JPH0349217A - Plasma doping device for semiconductor substrate - Google Patents

Abstract

PURPOSE:To activate impurity in a substrate surface layer introduced through plasma doping by forming one of electrodes, facing each other, of a thin resistance wire for generating light when current is fed to heat it and irradiating a semiconductor substrate placed on the other electrode. CONSTITUTION:A sealed container 1 is evacuated through an evaculating system 4 and then a vacuum valve 8 is closed to lower the evacuating speed, and at the same time, atmospheric gas is introduced into the sealed container 1 through a control circuit 6 and voltage is applied across the electrodes 2B and 2C to generate glow discharge therebetween so that a semiconductor region containing that impurity is formed on a semiconductor substrate 3 disposed on the electrode 2B. Then, the container 1 is evacuated again, and then the electrode 2C is heated by feeding current to a wire 7C for heating the thin resistance wire thus generating infrared rays. The generated infrared rays irradiate the surface of the substrate 3 uniformly to raise the surface temperature of the substrate 3. As a result, impurity atoms introduced before enter into the lattice positions of the semiconductor substrate from the interlattice positions to substitute for the substrate atoms thus increasing the concentration of the electrically activated impurity.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to an apparatus for introducing impurities into a semiconductor substrate,
Plasma doping that especially activates plasma-doped impurities! Regarding equipment.

[Conventional technology]

Thermal diffusion methods such as solid-phase diffusion and vapor-phase diffusion are known as methods for doping impurities into a semiconductor substrate to form a semiconductor region having an impurity concentration different from that of the substrate.
Diffusion is performed at high temperatures of 0°C to 1200°C,
Therefore, the equipment is complicated and expensive, and its maintenance is troublesome. Further, in the thermal diffusion method, there is a problem in the in-plane uniformity of impurities in the semiconductor substrate, and furthermore, it is difficult to form a shallow diffusion layer of 1 pm or less. Furthermore, the above-mentioned high-temperature heat treatment causes problems such as lattice defects being formed in the semiconductor substrate and heavy metal elements being diffused into the substrate, reducing the lifetime of carriers. This problem can be solved by lowering the processing temperature in the diffusion step, but at temperatures below 800° C., the diffusion coefficient of the impurity element to be doped is reduced, resulting in low economic efficiency and poor reproducibility.

The ion implantation method can solve various problems associated with the non-uniformity of impurity concentration within the semiconductor wafer surface and high temperature processing, and has come to be widely used in the manufacturing process of semiconductor devices. Since impurities are implanted into the semiconductor with high energy, there is an inherent problem of damaging the semiconductor surface.Also, since the impurity has low electrical activity in its original state, it is difficult to damage the semiconductor surface. 800°C to 12°C to recover and activate impurities
There is a problem that high temperature heat treatment of 50° C. is required and high temperature heat treatment cannot be completely eliminated.

In order to solve the problems of the conventional impurity introduction method, the present inventors have previously developed
No. 2 discloses a method of introducing impurities by plasma doping. In this method, a doping gas containing impurity elements to be introduced into a semiconductor substrate is diluted with hydrogen to form a gas, which is turned into plasma by glow discharge.
This method uses this plasma to decompose the doping gas and introduce impurities onto the surface of the semiconductor substrate. This method is 2
Since impurities can be introduced even at temperatures as low as 00° C., oxide film contamination, junction depth fluctuations, and lattice defects due to high heat do not occur in Brehner elements and MO8ICs. Furthermore, a plasma doping apparatus having an extremely simple structure can be used. Since the effort required to introduce the impurities is small, lattice defects on the surface of the semiconductor substrate are also less likely to occur. This plasma doping method differs from the ion implantation method in that the concentration of impurities doped at the surface of the semiconductor substrate is high (approximately 1022 atoms/d), and the concentration shows a profile in which the concentration decreases rapidly in the depth direction, and the concentration distribution is also approximately 0.
．． Extremely shallow at 2pm. Therefore, it can be effectively used for forming shallow junctions and shallow ohmic contact layers.

Furthermore, the applicant has previously proposed in Meikan Sho 63-18341 an apparatus for activating impurities introduced into a semiconductor substrate using this plasma doping method. Figure 4 shows the configuration of the device. This device includes a sealed container 1, two mesh electrodes serving as counter electrodes 2 and a flat electrode 2B, a semiconductor substrate 3, and a vacuum exhaust system 4. Feed gas diluted with doping gas 5. Adjustment circuit for adjusting gas pressure and flow rate 6. DC power source 7A for glow discharge, power source 7B for semiconductor heating, vacuum valve 8 for adjusting gas pressure during glow discharge. Vacuum gauge9. and multiple rod-shaped infrared lamps with tungsten filaments sealed in quartz glass tubes 10. Power supply for the lamp 11. It is composed of a reflecting plate 12 that reflects infrared rays generated from the lamp.

According to this installation, l! is applied to the flat electrode 2B by plasma doping. l! After introducing a predetermined impurity into the semiconductor substrate 3, only the surface of the semiconductor substrate 3 is heated in a short time by irradiating infrared rays from an infrared lamp IO through the mesh of the two mesh electrodes, Impurities can be made electrically active.

[aM that the invention attempts to solve]

However, in the method of introducing impurities by plasma doping disclosed in the above-mentioned publication, although the total concentration of introduced impurities is certainly high, the concentration of electrically active impurities is about 10'6 atoms/- Therefore, there is a problem that sufficient semiconductor characteristics cannot be obtained. For this purpose, as disclosed in Japanese Patent Application Laid-open No. 59-218728, the present inventors doped certain impurities into a semiconductor substrate using a C plasma doping method, and then activated the introduced impurities using argon plasma. The aim is to improve the However, this method requires a long time to introduce impurities because the entire process consists of two steps, resulting in a problem that it cannot be said to be an efficient method.

In the case of the configuration shown in FIG. 4 proposed in Sumita, Shogan No. 18341/1986, doping impurities also adhere to the bulb surface of the infrared lamp, which is the light source for heating the semiconductor substrate.
The light intensity of the light source decreases. Therefore, every time plasma doping is performed several times, it becomes necessary to remove and clean the bulb of the light source, resulting in a problem that maintenance of the apparatus becomes complicated.

The present invention has been made in view of the above-mentioned points, and its purpose is to heat shallow parts of the surface of the semiconductor substrate (areas with high concentration of electrically active impurities) by simply heating the impurity-introduced surface layer of the semiconductor substrate for a short period of time. It is an object of the present invention to provide a plasma doping apparatus for semiconductor substrates that can form FCL and facilitate maintenance of FCLL.

Means for Solving the CI'l1 Problem] In order to achieve the above objects, the present invention provides a counter electrode in a sealed container, and fills the sealed container with a fume gas diluted with a doping gas. , in a plasma doping apparatus for a semiconductor substrate in which a predetermined voltage is applied to the counter electrode to generate plasma in the air gas, one of the counter electrodes is electrically heated to generate light and dazzle to the other. It shall be formed by a resistive thin wire that irradiates the semiconductor substrate placed on the electrode. Note that it is desirable to provide a reflective plate for reflecting light on the opposite side of the semiconductor substrate to the counter electrode formed of the resistive thin wire.

As the doping gas containing an impurity element, an inorganic gas such as phosphine (PH3)-arsine (AsHs)'IF, or an organometallic compound gas containing a large number of impurity elements is used. The doping gas is diluted using helium gas, argon gas, hydrogen gas, nitrogen gas, or the like. The airtight container is filled with the air gas at a pressure of several Torr. When, for example, a DC voltage is applied between the opposing sleeping poles, the above-mentioned feces are turned into plasma by glow discharge.

This plasma decomposes the doping gas, and impurity atoms generated by the decomposition diffuse into the interior of the substrate. As the semiconductor substrate, crystalline or amorphous silicon, germanium, etc. are used. Heating the substrate surface layer into which impurities have been introduced is
This is carried out by irradiation with light generated by heating the resistive thin wire 9, for example, a thin tungsten wire, which forms one of the opposing electrodes.

[Effect]

Light irradiation by the resistive thin wire electrode takes place for a short period of time.

Since it is originally absorbed in the semiconductor substrate, the root strength near the surface layer is strong, and therefore, the surface layer is heated to the highest temperature by light irradiation. Due to this temperature rise in the surface layer, impurities introduced into the surface layer, in the case of a single crystal, are substituted from interstitial positions to atomic positions of the substrate and activated. Further, since the activation occurs in a short time, light irradiation can be performed for a short time, and crystal defects caused by temperature rise can be prevented. In addition, light irradiation is performed from one counter electrode itself formed of a thin resistance wire, and even if impurities are layered on the thin resistance wire, these impurities are removed during discharge, so it is similar to when using an infrared lamp. There will be no shortage of light due to contamination of the tube surface.

〔Example〕

Next, embodiments of the present invention will be described based on the drawings.

FIG. 1 shows the configuration of an apparatus used in Example 1 of the present invention, and the same members as in FIG.

One of the opposing electrodes serves as a resistive thin wire electrode 2C formed of a resistive thin wire. This resistance thin wire electrode 2C
IJL 7111 is a power supply for heating thin resistance wires 7C4
It is heated and emits infrared radiation. 12A is a reflective plate,
Among the infrared rays generated from the resistive thin wire electrode 2C, the infrared rays irradiated toward the side opposite to the semiconductor substrate 3 are reflected toward the semiconductor substrate 3 side.

The specific procedure for introducing impurities into the semiconductor substrate 3 in the above configuration is as follows.

First, the inside of the closed container l is evacuated by the vacuum evacuation system 4, and about 1
After creating a vacuum of
When air gas is introduced through the adjustment circuit 6 and a voltage is applied between the electrodes 2B and 2C using a known method to generate a glow discharge, the semiconductor containing the impurities is transferred to the semiconductor substrate 3 placed on the electrode 2B. A region is formed. Next, the inside of the sealed container 1 is evacuated again to a vacuum of about 1×10 TOrr, and then the resistive thin wire electrode 2C is heated with electricity by the resistive thin wire heating power source 7C to generate infrared rays. The generated infrared rays are uniformly irradiated onto the surface of the semiconductor substrate 3, and the surface temperature of the substrate 3 is increased by the irradiated infrared rays. As a result, the previously introduced impurity atoms enter the semiconductor substrate from interstitial positions to lattice positions, replacing the base atoms, and the concentration of electrically activated impurity atoms increases.

FIG. 2 is a profile diagram showing the concentration distribution of boron when boron atoms are introduced into the silicon single crystal substrate 3. FIG. In this case, impurities were introduced with the following charge.

Semiconductor substrate: silicon single crystal, n-type, specific resistance approximately 100Ω
cm, @Surface finish Substrate temperature: 200℃ Air gas: Diborane diluted to 100 ppm with water Pressure crab during glow discharge 4 T□rr Discharge power: DC900V, 2 mA/cs (
Distance between electrodes: 501 m Discharge time: 60 seconds Infrared irradiation time: 20 seconds, 40 seconds In Fig. 2, curve 13 shows the boron concentration distribution before infrared irradiation, and the electrically activated boron concentration distribution at this time. A curve 141 is shown. Curve 15 is resistance thin wire electrode 2C
Curve 16 shows the electrically activated boron concentration distribution when the semiconductor substrate 3 is heated for 7JO and irradiated with infrared rays for m seconds. In this way, as the irradiation time of infrared rays increases, the temperature of the surface of the substrate 3 increases, so the concentration of electrically activated boron increases. In the above case, the total boron concentration distribution shown in curve 13 is calculated using secondary ion mass spectrometry (5 secondary ion mass spectrometry).
n Mass Spectrometry S I M
S). Also, electrically active impurity t
The tlJia degree was measured by the spreading resistance method. Roughly speaking, the maximum m of the surface of the substrate 3 when the time for heating the resistive thin wire electrode 2C with τ and irradiating the substrate 3 with infrared rays is 40 seconds.
The box has a thermocouple (0,211φ) that is 900°C and 100°C, respectively.

This was confirmed in an experiment using platinum-platinum rhodium.

FIG. 3 is a profile diagram showing the concentration distribution of phosphorus when phosphorus is introduced as an impurity into the NRICON single crystal substrate 3. In this case, impurities were introduced under the following conditions.

Semiconductor substrate: silicon single crystal, P type, resistivity iooΩ
cm, mirror finish Substrate temperature: 200°C Dopant impurity gas: Phosphate diluted to loooppm with water Pressure crab during glow discharge 4 Torr Discharge power: DC90 (l V * 2 mA/c
Distance between m electrodes 111i: 50m1m Discharge time: 60 seconds Infrared irradiation time: 20 seconds, 40 seconds In Figure 3, track 11117 is the phosphorus concentration distribution before infrared irradiation, and the electrically active phosphorus concentration distribution at this time is 918. Song @19 has infrared irradiation time (9
) Second 1 curve 21 is the concentration distribution of electrically active phosphorus when the infrared irradiation time is 1 second.

〔Effect of the invention〕

According to the present invention, a counter electrode is provided in a sealed container, the airtight container is filled with a doping gas diluted, and a predetermined voltage is applied to the counter electrode to fill the airtight gas. In a plasma doping apparatus for a semiconductor substrate that generates plasma, one electrode of the counter electrode is
The resistor wire was formed of a thin resistive wire that generates light by heating and energizing it and irradiates the semiconductor substrate placed on the other electrode with the light.

Therefore, when this device is used, the heating effect due to light irradiation is on average smaller than ζ on the semiconductor substrate, and as a result, impurities in the surface layer of the substrate introduced by plasma doping can be electrically activated without causing crystal defects. be able to.

Furthermore, since activation of impurities is achieved by short-time light irradiation, the entire process of introducing impurities can be performed in a short time. Furthermore, since the process of impurity activation by light irradiation is achieved in a short time, the impurity region in the surface layer of the semiconductor substrate does not spread due to diffusion, so the impurity region obtained by plasma doping can be maintained as desired. The advantage of plasma doping, which allows impurities to be introduced into extremely shallow regions, can be utilized as is. Since the light irradiation is performed using the electrode eye made of a thin resistive wire as the light emitter, there is no problem of insufficient light intensity due to contamination of the lamp bulb surface, unlike when using an infrared lamp. Therefore, it is possible to activate impurities with good reproducibility, and it is also possible to improve maintainability.

Therefore, if the present invention is applicable to a radiation detection device, pn
Not only can a region such as a bonding layer that is insensitive to radiation be made thinner, but it can also be effectively used in forming a diffusion layer of MO8IC devices, three-dimensional devices, and the like.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a plasma doping apparatus according to an embodiment of the present invention, FIG. 2 is a profile diagram showing the boron concentration distribution according to an embodiment of the present invention, and FIG. 3 is an embodiment of the present invention. A profile diagram showing the concentration distribution of phosphorus related to
FIG. 4 is a block diagram of a device previously filed by the present applicant. l...Airtight container, 2.20...Counter electrode, 2A...
-Mesh electrode, 2B... Flat electrode, 2C... Resistance thin wire electrode, 3... Semiconductor substrate, 4... Vacuum exhaust system,
5... Air gas, 6... Gas pressure, gas flow rate adjustment circuit, 7A... DC power source for glow discharge, 7B... Power source for base heating, 7C... Power source for heating thin resistance wire, 8...
・Vacuum valve, 9...Vacuum gauge, 10...Infrared lamp, 11...Electric cable for lamp 4. Unexpected rain, threat of rejection of expenses (included) Figure 3

Claims (1)

[Claims] 1) A semiconductor that includes a counter electrode in a sealed container, fills the container with a doping gas diluted air gas, and applies a predetermined voltage to the counter electrode to generate plasma in the air gas. In the plasma doping apparatus for a substrate, one of the opposing electrodes is formed of a resistive thin wire that generates light by heating with electricity and irradiates the semiconductor substrate placed on the other electrode with the light. Plasma doping equipment for semiconductor substrates.