JPH07118443B2 - Manufacturing method of semiconductor device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a semiconductor device such as a thin film transistor (TFT).

Background Art and its Problems 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. First
The figure shows an example of a conventional method of manufacturing a thin film transistor on a glass substrate. First, as shown in FIG. 1A, after forming a gate electrode (2) of aluminum or indium tin oxide (hereinafter abbreviated as ITO) on a glass substrate (1), a SiO ₂ film (3), Hydrogenated amorphous silicon (hereinafter abbreviated as a-Si: H) film (4) and n-type a-Si: H (n ⁺ -a-Si: H) film (5) for ohmic contact are continuously plasma-enhanced by plasma CVD. It is deposited on the entire surface by the method. Then a-Si: H film (4)
And the n ⁺ -a-Si: H film (5) is patterned to form island regions in the portions necessary for producing thin film transistors. Next, as shown in FIG. 1B, Al / Mo2 is formed on the source and drain portions.
A source electrode (6) and a drain electrode (7) are formed of a layer film structure, molybdenum, titanium, or nichrome. Next, as shown in FIG. 1C, 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, and the n Eliminate leakage current. Then, as shown in FIG. 1D, a SiO ₂ layer (8) for passivation and liquid crystal alignment is formed on the entire surface, and a light shielding layer (9) is formed so as to cover a portion corresponding to the channel portion. To form a thin film transistor.

In this manufacturing method, as a mask used for photolithography, a-Si: H for pattern formation of the gate electrode (2) is used.
For forming island regions of the film (4), for forming patterns of the source and drain electrodes (6) and (7), and further for a light shielding layer (9)
At least four masks for pattern formation are required.
If the film thickness of a-Si: H (4) is about 0.5 μm, n ⁺ −
A sufficient thickness cannot be left when the a-Si: H film (5) is removed by etching, unevenness in the etching process of the n ⁺ -a-Si: H film (5), and the a-Si: H film (4) However, there is a drawback in that it is difficult to obtain a large number of thin film transistors having uniform characteristics over a wide area due to the unevenness of deposition. If the a-Si: H film (4) is thick, the thickness of the source and drain electrodes (6) and (7) is 1 μm.
If it is not so high, breaks easily occur.

Since such a thick a-Si: H film (4) has a large photoconductivity of a-Si: H, a light-shielding layer (9) for shielding light is required, which makes the manufacturing process more complicated. There is. a
-Si: H film (4) has been hydrogenated, so there are few defects in the film, an on / off ratio of 10 ⁶ is usually obtained, and the threshold voltage Vth = 5V.
You can get something. However, since it is amorphous, the effective mobility is as small as 0.1 to 0.5 cm ² / V · S, and fast switching characteristics cannot be obtained.

SUMMARY OF THE INVENTION In view of the above points, the present invention provides a method of manufacturing a semiconductor device such as a thin film transistor, which can be manufactured easily and whose performance can be improved.

SUMMARY OF THE INVENTION The present invention, after forming an amorphous silicon thin film having a film thickness of 100 Å ~ 1000 Å on an amorphous substrate, a short wavelength pulse laser light having a wavelength of 100 nm ~ 400 nm absorbed on the surface of the amorphous silicon thin film. A method for manufacturing a semiconductor device is characterized in that the amorphous silicon thin film is irradiated and heat treatment for polycrystallizing the amorphous silicon thin film is performed.

According to the manufacturing method of the present invention, the amorphous silicon thin film can be crystallized and impurities can be activated at a low temperature (room temperature) without raising the temperature of the entire substrate to improve the performance. In addition, manufacturing becomes easy.

Example In the present invention, when the amorphous silicon 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 amorphous silicon thin film, and then the internal portion of the thin film is thermally conductive. Is melted and recrystallized, or annealed to increase the size of crystal grains, thereby manufacturing a semiconductor device such as a thin film transistor.

For example, when an a-Si: H film is used as an amorphous silicon thin film and this is irradiated with XeCl excimer laser light with a wavelength of 308 nm, the absorption coefficient for this wavelength reaches 10 ⁶ cm ^-1 , so the surface (about 100 Å) Is absorbed by and converted into heat.
This heat is immediately transferred to the inside of the thin film by heat conduction. In this way, the surface or inside of the film is momentarily heated to a high temperature.
The Si: H film is crystallized without releasing hydrogen, and its characteristics change significantly. 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 crystal grain boundaries even after crystallization.

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 to 10 ⁸ W / c.
m ² or less, 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 200 to 500 mJ / cm ² . If such a short wavelength pulsed laser beam is used, local heating can be performed.

Next, embodiments of the present invention will be described with reference to the drawings. In addition, each example is a case where it is applied to manufacture of a thin film transistor similar to that in FIG.

FIG. 2 shows an embodiment of the present invention. In this example, first, as shown in FIG. 2A, after forming the gate electrode (2) of aluminum or ITO on the glass substrate (1), SiO 2 is formed.
_{The 2} film (3), the a-Si: H film (4) and the n ⁺ -a-Si: H film (5) are sequentially deposited on the entire surface by the plasma CVD method. Next a
By patterning the -Si: H film (4) and the n ⁺ -a-Si: H film (5), a portion for forming a thin film transistor is formed into an island region.

Next, as shown in FIG. 2B, a source electrode (6) and a drain electrode (7) made of, for example, molybdenum, titanium, or nichrome are formed, and both electrodes (6) and (7) are used as a mask to form a channel portion. The n ⁺ -a-Si: H film (5) on the corresponding portion is selectively removed by plasma etching or the like (FIG. 2C). The steps up to this point are the same as the steps shown in FIGS.

Next, as shown in FIG. 2D, after a SiO ₂ film (8) is formed on the entire surface, a short wavelength pulse laser beam, that is, UV
Irradiation with (ultraviolet) pulsed laser light (10) is performed to polycrystallize the channel portion (4C) of the a-Si: H film (4) to obtain the target thin film transistor.

In this manufacturing method, the mobility of the thin film transistor can be increased because the a-Si: H film of the channel portion (4C) can be crystallized without releasing hydrogen. Also, the crystallization of the a-Si: H film reduces the photoconductivity, and the generation of leak current is reduced even when exposed to light. Therefore, the conventional light-shielding layer (9) covering the channel portion and the masking process therefor can be omitted. The UV pulsed laser light (10) passes through the SiO ₂ film (8),
Since the light is reflected by the electrodes (6) and (7), the temperature does not rise, and the channel portion can be processed without damaging the electrodes (6) and (7). By the way, in a long-wavelength laser such as an argon laser or a YAG laser, when the film is thin, light absorption is small and irradiation is performed for a long time. Therefore, the temperature of the entire a-Si: H film rises and the heat of the substrate The influence is increased and the substrate is likely to be deformed, and the SiO ₂ film (8), the electrodes (6), (7) and the like are easily damaged.

In this way, laser irradiation (by so-called self-alignment) is performed by using the electrodes (6) and (7) as masks to perform local crystallization, thereby depositing the a-Si: H film (4), the electrode (6) ( Even after the formation of 7), it is possible to crystallize at a low temperature without raising the temperature other than the irradiated portion to a very high temperature. Therefore, the structure and manufacturing process of the thin film transistor can be simplified.

FIG. 3 shows another embodiment applied to a planar type thin film transistor manufacturing method.

This is done on the glass substrate (1) as shown in FIG. 3A.
A Si: H film (4) and a SiO ₂ film (3) are sequentially deposited and patterned to form island regions. Next in the channel section (4
A gate electrode (2) made of, for example, titanium, molybdenum, or nichrome is formed on the SiO ₂ film (3) corresponding to C), and the gate electrode (2) is used as a mask to form an a-Si: H film (4). Into the source part (4S) and the drain part (4D) of the above, the necessary impurities such as phosphorus or boron are ion-implanted.

Next, as shown in FIG. 3B, the source and drain portions (4
S) and (4D) are partially connected, such as molybdenum,
A source electrode (6) and a drain electrode (7) made of titanium, nichrome, ITO or the like are deposited, and a SiO ₂ film (8) is deposited. Then, UV pulse laser light (10) is irradiated from the glass substrate (1) side. As a result, the source and drain parts (4S) and (4D) are activated, and the channel part (4C) is crystallized.

In this case, if quartz glass or Pyrex glass is used for the glass substrate (1), laser light having a wavelength of 308 nm, for example, is transmitted, so the light changes to heat at the interface between the a-Si: H film (4) and the glass substrate (1). , A-Si: H film (4) is heat-treated. Thus, the target thin film transistor is obtained.

Further, since the UV pulsed laser light is used, only the a-Si: H thin 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 the long wavelength pulse (or There is no lateral impurity diffusion as when using continuous laser light.

In this embodiment, a of source and drain parts (4S) and (4D)
Since the -Si: H film is also crystallized without releasing hydrogen, the ohmic contact is completed and the impurities are sufficiently activated, so that the interface characteristics with the channel portion can be improved. Also, the a-Si: H film (4) can be made sufficiently thin, and the film thickness is 100
Since the range from Å to 1000Å is possible, the photoconductivity can be further reduced and the generation of leak current can be reduced due to the thin film thickness in addition to the crystallization of the a-Si: H film. . Furthermore, since the a-Si: H film (4) can be made thin, disconnection of the source and drain electrodes does not occur.

FIG. 4 shows another embodiment applied to a method of manufacturing a staggered thin film transistor.

This is done by forming a source electrode (6) and a drain electrode (7) of, for example, molybdenum, titanium, nichrome or ITO on the glass substrate (1) as shown in FIG.
-Si: H film (4), to form a SiO ₂ film (3). Further, for example, a gate electrode (2) made of aluminum or ITO is formed, and a SiO ₂ film (8) is deposited on the entire surface of the island region. Then, necessary impurities such as phosphorus or boron are ion-implanted into the a-Si: H film corresponding to the source and drain portions (4S) and (4D).

Next, as shown in FIG. 4B, UV pulse laser light (10) is irradiated from two directions on the surface and the glass substrate (1) side to crystallize the channel part (4C), and also to source and drain parts ( 4S) and (4D) are crystallized and impurities are activated. In this case, the source and drain parts (4S) and (4D)
And changing the irradiation condition of the laser light of the channel part (4C),
Select the appropriate conditions for each.

In this embodiment, the laser light irradiation conditions for the channel part (4C) and the source / drain parts (4S), (4D) can be selected as optimum conditions, so that the characteristics can be further improved. Also, a
The film thickness of the -Si: H film (4) can be made sufficiently thin.

5 and 6 show still another embodiment in which the ion implantation process is omitted. A metal having good ohmic characteristics, such as nichrome, is used for the source electrode (6) and the drain electrode (7) for both the a-Si: H film (4) which is not doped with impurities.
UV pulsed laser light (10) is applied from the front and back sides, and the channel part (4C), source part (4S), drain part (4)
Crystallize D). In this case, UV pulsed laser light (1
UV irradiation conditions (strength, time) are selected so that the electrode interface becomes sufficiently ohmic when the source / drain parts (4S) and (4D) are irradiated with (0). In some cases, for example, n ⁺
Phosphorus (P), arsenic (As), antimony (Sb) for shape
It is also possible to use source and drain electrodes (6), (7) containing trivalent elements such as boron (B), aluminum (Al), gallium (Ga), etc., for pentavalent elements such as P ^{+ type.} . As the source and drain electrodes (6) and (7), ITO, molybdenum, titanium or the like can be used in addition to nichrome. In this manufacturing method, the ion implantation step of impurities is omitted in particular, so that the manufacturing process is further simplified. The structure shown in FIG. 5 is obtained by omitting the n ⁺ -a-Si: H film (5) in the embodiment shown in FIG. 2, and therefore, compared with the structure shown in FIG. ) Can be made sufficiently thin, for example, can be set to about 200Å, its spectral conductivity is reduced, and the characteristics are further improved.

When the embodiment of FIGS. 2 to 6 is applied to a liquid crystal display or the like, it is necessary to cover the entire surface with an insulating layer for alignment such as SiO ₂ . When this layer is formed at a high temperature of about 300 ° C., Al cannot be used for the source and drain electrodes, but if a low temperature process such as vapor deposition is used, SiO ₂ and a
High-performance thin film transistor arrays can be fabricated by low temperature (room temperature) processes except for the deposition of -Si: H.

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 low temperature without releasing hydrogen without raising the temperature of the entire substrate. Fast switching characteristics can be obtained. Further, since the influence of heat on the substrate is less likely to occur, the substrate is less likely to be deformed.

Further, by crystallizing the a-Si: H film and making it sufficiently thin, the photoconductivity is small and the leak current becomes difficult to flow even when irradiated with light. Therefore, the light shielding layer is omitted. Also, by using a high-energy, short-time, short-wavelength pulsed laser light, the a-Si: H film can be crystallized at a low temperature, so that the crystallization process can be performed after the electrode formation and the passivation film formation. Become. Therefore, the structure and manufacturing process of the thin film transistor are simplified, and the production yield is improved. When applied to the manufacture of a thin film transistor array, uniform characteristics can be obtained for each transistor.

In the above example, the case of using the a-Si: H thin film was described, but in the case of an amorphous silicon thin film containing no hydrogen, the wavelength of 100 nm to 400 nm is the same as in the case of the a-Si: H thin film. For light, this light is absorbed at the polar surface and can be similarly implemented. At that time, regarding the ability to crystallize without causing substrate deformation, electrode formation, crystallization after formation of a passivation film, and activation of impurities, the same effect as in the case of an amorphous silicon thin film containing hydrogen can be obtained. is there.

EFFECTS OF THE INVENTION According to the present invention, by using a short-wavelength pulsed laser beam, only the extreme surface of the film is instantly heated, so that the influence of heat on the substrate is less likely to occur and the substrate is not deformed. The amorphous silicon thin film can be locally crystallized, impurities can be activated, and the amorphous silicon thin film can be converted into, for example, a thin film having high mobility. Moreover, since this crystallization and activation can be performed at a low temperature without raising the temperature of the entire substrate, the crystallization and activation steps can be performed after the electrode formation and the passivation film formation. In particular, when an amorphous silicon thin film with a film thickness of 100 Å to 1000 Å is irradiated with short-wavelength pulse laser light with a wavelength of 100 nm to 400 nm, the laser light is almost 10
Since it is absorbed by 0% and does not leak to the substrate side, it is possible to use a low heat resistant substrate such as a glass substrate, and it is possible to melt and crystallize the amorphous silicon thin film formed on this low heat resistant substrate. Becomes Therefore, when it is applied to, for example, a thin film transistor, its performance is improved and manufacturing is facilitated.

[Brief description of drawings]

FIG. 1 is a process drawing showing an example of a conventional thin film transistor manufacturing method, FIG. 2 is a process drawing showing an example of a thin film transistor manufacturing method according to the present invention, and FIGS. 3 to 6 are respectively thin film transistor manufacturing methods according to the present invention. It is sectional drawing which shows the other Example. (1) is a glass substrate, (2) is a gate electrode, (3) is Si
O ₂ film, (4) a-Si: H film, (5) n ⁺ -a-Si: H film,
(6) is a source electrode, (7) is a drain electrode, and (10) is short-wavelength pulsed laser light.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuo Kano 6-735 Kitashinagawa, Shinagawa-ku, Tokyo Sony Corporation (56) References JP-A-57-104217 (JP, A) JP-A-SHO 57-155726 (JP, A) JP-A-58-197717 (JP, A) JP-A-57-138129 (JP, A) JP-A-57-194518 (JP, A) JP-A-58-182816 (JP, A) A)

Claims (1)

[Claims] 1. An amorphous silicon thin film having a film thickness of 100Å to 1000Å is formed on an amorphous substrate, and then a short wavelength pulsed laser beam having a wavelength of 100 nm to 400 nm absorbed on the surface of the amorphous silicon thin film is irradiated. And a heat treatment for polycrystallizing the amorphous silicon thin film.