JP3334629B2 - Method for manufacturing thin film transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method of manufacturing a thin film transistor, and more particularly, to a method of manufacturing a semiconductor device in which a threshold control impurity is introduced into a semiconductor film with a simple control with a simple means.

[0002]

2. Description of the Related Art Thin film transistors
or: hereinafter, also referred to as TFT), for example, is used as a switching element for driving a pixel of a liquid crystal display device, using a semiconductor film formed on a substrate such as a glass substrate or a quartz substrate as an active film. MOS (Metal Oxi
de Semiconductor) type structure. As typical technologies for forming the TFT, a hydrogenated amorphous (amorphous) silicon TFT technology and a polycrystalline silicon TFT technology are known, and an amorphous silicon film and a polycrystalline silicon film formed by each technology are removed. It has been used as an active film.

In particular, in the case of the latter polycrystalline silicon TFT technology, a polycrystalline silicon film is formed by a high temperature process of about 1000 ° C. by applying an LSI manufacturing technology on a heat-resistant, for example, quartz substrate. By forming a TFT on the polycrystalline silicon film, a high carrier mobility of approximately 100 cm ² / Vsec can be obtained. The realization of such high carrier mobility is an advantage that when the TFT is applied to the above-described liquid crystal display device, a peripheral driving circuit portion can be formed simultaneously with a driving switching element for driving each pixel on the same substrate. Therefore, high added value such as reduction in manufacturing cost and miniaturization of liquid crystal panels can be expected.

In the above-described polycrystalline silicon TFT technology, a high-temperature process of about 1000 ° C. is used, so that a high temperature causes thermal shrinkage of the substrate, so that a deterioration in alignment accuracy becomes apparent in a lithography process in TFT manufacturing. Become like Therefore, polycrystalline silicon TFT
There is a need for a technology that can perform processes at low temperatures while maintaining the performance of the technology.

From such a viewpoint, low pressure CVD (Chemical
A technique of forming a polycrystalline silicon film by combining a vapor deposition method and a low-temperature annealing method has attracted attention. In this technique, after forming an amorphous silicon film by a low-pressure CVD method, the amorphous silicon film is crystallized by a laser such as an excimer laser into a polycrystalline silicon film. Since a crystalline silicon film can be formed into a polycrystalline silicon film at room temperature, a low-temperature process can be performed. Meanwhile, when manufacturing a TFT, control of a threshold voltage (hereinafter, also referred to as a threshold) has become an important issue along with realization of a low-temperature process. Considering this point, although the above-described low-temperature process has a certain effect, in the TFT using the polycrystalline silicon film formed by the low-temperature process, a shift (shift) of the threshold voltage cannot be avoided. Therefore, conventionally, ion implantation into a polycrystalline silicon film has been performed using a threshold controlling impurity such as boron (B) to prevent a shift in threshold.

FIGS. 6 (a) to 6 (c) and 7 (d),
(E) is a process drawing explaining a conventional method of manufacturing a thin film transistor in the order of processes. Hereinafter, a method for manufacturing the thin film transistor will be described in the order of steps with reference to FIGS. 6A to 6C and FIGS. 7D and 7E. First, FIG.
As shown in (a), after a first silicon oxide film 52 having a thickness of about 500 nm is deposited on an insulating substrate 51 made of, for example, a glass substrate by a low-pressure CVD method, the first silicon oxide film is formed by the low-pressure CVD method. The film thickness is approximately 100 nm on 52
A P-type amorphous silicon film 53 is formed.

Next, as shown in FIG. 6B, boron (B) ions are added to the amorphous silicon film 53 as impurities for controlling the threshold value by an ion implantation method as shown by an arrow 54 in FIG.
The implantation is performed at a dose of 1 × 10 ¹¹ to 1 × 10 ¹² ions / cm ² . In this case, as a gas source, for example, diborane (B
_{After 2} H ₆ ) is used to generate plasma and boron and hydrogen ions, only boron is separated and implanted by mass spectrometry. Next, the amorphous silicon film 53
Irradiates light with a laser such as an excimer laser,
The amorphous silicon film 53 is remelted and crystallized to be changed to a polycrystalline silicon film 55.

[0008] Next, as shown in FIG.
The thickness is approximately 50 nm on the polycrystalline silicon film 55 by the D method.
After the second silicon oxide film 56 is deposited, the second silicon oxide film 56 and the polycrystalline silicon film 55 are patterned into an island pattern by performing dry etching using the photoresist film 57 as a mask.

Next, as shown in FIG. 7D, after the photoresist film 57 is removed, a film thickness of approximately 1 is formed on the island-shaped second silicon oxide film 56 by a plasma CVD method.
A second amorphous silicon film 58 having a thickness of 00 nm and a tungsten silicide (W
After sequentially forming the Si) films 59, the tungsten silicide film 58 and the second amorphous silicon film 59 are dry-etched by using the photoresist film 60 having an area smaller than the above-described photoresist film 57 as a mask. Is patterned into an island pattern having an area smaller than that of the island pattern. Next, by removing the photoresist film 60, the tungsten silicide film 5 having an island pattern is formed.
8 and an insulated gate electrode 61 made of the second amorphous silicon film 59 are formed.

Next, as shown in FIG. 7E, for example, phosphorus (P) ions and hydrogen ions are ion-implanted through the second silicon oxide film 56 using the insulated gate electrode 61 as a mask. Into the
By forming the N-type source region 62 and the drain region 63, a thin film transistor is manufactured.

By the way, in such a conventional method of manufacturing a thin film transistor, boron as an impurity for controlling a threshold value is introduced by an ion implantation method. . That is, the ion implantation method is performed by a method in which boron ions are mass-analyzed and separated from other impurity ions such as hydrogen ions by using a mass spectrometric ion implantation apparatus, so that the process is complicated. . For this reason, an ion doping method using a non-mass spectrometric ion doping apparatus is known as a method for easily introducing a threshold control impurity. For example, JP-A-8-20
No. 4208 discloses a method of controlling the threshold voltage by injecting N-type or P-type impurities into a semiconductor film by using the same ion doping method.

[0012]

However, in the method of manufacturing a thin film transistor described in the above-mentioned publication, the ion doping apparatus used for injecting the impurity for controlling the threshold voltage has a complicated structure, so that the method is simple. There is a problem that it becomes difficult to implant a value controlling impurity. That is, since the above-described ion doping apparatus used in the conventional method of manufacturing a thin film transistor requires the first and second preliminary chambers in addition to the doping chamber, the threshold control impurities are implanted. The process is inevitably complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a method of manufacturing a thin film transistor in which an impurity for controlling a threshold value of a thin film transistor can be easily and efficiently introduced. It is an object.

In order to solve the above problem, the invention according to claim 1 relates to a method of manufacturing a thin film transistor for manufacturing an MIS transistor on a semiconductor film formed on an insulating substrate, wherein an amorphous semiconductor is formed on the insulating substrate. A non-crystalline semiconductor film forming step of forming a film, a substrate cleaning step of cleaning the formed non-crystalline semiconductor film in an acid solution, and spin drying of the non-crystalline semiconductor film subjected to the cleaning processing After being housed in the device and placed on the substrate holder, in a dry atmosphere containing the impurity for controlling the threshold of the MIS transistor,
Maintaining the insulating substrate to room temperature, the substrate holder rotates at a high speed, drying and simultaneously, the substrate drying / impurity implantation step of implanting the threshold controlling impurity into the amorphous semiconductor film, the threshold A substrate heat treatment step of heat-treating the amorphous semiconductor film into which the impurity for value control is implanted to form a polycrystalline semiconductor film, and an insulated gate electrode for forming an insulated gate electrode on the polycrystalline semiconductor film obtained as a result of the heat treatment Forming step;
Forming an active region comprising a source and a drain region in the polycrystalline semiconductor film on which the insulated gate electrode is formed.

According to a second aspect of the present invention, there is provided a method for manufacturing the thin film transistor according to the first aspect, wherein the inside of the spin drying apparatus used in the substrate drying / impurity implantation step is provided. It is characterized in that a filter containing a threshold control impurity is provided above.

According to a third aspect of the present invention, there is provided the method for manufacturing a thin film transistor according to the second aspect, wherein in the spin drying apparatus, an intake hole is provided above the filter, and exhaust air is provided below the substrate holder. It is characterized by having holes.

According to a fourth aspect of the present invention, there is provided a method for manufacturing a thin film transistor according to the first, second or third aspect, wherein the substrate is dried / impurity-implanted at a rotation speed of 1000 to 2000 rpm. It features high-speed rotation.

According to a fifth aspect of the present invention, there is provided a method for manufacturing the thin film transistor according to any one of the first to fourth aspects, wherein the impurity for controlling the threshold value comprises boron.

[0019]

[0020]

[0021]

Embodiments of the present invention will be described below with reference to the drawings. The description will be specifically made using an embodiment. 1 (a) to 1 (c) and 2 (d) to
(F) is a process diagram showing a method of manufacturing a thin film transistor according to an embodiment of the present invention in the order of steps, and FIG. 3 is a configuration diagram showing a configuration of a spin drying apparatus used in carrying out the method of manufacturing the thin film transistor. Hereinafter, FIGS. 1 (a) to 1 (c)
2 (d) to 2 (f), a method of manufacturing the thin film transistor will be described in the order of steps. First, FIG.
As shown in (a), a first film having a thickness of about 500 nm is formed on an insulating substrate 1 made of, for example, a glass substrate by a low-pressure CVD method.
After depositing the silicon oxide film 2, a P-type amorphous silicon film 3 having a thickness of about 100 nm is formed on the first silicon oxide film 2 by the low-pressure CVD method. Next, the insulating substrate 1 is cleaned by performing a cleaning process in a diluted hydrofluoric acid solution. Here, the first silicon oxide film 2 is used as a contamination prevention film for the insulating substrate 1, but the first silicon oxide film 2 is not necessarily required.

Next, the insulating substrate 1 is housed in a spin dryer 15 as shown in FIG.
Boron as a threshold control impurity is deposited on the amorphous silicon film 3 as shown in FIG. 1 (b) to form a boron layer 4, and further as shown in FIG. 1 (c). Boron is implanted into the amorphous silicon film 3.

The spin drying device 15 includes a substrate container 16
The upper portion of the container 16 is provided with an intake hole 17, while the lower portion of the container 16 is provided with an exhaust hole 18. Each of the holes 17 and 18 is provided with a valve 19.
A boron-containing filter 20 is provided by a support 21 at a position directly below the intake hole 17 in the upper portion of the container 16. A substrate holder 22 that supports the insulating substrate 1 is provided at a lower position of the container 16 that faces the boron-containing filter 20, and the substrate holder 22 supports the insulating substrate 1 rotatably by a rotation mechanism 23. .

First, in a state where the insulating substrate 1 is accommodated in the spin dryer 15, the valve 19 is opened, the atmosphere is flowed into the container 16 from the intake hole 17, and circulated through the container 16, and then the exhaust hole 18 is formed. Pour from At this time, the insulating substrate 1
Is maintained at a normal temperature, and the rotation speed is set to 1000 to 2000 rpm (revolution) through the substrate holder 22 by the rotation mechanism 23.
per minute), and rotate at high speed for about 10 minutes.
Is subjected to a drying treatment. At the time of this drying process, the air flowing in from the air inlet 17 passes through the boron-containing filter 20 and rapidly circulates in the container 16 by the action of the high-speed rotation while containing boron. 3 to deposit boron.

Thus, a boron layer 4 is formed as shown in FIG. Then, since the attached boron is small and light, it is injected into the amorphous silicon film 3 by the rapid circulation of the atmosphere as described above. That is, boron is taken into the amorphous silicon film 3 by rapid circulation of the atmosphere. Thus, a boron-implanted amorphous silicon film 5 is formed as shown in FIG. As described above, the spin dryer 15 has a function of drying the insulating substrate 1 and a function of injecting the boron adhered on the amorphous silicon film 3 into the amorphous silicon film 3 with good controllability.

FIG. 4 is a graph showing the relationship between the standing time (horizontal axis) and the boron concentration (vertical axis) when the insulating substrate 1 is left directly below the boron-containing filter 20. As is clear from the figure, the boron concentration increases in proportion to the standing time. FIG. 5 is a diagram showing the relationship between the depth from the silicon film surface (horizontal axis) and the boron concentration (vertical axis) when the attached boron is injected into the amorphous silicon film 3.
It shows the results of analysis and plotting by IMS (Secondary Ion Mass Spectroscopy: secondary ion mass spectrometer). As is clear from the figure, the boron concentration is about 2 × 10 ¹⁷ / cm at a depth of about 0.2 μm from the silicon film surface.
^It has a peak density of ³ and a sheet density of approximately 8 × 10 ¹¹ / cm ² . As is clear from the figure, it was confirmed that boron adhering to the silicon film was spiked by the spin dryer 15 to the deep bulk portion of the silicon film. According to this example, 5 × 10 ¹¹ to 1 × 10 ¹² ions / cm ^{2 in the} amorphous silicon film 3 in terms of dose amount.
Could be injected with good controllability.

Next, the boron-implanted amorphous silicon film 5 is irradiated with light using a laser such as an excimer laser to remelt and crystallize the amorphous silicon film 5 to convert it into a polycrystalline silicon film 6.

Next, as shown in FIG.
After a second silicon oxide film 7 having a thickness of approximately 50 nm is deposited on the polycrystalline silicon film 6 by the method D, dry etching is performed using the photoresist film 8 as a mask to perform the second silicon oxide film 7 and the polycrystalline silicon. The film 6 is patterned into an island pattern.

Next, as shown in FIG. 2E, after the photoresist film 8 is removed, a film thickness of about 100 is formed on the second silicon oxide film 7 having the island pattern by the plasma CVD method.
After the second amorphous silicon film 9 having a thickness of 100 nm and a tungsten silicide film 10 having a thickness of approximately 100 nm are sequentially formed by a sputtering method, a photoresist film 11 having an area smaller than that of the photoresist film 8 is used as a mask. By performing dry etching, the tungsten silicide film 10 and the second amorphous silicon film 9 are patterned into an island pattern having an area smaller than the above-described island pattern. Next, by removing the photoresist film 11, an insulated gate electrode 12 composed of the tungsten silicide film 10 and the second amorphous silicon film 9 in an island pattern is formed.

Next, as shown in FIG. 2F, for example, phosphorus ions and hydrogen ions are ion-implanted using the insulated gate electrode 12 as a mask to form the second silicon oxide film 7.
Is implanted into the boron-implanted polycrystalline silicon film 6 through
By forming the N-type source region 13 and the drain region 14, a thin film transistor is manufactured.

As described above, according to the configuration of this example, the insulating substrate 1 on which the amorphous silicon film 3 is formed is accommodated in the spin dryer 15 and boron as a threshold control impurity of the MOS transistor is formed. Is rotated at a high temperature at a normal temperature in a dry atmosphere in which a filter 20 containing Si is installed, and boron is injected into the amorphous silicon film 3 together with the drying process. Therefore, a spin dryer 15 having a simple configuration is used. This makes it possible to implant the threshold control impurity easily and with good controllability. Therefore, the threshold value of the thin film transistor can be easily controlled without requiring much time for the process, and the throughput can be improved.

Although the embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and the design may be changed without departing from the scope of the present invention. Is also included in the present invention. For example, the threshold control impurity is not limited to boron, and other P-type impurities or N-type impurities generally used for manufacturing a thin film transistor can be used.

The present invention is not limited to the case where the insulating substrate is accommodated in a spin dryer and the impurity for controlling the threshold is implanted into the amorphous silicon film. A substantially similar impurity implantation method may be applied. Further, the method for forming the silicon oxide film or the amorphous silicon film is not limited to the CVD method or the sputtering method, and may be performed by another method such as a thermal oxidation method or an epitaxial method. Also,
The condition of the thickness of each insulating film and semiconductor film is an example, and can be changed according to the use and purpose.

The metal constituting the insulated gate electrode is not limited to tungsten silicide, but may be molybdenum silicide (MoSi), tantalum silicide (TaSi),
Other metals generally known as refractory metals, such as titanium silicide (TiSi) can be used.

The insulated gate film of the thin film transistor is not limited to an oxide film, but may be a nitride film.
e Film) or a two-layer structure of an oxide film and a nitride film. In other words, MIS (Metal Insulator Semic
onductor) MNS (Metal Nitride Semiconductor)
A transistor may be used, or MNOS (Metal Ni
tride-Oxide Semiconductor) transistors. Further, the conductivity type of the polycrystalline silicon film forming the thin film transistor may be reversed between the P type and the N type.

[0036]

As described above, according to the method for manufacturing a thin film transistor of the present invention, the insulating substrate on which the amorphous semiconductor film is formed is washed in an acid solution and then housed in a spin dryer. an insulating substrate to room temperature in a dry atmosphere threshold controlling impurity of the MIS transistor is contained
By maintaining the substrate holder at a high speed and simultaneously injecting the impurity for controlling the threshold value into the amorphous semiconductor film at the same time as the drying, the spin drying device having a simple configuration is used, so that the substrate can be easily and simply dried. Threshold control impurities can be implanted with good controllability. Therefore, the threshold value of the thin film transistor can be easily controlled without requiring much time for the process, so that the throughput can be improved.

[Brief description of the drawings]

FIG. 1 is a process chart showing a method of manufacturing a thin film transistor according to an embodiment of the present invention in the order of steps.

FIG. 2 is a process chart showing a method for manufacturing the thin film transistor in the order of steps.

FIG. 3 is a configuration diagram showing a configuration of a spin dryer used for performing the method of manufacturing the thin film transistor.

FIG. 4 is a view showing a relationship between a boron standing time (horizontal axis) and a boron concentration (vertical axis) when an insulating substrate is left in the method of manufacturing the thin film transistor.

FIG. 5 is a diagram showing the relationship between the depth from the silicon film surface (horizontal axis) and the boron concentration (vertical axis) when boron is injected into the amorphous silicon film in the method of manufacturing the thin film transistor. is there.

FIG. 6 is a process chart showing a conventional method of manufacturing a thin film transistor in the order of steps.

FIG. 7 is a process chart showing a conventional method for manufacturing a thin film transistor in the order of steps.

[Explanation of symbols]

 Reference Signs List 1 insulating substrate 2 first silicon oxide film 3 amorphous silicon film 4 boron layer 5 boron implanted polycrystalline silicon film 6 polycrystalline silicon film 7 second silicon oxide film 8, 11 photoresist film 9 second amorphous silicon film 10 tungsten Silicide film 12 Insulated gate electrode 13 Source region 14 Drain region 15 Spin dryer 16 Substrate container 17 Intake hole 18 Exhaust hole 19 Valve 20 Boron-containing filter 21 Support 22 Substrate holder 23 Rotary mechanism

Continuation of the front page (56) References JP-A-1-316930 (JP, A) JP-A-3-218622 (JP, A) JP-A-4-179223 (JP, A) JP-A-7-94424 (JP) JP-A-7-153709 (JP, A) JP-A-9-7962 (JP, A) JP-A-9-92835 (JP, A) JP-A-57-27066 (JP, A) 10-340955 (JP, A) JP-A-11-16337 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 29/786 H01L 21/336 H01L 21/20 H01L 21 / 22 H01L 21/223 H01L 21/225

Claims (5)

(57) [Claims] An MIS is applied to a semiconductor film formed on an insulating substrate.
A method of manufacturing a thin film transistor for manufacturing the mold transistors, washed and an amorphous semiconductor film forming step of forming an amorphous semiconductor film on the insulating substrate, the film-formed the amorphous semiconductor film in an acid solution A substrate cleaning step to be processed; and a drying atmosphere containing the impurity for controlling the threshold voltage of the MIS transistor after accommodating the amorphous semiconductor film subjected to the cleaning processing in a spin dryer and mounting the substrate on a substrate holder. During the drying, the insulating substrate is maintained at a normal temperature, the substrate holder is rotated at a high speed , and simultaneously the substrate is dried and the impurity for controlling the threshold is injected into the amorphous semiconductor film.
An impurity implantation step, a substrate heat treatment step of heat-treating the amorphous semiconductor film into which the threshold control impurity is implanted to form a polycrystalline semiconductor film, and an insulating film on the polycrystalline semiconductor film obtained as a result of the heat treatment. A thin film transistor comprising: an insulated gate electrode forming step of forming a gate electrode; and an active region forming step of forming an active region including a source and a drain region in the polycrystalline semiconductor film on which the insulated gate electrode is formed. Manufacturing method. 2. A filter containing a threshold controlling impurity is provided inside the spin dryer used in the substrate drying / impurity injecting step and above the insulating substrate. A method for manufacturing a thin film transistor according to claim 1. 3. The method of manufacturing a thin film transistor according to claim 2, wherein in the spin drying device, an intake hole is provided above the filter, and an exhaust hole is provided below the substrate holder. 4. The substrate drying / impurity injecting step, wherein the insulating substrate is rotated at a high speed of 1000 to 2000 rpm at a high speed.
A method for manufacturing the thin film transistor according to the above. 5. The method of manufacturing a thin film transistor according to claim 1, wherein the impurity for controlling the threshold value comprises boron.