JPH0718765Y2 - Thin film forming equipment - Google Patents

Description

[Detailed description of the device] [Industrial applications]

The present invention relates to a barrel type thin film forming apparatus. In particular, the present invention relates to an improvement aimed at improving the consumption efficiency of raw material gas and increasing the thin film growth rate.

[Prior art]

A barrel type thin film forming apparatus according to a conventional example will be described with reference to FIG. A cylindrical susceptor 2 inside a vertical cylindrical chamber 3.
Is rotatably supported by the shaft 6. The top of the chamber 3 is hemispherical, and the inlet 4 for introducing the raw material gas is opened at the top. A hemispherical flow channel 1 for changing the flow of the raw material gas and distributing the gas evenly around the susceptor 2 is provided just below the inlet 4 and above the susceptor 2. A number of wafers 5 are attached to the susceptor 2 in a substantially vertical direction around the susceptor 2. Since the susceptor 2 resembles a barrel, it is commonly called a barrel type. The wafer 5 is a semiconductor wafer made of GaAs, InP, Si or the like. The source gas depends on the thin film to be formed on the wafer. For example, it is an organic metal gas containing a group III element such as trimethylgallium or triethylindium, a hydride gas of a group V element such as AsH ₃ or PH ₃ , or a mixed gas such as a dopant gas. A heater (not shown) is provided in the susceptor 2 so that the susceptor 2 and the wafer 5 can be heated to appropriate temperatures. Below the chamber 3, there is a gas outlet,
A vacuum exhaust device (not shown) is connected to the gas exhaust port. The raw material gas is excited by heat on the surface of the wafer 5 to cause a gas phase reaction, and the product is deposited as a thin film on the wafer 5. The state of the flow of the source gas strongly affects the thin film formation on the wafer. The flow channel 1 is provided above the susceptor 2 to make the flow of the raw material gas a preferable laminar flow.
The flow channel 1 has various shapes such as a semi-spherical shape, a polygonal pyramid shape, and a semi-rugby ball shape. In any case, the lower half of the flow channel 1 has a shape that smoothly follows the contour of the susceptor 2. The raw material gas forms a laminar flow by the flow channel 1 and is uniformly distributed to the peripheral surface of the susceptor. Since the susceptor 2 is rotating, the source gas is evenly supplied to the plurality of wafers 4.

[Problems to be solved by the device]

FIG. 4 shows main gas flow paths in the conventional apparatus. This confirmed the gas flow by the visualization experiment. The raw material gas flows from the top to the bottom between the susceptor and the chamber wall, and the portion of the highest linear velocity is shown by the solid line. For convenience of explanation, points K, L, M, N, and P are attached along the flow. Let K be the portion immediately below the gas inlet, L and M points along the flow channel 1, and let N be the vicinity of the boundary between the flow channel and the susceptor. The positions where the wafer should be attached are P and Q. The portion with the highest linear flow velocity is located closer to the flow channel 1 immediately below the inlet 4. However, Frochanel 1
At point L, the linear flow velocity becomes maximum at the midpoint between the flow channel and the chamber wall. For the sake of simplicity, hereinafter, the part where the linear flow velocity is maximum will be referred to as the maximum flow velocity point. It does not mean that the gas is stopped except at this point, and that it does not exist at any other point. However, the gas flow is the most active at the maximum flow velocity point, and if this point is focused on, it is possible to easily understand the complicated gas flow state. When moving to the point M below the point L, the maximum flow velocity point comes closer to the chamber. Even at the N point, which is the boundary between the flow channel and the susceptor, and the P and Q points where the wafer is attached, the maximum flow velocity points are biased toward the chamber wall. When the maximum flow velocity point is biased, the boundary layer near the wall surface on the biased side becomes thin, and the boundary layer near the wall surface on the far side becomes thick. FIG. 5 is a diagram for explaining the boundary layer of such a flow. Flow velocity distribution in a narrow flow path partitioned by parallel walls W and U
It is indicated by XZY. Since the flow velocity on the wall is 0, (X
= 0, Y = 0) A boundary layer is generated in the vicinity thereof. It is assumed that the flow velocity at point Z is maximum. If the point Z is biased to the wall U, the boundary layer D ₂ near the wall U is thin. On the contrary, the boundary layer D ₁ near the wall W is thick. The flow of the raw material gas is weak in the boundary layer, which makes it difficult for the raw material gas to travel toward the wall surface. In the boundary layer, the gas component can travel toward the wall surface by diffusion due to the difference in gas concentration. Since the diffusion is due to the difference in concentration, if the thickness D of the boundary layer is large, it takes a long time for the gas component to reach the wall surface. As shown in FIG. 4, in the flow having the maximum flow velocity far from the susceptor surface on which the wafer should be mounted, the boundary layer on the susceptor side becomes thick, and the raw material gas components almost reach the wafer surface. Can not. That is, the raw material gas is not effectively used and passes through a portion away from the wafer. This is discharged as it is and is wasted. The consumption efficiency of raw material gas is defined as follows. When the group III organometallic gas and the group V hydride gas are used, the gas ratio is often about 1:50 to 100. in this case,
The amount of V group hydride gas supplied, V taken into the wafer
The value obtained by dividing the family components is the consumption efficiency. The gas supply amount can be measured by a mass flow controller. The amount of the V group component taken into the wafer can be determined by measuring the film thickness of the thin film after forming the thin film and performing an appropriate conversion. In the cases shown in FIGS. 3 and 4, the amount of gas taken into the wafer and used for forming a thin film is small, so that it can be said that the consumption efficiency of the raw material gas is low. In order to solve this to some extent, in the structure shown in FIG. 4, the wafer mounting surface of the susceptor is not completely vertical,
A small angle θ (θ> 0) is set so that it spreads slightly downward. However, although there is a slight improvement, the current situation is that gas consumption efficiency is still low. this is,
This is because the point of maximum gas flow velocity passes near the chamber wall that is far from the wafer. With such a shape, the maximum flow velocity point cannot be moved to the vicinity of the wafer, and the consumption efficiency of the source gas cannot be increased. Increasing the consumption efficiency of the raw material gas and increasing the growth rate of the thin film are issues to be solved.

[Means for Solving the Problems]

A thin film forming apparatus having a vertically long chamber, a susceptor for mounting a wafer on a side surface provided in the chamber, and a flow channel provided above the susceptor,
The sidewall of the chamber is expanded to the outside above the susceptor, and the bottom of the susceptor is also expanded to the outside, and the extension line of the sidewall at the expansion point of the chamber is the midpoint of the wafer mounting portion of the susceptor. To pass between points 3 cm above the top of the wafer. This is a feature of the thin film forming apparatus of the present invention. A more detailed description will be given with reference to the drawings. FIG. 1 is a schematic vertical sectional view of a thin film forming apparatus of the present invention.
FIG. 2 is an enlarged view of the flow path. There is a vertically long cylindrical chamber 3 with a hemispherical upper part. This is different from the one shown in FIG. 3 and has a shape that expands outward from the point E in the middle, which is one of the features. There is a gas inlet 4 at the top of the chamber 3 and the raw material gas is introduced from there. Inside the chamber 3, a vertically elongated flow channel 1 having a hemispherical top is provided. Below the flow channel 1, there is provided a susceptor 2 having a truncated cone shape or a truncated pyramid shape with a wafer 5 attached to its side surface. The susceptor 2 is a shaft 6
Supported by. The shaft 6 can be rotated and moved up and down. A resistance heater (not shown) made of carbon or the like is provided in the susceptor 2. The susceptor 2 does not simply have a side surface extending in the vertical direction, but has a side surface facing slightly above the vertical direction, and a plurality of wafers 5 are attached thereto. That is, the susceptor 2 has a truncated cone and a truncated pyramid that have a wide bottom and a narrow top. Further, the upper end of the susceptor is F, the lower end is J, and both ends of the wafer mounting surface are IG. Also, let R be the midpoint of the wafer mounting surface and L be the point 3 cm above the upper end G of the wafer mounting surface. At a point E at which the chamber wall expands outwardly, a point T at which the extension of the tangent f to the wall cuts the susceptor wall. The point T should be between R and L.

[Action]

The trajectory of the maximum flow velocity point of the raw material gas will be described. For convenience of explanation, points A, B, and C are taken from the vicinity of the gas inlet 4 along the side surface of the flow channel 1. At point A, the maximum flow velocity point of the source gas is closer to the flow channel, but since it is repelled here, at points B and C, it is near the chamber wall. Since the chamber wall expands outward at point E, the flow with the maximum flow velocity goes vertically downward along the tangent of the chamber wall at point E. The susceptor follows the flow channel at point F. The side surface FJ of the susceptor has an angle of β with respect to the vertical line (β>
0). At point E, the chamber wall expands outward, but this angle is α (α> 0). The upper end point F of the susceptor is below the expansion point E of the chamber. The vertical distance is l (l> 0). The upper end of the wafer mounting portion on the susceptor is G, the lower end is I, the middle point is R, and the point 3 cm upward from the upper end is L. Since the extension of the tangent line f of the point E is between the line segments RL on the wall of the chamber, the flow with the maximum flow velocity descends from the point closest to the point E to just below, and is slightly inside the point T defined as the point between the points RL. At some point, you will hit the susceptor. Since this point and the T point are sufficiently close to each other, the T point can be regarded as a pseudo incident point of the flow having the maximum flow velocity. Pseudo has two meanings. One is that the straight line of the wall surface tangent line f at the point E is slightly deviated from the flow having the maximum flow velocity. On the other hand, the flow having the maximum flow velocity does not impinge on the susceptor in a straight line, but smoothly bends immediately before the impingement point, and does not impinge. However, since the purpose here is to geometrically limit the structure, point T is defined as the point of incidence of the flow with the maximum flow velocity (the locus of the portion with the highest linear velocity) to the susceptor. This is the general case (T lies between R and L). FIG. 6 shows the case where the T point coincides with the R point, FIG. 7 shows the case where the T point coincides with the G point, and FIG. 8 shows the case where the T point coincides with the L point. In FIG. 6, the flow having the maximum flow velocity is incident on the center point R of the wafer. The boundary layer is extremely thin in the lower half of the wafer. The flow of the source gas is sufficiently fast even in the upper half of the wafer, so that the boundary layer is thin. Since the boundary layer separating the wafer and the gas flow is thin, the consumption efficiency of the source gas is high. In FIG. 7, the flow having the maximum flow velocity is incident on the upper end R of the wafer. The boundary layer becomes extremely thin on the entire surface of the wafer. This is the optimal placement. In FIG. 8, the flow having the maximum flow velocity is incident on the point L 3 cm above the upper end R of the wafer. Also in this case, the boundary layer becomes extremely thin over almost the entire surface of the wafer. However, if the incident point T is more than 3 cm away from the upper end R, the incident point T
Since the lower edge I of the wafer is too far away, there is a possibility that the gas flow may be disturbed near the lower edge I. Therefore, the incident point T is limited to the point L which is 3 cm from the upper end of the wafer. Further, the distance D between the susceptor and the chamber wall at the upper end F of the susceptor and the distance d between the susceptor and the chamber wall at the lower end J of the susceptor are preferably D> d. The inclination angle α at the point E of the chamber wall is in the range of 0 <α <45 °. The inclination angle β between FJ of the susceptor wall is in the range of 0 <β <45 °. However, it is desirable that α <β, which corresponds to the above D> d. D> d or α <β is not an absolute condition, but if this is the case, the expansion of the chamber wall to the outside can be reduced, and the chamber can be easily manufactured. In the present invention, the chamber has a different shape, but it is more difficult to make a different shape than the susceptor. Therefore, it is preferable that D> d and α <β. More preferably, the inclination angle β of the susceptor is 3 ° to 15 °. That is, the absolute condition is l> 0 (1) 0 <α <45 ° (2) 0 <β <45 ° (3). The reason for l> 0 is that the flow having the maximum flow velocity can be incident on the wafer mounting surface of the susceptor. α, β
If the angle is larger than 45 °, manufacturing of chamber and susceptor becomes difficult. In particular, it is difficult to manufacture a susceptor that expands more than 45 ° below. Another problem is that if the susceptor is slanted, dust tends to accumulate on the wafer and susceptor surface. Although (1) to (3) are absolute conditions, it is more desirable that D> d (4) α <β (5) 3 ° <β <15 ° (6). Depending on other parameters, if β is smaller than 3 °, it becomes difficult for the flow having the maximum flow velocity straight from point E to hit the wafer mounting surface. The reason why β is preferably 15 ° or less is because it is difficult to make when the susceptor has a large degree of irregularity. As shown in FIGS. 6 to 8, the locus of the maximum flow velocity point of the source gas passes in the vicinity of the wafer surface. Therefore, the boundary layer near the wafer surface becomes extremely thin. Since the boundary layer is thinner than that of the conventional structure, the source gas reaches the wafer surface more easily and more quickly due to the diffusion due to the difference in concentration. For example, when a GaAs thin film is to be formed on a GaAs substrate, a large amount of carrier gas, hydrogen gas, is mixed with Group V hydride gas. In the present invention, however, Group V hydride gas is It becomes easier to pass through the boundary layer, which is mostly hydrogen, by diffusion. Compared with the conventional structure, the gas consumption efficiency is increased and the thin film growth rate is increased.

【Example】

In order to confirm the effect of the present invention, the chamber was made into a transparent quartz container, and TiCl ₄ and water were supplied from the inlet. The degree of vacuum is 10 ^{-1 to 1} Torr. White smoke of TiCl ₄ can be seen flowing in the chamber. It was confirmed that the portion with the highest linear velocity travels in the tangential direction of the chamber at the expansion point E of the chamber. Further, it was visually confirmed that the flow having the maximum flow velocity went straight and hits the portions L to R of the inclined surface of the susceptor.

【effect】

The flow rate of the source gas at the maximum flow velocity passes near the wafer, and the boundary layer of the gas near the wafer becomes thin. The diffusion allows the gas components to easily reach the wafer. Therefore, the consumption efficiency of the raw material gas is increased, and the thin film formation speed is increased.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a thin film forming apparatus of the present invention. FIG. 2 is an enlarged cross-sectional view for explaining the flow of maximum flow velocity in FIG. FIG. 3 is a schematic vertical sectional view of a thin film forming apparatus according to a conventional example. FIG. 4 is an enlarged cross-sectional view on one side for explaining the flow of maximum flow velocity in FIG. FIG. 5 is a diagram showing the thickness of the boundary layer in the case where the portion having the maximum linear flow velocity is biased near one wall in the flow path partitioned by the wall. FIG. 6 is a layout drawing when the extension of the flow having the maximum flow velocity passes through the midpoint R of the wafer. FIG. 7 is a layout drawing when the extension of the flow having the maximum flow velocity passes through the upper end G of the wafer. Figure 8 shows that the maximum flow velocity is 3 cm from the top of the wafer.
The layout drawing when passing through the upper point L. 1 ... Flow channel 2 ... Susceptor 3 ... Chamber 4 ... Inlet port 5 ... Wafer 6 ... Shaft

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Koichi Kamon 1-1-1 Kunyokita, Itami City, Hyogo Prefecture Sumitomo Electric Industries, Ltd. Itami Works (72) Tadayuki Okubo 1-Kunyo Kita, Itami City, Hyogo Prefecture No. 1-1 Sumitomo Electric Industries, Ltd. Itami Works (72) Inventor Hideyuki Doi 1-1-1 Kunyokita, Itami City, Hyogo Prefecture Sumitomo Electric Industries Itami Works (56) Reference JP-A-2-146725 (JP, A) JP-A 64-17423 (JP, A) Actual development 63-124735 (JP, U) JP 59-48789 (JP, B2)

Claims (2)

[Scope of utility model registration request] 1. A vertically long chamber 3 having an inlet 4 for introducing a raw material gas into the upper portion of the chamber 3, which can be evacuated to a vacuum, and a plurality of wafers 5 can be mounted on the side periphery of the chamber 3. Susceptor 2 and susceptor 2 in chamber 3
And a flow channel 1 for guiding the flow of the raw material gas to the side circumference of the susceptor, and the wall surface of the chamber 3 is outward at a point E below the boundary point F between the susceptor 2 and the flow channel 1. The susceptor 2 spreads at an angle α, and the susceptor 2 has a shape of a truncated cone or a truncated pyramid which is narrow at the upper side and wide at the lower side so as to form an inclination angle β. Line segment R determined by the midpoint R of the mounting surface and the point L 3 cm above the upper edge G of the wafer mounting surface
L is cut, and 0 <α <45 °, 0 <β
Thin film forming equipment characterized by being <45 °. 2. When the distance between the susceptor and the chamber wall at the upper and lower ends of the susceptor 2 is D and d, D> d and α <β, 3 ° <β <15 °. The thin film forming apparatus according to claim 1.