JP2829102B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a semiconductor device.

(Prior Art) In manufacturing a semiconductor device, a semiconductor film, for example, a polysilicon film is formed on a semiconductor substrate by a CVD method, and an impurity such as phosphorus is added to the polysilicon film to be used as an electrode and a wiring. Often. Currently, a method of forming a polysilicon film containing impurities includes a step of forming a silicon film containing no impurities on a semiconductor substrate and then adsorbing and diffusing impurities on the surface of the silicon film. An in-situ doped polysilicon deposition method that repeats the above is being studied. This forming method will be described below.

A semiconductor substrate is placed in a low-pressure CVD apparatus, and first, an SiH ₄ gas is thermally decomposed to form an undoped polysilicon film (a polysilicon film containing no impurities). Next, without continuously exposing the semiconductor substrate to the outside air, an impurity gas such as a pH ₃ gas is thermally decomposed to coat the impurity on the undoped polysilicon film. And continuously undoped
The SiH ₄ gas is thermally decomposed on the polysilicon film to form an undoped polysilicon film, and a structure in which an impurity layer is sandwiched between the undoped polysilicon films can be formed. The above steps are repeated if necessary, and annealing is performed to form a doped polysilicon film (polysilicon film containing impurities) as wiring and electrodes.

When this manufacturing method is used, for example, P is used as an impurity to be added, and in the step of forming an undoped polysilicon film subsequent to the step of coating an impurity on the undoped polysilicon film, the supply of SiH ₄ gas is performed. There is a disadvantage that an induction time occurs in which a silicon film is hardly formed on a silicon film covered with impurities for about 10 minutes from the start. This impurity coating layer (P layer) impurities adsorbed species in respect (PH ₃ molecule or P atom), the adsorption probability of SiH ₄ molecules is reduced, an intermediate in the dissociation reaction of the SiH ₄ molecules in the semiconductor substrate surface It is believed that this is because the generation of the product SiH ₂ molecules is suppressed. Due to the existence of such an induction time, the effective deposition rate of the doped polysilicon film is significantly reduced as the number of process repetitions increases.

(Problems to be Solved by the Invention) According to the conventional manufacturing method, when an impurity-doped semiconductor film is formed on a film not doped with an impurity following the step of coating the impurity-doped film on the film, the induction time is reduced. There is a problem that the effective deposition rate is significantly reduced by the occurrence. The present invention has been made in view of the above points,
Provided is a method for manufacturing a semiconductor device, which shortens an induction time and improves an effective deposition rate of a semiconductor film.

[Structure of the Invention] (Means for Solving the Problems) In a method for manufacturing a semiconductor device according to the present invention, a step of forming a first semiconductor film containing no impurities on a semiconductor substrate, and a step of forming the first semiconductor film Forming an impurity layer by adsorbing and diffusing impurities on the surface, and forming a second semiconductor film on the impurity layer by thermal decomposition of a reaction gas containing at least one of Si ₂ H ₆ and Si ₃ H ₈ And a step of performing

(Operation) In the present invention, after forming a first semiconductor film containing no impurities and adsorbing and diffusing impurities on the surface of the first semiconductor film, at least one of Si ₂ H ₆ and Si ₃ H ₈ is used. By generating SiH ₄ molecules by thermal decomposition of a reaction gas containing one, the induction time of the second semiconductor film formed thereon is reduced.

(Example) Hereinafter, an example of the present invention will be described.

A semiconductor substrate is placed in a low pressure CVD apparatus. The semiconductor substrate is placed horizontally and the gas flow is introduced from below and exhausted from above. Reaction temperature 580 ° C, reaction pressure 0.5 Torr, SiH ₄ gas 200sccm
Thermally decomposes the SiH ₄ gas to form a first undoped polysilicon film on the semiconductor substrate. Next, without exposing the semiconductor substrate to the outside air, the reaction temperature is 58%.
PH ₃ gas is thermally decomposed at 0 ° C., reaction pressure 0.5 Torr, pH ₃ gas flow rate 50 sccm, and P is coated on the undoped polysilicon film. Reaction temperature 580 ° C, reaction pressure 0.5 Torr, Si ₂ H ₆ gas flow rate 200sccm without continuous exposure to outside air.
Is supplied into the apparatus, and the first undoped
A second undoped polysilicon film is formed on the polysilicon film. Thus, a structure in which the P layer exists between the undoped polysilicon films can be formed.
The above steps are repeated if necessary, and annealing is performed to form a doped polysilicon film as a wiring / electrode.

FIG. 3 shows the gas outflow pattern in this case. T ₁
Represents the outflow time of SiH ₄ , T ₂ represents pH ₃ and T ₃ represents the outflow time of Si ₂ H ₆ and SiH ₄ . By using this method, the induction time for forming the second undoped polysilicon film on the first undoped polysilicon film covered with impurities can be shortened (FIG. 1), and the doped polysilicon can be reduced. The deposition rate of the silicon film increases (FIG. 2).

In addition, in the gas outflow time T3 when forming the second undoped polysilicon film of FIG. ₃ , the Si ₂ H ₆ gas,
Although the SiH ₄ gas is sequentially introduced, the same result can be obtained when the SiH ₄ gas is discharged in parallel as shown in FIG. Although the present embodiment relates to the deposition of a doped polysilicon film at a reaction temperature of 580 ° C., a case other than the reaction temperature of 580 ° C. may be used. Further, the film to be deposited may be an amorphous silicon film. In addition, the reaction pressure may take a value other than that of this embodiment.

[Effects of the Invention] From the above results, it is possible to shorten the induction time and improve the effective deposition rate of the semiconductor film by using the present invention.

[Brief description of the drawings]

Figure 1 is a diagram showing the relationship of undoped polysilicon thickness for gas outflow time T _3, FIG. 2 shows the relationship between the doped polysilicon film thickness for doped polysilicon film deposition time diagram, the 3 and 4 are pattern diagrams of the outflow of SiH ₄ , pH ₃ and Si ₂ H ₆ with respect to the outflow time of the gas according to the embodiment of the present invention.

Claims (3)

(57) [Claims] Forming a first semiconductor film 1. A no impurities on a semiconductor substrate, forming a first semiconductor film impurity layer is adsorbed and diffused impurities on the surface, Si ₂ H
Forming a second semiconductor film on the impurity layer by thermal decomposition of a reaction gas containing at least one of Si ₆ and Si ₃ H ₈ . 2. A method according to claim 1, wherein the reaction gas containing at least one of Si ₂ H ₆ and Si ₃ H ₈ contains SiH ₄ . 3. The semiconductor device according to claim 1, wherein the impurity in the impurity layer is at least one of P, As, Sb, B, Al, and Ga.
The manufacturing method of the semiconductor device described in the above.