric dopant may be used within a range not impairing the effects of the present invention. Examples of the dopant include In raw materials such as high-purity In and indium compounds (eg, high-purity indium arsenide (InAs)).

[0089] Elements that can be considered as dopants other than these include beryllium (Be), magnesium (Mg), aluminum (Al), carbon (C), germanium (Ge), tin (Sn), nitrogen (N), sulfur (S), selenium (Se), tellurium (Te), and further zinc (Zn), cadmium (Cd), chromium (Cr), and antimony (Sb). The amount of these elements that are inevitably mixed in is allowed, but it is preferably not added intentionally.

[0090] (Sealant)

[0091] Boron oxide (B2O3) 4 is used as a sealant. Boron oxide 4 contains more than 5 mol% SiO2 in terms of Si. If it is within this range, the amount of Si absorbed by B2O3 in the raw material melt is suppressed. In addition, it is possible to prevent B of B2O3 from entering the single crystal, and the Si concentration of the raw material melt can be controlled within a suitable range during stirring. The amount of SiO2 contained in boron oxide 4 is preferably 6 mol% or more in terms of Si. Since there is a limit to the amount of Si that can be solid-dissolved with boron oxide, the amount of SiO2 contained in boron oxide 4 can be set to less than 10 mol% in terms of Si, preferably less than 7 mol%.

[0092] From the perspective of inhibiting the escape of As from the raw material melt, the boron oxide 4 as a sealant can be set to more than 0.02wt%, preferably more than 0.03wt% relative to the GaAs raw material 9. In addition, from the perspective of preventing an excessive amount of Si introduced into the stirred sealant, it can be set to less than 0.10wt%, preferably less than 0.06wt%.

[0093] According to the manufacturing method of the GaAs ingot of the present invention, the following GaAs ingot can be obtained, which is a GaAs ingot with a straight body diameter of 140 mm or less, and the carrier concentration of the wafer obtained from the straight body of more than 70% (preferably more than 90%) is 1.5×10 18 ~2.9×10 18 cm -3 , and the maximum value of the corrosion pit density is 1200cm -2 or, a GaAs ingot having a straight body portion having a diameter greater than 140 mm, wherein the carrier concentration of the wafer obtained from more than 70% of the straight body portion is 1.5×10 18 ~2.9×10 18 cm -3 , and the maximum value of the corrosion pit density is 1500cm -2 the following.

[0094] That is, when the diameter of the straight body of the GaAs ingot is 140 mm or less, more than 70% (preferably more than 90%) of the total number of wafers cut out from the straight body satisfy the carrier concentration of 1.5×10 18~2.9×10 18 cm -3 Below and the maximum value of corrosion pit density is 1200cm -2 The maximum value of the corrosion pit density is more preferably 1000 cm -2 The lower limit of the maximum value of the corrosion pit density is not particularly limited, and may be zero.

[0095] More preferably, 92% or more of the wafers satisfy the above conditions. Alternatively, all wafers (100% of the wafers) may satisfy the above conditions.

[0096] When the diameter of the straight body of the GaAs ingot is greater than 140 mm, more than 70% of the total number of wafers cut from the straight body satisfy the carrier concentration of 1.5×10 18 ~2.9×10 18 cm -3 The maximum value of corrosion pit density is 1500cm -2 The following conditions apply. The lower limit of the maximum value of the etch pit density is not particularly limited and may be zero.

[0097] More preferably, 75% or more of the wafers satisfy the above conditions. Alternatively, all wafers (100% of the wafers) may satisfy the above conditions.

[0098] (Method for measuring carrier concentration)

[0099] The carrier concentration was obtained by cutting a wafer extracted from a GaAs ingot into a wafer with a size of 10 mm x 10 mm at the center of the wafer, attaching indium electrodes to the four corners, heating to 330 to 360° C., and measuring the carrier concentration by a Hall measurement based on the van der Pauw method.

[0100] (Measurement method of Etch Pit Density (EPD))

[0101] The determination of the etching pit density (EPD) is performed as follows: the surface of the wafer extracted from the GaAs ingot is pre-treated in a sulfuric acid mirror etching solution (H2SO4:H2O2:H2O=3:1:1 (volume ratio)), and then immersed in a KOH solution at a liquid temperature of 320°C for 35 minutes to generate etching pits, and the number of etching pits is measured. The etching pits that are composed of hexagonal shapes that appear to be unique to zinc-blende crystals and have a major diameter (the length of the diagonal line passing through the center) of 20μm or more are the measurement objects.

[0102] The etch pit density (EPD) was measured by setting an area with a diameter of 3 mm at 69 points or 37 points on the wafer, observing each area with a microscope, and counting the generated etch pits.

[0103] The 69-point or 37-point area is distributed over the entire wafer surface without omission.

[0104] In the case of a 6-inch wafer, a region of 69 points is set at positions evenly distributed at intervals of 15 mm, and in the case of a 3-inch wafer, a region of 37 points is set at positions evenly distributed at intervals of 10 mm.

[0105] When the 69-point areas are set at evenly dispersed positions, in the case of a 2-inch wafer, each area is 5 mm apart, in the case of a 4-inch wafer, each area is 10 mm apart, and in the case of an 8-inch wafer, each area is 20 mm apart.

[0106] exist Figure 2 FIG. 2 is a schematic diagram showing a region where 69 points are set on a 6-inch wafer.

[0107] Each area was observed using a 10x objective lens with a field of view diameter of 1.73 mm. For all areas, the field of view with the most pits observed in each area was found and the corrosion pits were counted. The count value of the corrosion pits was converted to per unit area (cm -2 ). The maximum value among the converted values ​​of the count values ​​of the corrosion pits in each region is taken as the maximum value of the corrosion pit density (EPD). In addition, the average value of the converted values ​​of the count values ​​of the corrosion pits in each region is taken as the average value of the corrosion pit density (EPD).

[0108] The GaAs wafer according to the present invention has strictly controlled carrier concentration and low dislocation density, and is suitable for a substrate of a surface emitting laser represented by a VCSEL (vertical cavity surface emitting laser).

[0109] The above is an example of a typical embodiment of the present invention, but the present invention is not limited to these.

[0110] Example

[0111] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples at all.

[0112] (GaAs raw material)

[0113] <GaAs raw material 1>

[0114] The GaAs raw material 1 is a GaAs polycrystal produced by synthesizing 6N (purity 99.9999% or more) Ga and 6N As.

[0115] <GaAs raw material 2>

[0116] GaAs raw material 2 is a Si-doped GaAs polycrystal synthesized by a vertical boat method using 350wtppm of high-purity Si relative to 6N (purity 99.9999% or more) Ga and 6N As, without using B2O3 as a sealant. The Si concentration converted from the measured value of the Hall measurement is 80wtppm relative to GaAs. Since B2O3 is not used, no boron is added to the Si-doped GaAs polycrystal.

[0117] <GaAs raw material 3>

[0118] GaAs raw material 3 is a recycled product obtained by crushing the portion other than the straight body portion of another single crystal ingot. The Si concentration calculated from the value measured by Hall measurement is 33 wtppm relative to GaAs. The raw material contains boron.

[0119] <GaAs raw material 4>

[0120] GaAs raw material 4 is a Si-doped GaAs polycrystal synthesized by a vertical boat method using 450wtppm of high-purity Si relative to 6N (purity 99.9999% or more) Ga and 6N As, without using B2O3 as a sealant. The Si concentration converted from the measured value of the Hall measurement is 175wtppm relative to GaAs. Since B2O3 is not used, no boron is added to the Si-doped GaAs polycrystal.

[0121] (Sealant)

[0122] <Sealing agent 1>

[0123] The sealing agent 1 is B2O3 containing 7 mol% of SiO2 in terms of Si.

[0124] <Sealing agent 2>

[0125] The sealing agent 2 is B2O3 containing 5.3 mol% of SiO2 in terms of Si.

[0126] (Crystal No. 1)

[0127] Use with Figure 3 The GaAs ingot was manufactured by using a manufacturing device with the structure shown in FIG. The stirring blades are made of four quadrilateral plate-shaped members made of carbon, BN or other materials that have no effect on the crystal properties, mounted on a rod, and the area formed by the rotation trajectory of the stirring blades when rotating is more than 50% of the area of ​​the interface formed by the GaAs melt and B2O3 in a static state.

[0128] <Filling the crucible with raw materials>

[0129] As a crucible, a PBN crucible with an inner diameter of 112 mm and an inner diameter of 6 to 6.5 mm at the seed crystal portion was prepared. Figure 4 As shown, in the crucible, 11900g of GaAs raw material 1 and GaAs seed crystals cut in such a way that the (100) face becomes the crystal growth face are filled. As for the diameter of the GaAs seed crystal, the one used is one adjusted in size by combining mechanical grinding and etching in such a way that it is 0.5mm smaller than the inner diameter of the seed crystal part of each crucible. In the middle of filling the GaAs raw material 1, 300wtppm of high-purity Si shot is filled as a dopant (Si raw material) relative to GaAs. Except for Si, no impurity elements are intentionally added. It should be noted that the granular dopant (Si raw material) 10 is filled in a state of being placed in a GaAs container in which a cylindrical GaAs polycrystal 9B is sandwiched between a circular plate-shaped GaAs polycrystal 9C, and the dopant therein does not go out of the GaAs container until the temperature at which the GaAs container melts.

[0130] <Crystal Growth>

[0131] After filling these raw materials, 550 g of sealing agent 1 was added. The filled crucible was placed in a crucible storage container (carrier). Figure 3 After the interior of the manufacturing apparatus shown was repeatedly evacuated and replaced with Ar gas to form an inert gas atmosphere, a single crystal was grown by the VGF method.

[0132] In the crystal growth process, a temperature gradient is first applied by a PID-controlled heater so that the GaAs seed crystal does not melt and the temperature on the seed crystal side becomes low, and the raw material in the crucible is heated to 1238°C or higher, which is the melting point of GaAs, to form a melt. Then, the temperature near the seed crystal is raised so that the upper part of the seed crystal melts, and then a temperature gradient is applied and the temperature of the entire furnace is gradually lowered at a rate of 0.5°C / h or less by heater control, thereby growing an n-type GaAs ingot with Si as a dopant.

[0133] When the crystal grows in the conical part and grows into a crystal ingot until it reaches the position of the straight body of the crystal, the stirring wing is placed in the sealant so that the distance between the interface of the sealant (boron oxide) and the raw material melt and the lower end of the stirring wing is less than 1 mm and the lower end does not contact the interface. As for the rotation speed of the stirring wing, the rotation speed is maintained at 0 rpm to grow to the middle, and it rotates at 0.5 rpm from the middle to the tail, and the stirring is continued until the growth of the tail is completed.

[0134] The conductivity type of the obtained GaAs crystal ingot is n-type.

[0135] <Evaluation>

[0136] The straight body of the grown GaAs ingot is sliced ​​into wafers using a wire saw. The wafer size is equivalent to 4 inches. Regarding the length of the straight body, the total number of wafers obtained from the straight body is 297, and the position of each wafer from the straight body seed crystal is calculated. For the wafers cut from the position from the straight body seed crystal shown in Table 1, the carrier concentration is measured by the above method. In addition, for the wafers cut from the position from the straight body seed crystal shown in Table 1, the average value and maximum value of EPD are measured by the above method.

[0137] In addition, for the wafer positions (1st to 287th wafers) measured in Table 1, that is, the carrier concentration and EPD from the seed crystal side to the tail side, the carrier concentration of the wafers in the measurement range from the seed crystal side to the tail side was calculated by connecting the intermediate values ​​of the measured values ​​with a straight line between the measured values. For the total number of wafers (297 wafers) cut from the GaAs ingot, the carrier concentration of the wafers in the measurement range from the seed crystal side to the tail side was calculated to be 1.5×10 18 ~2.9×10 18 cm -3 The maximum value of the corrosion pit density is 1200cm -2 The following ratios (ratios of wafers satisfying the prescribed conditions) are shown in Table 1. In calculating the ratio of wafers satisfying the prescribed conditions, wafers located outside the wafer closest to the tail and located on the side closer to 100% from the position of the straight seed crystal among the measurement target wafers are considered not to satisfy the prescribed conditions.

[0138] (Crystal No. 2-3)

[0139] GaAs ingots of Crystal Nos. 2 and 3 were produced and evaluated in the same manner as Crystal No. 1 except that the conditions were changed to those shown in Table 1. The conductivity type of the obtained GaAs ingots was n-type.

[0140] (Crystal No. 4)

[0141] After the GaAs seed crystal, GaAs raw material 1 and high-purity Si shot were filled, a quartz plate (disk shape with a diameter of 51 mm and a thickness of 5 mm) was placed thereon, and then a sealant 1 was filled. A GaAs ingot of crystal number 4 was prepared and evaluated in the same manner as crystal number 1. The conductivity type of the obtained GaAs ingot was n-type.

[0142] [Table 1]

[0143]

[0144] Table 1 shows GaAs ingots with a straight body diameter of 140 mm or less. For crystal numbers 2 and 3, 96.6% of all wafers (297 wafers) in the measurement range from the seed crystal side to the tail side in Table 1 satisfy the carrier concentration of 1.5×10 18~2.9×10 18 cm -3 The maximum value of the corrosion pit density is 1200cm -2 The following conditions.

[0145] Crystal No. 1 is an example of growing a GaAs ingot using a high-purity GaAs polycrystalline raw material not doped with Si, but the proportion of wafers satisfying the above conditions is only 60.9%.

[0146] In addition, crystal number 4 is an example of using a quartz plate to make a GaAs ingot, which corresponds to Patent Document 1. In this example, the quartz plate reduces the effect of suppressing the increase in Si concentration due to stirring, so the increase in carrier concentration after the center cannot be suppressed, and the proportion of wafers that meet the above conditions is only 67.6%.

[0147] For crystal numbers 1 and 4, even if the wafer located closer to 100% of the position of the straight seed crystal among the measurement target wafers still satisfies the specified conditions compared with the wafer closest to the tail, the proportion of wafers satisfying the conditions is less than 70%.

[0148] (Crystal No. 5)

[0149] <Filling the crucible with raw materials>

[0150] As a crucible, a PBN crucible with an inner diameter of 159.9 mm and an inner diameter of 6.0 to 6.5 mm for the seed crystal part is prepared. In the crucible, 20,000 g of GaAs raw material 1 and GaAs seed crystals cut in such a way that the (100) face becomes the crystal growth face are filled. Regarding the diameter of the GaAs seed crystal, the one adjusted in size by combining mechanical grinding and etching in such a way that it is about 0.5 mm smaller than the inner diameter of the seed crystal part of each crucible is used. In the middle of filling the GaAs polycrystal, 210 wtppm of high-purity Si shot is filled as a dopant (Si raw material) relative to the GaAs. Except for Si, no impurity elements are intentionally added.

[0151] <Crystal Growth>

[0152] After filling these raw materials, 965±10 g of sealing agent 2 is added. The filled crucible is placed in a crucible storage container (carrier). Figure 3 After the interior of the manufacturing apparatus shown was repeatedly evacuated and replaced with Ar gas to form an inert gas atmosphere, a single crystal was grown by the VGF method.

[0153] In the crystal growth process, a temperature gradient is first applied by a PID-controlled heater so that the GaAs seed crystal does not melt and the temperature on the seed crystal side becomes lower, and the raw material in the crucible is heated to 1238°C or higher, which is the melting point of GaAs, to form a melt. Then, the temperature near the seed crystal is raised so that the upper part of the seed crystal melts, and then a temperature gradient is applied and the temperature of the entire furnace is gradually lowered at a rate of 0.5°C / h or less by heater control, thereby growing an n-type GaAs ingot with Si as a dopant.

[0154] When the crystal grows in the conical part and grows to the position of the straight body of the crystal to form a crystal ingot, the stirring wing is placed in the sealant so that the distance between the interface of the boron oxide as the sealant and the raw material melt and the lower end of the stirring wing is less than 1 mm and the lower end does not contact the interface. As for the rotation speed of the stirring wing 20, the rotation speed is maintained at 0 rpm to grow to the middle, and the rotation is rotated at 0.5 rpm from the middle to the tail, and the stirring is continued until the growth of the tail is completed.

[0155] The conductivity type of the obtained GaAs crystal ingot is n-type.

[0156] <Evaluation>

[0157] The straight body of the growing GaAs ingot is sliced ​​into wafers using a wire saw. The wafer size is equivalent to 6 inches. Regarding the length of the straight body, the total number of wafers obtained from the straight body is 161, and the position of each wafer from the straight body seed crystal is calculated. The final cut section is a position 20 mm away from the opposite end of the ingot from the seed side (along the seed crystal side direction). For the wafers cut from the position from the straight body seed crystal shown in Table 2, the carrier concentration is measured by the above method. In addition, for the wafers cut from the position from the straight body seed crystal shown in Table 2, the average value and maximum value of the EPD are measured by the above method.

[0158] In addition, for the wafer positions (2nd to 148th wafers) measured in Table 2, that is, the carrier concentration and EPD from the seed crystal side to the tail side, the carrier concentration of the wafers in the measurement range from the seed crystal side to the tail side was calculated by connecting the middle values ​​of the measured values ​​with a straight line between the measured values. For the total number of wafers (161 wafers) cut from the GaAs ingot, the carrier concentration of the wafers in the measurement range from the seed crystal side to the tail side was 1.5×10 18 ~2.9×10 18 cm -3 The maximum value of corrosion pit density is 1500cm -2 The following ratios (ratios of wafers satisfying the prescribed conditions) are shown in Table 2. In calculation of the ratio of wafers satisfying the prescribed conditions, wafers located outside the wafer to be measured are regarded as not satisfying the prescribed conditions.

[0159] (Crystal No. 6)

[0160] A GaAs ingot of Crystal No. 6 was produced and evaluated in the same manner as Crystal No. 5 except that the conditions were changed to those shown in Table 2. The conductivity type of the obtained GaAs ingot was n-type.

[0161] (Crystal No. 7)

[0162] As shown in Table 2, GaAs raw material 4 (Si concentration 175 wtppm) was used, and the rotation speed of the stirring blade was kept at 0 rpm until the middle, and rotated at 2.5 rpm from the middle to the tail. A GaAs ingot of crystal number 7 was manufactured and evaluated in the same manner as crystal number 6. The conductivity type of the obtained GaAs ingot was n-type.

[0163] [Table 2]

[0164]

[0165] Table 2 shows GaAs ingots with a body diameter greater than 140 mm. For crystal number 6, 79.1% of all wafers (161) in the measurement range from the seed crystal side to the tail side obtained from the body satisfy the carrier concentration of 1.5×10 18 ~2.9×10 18 cm -3 The maximum value of corrosion pit density is 1500cm -2 The following conditions.

[0166] For crystal number 7, 77.1% of all wafers (161 wafers) in the measurement range from the seed crystal side to the tail side obtained from the straight body part satisfied the carrier concentration of 1.5×10 18 ~2.9×10 18 cm -3 The maximum value of corrosion pit density is 1500cm -2 The following conditions.

[0167] On the other hand, crystal number 5 is an example of growing a GaAs ingot using a high-purity GaAs polycrystalline raw material not doped with Si, but the proportion of wafers satisfying the above conditions is only 37.7%.

[0168] In the case of crystal number 5, even if the wafers located outside the wafer to be measured satisfy the prescribed conditions, the proportion of wafers satisfying the conditions is less than 70%.

[0169] Industrial Applicability

[0170] According to the present invention, a GaAs ingot and a method for manufacturing the same can be provided, which can efficiently obtain a GaAs wafer having a strictly controlled carrier concentration and a low dislocation density, and have high industrial usefulness.

[0171] Description of Reference Numerals

[0172] 1 Heater

[0173] 2 Crucible storage container (carrier)

[0174] 3 Crucible

[0175] Boron 4 Oxide

[0176] 5Compound semiconductor raw materials (raw material melt)

[0177] 6 Seed

[0178] 7. Airtight container

[0179] 8 Inert Gas

[0180] 9GaAs polycrystalline raw materials

[0181] 10Si Raw Materials

[0182] 14 Crucible lifting / rotation mechanism

[0183] 15 The point where the tapered part changes to a straight body

[0184] 16 Halfway between position 15 and position 17 (middle)

[0185] 17 Where the straight body ends

[0186] Straight body of 18GaAs ingot

[0187] 19The tapered part of GaAs ingot

[0188] 20 stirring wings

[0189] 21 Upper rod

[0190] 30 6-inch wafer

[0191] Area 31

Claims

1. A method for manufacturing a GaAs ingot, comprising placing a seed crystal, a Si raw material as a dopant, a GaAs raw material, and boron oxide as a sealant in a crucible, and growing the crystal by a vertical boat method, wherein: The GaAs raw material is Si-doped GaAs with a Si concentration of 20 to 200 wtppm relative to GaAs, The loading amount of the Si raw material is 200-300 wtppm relative to GaAs. The boron oxide contains more than 5 mol% of SiO2 in terms of Si, After the Si raw material, the GaAs raw material, and the boron oxide are melted by heating, crystal growth is performed while the liquid boron oxide is stirred.

2. The method for manufacturing a GaAs ingot according to claim 1, The present invention relates to a method for manufacturing a GaAs ingot having a straight body diameter of 140 mm or less, wherein the total amount of silicon loaded by adding Si in the GaAs raw material and the Si raw material is greater than 300 wtppm relative to GaAs, or, The invention relates to a method for manufacturing a GaAs ingot having a straight body diameter greater than 140 mm, wherein the loading amount of the Si raw material is 200 to 250 wtppm relative to GaAs, and the total silicon loading amount obtained by adding the Si in the GaAs raw material and the Si raw material is greater than 250 wtppm relative to GaAs.

3. A GaAs ingot, The GaAs ingot has a straight body portion with a diameter of 140 mm or less, and the carrier concentration of the wafer obtained from more than 70% of the straight body portion is 1.5×10 18 ~2.9×10 18 cm -3 , and the maximum value of the corrosion pit density is 1200cm -2 The following, or The GaAs ingot has a straight body portion with a diameter greater than 140 mm, and the carrier concentration of the wafer obtained from more than 70% of the straight body portion is 1.5×10 18 ~2.9×10 18 cm -3 , and the maximum value of the corrosion pit density is 1500cm -2 the following.

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