JPH03235329A - Apparatus for thermal diffusion for manufacturing semiconductor - Google Patents

Abstract

PURPOSE:To enable execution of more uniform oxidation diffusion by a method wherein a gas produced from a diffusion source is made to blow directly into a space between semiconductor wafers being rotated. CONSTITUTION:A gas supply pipe 2 is connected to the upper end face of a quartz reaction tube 1, and semiconductor wafers 3 are held by a boat 4, in a state of being separated at a prescribed interval from each other, and transferred through the intermediary of a table 5. By the rotation of a motor 7, the table 5 and the wafers 3 are rotated together simultaneously in the horizontal direction. A reverse-U-shaped gas introducing pipe 8 is disposed inside the tube 1 and a plurality of nozzles 8c are bored in a straight line at a prescribed pitch in the peripheral wall of a downward part 8b of the pipe 8. The pitch P1 between the nozzles is made smaller than a pitch P2 between semiconductor chips held by the boat 4. According to this constitution, a path of a process gas flowing through the furnace 1 is made long and the inside of the tube 1 is heated sufficiently by a gas blowing off from the nozzles 8c. The gas from the nozzles 8c is made to blow into a space between the wafers 3.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to semiconductor manufacturing, which is used when heat-treating a semiconductor wafer to diffuse impurities such as phosphorus in the manufacturing of semiconductor devices. The present invention relates to a heat diffusion device for use.

(Prior art) The above-mentioned heat diffusion device is capable of discharging gas containing impurities (
For example, it is used to heat-treat semiconductor wafers in vaporized P2O5), but in recent years, semiconductor wafers have been There is a trend of shifting from horizontal diffusion furnaces, which have less backflow of air during wafer transfer, to vertical diffusion furnaces.

The configuration of this type of general vertical diffusion furnace is shown in FIG.

A gas supply pipe 2 is connected to approximately the center of the upper end surface of a bottomed cylindrical quartz reaction tube 1 whose lower end is open and which extends upward. The semiconductor wafer 3 is held in a predetermined spaced state in a boat 4 and transported via a boat table 5, and the opening of the reaction tube 1 is arranged so that the semiconductor wafer 3 is held in a state where the semiconductor wafer 3 is kept separated from the boat 4 for a predetermined period. 3 is completely inserted, it is sealed with a cap 6 fixed to the boat table 5.

Here, when the semiconductor wafer 3 is transported, air is prevented from flowing into the reaction tube 1 by flowing an inert gas such as N2 into the reaction tube 1 from the gas supply pipe 2.

When performing phosphorus diffusion using, for example, 200 g3 as an impurity source with the opening of the reaction tube 1 sealed with the cap 6, the inside of the reaction tube 1 is kept at a high temperature atmosphere of approximately 900°C or higher. , inside this, N2 is supplied from the gas supply pipe 2.
．． A process gas, which is a mixed gas of o2, 200 g3 steam, is introduced and flows downward from the ceiling of the reaction tube 1.

As a result, the semiconductor wafer 3 is subjected to heat treatment by causing a reaction in a mixed gas of the diffusion source P 205 generated by the reaction of POCl3 and 02 and the inert carrier gas N2.

As a result of the above-mentioned phosphorus diffusion, FIG. 9 shows an example of controlling the sheet resistance around 100Ω when high-resistance phosphorus was diffused into 4000 polysilicon cells.

The diffusion conditions at this time were an atmosphere of 900° C. and a diffusion time of 15 minutes.

From this figure, when the variation σ of the in-plane sheet resistance ρ at each position in the boat is expressed as InaX; maximum value min of sheet resistance ρ; minimum value X of sheet resistance ρ; average value of sheet resistance ρ, It can be seen that this variation σ becomes extremely large at 24 to 25% at the position of each semiconductor wafer 3 within the boat 4.

Further, the distribution of sheet resistance ρ on the surface of the semiconductor wafer also exhibits a concentric distribution, with the sheet resistance ρ being low at the periphery and high at the center.

This is a diffusion source P2O5 between each semiconductor wafer 3, 3.
The supply of is the concentration of the diffusion source P2O5 here and the diffusion source P2O in the process gas flowing from top to bottom in the reaction tube 1.
5, that is, the process gas itself does not flow within the semiconductor wafers 3, 3, and therefore this concentration is high at the periphery of the semiconductor wafer 3.
This is believed to be because it gradually becomes lower toward the center and is not uniform over the entire surface of the semiconductor wafer 3.

(Problem B to be solved by the invention) However, looking at the state of phosphorus diffusion into polysilicon under the above conditions, the in-plane variation σ is 25
%, and even on the surface of the semiconductor wafer, the sheet resistance ρ at the periphery shows a concentric distribution that is lower than that at the center, and the variation in phosphorus diffusion within this plane is This will also affect the subsequent etching process. Furthermore, even when a process such as a ring getter using CVD is applied, differences in the amount of CVD film wear and variations in melt shape occur.

It is thought that such variations in phosphorus diffusion will become a particular problem as precise control will be required in future miniaturization.

Such a phenomenon of variation in phosphorus diffusion similarly occurs in a horizontal diffusion furnace.

In addition, even in normal oxidation, process gas is generally introduced from the ceiling along the peripheral wall of the reaction tube. The flow velocity is several meters/
see, so the temperature of this gas has not risen to the same temperature as inside the furnace. For this reason, the same situation occurs when air cooling is performed, and the ceiling side cools, disrupting cross-sectional uniform heating, and causing large variations in the oxide film within the plane.

In view of the above, an object of the present invention is to provide an improved vertical diffusion furnace that can perform more uniform oxidation diffusion.

(Means for Solving the Problems) In order to achieve the above object, a thermal diffusion device for semiconductor manufacturing according to the present invention includes a boat holding semiconductor wafers at a predetermined pitch inserted into a reaction tube and sealed; In a heat diffusion device for semiconductor manufacturing, which heat-treats semiconductor wafers by introducing a process gas into the reaction tube while maintaining the inside of the reaction tube in a high-temperature atmosphere, the inside of the reaction tube is heated along its length. A gas introduction pipe extending from the semiconductor wafer is arranged, and nozzles for blowing process gas toward the semiconductor wafer are provided on the peripheral wall of the gas introduction pipe at a pitch that is approximately equal to or smaller than the pitch of the semiconductor wafer. The boat is configured to blow out the process gas, and the boat is rotatable.

(Function) According to the present invention configured as described above, the process gas is heated in advance to cause a sufficient chemical reaction and a diffusion source is generated, and the gas is supplied from each nozzle while rotating the semiconductor wafer. The process gas can be blown directly between the semiconductor wafers, making the concentration of the diffusion source more uniform over the entire surface of the bracket, regardless of where the semiconductor wafers are held by the boat, and the process gas being blown directly between the semiconductor wafers. It is possible to prevent the wafer from being blown out in the direction of the semiconductor wafer before it is sufficiently warmed, to make the diffusion by the diffusion source more uniform, and to prevent variations in diffusion as much as possible.

(Example) Embodiments of the present invention will be described below with reference to FIG.

FIG. 1 shows a first embodiment of the present invention, in which a gas supply pipe 2 is connected to approximately the center of the upper end surface of a bottomed cylindrical quartz reaction tube 1 whose lower end is open and which extends upward. ing. The semiconductor wafer 3 is held in a boat 4 for a predetermined period of time and is transported via a boat table 5. When fully inserted, the boat table 5
It is designed to be sealed with a cap 6 fixed to.

Furthermore, a motor 7 is connected to the boat table 5,
By the rotation of this motor 7, the boat table 5 and further the semiconductor wafers 3 held by the boat 4 are simultaneously rotated in the horizontal direction. A gas introduction pipe 8 is formed of a thin tube formed in an inverted U-shape by a rising part 8a extending upward from the lower part along the line, and a descending part 8b bending 1000 degrees from the top of the rising part 8a and extending downward. The descending portion 8b of this gas introduction pipe 8
A plurality of nozzles 8c are linearly bored at a predetermined pitch along the length of the peripheral wall.

The pitch pl between each nozzle is smaller than the pitch p2 between each semiconductor chip held on the boat 4 (
pI p2) has been done.

The reason why the gas introduction tube 8 is bent into an inverted U shape is to lengthen the process gas bus that flows inside the reactor 1 along the gas introduction tube 8. The purpose of this is to heat the air sufficiently by rising to the ceiling and then descending to blow out air from the nozzle 8C. Also, the pitch p1 between the nozzles is made smaller than the pitch p2 between semiconductor wafers. This is to ensure that the process gas from the nozzle 8C is evenly blown between the semiconductor wafers 3, 3.

When the semiconductor wafer 3 is held by the board 4 and transported upward via the board table 5, a carrier gas such as N2 is introduced from the gas supply pipe 2, so that air can be transferred to the reaction tube. For example, when performing phosphorus diffusion using POC113 as an impurity source, after sealing the opening of the reaction tube 1 with the cap 6, the inside of the reaction tube 1 is approximately sealed. While maintaining the high-temperature atmosphere of 900° C. or higher, a process gas consisting of a mixture of N, O, POCR3 vapor, etc. is introduced from each nozzle 8C of the gas introduction tube 8 into the interior, and the semiconductor wafer 3 is heated by the motor 7. The semiconductor wafer \3 is heated at a predetermined temperature by rotating the wafer.

Using the above example, the results of phosphorus diffusion into polysilicon at 900°C for 15 minutes are shown below.
In place of the straight gas inlet pipe 8 and the straight inlet pipe (
A comparison is shown in FIG. 2 with one in which a nozzle 8C is provided on the circumferential wall of the rising portion 8a without providing the descending portion 8b.

As is clear from this, in the case of this example, the in-plane variation in sheet resistance ρ is 3 to 8%, which is an improvement of about 1/3 compared to the above-mentioned conventional example.

Note that if the gas introduction tube is configured with a straight tube instead of a U-shaped tube, the sheet resistance ρ will be much higher than the top of the reaction tube 1, and the position of the semiconductor wafer 3 in the boat 4 will be lower than the sheet resistance ρ. It can be seen that the uniformity of the sheet resistance ρ due to the difference becomes considerably poor.

This is because, in the phosphorus diffusion using POCI13, this pocIl and excess 02 react at about 450°C or higher to generate a diffusion source P20, but at the bottom, the inside of the straight tube moves quite quickly. The process gas flowing at the flow rate blows out in the direction of the semiconductor wafer 3 before it is sufficiently warmed up, resulting in a so-called air-cooled state where the process gas blows onto the semiconductor wafer, which reduces the concentration of the diffusion source. This is because the concentration at the bottom becomes very dark and there is a considerable difference in concentration from the concentration at the top.

That is, by using a U-shaped tube as the gas introduction tube 8, the passage path of the process gas passing through the reaction tube 1 is lengthened to sufficiently warm it, thereby making the concentration of the diffusion source P2O5 uniform. By blowing out the process gas from the nozzle 8C, phosphorus can be uniformly diffused into the semiconductor wafer 3 held in the reaction tube 1 regardless of the holding location within the port 4.

In Figure 3, the pitch p2 between semiconductor wafers is 4.76mya.
(+)2-4. 76 Dragon), and the nozzle pitch p is smaller than this, 4 mm (p1=4m11), and the pitch p is much larger than this, 20 mm (p1=4m11).
-20 mm) under the same conditions as above.

From this, when the pitch is 4 mm, the in-plane variation in sheet resistance p is small, but when the pitch is 20 mm, the difference in in-plane variation in sheet resistance ρ between adjacent semiconductor wafers is 3 It can be seen that the difference becomes quite large by ~25%.

This changes the nozzle pitch p1 to the semiconductor wafer pitch p
This is believed to be because if it is larger than 2, there will be some parts where the process gas blown out from the nozzle 8C does not directly hit the semiconductor wafer 3.

In addition, Fig. 4 shows the state of air intrusion when 20 g/win of N2 gas is introduced from the gas supply pipe 2 and when it is introduced from the gas introduction pipe 8 in order to prevent air from entering the reaction tube 1. The results of evaluation at 02 concentration are shown.

From this, in the case of a blowout from the ceiling, the 02 concentration is 11
The air entering from the furnace mouth is 2,001 pp or less, while the air entering from the nozzle is 450 pp.
Therefore, when transporting the semiconductor wafer 3, it is better to introduce the gas downflow from the ceiling through the gas supply pipe 2 than to introduce it from the side through the nozzle 8C to prevent backflow of air. It can be seen that this intrusion into the reaction tube 1 can be prevented.

Note that since different gases are introduced from the gas supply pipe 2 and the gas introduction pipe 8, as described above, they can be connected to different gas supply sources, but they can be connected to different gas supply sources. Alternatively, the switching may be performed collectively through a valve.

FIGS. 5 to 7 show different heating means for the process gas that are different from those of the above embodiments.

That is, the one shown in FIG. 5 uses a straight pipe extending linearly from the bottom to the top inside the reactor 1 as the gas introduction pipe 9, and also preheats the area around the externally exposed part of the gas introduction pipe 9. A heater 10 is disposed, and the process gas flowing through the gas introduction pipe 9 is heated by the heater 10, and the heated process gas is passed through the nozzle 9a.
It was designed to erupt from the air.

In addition, in the case shown in FIG. 6, the gas introduction tube 10 is connected to the reaction tube 1.
The process gas is heated around the reaction tube 1, and the heated process gas is The liquid is ejected from a nozzle 10a.

Furthermore, in the case shown in FIG. 6, a gas retention chamber 11 is formed by a double wall at the lower part of the reaction tube 1, and
A gas introduction pipe 12, which extends upwardly with its lower end open, is arranged inside the reaction tube 1, thereby introducing the process gas into the gas retention chamber 11 to reduce its velocity and heat it sufficiently. Thereafter, the heated process gas is introduced into the reaction tube 1 from the nozzle 12a of the gas introduction tube 12.

In addition, in other oxidation processes such as phosphorus diffusion, when cold gas is introduced through a thin tube, the speed of this gas is high, and the gas cannot be warmed sufficiently. Disturbance of uniform heating occurs, resulting in variations in film thickness.

Therefore, even in such a case, it is necessary to heat the process gas as described above and introduce the process gas into the reaction tube 1 in a state in which a sufficient reaction occurs.

〔Effect of the invention〕

Since the present invention has the above-described configuration, a gas that has been sufficiently heated to cause a chemical reaction and generate a diffusion source is blown directly between the wafers of the rotating semiconductor wafers. , the concentration of the diffusion source over the entire surface can be made more uniform regardless of the holding position of the semiconductor wafer. Therefore, there is an effect that the diffusion by the diffusion source can be performed more uniformly, and the occurrence of variations in diffusion can be prevented as much as possible.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an embodiment of the present invention, Fig. 2 is a graph showing the distribution of sheet resistance when a U-shaped nozzle and a straight nozzle are used as the gas introduction pipe, and Fig. 3 is a graph showing the nozzle pitch. A graph showing the distribution of sheet resistance when 4mm is smaller than the wafer pitch and 20+am is larger than the wafer pitch. Figure 4 is a graph showing the distribution of 02a degrees when gas is blown from the ceiling and when it is blown out from the nozzle. 7 to 7 are longitudinal sectional views showing different process gas heating means, FIG. 8 is a view corresponding to FIG. 1 showing a conventional example, and FIG. 9 is a view corresponding to FIG. 2. DESCRIPTION OF SYMBOLS 1...Reaction tube, Gas supply pipe, 3...Semiconductor wafer, 4...Boat, 5...Boat table, 6...
...Cap, 7...Motor, 8.9.10.12.
...Gas introduction pipe, 8c, 9a, 10a, 12a...nozzle. Fig. 8

Claims (1)

[Claims] A boat holding semiconductor wafers at a predetermined pitch is inserted into a reaction tube and sealed, and a process gas is introduced into the reaction tube to heat-treat the semiconductor wafers while maintaining a high temperature atmosphere inside the reaction tube. In the thermal diffusion apparatus for semiconductor manufacturing, a gas introduction tube extending along the length of the reaction tube is disposed inside the reaction tube, and a nozzle for blowing process gas toward the semiconductor wafer is provided on the peripheral wall of the gas introduction tube. A thermal diffusion device for semiconductor manufacturing, characterized in that the boat is provided at a pitch substantially equal to or smaller than the pitch of the wafer, and is configured so that preheated process gas is blown out from the nozzle, and the boat is rotatable. .