JPH0982661A - Manufacture of semiconductor device and ion doping system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit a temperature rise of an insulating substrate, which is generated during an ion doping, to improve the characteristics of a semiconductor thin film. SOLUTION: In order to manufacture a semiconductor device, a film-forming process for forming a semiconductor thin film 6 on an insulating substrate 7 is first performed. Then, an implantation process for doping selectively impurities to the thin film 6 is performed. After this, a processing process for forming by lamination a thin film transistor using the thin film 6 as its element region is performed. The implantation process is performed using an ion-doping system, a chamber 1 provided with cathode and anode electrodes 2 and 3 opposing to each other is first prepared and the substrate 7 is placed on the electrode 2. Then, gas containing impurities is introduced in the chamber 1 and high-frequency power is applied between the electrodes 2 and 3 to put the gas in the state of plasma 8. Impurity ions being contained in the plasma 8 are emitted to the film 6 by a self bias. At this time, the electrode 2 is cooled by a cooling mechanism 5 to inhibit a temperature rise of the substrate 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device in which thin film transistors and the like are integrated. Further, the present invention relates to an ion doping apparatus for implanting impurities into a semiconductor thin film which will be an element region of a thin film transistor.

[0002]

2. Description of the Related Art A semiconductor device in which a thin film transistor and a pixel electrode are integrated and formed on a transparent insulating substrate is suitable for a drive substrate of an active matrix type display device and has been actively developed in recent years. The thin film transistor has a semiconductor thin film made of amorphous silicon, polycrystalline silicon or the like as an element region, and a source region and a drain region are provided by implanting impurities at a high concentration on both sides of a channel portion aligned with a gate electrode. By the way, in a general IC manufacturing process using a silicon wafer as a substrate, impurities are selectively implanted into a semiconductor by using an ion implantation apparatus. This ion implantation apparatus is one in which impurity ions are accelerated by an electric field, mass separation is performed, and only a target species is injected, and it is characterized by high accuracy. However, when impurities are implanted into a large-area semiconductor device, throughput is poor and mass productivity is poor. For example, it cannot be applied to manufacture of a drive substrate used for an active matrix type display device having a large screen of 30 cm or more. Therefore, an ion doping apparatus is used instead of the ion implantation apparatus, and impurities are implanted into a large-area semiconductor thin film by collective irradiation. This ion doping apparatus is provided with parallel plate type electrodes in a chamber, generates plasma of a source gas, ionizes contained impurities, and irradiates a semiconductor thin film made of polycrystalline silicon or the like by self bias. Since mass separation is not performed, ions other than the target species are also irradiated, but the ion shower can be applied over a large area, resulting in excellent throughput.

[0003]

FIG. 6 schematically shows an impurity implantation process using an ion doping apparatus. A semiconductor thin film 102 made of polycrystalline silicon or the like is formed on the insulating substrate 101. A resist 103 is patterned on it. This insulating substrate 101 is put into a chamber and exposed to plasma 104 to implant impurity ions into the semiconductor thin film 102.
However, in this ion doping method, since the insulating substrate 101 itself is exposed to the plasma body when the plasma 104 is generated, a large amount of heat is generated. Therefore, resist 1
A hardened layer 105 is formed on the surface of No. 03. Since resist hardening occurs, it becomes difficult to peel off the resist 103 in a later step. In the ion doping apparatus, impurities such as P +, B +, As + are irradiated. In particular, when a transparent insulating substrate having a relatively low thermal conductivity such as glass is irradiated with impurities, if a patterned resist is present on the transparent insulating substrate, the substrate temperature rises because of insufficient heat dissipation, causing hardening of the resist. Therefore,
There is a problem that the resist cannot be completely removed by the peeling process in the subsequent step.

Another problem to be solved will be briefly described with reference to FIG. This drawing shows an example in which the semiconductor thin film 102 formed on the surface of the insulating substrate 101 is ion-doped with the impurity P. In general, when an electric field is accelerated and impurities are injected, the semiconductor thin film 102 becomes amorphous. However, in the conventional method, the amorphization process becomes incomplete due to the thermal energy at the time of ion doping, and the silicon microcrystals 10
6 is generated inside the film. Therefore, there is a problem that the activation of the impurity P is not sufficiently performed in the subsequent process. When the impurity ions P + are implanted into the semiconductor thin film 102, kinetic energy is converted into thermal energy, and the impurity region is not completely amorphized. As shown in the figure, some microcrystals 106 remain along the flight path of the impurity ions. Thereafter, when the impurities are activated by laser annealing, thermal annealing, or the like, the movement of impurities in the semiconductor thin film 102 is obstructed by the microcrystals 106, and the activation rate decreases.
Eventually, the resistance of the semiconductor thin film 102 cannot be lowered sufficiently or the resistance value varies.

Still another problem to be solved will be described with reference to FIG. As mentioned above, ion doping exposes a semiconductor thin film to a plasma. Therefore, plasma damage occurs and the characteristics of the thin film transistor deteriorate. In particular, the threshold voltage Vth shifts due to the increase of the interface state. The ion doping apparatus puts an insulating substrate in plasma and injects impurities into the semiconductor thin film therein. However, mass separation is not performed, and various ion species are irradiated, and the plasma generation region cannot be controlled. Therefore, the surface of the substrate is damaged by the irradiation of charged particles or active radicals other than the target species of impurities. Eventually, damage remains in the gate insulating film of the thin film transistor, and a transistor with a poor interface state is formed. Therefore, its characteristics become unstable. For example, as shown in the graph of FIG. 8, the threshold voltage Vth of the thin film transistor shifts to the depletion side.

[0006]

The following means have been taken in order to solve the above-mentioned problems of the prior art. That is, according to the present invention, the semiconductor device is manufactured by the following steps. Basically, a film forming step of forming a semiconductor thin film on an insulating substrate, an implanting step of selectively doping the semiconductor thin film with impurities, and a processing step of forming a thin film transistor by using the semiconductor thin film as an element region are integrated. To do. The injecting step includes a step of preparing a chamber having a cathode electrode and an anode electrode facing each other, placing the insulating substrate on the cathode electrode, and introducing a gas containing impurities into the chamber to introduce the cathode electrode and the anode. A step of applying high frequency power between the electrodes to plasmaize the gas to ionize the impurities and irradiate the semiconductor thin film is included. At this time, the injecting step includes a step of cooling the cathode electrode during irradiation to suppress a temperature rise of the insulating substrate.

The present invention also includes an ion doping apparatus suitable for the semiconductor device manufacturing method described above. This ion doping apparatus has a chamber, as a basic configuration,
A pair of cathode and anode electrodes, a high frequency power supply, and a cooling mechanism are provided. The chamber can introduce a gas containing impurities therein. The pair of cathode electrodes and anode electrodes are formed of parallel flat plates facing each other and are housed in the chamber, and the cathode electrodes can mount an insulating substrate on which a semiconductor thin film is previously formed. The high frequency power source applies high frequency power between the cathode electrode and the anode electrode to plasmaize the gas introduced into the chamber and ionize impurities to dope the semiconductor thin film. The cooling mechanism is incorporated inside the cathode electrode and cools the cathode electrode during doping to suppress the temperature rise of the insulating substrate. Preferably, the cooling mechanism uses water or liquid nitrogen as the refrigerant. Preferably, an additional electrode is provided between the cathode electrode and the anode electrode to remove at least part of charged particles other than impurity ions contained in plasma.

In the present invention, a coolant such as water or liquid nitrogen is circulated in the cathode electrode during ion doping so that heat generated in the substrate is taken out from the cathode electrode. Since this cooling is continuously performed during the ion doping, heat storage in the insulating substrate can be prevented.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic sectional view showing the structure of an ion doping apparatus according to the present invention. The ion doping apparatus includes a chamber 1, a pair of a cathode electrode 2 and an anode electrode 3, a high frequency power source 4,
The cooling mechanism 5 is provided. Chamber 1 can introduce the gas (PH _3, B ₂ H ₆ or the like) containing an impurity therein. The pair of cathode electrodes 2 and the anode electrodes 3 are parallel flat plates facing each other and are housed in the chamber 1. The cathode electrode 2 is grounded, while the anode electrode 3 is connected to one end of a high frequency power supply 4. The other end of the high frequency power source 4 is grounded. An insulating substrate 7 having a semiconductor thin film 6 formed thereon can be placed on the cathode electrode 2. The high frequency power supply 4 applies high frequency power between the cathode electrode 2 and the anode electrode 3 to turn the gas introduced into the chamber into a plasma 8. The impurities contained in the plasma 8 are ionized and the semiconductor thin film 6 is doped. As a characteristic feature, the cooling mechanism 5 is incorporated inside the cathode electrode 2, and cools the cathode electrode 2 during doping to suppress the temperature rise of the insulating substrate 7. The cooling mechanism 5 is composed of a cooling pipe embedded in the cathode electrode 2 and can circulate a coolant composed of water or liquid nitrogen. Insulating substrate 7
The cathode electrode 2 on which is mounted is cooled with water or liquid nitrogen to forcibly remove the heat accumulated in the insulating substrate 7. Refrigerant is introduced into and discharged from the cooling pipe embedded in the cathode electrode 2, so that the insulating substrate 7 causes the cathode electrode 2 to discharge.
Absorbs the heat conducted to. Thereby, heat storage of the insulating substrate 7 can be suppressed.

A semiconductor device manufacturing method according to the present invention will be described in detail with reference to FIG. In the present semiconductor device manufacturing method, first, a film forming step is performed to form the semiconductor thin film 6 made of polycrystalline silicon or amorphous silicon on the insulating substrate 7. Next, an implantation process is performed to perform patterned resist 9
Impurities are selectively doped into the semiconductor thin film 6 via the above. A post-processing step is then performed to form a thin film transistor by using the semiconductor thin film 6 as an element region. In the semiconductor device manufacturing method according to the present invention, the implantation step is performed using the ion doping apparatus shown in FIG. First, a chamber having a cathode electrode and an anode electrode facing each other is prepared, and the insulating substrate 7 is placed on the cathode electrode 2. Next, a gas containing impurities is introduced into the chamber, and high-frequency power is applied between the cathode electrode 2 and the anode electrode to plasmaize the gas and ionize the impurities to form the semiconductor thin film 6.
Irradiation. During irradiation, the cathode electrode 2 is cooled to suppress the temperature rise of the insulating substrate 7. As shown, the resist 9 and the semiconductor thin film 6 are exposed to plasma during ion doping.
The heat 10 generated in the above is conducted to the cathode electrode 2 and then absorbed by the refrigerant and removed. In this way, the temperature rise of the insulating substrate 7 is suppressed and the microcrystallization of the semiconductor thin film 6 at the time of ion doping is prevented. That is, when the insulating substrate 7 is cooled, even if the kinetic energy of the implanted impurities is converted into thermal energy, the semiconductor thin film 6 is not easily crystallized along the flight path thereof. Therefore, the region of the semiconductor thin film 6 that has received the impurity irradiation is in a substantially completely uniform amorphous state. When impurities are activated by thermal annealing, laser annealing, or the like in a later step, the impurities can easily move in the semiconductor thin film 6 and the bonding with silicon can be promoted. Also, since the temperature rise of the resist 9 can be prevented,
Curing does not occur and can be easily peeled off in a later process.

FIG. 3 is a schematic perspective view showing another embodiment of the ion doping apparatus according to the present invention. The basic structure is similar to that of the ion doping apparatus shown in FIG. 1, and corresponding parts are designated by corresponding reference numerals to facilitate understanding. The different point is that an additional ring electrode 11 is interposed between the cathode electrode 2 having a built-in cooling mechanism and the counter anode electrode 3. This ring electrode 11
Can remove at least part of the charged particles other than the impurity ions contained in the plasma 8. The ring electrode 11 is made of a metal plate formed in an annular shape, and is set so that a potential different from that of the anode electrode 3 and the cathode electrode 2 can be applied via the bias power source 12. By adjusting this potential, the generation region of the plasma 8 is adjusted so that extra damage and heat energy are not applied to the insulating substrate 7. The ring electrode 11 traps or removes charged particles such as electrons and confine it inside to adjust the generation region of the plasma 8. By controlling the generation region of the plasma 8, it is possible to suppress bombardment due to unnecessary active radicals and electrons contained in the plasma 8 and prevent the insulating substrate 7 from being damaged.

FIG. 4 is a schematic partial sectional view showing an example of a semiconductor device manufactured according to the present invention. This semiconductor device is manufactured for a drive substrate of a large-sized active matrix display device. As shown in the figure, a gate electrode 52 made of Mo / Ta or the like is patterned on a transparent insulating substrate 51 made of glass or the like. The surface of the gate electrode 52 is covered with an anodic oxide film 53 made of TaO _x or the like. The gate electrode 52 is the gate insulating film 5
It is covered by 4. The gate insulating film 54 is, for example, P
Has become the formed P-SiO ₂ / P-SiN having a two-layer structure in -CVD method. A semiconductor thin film 55 made of polycrystalline silicon or amorphous silicon is formed on the gate insulating film 54. This semiconductor thin film 55 is patterned in an island shape and becomes an element region of the bottom gate type thin film transistor 56. On the semiconductor thin film 55, a channel stopper 57 made of P-SiO ₂ or the like is patterned and formed in alignment with the gate electrode 56. Using the ion stopper shown in FIG. 1 or FIG. 3 with the channel stopper 57 as a mask, the semiconductor thin film 5 with high concentration of impurities is formed.
Then, a source region S and a drain region D are formed. The bottom gate type thin film transistor 56 having such a configuration is covered with a first interlayer insulating film 58 made of PSG or the like. A wiring electrode 59 made of Mo or Al is pattern-formed thereon, and is connected to the source region S and the drain region D of the thin film transistor 56 through a contact hole opened in the first interlayer insulating film 58. The wiring electrode 59 is covered with a second interlayer insulating film 60 also made of PSG or the like. On top of that, Ti
A metal light-shielding film 61 made of, for example, is patterned. The metal light shielding film 61 is covered with a third interlayer insulating film 62 made of SiO ₂ or the like. A pixel electrode 63 made of ITO or the like is patterned thereon. The pixel electrode 63 is electrically connected to the drain region D of the thin film transistor 56 via the metal light shielding film 61 and the wiring electrode 59.

FIG. 5 is a schematic partial cross-sectional view showing another example of a semiconductor device manufactured according to the present invention. Basically, the semiconductor device has a structure similar to that of the semiconductor device shown in FIG. 4, and corresponding parts are designated by corresponding reference numerals to facilitate understanding. The difference is that the second interlayer insulating film 60 is omitted and the metal light shielding film 61 and the wiring electrode 59 are in direct contact with each other. On the drain region D side, the metal light-shielding film 61 is interposed between the pixel electrode 63 and the wiring electrode 59, and also functions as a barrier layer that makes good electrical contact between both electrodes.

[0014]

As described above, according to the present invention, the temperature rise of the insulating substrate is suppressed by forcibly cooling the cathode electrode during the impurity implantation process using the ion doping apparatus. As a result, the resist patterned on the surface of the insulating substrate is not cured, and the resist can be easily removed in a later step. Moreover, since the insulating substrate is forcibly cooled, the growth of fine crystals due to the implantation of impurity ions in the semiconductor thin film does not occur, and the efficiency is improved when activating the impurities in the subsequent process, which in turn results in the semiconductor. The resistance of the impurity regions of the thin film is reduced. Also, by adjusting the plasma region by interposing an additional electrode between the anode electrode and the cathode electrode, plasma damage to the thin film transistor can be eliminated, and stable transistor characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic block diagram showing a structure of an ion doping apparatus according to the present invention.

FIG. 2 is a schematic view showing a semiconductor device manufacturing method according to the present invention.

FIG. 3 is a schematic perspective view showing another embodiment of the ion doping apparatus according to the present invention.

FIG. 4 is a schematic partial cross-sectional view showing an example of a semiconductor device manufactured according to the present invention.

FIG. 5 is a schematic partial cross-sectional view showing another example of a semiconductor device manufactured according to the present invention.

FIG. 6 is a schematic view showing a problem of the conventional technique.

FIG. 7 is a schematic diagram showing a problem of the conventional technique.

FIG. 8 is a graph showing a problem of the conventional technique.

[Explanation of symbols]

 1 Chamber 2 Cathode Electrode 3 Anode Electrode 4 High Frequency Power Supply 5 Cooling Mechanism 6 Semiconductor Thin Film 7 Insulating Substrate 8 Plasma 9 Resist 10 Heat 11 Ring Electrode 12 Bias Power Supply

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H01L 21/336 H01L 29/78 616L H05H 1/46

Claims (4)

[Claims] 1. A film forming step of forming a semiconductor thin film on an insulating substrate, an implanting step of selectively doping the semiconductor thin film with impurities, and a processing step of integrally forming a thin film transistor using the semiconductor thin film as an element region. A method of manufacturing a semiconductor device, comprising: a step of preparing a chamber having a cathode electrode and an anode electrode facing each other, placing the insulating substrate on the cathode electrode, and a gas containing impurities. Is introduced into the chamber, high-frequency power is applied between the cathode electrode and the anode electrode to plasmaize the gas, ionize impurities to irradiate the semiconductor thin film, and the cathode electrode is cooled during irradiation to insulate the substrate. A method of manufacturing a semiconductor device, comprising: 2. An ion doping apparatus comprising a chamber, a pair of a cathode electrode and an anode electrode, a high frequency power source, and a cooling mechanism, wherein the chamber can introduce a gas containing impurities therein. The pair of cathode electrodes and anode electrodes are formed of parallel flat plates facing each other and are housed in the chamber, and the cathode electrodes can mount an insulating substrate on which a semiconductor thin film is formed in advance. High frequency power is applied between the cathode electrode and the anode electrode to plasmaize the gas introduced into the chamber to ionize impurities to dope the semiconductor thin film, and the cooling mechanism is incorporated inside the cathode electrode. An ion doping apparatus characterized in that a cathode electrode is cooled during doping to suppress a temperature rise of the insulating substrate. 3. The ion doping apparatus according to claim 2, wherein the cooling mechanism uses water or liquid nitrogen as a refrigerant. 4. An additional electrode interposed between the cathode electrode and the anode electrode to remove at least a part of charged particles other than impurity ions contained in plasma. Ion doping equipment.