JP2773339B2 - Liquid phase epitaxial growth method - Google Patents

Description

The present invention relates to a liquid phase epitaxial growth method using a vertical dipping method.

(Prior Art) A vertical dipping method, which is one of the liquid phase epitaxial growth methods, is well known as a method excellent in mass productivity. FIG. 3 is an explanatory view of a liquid phase epitaxial growth apparatus used in this method. As shown in FIG. 1A, a material solution 4 prepared by melting a growth material such as a solvent, a solute and a dopant is accommodated in a crucible 5, while the wafer 1 is placed in a cassette 3. A plurality of dishes 2 are stacked. In FIG. 2B, the cassette 3 is immersed in the crucible 5 and the raw material solution 4 is introduced onto the wafer 1, and the temperature of the crucible 5 is gradually cooled, whereby epitaxial growth is performed on the wafer 1. After the predetermined epitaxial growth is completed, the cassette 3 is pulled up from the crucible 5 and the raw material solution 4 is removed from the surface of the wafer 1 as shown in FIG.
Is removed. Thereafter, the growth operation is completed by cooling to room temperature.

(Problems to be Solved by the Invention) However, in the vertical dipping method, after the epitaxial growth is completed, the raw material solution is removed from the wafer surface (liquid exhaustion)
However, there is a disadvantage that the raw material solution is apt to remain (liquid remaining) partially on the wafer surface. Since the characteristics of the epitaxial layer, such as the layer thickness, are different between the portion where the raw material solution remains and the portion where the raw material solution does not remain, the wafer is regarded as defective if any liquid remains on the wafer surface. Therefore, the wafer has been tilted and accommodated in a cassette to improve the liquid drainage rate.

However, depending on the specifications of the characteristics of the epitaxial layer,
Increasing the tilt angle of the wafer may increase the in-plane distribution of the characteristics and deviate from the specifications. In addition, the liquid drainage rate varies depending on the height (liquid thickness) of the raw material solution on the wafer. In addition, it has been necessary to repeatedly determine a plurality of experiments to determine the optimum liquid drainage conditions for the target epitaxial layer.

An object of the present invention is to solve the above problems and to provide a liquid phase epitaxial growth method capable of stably growing an epitaxial layer having no liquid residue on a wafer surface.

(Means for Solving the Problems) According to the present invention, a cassette, in which a plurality of wafers are housed at regular intervals in a vertical direction, is immersed in a raw material solution, and the raw material solution is introduced into the cassette to form a predetermined epitaxial layer. In the liquid phase epitaxial growth method in which the cassette is pulled up from the raw material solution after growing the cassette, the cassette pulling speed is set so that the raw material solution passing speed on the wafer surface at the time of pulling up the cassette is 10 mm / min or less. This is a liquid phase epitaxial growth method.

(Operation) In the vertical dipping method, the present inventors can increase the wafer tilt angle, the cassette pulling speed, the liquid thickness, and the like as the main factors affecting the liquid shortage of the wafer. Attention was paid to the moving speed of the raw material solution on the wafer surface when pulling up from the raw material solution, and the relationship with the liquid shortage of the wafer was examined.

That is, the moving speed can be obtained as follows. First, it was assumed that the inclination angle of the wafer was 0. As shown in FIGS. 1 (a) and 1 (b), the volume of the raw material solution 4 contained in the dish 2 is Vm, the height of the dish is tm, and the sectional area of the slit portion of the cassette 3 is Ss, Assuming that the bottom area of the cassette 3 is Sc and the pulling speed of the cassette is Cc, the descending speed Cm of the raw material solution inside the cassette can be expressed as follows.

(Vm / tm + Cs) · Cm = Sc · Cc Therefore, Cm = Sc · Cc / (Vm / Tm + Ss). Taking into account the tilt angle θ of the wafer, the raw material solution passing speed Cw on the wafer surface becomes Cw = Cm / sinθ. For example, wafer diameter 51mm, thickness 0.3mm, dish inner diameter 52m
m, height 3mm, bottom thickness 1mm, cassette wall thickness 5mm, slit width
Vm = 3.6 × 10 ³ mm ³ , tm = 3 m for 5 mm and 64 mm outer diameter
m, Ss = 50 mm ² , Sc = 3.2 × 10 ³ mm ² . Here, if the lifting speed is Cc = 0.5 mm / min and the inclination angle θ is 15 °, Cm = 1.3 mm / min and Cw = 4.9 mm / min. Based on this definition, under various epitaxial growth conditions, the surface passing speed of the raw material solution at the time of pulling and the liquid drainage rate in that case were examined, and FIG. 2 was obtained. From this figure, it can be seen that there is a clear relationship between the passing speed of the raw material solution on the wafer surface and the liquid drainage rate. That is, by setting the raw material solution passage speed on the wafer surface at the time of lifting to 10 mm / min or less, the liquid can be completely drained.

(Example) Using the above-described apparatus, an attempt was made to grow an Al _0.3 Ga _0.7 As epitaxial layer on a Si-doped n-type (100) GaAs wafer having a diameter of 51 mm and a thickness of 300 μm.

The crucible contains 300 g of gallium, 14 g of GaAs polycrystal, and 480 g of Al.
mg. In the cassette, the above-mentioned wafer was placed on a plate having a height of 2 mm, and ten such plates were set at an inclination angle of 10 °. Then, the temperature of the raw material solution was lowered from 845 ° C. to 790 ° C. at a rate of 0.5 ° C./min to perform epitaxial growth. Thereafter, the cassette was lifted at a lifting speed of 0.33 mm / min. The speed at which the raw material solution passes through the wafer surface for this pulling speed is 7.6 mm / mi
n, which satisfies the conditions of the present invention. Obtained Al _0.3
The Ga _0.7 As epitaxial layer had an average thickness of 8.5 μm, no residual raw material solution was observed on the surface, and the in-plane distribution was uniform with a variation within 10%.

In order to obtain a thicker epitaxial layer, the height of the dish was set to 4 mm and the inclination angle was set to 5 °, and the epitaxial growth was performed under the same conditions as described above. In this case as well, the material solution passed through the surface at a speed of 8.2 mm / min, which satisfies the conditions of the present invention, has no liquid residue, has an average thickness of 23.5 μm, and has excellent uniformity within 7%. A layer was obtained.

(Effects of the Invention) According to the present invention, by adopting the above configuration, an epitaxial wafer having no liquid residue on the wafer surface can be grown stably.

[Brief description of the drawings]

FIGS. 1 (a) and 1 (b) are diagrams for explaining the speed of a raw material solution passing through a wafer surface, FIG. 2 is a graph showing the relationship between the wafer surface passing speed and a liquid drainage rate, and FIG. 3 (a). (C) is a figure for explaining the procedure of the vertical dipping method.

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Claims (1)

(57) [Claims] A cassette accommodating a plurality of wafers at predetermined intervals above and below is immersed in a raw material solution, and the raw material solution is introduced into the cassette to grow a predetermined epitaxial layer. Liquid phase epitaxial growth method, wherein the cassette pulling speed is set so that the raw material solution passing speed on the wafer surface is 10 mm / min or less when the cassette is pulled up.