JP2703029B2 - Method of introducing impurities into substrate - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a method for introducing impurities into a substrate, which is particularly suitable for obtaining good electrical characteristics of a device.

[Conventional technology]

In recent years, as a switching element for flat displays,
A polycrystalline silicon thin film transistor integrated with a display element has been used, and studies to increase the size of the element have begun.

In a process of forming a polycrystalline thin film transistor, introduction of impurities for forming a source and a drain has become an important technique. In order to increase the speed of the device, it is necessary to form a thin semiconductor region.

As a method for introducing impurities, a thermal diffusion method and an ion implantation method are well known, but the former requires a high temperature of about 800 ° C. or higher, and the latter uses high-energy ions.
It is very difficult to form an extremely thin semiconductor region, the equipment is expensive, and a large area implantation requires a long time.

Conventionally, as a method for solving some of these problems, Japanese Patent Application Laid-Open No. Sho 59-218727 describes a method in which a semiconductor substrate is placed in an atmosphere containing predetermined impurities and glow discharge is performed to introduce the impurities. Have been. Although this method can form an extremely thin semiconductor region and can introduce impurities into a large area, high-speed processing is not sufficiently considered and is not always economical.

Further, there are other methods, such as IEICE Transactions C and Vo.
L.J70-C, No.11, pp1473-1478 (November 1987), extracts impurity ions from plasma (ionized gas) containing impurity ions generated by high-frequency glow discharge and irradiates them to the substrate. A method is described. According to this method, an extremely thin semiconductor region can be formed and impurities can be introduced at high speed, but sufficient consideration has not been given to the introduction of impurities having a large area.

[Problems to be solved by the invention]

The above prior art does not consider a technique that satisfies both high-speed processing and large-area processing that enable economical element formation, and has a problem that productivity is not sufficiently improved by any of the methods. .

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for introducing impurities into a substrate capable of processing a large area at a high speed in order to economically form a high-performance device.

[Means for solving the problem]

The above object is to evacuate the processing chamber and the adjacent discharge chamber while keeping the airtight, and supply electrons of about several tens to one hundred and several tens electron volts to the discharge chamber while spatially generating electrons by a magnetic field or an electric field. Gas containing impurities in the discharge chamber,
In addition, plasma is generated by introducing a dilution gas, and the plasma is irradiated with an ion beam containing impurity ions from the plasma on a substrate fixed to a cooled substrate holder.

[Action]

In the discharge chamber evacuated to a vacuum, the electrons uniformly held spatially collide with the gas containing the introduced impurities and the dilution gas, and ionize the gas with a certain probability. The probability depends on the pressure and type of the gas to be collided, the energy of the colliding electrons, etc., but the electrons are held almost uniformly spatially by a magnetic field or an electric field. The impurity ions are substantially uniform spatially. Therefore, the ions of the impurities drawn into the processing chamber therefrom are applied to the substrate almost uniformly, and the impurities are introduced into the substrate at a substantially uniform concentration. The substrate is cooled and does not exceed the maximum temperature allowed in the device manufacturing process.

〔Example〕

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

FIG. 1 is a schematic diagram of an apparatus for carrying out the present invention. The apparatus comprises a processing chamber 8 which is kept airtight with the discharge chamber 1 and is connected via an insulator 2, and is connected to an exhaust device (not shown) via an exhaust pipe 15. Permanent magnets 3 are arranged around the discharge chamber 1 so that the magnetic poles of adjacent magnetic poles are reversed, and a gas supply pipe 5, an electron supply device 4 insulated by an insulator 2, a porous (multiple) A (perforated) ion extraction electrode 7 is mounted. A substrate holder 12 cooled by a water cooling mechanism 13, a substrate 11 attached thereto, and a heater 14 for heating the substrate are placed in the processing chamber 8, and an electron generator 9 is arranged in the processing chamber 8. I have. In addition, DC power supplies 17, 18, and 19 for applying a potential to each section are connected as shown in the figure. The electron supply device 4 shown in FIG. 2A was used. The apparatus comprises a parallel-plate high-frequency discharge electrode 31 placed in a cylindrical container at least partially closed at the top and bottom, and a porous electron extraction electrode 32 attached to almost the center of the lower high-frequency discharge electrode 31. Is provided with a gas supply pipe 35. The matching box 33 and the high-frequency power supply 34 are connected.

The discharge chamber 1 and the processing chamber 8 are evacuated to about 1 × 10 ^-6 To
Apply rr vacuum. When a voltage of V ₁ = 50 V is applied to the DC power supply 17, electrons 6 of about 60 electron volts are supplied from the electron supply device 4. The electrons 6 travel toward the side wall of the discharge chamber, but most of them are repelled by the multipole magnetic field created by the permanent magnetic field 3 and are kept at a substantially uniform density at a central portion about 40 mm away from the side wall. Diluted with helium (He) from gas supply pipe 5
0.5% Phosphine (PH ₃ ) is applied to the processing chamber 8 at about 1 × 10 ^-4
It is introduced into the discharge chamber 1 so that the pressure becomes Torr. High-speed electrons 6 collide with these gas molecules and are ionized, thereby generating a plasma containing ions such as helium and phosphorus. By applying V ₂ = 3 KV to the DC power supply 18 and V ₃ = −500 V to the DC power supply 19, the ion extraction electrode 7 (drawing diameter: 350
mm), the ion beam 16
Can be pulled out. The extracted ion beam is applied to a polycrystalline silicon substrate 11 of 200 mm square. At this time, the substrate 11
The substrate holder 12 is water-cooled to prevent overheating and
By operating the power supply 10, the substrate is removed from the electron supply 9.
Supply electrons to 11. The irradiation time is 10 minutes. In addition,
Regarding the operation of the electron supply device 4, helium gas is introduced from the gas supply pipe 35, and high frequency glow discharge is performed by applying 13.56 MHz, 200 W high frequency power from the high frequency power supply 34 to the upper high frequency electrode 31. , Producing a helium plasma. The generated plasma moves into the electron extraction electrode 32 by diffusion and supplies necessary electrons to the discharge chamber.

In order to realize uniform introduction of impurities into the substrate, it is necessary to irradiate the substrate with impurity ions. Fig. 3 (a)
Is to examine the density distribution of all ions and phosphorus ions to be irradiated at the substrate position before introducing phosphorus into an actual substrate. All ions were measured with a Faradec cup, and phosphorus ions were values estimated from the signal intensity of the spectrum of the quadrupole mass spectrometer. The density of the irradiated phosphorus ions may be considered to be substantially uniform on the substrate. FIG. 3 (b) shows the phosphorus concentration distribution in the polycrystalline silicon substrate after the introduction of phosphorus ions (including neutralized ones). Secondary ion mass spectrometry was used for the measurement. Compared to conventional ion implantation methods, etc.
It can be seen that an extremely thin semiconductor region can be formed. The uniformity of phosphorus ion introduction on a 200 mm square substrate was evaluated by source / drain sheet resistance. As a result, the average sheet resistance was 2.6 × 10 ³ (Ω / □), and the variation in sheet resistance was ± 200 (Ω / □) (silicon film thickness: 600 mm, after heat treatment). You can see that.

According to this embodiment, since the entire substrate can be uniformly irradiated with the impurity ions, the variation in the sheet resistance obtained as a result of the impurity introduction is as small as about ± 8%.
It can be processed in a short time of / 6.

In this embodiment, an apparatus with a 350 mm ion beam extraction diameter is used to process a 200 mm square substrate. However, if the substrate to be processed is further enlarged, the ion beam extraction diameter, and the discharge chamber It is necessary to increase the diameter of 1. At this time, by devising the number and arrangement of the permanent magnets generating the multi-pole magnetic field and the capacity and number of the electron supply device 4, electrons can be uniformly held in the discharge chamber 1 and uniform impurities can be obtained over a large area. Ions can be extracted. If a multi-pole magnetic field is used, not only a circular or square ion beam but also a rectangular (longitudinal) ion beam can be generated in the ion extraction section, and an optimal process for the element forming process can be performed.

In the present embodiment, a method of extracting electrons from plasma generated by high-frequency glow discharge is used as the electron supply device 4, but there is also a method of using microwave discharge as shown in FIG. 2 (b). . In this device, a permanent magnet 3 is arranged so as to generate an axial magnetic field around a cylindrical container whose upper and lower parts are at least partially closed. The container is provided with a waveguide 37, a gas supply tube 35, and a porous electron extraction electrode 32 with a quartz window 36 for airtightness interposed therebetween. After evacuating the inside of the cylindrical container, helium gas was introduced and generated by a magnetron oscillation tube (not shown)
When a microwave of 2.45 GHz is introduced into the cylindrical container from the quartz window 36, helium plasma is generated by a microwave discharge with a magnetic field. From there, the electrons 6 can be extracted. In addition, a hollow cathode,
Alternatively, the use of thermal filaments can also be used in FIGS.
There is an effect similar to that obtained in the embodiment of FIG. However, in the case of heat filament, there is a problem that replacement of the filament is troublesome because the filament is consumed.

A second embodiment of the present invention will be described with reference to FIGS.

FIG. 4 is a system diagram of a second embodiment of the present invention. This apparatus comprises a discharge chamber 1 and a processing chamber 8, and the processing chamber 8 is the same as the embodiment of FIG. In the discharge chamber 1, a ring-shaped anode ring 40 is supported electrically insulated from the others. An electron supply device 4 is provided above the discharge chamber, and an ion extraction electrode 7 is provided below the discharge chamber. In the electron supply device 4, a high-frequency discharge electrode 31 and a porous high-frequency discharge electrode 38 are arranged to face each other in a cylindrical container whose upper part is closed. Below the porous high-frequency discharge electrode 38, an electron extraction electrode 39, a reflection electrode
42 are arranged so that the positions of the small holes are aligned. High frequency power supply 34, matching box 33, DC power supply
18, 19, 41 and a voltage dividing resistor 45 are connected as shown in the figure.

The discharge chamber 1 and the processing chamber 8 including the electron supply device 4 are
A vacuum of about 1 × 10 ⁻⁶ Torr is created by an exhaust device. While introducing helium gas from the gas supply pipe 35,
From 13.56MHz, 300W high frequency power, high frequency discharge electrode
31 to generate glow discharge to generate helium plasma. By applying V ₄ = 150 V to the DC power supply 41, acceleration is performed between the high-frequency discharge electrode 38 and the electron extraction electrode 39 and deceleration is performed between the high-frequency discharge electrode 38 and the reflection electrode 42.
Has an energy of several electron volts, and the electrons 6 are accelerated downward due to the limit created by the anode ring 40. When passing through the anode ring 40, the speed is reduced conversely,
The electrons are reflected in front of the ion extraction electrode 7, and the electrons are directed upward, and further, are reflected by the reflective electrode 42 and directed downward. Electrons repeat such upward and downward reflexes. as a result,
Spatially, electrons are held almost uniformly. When a 0.5% phos fin diluted with helium is introduced from the gas supply pipe 5 so as to be about 1 × 10 ⁻⁴ Torr in the processing chamber 8, the high-speed electrons 6 collide with those gas molecules, and Is generated, a plasma containing ions of helium, phosphorus, and the like is generated. V ₂ = 3KV for DC power supply 18, V for DC power supply 19
By applying ₃ = 500 V, an ion beam can be extracted from the generated plasma by the ion extraction electrode 7 (extraction diameter: 350 mm). The extracted ion beam is 200m
Irradiation is performed on the substrate 11 of polycrystalline silicon having an m-square. On this occasion,
The substrate holder 12 is water-cooled, and supplies electrons to the substrate 11 from the electron supply device 9. The irradiation time is 10 minutes.

FIG. 5 shows the distribution of the density of all ions and phosphorus ions irradiated at the substrate position. The variation of the phosphorus ion density on the substrate is about ± 7%. The results of evaluating the source / drain sheet resistance after introducing phosphorus ions into a 200 mm square polycrystalline silicon substrate are as follows: Average sheet resistance: 2.8 × 10 ³ (Ω / □) Variation in sheet resistance: ± 450 (Ω / □) (Silicon film thickness 600 後, after heat treatment), and good phosphorus ion introduction is performed in a short time.

According to this embodiment, as in the embodiment using the apparatus shown in FIG. 1, impurities can be uniformly introduced into the entire substrate in a short time, and good electric characteristics can be obtained.

A third embodiment of the present invention will be described with reference to FIG.
FIG. 1 is a longitudinal sectional view of an apparatus for carrying out the present invention. This apparatus is obtained by removing the ion extraction electrode 7, the DC power supply 19, the electron supply device 9, and the power supply 10 from the apparatus shown in FIG.

The generation of plasma containing spatially uniform ions such as helium and phosphorus in the discharge chamber 1 by introducing a helium-diluted 0.5% phos fin from the gas supply pipe 5 is performed using the apparatus shown in FIG. Same as the example. V ₂ = DC voltage 18
Apply 350V. The generated plasma protrudes toward the substrate 11 in the processing chamber 8, and a potential gradient called an ion sheath is generated near the substrate 11. The ions in the plasma are accelerated by the potential gradient and are irradiated on the substrate 11. Since the density of the phosphorus ions in the generated plasma is spatially uniform, the density of the phosphorus ions applied to the substrate 11 is also relatively uniform. The processing time is 30 minutes. Source / drain after introducing phosphorus ions into 200mm square polycrystalline silicon substrate
As a result of evaluating the sheet resistance, the average of the sheet resistance is 4.2 × 10 ³ (Ω / □) and the variation of the sheet resistance is ± 900 (Ω / □).

The sheet resistance value in this embodiment is slightly higher than the values in the above-described two embodiments, and the variation is large. However, these properties are in a practically acceptable range. In this embodiment, since there is no ion extraction electrode, the electrode is spattered, and there is no contamination of the substrate 11 by the emitted particles. The method of the present embodiment is suitable for forming an element in which contamination by sputter particles is particularly problematic.

According to this embodiment, as in the embodiment using the apparatus shown in FIGS. 1 and 4, impurities can be uniformly introduced into the entire substrate.

In the embodiments described so far, fuos fin diluted with helium was used as the gas introduced into the discharge chamber.
Hydrogen may be used as a diluent gas instead of helium.
Although only the case of phosphorus as an impurity has been described, an impurity such as boron, antimony, arsenic, or potassium can be introduced into a substrate by using the present invention. The same effect can be obtained not only for polycrystalline silicon but also for single-crystal silicon and amorphous silicon. The present invention can be applied to the introduction of a different substance into another metal substrate.

〔The invention's effect〕

According to the present invention, the entire substrate can be irradiated with impurity ions (including neutralized ones) at a substantially uniform density.
As a result of introducing impurities into the 0 mm square polycrystalline silicon, a sufficiently low sheet resistance of the source / drain sheet resistance was obtained, and the processing time was significantly reduced. An economical element can be formed.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of one embodiment of the present invention, FIG. 2 is a longitudinal sectional view of an electron supply device, FIG. 3 is a graph for explaining the effect of the embodiment of FIG. 1, and FIG. FIG. 5 is a system diagram of a second embodiment of the present invention, FIG. 5 is a graph for explaining the effect of the embodiment of FIG. 4, and FIG. 6 is a system diagram of a third embodiment of the present invention. 1 ... discharge chamber, 2 ... insulator, 3 ... permanent magnet, 4 ...
Electron supply device, 5: gas supply pipe, 7: ion extraction electrode, 8: processing chamber, 11: substrate, 12: substrate holder, 17, 18, 19, 41 ... DC power supply, 34 ... High frequency power supply, 40
…… Anode ring, 42 …… Reflection electrode.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Akio Mimura 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (56) References JP-A-63-194326 (JP, A)

Claims (3)

(57) [Claims] A gas containing impurities to be introduced into a substrate and a diluent gas are used as an introduction gas, these gases are discharged and dissociated in a discharge chamber, and the gas is covered in a processing chamber provided in the discharge chamber in an airtight manner. When introducing impurities into the processing substrate, substantially uniformly spatially uniform electrons are held in the discharge chamber using an electrode system capable of repeatedly reflecting, and a gas containing the impurity and a diluent gas are supplied to the discharge chamber. A method for introducing impurities into a substrate, comprising: extracting charged particles containing the impurity ions from an ionized gas containing the impurity ions generated in the substrate; and irradiating the particles with the particles. 2. A gas containing impurities to be introduced into a substrate and a diluent gas are used as an introduction gas, these gases are discharged and dissociated in a discharge chamber, and the gas is removed in a processing chamber provided in the discharge chamber in an airtight manner. When introducing impurities into the processing substrate, high-frequency discharge, or extracting electrons from plasma generated by microwave discharge and supplying the electrons to the discharge chamber, while maintaining substantially spatially uniform electrons in the discharge chamber, Supplying the gas containing the impurity and the diluent gas, extracting the charged particles containing the impurity ions from the ionized gas containing the impurity ions generated therein, and irradiating the substrate with the charged particles. How to introduce impurities. 3. A gas containing impurities to be introduced into a substrate and a diluent gas are used as an introduction gas, these gases are discharged and dissociated in a discharge chamber, and the gas is covered in a processing chamber provided in the discharge chamber in an airtight manner. When introducing impurities into the processing substrate, the discharge chamber holds spatially substantially uniform electrons, supplies the gas containing the impurities and the diluent gas to the discharge chamber, and ionizes ions containing impurity ions generated therein. A method of introducing impurities into a substrate, comprising: extracting charged particles containing the impurity ions from a gas using an ion sheath generated between the ionized gas and the substrate; and irradiating the substrate with the ions.