JPH03223200A - Production of gaas single crystal - Google Patents

Abstract

PURPOSE:To eliminate the wetting of a quartz boat and a crystal and uniformize the concentrations of dopant Cr and residual Si by using a horizontal zone- melting method concentrating spontaneously migrated oxygen into a melt zone, foregoingly to the crystal growth. CONSTITUTION:The objective GaAs single crystal is grown by a following method: (a) A quartz boat 1 containing a seed crystal 2, Ga or GaAs polycrystalline substance and dopants Cr and As 10 are received in a quartz ample 12; (b) Whole of the quartz ample 12 is vacuum-treated with heating; (c) The As 10 and the quartz boat 12 are heated and Ga is made to react with As vapor or GaAs polycrystalline substance, is melted to form GaAs melt 3 in the quartz boat 1; (d) The system is held in the state for an enough time to sufficiently dissolve residual oxygen or oxide in the quartz ample 12 into the melt 3; (e) Zone of the melt is transferred to the seed crystal 2 to narrow breadth of the melt zone to a fixed value and the melt 3 is cooled at a cooling rate of <=80mm/hr to solidify; (f) The seed is attached to the melt at the seed crystal 2 side in attaining to a fixed melt zone breadth X and (g) the melt zone is transferred to a reverse direction of the seed crystal 2 under keeping the melt zone breadth X.

Description

[Detailed description of the invention]

, -Industrial application field The present invention is directed to the removal of impurities (Cr, S) by the horizontal zone melting method.
i) A method for producing a semi-insulating GaAs single crystal with uniform concentration. [Prior art] Semi-insulating GaAs single crystals produced by the boat method are usually manufactured using the horizontal Bridgman method (HB method) and the temperature gradient method (GF method).
Manufactured by. These methods are based on so-called normal freezing, in which the seed crystal in the boat is removed, the entire GaAs is made into a melt, seeding is performed, and the seeding is crystallized from a portion. By the way, in order to realize semi-insulating properties of GaAs single crystal, it is generally doped with impurities such as Cr or 0. However, the above method is normally free/
Due to the pufferfish, especially in the case of Cr having a small segregation coefficient, the concentration changes extremely along the length direction of the crystal (for example, the concentration changes by a factor of 10 to 100 at a solidification rate of 0°9). On the other hand, in the case of Si, which is a residual impurity, the change is about five times. In other words, residual Si mixed in from the quartz boat
Regarding a degree, there is no usual segregation phenomenon. residual 5i
7II is determined according to the oxygen concentration in the melt by the chemical reaction shown in equation (1). 5ift-3i(in GaAs melt)+20
(in GaAs melt) - (1) k (constant) =
[S i ] [0]” In other words, if the oxygen concentration in the GaAs melt is high, the Si concentration will decrease, and conversely, if the oxygen concentration is low, the Si concentration will increase. This means that the residual Si concentration can be reduced. Therefore, the HB method
In the GF method, the concentration of oxygen in the melt also changes along the length of the crystal, and oxygen is condensed at the rear end of the crystal. It becomes moderately low. Therefore, a horizontal zone melting method has been considered for the purpose of alleviating the change in impurity concentration due to the above-mentioned segregation (see Japanese Patent Publication No. 14382/1982). In general, in the zone melt method, a melt zone with a width as small as possible than the length of the port or crystal is created, and the melt is moved from the rear end of the crystal toward the seed crystal while maintaining this zone width, and then seeded. After that, the seeding device is moved from the part toward the rear end to produce a single crystal. In this method, if it is an impurity that normally causes segregation (for example, Cr), if the melt width is X and the crystal length is Q, then the seeding will be from part to Q-x.
In other words, the impurity concentration can be kept constant up to the portion where the trailing end of the crystal is left with a length corresponding to the melt width. [Problems to be Solved by the Invention] Now, in order to keep the electrical properties of the Cr-topped semi-insulating crystal constant, it is necessary to keep the Cr concentration constant and the residual Si concentration constant, but the above-mentioned normal zone melt method According to the authors, because the melt zone width is narrow, even if oxygen is dissolved into the melt, as it grows from the seed crystal, oxygen is taken in by segregation into the grown single crystal, Since no new supply can be expected into the melt moving toward the crystal, the oxygen concentration decreases toward the rear end of the crystal, and conversely, the SiJ degree increases. In other words, even if the Cr concentration can be made uniform, only the residual Si concentration or the non-uniform crystal along the length direction of the crystal can be obtained. Therefore, in order to solve these drawbacks, the GaAs in the boat, excluding the seed crystal, was intentionally doped with oxygen or an oxide, and the entire GaAs in the boat was placed in a wide melt zone.
The entire GaAs is made into a melt. The melt is left in the melt state for a predetermined period of time, and then the melt zone is solidified by gradually narrowing the melt zone width from the side opposite to the seed crystal, until the melt zone reaches the predetermined width on the seed crystal side. A method for producing a single crystal has been proposed in which seeding is performed at the time of melting, and then the melt zone is moved in the opposite direction of the seed crystal while maintaining the zone width to solidify the crystal (Japanese Unexamined Patent Publication No. 64-65099). . However, with this method, the narrower the zone width, the more oxygen is concentrated in the melt during seeding, and a phenomenon called "wetting" occurs, where the port and the rear end of the crystal are sewn together. However, the single crystal cannot be taken out without destroying the quartz boat.Usually, the quartz boat can be reused 3 to 5 times,
The above-mentioned method of generating quartz boats has the disadvantage of being very uneconomical in terms of the life of the quartz boat. The purpose of the present invention is to eliminate the drawbacks of the conventional horizontal zone melting method described above, and to eliminate "wetting" between the quartz boat and the crystal.
Moreover, it is an object of the present invention to provide a method for manufacturing a semi-insulating GaAs single crystal in which not only the added impurities such as Cr but also the residual Si concentration are uniform along the length direction of the crystal. [Means for Solving the Problems] The present invention provides a method for manufacturing a Cr-doped semi-insulating GaAs single crystal without intentionally doping oxygen using a quartz boat, in which a seed crystal is placed on one end side of a quartz ampoule as a raw material. Ga or GaAs polycrystals and C as a dopant
After placing a quartz boat containing r and placing As on the other end side of the quartz ampoule, the entire quartz ampoule is heated and vacuumed, and then the internal pressure of the quartz ampoule is approximately equal to the dissociation of GaAs. The As is heated to a pressure (1 atm), and the quartz boat excluding the seed crystal is placed in a melt zone and heated uniformly to cause a synthetic reaction between the Ga and the As vapor. or by melting the GaAs polycrystal, forming a GaAs melt in the quartz boat. Then, while the GaAs melt is formed in the quartz boat, oxygen or oxides remaining in the quartz ampoule that cannot be removed by the vacuum treatment are removed by the G
Leave it for a sufficient time to fully dissolve it in the aAs melt1.
, Then, by moving the melt zone from the opposite side of the seed crystal toward the seed crystal until the melt zone forming the GaAs melt is narrowed to a predetermined width, the GaAs@ liquid is heated at a rate of 80 mm/hr or less. The melt is gradually cooled and solidified as polycrystals at a high speed, and the oxygen dissolved in the melt is concentrated in the melt zone. When a predetermined melt zone width is reached on the seed crystal side, a note is attached, and then,
While maintaining the zone width of the melt zone, the melt zone is moved in a direction opposite to the seed crystal, and the GaAs
It is designed to grow a single crystal. Effect] The difference between the method of the present invention and the invention described in JP-A No. 64-65099 is that oxygen or oxides are intentionally added in the invention described in the publication, whereas in the present invention, oxygen or oxides are intentionally added. The vacuum treatment performed before sealing the quartz ampoule containing the quartz boat cannot completely eliminate the oxygen that naturally exists on the inner wall surface of the quartz ampoule. is concentrated in the melt zone. This is because, as mentioned above, if oxygen is intentionally doped, as the melt zone width is narrowed, oxygen becomes too concentrated and "wetting" is likely to occur. Temperature 13
0-2500C and a pressure of 5 x 1'O-'torr for at least 1 hour. When the temperature is lower than 1500°C, the water adsorbed in the ampoule can be effectively removed, and when the temperature is higher than 250°C, the loss of As introduced to control the atmospheric pressure inside the ampoule increases. Therefore, the heating temperature is preferably 150 to 250'C. In addition, once the entire GaAs in the boat has been made into a melt, the speed at which it is solidified from the rear end of the boat is at least 80 mm/mm, since it is necessary to concentrate the oxygen in the melt due to segregation.
It must be allowed to solidify at a rate slower than h. If it is faster than this, the segregation effect will be reduced and oxygen will not be concentrated in the melt, so the effect of making the Si concentration uniform will be lost, and the Si concentration in the crystal will increase, making it no longer semi-insulating. This is because it will be put away. [Example. Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIGS. 1 to 4 show G a , A, and A of this example, respectively.
It is a figure showing the manufacturing process of s single crystal. In Figures 1 to 3, 1 is a quartz boat, 2 is a GaA
s seed crystal, 3 indicates GaAs melt, 4 indicates GaAs single crystal or polycrystal, T, to T3 indicate the temperature distribution in the furnace corresponding to the position of quartz boat l, M3. M3 indicates the temperature distribution or the direction of movement of the furnace. The region falling within the A li distribution T, -T3 is the melt zone, and its width is the melt zone width. In FIG. 4, 12 is a quartz boat 1 and a quartz ampoule containing As1O for maintaining the atmospheric pressure at about 1 atm, 14 is a horizontal zone melting device, 14a is a high temperature furnace, 14b is a low temperature furnace, and 16 is a melt forming Department. First, a GaAs seed crystal 2. G
Set the quartz boat 1 containing the As original t4 and the diffusion barrier 17, align the opening of the ampoule piece 12a with the opening of the other ampoule piece +2b containing As1O, and place the central part 12C. Weld with. Next, the small diameter opening 12 at the end of one ampoule piece 12a
Connect a vacuum pump (not shown) to d, heat the entire ampoule 12 at a temperature of 150 to 250°C for about 1 hour, and heat it for at least 1 hour while maintaining its quality.
Vacuum treatment is performed below XIO-'torr. After that, the small diameter opening 12d is sealed off, and the ampoule 12
Moisture and oxygen adsorbed on the inner wall surface of the GaAs raw material, such as GaAs,
A sealed ampoule 12 is prepared which excludes most of the oxides such as ATOL and AS 208. However, what is important here is that it is impossible to completely remove the oxygen and oxides present in the ampoule 12 with the above-mentioned evacuation process; or that it still exists. The temperature distribution shown in FIG. 4 will be explained later along with specific examples. After preparing the sealed ampoule 12 as described above, as shown in FIG. As shown, GaAs has a melting point or higher (1245
The melt 3 is heated to 1255°C, preferably 1250°C. At this time, oxygen that could not be completely removed by the vacuum treatment is present in the quartz ampoule 12, for example, in the ampoule inner wall surface 1, in the quartz boat, and on the surface of the GaAs melt. Oxides are present. Therefore, in this embodiment, in order to dissolve the naturally mixed trace amount of oxygen and oxides into the melt 3, the melt 3 is left to stand for at least 30 minutes or more, preferably for about 5 hours. Next, as shown in FIG. 2, from the temperature distribution T up to that point, the width of the melt zone can be sandwiched from the rear end 1b side toward the seed crystal 2, as shown by the arrow x42.
Lower the furnace temperature too much (crystal temperature: 4000~120)
00C) Go. In this way, the GaAs melt 3 is solidified from the rear end 1b to the vicinity of the seed crystal 2 to form a polycrystal 4b as shown by temperature distribution T2. Then, when the melt 3 on the side of the seed crystal 2 reaches a width of /-7 or a predetermined width X, /-t is attached to form a single crystal from the seed crystal 2. That is, as shown in FIG. 3, by moving the melt zone while maintaining the melt zone width X, the melt 3 is moved in the direction of the arrow so that the temperature distribution T3 as shown in the figure is obtained in the direction opposite to the seed crystal 2. As shown by M, a single crystal 4a of length Q is formed while moving. This melt zone width X is x/Q=1/3 to 1/20, preferably l/10 to the length.
shall be. Moreover, the moving speed is 4 to 15 mm/h. By forming a GaAs single crystal in this way, the SiA degree and the Cr concentration when Cr is used as a dopant have a constant distribution between the seed crystal 2 and the solidification rate (1-x/Q), and the Si The change in degree of impurity of Cr and Cr is ±50% or less between the solidification rates (1-x/12). Hereinafter, specific examples of the present invention and comparative examples will be described together. (Example 1) As shown in FIG. 4, one quartz ampoule piece 12a has
Seed crystal 2. A quartz boat 1 carrying 2,500 g of Ga and 500 rr of Cr as a dopant + 9 and a diffusion barrier 17 were set, 2.790 g of As 10 was put into the other quartz ampoule piece + 2 b, and these openings were overlapped. The central portion 12c is welded. Next, after heating the entire ampoule 12 to 200'C and holding it for 1 hour, the ampoule piece 12 a (D small diameter opening 12
5 x 1 by vacuum pump (not shown)
After evacuation for 1 hour at 0-" Torr or less, the small diameter opening 12d was sealed off to prepare a sealed quartz ampoule 12. This ampoule 12 was transferred to the horizontal zone melting apparatus 1
4, the temperature t0 of the melt forming part 16 in the high temperature furnace 14a is set to 1,250'C1, and the other temperature t1 is set to 1,250'C1.
Adjusted to 2000C. The low temperature furnace 14b has an ampoule 12
In order to maintain the As pressure inside the tank at I atm, the temperature t was set to about 600
Adjusted to 'C. Next, before starting growth, the overall temperature of port 1 excluding seed crystal 2 is

[6] was raised to 1.250°C to form GaAs melt 3, left in this state for 5 hours, and then the width of the melt zone was narrowed from the rear end side while maintaining the overall temperature t6. By gradually lowering the temperature of the furnace, the mixture was solidified into a polycrystalline form at a rate of 2 mm/h using normal freezing. However, a portion of the melt near the seed crystal with a length of 60 mm was left. Next, after seeding, by moving either the melting device 14 or the ampoule 12 while maintaining the melt zone width at a speed of 5 mm / h,
The zone was moved to the opposite side to finally grow a single crystal of 600 mm, and then cooled to room temperature at 100 deg/h. There is no "wetting" between the crystal and the boat, and after slicing and polishing the front and rear ends of the crystal with one surface of floo, the dislocation density (E D P : Etch Pit Density
) was found to be a good crystal with FDP≦5,000 cm-'. Cr and 5laIj in the length direction of this single crystal are CD
The results measured by MS are shown in concentration distribution 56 in FIG. C
The rLfa degree distribution 5 is approximately 54 cm (y-1-x/Q=0
．． 9) The concentration is maintained at a nearly constant level of 40 x 1016 cm-3, and the Si concentration distribution 6 is also approximately 54 cm (it = 0.
9) while maintaining a nearly constant ts degree of 0.6 x 10" cm ~ 3 and 9= for the total impurity amount (Cr-81)
Between 0.9 and 50% or less. (Example 2) When an undoped semi-insulating crystal not doped with Cr was produced in the same manner as in Example 1, the same result as in Example 1 was obtained for the s1 concentration distribution. Note that "wetting" did not occur. (Example 3) In Example 1, when the speed at which the melt is solidified into a polycrystalline form from the rear end of the port is 80 mm/h, the Si4 degree is g
= o, I is 0.8X I O” cmg = 0.9 is 0.9
x 10"cm-3. No wetting occurred. (Example 4) In Example 1, the speed at which the melt solidified into a polycrystalline form from the rear end of the port was set to 50 mm/h. When, S''rI degree is g=('), 1 is 0.6X1016 cmg-09 is 0
．． 7 x 10"cm-': There was no wetting. (Comparative Example 1) An ampoule similar to Example 1 was prepared, and the crystal length was 600 mm.
On the other hand, the temperature of the entire melt outside the melt zone was rapidly lowered so that the melt zone width was 60 mm, and the entire melt was solidified at once. Next, by seeding and moving to the opposite side at a speed of 5 mm/h, a single crystal with a halo of 00 mm was finally grown. Thereafter, it was cooled to room temperature at 1100 de/h. Although "wetting" between the crystal and the port did not occur, when the crystal was taken out and its properties were measured, no significant difference in dislocation density or Cra degree was observed compared to the crystal of Example 1, but Si7 $i is 2. OX1
016 cm-3, and as distribution 7 in Fig. 5 shows, it becomes even higher toward the rear end (g = 09, 10X
It was 1016cm-3. Therefore, it can be seen that there is a difference in the specific resistance value in the length direction of the crystal. (Comparative Example 2) Under the same conditions as in Example 1, except that the entire G a and A s were left in the melted state for 30 minutes, the /- marked portion was 0. Approximately 54c for 8x l 016cm-3
m (g = 0.9), the Si concentration of the crystal grown was approximately 15 times as high as 1.2 (Comparative Example 3) Crystal growth was performed in the same manner as in Example 1, except that the rate at which GaAs@1ffl was solidified from the rear end of the boat was 100 mm/h. However, the part with /-g is S】LRV l,
OX 10 "Cm-' or about 1 for Example 1
．． The crystal size was increased to 5 times, and the obtained crystal was probably a hand-insulating crystal, or the characteristics after annealing were unstable. "No wetting occurred. (Comparative Example 4) Crystal growth was performed in the same manner as in Example 1, except that the speed at which the G a S melt was solidified from the rear end of the boat was 150 mm/h. , / - The S concentration at the end is approximately twice as high as l, 5 x 1016 cm -3, and at the rear end of the crystal (g = 0.9) it is 5.0 x 10" cm -3, resulting in a The resulting crystal is no longer semi-insulating over almost its entire length. There was no occurrence of "wetting". (Comparative Example 5) In Example 1, when 350 mg of Gat0 was placed in a quartz boat and grown, the Si concentration was almost constant until g=09. I x 10 ``cm-'', but the crystal and boat were completely burned. (Comparative Example 6) In Example 1, when the heating mW during vacuuming treatment was set to 120'C. , the Si concentration was almost constant up to g-09 of 0.2 x 1018 cm, or the crystal and boat were completely burned out. Effects of the Invention 1 As explained above, according to the present invention, the following are achieved. (1) Without intentionally doping oxygen or oxides, naturally occurring oxygen is concentrated in the zone melt shell before crystal growth. /- indicates the la of Cr and residual S1 from the part to the position near the rear end of the crystal.
It is possible to obtain a GaAs semi-insulating crystal which has a substantially constant temperature and is completely free from seizure between the boat and the crystal. (2) At the same time, variations in characteristics such as resistance values are eliminated, and high resistance within the wafer surface, which is important for semi-insulating crystals, can be made uniform.

[Brief explanation of drawings]

1 to 4 are schematic process diagrams showing an embodiment of the GaAs single crystal manufacturing method of the present invention, and FIG.
Explanatory diagram showing that the entire s is left in a melted state for a predetermined time, 2nd
The figure is an explanatory diagram of cooling and solidifying from the opposite side of the seed crystal at a speed below a predetermined speed, and Figure 3 shows the melt zone being moved from the opposite side of the seed crystal to the same side while maintaining the melt zone width. Fig. 4 is a temperature distribution characteristic diagram in the axial direction according to this example, and Fig. 5 is a longitudinal temperature distribution diagram of crystals obtained by the manufacturing method example of the present invention and the Toto method. It is a characteristic diagram showing the Cr and Si concentration distribution. 1 is a quartz boat, 2 is a seed crystal, 3 is a Ga, As melt, 4a is a single crystal, 4b is a polycrystal, X is the width of the melt zone, Q is the length of the crystal. 1. Explanatory diagram of the quartz book left unused according to this example. Figure 2: Solidification of crystals in the direction of the rear end according to this example. Temperature characteristics in the furnace axis direction according to this example. Figure 4

Claims (1)

[Claims] In a method for producing a Cr-doped semi-insulating GaAs single crystal without intentionally doping oxygen using a quartz boat, (a) a seed crystal is placed on one end side of a quartz ampoule, Ga as a raw material or GaAs polycrystal and Cr as a dopant
After placing a quartz boat containing As and placing As on the other end side of the quartz ampoule, (b) vacuuming the entire quartz ampoule while heating it, and (c) reducing the internal pressure of the quartz ampoule. At the same time, the As is heated to approximately the dissociation pressure of GaAs, and the quartz boat excluding the seed crystal is placed in the melt zone and heated uniformly, so that the Ga and As vapors undergo a synthesis reaction. or by melting the GaAs polycrystal, a GaAs melt is formed in the quartz boat, and (d) in that state, the GaAs melt cannot be removed by the vacuum treatment and remains in the quartz ampoule. (e) After standing, the seed crystal is allowed to stand for a sufficient period of time to sufficiently dissolve the oxygen or oxide present in the GaAs melt; and (e) after the standing, the seed crystal is By moving the melt zone toward the seed crystal from the opposite side, the GaAs melt is gradually cooled and solidified as polycrystals at a speed of 80 mm/hr or less, and the oxygen dissolved in the melt is removed from the melt zone. (f) seeding is performed when the melt zone reaches a predetermined width on the seed crystal side; (g) after that, the melt zone is seeded with the seed while maintaining the zone width of the melt zone; A method for producing a GaAs single crystal, comprising growing the GaAs single crystal by moving the crystal in the opposite direction.