JP2001144022A - Producing method for semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photodiode for short wavelength photodetection and an integrated circuit device having satisfactory characteristics through a simple process. SOLUTION: An impurity can be easily diffused over single crystal silicon while using polycrystal silicon and a thin oxide film. It is not necessary for this process to add a lot of steps to a conventional process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodiode and a photodetector with a built-in circuit, and more particularly to a method for improving the light sensitivity of a photodiode used for detecting short-wavelength light.

[0002]

2. Description of the Related Art FIG. 3 is a schematic sectional view showing a semiconductor device according to a conventional manufacturing method in the order of steps. In FIG. 3A, a thick silicon oxide film 12 is formed on an N-type semiconductor substrate 11.
Then, a thin silicon oxide film 13 is formed. Then, FIG.
As shown in (b), B or BF2 as an impurity is diffused into the N-type semiconductor substrate 11 through the thin silicon film 13 to form a P-type diffusion layer 14, thereby forming a pn junction type diode.

[0003] Such a photodiode is conventionally used, for example, as a signal detecting element of an optical pickup. To detect a relatively wide wavelength range from outside light to infrared light, a pn junction type Si photodiode is used. A pn junction type Si photodiode is simple, inexpensive, and widely used. Usually pn
Ion implantation is often used to introduce impurities for forming a junction as shown in FIG.

[0004]

The light receiving sensitivity characteristics of the conventional pn junction type Si photodiode are reduced on the short wavelength side of 400 nm or less, and there is a problem in application to short wavelength light. An object of the present invention is to provide a photodiode suitable for short wavelength light, which has high photosensitivity even in a short wavelength region of 400 nm or less, and a method of manufacturing the same.

[0005]

According to the present invention, impurity diffusion into single crystal silicon is controlled by using polycrystalline silicon and a thin oxide film.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the thickness of each layer is exaggerated for simplicity. FIG. 1 is a schematic cross-sectional view in the order of steps showing one embodiment of a semiconductor device according to the manufacturing method of the present invention.

As shown in FIG. 1A, a thick oxide film called Locos oxide film is formed on a part of a silicon semiconductor substrate 1, for example, a silicon semiconductor substrate of N type conductivity having a resistivity of 2 to 4 Ω · cm. 2 are formed. The thick oxide film 2 is not an essential part in the present invention. You don't have to. A thin oxide film 4 is formed on the silicon semiconductor substrate surface region 3 where the thick oxide film 2 is not formed. This thin oxide film 4 can be formed by CVD even if it is thermally oxidized.
An oxide film may be deposited on the silicon surface, or a chemical oxidation of the silicon surface may be performed using a chemical solution.

The chemical is, for example, hot nitric acid. The thickness of the oxide film is preferably 0.5 nm to 30 nm, but can be arbitrarily selected depending on the junction depth to be obtained. Next, as shown in FIG. 1B, after forming the thin oxide film 4, a polycrystalline silicon layer 5 is deposited by a CVD method. The thickness of the polycrystalline silicon layer 5 is 5 nm to 500 nm.
And preferably 5 nm to 100 nm. Here, depending on the film quality of the polycrystalline silicon layer, short-wavelength light may be easily absorbed. In such a case, improvement can be made by reducing the film thickness. The film thickness at that time is 5 nm to 10 nm.

Next, as shown in FIG. 1C, impurities are introduced into the polycrystalline silicon layer 5. For example, B (boron) or BF2 is ion-implanted. At this time, the impurity implanted by the ion implantation contains polycrystalline silicon layer 5 and
It is important to perform ion implantation at a setting implantation energy that does not penetrate the thin silicon oxide film 4 and reach the silicon semiconductor substrate 1. The impurity concentration in the polycrystalline silicon layer 5 is 1 × 10 ¹⁸ atoms / c.
It is desirable to set m ³ to 1 × 10 ²¹ atoms / cm ³ . Further, the introduction of impurities is not limited to ion implantation. Doped polycrystalline silicon doped with impurities may be used simultaneously with the deposition of the polycrystalline silicon layer.

Next, as shown in FIG. 1D, the polycrystalline silicon layer 5 is patterned to remove a part of the polycrystalline silicon. Next, as shown in FIG. 2E, impurities in the patterned polycrystalline silicon 6 are diffused into the silicon. Due to its properties, B (boron) is easily taken into the silicon oxide film from the polycrystalline silicon layer,
Since a thin oxide film easily reaches the interface between the oxide film and the single crystal silicon, the diffusion condition at this time is preferably set at a low temperature of about 700 ° C. to 900 ° C. in the case of diffusion using a thermal diffusion furnace. Basically, the impurity diffusion at this temperature is sufficient, so that a special diffusion step is not performed, and only a thermal step performed later on device formation (interlayer insulating film, wiring, etc.) is possible. Further, diffusion may be performed by an RTA apparatus (lamp annealing apparatus). The temperature at this time is 800 ° C. to 1050 ° C.

As a result, a shallow P-type diffusion layer 7 is formed. Next, as shown in FIG. 2F, a P-type impurity is implanted by ion implantation using the patterned polycrystalline silicon 6 as a mask to form a deep P-type diffusion layer 8. Although the case where the P-type impurity is introduced into the N-type substrate has been described above, the present invention can be realized even if the P-type and the N-type are reversed for the conductivity type. However, N
When introducing a type impurity, the thickness of the silicon oxide film should be 0.5 nm to 5 nm. The diffusion temperature is 800 ° C. to 1000 ° C. in the case of thermal diffusion using a diffusion furnace.
900 ° C to 1100 ° C for diffusion by RTA
It is good to

The above-mentioned polycrystalline silicon may be removed after the impurity diffusion. Further, the above-mentioned “semiconductor substrate” can of course be replaced with an N-type or P-type epitaxial layer. Through the steps described above, a shallow junction can be formed in single-crystal silicon by a simple method, and as a result, a photodiode with high sensitivity to short-wavelength light is realized.

[0013]

According to the present invention, there is provided a pn junction,
In a photodiode in which photodetection is performed by photocarriers generated in a depletion layer formed by an n-junction, the pn junction is formed by single-crystal silicon, a silicon oxide film formed thereon, and a polycrystalline silicon layer thereon. Is formed, a shallow junction can be realized, and there is an effect of increasing the detection sensitivity of short-wavelength light.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a method of manufacturing a photodiode according to an embodiment of the present invention in the order of steps.

FIG. 2 is a cross-sectional view illustrating a method of manufacturing a photodiode according to an embodiment of the present invention in the order of steps.

FIG. 3 is a process order sectional view showing a process of a conventional photodiode manufacturing method.

[Explanation of symbols]

 Reference Signs List 1 N-type substrate 2 Thick oxide film 3 Thin oxide film region 4 Polycrystalline silicon layer 6 Polycrystalline silicon 7 Shallow P-type diffusion layer 8 Deep P-type diffusion layer

Claims (7)

[Claims] A step of forming a polycrystalline silicon layer in a specific region on a substrate layer made of a semiconductor material of a first conductivity type;
Doping impurities into the polycrystalline silicon layer to form a second
Forming a junction by forming a conductive-type polycrystalline silicon layer and diffusing impurities in the second conductive-type polycrystalline silicon layer into the semiconductor substrate layer. Method. 2. The method according to claim 1, wherein the method of introducing impurities into the polycrystalline silicon layer is ion implantation. 3. The polycrystalline silicon layer has a thickness of 5 nm to 3 nm.
2. The method according to claim 1, wherein the thickness is 100 nm. 4. The method of manufacturing a semiconductor device according to claim 1, wherein an insulating film is formed between said first conductive type semiconductor substrate layer and said second conductive type polycrystalline silicon layer. Method. 5. The semiconductor device according to claim 4, wherein said insulating film between said first conductive type semiconductor substrate layer and said second conductive type polycrystalline silicon layer is a silicon oxide film. Manufacturing method. 6. The silicon oxide film has a thickness of 0.5 nm to 30 nm.
6. The method for manufacturing a semiconductor device according to claim 5, wherein 7. The polycrystalline silicon layer of the second conductivity type,
2. The method of manufacturing a semiconductor device according to claim 1, wherein impurities in the second conductivity type polycrystalline silicon layer are diffused into the first conductivity type semiconductor substrate layer and then removed.