JPH09199438A - Heat treating jig - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent crystal defects which are called slips and warp when, by use of a heat treating jig provided with a ring-like tray, a silicon wafer of 12-inch size is heated in a vertical heating furnace. SOLUTION: Ring-like trays 3 are respectively horizontally fixed to a plurality of vertical props to constitute a heat treating jig. The inner radius R of the ring-like tray is 220mm to 250mm, the thickness D of a support face is 2 to 4mm and the array pitch is 18mm to 22mm. In order to determine the inner radium of the ring-like tray, in comparison with simulation results as to how a shearing stress is changed by the weight of a wafer W of 12-inch size according to the inner radius and an allowable stress (yield shearing stress) of silicon at 1150 deg.C, the relation between the difference in temperature in a wafer face when a temperature increases or decreases and the inner radius is grasped, so that determination is made from both aspects of the shearing stress of a wafer by the weight and the shearing stress by the difference in temperature in a face.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment jig used for performing heat treatment on a 12-inch size silicon wafer in a vertical heat treatment furnace.

[0002]

2. Description of the Related Art Semiconductor wafers (hereinafter referred to as "wafers")
There is a process of performing heat treatment at a high temperature in order to form an oxide film, diffuse a dopant, and the like. In a vertical heat treatment apparatus that performs this heat treatment, the wafers are loaded into a heat treatment furnace by a heat treatment jig that mounts a large number of wafers vertically at intervals, and a predetermined heat treatment is performed. With such a heat treatment jig, 4
In general, a support groove is formed on a column of a book, and the wafer is held in the support groove to support four points on the outer peripheral edge of the wafer. There is known a structure called a ring boat in which the wafers are arranged and placed on the ring tray.

This ring boat is applied to, for example, a heat treatment apparatus having a high temperature raising / lowering rate. The reason for this is that the wafers arranged in the heat treatment jig are vertically close to each other, so that the upper wafer shields the heat rays from the heater on the lower wafer, so that the edge of the wafer is blocked. In comparison, the rate of temperature rise in the central part becomes slower. Further, since the space around the edge portion of the wafer is a space when the temperature is lowered, the edge portion radiates heat faster than the center portion, and the temperature lowering rate becomes faster. Therefore, when the temperature is raised or lowered, especially when the rate of temperature increase or decrease is high (the rate of temperature decrease is accelerated by, for example, forced cooling), the degree of non-uniformity of the temperature distribution in the wafer surface becomes large, and a large shear stress is generated due to the in-plane temperature difference. Since it occurs on the wafer, there is a possibility that crystal defects called slips may occur. The slip is a minute slice that is difficult to visually confirm, and can be seen with a magnifying glass or a microscope. Therefore, by placing the wafer on a ring-shaped tray made of a material having a large heat capacity, such as SiC, SiC is brought into contact with the lower surface of the edge portion of the wafer to raise the temperature (cool down).
The temperature difference between the edge portion and the center portion of the wafer is made uniform in this way.

[0004]

In the ring boat, the stress caused by the temperature difference in the wafer surface has been considered so far, but the stress caused by the weight of the wafer and the stress caused by the weight of the wafer have been considered. Very little consideration is given to the synergistic effect between the stress and the stress caused by the temperature difference in the wafer surface.

On the other hand, the diameter of wafers is increasing,
The size is being considered for transition from 8 inches to 12 inches. However, when the wafer is 12 inches in size, the following problems occur when simply using a conventional jig with each dimension changed. That is, when the heat treatment is performed at a temperature close to the melting point of silicon, for example, at a temperature of about 1000 ° C., the synergistic action of the above stress may cause slipping or warping of the wafer.

The present invention has been made under such circumstances, and an object thereof is to provide a heat treatment jig capable of preventing the occurrence of slippage and warping when heat treating a 12-inch size silicon wafer. To do.

[0007]

According to a first aspect of the invention, ring-shaped support members are provided on a support column at intervals in the vertical direction.
In a heat treatment jig for loading and unloading a 2-inch size silicon wafer into and out of a vertical heat treatment furnace, the ring-shaped support member has an inner diameter of 120 mm to 2
It is characterized by being 50 mm.

According to a second aspect of the invention, in the first aspect of the invention, the ring-shaped support member has an inner diameter of 220 mm to 250 m.
m, the thickness of the supporting surface is 2 to 4 mm, and the arrangement pitch is 1
It is characterized by being 8 mm to 22 mm. The invention of claim 3 is the same as the invention of claim 1 or 2,
It is characterized in that it is used at a processing temperature of 0 ° C. or higher.

[0009]

1 is an external perspective view showing a part of a vertical heat treatment apparatus including a heat treatment jig according to an embodiment of the present invention, and FIGS. 2 and 3 show heat treatment jigs. It is a figure which shows a part. The heat treatment jig 1 includes a circular top plate 11 and a bottom plate 12 which are arranged to face each other in the vertical direction, and a plurality of, for example, four columns 21 to 24 are fixed between them. Although the top plate 11 is circular for convenience of illustration, it may be ring-shaped or the number of columns may be six.

Between the top plate 11 and the bottom plate 12, for example, 3
Four ring-shaped support members, which are four ring-shaped support members, are arranged in parallel at a predetermined interval. In this embodiment, the array pitch P of the wafers W (array pitch of tray-3) is set to 20 mm. As for the method of fixing the ring-shaped tray-3, as shown in FIG.
The peripheral portion of the ring-shaped tray 3 is inserted and held in the groove 20 formed in the No. 4. As a material for the heat treatment jig 1, SiC, quartz, or the like is used. The ring-shaped tray-3 has a peripheral edge formed as a step portion 30 slightly higher than the supporting surface of the wafer W, and has an inner diameter Rw of 240 mm,
The outer diameter r is 315 mm, the thickness D on the supporting surface is 3 mm,
The width of the step portion 30 is set to 5.5 mm.

The wafer boat 1 configured as described above
Is detachably mounted on a heat retaining tube 4 having a flange portion 40 at the bottom as shown in FIG.
Is mounted on the boat elevator 41. A vertical furnace 5 is arranged above the wafer boat 1. 5
Reference numeral 1 is a gas supply pipe for supplying a predetermined gas into a reaction tube which is not visible in the vertical heat treatment furnace 5, and 52 is an exhaust pipe for exhausting the reaction tube.

Next, the above operation will be described. First, in another area, the wafer W is transferred to the wafer boat 1. In this transfer, a push-up mechanism (not shown) is lifted so as to pass through the ring-shaped tray-3, and the wafer W is transferred onto the transfer arm 12. It is carried out by placing an inch-sized silicon wafer W on the ring-shaped tray-1 via the push-up mechanism.

Such delivery of the wafers W is sequentially performed from the upper side of the wafer boat 1, for example, and a predetermined number of wafers, for example 34 wafers, are mounted on the wafer boat 1, and then the boat elevator 4 is operated.
The wafer boat 1 is transferred onto the heat-retaining cylinder 4 on the upper surface 1 and the boat elevator 41 is lifted to transfer the wafer W to the vertical heat treatment furnace 5.
To load in. For example, when heat treatment is performed at a temperature of about 1150 ° C., the inside of the vertical heat treatment furnace 5 is heated to, for example, about 800 ° C., and after the wafer W is loaded, for example, at a maximum temperature rising rate of 50 ° C./minute, about 1150 ° C. The temperature is raised to and a predetermined heat treatment is performed. Thereafter, the boat elevator 41 descends, the wafer W is unloaded, the wafer boat 1 is transferred to another area, and the wafer W is taken out of the wafer boat 1 by the operation reverse to the above.

According to such an embodiment, 1000
Even if the heat treatment is performed at a temperature of, for example, about 1150 ° C. that exceeds the temperature of the wafer W, there is no risk of slipping or warping of the wafer W because the inner diameter of the ring-shaped tray 3 is set to 240 mm. The reason for this is, as will be understood from the description below, that the internal diameter of the ring-shaped tray-3 is 1
Simulation results of how the shear stress due to the weight of the 2-inch wafer W changes and 11
The allowable stress (yield shear stress) of silicon at 50 ° C. is compared, and the relationship between the temperature difference in the wafer surface and the inner diameter of the ring-shaped tray-3 at the time of raising and lowering the temperature is grasped. This is because the inner diameter of the ring-shaped tray-3 is determined from both sides of the shear stress and the shear stress due to the in-plane temperature difference.

In the above example, when the surfaces of all the wafers after the heat treatment were observed, no slip was observed and no wafer was warped. However, a 12-inch size wafer means that the diameter of the wafer is approximately 12 inches, and includes a 300 mm wafer.

The process leading to the present invention will be described below. With conventional 8-inch wafers, the self-weight stress of the wafer is small, and there was no fear that this self-weight stress would be close to the allowable stress and slip would occur, so what is the allowable value of the inner diameter of the ring-shaped tray? I'm glad I didn't think about it. Here, when the wafer size becomes 12 inches, the weight of the wafer becomes large.
On the other hand, the heat treatment at a treatment temperature of over 1000 ° C. is started, and the allowable stress becomes smaller at higher temperatures.
As a result, slips may occur, so the inventors focused on minimizing the shear stress of the wafer by selecting an appropriate value for the inner diameter of the ring-shaped tray.

The permissible value of the inner diameter of the ring-shaped tray on which a 12-inch wafer is placed will be described below. In the case of a ring-shaped tray, there is no guarantee that the wafer is supported in a perfect plane. This is because the wafer is distorted by its own weight into a bowl shape in which the central portion is lower than the peripheral portion. Therefore, the inner diameter of the ring-shaped tray can be regarded as the support diameter. Depending on how the wafer is distorted, there may be only three support points, and at this time, the shear stress applied to the wafer becomes maximum. For this reason, it is necessary to design so that the shear stress of the wafer when supporting at three points does not exceed the allowable stress.

FIG. 4 shows the maximum value of the self-weight stress with respect to the support diameter when the wafer is supported at three points. That is, FIG.
As shown in, the supporting points S1 to S3 are set at the positions corresponding to the vertices of the equilateral triangle, and the circle C including the supporting points S1 to S3.
The horizontal axis represents the diameter of R, i.e., the support diameter Rw. FIG. 4
In, the dotted lines (a), (b), (c), and (d) indicate the allowable stress (descending shear stress) of the silicon wafer at 1000 ° C., 1100 ° C., 1150 ° C., and 1200 ° C., respectively.

This allowable stress decreases as the temperature increases, and at 1200 ° C., the maximum shear stress exceeds the allowable stress regardless of the value of the support diameter. Therefore, theoretically, the processing temperature of 1200 ° C. In this case, the wafer will slip. The maximum processing temperature actually performed on the wafer in the heat treatment furnace is about 1150 ° C. Therefore, in order to prevent the occurrence of slip, the maximum shear stress should be lower than the allowable stress line at 1150 ° C. It is necessary to have a proper support diameter. However, when a shear stress equivalent to the allowable stress is generated in the wafer, a small amount of slip is introduced, so that the support diameter needs to be 120 mm to 250 mm.

In the above, the maximum value of the self-weight stress shown in FIG. 4 is calculated by the finite element method using a computer.
The allowable stress of the wafer was calculated based on the following equation. τyld = 23.17exp (16.1-0.00916T) *
(Dτ / dt) ^0.4 However, the unit of stress is Pascal, T is temperature (° C.), t is time (sec), and stress rate dτ / d
For t, the empirical formula 2.5 * 10 ⁵ (pa / s) is used.

On the other hand, when the temperature of the wafer is raised or lowered, a temperature difference occurs in the plane of the wafer. This is because the radiation form factor from the heater to the wafer sharply increases at the wafer edge. The radiative form factor is qualitatively easy to warm and is represented by (Equation 1).

[0022]

[Equation 1] That is, if this radiation form factor is large, the temperature rising / falling speed is fast,
Since the wafer edge portion has a faster temperature raising / lowering speed than the wafer central portion, an in-plane temperature difference occurs when the temperature of the wafer is raised / lowered. FIG.
Is a graph showing the relationship between the wafer position (distance from the wafer center) and the radiation form factor, and a, b, and c are wafer pitches on the wafer boat (distance between wafers) of 18 mm, 20 mm, and 22 mm, respectively. The radiation form factor is shown below. The value of the wafer pitch is set between 18 mm and 22 mm. If it is narrower than 18 mm, it becomes difficult to transfer wafers by the transfer arm, and if it is wider than 22 mm, the maximum number of wafers mounted becomes small, which is not realistic.

By the way, the role of the ring-shaped tray is to bring the lower surface of the edge portion of the wafer into contact with a material having a large heat capacity to slow down the temperature raising / lowering rate, thereby making the temperature raising / lowering rate of the central portion and the edge portion of the wafer uniform. Therefore, it is necessary to position the inner end of the ring-shaped tray at a point where the radiation form factor increases and the temperature rising / falling rate starts to increase. From such a fact, when the optimum inner end position of the ring-shaped tray is obtained based on FIG. 6, when the pitch is 18 mm, 20 mm, and 22 mm, respectively 113 m
m, 120 mm (the optimum position is not shown in the graph b for convenience) and 124 mm, but even if it deviates a little from this point, in-plane temperature uniformity can be secured, so in terms of diameter, the inner diameter of the ring-shaped tray Is 220 mm
From 250 mm.

As described above, from the viewpoint of improving the inner diameter of the ring-shaped tray determined by the shear stress due to the weight of the wafer and the in-plane temperature uniformity during temperature raising and lowering to minimize the shear stress due to the in-plane temperature difference. The range of overlap with the inner diameter of the ring tray determined is 220 mm to 250 m
The inner diameter of the ring-shaped tray used for a 12-inch size silicon wafer should be set in this range.

For example, in the case of a vertical heat treatment furnace having a fast temperature rising / falling rate of 20 ° C./minute or more, the inner diameter of the ring-shaped tray is preferably within the above range, but the present invention (the invention of claim 1 ), When the temperature raising / lowering speed is slow, it is not always the case in FIG.
The value is not limited to the value determined from the characteristics of the radiation form factor shown in, and may be 120 mm to 250 mm.

Here, regarding the ring-shaped tray having a thickness of 3 mm and a material of SiC, the inner diameters are 250 mm and 260 m.
3 pieces each of m in size were prepared, mounted on a support of a wafer boat, and a 12-inch wafer was held thereon, and the temperature was raised to 1150 ° C. in the heat treatment furnace at a maximum heating rate of 50 ° / min. The temperature was raised to 1 hour and heated for 1 hour. After that, the wafer was taken out of the furnace and the surface was observed.
A small amount of slip was observed on the wafer using the 60 mm ring tray, but no slip was observed on the wafer using the 250 mm inner diameter tray.

[0027]

As described above, according to the present invention, the relationship between the inner diameter of the ring-shaped tray and the shear stress due to the weight of the wafer when the 12-inch size silicon wafer is heat-treated using the ring-shaped tray. Since the inner diameter of the ring-shaped tray is set based on the result of the simulation, there is no risk of slipping or warping.

[Brief description of drawings]

FIG. 1 is a perspective view showing an entire embodiment of the present invention.

FIG. 2 is a perspective view and a sectional view showing a ring-shaped tray according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a part of a wafer boat.

FIG. 4 is a characteristic diagram showing a relationship between a wafer support position and maximum shear stress.

FIG. 5 is an explanatory diagram showing a supporting position of a wafer.

FIG. 6 is a characteristic diagram showing a relationship between a radial position of a wafer and a radiation form factor.

[Explanation of symbols]

 W Wafer (Substrate to be Processed) 1 Wafer Boat 21 to 24 Support 20 Groove 3 Ring Tray 30 Step Part R Inner Diameter of Ring Tray r Outer Diameter of Ring Tray

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Osamu Monoe 1-241, Machiya, Shiroyama-cho, Tsukui-gun, Kanagawa Prefecture Tokyo Electron Tohoku Co., Ltd. Sagami Business Office

Claims (3)

[Claims] 1. A heat treatment jig in which ring-shaped support members are provided on columns and vertically spaced from each other, and a 12-inch size silicon wafer is supported by the ring-shaped support members and carried into and out of a vertical heat treatment furnace. The inner diameter of the ring-shaped support member is 120 mm to 250 mm
A jig for heat treatment characterized in that 2. The inner diameter of the ring-shaped support member is 220 mm to
The heat treatment jig according to claim 1, wherein the jig has a thickness of 250 mm, a supporting surface has a thickness of 2 to 4 mm, and an arrangement pitch is 18 mm to 22 mm. 3. The heat treatment jig according to claim 1, which is used at a treatment temperature of 1000 ° C. or higher.