JPH1098194A - Manufacture of thin-film semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin-film semiconductor device which can reduce its manufacturing costs and enhance its performance by optimizing a process temperature. SOLUTION: In order to fabricate a thin-film semiconductor device, a film formation step is first carried out, that is, a single-crystal semiconductor thin film 3 is formed on a glass substrate 1. In the next recrystallizing step, the glass substrate 1 is irradiated with a laser beam while heated at a temperature of 400 to 800 deg.C to transform the semiconductor thin film 3 from non-single crystal into 9 polycrystal. Thereafter, a processing step is carried out to form a thin-film transistor 9 having the polycrystallized semiconductor thin film 3 as its element region. In this case, a gate oxide film 4 is formed on the semiconductor thin film 3 of polycrystalline silicon at a treatment temperature of 400 to 800 deg.C, and then a gate electrode 5 of metal silicide is formed on the gate oxide film 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a thin film semiconductor device. More specifically, polycrystalline silicon or the like is employed as the active layer of the thin film transistor and the temperature is 400 ° C.
The present invention relates to a method for manufacturing a thin film semiconductor device using a medium temperature process at 00 ° C.

[0002]

2. Description of the Related Art A thin film semiconductor device is suitable for a drive substrate of an active matrix type liquid crystal display device, and is being actively developed. Polycrystalline silicon or amorphous silicon is used for the active layer of the thin film transistor. Especially,
The polycrystalline silicon thin film transistor has been attracting attention because it can realize a small and high-definition active matrix type color liquid crystal display device. In order to form a thin film transistor as a pixel switching element on a transparent glass substrate, a technique using a polycrystalline silicon thin film, which has been used only as an electrode material or a resistance material in the conventional semiconductor technology, for an active layer. This is the only technology that can realize a high-performance thin film transistor for a switching element that can be designed with high density to achieve the image quality required in the market. At the same time, it has also become possible to form a peripheral drive unit, which has conventionally used an external IC, on the same substrate as the pixel unit by the same process. It is possible to realize an active matrix type liquid crystal display device having a high definition and a peripheral driving unit integrated type, which cannot be realized by an amorphous silicon thin film transistor.

Since polycrystalline silicon has a higher carrier mobility than amorphous silicon, the current driving capability of the polycrystalline silicon thin film transistor is increased, and peripheral driving units such as a horizontal scanning circuit and a vertical scanning circuit which require high-speed driving are required. It can be simultaneously formed on the same substrate as the pixel switching thin film transistor. Therefore, the number of signal lines to be extracted from the thin film semiconductor device to the outside can be significantly reduced.
As a result, excellent productivity and reliability can be achieved, and the outer size of the active matrix type liquid crystal display device can be reduced. Further, a so-called CMOS circuit in which N-channel and P-channel thin film transistors are integrated and formed can be formed on-chip, a level shift circuit can be built in, and low-voltage driving of timing-related signals can be performed. This is advantageous for reducing power consumption and reducing unnecessary radiation. Furthermore, LSI
By applying the microfabrication technology, the pixel pitch can be made extremely fine, and the display device can be easily made high definition. Of course, since the peripheral drive section is built in, connection to an external IC is not required, and the pixel pitch can be miniaturized. In addition, when polycrystalline silicon is used as the active layer, the device size of the thin film transistor can be reduced, so that a large pixel aperture ratio can be secured even if the display device is made finer by reducing the pixel pitch. Therefore, the transmittance of incident light is increased, and a bright display device can be obtained. As described above, a thin film semiconductor device in which a polycrystalline silicon thin film transistor having excellent characteristics is integrated and formed is utilized in various applications by utilizing its fineness and high definition.

[0004]

The polycrystalline silicon thin film transistor has advantages over the amorphous silicon thin film transistor in characteristics and structure. For example, there is a point that the characteristic change is small with respect to the incident light, and that there is no characteristic deterioration during high-temperature operation. The thin film transistor that drives the liquid crystal display device has a role of applying a signal voltage to the liquid crystal or holding the signal voltage, and has a function of a switch. That is, it is important to supply as much drive current as possible when the switch is on, and to minimize the leakage current as much as possible when the switch is off. Conventionally, various device technologies and process technologies have been proposed to suppress the leak current while increasing the current driving capability. A high-temperature process technology typically using a processing temperature of 1000 ° C. or higher has been established. The feature of this high temperature process is that a semiconductor thin film formed on a high heat resistant substrate such as quartz is modified by solid phase growth. This solid phase growth method is disclosed in, for example, JP-A-60-136262, JP-A-60-164316, and
No. 27118, for example. Solid phase growth method is 1
This is a method of heat-treating a semiconductor thin film at a temperature of 000 ° C. or more. In a film formation stage, each crystal grain contained in polycrystalline silicon, which is a set of fine silicon crystals, is enlarged.
The polycrystalline silicon obtained by this solid phase growth method is 100
High carrier mobility of about cm ² / v · s can be obtained. Incidentally, the mobility of amorphous silicon is about 0.5 cm ² / v · s, and the mobility of polycrystalline silicon obtained by solid phase growth can be 100 times or more. In addition, a high-quality thermal oxide film formed at a process temperature exceeding 1000 ° C. is also used as a gate oxide film that greatly affects the operation characteristics of the thin film transistor. In order to carry out such a high-temperature process, it is essential to use a substrate having excellent heat resistance, and conventionally expensive quartz or the like has been used. However, quartz is disadvantageous from the viewpoint of reducing manufacturing costs.

[0005] Instead of the high temperature process described above,
Low temperature processes employing the following processing temperatures have been developed. In some cases, low-temperature processes in which the maximum process temperature is suppressed to 400 ° C. or less have been studied. Laser annealing using a laser beam has attracted attention as a part of a method for making a manufacturing process of a thin film semiconductor device a low-temperature process. This is because a non-single-crystal semiconductor thin film such as amorphous silicon or polycrystalline silicon formed on a low heat-resistant insulating substrate such as glass is irradiated with a laser beam, locally heated and melted, and then cooled. In the process, the semiconductor thin film is crystallized. Using the crystallized semiconductor thin film as an active layer (channel region), a polycrystalline silicon thin film transistor is integrated and formed. Since the crystallized semiconductor thin film has high carrier mobility, the performance of the thin film transistor can be improved to some extent.
However, a low-temperature process using laser annealing still has insufficient crystallization of a polycrystalline silicon semiconductor thin film compared to a high-temperature process using a solid-phase growth method. Recent demands for miniaturization are strong, and there is a need to further improve the performance of polycrystalline silicon thin film transistors. In recent years, a panel of 2 million pixels or more such as a panel for HD and a panel for SXGA has been required. In order to respond to this, it is necessary to achieve a reduction in the pixel pitch by miniaturization of the thin film transistor. It is necessary to improve image quality by changing from dot sequential driving to line sequential driving. It is also necessary to promote system-on-chip. Polycrystalline silicon that satisfies this requirement must have a large mobility, a small variation, and a small trap level. That is, it is important to produce a crystal in which the size of crystal grains (grains) is smaller than the channel length, the number of grain-line traps is small, and the number of boundary traps is small. Furthermore, a high-quality gate oxide film is required, and it is important to reduce the interface state between the gate oxide film and polycrystalline silicon.

[0006]

The following means have been taken in order to solve the above-mentioned problems of the prior art. That is, according to the present invention, the thin film semiconductor device is manufactured by the following steps. First, a film forming step is performed, and a non-single-crystal semiconductor thin film is formed on a glass substrate. Next, a recrystallization step is performed, and the semiconductor thin film is converted from non-single crystal to polycrystal by irradiating a laser beam while heating the glass substrate in a temperature range of 400 ° C. to 800 ° C. Finally, a processing step is performed to form a thin film transistor using the polycrystallized semiconductor thin film as an element region.

Preferably, in the film forming step, a semiconductor thin film made of amorphous silicon is formed to a thickness of 50 nm or less, and in the recrystallization step, the amorphous silicon is irradiated with excimer laser light to convert the amorphous silicon into polycrystalline silicon. In the processing step, a gate oxide film is formed on the polycrystalline silicon at a processing temperature of 400 ° C. to 800 ° C., and then a gate electrode made of metal or metal silicide is formed thereon. Preferably, the processing step includes a step of thermally oxidizing the surface of the polycrystalline silicon to a thickness of 10 nm or less before or after forming the gate oxide film. Preferably, in the film forming step, SiN and / or Si is formed on the surface of the glass substrate prior to forming the semiconductor thin film.
The method includes a process of forming a base film made of O ₂ and prevents lithium, sodium, boron, aluminum, or potassium contained in the glass substrate from diffusing into the semiconductor thin film. Preferably, in the recrystallization step, the entire surface of the glass substrate is collectively irradiated with laser light.

The present invention also includes a method of manufacturing an active matrix type display device. First, a non-single-crystal semiconductor thin film is formed on one glass substrate. Then, the semiconductor thin film is converted from non-single-crystal to polycrystalline by irradiating the glass substrate with laser light while heating the glass substrate at a temperature in the range of 400 to 800 ° C. Next, thin film transistors are integratedly formed using the polycrystalline semiconductor thin film as an element region. Further, a pixel electrode is integrated with the thin film transistor. After this,
The other substrate on which the counter electrode is formed in advance is bonded to the one glass substrate via a predetermined gap. Finally, an electro-optical material is introduced into the gap to complete an active matrix display device.

According to the present invention, a new medium temperature process employing a process temperature of 400 ° C. to 800 ° C. is employed in place of the conventional high temperature process or low temperature process. This makes it possible to use crystallized glass or the like as a substrate instead of expensive quartz. Further, it is possible to integrate and form a thin film transistor having higher performance than the low temperature process. Specifically, the semiconductor thin film is converted from non-single crystal to polycrystal by irradiating a laser beam while heating the glass substrate in a temperature range of 400 ° C. to 800 ° C. Conventionally, 400 ° C
By increasing the substrate heating temperature to 800 ° C. in the recrystallization step in which only the following heat treatment has been performed, it is possible to greatly improve the crystallinity of the semiconductor thin film. A high-performance gate oxide film such as HTO is formed on the polycrystalline silicon at a processing temperature of 400 ° C. to 800 ° C. Thereby, the gate oxide film and the interface between the gate oxide film and the polycrystalline silicon can be modified. In addition, a thin high-quality gate oxide film of 10 nm or less can be added by thermally oxidizing the surface of polycrystalline silicon at a temperature of 800 ° C. or less before or after the gate oxide film is formed. As mentioned above,
In the present invention, the low-cost and high-quality thin-film semiconductor devices are achieved at the same time by employing a middle-temperature process at 400 ° C. to 800 ° C.

[0010]

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 schematic partial sectional view showing a completed state of a thin film semiconductor device manufactured according to the present invention. In order to facilitate understanding, only one thin film transistor and the corresponding pixel electrode are shown.
First, a base film 2 is formed on a glass substrate 1 made of crystallized glass such as neoceram. This underlayer is made of SiN
And / or SiO ₂ to prevent upward diffusion of lithium, sodium, boron, aluminum or potassium contained in the glass substrate 1. Next, a semiconductor thin film 3 made of amorphous silicon or polycrystalline silicon is grown on the base film 2 by a CVD method. The thickness of the semiconductor thin film 3 is 100 nm in consideration of the threshold voltage of the thin film transistor.
It is necessary to set the following. In consideration of the operation characteristics of the thin film transistor and the crystallinity of the semiconductor thin film 3, it is advantageous to make the thickness of the semiconductor thin film 3 as small as possible.
Taking into account the finished film thickness and the decrease in film thickness during the process, it is desirable that the semiconductor thin film 3 be formed to a thickness of 50 nm or less. Subsequently, the glass substrate 1 is heated at 400 ° C. to 80 ° C.
The semiconductor thin film 3 is converted from a non-single crystal to a polycrystal by irradiating a laser beam while heating in a temperature range of 0 ° C. By simultaneously irradiating the glass substrate 1 with laser light while heating it in this temperature range, the semiconductor thin film 3 can have high performance and the energy of laser light can be reduced. Conventionally, in a recrystallization process using a laser beam, the glass substrate 1 is 400 ° C.
It was heated only at the following temperature, and the crystallization state was insufficient. By increasing the heating temperature to about 800 ° C., the recrystallization process by laser annealing is improved, and a polycrystal having a large grain size can be obtained. Thereafter, in order to separate the semiconductor thin film 3 into each element region of the thin film transistor, patterning is performed in an island shape by a photoresist method and an etching method.

The used photoresist is removed, and the surface of the glass substrate 1 is washed with a mixed solution of ammonia and hydrogen peroxide solution. Then, SiO ₂ is grown by a CVD method to provide a gate oxide film 4. In the present invention, a low pressure CVD method is adopted, and SiH ₄ or SiH ₂ Cl ₂ gas and N ₂ O or O ₂ gas are reacted at a temperature between 400 ° C. and 800 ° C. under a vacuum of 0.1 Torr to 5 Torr. , A gate oxide film 4 called so-called HTO is formed. HTO formed by a low pressure CVD method has superior quality to LTO formed by a normal pressure CVD method. The atmospheric pressure CVD method is employed in a low-temperature process, and is a method in which a SiH ₄ gas and an O ₂ gas are reacted at a temperature of about 400 ° C. under atmospheric pressure. Next, in order to improve the interface between the semiconductor thin film 3 and the gate oxide film 4, the gate oxide film 4 is grown by a low pressure CVD method, and then a heat treatment is performed at a temperature higher than the growth temperature. The surface of No. 3 is oxidized to a thickness of about 10 nm. Although the thermal oxide film formed by this thermal annealing is as thin as about 10 nm, the interface between the semiconductor thin film 3 and the gate oxide film 4 can be remarkably modified, thereby improving the performance of the thin film transistor. To contribute. In some cases, heat treatment in an oxygen atmosphere can be used instead of thermal annealing in an inert atmosphere such as nitrogen or argon, and thermal oxidation of the surface of the semiconductor thin film 3 can be promoted. The formation of the thermal oxide film may be performed before the gate oxide film 4 is grown by the CVD method.

After forming the gate oxide film 4, a gate material is deposited by a CVD method and a sputtering method. Its film thickness is 20
About 0 to 400 nm, and Al, M
Metal such as o and W or metal silicide is used. Considering future high performance, a stacked structure of silicide and metal is ideal. Thereafter, the formed gate material is patterned by a photoresist method and an etching method, and is processed into a gate electrode 5. Using the gate electrode 5 as a mask, an impurity is implanted into the semiconductor thin film 3 by ion implantation to form a source region S and a drain region D. N
When a channel thin film transistor is formed, arsenic or phosphorus is used as an impurity, and when a p-channel thin film transistor is formed, boron is used as an impurity.
Thereafter, the implanted impurities are activated. Thermal annealing,
This activation can be performed by instantaneous annealing using a lamp light, laser annealing, or the like.

Next, SiO ₂ or PSG is deposited by a CVD method to provide an interlayer insulating film 6. A contact hole communicating with the source region S and the drain region D is opened in the interlayer insulating film 6. Aluminum (Al) is deposited on the interlayer insulating film 6 by a sputtering method, and is patterned into a predetermined shape by a photoresist method and an etching method to provide a pair of wiring electrodes 7. One wiring electrode 7 is electrically connected to the source region S via a contact hole, and the other wiring electrode 7 is electrically connected to the drain region D via a contact hole. SiN is deposited on these wiring electrodes by a plasma CVD method, and a cap film 8 is provided. In this state, a heat treatment at about 400 ° C. is performed to form a semiconductor thin film 3 made of polycrystalline silicon.
Is modified. That is, by introducing hydrogen contained in the interlayer insulating film 6 and the like into the semiconductor thin film 3, dangling bonds and the like of polycrystalline silicon are terminated and the crystal structure is modified.
This heat treatment also improves the electrical contact between the wiring electrode 7 and the semiconductor thin film 3 at the same time. Thus, the polycrystalline silicon thin film transistor 9 is completed. Thereafter, an acrylic resin or the like is applied to flatten the surface of the glass substrate 1 to form a flattening film 10.
Is provided. After opening a contact hole in the flattening film 10, a transparent conductive film such as ITO is deposited by a sputtering method. This transparent conductive film is patterned into a predetermined shape and processed into the pixel electrode 11. This pixel electrode 11 is used for the planarizing film 10.
Is connected to the wiring electrode 7 through a contact hole opened at the bottom.

As described above, according to the present invention, the thin film semiconductor device is manufactured by the middle temperature process at 400.degree.
First, a film forming step is performed, and a non-single-crystal semiconductor thin film 3 is formed on the glass substrate 1. Next, a recrystallization step is performed, and the semiconductor thin film 3 is converted from a non-single crystal to a polycrystal by irradiating a laser beam while heating the glass substrate 1 in a temperature range of 400 ° C. to 800 ° C. Subsequently, a processing step is performed, and the polycrystalline semiconductor thin film 3 is used as an element region to form a thin film transistor 9.
To form Specifically, the film forming step forms a semiconductor thin film made of amorphous with a thickness of 50 nm or less, and the recrystallization step irradiates excimer laser light to convert amorphous silicon to polycrystalline silicon, Processing step is 40 on polycrystalline silicon.
After a gate oxide film 4 is formed at a processing temperature of 0 ° C. to 800 ° C., a gate electrode 5 made of metal or metal silicide is formed thereon. The processing step includes a process of thermally oxidizing the surface of the polycrystalline silicon to a thickness of 10 nm or less before or after the gate oxide film 4 is formed. In the film forming step, SiN and / or SiN is formed on the surface of the glass substrate 1 prior to forming the semiconductor thin film 3.
Or a process of forming a base film 2 made of SiO ₂ , wherein lithium, sodium,
The diffusion of impurities such as boron, aluminum, or potassium into the semiconductor thin film 3 is prevented.

FIG. 2 is a schematic plan view for explaining a specific laser beam irradiation method in the recrystallization step by laser irradiation. In this example, a plurality of sections 21 separated from each other by vertical and horizontal boundaries are defined along the surface of a planar substrate (wafer) 1a made of an insulator such as crystallized glass. Is formed, and a peripheral driving section 23 is formed in a peripheral region. When irradiating the wafer 1a with a laser beam, a laser beam having a large area spot shape corresponding to the area dimension of each section 21 can be used. The laser beam is applied to each section 21 one shot at a time, and laser annealing of the wafer 1a is performed by a step-and-repeat method. Alternatively, the laser beam may be formed into a linear beam, and scanning irradiation may be performed while overlapping in the width direction. In some cases, it is possible to perform laser annealing by scanning a laser beam having a small spot size in a two-dimensional direction. In any case, it is important to irradiate a laser beam while heating the wafer 1a at a temperature of 400 ° C. to 800 ° C. In this way, it is possible to convert the semiconductor thin film in each section 21 from non-monocrystalline to polycrystalline. Thereafter, the semiconductor thin film belonging to the peripheral region is processed to form a thin film transistor for a circuit element in an integrated manner, and a peripheral driving unit 23 is provided. or,
A thin film transistor for a switching element is integrated and formed by processing a semiconductor thin film belonging to the central region, and a pixel electrode connected thereto is integrally formed to provide a pixel portion 22. Finally, the wafer 1a is cut along the boundary, and the display thin-film semiconductor devices formed in each section are individually separated.

Finally, an example of an active matrix type display device using a thin film semiconductor device manufactured according to the present invention as a driving substrate will be briefly described with reference to FIG. This display device has a panel structure including a driving substrate 101, a counter substrate 102, and an electro-optical material 103 held between the two. As the electro-optical material 103, a liquid crystal material or the like is widely used. The drive substrate 101 is manufactured by a medium temperature process according to the present invention, and relatively low cost crystallized glass or the like can be used. The pixel portion 104 and the peripheral drive portion are formed integrally on the drive substrate 101, and a monolithic structure can be adopted. That is, in addition to the pixel portion 104, a peripheral driving portion can be integrally incorporated. The peripheral driving unit is divided into a vertical scanning circuit 105 and a horizontal scanning circuit 106. Further, a terminal portion 107 for external connection is formed at an upper end of a peripheral portion of the drive substrate 101. The terminal unit 107 is connected to a vertical scanning circuit 105 and a horizontal scanning circuit 106 via a wiring 108. On the other hand, a counter electrode and a color filter (not shown) are formed on the entire inner surface of the counter substrate 102. A row-shaped gate line 109 and a column-shaped signal line 110 are formed in the pixel portion 104.
The gate line 109 is connected to the vertical scanning circuit 105, and the signal line 110 is connected to the horizontal scanning circuit 106. At the intersection of the two lines, a pixel electrode 111 and a thin film transistor 112 for driving the pixel electrode 111 are integrally formed. Further, thin film transistors are also integratedly formed in the vertical scanning circuit 105 and the horizontal scanning circuit 106.

[0017]

As described above, according to the present invention,
The thin-film semiconductor device is manufactured by a middle temperature process at 400 ° C. to 800 ° C., and a relatively inexpensive crystallized glass or the like can be used as an insulating substrate in place of expensive quartz used in a high temperature process. High performance thin film transistors can be integrated on an insulating substrate. The intermediate temperature process includes a recrystallization step of irradiating a laser beam while heating in a temperature range of 400 ° C. to 800 ° C. to convert a semiconductor thin film from a non-single crystal to a polycrystal, or a 400 ° C. to 800 ° C. A processing step of forming a gate oxide film at a processing temperature of ° C. is included.

[Brief description of the drawings]

FIG. 1 is a schematic partial sectional view showing a basic configuration of a thin film semiconductor device manufactured according to the present invention.

FIG. 2 is a schematic plan view showing a recrystallization step included in the method for manufacturing a thin film semiconductor device according to the present invention.

FIG. 3 is a perspective view showing an example of an active matrix display device assembled using a thin film semiconductor device manufactured according to the present invention as a driving substrate.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... Base film, 3 ... Semiconductor thin film, 4 ... Gate oxide film, 5 ... Gate electrode, 6 ... Interlayer insulating film, 9 ... Thin film transistor, 11 ... Pixel electrode

Claims (6)

[Claims] 1. A film forming step of forming a non-single-crystal semiconductor thin film on a glass substrate, and irradiating a laser beam while heating the glass substrate in a temperature range of 400 ° C. to 800 ° C. A method for manufacturing a thin film semiconductor device, comprising: a recrystallization step of converting a non-single crystal into a polycrystal; and a processing step of forming a thin film transistor using the polycrystallized semiconductor thin film as an element region. 2. The film forming step forms a semiconductor thin film made of amorphous silicon with a thickness of 50 mm or less, and the recrystallization step irradiates an excimer laser beam to convert the amorphous silicon into polycrystalline silicon. 2. The method according to claim 1, wherein the processing step forms a gate oxide film on the polycrystalline silicon at a processing temperature of 400 ° C. to 800 ° C., and then forms a gate electrode made of metal or metal silicide thereon. A method for manufacturing a thin film semiconductor device. 3. The method according to claim 2, wherein said processing step includes a step of thermally oxidizing the surface of the polycrystalline silicon to a thickness of 10 mm or less before or after forming the gate oxide film. 4. The film forming step includes a step of forming a base film made of SiN and / or SiO _{2 on} the surface of the glass substrate prior to forming the semiconductor thin film, wherein lithium contained in the glass substrate is formed. 2. The method according to claim 1, wherein sodium, boron, aluminum or potassium is prevented from diffusing into the semiconductor thin film. 5. The method for manufacturing a thin film semiconductor device according to claim 1, wherein in the recrystallization step, the entire surface of the glass substrate is irradiated with laser light at a time. 6. A step of forming a non-single-crystal semiconductor thin film on one glass substrate, and irradiating a laser beam while heating the glass substrate in a temperature range of 400 ° C. to 800 ° C. A step of converting a non-single crystal to a polycrystal, a step of integrating and forming a thin film transistor using the polycrystallized semiconductor thin film as an element region, a step of integrating and forming a pixel electrode by connecting to the thin film transistor, A method for manufacturing an active matrix display device, comprising: a step of bonding the other substrate on which is formed to the one glass substrate via a predetermined gap; and a step of introducing an electro-optical material into the gap.