JPH0758341A - Production of thin-film transistor - Google Patents

Abstract

PURPOSE:To produce a thin-film transistor easily, improve its performance and form it on a low heat-resistance amorphous substrate. CONSTITUTION:When the thin-film transistor is produced to form a gate electrode, gate insulation film, source area, drain area, and channel area on an amorphous substrate, two processes are prepared to form an amorphous semiconductor film 4 on the amorphous substrate 1 and to inject impurities into areas 4S and 4D on which a source and drain of the film 4 are to be formed. Then, a further process is added thereto in order to heat/melt at least the regions 4S and 4D by irradiating a short-wavelength pulse laser of 100-400nm in wavelength and to inactivate the impurities for polycrystalization.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a thin film transistor (T
FT) manufacturing method.

[0002]

2. Description of the Related Art For example, in a transmissive liquid crystal display, a thin film transistor is used as a switching element for turning on and off each picture element. In this case, a large number of thin film transistors are arranged and formed on the transparent glass substrate. FIG. 3 shows an example of a conventional method of manufacturing a thin film transistor on a glass substrate. First, as shown in FIG. 3A, a gate electrode 2 made of aluminum or indium tin oxide (hereinafter abbreviated as ITO) is formed on a glass substrate 1 and then a SiO ₂ film 3 and hydrogenated amorphous silicon (hereinafter a-Si) are formed. : H) 4 and an n-type a-Si: H (n ⁺ -a-Si: H) film 5 for ohmic contact are continuously deposited on the entire surface by plasma CVD. Next is aS
The i: H film 4 and the n ⁺ -a-Si: H film 5 are patterned to form an island region in a portion necessary for manufacturing a thin film transistor. Next, as shown in FIG. 3B, an Al / Mo2 layer film structure, a source electrode 6 and a drain electrode 7 made of molybdenum, titanium, or nichrome are formed on the source and drain portions. Next, as shown in FIG. 3C, the n ⁺ -a-Si: H film 5 facing between the source electrode 6 and the drain electrode 7 is removed by a plasma etching method or the like to eliminate the leak current between the source and the drain. Thereafter, as shown in FIG. 3D, a SiO ₂ layer 8 for passivation and liquid crystal alignment is formed on the entire surface, and a light shielding layer 9 is further formed so as to cover a portion corresponding to the channel portion to form a thin film transistor.

[0003]

In this manufacturing method, the gate electrode 2 is used as a mask for photolithography.
Pattern formation, for forming the island region of the a-Si: H film 4,
At least four masks are required for patterning the source and drain electrodes 6 and 7, and for patterning the light shielding layer 9. Also, a-Si: H film thickness of the film 4 is about 0.5μm about and without n ⁺ -a-Si: H film 5 not leave a sufficient thickness when etching is removed, n ⁺ -a-Si : H
There are drawbacks such as unevenness in the enching process of the film 5 and unevenness in the deposition of the a-Si: H film 4, which makes it difficult to obtain a large number of thin film transistors having uniform characteristics over a wide area. a-S
If the i: H film 4 is thick, the source / drain electrodes 6 and 7 are liable to cause step breaks unless the thickness is about 1 μm.

Since such a thick a-Si: H film 4 has a high a-Si: H photoconductivity, a light-shielding layer 9 for shielding light is required, which further complicates the manufacturing process. . Since the a-Si: H film 4 is hydrogenated, there are few defects in the film, an on / off ratio of 10 ⁶ is usually obtained, and a threshold voltage Vth = about 5 V is obtained. However, the effective mobility is 0.1 to 0.5 cm ² / V due to the relative crystal quality.
-Small and small, and fast switching characteristics cannot be obtained.

In view of the above points, the present invention provides a thin film transistor which can be manufactured easily and can be thinned and crystallized to improve the performance of the thin film transistor, and further, the thin film transistor can be formed on a low heat resistant substrate. It provides a manufacturing method.

[0006]

The present invention is directed to an amorphous substrate 1
The gate electrode 2, the gate insulating film 3, the source region 4S,
In the method of manufacturing a thin film transistor for forming the drain region 4D and the channel region 4C, a step of forming the amorphous semiconductor thin film 4 on the amorphous substrate 1 and a region 4S, 4D where the source and drain of the semiconductor thin film 4 are formed are formed. A step of implanting impurities, and a step of irradiating the regions 4S and 4D in which the source and drain are to be formed with a short-wavelength pulse laser 10 having a wavelength of 100 nm to 400 nm to melt and heat them to activate the impurities and polycrystallize them. Have and.

[0007]

According to the manufacturing method of the present invention, impurities are implanted into the regions 4S and 4D of the amorphous semiconductor thin film 4 where the source and drain are formed, and the regions 4S and 4D are filled with 100 nm to 400 n.
By irradiating a short-wavelength pulse laser of m, the thin film is polycrystallized, and at the same time, the impurities are sufficiently activated. At this time, since it is the short wavelength pulse laser 10,
Since only the amorphous semiconductor thin film 4 is heated for a short time and then cooled, lateral impurity diffusion does not occur. Due to this polycrystallization, the thin film has a high carrier mobility. Also,
In addition to crystallization, the conventional formation of a film having a high impurity concentration can be omitted, and the film thickness of the semiconductor thin film 4 can be made sufficiently thin, so that the photoconductivity can be reduced and the occurrence of leak current can be eliminated. Therefore, the performance of the thin film transistor can be improved.

Further, since the short-wavelength pulse laser 10 having a wavelength of 100 nm to 400 nm is used, the semiconductor thin film 4 can be polycrystallized at a low temperature (room temperature) without raising the temperature of the entire substrate, and a low heat resistance amorphous. It is possible to form a high-performance thin film transistor on a quality substrate.

Further, since the conventional light shielding layer covering the channel portion 4C and the masking step for the layer can be omitted, the manufacturing is easy.

[0010]

EXAMPLES In the present invention, when a semiconductor thin film to be crystallized is irradiated with a short-wavelength pulse laser, the laser light is absorbed only by the extreme surface of the semiconductor thin film, and then the inside of the thin film is melted by heat conduction and re-formed. A thin film transistor is manufactured by utilizing the fact that crystal grains become large by being crystallized or annealed.

For example, when an a-Si: H film is used as a semiconductor thin film and is irradiated with XeCl excimer laser light having a wavelength of 308 nm, the absorption coefficient for this wavelength is 10.
Since it reaches ⁶ cm ^-1 , it is absorbed on the very surface (about 100 Å) and converted into heat. This heat is immediately transferred to the inside of the thin film by heat conduction. Since the surface or the inside of the film is instantaneously heated to a high temperature in this way, the a-Si: H film is crystallized without producing hydrogen and its characteristics are significantly changed. For example, the mobility of the film is significantly increased and the photoconductivity is reduced. Further, the ion-implanted film has its impurities activated.

When such a high-energy pulsed laser beam having a short wavelength is irradiated, hydrogen in the a-Si: H film is not released, and it functions to eliminate dangling bonds at grain boundaries even after crystallization. To do.

The short-wavelength pulsed laser light used in the present invention has a laser wavelength of 100 to 400 nm, a practical range of 150 to 350 nm, and a pulse width of 100 nsec or less, preferably 10 to 50 nsec, especially 20 nsec. The peak intensity of the pulse is 10 ⁶ W / cm ² or more.
10 ⁸ W / cm ² or less, and fluence (energy of one pulse) is 1 J / cm ² or less, preferably 50
mJ / cm ² or more to 500 mJ / cm ² or less, more preferably 100 mJ / cm ^2. If such a short wavelength pulsed laser beam is used, local heating can be performed.

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, which is applied to a method of manufacturing a planar type thin film transistor.
In this example, as shown in FIG. 1A, an a-Si: H film 4 and a SiO ₂ film 3 are sequentially deposited on a glass substrate 1 and patterned to form island regions. Next, the gate electrode 2 made of, for example, titanium, molybdenum, or nichrome is formed on the SiO ₂ film 3 corresponding to the channel portion 4C, and the gate electrode 2 is used as a mask to form the source portion 4S and the source portion 4S of the a-Si: H film 4. The necessary impurities such as phosphorus or boron are ion-implanted into the drain portion 4D.

Next, as shown in FIG. 1B, a source electrode 6 and a drain electrode 7 made of, for example, molybdenum, titanium, nichrome or ITO are deposited and formed so as to be partially connected to the source and drain portions 4S and 4D, and further, The SiO ₂ film 8 is deposited. After that, a short-wavelength pulse laser light from the glass substrate 1 side, that is, a UV (ultraviolet) pulse laser light 1
Irradiate 0. As a result, the source and drain section 4S
And 4D are activated, and the source and drain parts 4S and 4D and the channel part 4C are polycrystallized.

In this case, if quartz glass or Pyrex glass is used for the glass substrate 1, for example, a laser beam having a wavelength of 308 nm is transmitted, so that the a-Si: H film 4 and the glass substrate 1 are formed.
At the interface of, the light changes to heat, and the a-Si: H film 4 is heat-treated. Thus, the target thin film transistor is obtained. 8 is S
This is an iO ₂ film.

In the manufacturing method of this embodiment, since the a-Si: H film of the channel portion 4C can be polycrystallized without producing hydrogen, the mobility of the thin film transistor can be increased. Since the a-Si: H films of the source part 4S and the drain part 4D are also crystallized without releasing hydrogen, ohmic contact is completed and impurities are sufficiently activated to improve the interface characteristics with the channel part. be able to. Also U
Since the V pulse laser light is used, only the a-Si: H film is heated for a short time and then rapidly cooled, so that the impurity atoms in the source and drain parts are activated, but a long wavelength pulse (or continuous) is generated. There is no lateral impurity diffusion as when using laser light. Further, since the conventional n ⁺ -a-Si: H film 5 is omitted, the a-Si: H film 4 can be made sufficiently thin, and for example, the film thickness can be in the range of 100Å to 1000Å.
In addition to crystallization of the Si: H film, the thin film thickness can further reduce the photoconductivity and the generation of leak current. Therefore, the light-shielding layer 9 covering the channel portion and the masking process therefor can be omitted. Further, since the a-Si: H film 4 can be thinned, the disconnection of the source and drain electrodes does not occur.

Therefore, in this embodiment, a highly reliable thin film transistor can be obtained, and its structure and manufacturing process can be simplified.

By using the UV pulsed laser beam 10, the a-Si: H film 4 can be melted and crystallized in a low temperature (room temperature) atmosphere, whereby a thin film transistor can be formed on a low heat resistant substrate such as the glass substrate 1. Can be formed.

FIG. 2 shows another embodiment of the present invention, which is applied to a method of manufacturing a staggered thin film transistor. In this example, as shown in FIG. 2A, after forming a source electrode 6 and a drain electrode 7 of, for example, molybdenum, titanium, nichrome or ITO on a glass substrate 1, a-S
i: H film 4 and SiO ₂ film 3 are formed. Further, for example, the gate electrode 2 made of aluminum or ITO is formed, and the SiO ₂ film 8 is formed on the entire surface of the island region. Then, a− corresponding to the source and drain parts 4S and 4D
Ions are implanted into the Si: H film with necessary impurities such as phosphorus or boron.

Next, as shown in FIG. 2B, UV pulsed laser light 10 is irradiated from two directions of the surface and the glass substrate 1 side to crystallize the channel portion 4C and crystallize the source portion 4S and the drain portion 4D. The impurities are activated together with the activation. In this case, the irradiation conditions of the laser light of the source and drain parts 4S and 4D and the channel part 4C are changed to select the respective appropriate conditions.

In this embodiment, the channel portion 4C and the source,
Since the irradiation conditions of the laser light to the drain portions 4S and 4D can be selected as optimum conditions, the characteristics can be further improved.
Also, the film thickness of the a-Si: H film 4 can be made sufficiently thin. Also, in this embodiment, the same operational effects as those described in the embodiment of FIG. 1 are also obtained.

When the embodiment of FIGS. 1 and 2 is applied to a liquid crystal display or the like, it is necessary to cover the entire surface with an alignment insulating layer such as SiO ₂ . When this layer is formed at a high temperature of about 300 ° C., A1 cannot be used for the source and drain electrodes, but if a low temperature process such as vapor deposition is used, all except low temperature deposition of SiO ₂ and a-Si: H by plasma ( It is possible to fabricate a high-performance thin film transistor array by the (room temperature) process.

According to the above-described embodiment, the mobility of the thin film transistor can be increased by crystallizing the a-Si: H film of the channel portion at a so-called room temperature without producing hydrogen without raising the temperature of the entire substrate. Therefore, fast switching characteristics can be obtained. In addition, the a-Si: H film is crystallized and the n ⁺ -a-Si: H film 5 can be omitted so that the film thickness can be made sufficiently thin, so that the photoconductivity is small and the leak current does not flow even when light is irradiated. Like Therefore, the light shielding layer can be omitted.

By using short-wavelength pulsed laser light of high energy and short time, crystallization and activation of impurities after ion implantation can be performed at the same time. Further, by using this short wavelength pulsed laser light, aS
The i: H film can be crystallized, so that the crystallization process can be performed after the electrode formation and the passivation film formation.

Therefore, the structure and manufacturing process of the thin film transistor are simplified, and the production yield is improved.

Further, since the amorphous semiconductor thin film can be polycrystallized in a low temperature atmosphere by using the short wavelength pulsed laser light, it is possible to form a high performance thin film transistor on the glass substrate 1 having low heat resistance. You can

In particular, when an amorphous semiconductor thin film having a film thickness of 100Å to 1000Å is irradiated with short-wavelength pulsed laser light having a wavelength of 100 nm to 400 nm, the laser light is absorbed almost 100% inside the thin film, and the laser light is absorbed on the substrate side. Since it does not leak, a low heat resistant substrate such as a glass substrate can be used as the substrate, and the melt crystallization of the amorphous semiconductor thin film formed on this low heat resistant substrate becomes possible. And with crystallization,
When the film thickness is as thin as 100Å to 1000Å, the photoconductivity is further reduced and the generation of leak current can be eliminated.
A thin film transistor with excellent characteristics can be obtained.

When applied to the manufacture of a thin film transistor array, uniform characteristics can be obtained for each transistor.

[0031]

According to the present invention, the amorphous semiconductor thin film on the amorphous substrate can be polycrystallized by using the short-wavelength pulsed laser light, and can be converted into a thin film having high mobility.

Further, since the polycrystal is formed, the ohmic contact between the source and drain portions is completed, and the impurities are sufficiently activated at the same time as the polycrystallization, so that the interface characteristic with the channel portion is improved. You can Since polycrystallization and activation of impurities are performed at the same time, the process can be simplified.

Moreover, since this polycrystallization and activation can be performed at so-called room temperature without raising the temperature of the entire substrate, the polycrystallization and activation steps can be performed after the electrode formation and the passivation film formation. Therefore, a thin film transistor with improved performance can be manufactured on an amorphous substrate, and the manufacturing thereof is facilitated.

Further, as described above, by using the short-wavelength pulsed laser light, without raising the temperature of the entire substrate,
Therefore, since the amorphous semiconductor thin film can be polycrystallized in a low temperature (room temperature) atmosphere, a low heat resistant substrate such as a glass substrate can be used as the substrate, and the above high quality thin film transistor can be formed on the low heat resistant substrate. It becomes possible to do.

[Brief description of drawings]

FIG. 1A is a process drawing showing an example of a method of manufacturing a thin film transistor according to the present invention. B is a process drawing showing an example of a method of manufacturing a thin film transistor according to the present invention. FIG.

2A is a process drawing showing another embodiment of the method for producing the thin film transistor according to the present invention. FIG. B is a process drawing showing another embodiment of the method for manufacturing the thin film transistor according to the present invention. FIG.

FIG. 3A is a process drawing showing an example of a conventional method for manufacturing a thin film transistor. B is a process drawing showing an example of a method of manufacturing a conventional thin film transistor. C is a process drawing showing an example of a conventional method for manufacturing a thin film transistor. D is a process drawing showing an example of a conventional method of manufacturing a thin film transistor.

[Explanation of symbols]

1 glass substrate 2 gate electrode 3 SiO ₂ film 4 a-Si: H film 4S source region 4D drain region 4C channel unit 5 n ⁺ -a-Si: H film 6 source electrode 7 drain electrode 8 SiO ₂ film 10 short-wavelength pulse Laser light

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication H01L 21/20 8122-4M 21/265 21/268 Z 8617-4M 27/12 R 8617-4M H01L 21/265 B

Claims (1)

[Claims] 1. A method of manufacturing a thin film transistor in which a gate electrode, a gate insulating film, a source region, a drain region and a channel region are formed on an amorphous substrate, wherein an amorphous semiconductor thin film is formed on the amorphous substrate. And a step of injecting an impurity into a region of the semiconductor thin film where a source and a drain are formed, and at least a region where the source and the drain are formed are melted and heated by irradiation with a short wavelength pulse laser having a wavelength of 100 nm to 400 nm. A method of manufacturing a thin film transistor, comprising the steps of activating impurities and polycrystallizing.