JP3093695B2 - Vertical diffusion furnace and diffusion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical diffusion furnace and a diffusion method, and more particularly to a vertical diffusion furnace in an impurity diffusion process for diffusing impurities such as phosphorus into the surface of a semiconductor substrate (semiconductor wafer) in the manufacture of semiconductor devices. And diffusion methods.

[0002]

2. Description of the Related Art In a conventional vertical diffusion furnace, as shown in FIG. 3, a semiconductor substrate 2 is inserted into a furnace core tube 1 heated to a high temperature by a heater 8, and impurities containing impurities such as phosphorus oxychloride are contained. Mass flow of nitrogen gas 12 into the source container 4
The gas is vaporized by blowing through a controller (hereinafter referred to as MFC) 6, a main gas such as phosphorus oxychloride is introduced from a gas outlet 5 S of a gas injector 5, and a gas supply pipe 7 provided in a furnace tube is blown out. A process of introducing an auxiliary gas 13 such as oxygen or nitrogen from the mouth and diffusing impurities such as phosphorus into the semiconductor substrate while rotating the quartz boat 3 loaded with a large number of semiconductor substrates 2 by the turntable 31 has been performed. .

However, in a conventional diffusion furnace, a quartz boat 33 is used.
The distance from the gas outlets 5S arranged in the vertical direction of the gas injectors 5 in the plane on the surface of the semiconductor substrate placed in the horizontal direction differs. That is, since the processing is performed while the semiconductor substrate is rotating, the outer peripheral portion is constant, but the central portion in the plane is farther from the outlet. Therefore, the probability of impurity adsorption by the main gas is lower at the central portion in the plane than at the peripheral portion in the plane. As described above, there is a problem that the adsorption probability of the impurity differs in the plane of the semiconductor substrate, and the in-plane variation of the impurity diffusion amount increases.

[0004] This tendency becomes larger as the diameter of the semiconductor substrate becomes larger, and particularly in a place where the gas supply is insufficient, such as near the exhaust port of the furnace core tube, and the tendency becomes stronger. Variations were growing.

[0005]

As described above, the amount of impurity diffusion in the surface of the semiconductor substrate varies, and the impurity concentration is particularly low at the center of the surface.

The reason is that, in the conventional vertical diffusion furnace, since the outer peripheral portion of the semiconductor substrate surface is always near from the gas injector and the central portion is far away from the gas injector, impurities on the semiconductor substrate surface at the outer peripheral portion and the central portion are present. This is because the adsorption probabilities differ from each other, and the diffusion amount of the impurities varies in the plane.

[0007] The impurity gas comes to the surface of the substrate while performing Brownian motion. However, when a plurality of semiconductor substrates are loaded on a single quartz boat at regular intervals in parallel with the gas blowing direction, the impurity gas is removed. The Brownian motion is hindered by the upper and lower substrates and is adsorbed, so that the longer the distance from the outlet is, the lower the probability of arrival of the impurity gas is.

As described above, the variation in the amount of impurity diffusion (impurity concentration) in the plane becomes large, so that the amount of impurity diffused in the gate polysilicon film becomes large, for example, and is formed by etching. Variations in the wiring resistance of the gate electrode have occurred. Further, when the gate polysilicon film is etched to form the gate electrode, the variation in the impurity concentration in the polysilicon film is large, so that the etching rate varies, and as a result, the gate length varies.

Therefore, in a semiconductor device manufactured according to the prior art, the yield is reduced due to, for example, variations in the wiring resistance and gate length of the polysilicon gate of the transistor.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a vertical diffusion furnace and a diffusion method in which variations in the amount of impurity diffusion (impurity concentration) in the plane of a semiconductor substrate are suppressed.

[0011]

SUMMARY OF THE INVENTION A feature of the present invention is that a gas injector in which gas outlets are arranged in a vertical direction;
In a vertical diffusion furnace having a boat on which a large number of semiconductor substrates are placed at a predetermined interval from each other with a plurality of columns and a turntable for rotating the semiconductor substrate together with the boat, each of the columns has A first portion fixed to the turntable, and a second portion slidable up and down with respect to the first portion and supporting the semiconductor substrate; The vertical diffusion furnace rotates by maintaining the state of the semiconductor substrate facing the gas injector by inclining the surface of the semiconductor substrate on which the diffusion processing is performed by the sliding motion. Here, the inclination angle from the horizontal direction of the semiconductor substrate to the gas injector is 1
It is preferable that the angle is 5 ° to 60 °. Also, the first portion of the column may be an outer portion, and the second portion may be an inner portion.

Further, a non-rotatable tilt table is provided inside the rotary table, and a groove (or projection) having an angle θ from the horizontal direction toward the gas injector is formed on the entire side surface of the tilt table. The column is rotated by fitting a convex portion (or concave portion) formed in the second portion into a groove (or projection) of the inclined base, thereby rotating the second portion.
A vertical sliding motion of the portion can be performed. In this case, the angle θ is preferably an angle of 15 ° to 60 °.

Another feature of the present invention is a diffusion method for diffusing impurities into a semiconductor substrate using any of the above vertical diffusion furnaces.

As described above, according to the present invention, the direction of the gas injector (the direction of the gas outlet) provided in the furnace core tube is 15 degrees.
It has an inclined base having a part inclined at an angle of 60 ° and a quartz boat in which a part of the column can slide up and down. The rotating table is rotated by the motor to diffuse the impurities while rotating the quartz boat, but when the boat rotates,
Because a part of the column rotates while sliding up and down along the inclined table, the semiconductor substrate loaded in the quartz boat rotates in the direction of the gas outlet while the surface always keeps a certain angle. Having.

Further, the distance (wafer pitch) between one semiconductor substrate and another substrate loaded above and below one semiconductor substrate is such that at least half the area of the surface of the semiconductor substrate is loaded in the groove of the boat above. It is preferable that the design is made so as not to be shadowed by the substrate.

For example, when a semiconductor substrate having a diameter of 6 inches is inclined by 30 °, the wafer pitch is about 43 mm.

Although the impurity gas flies to the surface of the semiconductor substrate while performing Brownian motion, the surface of the semiconductor substrate constantly rotates at a constant angle in the direction of the gas outlet, and the distance between the semiconductor substrates increases. Lower side of substrate surface 1 /
Since the area of two or more does not become a shadow of the upper substrate, the flying impurities reach the substrate surface without hindering their progress. Next, when the substrate is rotated by 180 °, the portion that was initially shaded by the substrate immediately above is no longer shaded, so that the surface adsorption of the impurity gas proceeds.

In this manner, the substrate surface always rotates at a constant rotational speed toward the gas outlet, so that the state in which the upper substrate is shaded and the state in which it is not shaded are uniform, and the substrate surface is uniform. And uniform impurity diffusion proceeds.

That is, since the impurity gas reaches the surface without impairing the Brownian motion on the upper substrate as in the prior art, the influence of the difference in the distance from the outlet to the arrival point (difference in the adsorption probability) ) Is much smaller than in the prior art. Furthermore, since the substrate is tilted, the distance of the center of the surface becomes closer to the outlet, so that the difference in the distance from the outlet at the in-plane outer peripheral portion and the center is smaller, and the adsorption probability of the impurity gas is reduced. Becomes uniform.

As described above, by constantly rotating the semiconductor substrate surface in the direction of the gas outlet while maintaining a constant angle, the probability of adsorption of the impurity gas on the surface becomes uniform in the surface, and the uniform impurity Diffusion proceeds. As a result, the uniformity of the in-plane impurity concentration is improved.

The reason why the inclination angle is set to 15 ° to 60 ° is that when the angle is 15 ° or less, the effect of improving the uniformity is small, and when the angle is 60 ° or more, the productivity is greatly reduced.

As described above, when the direction of the gas outlet
Includes an inclined base with a side part inclined at 60 ° and a quartz boat in which a part of the support is slidable in the vertical direction, and the semiconductor substrate is turned toward the gas outlet while the surface of the semiconductor substrate is always kept at an angle. By doing so, the amount of impurity gas adsorbed on the surface of the semiconductor substrate can be made uniform in the plane, and the amount of impurity diffused into the semiconductor substrate can be made uniform.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an outline of the configuration of a vertical diffusion furnace according to an embodiment of the present invention. 2: is the figure which expanded and showed the A section of FIG. 1, (A) is a perspective view, (B) is sectional drawing which cut | disconnected (A) by cutting line BB and looked at the direction of arrow. is there.

First, referring to FIG. 1, the inside of a furnace tube 1 is heated to a predetermined temperature by a heater 8 to tilt a large number of semiconductor substrates 2 at a constant angle θ (θ = 15 ° to 60 °). An inclined table 9 having an inclined groove 19 and a quartz boat 3 in which a part of a support for supporting a semiconductor substrate slides up and down along the inclined table are provided. Up and down movement and rotation by a motor are possible by an elevator supporting the car.

The pitch of the quartz boat (the distance between one semiconductor substrate and another substrate loaded above and below one semiconductor substrate) is such that the area of at least half of the surface of the semiconductor substrate is equal to the groove of the boat above. It is designed not to shadow the loaded substrate.

For example, a semiconductor substrate having a diameter of 6 inches is set at 30 °
When tilted, the wafer pitch is about 43 mm.

A gas injector 5 in which a plurality of gas blowing ports 5S for blowing gas are vertically arranged in the furnace core tube is provided extending vertically.
An MSC 6 for controlling the flow rate of the main gas for diffusion is connected to the gas injector 5.

Then, the nitrogen gas 12 is vaporized by blowing it into the impurity source container 4 containing impurities such as phosphorus oxychloride through the MFC 6, and a main gas such as phosphorus oxychloride is introduced from the gas outlet 5S of the gas injector 5; In addition, the auxiliary gas 13 such as oxygen and nitrogen is introduced from the outlet of the gas supply pipe 7 provided in the furnace core tube, and the quartz boat 3 loaded with a large number of semiconductor substrates 2 is rotated by the turntable 11 to rotate the semiconductor boat. Impurities such as phosphorus are diffused into the substrate.

Next, with reference to FIGS. 2A and 2B, the main part of the embodiment of the present invention will be described in detail.

An inclined table 9 is provided so as to be surrounded by a rotating table 11 which rotates in the direction of the arrow. The inclined table 9 is a member that does not rotate, and has an angle θ (θ = 15) from the horizontal direction toward the gas injector 5 (FIG. 1) over the entire side surface of the inclined table.
(° to 60 °).
The upper surface is also an inclined surface having an angle θ.

The quartz boat 3 comprises three pillars 20 made of quartz. Each of the columns 20 has an outer portion (first portion) 21 fixed to the fixing base 11 and extending in the vertical direction.
And an inner part (second part) 22 slidable vertically with respect to the outer part. still,
FIG. 2A is a perspective view, in which the inside portion 22 is hatched to the right in order to clearly show it.

In the inner part 22 of the column, the inclined groove 1 of the inclined table is provided.
9, a convex portion 23 which rotates while being fitted to the groove 9, and which supports a large number of semiconductor substrates 2 at predetermined intervals.
4 are arranged in the vertical direction.

With this configuration, when the turntable 11 is rotated by a motor (not shown) during the diffusion process, the convex portion 23 is fitted into the inclined groove 19, so that the inner portion 22 of the column is indicated by an arrow. As shown in FIG.
In FIG. 2A, the position is the highest when it is located on the right, and then falls at an angle θ, and when it is located on the left in FIG. 2A, it becomes the lowest state, and then rises at an angle θ.

As a result, the semiconductor substrate 2 supported by the groove 24 in the inner portion of the support column has an angle θ (θ = 15 ° -6 °) from the horizontal direction toward the gas injector 5 (FIG. 1).
(0 [deg.]) And the gas injector 5 (FIG. 1) rotates while always keeping the processing surface facing the gas injector 5 (FIG. 1).

In the drawings of this embodiment, an example is shown in which the inclined base 9 is provided with an inclined groove 19 and the projection 23 of the inner portion of the column is fitted into the inclined base 19 and rotated. The same operation is performed when an inclined protrusion inclined at an angle θ (θ = 15 ° to 60 °) is provided and rotated by fitting a concave portion separately provided in an inner portion of the support column.

Next, the operation of the embodiment will be described.

The elevator is raised into the furnace core tube 1 heated at a high temperature, and the quartz boat 3 loaded with the semiconductor substrate 2 is inserted. Then, as described above, when the quartz boat is rotated by the motor through the turntable due to the action of the inner portion of the column that can be slid in the vertical direction and the inclined table, the surface of the semiconductor substrate loaded in the quartz boat is always constant. When the semiconductor substrate is rotated by 180 degrees in the direction of the gas outlet (the direction of the injector 5) while maintaining the angle of, the shaded portion of the upper semiconductor substrate at first is now shaded. By repeating the rotation, the surface adsorption of the impurity gas proceeds uniformly in the plane,
Uniform impurity diffusion proceeds.

[0039]

As described above, according to the present invention, the surface of the semiconductor substrate is always rotated in the direction of the gas outlet while maintaining a constant angle, so that the probability of adsorption of the impurity gas on the surface is reduced. In the semiconductor substrate, the amount of impurities diffused to the surface can be made uniform because the diffusion of the impurities proceeds uniformly.

As described above, since the uniformity of the diffusion amount (impurity concentration) of the impurity in the surface of the semiconductor substrate can be improved, for example, the dispersion of the impurity amount diffused in the gate polysilicon film can be reduced. Can reduce the variation in the wiring resistance of the gate electrode formed by etching the gate electrode, and can reduce the variation in the impurity concentration in the polysilicon film when the gate electrode is formed by etching the gate polysilicon film. Therefore, the etching rate can be stabilized, and variations in the gate length can be reduced.

Therefore, the wiring resistance and gate length of the polysilicon gate of the transistor can be stabilized, and the yield as a semiconductor device can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a vertical diffusion furnace according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a portion A in FIG. 1, and FIG.
Is a perspective view, and (B) is a cross-sectional view of (A) taken along a cutting line BB and viewed in the direction of an arrow.

FIG. 3 is a view showing an outline of a conventional vertical diffusion furnace.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Furnace tube 2 Semiconductor substrate 3, 33 Quartz boat 4 Impurity source container (phosphorus oxychloride) 5 Gas injector 5S Gas outlet 6 MFC 7 Gas supply pipe 8 Heater 9 Inclined table 11, 31 Turntable 12 Nitrogen gas 13 Sub gas (Nitrogen gas, oxygen gas) 19 Inclined groove 20 Quartz boat support 21 Outer part of support 22 Inner part of support 23 Convex part 24 Groove

Claims (6)

(57) [Claims] 1. A gas injector in which gas outlets are arranged in a vertical direction, a boat on which a plurality of semiconductor substrates are mounted at predetermined intervals on a plurality of semiconductor substrates by a plurality of columns, and the semiconductor substrate is rotated together with the boat. In a vertical diffusion furnace having a turntable to be rotated, a first portion fixed to the turntable and a slidable up and down direction with respect to the first portion and supporting the semiconductor substrate are provided on each of the columns. The semiconductor substrate is rotated while maintaining its state directed toward the gas injector by inclining the surface of the semiconductor substrate on which the diffusion process is performed by the vertical sliding movement of the second portion. A vertical diffusion furnace. 2. The vertical diffusion furnace according to claim 1, wherein an inclination angle of the semiconductor substrate from the horizontal direction toward the gas injector is 15 ° to 60 °. 3. A non-rotating tilt table is provided inside the rotary table, and a groove (or projection) having an angle θ from the horizontal direction toward the gas injector is formed on the entire side surface of the tilt table. The column is caused to perform a vertical sliding movement of the second portion by rotating while fitting the convex portion (or concave portion) formed in the second portion into the groove (or projection) of the inclined base. The vertical diffusion furnace according to claim 1, characterized in that: 4. The vertical diffusion furnace according to claim 3, wherein said angle θ is an angle of 15 ° to 60 °. 5. The vertical diffusion furnace according to claim 1, wherein the first portion of the column is an outer portion, and the second portion is an inner portion. 6. A diffusion method comprising performing impurity diffusion on a semiconductor substrate using the vertical diffusion furnace according to claim 1.