JPH02306620A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To uniformly take out impurity outside semiconductor with superior reproducibility, and introduce impurity into the semiconductor at a low temperature, by projecting radio waves having energy larger than or equal to the bonding dissociation energy on a semiconductor substrate, and changing the distribution of impurity contained in the substrate. CONSTITUTION:A semiconductor substrate 1 is irradiated with radio waves 2 whose energy is larger than or equal to the bonding dissociation energy, and impurity atoms are outwardly diffused by releasing the impurity atoms in the semiconductor from the bonded state. At this time, it is effective that the atmosphere is kept at a vacuum state or a reduced pressure state, and the substrate 1 is heated at a temperature wherein heat is not dissipated. As to the radio waves 2, synchrotron radiation ray SR is practically used because of large energy. When the atmosphere is made to contain impurity while the radio waves 2 is projected, Si-Si bond is cut by the same reason as the case of outward diffusion, e.g. light irradiation. Thereby impurity can be uniformly taken out from semiconductor with superior reproducibility, and introduced into the semiconductor at a low temperature.

Description

[Detailed description of the invention] 〔overview] Regarding methods of controlling impurity concentrations in semiconductors.

The objective is to obtain a method for extracting impurities from the outside of a semiconductor and a method for introducing them into the semiconductor at low temperatures with uniform reproducibility.

The semiconductor substrate is configured to be irradiated with electromagnetic waves having an energy greater than the bond dissociation energy of the semiconductor atoms to change the distribution of impurities contained in the substrate.

[Industrial application field]

The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of controlling impurity concentration within a semiconductor.

In recent years, semiconductor devices have become more and more sophisticated, and in their manufacturing process, it is required to precisely control the donor or acceptor impurity concentration in the semiconductor substrate, especially in the vicinity of its surface.

The present invention can be used to meet this requirement.

[Conventional technology]

Thermal diffusion method is a method for introducing impurities into semiconductors.

Ion implantation methods have been developed and have been widely used.

However, all of these methods introduce impurities into the semiconductor from the outside, and do not, on the contrary, extract impurities from the semiconductor.

On the other hand, methods for extracting impurities from semiconductors include heating the semiconductor in vacuum, or reducing the 81 degrees in Si by utilizing the difference in segregation coefficients, such as boron (B) at the Si/SiO□ interface. It was thought possible.

[Problem to be solved by the invention]

However, the conventional method for removing impurities from semiconductors has poor reproducibility and uniformity, and has not been a practical technology.

Further, as elements become smaller and more reliable, lowering the process temperature is becoming more important, and it is desirable to introduce impurities into semiconductors at lower temperatures as well.

An object of the present invention is to obtain a method for extracting impurities to the outside of a semiconductor and a method for introducing impurities into the semiconductor at low temperature, uniformly and reproducibly.

[Means to solve the problem]

The above problem is solved by a method of manufacturing a semiconductor device in which a semiconductor substrate is irradiated with electromagnetic waves having an energy higher than the bond dissociation energy of the semiconductor atoms to change the distribution of impurities contained in the substrate.

Here, it is effective to satisfy the following conditions depending on the purpose.

■ Synchrotron radiation is used as the electromagnetic wave.

Diffusion of impurities into the substrate.

■ Place the semiconductor substrate in a vacuum or reduced pressure atmosphere.

Diffuse impurities out of the substrate.

■Heat the semiconductor substrate to 1000°C or less.

■ Apply an electric field to the surface of the semiconductor substrate.

■ Place the semiconductor substrate in an atmosphere containing impurity gas,
Diffusion of impurities into the substrate.

[Operation] In the present invention, a semiconductor substrate is irradiated with electromagnetic waves having an energy higher than its bond dissociation energy to release impurity atoms in the semiconductor from a bound state, thereby causing the impurity atoms to diffuse outward.

At this time, it is effective to set the atmosphere to vacuum or reduced pressure and to heat the substrate to such an extent that thermal diffusion will not occur.

As an electromagnetic wave, synchrotron radiation has a large amount of energy and is practical. The irradiation energy at this time is 10 to 120
It is about eV.

Also, when impurity gas is included in the atmosphere while irradiating the electromagnetic waves mentioned above, for the same reason as in the case of outward diffusion, namely,
By cutting the 5i-3i bond by light irradiation, impurities can be diffused into the semiconductor at a lower temperature than conventional thermal diffusion.

[Example〕 FIG. 1 is a sectional view illustrating an embodiment of the present invention.

In the figure, a Si substrate 1 with a phosphorus (P) concentration of 10"cm-" is irradiated with synchrotron radiation (SR) 2 for 10 minutes in a vacuum of 10-9 Torr.

At this time, the SR irradiation energy was 100 eV, and the substrate temperature was 500°C.

FIG. 2 shows an impurity concentration profile in the depth direction from the substrate surface after SR irradiation.

As shown in the figure, P is extracted by outward diffusion by SR irradiation, and the surface concentration of one substrate is reduced to 10 cm-'. In the figure, the dotted line indicates the initial state.

This structure is based on the collector layer of the bipolar transistor.
Applicable to n'' structure.

The concentration profile can be controlled by adjusting the SR irradiation energy, substrate temperature, and irradiation time.
' In the present invention, it is necessary to make the irradiation energy higher than the bond dissociation energy of the semiconductor, but for reference, the bond dissociation energy 1) of the main semiconductors is shown below.

Semiconductor Bond dissociation energy (KJ/mol, 298.15X) Si 311 Ge 277 Ge-3i 302 Ge-SiGe 3921) Bond
dissociation energy va
luesin silicon-cotaining
compounds and some off
eir implications.

Acc, Chem, Res, 14. 246
(1981).

Here, the bond dissociation energy of a substance is determined from the energy (wavelength) generated by atoms that dissociate and become free when the substance is irradiated with light with different energy (spectrum), and
The irradiation energy can be determined from the wavelength of the light and the amount of heat (calorimeter).

For reference, the energy dimension conversion is shown below.

1 eV = 1.6x10-19J = 1.6xlO
-” KJ=96 KJ/mol.

FIG. 3 is an impurity concentration profile explaining an example of impurity introduction.

While irradiating a Si substrate with a phosphorus (P) concentration of 10 cm-' with synchrotron radiation, phosphine (P) l*) was introduced as a doping gas and the gas pressure was increased to 10-' Tor.
Keep at r for 60 minutes.

At this time, the SR irradiation energy was 100 eV, and the substrate temperature was 500°C.

As a result, as shown in the figure, P is introduced into the substrate at a lower temperature than conventional thermal diffusion (approximately 1000°C) by SR irradiation, and the surface concentration increases to 10 cm.

The mechanism of diffusion promotion in this case was described in the section of the effect, but it is further thought to be as follows.

(2) Electron-hole pairs are created on the substrate surface by the irradiation light, and since electrons with a high diffusion rate move, the two surfaces become hole-rich. This causes the surface to become positively charged.

■ Electrons are transferred to the doping gas adsorbed on the substrate surface,
Attracted by positive charges on the substrate surface.

■ To further accelerate this phenomenon, an electric field may be applied from the outside. For example, doping is performed by biasing the substrate to +100V with respect to the chamber while irradiating the substrate with light.

°Next, numerical examples showing the effects of the present invention with respect to controllability of impurity depth are shown in the following table in comparison with conventional examples.

Item Example Conventional example Controllable phosphorus depth 0.1 μm or less Accuracy of 0.1 μm or more
±0.01μm ±0.05μm Diffusion of other impurities in the substrate None Yes (diffusion temperature
500°C1000°C) [Effects of the Invention] As explained above, according to the present invention, it is possible to obtain a method for extracting impurities to the outside of a semiconductor and a method for introducing impurities into the semiconductor at a low temperature with good reproducibility. It can contribute to miniaturization and higher performance of semiconductor devices.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view illustrating an embodiment of the present invention. Figure 2 shows the impurity concentration profile in the depth direction from the substrate surface after SR irradiation. FIG. 3 is an impurity concentration profile explaining an example of impurity introduction. In fig. 1 is a Si substrate.

Claims (1)

[Claims] 1. A method of manufacturing a semiconductor device, comprising irradiating a semiconductor substrate with electromagnetic waves having an energy greater than the bond dissociation energy of the semiconductor atoms to change the distribution of impurities contained in the substrate.