JPH08340117A - Manufacture of thin film semiconductor device - Google Patents

Abstract

PURPOSE: To uniformly lightly dope a semiconductor thin film at a low tempera ture. CONSTITUTION: A material gas which is formed by mixing the dopant gas to a semiconductor film forming gas is used for chemical vapor deposition, and a non-single crystal semiconductor thin film 2, which serves as the active layer of a transistor, is deposited on an insulated board 1. The dopant contained in the semiconductor thin film 2 is activated by irradiation with energy beams 3 and the threshold voltage of the transistor is adjusted in advance. The transistor is formed by integration by processing the semiconductor thin film 2.

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 thin film semiconductor device in which thin film transistors are integrated and formed on an insulating substrate. More specifically, it relates to a method for manufacturing a thin film semiconductor device by a low temperature process (for example, the maximum process temperature is 600 ° C. or lower). More specifically, the present invention relates to a film forming technique of a semiconductor thin film which becomes an active layer of a thin film transistor and a low concentration doping technique of impurities. The thin film semiconductor device is used, for example, as an active element substrate (driving substrate) of an active matrix type liquid crystal display.

[0002]

2. Description of the Related Art Thin film transistors are widely used as switching elements in active matrix liquid crystal displays. In particular, polycrystalline silicon has been conventionally used for a semiconductor thin film that becomes an active layer of a thin film transistor. Polycrystalline silicon thin film transistor (poly-Si)
The TFT) can be used not only as a switching element but also as a circuit element, and a peripheral drive circuit can be incorporated together with the switching element on the same substrate. or,
Since the poly-Si TFT can be miniaturized, the area occupied by the switching element in the pixel structure can be reduced and a high aperture ratio of the pixel can be achieved. By the way, conventionally, poly-
Si TFT has a maximum process temperature of 1000 in the manufacturing process.
Quartz glass or the like, which has reached a temperature of about ℃ and has excellent heat resistance, has been used as an insulating substrate. It was difficult to use a glass substrate having a relatively low melting point in the manufacturing process. However, in order to reduce the cost of liquid crystal displays, it is essential to use a low melting point glass plate material. Therefore, in recent years, development of a so-called low temperature process in which the maximum process temperature is 600 ° C. or lower has been underway. Particularly, the low temperature process is extremely advantageous in terms of cost when manufacturing a large liquid crystal display. Along with the increase in size of liquid crystal displays, an ion doping method that can inject impurities into a large-area semiconductor thin film with high throughput is drawing attention in low-temperature process poly-Si TFTs. In this ion doping method, after ionizing an impurity gas, electric field acceleration is performed without mass separation, and large-area semiconductor thin films are collectively irradiated with impurity ions. On the other hand, the ion implantation is a method of irradiating a semiconductor thin film with an ion beam after performing mass separation of impurity ions.

[0003]

According to the ion doping method, impurities can be implanted into a semiconductor thin film in a short time with a high dose amount of about 10 ¹⁵ to 10 ¹⁶ / cm ² . However, it is theoretically difficult to control the dose amount of impurities with a precision of 10 ¹⁴ / cm ² or less. A high dose of impurities is used, for example, to form a source region / drain region of a thin film transistor, while a low dose is used to control a threshold voltage of a thin film transistor, for example. In order to adjust the threshold voltage, an attempt has been made to dilute the dopant gas and perform ion doping to control the dose amount to be low. However, even with this method, it is difficult to accurately control the dose amount of about 10 ¹² / cm ² required for controlling the threshold voltage of the poly-Si TFT. On the other hand, in conventional ion implantation, although it is possible to control a low dose amount, it is not possible to implant impurities into a large-area semiconductor thin film at once, and there is a problem that throughput deteriorates when manufacturing a liquid crystal display. there were.

[0004]

In order to solve the above-mentioned problems of the conventional technique, the present invention adjusts the threshold voltage of a thin film transistor by introducing impurities into a large-area semiconductor thin film with a low dose and high accuracy in a low temperature process. It is an object of the present invention to provide a method of manufacturing a thin film semiconductor device that enables the manufacturing. The following measures have been taken in order to achieve this object. That is, the thin film semiconductor device according to the present invention is manufactured by the following steps. First, a film forming step is performed, and chemical vapor deposition is performed using a raw material gas in which a dopant gas is mixed with a semiconductor film forming gas to deposit a non-single crystalline semiconductor thin film to be an active layer of a transistor on an insulating substrate. Next, an irradiation step is performed to irradiate an energy beam to activate the dopant (impurity) contained in the semiconductor thin film and adjust the threshold voltage of the transistor in advance. Finally, a processing step is performed to process the semiconductor thin film to form transistors in an integrated manner. Preferably, in the irradiation step, the non-single-crystal semiconductor thin film is crystallized simultaneously with activation of the dopant. In this irradiation step, for example, an excimer laser beam is used as the energy beam. Further preferably, in the film forming step, PH ₃ or B ₂ H diluted with hydrogen or helium as a dopant gas is used.
₆ is used, while SiH ₄ or S is used as a semiconductor film forming gas.
i ₂ H ₆ is used.

The present invention can be applied to a method of manufacturing a display device. In this case, the display device is manufactured by the following steps. First, a film formation process is performed, chemical vapor deposition is performed using a source gas in which a semiconductor deposition gas is mixed with a dopant gas, and a non-single crystalline semiconductor thin film to be an active layer of a transistor is formed on one insulating substrate. Deposit on. Next, an irradiation step is performed to irradiate an energy beam to activate the dopant contained in the semiconductor thin film and adjust the threshold voltage of the transistor in advance. Then, a first processing step is performed to process the semiconductor thin film to form transistors in an integrated manner. Further, a second processing step is performed to connect to the transistor and form pixel electrodes in an integrated manner. Finally, an assembling process is performed to bond the other insulating substrate, on which the counter electrode is formed in advance, to the one insulating substrate through a predetermined gap, and dispose the electro-optical material in the gap. With the above, an active matrix type display device is completed.

[0006]

According to the present invention, the semiconductor film forming gas (SiH
₄ , Si ₂ H ₆ etc.) with a dopant gas (PH ₃ , B ₂ H
Chemical vapor deposition is carried out using a source gas mixed with ₆ ) to deposit a semiconductor thin film on an insulating substrate. By adjusting the mixing ratio of the dopant gas to the semiconductor film forming gas, the dopant (impurity) can be contained in the semiconductor thin film at a desired low dose amount. In this state, the dopant is not activated and does not contribute to the conduction of carriers in the semiconductor thin film. Therefore, after the film formation step, an energy beam such as an excimer laser beam is irradiated to activate the dopant contained in the semiconductor thin film. Thereby, the threshold voltage of the thin film transistor can be adjusted in advance. For example, when a p-type impurity (for example, boron B) is introduced into a semiconductor thin film made of silicon (Si), N
In the channel type thin film transistor, its threshold voltage can be adjusted in the enhancing direction according to the dose amount.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. 1 and 2 are process diagrams showing a first embodiment of a method of manufacturing a thin film semiconductor device according to the present invention. In this embodiment, N-channel thin film transistors are integrated and formed on an insulating substrate to form a thin film semiconductor device used as an active element substrate of an active matrix display device.
The same applies to the case of forming a P-channel type thin film transistor. First, in step (a) of FIG. 1, chemical vapor deposition (CVD) is performed using a source gas in which a semiconductor deposition gas is mixed with a dopant gas, and a non-single-crystal semiconductor thin film 2 to be an active layer of a transistor 2 is formed. Are deposited on the insulating substrate 1. In this example, the semiconductor thin film 2 made of polycrystalline silicon is formed by about 20 to 20 by a method such as plasma CVD or LPCVD.
It is deposited with a film thickness of 100 nm. If necessary, a SiO ₂ film, a SiN _x film or the like as a buffer layer may be formed on the surface of the insulating substrate 1 made of transparent glass or the like in advance to a thickness of about 100 to 200 nm.
You may form into a film with the thickness of. When the semiconductor thin film 2 is formed by CVD, a mixture of a semiconductor film forming gas and a dopant gas is used as a source gas. As the semiconductor film forming gas, for example, a 100% concentration gas of SiH ₄ or SiH ₆ is used. On the other hand, the dopant gas is B ₂ diluted with hydrogen or helium.
H ₆ is used. Set the dilution concentration to about 10 to 100 ppm. In this example, SiH ₄ 100% gas 30 sccm and B ₂
H ₆ 20 ppm Hydrogen diluting gas 1.0 sccm was used as a raw material gas, and the plasma CVD method was used to obtain a substrate temperature of 150 to 350.
The semiconductor thin film 2 was formed at a temperature of ° C. Obtained semiconductor thin film 2
A dose amount equivalent to 1 × 10 ¹² / cm ² was obtained when B + was doped by the usual ion implantation method. CV
Due to the doping by D, even if the film was formed over a large area of about 300 × 400 mm ² , there was almost no variation in the dose amount within the wafer surface. Generally, it is relatively easy to suppress the dose amount within ± 1% within the wafer surface. The film forming method is not limited to the plasma CVD method. For example, when SiH ₆ gas and B ₂ H ₆ 20 ppm dilution gas are used in the LPCVD method, a semiconductor thin film made of amorphous silicon is decomposed at about 450 ° C. It can be obtained with a low dose. In this example, B ₂ H ₆ is used as the p-type dopant gas in order to control the threshold voltage (Vth) of the N-channel type thin film transistor in advance. When doping n-type impurities, for example, PH ₃ gas or the like may be used.

Subsequently, the energy beam 3 is irradiated to activate the dopant contained in the semiconductor thin film 2, and the threshold voltage of the transistor is adjusted in advance. An excimer laser beam can be used as the energy beam 3, for example. In this irradiation step, the non-single-crystal semiconductor thin film 2 may be crystallized at the same time as the activation of the dopant. For example, a semiconductor thin film 2 made of amorphous silicon by the LPCVD method.
When the film is formed, the dopant is not activated as it is. Therefore, in order to activate the dopant and crystallize the amorphous silicon at the same time, the wavelength is 150 to 350.
Irradiation with an excimer laser beam of nm at an energy density of 180 to 800 mJ / cm ² converts the amorphous silicon into polycrystalline silicon. In this way, the crystal grain size is 100 to 50
A 0 nm P-type polycrystalline silicon is obtained. By irradiating the excimer laser pulse with one shot, the semiconductor thin film 2 for one chip is collectively heat-treated (annealed). By this collective heating, the amorphous silicon is once melted and then crystallized to obtain polycrystalline silicon having a relatively large grain size.
Since the excimer laser beam is a strong pulsed ultraviolet light,
Absorbed by the surface layer of the semiconductor thin film 2 made of silicon or the like,
Although the temperature of that portion is increased, the insulating substrate 1 is not heated. Thus, the high-performance semiconductor thin film 2 can be formed on the insulating substrate 1 made of a glass material having a relatively low melting point by a low temperature process.

Next, in step (b) of FIG. 1, the semiconductor thin film 2 is patterned in an island shape. Thereby, the element region of the thin film transistor can be formed. Subsequently, SiO ₂ is deposited to a thickness of about 50 to 200 nm by plasma CVD method, LPCVD method, APCVD method or the like. As a result, the gate insulating film 4 covering the semiconductor thin film 2 is obtained. In some cases, the gate insulating film 4 may be formed by continuously forming SiN _x on the SiO ₂ .

In step (c), the gate electrode 5 is patterned on the gate insulating film 4. For example, Al, M
A metal film of o, Ta, Ti, Cr or the like, a polycrystalline silicon film doped with a high concentration of impurities, a laminated film of highly doped polycrystalline silicon and a metal, or an alloy film of the above-described material is formed, Then, the gate electrode 5 is processed by patterning in the shape of.

In step (d), after forming the gate electrode 5, an n-type impurity is implanted at a high concentration by ion doping 6 to form a source region 7 and a drain region 8 in the semiconductor thin film 2. This ion doping is performed by self-alignment using the gate electrode 5 as a mask. Thereby, a top gate type N-channel thin film transistor can be formed. Further, the source region 7 and the drain region 8 are activated by laser annealing or the like.

Moving to step (e) in FIG. 2, the APCVD method,
The interlayer insulating film 9 is formed by depositing SiO ₂ with a thickness of about 400 to 600 nm by using the LPCVD method, the plasma CVD method or the like.

Finally, in step (f), contact holes are opened in the interlayer insulating film 9 by etching. The contact hole communicates with the source region 7. Subsequently, an alloy of Al and Si is formed into a film with a thickness of about 600 nm and patterned into a predetermined shape to form the wiring electrode 10. As shown in the figure, the wiring electrode 10 is connected to the source region 7 of the thin film transistor via a contact hole. Subsequently, the SiO ₂ about 40
The passivation film 11 is formed with a thickness of 0 nm. The passivation film 11 covers the thin film transistor and the wiring electrode 10. After that, if necessary, the substrate is heated to diffuse hydrogen atoms contained in the interlayer insulating film 9 into the semiconductor thin film 2 by using the passivation film 11 as a cap film, and a so-called hydrogenation process is performed. Finally, a transparent conductive film made of ITO or the like is formed on the surface of the passivation film 11, patterned into a predetermined shape, and processed into the pixel electrode 14. The pixel electrode 14 is connected to the drain region 8 of the thin film transistor through a contact hole previously opened in the passivation film 11 and the interlayer insulating film 9. Through the above steps, the thin film semiconductor device is completed. When assembling an active matrix type display device using this thin film semiconductor device as an active element substrate, another insulating substrate having counter electrodes formed in advance is bonded to the insulating substrate 1 through a predetermined gap, and An electro-optical material such as liquid crystal may be placed in the gap.

Next, a second embodiment of the method of manufacturing a thin film semiconductor device according to the present invention will be described with reference to FIG. In this example, bottom gate type thin film transistors are integrally formed. The basic manufacturing process is the same as in the first embodiment,
Corresponding parts are designated by corresponding reference numerals to facilitate understanding. First, in step (a), the gate electrode 5 is formed on the insulating substrate 1. Specifically, Al, Mo, Ta, T
A metal film of i, Cr or the like, a polycrystalline silicon film doped with a high concentration of impurities, a laminated film of highly doped polycrystalline silicon and a metal, or an alloy film of these materials is formed and patterned into a predetermined shape. To form the gate electrode 5. Then AP
CVD method, LPCVD method or plasma CVD method
The N _x film 41 and the SiO ₂ film 42 are continuously formed to form the gate insulating film 4. The thickness of the gate insulating film 4 is 10 to 20.
It is set to 0 nm. After that, the semiconductor thin film 2 made of amorphous silicon is processed to about 10 by the same method as in the first embodiment.
The film is formed to a thickness of -100 nm. An energy beam 3 such as an excimer laser is irradiated. This laser annealing converts amorphous silicon into polycrystalline silicon,
The dopant previously contained in the semiconductor thin film 2 is activated.

In step (b), the SiO ₂ film is formed to a thickness of about 100 nm.
After being formed into a film having the above thickness, the etching stopper 13 is processed by patterning into a predetermined shape. In this case, the etching stopper 13 is patterned so as to be aligned with the gate electrode 5 by using the backside exposure technique. Impurities are injected into the semiconductor thin film 2 at a high concentration by ion doping 6, and the source region 7 and the drain region 8 are formed by self-alignment using the etching stopper 13 as a mask. The source region 7 and the drain region 8 are activated by laser annealing or the like. At this stage, the semiconductor thin film 2 is etched to remove unnecessary portions from the insulating substrate 1.

In step (c), SiO ₂ is about 600 nm.
To be the interlayer insulating film 9.

Finally, in step (d), contact holes are opened in the interlayer insulating film 9, and the source region 7 and the drain region 8 are formed.
Expose part of. Then Al-Si alloy or Mo
And the like are formed into a film with a thickness of about 600 nm, patterned into a predetermined shape, and processed into the wiring electrode 10. Further, if necessary, hydrogenation treatment is performed, and finally the pixel electrode 14 is formed to complete the thin film semiconductor device.

An example of an active matrix type liquid crystal display device in which the thin film semiconductor device manufactured according to the first embodiment or the second embodiment is assembled as an active element substrate will be described with reference to FIG. As shown, the display device has a panel structure including an active element substrate 101, a counter substrate 102, and an electro-optical material 103 held between the active element substrate 101 and the counter substrate 102. A liquid crystal material or the like is widely used as the electro-optical substance 103. A pixel array section 104 and a driving circuit section are integrally formed on the active element substrate 101. The drive circuit section is divided into a vertical drive circuit 105 and a horizontal drive circuit 106.
Further, a terminal portion 107 for external connection is formed on the upper end of the peripheral portion of the active element substrate 101. Terminal section 107 is wiring 1
08 through the vertical drive circuit 105 and the horizontal drive circuit 10
Connected to 6. Row-shaped gate wirings 109 and column-shaped signal wirings 110 are formed in the pixel array section 104. A pixel electrode 111 and a thin film transistor 112 that drives the pixel electrode 111 are formed at the intersections of the two wirings. The gate electrode of the thin film transistor 112 corresponds to the corresponding gate wiring 10.
9 and the drain region corresponds to the corresponding pixel electrode 111.
And the source region is connected to the corresponding signal line 110. The gate wiring 109 is connected to the vertical driving circuit 105, while the signal wiring 110 is connected to the horizontal driving circuit 106. The thin film transistor 112 for switching and driving the pixel electrode 111 and the thin film transistors included in the vertical drive circuit 105 and the horizontal drive circuit 106 are manufactured according to the present invention. That is, chemical vapor deposition is performed using a raw material gas in which a semiconductor film forming gas is mixed with a dopant, and a non-single crystalline semiconductor thin film to be an active layer of a thin film transistor is first formed into an insulating substrate (active element substrate 10).
1) Deposit on top. Irradiation with an energy beam activates the dopant contained in the semiconductor thin film, and the threshold voltage of the thin film transistor is adjusted in advance. Finally, the semiconductor thin film is processed to integrally form a thin film transistor.

[0019]

As described above, according to the present invention, chemical vapor deposition is performed using a source gas in which a dopant gas is mixed with a semiconductor film-forming gas at a low concentration to form a non-active layer of a transistor. A monocrystalline semiconductor thin film is deposited on an insulating substrate. Furthermore, the energy beam is irradiated to activate the dopant contained in the semiconductor thin film, and the threshold voltage of the transistor is adjusted in advance. This makes it possible to easily perform low-concentration impurity implantation (light doping) for controlling the threshold voltage in a low temperature process. Moreover, since impurities can be lightly doped with good uniformity over a large area, it can be applied to one side of a large-screen liquid crystal display device, or to multiple sides of a small or medium-sized liquid crystal display device, and the effect is great. There is.

[Brief description of drawings]

FIG. 1 is a first thin film semiconductor device manufacturing method according to the present invention.
It is process drawing which shows an Example.

FIG. 2 is also a process drawing of the first embodiment.

FIG. 3 is a second thin film semiconductor device manufacturing method according to the present invention.
It is process drawing which shows an Example.

FIG. 4 is a schematic perspective view showing an example of an active matrix type display device manufactured according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 2 Semiconductor thin film 3 Energy beam 4 Gate insulating film 5 Gate electrode 6 Ion doping 7 Source region 8 Drain region 9 Interlayer insulating film 10 Wiring electrode 11 Passivation film 13 Etching stopper 14 Pixel electrode

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H01L 27/12 H01L 29/78 618A

Claims (5)

[Claims] 1. A film forming method in which a chemical vapor deposition is performed using a source gas in which a dopant gas is mixed with a semiconductor film forming gas to deposit a non-single crystalline semiconductor thin film to be an active layer of a transistor on an insulating substrate. A thin film that performs a process, an irradiation process of irradiating an energy beam to activate a dopant contained in the semiconductor thin film to adjust a threshold voltage of the transistor in advance, and a processing process of processing the semiconductor thin film to integrally form a transistor Manufacturing method of semiconductor device. 2. The irradiation step crystallizes the non-single-crystal semiconductor thin film simultaneously with activation of a dopant.
A method for manufacturing a thin film semiconductor device according to claim 1. 3. The thin film according to claim 1, wherein in the film forming step, PH ₃ or B ₂ H ₆ diluted with hydrogen or helium is used as a dopant gas, and SiH ₄ or Si ₂ H ₆ is used as a semiconductor film forming gas. Manufacturing method of semiconductor device. 4. The method for manufacturing a thin film semiconductor device according to claim 1, wherein the irradiation step uses an excimer laser beam as an energy beam. 5. A chemical vapor deposition is performed by using a source gas in which a dopant gas is mixed with a semiconductor film forming gas, and a non-single crystalline semiconductor thin film to be an active layer of a transistor is deposited on one insulating substrate. A film forming step, an irradiation step of irradiating an energy beam to activate a dopant contained in the semiconductor thin film and previously adjusting a threshold voltage of the transistor, and a first processing step of processing the semiconductor thin film to integrally form a transistor. And a second pixel electrode connected to the transistor to integrally form a pixel electrode
A method of manufacturing a display device, which includes a processing step and an assembly step of bonding the other insulating substrate on which a counter electrode is formed in advance to the one insulating substrate through a predetermined gap and disposing an electro-optical substance in the gap. .