JPH0864837A - Fabrication of thin film semiconductor device - Google Patents

Abstract

PURPOSE: To eliminate the need of a laser antireflection film on an existing semiconductor thin film by radiating the laser beam from the rear surface side of a transparent insulating substrate. CONSTITUTION: The transparent insulating substrate 1 is irradiated with a laser beam having adequate energy from the rear side of a transparent insulating substrate 1 to crystallize a semiconductor thin film 2 and activate impurity. Since the gate electrode G is exposed in direct to the laser beam from the rear side in this processing, crystallization can be enabled. Since radiation of laser beam is performed from the rear side, the transparent insulating substrate 1 must be selected from the materials which do not absorb the laser beam. To limit the reflection at the rear side, it is preferable to determine the thickness of the transparent insulating substrate 1 in accordance with wavelength of the laser beam, which eliminates the need of a conventional antireflection coating on the semiconductor film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thin film semiconductor device. More specifically, it relates to a method of heat-treating a semiconductor thin film by laser light irradiation.

[0002]

2. Description of the Related Art As a high-resolution display, a large-sized and high-definition liquid crystal display panel using a polycrystalline silicon thin film transistor as a switching element is considered promising. In order to mass-produce a large-scale high-definition liquid crystal display panel using a polycrystalline silicon thin film transistor, it is essential to establish a low temperature process that can adopt a low-priced glass substrate. A technique that has been widely expected as a low-temperature process technique is a technique of irradiating a semiconductor thin film such as amorphous silicon with laser light to form high-quality polycrystalline silicon on a low-melting-point glass substrate.

[0003]

By the way, conventionally, when crystallizing or re-crystallizing a semiconductor thin film by laser light irradiation, it is general that an antireflection film is previously formed on the surface of the semiconductor thin film. Is. The antireflection film can improve the absorption efficiency of the irradiation energy of laser light, and is effective in completely melting the semiconductor thin film and promoting its crystallization. However, in the conventional method, the antireflection film (for example, SiO ₂ film, SiN film, etc.) which has been used is removed by etching or the like, and a semiconductor process is applied thereon to integrally form thin film transistors and the like. There is a problem that the number of manufacturing steps of the thin film semiconductor device is increased because the antireflection film that has been formed is removed. Laser light irradiation is used not only for crystallization of a semiconductor thin film but also for activation of impurities implanted in the semiconductor thin film. For example, a gate electrode is formed on a semiconductor thin film, impurities are injected by self-alignment, and then laser light is irradiated for activation.
However, in this state, the laser light does not reach the channel portion provided directly below the gate electrode, so that the channel portion cannot be crystallized. Therefore, in order to crystallize the channel portion, it is necessary to separately perform laser light irradiation before forming the gate electrode, which causes a problem that the number of steps is increased. Further, even if laser light irradiation is performed at the stage of forming the semiconductor thin film to achieve crystallization, defects may occur in the semiconductor thin film in the transistor manufacturing process in a later step. In this case, there is a problem that efficient defect removal is difficult because high-temperature heat treatment cannot be performed after the thin film transistor is formed.

[0004]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the conventional technique, an object of the present invention is to improve the manufacturing efficiency and the quality of a thin film semiconductor device by devising a process of laser light irradiation. To do. The following measures have been taken in order to achieve this object. That is, according to the present invention, the thin film semiconductor device is manufactured by the following steps. First, a film forming step of forming a semiconductor thin film on the surface side of a transparent insulating substrate is performed. Next, a processing step is performed to form thin film transistors by using the semiconductor thin film as an element region. As a feature of the present invention, a processing step of crystallizing the semiconductor thin film by irradiating a laser beam from the rear surface side of the transparent insulating substrate is performed before or after the processing step. For example, the processing step includes a step of patterning a gate electrode on the semiconductor thin film, and the processing step is performed after the gate electrode is patterned, and the processing step includes a portion located immediately below the gate electrode. Crystallize a semiconductor thin film. Further, the processing step includes a step of implanting impurities into the semiconductor thin film by self-alignment using the gate electrode patterning formation as a mask, and the processing step is performed after the impurity implantation and crystallization of the semiconductor thin film. At the same time, the impurities are activated. More generally, the processing step includes a step of implanting an impurity into the semiconductor thin film, and the processing step is performed after implanting the impurity so as to crystallize the semiconductor thin film and simultaneously activate the impurity. . In addition, the processing step includes a step of removing an unnecessary portion of the semiconductor thin film by etching, leaving the element region after the processing step. Furthermore, after the thin film transistors are integrated and formed, an electrode step of forming pixel electrodes connected to the individual thin film transistors may be performed.

The present invention is widely applicable to a method of manufacturing a thin film semiconductor device, but is particularly preferably applicable to a method of manufacturing an active matrix type liquid crystal display panel. In this case, first, a film forming step of forming a semiconductor thin film on the surface side of the transparent insulating substrate is performed. Next, a processing step is performed to form thin film transistors by using the semiconductor thin film as an element region.
As a feature, a processing step of crystallizing the semiconductor thin film by irradiating a laser beam from the back surface side of the transparent insulating substrate is performed before or after the processing step or in the middle. After that, an electrode process of connecting to each thin film transistor to form a pixel electrode is performed. Then, an assembling process is performed to bond the counter substrate to the front surface side of the transparent insulating substrate with a predetermined gap. Finally, a sealing process of injecting liquid crystal into the gap is performed to complete an active matrix type liquid crystal display panel.

[0006]

According to the present invention, the semiconductor thin film is crystallized by irradiating a laser beam from the back surface side of the transparent insulating substrate before, after or in the middle of the processing step of forming the thin film transistor in an integrated manner. By irradiating the laser beam from the back surface side of the transparent insulating substrate, the antireflection film for the laser beam, which is conventionally formed on the semiconductor thin film, is not required, and the number of manufacturing steps can be reduced. By setting the thickness of the transparent insulating substrate appropriately instead of the antireflection film for laser light, the transparent insulating substrate itself can perform the antireflection function. Further, since the semiconductor thin film is crystallized by irradiating the laser beam in the step of processing the thin film transistor, it is possible to efficiently remove crystal defects generated during the step of processing the thin film transistor. According to the present invention, the semiconductor thin film which becomes the element region (active layer) of the thin film transistor is formed on the front surface side of the transparent insulating substrate, while the laser beam is irradiated from the back surface side of the transparent insulating substrate. Therefore, the crystallization of the semiconductor thin film and the activation of the impurities implanted in the semiconductor thin film can be easily performed simultaneously at an appropriate stage of the process for forming the transistor.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a process diagram showing a method of manufacturing a thin film semiconductor device according to the present invention. First, in step (A), the semiconductor thin film 2 is formed on the front surface side of the transparent insulating substrate 1. That is, the semiconductor thin film 2 to be the element region (active layer) of the thin film transistor is formed with a thickness of 40 to 150 nm. For example,
A semiconductor thin film 2 made of amorphous silicon and having a thickness of 60 nm is directly formed on the transparent insulating substrate 1 by low pressure CVD at a temperature of 500 ° C. When the semiconductor thin film 2 is formed by the CVD method or the like, the adhesion film 3 is accompanied on the back surface side of the transparent insulating substrate 1. In this film forming step, in order to suppress impurities contained in the transparent insulating substrate 1, a base film such as SiO ₂ or SiN may be formed between the semiconductor thin film 2 and the transparent insulating substrate 1. However, the base film is limited to a material that does not reflect and absorb the laser light. Next, in step (B), the gate insulating film 4 is formed on the semiconductor thin film 2. In this example, SiO ₂ is subjected to atmospheric pressure CVD.
To form a film having a thickness of 120 nm. Next, in step (C),
The gate electrode G is patterned on the gate insulating film 4. Then, in step (D), the source region S and the drain region D are provided by implanting impurities into the semiconductor thin film 2 by self-alignment using the gate electrode G as a mask. In this example, in order to form an N-channel type thin film transistor for switching driving of the pixel electrode, arsenic was ion-implanted as an impurity at a dose of 5 × 10 ¹⁵ / cm ² . When forming a P-channel type thin film transistor, for example, boron may be ion-implanted at a dose amount of 5 × 10 ¹⁵ / cm ² . In the semiconductor thin film 2, a channel region ch is defined between the source region S and the drain region D provided on both sides of the gate electrode G. This channel region ch is located immediately below the gate electrode G. The processes (B), (C), and (D) described above are the pre-stages of the processing steps for forming the thin film transistors by using the semiconductor thin film 2 as an element region.

Next, in step (E), the various adhering films 3 deposited on the back surface side of the transparent insulating substrate 1 are removed. Subsequently, in step (F), laser light of appropriate energy is irradiated from the back surface side of the transparent insulating substrate 1 to crystallize the semiconductor thin film 2 and activate impurities. In this processing step, the channel region ch located directly below the gate electrode G is exposed to the laser beam directly from the back surface side of the transparent insulating substrate 1, so that it can be crystallized. At the same time, the impurities implanted in the source region S and the drain region D can be activated. In this example, a XeCl laser was used to perform laser light irradiation at an energy density of 450 mJ / cm ² . In the present invention, since laser light irradiation is performed from the back surface side, it is necessary to select a material that does not absorb laser light for the transparent insulating substrate 1. It is preferable to set the thickness of the transparent insulating substrate 1 according to the wavelength of the laser light in order to suppress back reflection of the laser light. By doing so, it is not necessary to separately provide an antireflection film. At this time, the laser light irradiation region covers at least an area corresponding to one chip or more of the thin film semiconductor device, and crystallization and activation are realized by one laser light pulse irradiation. One chip of this thin film semiconductor device is used for assembling an active matrix type liquid crystal display panel in a later step. In this processing step, a passivation film may be formed in advance on the thin film transistor if necessary.

Next, in step (G), the semiconductor thin film 2 that has been subjected to the laser light irradiation process is etched in accordance with the element region of the thin film transistor. That is, unnecessary portions of the semiconductor thin film 2 are removed by etching, leaving the element region after the irradiation process. If the semiconductor thin film 2 is etched according to the shape of the element region before the laser light irradiation, the heating temperature distribution due to the laser light irradiation becomes uneven, and there is a possibility that a part of the semiconductor thin film may be lost. is there. Subsequently, in step (H), the thin film transistor is covered with the first passivation film 5. For example, SiO ₂ is deposited to a thickness of 300 nm to form the first passivation film 5. Further, a contact hole is opened in the first passivation film 5, and a wiring 6 communicating with the source region S of the thin film transistor is provided. The steps (G) and (H) described above are the latter stages of the processing steps for forming the thin film transistor in an integrated manner. Therefore, the processing step of irradiating the laser beam is performed in the middle of a series of processing steps of the thin film transistor.

Finally, in step (I), a second passivation film 7 is formed to cover the wiring 6. For example, SiO ₂ is 3
The second passivation film 7 is formed with a thickness of 00 nm. Then, a contact hole is opened through the second passivation film 7 and the first passivation film 5, and a pixel electrode 8 connected to the drain region D is provided. This pixel electrode 8
Is made of a transparent conductive film such as ITO. Through the above steps, the thin film semiconductor device is completed. After that, when assembling the active matrix type liquid crystal display panel, an assembling step of joining the counter substrate to the front surface side of the transparent insulating substrate 1 through a predetermined gap is performed. Then, a sealing process of injecting liquid crystal into the gap is performed to complete the active matrix type liquid crystal display panel.

In the embodiments described above, at the stage where impurities are injected into the semiconductor thin film by self-alignment after the patterning of the gate electrode, laser light is irradiated from the back surface side of the transparent insulating substrate to crystallize the semiconductor thin film and the impurities are simultaneously formed. I am trying to activate. However, the present invention is not limited to this process order, and in general, after forming a semiconductor thin film to be the active layer of a thin film transistor, laser light is irradiated from the back surface side of the transparent insulating substrate at an appropriate process step to perform crystallization or activation. Can be implemented. If laser light irradiation is performed before the impurity is injected, only crystallization of the semiconductor thin film can be performed. On the contrary, if impurities are injected into the crystallized semiconductor thin film first and then laser light is irradiated again, it is possible to activate the impurities mainly.

FIG. 2 is an explanatory view showing a concrete example of laser light irradiation performed in the step (F) shown in FIG. Generally, the transparent insulating substrate 1 is composed of a large wafer so that a large number of display thin film semiconductor devices (hereinafter referred to as display semiconductor chips) can be obtained. That is, a plurality of sections 11 are set in advance on the transparent insulating substrate 1, and in the laser beam irradiation step, each section 11 is sequentially irradiated with a laser pulse 12 in one shot. In this example, the section 11 has a rectangular shape, and a laser pulse 12 having a rectangular laser beam cross section 13 aligned with this is irradiated in one shot from the back surface side of the transparent insulating substrate 1.

FIG. 3 is a graph showing the electrical characteristics of the thin film transistor formed according to the manufacturing method of FIG. For comparison, (A) shows the characteristics of a thin film transistor not irradiated with laser light, and (B) shows the characteristics of a thin film transistor irradiated with laser light. In each graph, the vertical axis represents the drain current Ids and the horizontal axis represents the gate voltage Vgs. The thin film transistor that has not been subjected to the irradiation process has a relatively low on-current and a relatively high off-current. On the other hand, the thin film transistor subjected to the irradiation treatment has a sufficiently high on-current and the off-current is significantly suppressed. Therefore,
When incorporated as an active matrix type liquid crystal display panel, the thin film transistor according to the present invention has excellent characteristics for switching pixel electrodes.

FIG. 4 is a schematic perspective view showing an example of a display semiconductor chip manufactured according to the present invention. In order to manufacture the display semiconductor chip 50, first, a film forming process is performed, and a semiconductor thin film 52 is formed on a transparent insulating substrate 51 made of a glass material having a relatively low melting point (for example, 600 ° C. or lower).
To form. The semiconductor thin film 52 is amorphous or polycrystalline having a relatively small grain size in the precursor state, and is made of, for example, amorphous silicon or polycrystalline silicon. Next, a series of treatments including a heat treatment of the semiconductor thin film 52 is performed, and thin film transistors are integratedly formed in the partition 53 for one chip. In this example, the pixel array section 54 and the horizontal scanning circuit 5 are provided in the section 53.
5, a vertical scanning circuit 56 is included. A thin film transistor is integrally formed on each of these. Finally, a pixel electrode for one screen is formed in the pixel array section 54 to complete the display semiconductor chip 50. The above-described heat treatment is performed by laser light irradiation, and the section 53 is irradiated with a laser pulse in one shot from the back surface side of the transparent insulating substrate 51, and the semiconductor thin film 52 for one chip is collectively heat-treated. This laser light irradiation is intended to crystallize the semiconductor thin film 52 by batch heating. For example, when the semiconductor thin film 52 is amorphous silicon in the precursor state, it is once melted by batch heating and then crystallized to obtain polycrystalline silicon having a relatively large grain size. When the semiconductor thin film 52 is a polycrystal with a relatively small grain size in the precursor state, it can be melted by batch heating and then recrystallized to be converted into a polycrystal with a relatively large grain size. The laser light irradiation is not limited to the case of crystallization, but is also used in the case of activating impurities by batch heating after the impurities are injected into the semiconductor thin film 52. Furthermore, crystallization of the semiconductor thin film 52 and activation of impurities can be simultaneously performed by batch heating. Excimer laser light can be used as the laser pulse. Since the excimer laser light is a strong pulsed ultraviolet light, it is absorbed by the semiconductor thin film 52 made of silicon or the like and raises the temperature of that portion. However, since the transparent insulating substrate 51 is made of a material that hardly absorbs excimer laser light, there is no fear that the substrate temperature will rise even if it is directly irradiated with laser light. As the precursor film formed on the transparent insulating substrate 51, a plasma CVD silicon film or the like that can be formed at a low temperature can be selected. For example, when a plasma CVD silicon film having a thickness of 30 nm is formed on the transparent insulating substrate 51 made of a glass material, the melting threshold energy when irradiated with XeCl excimer laser light is 1
It is about 30 mJ / cm ² . Energy of about 220 mJ / cm ² is required for melting the entire film thickness. The time from melting to solidifying is about 70 ns.

As described above, the present invention is characterized in that the large-area display semiconductor chip 50 is annealed at one time from the back surface side of the transparent insulating substrate with a pulse energy laser. The pixel array section 5 is provided in the section 53 which is the laser irradiation area.
4, a horizontal scanning circuit 55, and a vertical scanning circuit 56 are provided, each including a thin film transistor. In this display semiconductor chip 50, the total number of thin film transistors is 100 kbit or more, and the diagonal dimension of the partition 53 is 15
mm or more. This diagonal dimension extends to, for example, about 3 inches. For example, the wavelength is 300 nm to 35 with respect to the section 53.
The excimer laser beam 0nm irradiated from the back side of the substrate, its energy density is set to about ^{200mJ / cm 2 ~450mJ / cm 2} .

FIG. 5 is a schematic perspective view showing an example of an active matrix type liquid crystal display panel assembled using the display semiconductor chip as shown in FIG. As shown in the figure, the active matrix type liquid crystal display panel has a laminated structure including a transparent insulating substrate 101, a counter substrate 102, and a liquid crystal 103 held between them. A pixel array section 104 and a drive circuit section are integrally formed on the transparent insulating substrate 101. The drive circuit section is divided into a vertical scanning circuit 105 and a horizontal scanning circuit 106. A terminal portion 107 for external connection is formed on the upper edge of the peripheral portion of the transparent insulating substrate 101. The terminal portion 107 is connected to the vertical scanning circuit 105 and the horizontal scanning circuit 106 via the wiring 108. In the pixel array section 104, pixel electrodes 109 arranged in a matrix and corresponding thin film transistors 110 are integrally formed. The pixel electrode 109 and the thin film transistor 110 are integrated and formed on the transparent insulating substrate 101 according to the process shown in FIG.

[0017]

As described above, according to the present invention, the semiconductor thin film is crystallized by irradiating a laser beam from the back surface side of the transparent insulating substrate. Since the transparent insulating substrate itself functions as an antireflection film, there is no need to separately provide an antireflection film on the semiconductor thin film as in the conventional case, and the number of steps can be reduced. Since the semiconductor thin film is crystallized by irradiating laser light in the stage of forming the thin film transistor, there is an effect that it is possible to efficiently remove crystal defects generated in the process of forming the transistor. Further, while the semiconductor thin film is formed on the front surface side of the transparent insulating substrate and the back surface side is irradiated with laser light, crystallization of the semiconductor thin film and impurities injected into the semiconductor thin film can be easily performed at any stage of transistor formation. This has the effect of increasing the degree of freedom in process design by enabling activation of the process.

[Brief description of drawings]

FIG. 1 is a process drawing showing a method of manufacturing a thin film semiconductor device according to the present invention.

FIG. 2 is an explanatory diagram showing a specific example of laser light irradiation.

FIG. 3 is a graph showing electric characteristics of a thin film transistor.

FIG. 4 is a perspective view showing an example of a thin film semiconductor device manufactured according to the present invention.

FIG. 5 is a perspective view showing an example of an active matrix type liquid crystal panel assembled using the thin film semiconductor device manufactured according to the present invention.

[Explanation of symbols]

 1 Transparent Insulating Substrate 2 Semiconductor Thin Film 3 Adhesive Film 4 Gate Insulating Film 8 Pixel Electrode 11 Section 12 Laser Pulse 13 Laser Light Cross Section

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H01L 21/268 Z (72) Inventor Shizuo Nishihara 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soniー Incorporated (72) Inventor Hisao Hayashi 6-735 Kitashinagawa, Shinagawa-ku, Tokyo Sony Incorporated

Claims (7)

[Claims] 1. A film forming step of forming a semiconductor thin film on the front surface side of a transparent insulating substrate, a processing step of integrally forming thin film transistors using the semiconductor thin film as an element region, and the transparent insulating substrate before or after the processing step. A method of irradiating a laser beam from the rear surface side of the substrate to crystallize the semiconductor thin film, 2. The processing step includes a step of patterning a gate electrode on the semiconductor thin film, and the processing step is performed after the gate electrode is patterned, and a portion directly below the gate electrode is also formed. The method of manufacturing a thin film semiconductor device according to claim 1, further comprising crystallizing the semiconductor thin film. 3. The processing step includes a step of implanting an impurity into the semiconductor thin film by self-alignment after patterning the gate electrode and using the patterning as a mask, and the processing step is performed after the impurity implantation. 3. The method for manufacturing a thin film semiconductor device according to claim 2, wherein activation of the impurities is performed simultaneously with crystallization of. 4. The processing step includes a step of implanting an impurity into the semiconductor thin film, and the processing step is performed after implanting the impurity so as to crystallize the semiconductor thin film and simultaneously activate the impurity. Item 2. A method of manufacturing a thin film semiconductor device according to Item 1. 5. The method of manufacturing a thin film semiconductor device according to claim 1, wherein the processing step includes a step of etching away an unnecessary portion of the semiconductor thin film leaving the element region after the processing step. 6. The method of manufacturing a thin film semiconductor device according to claim 1, wherein after the thin film transistors are integrated and formed, an electrode step of forming a pixel electrode connected to each thin film transistor is performed. 7. A film forming step of forming a semiconductor thin film on the surface side of a transparent insulating substrate, a processing step of integrally forming thin film transistors using the semiconductor thin film as an element region, and the transparent insulating substrate before or after the processing step. Of the semiconductor thin film by irradiating the semiconductor thin film with laser light from the back side of the electrode, an electrode step of forming a pixel electrode by connecting to each thin film transistor, and a surface side of the transparent insulating substrate through a predetermined gap. A method for manufacturing an active matrix type liquid crystal display panel, comprising: an assembling step of joining opposite substrates; and a sealing step of injecting liquid crystal into the gap.