JPS6261322A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To form an impurity diffused layer at low concentration under sufficient control by making use of nuclear conversion. CONSTITUTION:When monosilane (SiH4) containing 50% of <30>Si as a material gas is used to form an epitaxial layer 5 on a silicon substrate 4, the epitaxial layer 5 contains 50% of <30>Si compared with 4% of <30>Si contained in the substrate 4 as the natural isotope ratio. When they are irradiated with neutrons n, phosphorus P with concentration of 10<15>cm<-3> is produced in the substrate 4 by reaction while phosphorus P with that of 10<16>cm<-3> is produced in the epitaxial layer 5. Later, P is diffused from the epitaxial layer 5 to the substrate 4 to form a diffused layer 6 with low concentration of P by heat-treatment at 1,100 deg.C for three hours in nitrogen atmosphere to cope with the crystal- defective annealing resultant from the n irradiation.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for manufacturing a semiconductor device, and more specifically to a method for manufacturing a semiconductor device in which impurities are generated through nuclear transmutation using neutron irradiation and the impurities are used as a diffusion source. .

[Background of the invention]

In the conventional manufacturing of semiconductor devices, low concentration impurity diffusion layers have been formed by ion implantation. However, in the normal ion implantation method.

It is impossible to form a uniform impurity diffusion layer in a structure with an uneven surface. For example, in a structure in which a groove 2 is formed in a semiconductor substrate 1 as shown in FIG. 2, it is possible to dope the side wall 3 of the groove 2 with controlled impurities using conventional ion implantation methods as well as heat treatment. The diffusion method was also extremely difficult from an engineering perspective.

[Purpose of the invention]

An object of the present invention is to provide a means that makes it possible to form a low-concentration diffusion layer into a complex structure, which has been impossible in terms of engineering with the above-mentioned conventional techniques.

[Summary of the invention]

In order to achieve the above object, the present invention forms a low concentration impurity using, for example, a nuclear transmutation reaction using neutrons, and uses this as a diffusion source to form a low concentration impurity expansion layer. That is, the first
As shown in Figure (a), when forming an epitaxial layer 5 on a silicon substrate 4, 30S is used as a raw material gas.
When monosilane (SiH4) containing 50% i is used, the substrate 4 contains only 4% of the natural isotope ratio, whereas the epitaxial layer 5 contains 50% "Si" is included. In this, neutron n
When irradiated with , phosphorus (P) is generated in the substrate 4 at a concentration of 1.01 s rho3, while in the epitaxial layer 5 at a concentration of 10''cm-'.

Thereafter, in order to anneal the crystal defects caused by the n-irradiation, heat treatment is applied for 3 hours at 1100'l'r in a nitrogen atmosphere, so that the epitaxial layer is removed from the substrate 4 as shown in FIG. 1(b). P is diffused to form a low concentration P diffusion layer 6.

As described in detail below, according to the present invention, by utilizing nuclear transmutation, it is possible to form a low concentration impurity diffusion layer with sufficient control.

[Embodiments of the invention]

The present invention will be described in detail below based on examples.

Example 1 This example shows a method of forming an insulating film by the CVD method and diffusing impurities through the insulating film.

FIG. 3(a) shows a state in which 1f11 is formed on a P-type (100) plane, 10Ω'On silicon substrate 10, and an SiO□ layer 2 is further formed by CVD. The Si
The n2 layer is SiH4 with 30 Si concentrated to 50%.
was used as a raw material gas, and was deposited by reacting with oxygen 02. The growth conditions at this time were a temperature of 730°C.

Pressure is 2 torr, flow ratio of S i H4 and 02 is 1
:20. The film thickness of 200nm is approximately 5
I was able to deposit it in minutes.

In FIG. 3(b), the semiconductor substrate is irradiated with neutrons, and then annealed at too much degree Celsius for 10 hours.

A state in which a phosphorus diffusion layer 13 is formed is shown.

Since the segregation coefficient of phosphorus at the SiO2/Si interface is about IO, phosphorus at a concentration about 10 times the phosphorus concentration in the Si can diffuse into the Si surface. Therefore, the surface concentration of the phosphorus diffusion layer at this time is about 10"'ra-', while the phosphorus number Sg-exchanged 3uSi in the semiconductor substrate is on the order of 10"cxn-" since 'aJjL is 4%. , had no effect on the specific resistance of the substrate.

FIG. 3CQ) is an example in which impurity diffusion is performed only in the groove 11, and in a structure having a Si substrate 10 and an oxide film 14 that does not substantially contain 30Si, 50% of 30Si is
The phosphorus diffusion layer 13 is shown in a state in which the phosphorus diffusion layer 13 is formed in the Si substrate in contact with the oxide film 12 containing 0%.
Since the junction depth depends on the heat treatment time and temperature after neutron irradiation, it is necessary to appropriately select the heat treatment conditions to form a diffusion layer with a desired junction depth.

Example 2 This example shows a method for diffusing impurities from Si spheres deposited by the CVD method.

FIG. 4(a) shows a state in which a Si single crystal layer is deposited to a thickness of 3 μm by an epitaxial method on an n-type (100) plane Si substrate 20 of 40Ω.

The single layer is deposited using a mixed gas of SiH4 and H2,
The temperature was 1000°C. The first 0.5 μm thick region 21 was formed using SiH4 containing 70% Si, and then the remaining 2.5 μm thick was formed using SiH4 containing 70% Si, then changing the gas and using regular S jH4 (containing 4% S j ). A 5 μm film 22 was deposited.

Figure 4(b) shows neutron irradiation.

After the formation, short-time annealing is performed at 1100℃30
A heat treatment is performed for a second to remove crystal damage caused by neutron irradiation, and a phosphorus diffusion layer 23 is formed. Due to the heat treatment at this time, the phosphorus expansion layer 23 changes from the initial 0.5 μm thick portion of the single crystal layer 21 to the Si substrate 20 and the 2.5 μm thick portion of the previous crystal layer. The light is diffused by 0.1 μm in each direction.

As shown in this example, according to the present invention, it is possible to change the impurity doping distribution in a single crystal simply by changing the isotope concentration in the source gas for epitaxial growth.
It becomes easier to control the impurity concentration distribution such as auto-doping, which was a problem with the Jagrai technology. Furthermore, according to the invention, 10
1. It is possible to form a low-a impurity doped layer of about 'aa-3 with high precision in a controlled state, which is particularly advantageous for forming MO5M type integrated circuits. In this example, the surface concentration is 1
×10” an-'t n-type buried diffusion layer t ×t o
Doping with impurities at a low concentration of I G am -3 can be achieved with high precision, and the threshold voltage of a MOS transistor formed on this crystal can be reduced. The variation in □ was suppressed to ±10 mV, less than 1/4 of that of the conventional technology.

〔Effect of the invention〕

” - As is clear from the description, according to the present invention, it is not possible to form an impurity diffusion layer, dope into an uneven structure that was a problem with the prior art, or form a low concentration impurity doped layer. This has become possible, and the engineering effect is enormous.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle of the present invention, FIG. 2 is a diagram showing the prior art, and FIGS. 3 and 4 are diagrams showing different embodiments of the present invention. 1.4, 10.20...Silicon substrate, 5 H12g
21...Diffusion source, 6,13.23...Diffusion layer.

Claims (1)

[Claims] 1. A step of forming on a semiconductor substrate a layer containing atoms that are transmuted to produce impurities by neutron irradiation, a step of irradiating the semiconductor substrate with neutrons, and a heat treatment to remove the impurities generated by the neutron irradiation from the substrate. Alternatively, a method for manufacturing a semiconductor device comprising the step of diffusing into a layer containing the impurity to form a layer having an impurity concentration distribution.