JP3068522B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming an impurity-doped thin film by a chemical vapor deposition (CVD) method.

[0002]

2. Description of the Related Art In manufacturing a semiconductor device, various materials constituting the semiconductor device are formed by a CVD method. Examples of such a material include a silicon oxide film and a silicon nitride film as an insulating film, a polycrystalline silicon film as a semiconductor film, and a high melting point metal film such as a tungsten film as a conductor film.

[0003] As the CVD method, a low pressure CVD method,
A normal pressure CVD method, a plasma CVD method and the like are widely used as typical ones.

In recent years, a technique of introducing impurities during film formation (hereinafter referred to as In-Situ doping) has become important. For example, when depositing a silicon thin film by a low-pressure CVD method, it is indispensable in a semiconductor device manufacturing process to form a phosphorus impurity-containing silicon thin film by performing In-Situ doping of a phosphorus impurity.

A conventional technique for forming a phosphorus-doped polysilicon thin film by a low pressure CVD method will be described below with reference to FIGS. FIG. 4 is a cross-sectional view of a typical low pressure CVD apparatus. FIG. 5 is a graph showing variations in phosphorus impurities when a phosphorus-doped polysilicon thin film is deposited using such an apparatus.

Hereinafter, the low pressure CVD apparatus will be described with reference to FIG. As shown in FIG.
Furnace tube 11 which is a chemical reaction chamber, heater 12 for keeping the inside of furnace tube 11 at a desired temperature, wafer 13 which is a semiconductor substrate, boat 14 on which wafer 13 is mounted, furnace tube 11
A pump 15 for reducing the pressure inside and exhausting the reaction gas and a hatch 16 for hermetically closing the furnace core tube 11 are provided as main parts.

In addition, this reduced pressure CVD apparatus is provided with a reaction gas introduction pipe 1 for introducing a reaction gas for film formation.
7. It has impurity gas introduction pipes 18 and 19. Further, a furnace core tube 20 is provided to guide the exhaust gas to the pump 15 while suppressing and controlling the chemical reaction.

Next, a case where a polysilicon thin film is formed using such a low pressure CVD apparatus will be described.

First, a boat 14 on which a wafer 13 is mounted is inserted into a furnace core tube 11 maintained at a desired temperature of, for example, about 600 ° C. by a heater 12, and the furnace core tube 11 is sealed by a hatch 16. Furnace core tube 1 by pump 15
The pressure in 1 is reduced to a desired pressure, for example, about 1 Torr.
Then, the temperature is maintained until the temperature of the wafer 13 is stabilized.

Next, silane (SiH ₄ ) as a reaction gas is used.
Is supplied from the reaction gas introduction pipe 17 and phosphine (PH ₃ ) as an impurity gas is supplied into the furnace core tube 11 through the impurity gas introduction pipes 18 and 19 to deposit a phosphorus-doped polysilicon thin film on the surface of the wafer 13. here,
The unreacted gas is exhausted out of the furnace core tube 11 by the pump 15. The arrows shown on the furnace core tube 11 and the furnace core tube 20 indicate the flow direction of the reactant gas, impurity gas or unreacted gas.

In the formation of such a phosphorus-doped polysilicon thin film, it is difficult to reduce the variation of phosphorus impurities in the polysilicon thin film. In particular, it is difficult to reduce the variation of the phosphorus impurity at the position of the boat 14 of the wafer 13. In order to reduce such variations at the boat position, a plurality of impurity gas introduction pipes are usually provided as described with reference to FIG.

FIG. 5 is a graph showing the relationship between the above-mentioned variation of the phosphorus impurity and the position of the boat boat in the formation of the phosphorus-doped polysilicon thin film. Here, the results are shown in the case where one impurity gas introduction pipe is provided in the lower part and in the case where one impurity introduction pipe is provided in each of the lower part and the upper part as shown in FIG. I have.

As can be seen from FIG. 5, when one impurity gas introduction pipe is provided at the bottom, the concentration of phosphorus impurities in the wafer below the boat position is high, and the concentration of phosphorus impurities in the wafer above the boat position is high. The concentration will be lower. The variation of the phosphorus impurities in the boat becomes about 10%. On the other hand, when one impurity gas introduction pipe is provided at each of the lower portion and the upper portion, the variation of the phosphorus impurity in the boat is about 7%. This is because the phosphine gas is supplied to the wafer above the boat position by the upper impurity gas introduction pipe. However, with such a method, it is difficult to significantly reduce the variation of the phosphorus impurity in the boat.

[0014]

As described above, it is difficult to greatly reduce the dispersion of phosphorus impurities in a boat by the conventional film forming technique. In order to reduce the variation in the phosphorus impurity, a method of increasing the number of impurity gas introduction pipes to be installed and increasing the supply locations of the impurity gas can be considered. For example, there is a method in which an impurity gas introduction pipe extending from a lower portion to an upper portion in a furnace core tube is provided, and a number of holes are attached at predetermined positions from the lower portion to the upper portion of such an impurity gas introduction tube.

However, in the process of forming a silicon thin film by such a low-pressure CVD method, the silicon film is formed not only on the wafer but also on the inner wall of the furnace core tube of the low-pressure CVD apparatus and the above-mentioned wall of the impurity gas introduction pipe. Alternatively, a silicon thin film is also deposited on the above holes. Then, the silicon thin film deposited on the tube wall of the furnace core tube or the impurity gas introduction tube easily peels off and becomes a source of dust.

Further, when the silicon thin film is deposited in the hole of the impurity gas introducing pipe, the diameter of the hole becomes small, the supply amount of the impurity gas decreases, and the impurity concentration in the silicon thin film cannot be controlled. Alternatively, some of the many holes are closed, so that no impurity gas is supplied. In such a case, the dispersion of the phosphorus impurities is rather increased.

An object of the present invention is to provide a method of manufacturing a semiconductor device which improves the uniformity of impurities in a furnace core tube when a thin film is subjected to In-Situ doping by CVD method. .

[0018]

To this end, a method of manufacturing a semiconductor device according to the present invention is a method of forming a thin film containing impurities on a semiconductor substrate by a chemical vapor deposition method. The impurity gas for doping the impurity is mixed with the carrier gas and introduced into the thin film deposition reactor.
Alternatively, an impurity gas for doping a predetermined impurity is mixed with the carrier gas in the reaction furnace. The flow rate of the carrier gas is high so that the impurity gas mixed into the carrier gas is not thermally decomposed between the end of the boat position where the wafer as the substrate to be formed in the reaction furnace is mounted. Is set.

Here, the impurity gas is a phosphine gas, and a silane gas or a dichlorosilane gas is introduced into the reaction furnace to form a polysilicon thin film.
Alternatively, the impurity gas is a phosphine gas, and a silane gas is introduced into the reaction furnace to form an amorphous silicon thin film.

Alternatively, the impurity gas is a phosphine gas, and a disilane gas is introduced into the reaction furnace to form a polysilicon thin film or an amorphous silicon thin film.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a first embodiment of the present invention will be described with reference to FIGS. Here, FIG. 1 is a sectional view of a low pressure CVD apparatus used in the present invention. FIG. 2 shows film forming conditions for explaining the present invention. FIG. 3 is a graph for explaining the effect of the present invention.

First, a low pressure CVD apparatus will be described with reference to FIG. As shown in FIG.
As described in the prior art, a furnace core tube 1 as a reaction furnace, a heater 2 for maintaining the inside of the furnace core tube 1 at a desired temperature, a wafer 3 as a semiconductor substrate, and a boat 4 for mounting the wafer 3 A pump 5 for depressurizing the inside of the furnace core tube 1 to exhaust the reaction gas and a hatch 6 for hermetically sealing the furnace core tube 1 are provided as main parts.

The low pressure CVD apparatus has a reaction gas introduction pipe 7 for introducing a reaction gas for film formation and one impurity gas introduction pipe 8. and again,
A furnace core tube 9 is provided to guide the exhaust gas to the pump 5 while suppressing and controlling the chemical reaction.

Next, a case where a polysilicon thin film is formed using such a low pressure CVD apparatus will be described.

First, the boat 4 on which the wafer 3 is mounted is inserted into the furnace core tube 1 maintained at a desired temperature, for example, about 600 ° C. by the heater 2, and the furnace core tube 1 is sealed by the hatch 6. The pressure inside the furnace core tube 1 is reduced to a desired pressure, for example, about 2 Torr by the pump 5. Then, the temperature is maintained until the temperature of the wafer 3 is stabilized.

Next, silane as a reaction gas is introduced from a reaction gas introduction pipe 7. Then, a carrier gas mixed with phosphine is supplied into the furnace core tube 1 from the impurity gas introduction tube 8. Thus, a phosphorus-doped polysilicon thin film is deposited on the surface of the wafer 3. Here, the effect of reducing the variation of the phosphorus impurity in the carrier gas containing phosphine, which is a feature of the present invention, will be described with reference to FIG. In FIG. 2, the horizontal axis represents the total gas pressure during film formation. Here, the partial pressure of the silane gas is fixed at 1 Torr.
The vertical axis represents the variation of the phosphorus impurities at the wafer boat position. Further, a carrier gas containing phosphine is a parameter for film formation. As can be seen from FIG. 2, the dispersion of the phosphorus impurities decreases as the flow rate of the carrier gas increases. Here, the partial pressure of the phosphine gas mixed into the carrier gas is set to be constant regardless of the flow rate of the carrier gas. In addition, an inert gas such as nitrogen gas or argon is used as the carrier gas.

As described above, when the flow rate of the carrier gas is increased, the variation in the phosphorus impurity is reduced because the phosphine gas mixed into the carrier gas and introduced from the impurity gas introduction pipe 8 is heated by the heater 2 and activated. This is because the boat reaches the upper position before the boat.

As described above, the polysilicon thin film is formed, and the unreacted gas is exhausted out of the furnace core tube 1 by the pump 5. The arrows shown on the furnace core tube 1 and the furnace core tube 9 indicate the flow direction of the reactant gas, the carrier gas or the unreacted gas.

Next, the effect of the present invention will be described with reference to FIG. FIG. 3 is a graph showing the relationship between the concentration of phosphorus impurities and the position of a boat boat in the formation of a phosphorus-doped polysilicon thin film. Here, there are shown a case where the phosphine gas is mixed with the carrier gas and introduced, and a case where the phosphine gas is introduced without being mixed with the carrier gas.

As can be seen from FIG. 3, when the phosphine gas is not mixed into the carrier gas, the variation of the phosphorus impurity concentration at the boat position is 10%. In contrast,
When phosphine gas is mixed into carrier gas,
This value is 5% or less, which is reduced to 1/2 or less of the conventional value. Here, the flow rate of the carrier gas is 2000 sccm.
It has become about. The total gas pressure during film formation is 2T
orr is set.

In the first embodiment, a case is described in which a polysilicon thin film is formed using silane gas. However, dichlorosilane gas (SiH ₂ Cl ₂ ) may be used instead of silane gas. However, in this case, the temperature of the reaction furnace is about 700 ° C., which is higher than in the case of silane gas.

Next, a second embodiment of the present invention will be described. In this case, the amorphous silicon thin film is doped with In-Situ phosphorus.

Here, the low pressure CVD apparatus used is the same as that described with reference to FIG. First with this CVD equipment,
A boat 4 on which a wafer 3 is mounted is inserted into a furnace core tube 1 maintained at a desired temperature, for example, about 400 ° C. by a heater 2, the furnace core tube 1 is sealed by a hatch 6, and then a furnace core tube is pumped by a pump 5. The pressure in 1 is reduced to a desired pressure, for example, about 1 Torr. Then, the temperature is maintained until the temperature of the wafer 3 is stabilized.

Next, the reaction gas disilane (Si ₂ H
₆ ) is introduced through the reaction gas introduction pipe 7. Then, a carrier gas mixed with phosphine is supplied into the furnace core tube 1 from the impurity gas introduction tube 8. Thus, a phosphorus-doped amorphous silicon thin film is deposited on the surface of the wafer 3. Also in this case, a carrier gas mixed with phosphine, which is a feature of the present invention, is used. Here, when the flow rate of the carrier gas increases, the variation of the phosphorus impurity in the amorphous silicon thin film decreases as in the case of forming the polysilicon thin film described in the first embodiment. This is because the phosphine gas introduced into the carrier gas and introduced from the impurity gas introduction pipe 8 reaches the upper portion of the boat position before being heated and activated by the heater 2. As described above, an amorphous silicon thin film having a small variation in the phosphorus impurity is formed.

As described above, the gist of the present invention resides in that a thin film is formed by increasing the flow rate of the impurity gas in the reaction furnace, and the dispersion of the impurities in the thin film is reduced. In this method, in addition to the method described in the embodiment in which the impurity gas is mixed into the carrier gas and introduced into the reaction furnace, the reaction gas and the impurity gas are mixed into the carrier gas and introduced into the reaction furnace. Or a method in which a reaction gas and an impurity gas are introduced into a reaction furnace, a carrier gas is introduced from another gas introduction pipe, and the reaction gas and the impurity gas are mixed into the carrier gas in the reaction furnace. It may be a method to make it. It should be noted that such a method can be variously considered.

In the embodiment of the present invention, the case where the silicon thin film is doped with a phosphorus impurity by In-Situ is described, but the effect of the present invention is not limited to this case. In addition, the present invention can be similarly applied to a case where impurities are introduced into a high melting point metal by a CVD method or a case where impurities are introduced into an insulating film such as a silicon oxide film.

[0037]

As described above, the method of manufacturing a semiconductor device according to the present invention provides a method of forming an impurity-doped thin film on a semiconductor substrate by chemical vapor deposition. The gas is mixed with the carrier gas and introduced into the reactor for film formation. Alternatively, a reaction gas for film formation and an impurity gas are mixed with a carrier gas and introduced. Here, the flow rate of the carrier gas is high so that the impurity gas mixed into the carrier gas is not thermally decomposed between the end of the boat position where the wafer, which is the substrate on which the film is to be formed, is loaded in the reaction furnace. Is set. Then, a polysilicon thin film or an amorphous silicon thin film containing a phosphorus impurity is formed as such a thin film.

As described above, in the film forming method of the present invention, the dispersion of the phosphorus impurities in the boat is greatly reduced.

The silicon thin film deposited on the furnace core tube of the reaction furnace or the tube wall of the impurity gas introduction tube as described in the prior art is also greatly reduced from being easily peeled off and becoming a source of dust. Become like

As described above, the present invention greatly improves the uniformity of thin film formation required for a semiconductor device, and further promotes high integration or high speed of the semiconductor device.

[Brief description of the drawings]

FIG. 1 is a sectional view of a low pressure CVD apparatus for explaining the present invention.

FIG. 2 is a graph for explaining film forming conditions according to the embodiment of the present invention.

FIG. 3 is a graph for explaining effects of the embodiment of the present invention.

FIG. 4 is a cross-sectional view of a low pressure CVD apparatus for explaining a conventional technique.

FIG. 5 is a graph for explaining a problem of the related art.

[Explanation of symbols]

 1,11 Furnace core tube 2,12 Heater 3,13 Wafer 4,14 Boat 5,15 Pump 6,16 Hatch 7,17 Reaction gas introduction tube 8,18,19 Impurity gas introduction tube 9,20 Furnace inner tube

Claims (4)

(57) [Claims] An impurity is formed on a semiconductor substrate by chemical vapor deposition.
A method for forming a thin film containing
Impurity gas for doping certain impurities
Mixed with the carrier gas between the ends of the boat where the wafers, which are the substrates to be formed in the reaction furnace, are mounted.
Method of manufacturing a semi-conductor device that impurity gas to said that you set the flow rate of the carrier gas so as not to thermally decompose. Wherein said impurity gas is phosphine gas, the production of the reactor according to claim 1 Symbol mounting of the semiconductor device is introduced silane gas or dichlorosilane gas polysilicon thin film is characterized in that it is deposited in the Method. Wherein the impurity gas is phosphine gas, a method of manufacturing a semiconductor device according to claim 1 Symbol placing the silane gas is introduced into the reactor in the amorphous silicon thin film is characterized in that it is deposited. Wherein a said impurity gas is phosphine gas, the reactor according to claim 1 Symbol mounting of the semiconductor device disilane gas polysilicon film or an amorphous silicon thin film is introduced, characterized in that it is deposited in the Manufacturing method.