JP3326650B2 - Method for manufacturing semiconductor device - Google Patents

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 semiconductor device used for a drive substrate of an active matrix type liquid crystal display panel. More specifically, the present invention relates to a method for forming a polycrystalline semiconductor thin film used as an active layer.

[0002]

2. Description of the Related Art The development of an active matrix type liquid crystal display panel using a thin film transistor having a hydrogenated amorphous silicon thin film as an active layer has been advanced, and an image quality equal to or higher than that of a CRT has been realized. Is building its position. Since hydrogenated amorphous silicon thin film transistors can be formed at a process temperature of, for example, 350 ° C. or less and a low-cost glass substrate can be used, expectations for practical use of large-area displays are attracting attention. However, there are many problems that must be solved in order to achieve a manufacturing cost equivalent to that of a CRT. For example, the problem of peripheral driver circuits using IC chips and their mounting costs cannot be ignored.

[0003] Even a liquid crystal display panel compatible with HDTV or a large-screen high-definition liquid crystal display panel poses a serious problem. In these cases, it is necessary to increase the number of lines and increase the storage capacity of the pixel, and it is difficult to secure the aperture ratio of the pixel by reducing the device size of a hydrogenated amorphous silicon thin film transistor having a small mobility. Furthermore, plasma CV
There are many traps in the amorphous silicon thin film formed by D, which makes the operation of the transistor unstable.

Considering the limitations of such hydrogenated amorphous silicon thin film transistors, there is an increasing need for a process technology for forming a thin film transistor using a low-temperature polycrystalline silicon thin film as an active layer, which can be formed by a manufacturing process substantially equivalent to this. ing. The development of an active matrix type liquid crystal display panel in which peripheral driver circuits are integrated on a glass substrate using this is expected.

In a hydrogenated amorphous silicon thin film transistor, there are many metastable defects in a channel layer. This contributes to the change with time of the threshold voltage. On the contrary,
Polycrystalline silicon contains no hydrogen and has a small number of metastable defects. Therefore, the polycrystalline silicon thin film transistor can be expected to operate stably. Instead, polycrystalline silicon has many dangling bonds at grain boundaries. These defects are located at the center of the band gap and serve as generation and recombination centers for carriers. Therefore, the polycrystalline silicon thin film transistor generates a large leak current particularly in a high electric field region near the drain. The advantage of polycrystalline silicon is that the carrier mobility is large. It is larger than hydrogenated amorphous silicon by at least two orders of magnitude. The carrier mobility of polycrystalline silicon is governed by the potential barrier at the grain boundaries. The field effect mobility varies exponentially with the size of this barrier. The development of high mobility polycrystalline silicon has been studied with a focus on reducing the total number of defect densities by making the crystal grains as large as possible. It is also important to lower the height of the barrier by reducing the defect density at the crystal grain boundaries.

[0006]

As a technique for producing high-quality polycrystalline silicon on a glass substrate by a low-temperature process of 650 ° C. or lower, a solid phase growth method has been conventionally known. In this method, a silicon film is formed as a precursor film by an LPCVD method, and this is thermally annealed. Looking at the film forming conditions of the LPCVD method and the relationship between the annealing conditions performed subsequently and the crystal grain size, amorphous silicon is formed at a low temperature of, for example, 580 ° C. or less in order to obtain polycrystalline silicon having a large grain size. It has been found that annealing this at a low temperature of about 600 ° C. is good. In the case of thermal annealing solid phase growth, it is necessary to heat the amorphous silicon film at, for example, 600 ° C. for a long time, but a film having a large crystal grain size and thus a high mobility has been realized. However, in the solid phase growth of the thermal annealing, the crystal type is not constant, and many twin defects are found in the crystal grains according to the crystal image. Further, an amorphous portion remains between the crystal grains. There is a problem that these defects cause deterioration of the thin film transistor.

As a technique for forming a high-quality polycrystalline silicon film at a low temperature, a laser annealing method has been conventionally used, and is disclosed in, for example, Japanese Patent Application Laid-Open No. 60-245124. In this method, the silicon thin film can be crystallized at a relatively low temperature without increasing the temperature of the entire substrate. When a short-wavelength laser pulse is applied to the silicon thin film to be crystallized, the laser light is absorbed only at the very surface of the silicon thin film, and then the inside of the thin film is melted and recrystallized by heat conduction. Alternatively, the crystal grains are enlarged by annealing. In the polycrystalline silicon thin film formed by this method, granular crystal grains are substantially uniformly distributed. Looking at the lattice image, it is characteristic that the number of twin defects is very small as compared with the case of solid phase growth, and that the lattice image is not disturbed at the crystal grain boundaries. However, in the case of laser annealing, there is a problem that the size of crystal grains is relatively small, for example, 60 to 100 nm, and there are many crystal grain boundaries, which leads to deterioration of characteristics of the thin film transistor.

[0008]

SUMMARY OF THE INVENTION In view of the above-mentioned problems in the prior art, an object of the present invention is to produce a high-quality semiconductor thin film by a low-temperature process. The following measures were taken to achieve this purpose. That is, in a method of manufacturing a semiconductor device including a thin film element having a semiconductor thin film formed on an insulating substrate as an active layer, an amorphous semiconductor thin film or a crystalline
Forming a polycrystalline semiconductor thin film having grains and annealing the semiconductor thin film in comparison with the formed semiconductor thin film.
In comparison , a step of solid-phase growth of large crystal grains and a one-shot method of irradiating the semiconductor thin film with laser light all at once.
Characterized in that a step of performing only the crystallization of the amorphous portion and facilities bets irradiation remains between removal and grain defects remaining in crystal grains.

Further, in a semiconductor device including a thin film element having a polycrystalline semiconductor thin film formed on an insulating substrate as an active layer, the active layer contains crystal grains which are solid-phase grown by annealing, and emits laser light . One to irradiate all at once
Characterized in that Mino crystallization of the noncrystalline regions intervening between the crystal grains is achieved with defects from the crystal grains are removed by the shots.

Further, the semiconductor device has a flat panel structure including an insulating substrate and a counter substrate which are arranged to face each other with a predetermined gap therebetween, and a liquid crystal layer held in the gap. A thin film transistor and a pixel electrode are integrally formed, and the counter substrate is provided with a counter electrode. In the liquid crystal display device, the active layer contains crystal grains which are solid-phase grown by annealing, and characterized in that Mino crystallization of the noncrystalline regions intervening between the crystal grains is achieved with defects from the crystal grains are removed by the one-shot irradiation of irradiating at once light at a time.

[0011]

According to the present invention, a high-quality polycrystalline semiconductor thin film is formed by a low-temperature process of 650 ° C. or less by using both thermal annealing and laser annealing. First, a semiconductor thin film having an amorphous or relatively small particle diameter is thermally annealed to grow relatively large crystal grains in a solid phase.
Next, laser annealing is performed to remove defects remaining in the crystal grains and to crystallize an amorphous portion remaining between the crystal grains. This makes for close to single crystal grains contained in the active layer such as a thin film transistor thin film element is increased, and the amorphous areas between the crystal grains is likely current flows to crystallize, the on current increase of the thin film transistor Contribute.
Further, since the carrier trap density included in the active layer of the thin film transistor is reduced, the leak current can be reduced.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a process chart showing a semiconductor device manufacturing method according to the present invention. First, in step (A), a semiconductor thin film 2 to be an active layer of a thin film element such as a thin film transistor is placed on a transparent insulating substrate 1 made of low melting point glass or the like in an amount of 40 to 15 minutes.
The film is formed with a thickness of 0 nm. In this example, 5
At a temperature of 00 ° C., a 60 nm-thick amorphous silicon film was formed. Next, thermal annealing was performed in a nitrogen atmosphere at a temperature of 600 ° C. for 10 hours to grow relatively large crystal grains in a solid phase. Next, the process proceeds to step (B), where a photoresist 3 is patterned on the surface of the semiconductor thin film 2. This photoresist 3
Using the mask as a mask, impurities are ion-implanted into the semiconductor thin film 2 to form a source region S and a drain region D. Arsenic ions were implanted into the N-channel transistor, and boron ions were implanted into the P-channel transistor. The dose of the impurity was set to, for example, 5 × 10 ¹⁵ / cm ² . Next, in the step (C), after removing the used photoresist 3, an antireflection film 4 was formed on the semiconductor thin film 2. This is used to prevent reflection of laser light irradiation performed in a later step, and is made of, for example, SiO ₂ or Si ₃ N ₄ . The antireflection film 4 is formed in a thickness of 20 to 100 nm according to the wavelength of the laser beam to be used. To use an XeCl excimer laser as a laser light source in the present embodiment, a SiO ₂ 6
A film having a thickness of 0 nm was formed as an antireflection film 4. Next, the process proceeds to the step (D), in which the laser pulse is
Irradiation is performed at an energy density of 00 mJ / cm ^{2 to} 700 mJ / cm ² . At this time, the irradiation region of the laser beam includes an area section corresponding to at least one chip of the semiconductor device, and one-shot irradiation of a laser pulse is performed. The crystallization of the amorphous portions remaining between the removal and binding <br/> Akiratsubu defects remaining in crystal grains in the semiconductor thin film 2 is accelerated by the laser annealing.

Proceeding to step (E), the used anti-reflection coating 4 after laser irradiation is peeled off. Next, in step (F),
The crystallized silicon semiconductor thin film 2 is patterned into a predetermined shape to form an element region 5. Next, a gate insulating film 6 is formed so as to cover the element region 5 in a step (G). In this example, a gate insulating film 6 was formed by depositing SiO ₂ to a thickness of 120 nm by normal pressure CVD. Next, in a step (H), the gate electrode 7 is provided between the source region S and the drain region D formed earlier.
Was formed. In this example, a metal gate electrode 7 was formed by forming a metal film on the gate insulating film 6 and then patterning it into a predetermined shape. Subsequently, in step (I), SiO ₂ was formed to a thickness of 300 nm to form a first passivation film 8. Next, in a step (J), a contact hole was opened in the first passivation film 8, and a wiring 9 communicating with the source region S was formed.
Further, in the step (K), a second passivation film 10 was formed by forming SiO ₂ to a thickness of 300 nm. Finally, step (L)
Then, a contact hole is opened through the second passivation film 10 and the first passivation film 8 to expose the drain region D. After that, a transparent conductive film such as ITO is formed and then patterned into a predetermined shape to form the pixel electrode 11.

As described above, a semiconductor device including a thin film transistor having the polycrystalline semiconductor thin film 2 formed on the insulating substrate 1 as an active layer is completed. The active layer of the thin film transistor, that is, the element region 5 contains crystal grains which have been solid-phase grown by thermal annealing. Defects are removed from the crystal grains by laser annealing. Is being planned.

A specific method of laser annealing will be described in detail with reference to FIG. As described above, in the semiconductor device manufacturing method according to the present invention, first, the semiconductor thin film 22 is formed on the insulating substrate 21. Next, a series of processes including a heating process of the semiconductor thin film 22 are performed, and thin film transistors are integratedly formed in the area partition 23 for one chip. Finally, pixel electrodes for one screen are formed in the area section 23. Thus, a semiconductor device to be the display semiconductor chip 27 is manufactured. In such a step, in the laser annealing, the area section 23 is irradiated with the laser pulse 28 in one shot to collectively crystallize the semiconductor thin film 22 for one chip. As shown, the cross-sectional shape of the laser pulse 28 matches the shape of the area section 23. In the area section 23, a matrix array 24, a horizontal scanning circuit 25, and a vertical scanning circuit 26 are finally formed in an integrated manner. Matrix array 2
Reference numeral 4 includes a thin film transistor and a pixel electrode, while the horizontal scanning circuit 25 and the vertical scanning circuit 26 of the peripheral driver section are constituted by thin film transistors.

FIG. 3 shows a method of laser irradiation performed when a large number of display semiconductor chips are formed from a large-sized transparent insulating substrate 51. As shown in the figure, a semiconductor thin film 52 is entirely formed on a transparent insulating substrate 51. Further, an antireflection film 53 is formed thereon. The laser annealing described above is performed by irradiating a laser pulse 54 through the antireflection film 53. At this time, a one-shot laser pulse 54 is sequentially applied to a plurality of area sections 55 set in advance on the transparent insulating substrate 51. Thereby, the throughput of the film forming process can be remarkably improved.

FIG. 4 is a schematic perspective view showing an example of an active matrix type liquid crystal display device assembled using the display semiconductor chip shown in FIG. As shown in the figure, the liquid crystal display device has a flat panel structure including an insulating substrate 101 and an opposing substrate 102 which are disposed to face each other with a predetermined gap therebetween, and a liquid crystal layer 103 held in the gap. A thin film transistor 104 having a polycrystalline semiconductor thin film as an active layer and a pixel electrode 105 are provided on the lower transparent insulating substrate 101.
Are integrated and formed, and the matrix array 106 is formed. Further, a horizontal scanning circuit 107 and a vertical scanning circuit 108 which are also formed of thin film transistors are formed around the insulating substrate 101. On the other hand, upper counter substrate 1
An opposing electrode (not shown) is formed on the inner surface of 02. In such a configuration, the active layer serving as an element region of the thin film transistor 104 contains crystal grains that have been grown in a solid phase by thermal annealing. Partial crystallization is achieved.

Finally, the effects of the present invention will be described with reference to the graphs of FIGS. These graphs all show the gate voltage Vgs / drain current Ids characteristics of the thin film transistor. The drain current Ids is represented by a logarithmic memory. FIG. 5 shows a case where a silicon polycrystalline semiconductor thin film formed only by conventional solid phase growth is used as an active layer, and FIG. 6 shows a case where a silicon polycrystalline semiconductor thin film formed only by conventional laser annealing is used as an active layer. FIG. 7 shows a case where a silicon polycrystalline semiconductor thin film formed by combining solid phase growth and laser annealing according to the present invention is used as an active layer. With only solid phase growth, crystal defects are included in the crystal and non-crystalline portions remain between crystal grains. Therefore, as shown in the graph of FIG. 5, the characteristics of the thin film transistor are not always satisfactory. On the other hand, when crystallized by laser annealing, the crystal grains are generally small and there are many boundaries between the crystal grains. Therefore, as shown in the graph of FIG. 6, the electrical characteristics of the thin film transistor are not always satisfactory. On the other hand, when solid-phase growth and laser annealing are combined, the crystal grains of the thin film transistor active layer become large and thus close to a single crystal, and the current flows because the amorphous region between the crystal grains is crystallized or recrystallized. Easy to flow. Therefore, as shown in the graph of FIG. 7, the on-current of the thin film transistor is increased as compared with the case of FIGS. Also, the carrier trap density of the thin film transistor active layer is reduced. Therefore, the leak current is reduced as shown in the graph of FIG.

[0019]

As described above, according to the present invention, a semiconductor thin film is first thermally annealed to grow relatively large crystal grains in a solid phase. Next, laser annealing is performed to remove crystals remaining in the crystal grains and to crystallize the non-crystal portions remaining between the crystal grains. As a result, the crystal grains of the thin film transistor active layer become large, so that they are close to a single crystal, and an amorphous region between the crystal grains is crystallized, so that current easily flows, which contributes to an increase in the on-current of the thin film transistor. Further, there is an effect that the carrier trap density of the thin film transistor active layer is reduced, and the leak current can be reduced.

[Brief description of the drawings]

FIG. 1 is a process chart showing a semiconductor device manufacturing method according to the present invention.

FIG. 2 is a schematic diagram illustrating an example of a laser annealing process.

FIG. 3 is a schematic view similarly showing a laser annealing process.

FIG. 4 is a schematic perspective view showing an example of a liquid crystal display device assembled using a semiconductor device manufactured according to the present invention.

FIG. 5 is a graph showing electric characteristics of a thin film transistor having a polycrystalline semiconductor thin film formed by thermal annealing as an active layer.

FIG. 6 is a graph showing electric characteristics of a thin film transistor having a polycrystalline semiconductor thin film formed by laser annealing as an active layer.

FIG. 7 is a graph showing the electrical characteristics of a thin film transistor having a polycrystalline semiconductor thin film formed as an active layer formed by using both solid phase growth and laser irradiation.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 insulating substrate 2 semiconductor thin film 4 anti-reflection film 5 element region 6 gate insulating film 7 gate electrode 11 pixel electrode

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shizuo Nishihara 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Hisao Hayashi 6-35-35 Kita-Shinagawa, Shinagawa-ku, Tokyo (56) References JP-A-3-22540 (JP, A) JP-A-5-82442 (JP, A) JP-A-5-34718 (JP, A) (58) Fields investigated ( Int.Cl. ⁷ , DB name) H01L 29/786 H01L 21/336 H01L 21/20 G02F 1/1368

Claims (3)

(57) [Claims] In a method of manufacturing a semiconductor device including a thin film element having a semiconductor thin film formed on an insulating substrate as an active layer, an amorphous semiconductor thin film or a polycrystalline semiconductor thin film having crystal grains is formed on the insulating substrate. A film forming step, and a semiconductor thin film formed by annealing the semiconductor thin film.
Compared with the step of solid phase growth of crystal grains of large grain diameter, Wanshi irradiating in bulk laser beam at a time to the semiconductor thin film
The method of manufacturing a semiconductor device, characterized in that a step of performing a non-crystalline portion only crystallization of and facilities for-shot irradiation remaining between removal and <br/> grain defects remaining in crystal grains. 2. A semiconductor device comprising a thin-film element having a polycrystalline semiconductor thin film formed on an insulating substrate as an active layer, wherein the active layer contains crystal grains which have been solid-phase-grown by annealing, and has been irradiated with laser light once. One-shot irradiation
The semiconductor device, characterized in that crystallization of only the non-crystalline portion interposed between the crystal grains is achieved with defects from the crystal grains by Tsu preparative irradiation is eliminated. 3. A flat panel structure including an insulating substrate and a counter substrate disposed facing each other with a predetermined gap therebetween and a liquid crystal layer held in the gap, wherein the insulating substrate includes a polycrystalline semiconductor thin film as an active layer. A liquid crystal display device in which a thin film transistor and a pixel electrode are integrally formed and a counter electrode is formed on the counter substrate, wherein the active layer includes crystal grains that are solid-phase grown by annealing. And one-shot that irradiates laser light all at once
The liquid crystal display device, characterized in that crystallization of only the non-crystalline portion interposed between the crystal grains is achieved with defects from the crystal grains by Tsu preparative irradiation is eliminated.