JPS63288011A - Vapor crowth method - Google Patents

Abstract

PURPOSE:To widen the range of flow rate of raw gas in which film thickness is made uniform, and the film thickness of a vapor growth layer is easily made uniform not only on the wafer surface but also on the region between the wafers by a method wherein the main jetting direction of raw gas is prevented rom becoming coincident with the direction in which a gas feeding nozzle and a wafer rotation center are linked. CONSTITUTION:In the diagram showing a wafer 11 and a gas feeding nozzle 16, 19 shows the raw gas came out from a jetting-out hole, and x' shows the main jetting-out direction of raw gas. O indicates the center of rotation of the wafer 11. The direction linking the nozzle 16 and the rotational center O is shown by (x). (l) indicates the length of a vertical line brought down to x'-axis from the center of rotation of the wafer. The distribution of concentration of raw gas in the direction vertical to the x'-axis from the point P can be brought to approximate to g.e<-p2/delta2> using the distance P in y'-axis direction measured from the point P. However, (g) is the concentration of raw gas at the point P, and delta shows the direction in which the concentration of raw gas becomes 1/e. By using the approximate expression as above-mentioned, the relation of the jetting direction and the x-axis is formed in such a manner that the distance (l) becomes about 40%-80% of the attenuation distance delta.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an apparatus and method for forming a vapor phase growth layer on the surface of a semiconductor wafer, and particularly relates to a vapor phase growth method suitable for uniformly forming a vapor phase growth layer. Concerning a growth method and its apparatus.

[Conventional technology]

Increasing the diameter of semiconductor wafers (hereinafter referred to as wafers) for the purpose of reducing process costs and improving product yields (diameter 6
Due to the demand for higher integration and higher speed of devices (inches or larger), it is necessary for the thin films to be formed to have a uniform thickness on large wafers.

Therefore, as described in Japanese Patent Application No. 60-30459, a large number of wafers were placed in a reaction vessel so as to substantially surround the wafers, with their main surfaces substantially horizontal and arranged at regular intervals. The wafer is heated by a cylindrical heating body, and a reactive gas is supplied from one side around the wafer between the wafers using a nozzle having holes, and the wafer is rotated in a horizontal plane about the center of its main surface. A CVD method and its apparatus have been proposed for forming vapor phase growth (hereinafter abbreviated as CVD) III on a large number of wafers at once.

[Problem that the invention seeks to solve] However, in the conventional CVD apparatus described above.

Insufficient consideration was given to the direction of the raw material gas ejected from the nozzle (hereinafter abbreviated as the main ejection direction).

An example is shown in Figure 9, when the growth temperature is 1100°C or higher,
The film thickness of the vapor phase growth layer is proportional to the raw material gas concentration. When the main ejection direction of the raw material gas passes through the rotation center O of the wafer, the change in the raw material concentration due to the change in the raw material gas flow rate at the rotation center 0 is larger than the above change at the periphery of the wafer, and the change in the raw material concentration with respect to the film thickness of the vapor growth layer is Large impact (see Figure 9-b)
Therefore, if the flow rate of the raw material gas (not the flow rate of the raw material gas 19 ejected from the nozzle 16) differs, the film thickness distribution will vary greatly as shown in FIG. 9-c.

Therefore, the conventional method described above has a problem in that it is not easy to make the thickness of the vapor growth layer uniform on large wafers.

An object of the present invention is to propose a method for easily uniformizing the thickness of a vapor-phase growth layer.

[Means for solving problems]

The above object is achieved by making sure that the main jetting direction of the 1M material gas does not coincide with the direction connecting the gas supply nozzle and the wafer rotation center (hereinafter abbreviated as the X axis).

The relationship between the main jetting direction and the X-axis is described below using Figure 2.If the jetting direction is the X'-axis, then the length of the perpendicular drawn from the wafer rotation center on the X-axis to the X'-axis is (hereinafter simply abbreviated as distance a).

The relationship between the ejection direction (x/axis) and the X-axis can be shown (however, the X-axis and the The concentration distribution of the source gas in the direction perpendicular to the X' axis (abbreviated as the y' axis) from point P is approximated by 1g·ep''/62 using the distance ρ in the y' axis direction measured from point P. Yes, but g
is the concentration of the source gas at point P, and δ is the attenuation distance below the distance fllc at which the concentration of the source gas becomes 1/e (abbreviated as δ) (see Figure 10). Using this approximate expression, As will be shown later, the means to achieve the objective is to adjust the relationship between the ejection direction and the X axis so that the distance WIQ is approximately 40 degrees
% to approximately 80%.

[Effect]

As is clear from FIG. 9C, the uniformity of the vapor grown layer is determined by the center of the wafer (i.e., the center of rotation).
This is due to the following reasons. The concentration distribution of the source gas is averaged in the circumferential direction by rotation. Because the circumference is long at the periphery of the wafer, when looking at one point on the circumference, the change in film thickness caused by the difference in raw material gas concentration due to changes in the raw material gas flow rate is small, whereas at the center of the evaporator, the circumference is short. To,
The above film thickness change at one point on the circumference becomes large. Therefore, when the flow rate changes, the film thickness changes greatly at the center of the wafer.

On the other hand, if the main ejection direction of the source gas does not match the X-axis, the concentration of the source gas due to the change in the source gas flow rate at the center of the wafer will be lower than when the main ejection direction and the X-axis coincide. The difference becomes absolutely small. As a result, the change in film thickness at the center of the wafer becomes small, and uniformity in the thickness of the vapor-phase grown layer can be easily obtained.

〔Example〕

The present invention will be described below with reference to FIG. 1 using Si epitaxial growth as an example.

FIG. 1 is a schematic longitudinal sectional view of the vapor phase growth apparatus.

Reference numeral 11 denotes silicon single crystal wafers, and a total of 20 wafers are set in a quartz holder 12 with two wafers each in 10 stages with the main surface facing up. The holder 12 is rotated by a motor 18 with the center of the main surface of the wafer as the rotation axis. The wafer 1 is surrounded by a cylindrical carbon susceptor 14, and the susceptor 14 is heated by induction using a high-frequency coil 15 to uniformly heat the wafer 1 to an epitaxial growth temperature. 16 is a nozzle for supplying raw material gas, and has a raw material gas jet port 16a.

17 is a waste gas exhaust pipe. 13 is a bell jar made of quartz that serves as a reaction vessel.

FIG. 2 shows a first embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view of FIG. 1 in which only the wafer 11 and gas supply nozzle 16 are extracted and shown. Reference numeral 19 denotes raw material gas spouted from the jet nozzle, and x' is the main jetting direction of the raw material gas. 0 is the rotation center of the wafer 11. X is the direction connecting the nozzle 16 and the rotation center O. Q is the length of a perpendicular line drawn from the rotation center 0 to the X' axis.

The thickness uniformity of a vapor-phase grown layer obtained by epitaxial growth using a large-diameter wafer having a diameter of 12.701 (5 inches) will be explained. Wafer 11 is 2Orpm
Rotate with. Hydrogen gas 4 from nozzle 6 Q Q /wi
After supplying n for 10 minutes to create a hydrogen atmosphere in the furnace, the high frequency coil 15 is energized and the temperature of the susceptor 14 is raised to 1150°C. Approximately 1.8iCQaJjjl material is added to hydrogen gas.
Add 5moQS m and start epitaxial growth.

At this time, the mixed raw material gas of hydrogen and S i CQ a at a predetermined flow rate (25 to 45 n/win) is supplied to the nozzle 16 and is uniformly distributed on each wafer 11 from the jet port 16a with a width of 0.6 m and a length of 260 m. supplied to The waste gas is discharged outside the bell jar 13 through the exhaust nozzle.

After epitaxial growth for a given time.

The supply of S i CQ 4 is stopped, the temperature of the susceptor 14 is lowered, and when the wafer temperature becomes low, the bell jar 13 is opened and the wafer 11 is taken out.

In the above operation, the film thickness uniformity of the epitaxial layer obtained when varying a from 0 to 20Ell is shown in FIG. When compared with uniformity of ±10% or less, Q=
In the case of O-, the uniformity is less than ±10% only in the flow rate range of 32.6 ±0.4117w1n, whereas j
When l=10m, 33.5 ±Q, 5 Q/w
In, the flow rate range where the flow becomes uniform is increased by 25%.

In this example, the attenuation distance δ in the y' direction is about 23-, and the result obtained in FIG. 3 is 2/δ20.44. When δ/Ω<0.4, the flow rate range in which uniformity of ±10% or less can be obtained is almost the same as when δ/Q=O, and
When δ/Q>0.8, uniformity of ±10% cannot be obtained.
δ/n) 0.8, the raw material gas concentration at the center of the wafer becomes too low, and as shown in Figure 4, even if the gas flow rate is increased, the film thickness at the center of the wafer remains at a radius of approximately 20 mm from the center of the wafer.
It becomes thicker than the film thickness at ~40 m. Or because they are not the same.

Next, as a second embodiment, a case where there are two gas supply nozzles will be described with reference to FIG.

FIG. 5 is a schematic cross-sectional view showing only the wafer 11 and the nozzles when there are two gas supply nozzles 16 in FIG. 1. Reference numerals 26 and 36 are gas supply nozzles, each having a gas outlet 26 similar to the first embodiment.
a, 36a.

The X5' axis and the Xi' axis have nozzles 26 and 36, respectively.
eQ1p bag z showing the main ejection direction of the raw material gas ejected from
are the lengths of perpendicular lines drawn from the rotation center O of the wafer 11 to the xL/axis and the Let's call it a nozzle.

The film thickness uniformity obtained by changing the flow rate of the raw material gas in the same manner as in the first example was measured in the sixth example. It is shown in FIG.

However, Ω2 was all set to 40 as. Figure 6 shows Q1=O
In case III, the gas flow rate of the second nozzle 36 is set to 4.
The film thickness uniformity obtained by setting the gas flow rate of the first nozzle 26 in stages is shown. In this case, the film thickness uniformity is much better than in the example of cylinder 1, and the best is ±
4% was obtained. Considering ±5% as the target uniformity, when the gas flow rate of the second nozzle 36 is 32.3 Jl/win, the gas flow rate range of the first nozzle 26 is 36.3 ±0.
．． 3Qlin (in addition, the second
The gas flow range of the nozzle 36 is 32.8±1.6 Jl,/s when the gas flow rate of the first nozzle is 36.3Q/+*in.
).

FIG. 7 shows the film thickness uniformity obtained in the same manner as FIG. 6 when Q1=15 m. In this case, the film thickness uniformity is further improved than Ql:O, and the best is ±
1% was obtained. Furthermore, the gas flow rate range of the first nozzle that is ±5% or less is such that the flow rate of the second nozzle 36 is 30.8Q/
When compared to the case where mn5=o, which was 38.4±0, 8 Q/win, the gas flow range of the first nozzle, which is less than ±5%, is improved by 2.7 times. Second
The gas flow range of the nozzle is also improved by more than three times.

In order to clarify these results, FIG. 8 shows the range of gas flow rates of the first and second nozzles in which film thickness uniformity of ±5% or less is obtained, using the value of Ql as a parameter.

As can be seen from this figure, Ω1 = Om and 5ff11
Compared to case 1, when flz = 10 oi and 15+m, the gas flow range of the first and second nozzles in which the film thickness uniformity was ±5% or less became significantly larger.

In the case of this embodiment as well, as in the first embodiment, the attenuation distance δ is approximately 23 −. Therefore, a uniform film thickness distribution can be obtained as follows. Ratio Q1 of the gas supply nozzle with the shortest vertical length from the rotation center of the wafer with respect to the main ejection direction of the source gas (i.e., when nozzle 2e>I, the length of the perpendicular line, i.e., Qs) and the attenuation distance δ /δ, Q1
When /δ≦0.8, uniformity of ±5% or less is obtained, but when Ql/δ>0.8, the uniformity is greater than ±5%. 'The reason for this is that, as shown in the first embodiment, even if the gas flow rate is increased, the film thickness at the center of the wafer becomes thicker than at a radius of approximately 20 to 40 mm from the center of the wafer.
Or maybe it's because they will never be the same. Furthermore, looking at the size of the gas flow rate range where the film thickness becomes uniform, it is found that 0
．． When 4≦Q1/δ≦0.8, compared to the case where Qs/δ=0.

The size of the above gas flow rate range is approximately 2.5 to 4 times larger.

Therefore, even if there are two gas supply nozzles, in the gas supply nozzle for which the length a of the heavy line is the shortest, 0.4≦Q1
When /δ≦0.8, the thickness of the epitaxial layer becomes the most uniform, and the flow rate range of the source gas that becomes uniform becomes the widest.

In the above embodiments, the cases where there are one and two gas supply nozzles have been described, but the same effect can be obtained even when there are three or more gas supply nozzles.

In the case of two gas nozzles, in the second embodiment above.

The case where the main ejection direction of the gas ejected from each nozzle is on the opposite side of the wafer rotation center has been explained.
A similar effect occurs even when the side is not opposite. The same applies to the case of three or more.

Further, in the above embodiment, a wafer with a diameter of 12.7 m was described, but the same effect can be obtained when the wafer diameter is larger or smaller than this.

Furthermore, although the case where the attenuation distance of the raw material gas concentration in the direction perpendicular to the gas ejection direction is 23 m has been described, the effect is the same when the attenuation distance is larger or smaller than this.

The shape of the gas outlet is not limited to the slit shape as in the above embodiment, but may be a circular or elliptical hole, for example, with the same effect.

Although the above embodiment describes the case where Si is epitaxially grown, the present invention is not limited to this, and the present invention can be applied to any device structure shown in FIG. 1.

[Effects of the Invention] As described above, according to the present invention, the flow rate range of the source gas in which the film thickness becomes uniform is widened, so that the film thickness of the vapor growth layer can be adjusted to
There is an effect that uniformity can be easily achieved not only within the wafer surface but also between wafers.

Furthermore, when a plurality of gas supply nozzles are present, application of the present invention has the effect of making the thickness of the vapor growth layer more uniform.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view of a vapor phase growth apparatus for explaining the first and second embodiments of the present invention, FIG. 2 is a diagram showing the main parts of FIG. 1, and FIG. FIG. 4 is a diagram showing an example of the film thickness distribution of the epitaxial layer in the radial direction of the wafer, and FIG. 5 is a diagram showing the thickness uniformity of the epitaxial layer according to the second embodiment. FIG. 6 is a diagram showing the film thickness uniformity according to the conventional method, and FIG. 7 is a diagram showing the film thickness uniformity according to the second embodiment of the present invention. Figure 8 is a diagram showing the range of raw material gas flow rate with uniformity of ±5% or less in the second embodiment, Figure 9 (a) is a schematic diagram showing the conventional method, and Figure 9 (b) is a diagram showing the gas jetting. Figure 9 (Q) is a diagram showing an example of the distribution of the raw material gas concentration in the direction, Figure 9 (Q) is a diagram showing an example of the film thickness distribution of the epitaxial layer in the wafer radial direction by the conventional method, Figure 10 is the direction perpendicular to the gas ejection direction. FIG. 2 is a diagram showing an example of the distribution of raw material gas concentration for FIG. 11... Semiconductor wafer, 16... Gas supply nozzle. 16a... Gas ejection port of nozzle 16, 19... Raw material gas ejected from ejection port 16a, 26... First gas supply nozzle, 26a... Ejection port of nozzle 26, 29...
Raw material gas ejected from the ejection port 26a, 36... second gas supply nozzle, 36a... ejection port of the nozzle 36. 39... Raw material gas ejected from the ejection port 39a, O...
- Center of rotation of the wafer, X'...Main ejection direction of raw material gas, XI'...Main ejection direction of gas ejected from the ejection port 26a, X2'...Main ejection direction of the gas ejected from the ejection port 36a Direction, Q...Length of the perpendicular drawn from ○ to the X' axis, Ql...Length of the perpendicular drawn from 0 to the xt' axis, Ω2...Length of the perpendicular drawn from ○ to the x2' axis length. δ... Positive amount of attenuation in the direction perpendicular to the X' axis of the raw material gas concentration 10 16... Force' or I# is set to lk...
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Claims (1)

[Claims] 1. A large number of semiconductor wafers are stored vertically in a reaction vessel with their main surfaces horizontal and parallel to each other, and while being heated, raw materials are supplied from one end of a gas supply nozzle installed in the reaction vessel. In the method of forming a vapor phase growth layer by introducing a gas, rotating the semiconductor wafer in a horizontal plane about the center of its principal surface, and supplying a raw material gas from the outer periphery of the semiconductor wafer substantially parallel to the principal surface, the gas supplying A vapor phase growth method characterized in that the direction in which the raw material gas is ejected from the nozzle does not coincide with the direction connecting the gas supply nozzle and the rotation center of the semiconductor wafer. 2. In claim 1, the distance between the wafer rotation center and a straight line passing through the gas supply nozzle and drawn in the direction in which the raw material gas is ejected from the gas supply nozzle is equal to the distance between the straight line and the semiconductor A vapor phase growth method characterized in that the distance in the vertical direction of the straight line from the intersection point is about 40% to about 80% such that the concentration of the raw material is 1/e of the concentration of the raw material at the intersection point with the upstream end of the wafer. 3. In claim 1, in the vapor phase growth method comprising a plurality of gas supply nozzles, the direction in which the raw material gas is ejected from all the gas supply nozzles is based on the rotation of the gas supply nozzles and the wafer. A vapor phase growth method characterized by not matching the direction connecting the centers. 4. In claims 2 and 3, the distance between the wafer rotation center and a straight line passing through the gas supply nozzle and drawn in the direction in which the raw material gas is ejected from the gas supply nozzle is equal to A vapor phase growth method characterized in that the distance is about 40% to about 80% of the vertical distance with respect to the shortest gas supply nozzle among the supply nozzles.