JPH07335896A - Manufacture of thin film transistor - Google Patents

Abstract

PURPOSE:To prevent damage on an Al gate electrode in the case of high dosage, by forming a protective film on the gate electrode composed of aluminum which film is composed of material having a sputtering resistance higher than aluminum. CONSTITUTION:After a-Si is deposited on a glass substrate 1, the a-Si is crystallized by excimer laser annealing, and a poly-Si film 2-0 turning to an operating layer is obtained. After aluminum is deposited and then molybdenum is deposited, by using a sputtering equipment, on the poly-Si film 2 patterned in an island type, a protective metal layer 5-1 and a gate electrode 5 are formed. These are used as masks, and impurities are introduced in a source electrode part 4-1 and a drain electrode part 4-2 by using an ion doping equipment. In a poly-Si TFT which is formed further by necessary processes, the damage on the gate electrode can be prevented in the case of high impurity dosage, because the aluminum of the gate electrode 5 is covered with the protective metal layer 5-1 composed of molybdenum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thin film transistor, and more particularly to a method of manufacturing a thin film transistor using a polycrystalline silicon layer provided on an insulating substrate.

[0002]

2. Description of the Related Art In recent years, active matrix liquid crystal display devices using polysilicon thin film transistors (hereinafter referred to as "poly-Si TFTs") have been actively researched, which are two digits larger than those of conventional amorphous silicon (a-Si) thin film transistors. Due to the high operation speed, it is possible to reduce the size by reducing the size and integrating a drive IC, which has been conventionally arranged outside the display panel, into the panel. The RC time constant becomes large and becomes a problem, so the literature, Extended Abstracts o
f the 1993 International C
onence on Solid State
Devices and Materials, 199
3, pp. As shown in No. 425-427, the gate electrode is made of aluminum (Al) having a very low sheet resistance.
A structure using a gate line has been proposed.
Attempts have been made to reduce the time constant.

A production process in such a case is shown in FIG. LPCVD or p-CVD on glass substrate (11)
After depositing a-Si by the method such as pol, it is crystallized by furnace annealing or laser annealing to become an operating layer
A y-Si film (21-0) is obtained (a). Then poly
-Si film is patterned into islands (21), ECR-
A gate insulating film such as SiO ₂ (3
1) is deposited (b). Al as the gate electrode (51)
After depositing and patterning, the gate electrode is used as a mask and the source electrode part (41-1) / drain electrode part (41-
Impurity is introduced into 2) (c). Here, when a glass substrate which has a large area but has a strain point near 600 ° C. and must be set to a comparatively low temperature of 600 ° C. or lower is used as an impurity introducing device. Ion doping equipment is often used. Here, in general, an ion doping apparatus is different from an ion implantation apparatus in that it cannot perform mass separation. Therefore, at present, all the ions generated from the ion source are introduced into the material. However, since the area of the ion beam itself taken out from the ion source is large, it is a device that can easily process a large area substrate in a short time. Moreover, the temperature of the impurity activation annealing after introduction is about 300 ° C to 500 ° C. It has the important feature that it can be carried out at extremely low temperatures. The reason for the latter is due to the effect of so-called hydrogen beam annealing (hydrogen beam assist), which is caused by the simultaneous implantation of a large amount of hydrogen generated in the ion source when introducing impurities as described in the above-mentioned document. It is generally said that there is. It is known that Al deteriorates when it is subjected to heat treatment at 500 ° C. or higher. Therefore, in a manufacturing process using Al for a gate electrode, as a means for introducing impurities, such as an ion doping apparatus, implantation is performed. It is very important to use a device that can cool the subsequent annealing temperature to a relatively low temperature. Conversely, the realization of such a device solves the problem that until now, only chromium or tantalum, which has high temperature resistance but high sheet resistance, can be used. Furthermore, in the process of manufacturing the TFT, S
An interlayer insulating film (61) such as iO ₂ is deposited, openings (71-1, 71-2) for taking out electrodes are formed, and Al is deposited and patterned to form a wiring (81).
-Si TFT was formed (d).

[0004]

By the way, in this way, A
l When the impurities are introduced into the source electrode part / drain electrode part with an ion doping device using the gate electrode as a mask, the Al electrode is damaged, and the film is slipped or a part of the linear Al electrode pattern is uneven. The present inventor has found out that there is a problem that it will occur. The former increased the sheet resistance of the gate electrode, and the latter varied the channel length defined by the gate electrode in the substrate. This is because Al, which has a small mass, is easily sputtered by phosphorus (P) and boron (B) which are the implantation impurities, and particularly when the accelerating voltage at the time of implantation is high or the implantation dose amount is large. Met. Generally, the sheet resistance of the source and drain electrodes is 1 kΩ
It is necessary to have a low value of □ / □ or less. For that purpose, the dose amount of impurities is 5 × 10 ¹⁵ / cm ³ to 1 × 10 5.
^It is necessary to implant impurities of about ¹⁶ / cm ³ . Here, if the dose amount is reduced, the sheet resistance of the source electrode / drain electrode increases and the contact resistance with the Al wiring also increases. However, 1 × 10
^{When the} dose amount is as high as ¹⁶ / cm ³ , Al is sputtered violently, and the pattern disappears in some cases, so that there is a serious problem that the Al gate electrode itself cannot be formed. Therefore, conventionally, it has been difficult to use Al for the gate electrode, which can reduce the RC time constant of the gate electrode line. Alternatively, even if Al is used for the gate electrode, in this case, a sufficient amount of impurities cannot be introduced into the source / drain electrode portion, so that the source / drain electrode portion is removed.
There is a problem that the sheet resistance of the drain electrode and the contact resistance with the Al wiring become high, and the device performance of the display device and the like becomes insufficient.

Further, for example, an n-channel TFT is formed on the substrate.
In the process of manufacturing only Al, for example, a resist mask on Al used when processing the Al gate may be arranged as it is, and Al may not be directly exposed to impurities when impurities are introduced. But,
In that case, the temperature of the resist mask is likely to rise due to a large amount of implanted hydrogen or the like, as shown in the above-mentioned document. As a result, the resist is hardened, which causes a serious problem that it becomes difficult to remove the resist after the injection. Also,
Since the resist mask is sputtered, there is a problem that the inside of the doping apparatus is contaminated by the scattered resist. Therefore, it is actually difficult to leave the resist mask on Al used when processing the Al gate as it is and introduce impurities.

[0006] Further, in terms of the performance of the device to be manufactured, a-Si
One of the important advantages of using a poly-Si TFT, unlike a TFT, is that both n-channel and p-channel types can be formed on the same substrate, and a so-called CMOS circuit can be built in. However, when this CMOS circuit is formed, the gate electrodes of both the n-channel TFT and the p-channel TFT are exposed to the impurities, and the above problems occur. This is because, in the case of forming both channels, the processing mask (resist or the like) used when forming the gate electrode is removed, and thereafter, for example, the p channel portion is protected by using a new mask and impurities are implanted. The source of the n-channel section is
This is because an impurity (for example, phosphorus) is selectively injected into the drain portion. Next, protect the n-channel part and p
Even when implanting an impurity (for example, boron) into the source / drain portion of the channel portion, the Al gate electrode of the p-channel portion is exposed to the impurity. Therefore, when the Al gate electrode is used, a poly-Si TFT is formed on the substrate.
Therefore, the CMOS circuit cannot be configured, which is a problem.

[0007]

In order to solve the above problems, according to the present invention, a polycrystalline silicon layer, a gate insulating layer and a gate electrode layer made of aluminum are sequentially provided on an insulating substrate, and the gate made of aluminum is formed. In a method of manufacturing a thin film transistor in which an impurity is introduced into the polycrystalline silicon layer by an ion doping method or an ion implantation method using an electrode as a mask to form a source / drain region, aluminum is formed on the gate electrode made of aluminum before the introduction of the impurity. The problem is solved by providing a protective film made of a material having a higher sputtering resistance than that of the above. When impurities are introduced into the polycrystalline silicon layer by the ion implantation method, hydrogen ions are implanted at the same time when the impurities are introduced.

According to the invention of claim 3, claim 1
In the method of manufacturing a thin film transistor described above, the problem is solved by the protective film being made of a refractory metal or a refractory metal alloy.

According to the invention of claim 4, claim 1
In the method of manufacturing a thin film transistor described above, the problem is solved by the protective film being an inorganic insulating film.

[0010]

According to the present invention, the activation annealing temperature can be lowered by introducing impurities into the polycrystalline silicon layer by the ion doping method or the ion implantation method in which hydrogen ions are simultaneously implanted. By forming a protective film made of a material having higher sputtering resistance than aluminum on the gate electrode made of aluminum, it is possible to prevent damage to the Al gate electrode even with a high dose amount.

[0011]

EXAMPLES The present invention will be specifically described below based on examples. (Embodiment 1) A first embodiment of the present invention is shown in FIG. First, 450 ° by the LPCVD method on the glass substrate (1).
248 after depositing 100 nm thick a-Si in C
A poly-Si film (2-0) was obtained which was crystallized with an energy of 450 mJ / cm ² by using excimer laser annealing with a wavelength of nm and a pulse width of 25 nsec to form an operating layer (a). The a-Si is momentarily heated to 1000 ° C or higher by a laser and melted, but the melting time is about 100
Since it is extremely short, about nsec, the glass substrate is not damaged by heat. Subsequently, the poly-Si film was patterned into an island shape (2), and a gate insulating film (3) made of SiO ₂ and having a thickness of 100 nm was deposited at room temperature by the ECR-CVD method (b). As a gate electrode, Al (5) with a thickness of 400 nm is deposited at 150 ° C. by a sputtering device, and molybdenum (M) is continuously deposited in the same device.
o) (5-1) was deposited to 100 nm. A resist pattern was formed on the gate electrode by using a photolithography technique, and Mo / Al was continuously etched by using a solution of phosphoric acid / nitric acid with the resist as a mask. After the resist is peeled off to form a pattern, the gate electrode is used as a mask and the source electrode portion (4-
1) -Impurities were introduced into the drain electrode portion (4-2) (c). The implantation conditions are different depending on whether the source / drain electrode portion is of n ⁺ type or p ⁺ type.
5% PH ₃ diluted with hydrogen at 100 keV 1 × 10 ¹⁶ cm
^-2 , 40 keV ^{1x10 16} of 5% B ₂ H ₆ diluted with hydrogen
It was cm ^-2 . After introduction, activation annealing of impurities was performed at 400 ° C. for 1 hour in a nitrogen atmosphere. If the activation annealing temperature is such a low temperature, Al itself will not be altered by heat. 250 ° by p-CVD
Interlayer insulating film made of SiO ₂ with a thickness of 1 μm at C (6)
And deposit openings (7-1, 7-
2) was opened by wet etching with hydrofluoric acid, and Al having a thickness of 1 μm was deposited and patterned at 150 ° C. by a sputtering device to form a wiring (8) (d).

Poly-Si produced in this way
The sheet resistance of the source and drain electrodes of the TFT is n ⁺
Type and p ⁺ type were 590 Ω / □ and 940 Ω / □, respectively. In addition, although the impurity dose amount as high as 1 × 10 ¹⁶ cm ^-2 was introduced, since the Al of the gate electrode was covered with Mo, the attack due to the introduction did not occur, and the alteration or damage of the gate electrode or the film formation. There was no slip. The sheet resistance of the gate electrode of the produced poly-Si TFT was 0.8Ω / □, which was a good value. It was found that not only Mo but also tantalum, chromium, and titanium have such doping resistance.
By covering the Al surface with a refractory metal such as Mo,
It is possible to avoid attack on Al when introducing impurities. This is because refractory metals and their alloys are generally less likely to be sputtered than Al. Therefore, according to the present invention, a high-performance and highly uniform poly-Si TFT mainly composed of Al having a low sheet resistance could be manufactured.

When a metal material is used as the protective film, the metal protective film can be continuously deposited at the time of Al deposition, and the process can be simplified because the Al gate electrode can be processed all at once. The thickness of the metal film for protecting Al is preferably 10 nm or more, and more preferably 100 nm or more. This is because when a metal film is deposited by a sputtering device or an electron beam evaporation device, if the film thickness is as thin as 10 nm or less, the metal has an island shape and has not grown to a film.
In that case, the film quality including the sheet resistance becomes unstable, and the protective metal film cannot be formed with good reproducibility. Further, if the film thickness of the metal film is too thin, Al under the metal film is sputtered, so a film thickness of 100 nm or more is desirable if possible. If there is no other problem, the protective metal film on Al may be used only at the time of introducing impurities and finally removed.

(Embodiment 2) A second embodiment of the present invention is shown in FIG.
Shown in. First, 100-nm-thick a-Si was deposited on a glass substrate (1) at 450 ° C. by LPCVD, and then an excimer laser annealing with a pulse width of 25 ns and a wavelength of 248 nm was used at an energy of 450 mJ / cm ² . Poly-Si film (2-0) that crystallizes and becomes an operating layer
Was obtained (a). Subsequently, the poly-Si film is patterned into an island shape (2), and is subjected to 1 at room temperature by ECR-CVD method.
A gate insulating film (3) made of SiO ₂ having a thickness of 00 nm was deposited (b). As a gate electrode, Al (5) having a thickness of 400 nm is deposited at 150 ° C. by a sputtering device,
Further, silicon oxide (SiO ₂ ) (5-2) was deposited to 100 nm by the p-CVD method at 250 ° C. A resist pattern was formed on the gate electrode by photolithography, SiO ₂ was etched with hydrofluoric acid, and then Al was etched with a solution of phosphoric acid / nitric acid. After removing the resist and forming the pattern,
Using this gate electrode as a mask, impurities were introduced into the source electrode portion (4-1) and the drain electrode portion (4-2) by an ion doping apparatus (c). The implantation conditions differ depending on whether the source / drain electrode portion is of n ⁺ type or p ⁺ type, and 5% PH ₃ diluted with hydrogen at 100 keV is used at 1 × 10 ¹⁶ cm ^-2 and 40 keV, respectively. 5% diluted B ₂ H ₆
^Was 1 × 10 ¹⁶ cm ^-2 . After introduction, activation annealing of impurities was performed at 400 ° C. for 1 hour in a nitrogen atmosphere. Furthermore, an interlayer insulating film (6) made of SiO ₂ having a thickness of 1 μm is deposited at 250 ° C. by p-CVD, and openings (7-1, 7-2) for taking out electrodes are formed by wet etching with hydrofluoric acid. Aperture, 1 by sputtering equipment
Wiring (8) was formed by depositing and patterning 1 μm thick Al at 50 ° C. (d).

The poly-Si produced in this way
The sheet resistance of the source and drain electrodes of the TFT is n ⁺
Type and p ⁺ type were 590 Ω / □ and 940 Ω / □, respectively. In addition, although the impurity dose amount as high as 1 × 10 ¹⁶ cm ^-2 was introduced, since the Al of the gate electrode was covered with SiO ₂ , the attack due to the introduction did not occur and the alteration or damage of the gate electrode or There was no membrane slip. The sheet resistance of the gate electrode of the produced poly-Si TFT was as good as 0.9Ω / □. Not only SiO ₂ but also silicon nitride (S
It has been found that iN) and silicon nitride / silicon oxide (SiON) also have such doping resistance. By covering the Al surface with an inorganic insulating film having high sputtering resistance, it is possible to avoid attack on Al when introducing impurities.
Therefore, according to the present invention, a high-performance and highly uniform poly-Si TFT mainly composed of Al having a low sheet resistance could be manufactured.

The second embodiment is different from the first embodiment in that the protective film of the Al gate electrode is not a metal but an inorganic insulating film. As the protective film for the Al gate electrode, an inorganic insulating film is generally preferable because it has higher sputtering resistance than metal. The thickness of the inorganic insulating film that protects Al is 1
It is preferably 0 nm or more, and preferably 100 nm or more. This is because, similarly to the first embodiment, it is desirable that the inorganic insulating film having a stable film quality is formed and Al under the protective film is not sputtered. If there are no other problems, this A
As in the first embodiment, the protective film on l may be used only at the time of introducing impurities and may be finally removed.

(Embodiment 3) In the third embodiment, an ion implantation apparatus is used as an impurity introducing means instead of an ion doping apparatus. In the normal operation of the ion implantation device, only the desired ions (for example, phosphorus) among the ions generated from the ion source are separated into the material, and the desired ions and hydrogen ions are also implanted in the ion implantation device. By doing so, the hydrogen beam annealing effect similar to that of the ion doping apparatus can be realized. This embodiment will be specifically described with reference to FIG. 1 used in the first embodiment.

First, 100-nm-thick a-Si was deposited on the glass substrate (1) at 450 ° C. by the LPCVD method, and then 450 mJ / cm ² was obtained by using excimer laser annealing with a pulse width of 25 nsec at a wavelength of 248 nm. A poly-Si film (2-0) which was crystallized by energy and became an operation layer was obtained (a). 1 for a-Si by laser
The glass substrate is momentarily heated to 000 ° C. or higher and melted, but the melting time is extremely short, about 100 nsec, so that the glass substrate is not thermally damaged. Then poly
-Si film is patterned into islands (2), ECR-C
A gate insulating film (3) made of SiO ₂ and having a thickness of 100 nm was deposited at room temperature by the VD method (b). As a gate electrode, Al (5) having a thickness of 400 nm was deposited at 150 ° C. by a sputtering device, and then 100 nm of molybdenum (Mo) (5-1) was continuously deposited in the same device. A resist pattern was formed on the gate electrode by using a photolithography technique, and Mo / Al was continuously etched by using a solution of phosphoric acid / nitric acid with the resist as a mask. After the resist was peeled off to form a pattern, impurities were introduced into the source electrode portion (4-1) and the drain electrode portion (4-2) by an ion implantation device using this gate electrode as a mask (c). The implantation conditions are as follows:
^The difference between the case of the ⁺ type and the case of the p ⁺ type is that P (phosphorus) is 1 × 10 ¹⁶ cm ⁻² and 4 at 100 keV, respectively.
B (boron) was 1 × 10 ¹⁶ cm ^-2 at 0 keV. However, at the same time, hydrogen was also introduced at 1 × 10 ¹⁶ cm ^{-2 at} 100 keV or 40 keV, respectively. In order to introduce hydrogen ions in addition to the desired ions at the same time, at least two ion sources were provided so that this simultaneous injection could be performed. After introduction, activation annealing of impurities was performed at 400 ° C. for 1 hour in a nitrogen atmosphere. If the activation annealing temperature is such a low temperature, Al itself will not be altered by heat. 250 ° C by p-CVD
At this time, an interlayer insulating film (6) made of SiO ₂ having a thickness of 1 μm is deposited, and openings (7-1, 7-2) for taking out electrodes are formed.
Is opened by wet etching with hydrofluoric acid, and Al having a thickness of 1 μm is deposited at 150 ° C. by a sputtering device.
The wiring (8) was formed by patterning (d).

The poly-Si produced in this way
The sheet resistance of the source and drain electrodes of the TFT is n ⁺
Type and p ⁺ type were 590 Ω / □ and 940 Ω / □, respectively. In addition, although the impurity dose amount as high as 1 × 10 ¹⁶ cm ^-2 was introduced, since the Al of the gate electrode was covered with Mo, the attack due to the introduction did not occur, and the alteration or damage of the gate electrode or the film formation. There was no slip. The sheet resistance of the gate electrode of the produced poly-Si TFT was 0.8Ω / □, which was a good value. Therefore, according to the present invention, a high-performance and highly uniform poly-Si TFT mainly composed of Al having a low sheet resistance could be manufactured. In the third embodiment, unlike the first embodiment, the ion implantation apparatus is used, so that the size of the ion beam is small, and thus the throughput is lower than that in the first embodiment. However, since hydrogen can be injected at the same time, the annealing temperature after the introduction can be maintained at a relatively low temperature and a good sheet resistance can be realized, as in the ion-ooping apparatus.

[0020]

According to the present invention, a gate electrode made of aluminum having a low sheet resistance can be manufactured without causing damage. Further, by providing a protective film made of a material having a higher sputtering resistance than aluminum on the gate electrode, the source / drain electrode can be formed without damaging the gate electrode even with a high dose amount. Therefore, high performance and highly uniform poly-Si TF
T can be provided.

[Brief description of drawings]

FIG. 1 is a sectional view of an element in each step for explaining first and third embodiments of the present invention.

FIG. 2 is a sectional view of an element in each step for explaining a second embodiment of the present invention.

FIG. 3 is a sectional view of an element in a conventional method for manufacturing a poly-Si TFT.

[Explanation of symbols]

1, 11 ... Glass substrate, 2, 21 ... poly-
Si operating layer, 3, 31 ... Gate insulating film, 4-1, 4
1-1 ... Source electrode part, 4-2, 41-2 ... Drain electrode part, 5, 51 ... Al gate electrode, 5-1
... Protective metal layer, 5-2 ... Protective insulating film layer, 6,6
DESCRIPTION OF SYMBOLS 1 ... Interlayer insulating film, 7-1, 71-1 ... Source electrode part opening, 7-2, 71-2 ... Drain electrode part opening, 8, 81 ... Al wiring

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location 9056-4M H01L 29/78 311 G

Claims (4)

[Claims] 1. A polycrystalline silicon layer, a gate insulating layer, and a gate electrode layer made of aluminum are sequentially provided on an insulating substrate, and impurities are doped into the polycrystalline silicon layer by an ion doping method using the gate electrode made of aluminum as a mask. In a method of manufacturing a thin film transistor in which a source / drain region is formed by introduction, a protective film made of a material having higher sputtering resistance than aluminum is provided on the gate electrode made of aluminum before the introduction of the impurities. Production method. 2. A polycrystalline silicon layer, a gate insulating layer, and a gate electrode layer made of aluminum are sequentially provided on an insulating substrate, and impurities are added to the polycrystalline silicon layer by an ion implantation method using the gate electrode made of aluminum as a mask. In a method of manufacturing a thin film transistor in which a source / drain region is formed by introducing, a protective film made of a material having higher sputtering resistance than aluminum is provided on the gate electrode made of aluminum before the introduction of the impurity, and the introduction of the impurity is performed. A method of manufacturing a thin film transistor, which comprises simultaneously implanting hydrogen ions. 3. The method of manufacturing a thin film transistor according to claim 1, wherein the protective film is made of a refractory metal or an alloy of a refractory metal. 4. The method of manufacturing a thin film transistor according to claim 1, wherein the protective film is an inorganic insulating film.