JPH0516656B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an impurity doping method for doping a semiconductor substrate with an impurity using plasma.

[Conventional technology]

Low-temperature processing of semiconductors has been required in conventional device manufacturing processes because it suppresses thermal metamorphosis, changes in impurity distribution, and changes in lifetime. It is an indispensable technology for avoiding adverse effects on the underlying devices that have already been formed during device manufacturing, and is becoming more and more sought after as semiconductor devices become smaller.

Currently, ion implantation is becoming the mainstream method for introducing impurities into semiconductor substrates, replacing thermal diffusion.
In particular, boron, which is a light element, is easily implanted deeply and it is difficult to form a shallow P region.

However, this is also possible if the energy is lowered to about 10 keV, but in this case, the beam current decreases, which increases processing time and reduces mass productivity. Furthermore, there are various problems with miniaturization in the depth direction of the substrate, such as the need for heat treatment at a relatively high temperature for activation of impurities after implantation and damage recovery.

[Problem that the invention seeks to solve]

As mentioned above, when introducing impurities into a semiconductor substrate, it is difficult to create a shallow P region in the case of boron, which is a light element, and the process takes a long time or requires high-temperature heat treatment, making it unsuitable for mass production. Various problems arose.

This invention was made to solve these problems, and is suitable for mass production because it is easy to create a shallow region of impurities, can be done in a relatively short time, and does not require high-temperature heat treatment. It is an object of the present invention to provide a method for doping impurities into a semiconductor substrate.

[Means and effects for solving the problems] In the doping method of the present invention, a semiconductor substrate is placed on a stage of a plasma generation device, and a silicon electrode containing the same element as the element to be doped is provided as a counter electrode, and the stage The method is characterized in that plasma is generated by applying a DC voltage with the stage side being negative between the electrode and the corresponding electrode with the polarity reversed, and impurities are implanted by ion implantation.By reversing the polarity of the voltage, energy is released. The diffusion of impurity atoms is promoted by irradiating the substrate with the retained electrons and imparting the energy to the substrate lattice. Diffusion to a desired depth is achieved by controlling this accelerating voltage.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

This embodiment shows the case where boron is diffused into an N-type substrate.

In FIG. 1, 1 is a parallel plate type plasma generator, 2 is its stage, 3 is a counter electrode, and 4 is a heater.

A silicon N-type single crystal substrate 5 is placed on the stage 2.
was placed and used as a negative electrode, and a P-type single crystal with a specific resistance of 0.05 Ω was placed on the counter electrode 3 provided 50 mm above the negative electrode. Stage 2 is heated to 200 to 400°C by heater 4. In the plasma generator 1, B ₂ H ₆ 2000ppm based on H ₂
diluent gas is sealed at a pressure of 2 to 4.5 Torr, and a DC voltage of 400 to 600 V is applied between the stage 2 and the counter electrode 3 to generate plasma discharge.

In the figure, 6 indicates a direct power supply, and 7 indicates a polarity converter.

That is, as shown in FIG. 3, a cycle was repeated twice in which a voltage was applied for 30 minutes so that the N-type single crystal substrate 5 became negative on the side of the stage 2, and then the polarity was reversed and electron injection was performed for 10 minutes. The spreading resistance of the diffusion layer during the test is as shown in Figure 2, and the diffusion depth is
It was 0.1μ.

Incidentally, this polarity change is carried out by appropriately selecting the cycle and the absolute values of the positive and negative voltages depending on the diffusion depth, as shown in FIG.

Thus, it was revealed that the characteristics did not change even after the subsequent lamp annealing, and that the impurities were sufficiently activated. In addition, no lattice defects or heavy metal levels were observed in deep level measurements using DLTS.

Note that the cathode fall in the plasma is several tens of volts,
Although the impact of positive ions caused by this has low energy, the impact cross section is large, so although it is limited to the surface, surface roughness will inevitably occur.

These defects are thought to cause movement of substrate atoms, disorder of atomic arrangement, and pairs of atomic vacancies and interstitial atoms.

Next, energetic boron ions repeatedly exchange positions with these atomic vacancies, and interstitial atoms exchange positions with atoms at lattice points and diffuse respectively.

It is inferred that the diffusion occurs through the Vacancy mechanism and INTERSTITIALCY mechanism involving the dot holes generated in the crystal.

However, since the incident energy for this diffusion is low, the energy imparted to the constituent lattice at the bottom of the surface layer of the substrate is small, and the boron atoms replaced by the lattice become negative acceptor ions, so they are repelled by the external electric field and diffuse into the interior. is difficult.

Therefore, the polarity of the applied voltage is reversed when the surface layer is doped with boron at a high concentration to some extent.

As a result, the substrate is irradiated with energetic electrons, and by controlling this accelerating voltage, the energy possessed by the electrons is applied to the substrate lattice up to the desired diffusion depth, and the energy is reversed. Since the substrate side becomes the positive electrode, the boron acceptor ions localized in front of the substrate are accelerated to diffuse due to the drift of this electric field.

Since diffusion is facilitated by the positive polarity reversal effect, the applied voltage can be relatively low, which has the advantage of reducing stress on the mask material and the insulating film of the multilayer structure. Further, in this case, an annealing effect due to electron irradiation is also considered.

The energy imparted to the lattice by the electron beam does not change depending on the electrical and optical properties of the substrate material, and there is no interference effect, so the energy is not emitted only in a specific place and can be seen from a two-dimensional view. The uniformity of the doping can be obtained when

Furthermore, since activation is performed by the energy of incident electrons, a freezing phenomenon of high concentration impurities exceeding the metastable solid solubility limit occurs, and a high surface concentration is maintained without redistribution.

Note that the critical displacement energy of incident electrons for Si atoms is as high as 125 keV, so when the energy is low as in the method of this invention, it can be seen that no lattice defects will occur due to this.

Next, as is the case with general plasma processes, there is the problem of precious metal contamination from vessel walls, electrodes, etc. In particular, in doping methods using plasma such as the method of this invention, Fe, Ni, etc., which form deep impurity levels, diffuse through an interstitial mechanism, so the diffusion coefficient is significantly larger than that of boron, etc., and is a problem that cannot be ignored. be.

For example, when using SUS (stainless steel) electrodes, the substrate contains Fe, Cr, and Ni of 0.35ev~
A tape level level of 0.55ev is seen and the lifetime is also reduced.

This phenomenon is also seen in the case of SUS anodes and substrate cathodes, but the metal splash effect on the SUS cathode is particularly effective when the polarity is reversed.

Therefore, in the embodiment of the present invention, this problem is solved by using a single crystal silicon electrode containing a high concentration of the same element as the element to be doped into the counter electrode 3 to prevent contamination.

It should be noted that the present invention is not limited to the above-described embodiments, and may have different configurations without changing the gist.

〔Effect of the invention〕

As described above, according to the present invention, it is easy to create a shallow region of impurities, it can be done in a relatively short time, and it does not require high-temperature heat treatment, making it suitable for mass production. method can be provided.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an embodiment of the present invention;
FIG. 2 is a curve diagram showing the characteristics of the spreading resistance of the diffusion layer with respect to the depth from the surface in the same example, and FIG. 3 is a waveform diagram showing the voltage applied between the stage and the counter electrode in the same example. . 1... Plasma generator, 2... Stage, 3
...Counter electrode, 4...Heater, 5...N-type single crystal substrate, 6...DC power supply, 7...Polarity changer.

Claims (1)

[Claims] 1. A semiconductor substrate is placed on a stage that forms one electrode of a plasma generator, and a silicon electrode containing an element to be doped is provided as a counter electrode, and a direct current voltage with the stage side being negative is applied between the stage and the counter electrode. A substrate for a semiconductor, characterized in that the DC voltage is applied for a predetermined period of time to cause plasma discharge, and then the polarity of the DC voltage is reversed to implant generated dope element ions into the substrate for a second predetermined period of time. impurity doping method for.