JP3413709B2 - Method of manufacturing thin-film semiconductor device for display - 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 thin film semiconductor device for display in which thin film transistors having a semiconductor thin film formed on an insulating substrate as an active layer are integrally formed. More specifically, it relates to a laser beam irradiation technique (laser annealing) performed for the purpose of crystallization of a semiconductor thin film formed on an insulating substrate.

[0002]

2. Description of the Related Art Thin-film semiconductor devices for display are used in active matrix type liquid crystal displays and the like, and are under active development. Semiconductor thin films used as active layers of thin film transistors include polycrystalline silicon (polysilicon) and amorphous silicon (amorphous silicon). The polysilicon thin film transistor is small and can make a high-definition color liquid crystal display. Since thin film transistors are integrated and formed on a transparent substrate, polysilicon used as an electrode or a resistance material in the conventional semiconductor technology is used as an active layer.
A high-performance thin film transistor capable of high-density design can be realized. At the same time, it becomes possible to form the drive circuit section, which conventionally uses an external IC, on the same substrate as the display section (pixel array) in the same process. It is possible to realize a high-definition and drive circuit integrated type liquid crystal display that could not be realized with an amorphous silicon transistor. Since polysilicon has a high mobility and the current driving capability of a thin film transistor can be increased, a horizontal scanning circuit and a vertical scanning circuit of a driving circuit portion which requires high speed driving can be formed at the same time as a pixel transistor on the same substrate. Therefore, the number of signal lines taken out from the substrate to the outside can be significantly reduced. The conventional LSI microfabrication technology can be applied to the polysilicon transistor, and the pixel pitch can be extremely miniaturized, and high definition can be easily achieved. Furthermore, since the size of the thin film transistor can be reduced, a large aperture ratio can be secured even if the liquid crystal display is made finer by making the pixel pitch finer. Therefore, the transmittance is increased, and a bright liquid crystal display can be obtained. As described above, the thin film display semiconductor device for display in which the polysilicon thin film transistor having the excellent characteristics is integrated and formed is expanding its application range to various uses by taking advantage of its small size and high definition.

[0003]

Laser annealing using a laser beam has been developed as a part of a method for improving the efficiency of the manufacturing process of a display thin film semiconductor device and making it a low temperature process. This is to crystallize a semiconductor thin film in the cooling process after irradiating a non-single crystalline semiconductor thin film such as amorphous silicon or polysilicon formed on an insulating substrate with a laser beam to locally heat and melt it. Is. A thin film transistor is integrally formed by using this crystallized semiconductor thin film as an active layer (channel region). Since the crystallized semiconductor thin film has high carrier mobility, the thin film transistor can have high performance. As a laser beam irradiation method, for example, there is a method in which a laser spot having a small area is two-dimensionally scanned to irradiate the entire surface of the substrate. There is also a method in which a laser beam is shaped into a line and scanning is performed while partially overlapping in a one-dimensional direction. Further, there is a method of irradiating a laser beam by step-and-repeat with a large-area laser beam spot having a size of at least 1 chip or more. By the way, when comparing the thin film transistor formed in the peripheral drive circuit with the thin film transistor formed in the pixel array portion, the former needs to have higher performance than the latter. However, in the conventional laser beam irradiation method, consideration of this point is insufficient, and there has been a problem to be solved.

[0004]

SUMMARY OF THE INVENTION The present invention defines a plurality of sections separated from each other by vertical and horizontal boundaries along the surface of a flat substrate (wafer) made of an insulator, and a pixel is formed in a central region in each section. A method of manufacturing a thin film display semiconductor device for display, in which an array is formed and a drive circuit is formed in a peripheral region. First, a film forming process is performed to form a non-single-crystal semiconductor thin film on the entire surface of the flat substrate. Next, an irradiation step is performed to sequentially and selectively irradiate a laser beam shaped into a band with a predetermined width along each boundary sequentially, and at least a semiconductor thin film belonging to the peripheral region in each section adjacent to each boundary is formed. Converts from non-single crystalline to polycrystalline. Is the irradiation process on both sides of one boundary?
Irradiate the peripheral areas on both sides included in the adjacent sections at once
In order to do so, a laser beam having a sufficient width is used. Subsequently, a first processing step is performed to process the semiconductor thin film belonging to the peripheral region to form thin film transistors for circuit elements in an integrated manner and provide a drive circuit. Further, a second processing step is performed to process the semiconductor thin film belonging to the central region to integrally form thin film transistors for switching elements, and pixel electrodes connected to these are integrally formed to provide a pixel array. The first processing step and the second processing step include processes that are simultaneously performed. Finally, a cutting step is performed to cut the flat substrate along each boundary to separate the display thin film semiconductor devices formed in each section.

Preferably , in the irradiation step, a laser beam is irradiated along both vertical and horizontal boundaries, and a semiconductor thin film belonging to a peripheral region arranged vertically and horizontally along at least two mutually orthogonal sides of each section is non-single crystalline. To polycrystalline. Further preferably, the irradiation step includes a step of collectively irradiating a central region included in each section with a laser beam shaped like a plane, and the semiconductor thin film belonging to the central region is also converted from non-single crystalline to polycrystalline. To do. Alternatively, the irradiation step includes a step of scanning irradiation while partially overlapping a laser beam shaped linearly with respect to a central region included in each section,
The semiconductor thin film belonging to the central region may also be converted from non-single crystalline to polycrystalline. In the irradiation process, the flat substrate is
You may irradiate a laser beam, heating in the temperature range (degreeC-800 degreeC).

According to the present invention, a laser beam shaped into a band with a predetermined width is irradiated along each boundary, and the semiconductor thin film belonging to the peripheral region in the section adjacent to the boundary is selectively non-single crystalline. Has changed to polycrystalline. After that, the semiconductor thin film belonging to the peripheral region is processed to form thin film transistors for circuit elements in an integrated manner to provide a drive circuit. By selectively irradiating the peripheral region in which the drive circuit is formed in advance with the laser beam in this way, it becomes possible to crystallize the semiconductor thin film belonging to the peripheral region under the optimum conditions, and configure the drive circuit. The thin film transistor can be improved in performance. Further, the laser beam can be irradiated to the central region under the condition different from the peripheral region, and the thin film transistor for the pixel switching element can also be crystallized under the desired condition. In this way, the laser beam irradiation conditions can be set separately for the peripheral region to which the drive circuit belongs and the central region to which the pixel array belongs, and laser annealing can be optimized for each region and efficiency can be improved.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic plan view showing an outline of a method of manufacturing a display thin film semiconductor device according to the present invention. As shown in the figure, the present manufacturing method defines a plurality of sections 2 separated from each other by horizontal and vertical boundaries X and Y along the surface of a flat substrate (for example, a glass plate wafer 1) made of an insulator, The pixel array 4 is formed in the central region 3 in each section 2 and the drive circuit 6 is formed in the peripheral region 5. First, a film forming process is performed to form a non-single crystalline semiconductor thin film on the entire surface of the wafer 1. Next, an irradiation process is performed, and a laser beam 7 shaped in a band shape with a predetermined width W in advance is sequentially and selectively irradiated along each boundary.
In the illustrated state, the laser beam 7 is emitted along the vertical boundary Y located on the leftmost side. As a result, the semiconductor thin film belonging to the peripheral region 5 in each section 2 adjacent to the boundary Y is converted from non-single crystalline to polycrystalline. After that, a first processing step is performed to process the semiconductor thin film belonging to the peripheral region 5 to form thin film transistors for circuit elements in an integrated manner to provide the drive circuit 6. Further, the second processing step is performed, and the central region 3
The thin film transistor for the switching element is integrally formed by processing the semiconductor thin film belonging to the above, and the pixel electrode connected to these is integrally formed to provide the pixel array 4.
In the first processing step and the second processing step, thin film transistors are integrated and formed simultaneously. Finally, the wafer 1 is cut along the horizontal and vertical boundaries X and Y, and the display thin film semiconductor device 8 formed in each section 2 is individually separated.

Preferably, the laser beam 7 has a width sufficient to irradiate a peripheral region on both sides included in the section 2 adjoining one boundary (one vertical boundary Y in the illustrated state) from both sides at a time. Have W. As a result, in the left section 2, the right side of the peripheral area receives the laser irradiation, and in the right section 2, the left side of the peripheral area 5 receives the laser beam irradiation. Such a laser irradiation method is suitable when the drive circuit 6 is formed on the left side and the right side of the peripheral region 5 in one section 2. For example, there is a case where a pair of vertical scanning circuits is provided on the right side and the left side of the peripheral region 5. Further, in the irradiation step, by irradiating the laser beam 7 along both the horizontal and vertical boundaries X and Y, the peripheral region 5 arranged in the horizontal and vertical directions along at least two sides of each section 2 orthogonal to each other. The semiconductor thin film to which it belongs can be converted from non-single crystalline to polycrystalline. For example,
When the laser beam 7 is irradiated along the vertical boundary Y, the left side and / or the right side of the peripheral region 5 can be crystallized as described above, and the laser beam 7 is irradiated along the horizontal boundary X. In this case, the semiconductor thin films belonging to the upper side and / or the lower side of the peripheral region 5 can be irradiated with laser. Peripheral area 5
A horizontal scanning circuit or the like of the drive circuit 6 is formed on the upper side and / or the lower side. When switching the laser beam 7 between the vertical direction and the horizontal direction, for example, the wafer 1 mounted on the stage may be rotated by 90 °. As described above, according to the present invention, the laser beam 7 formed in a strip shape along the vertical and horizontal boundaries.
The desired conditions (laser beam energy and laser beam irradiation time) can be optimized by irradiating
The thin film transistor included in can be selectively made high in performance.

In the irradiation step, the peripheral region 5 of each section 2
It is possible to irradiate the central region 3 included in each section 2 with the laser beam under a condition different from the above. For example, by stepwise irradiating each section 2 with a laser beam shaped like a plane in accordance with the shape of the central region 3, each central region 3
It is possible to collectively convert the non-single-crystal semiconductor layer from the non-single-crystal semiconductor thin film in one shot. Alternatively, by irradiating the central region 3 included in each section 2 with a linearly shaped laser beam while partially overlapping, scan irradiation is performed,
The semiconductor thin film belonging to the central region 3 can be converted from non-single crystalline to polycrystalline. As described above, the central region 3 can be irradiated with the laser under a condition different from that of the peripheral region 5, so that the semiconductor thin film suitable for the thin film transistor for the pixel switching element can be crystallized.

In some cases, the irradiation step can be performed while heating the substrate. By using the substrate heating together, the energy of the laser beam can be saved. For example, when the peripheral region 5 is irradiated with the laser beam, the wafer 1 is heated in the temperature range of 400 ° C. to 800 ° C. As a result, a high-performance semiconductor thin film with advanced crystallization can be obtained. On the other hand, when the central region 3 is irradiated with the laser beam, for example, the wafer 1
It heats in the temperature range of 00 degreeC-500 degreeC. In this case, since the heating temperature is low, the crystallinity of the semiconductor thin film in the central region is somewhat inferior to that in the peripheral region, but there is no operational problem as a thin film transistor for a pixel switching element.
By setting the substrate heating temperature lower in the central area irradiation than in the peripheral area irradiation, the process load is reduced. However, the substrate heating conditions described above are merely examples, and do not limit the scope of the present invention. Depending on the case, the same heating condition may be adopted in the peripheral region and the central region.

FIG. 2 schematically shows a process of scanning irradiation while partially overlapping a laser beam shaped like a line (line shape) on the central region 3 of the section 2. In this laser annealing, the central region of the section 2 is intermittently irradiated with a pulse of a laser beam 7a formed in a line along the vertical direction (Y direction), for example. As the laser light source, for example, an excimer laser having a wavelength of 380 nm can be used. At this time, at the same time, the laser beam 7a is moved in the lateral direction (X direction) relative to the section 2 while partially overlapping the irradiation region. In the illustrated example, the section 2 is step-moved in the -X direction with respect to the fixed irradiation area of the laser beam 7a. In this way, by overlapping the laser beams 7a, the semiconductor thin film can be crystallized relatively uniformly. The overlap ratio is set to 90%, for example. The width of the laser beam 7a shaped into a line is set to about 0.3 mm, for example.

FIG. 3 shows an example of an active matrix type display display in which the thin film display semiconductor device 8 for display manufactured according to the present invention is assembled as a drive substrate.
This display includes a thin film semiconductor device (driving substrate) 8, a counter substrate 12, and an electro-optical substance 13 held between the two.
And a panel structure including. A liquid crystal material is widely used as the electro-optical material 13. The drive substrate 2 has the pixel array 4 and the drive circuit formed in an integrated manner, and can adopt a monolithic structure. That is, the pixel array 4 in the central area
In addition to this, the drive circuit in the peripheral region can be integrated. The drive circuit is a vertical scanning circuit 15 and a horizontal scanning circuit 16
It is divided into A terminal portion 17 for external connection is formed on the upper end of the peripheral portion of the drive substrate. Terminal 1 is wiring 1
8 to the vertical scanning circuit 15 and the horizontal scanning circuit 16. On the other hand, a counter electrode (not shown) is entirely formed on the inner surface of the counter substrate 12. Pixel array 4
Row-shaped gate lines 19 and column-shaped signal lines 20 are formed in the. The gate line 19 is a vertical scanning circuit 15
, And the signal line 20 is connected to the horizontal scanning circuit 16. A pixel electrode 21 and a thin film transistor 22 as a switching element for driving the pixel electrode 21 are integrally formed at the intersection of both lines. Of course, thin film transistors are also integrally formed as circuit elements in the vertical scanning circuit 15 and the horizontal scanning circuit 16.

Finally, FIG. 4 shows a specific example of the structure of the display thin film semiconductor device 8 shown in FIG. In the figure, for ease of understanding, only one thin film transistor 22 formed in the pixel array and the corresponding pixel electrode 21 are shown. The thin film transistors formed in the peripheral drive circuit have the same structure as the pixel switching thin film transistor 22. A buffer layer 31 is provided on an insulating substrate such as a quartz wafer 1. The buffer layer 31 has a function of preventing diffusion of impurities such as lithium, sodium, boron, aluminum and potassium contained in the wafer 1. The buffer layer 31 is made of, for example, a SiN film or a composite film of SiN and SiO ₂ . A semiconductor thin film 32 made of amorphous silicon or polysilicon is formed on the buffer layer 31. The semiconductor thin film 32 is formed by, for example, the CVD method. The film thickness is set to 100 nm or less in order to optimize the threshold voltage of the thin film transistor 22. Considering the crystallinity of the semiconductor thin film 32, it is preferable to make it as thin as possible. Considering the film thickness in the completed state and the decrease in the film thickness during the process, the semiconductor thin film 32 is preferably formed with a film thickness of 50 nm or less. This semiconductor thin film 32 is irradiated with an excimer laser beam or the like according to the present invention to grow crystals. In order to separate the semiconductor thin film 32 crystallized in this way into each element region of the thin film transistor 22, patterning is performed in an island shape by a photoresist method and an etching method. Then, the photoresist is stripped off and washed with a mixed solution of ammonia and hydrogen peroxide. Subsequently, SiO ₂ is deposited by the CVD method to form the gate insulating film 33. There are several types of this CVD method, and one is atmospheric pressure CVD. S under atmospheric pressure
iH ₄ gas and O ₂ gas is reacted at about 400 ° C., SiO ₂
Deposit. Two are low pressure CVD, 0.1 Torr to 5 Torr
Is a method of reacting SiH ₄ gas or SiH ₂ Cl ₂ gas with N ₂ O or O ₂ gas at a temperature between 400 ° C. and 800 ° C. under vacuum. The silicon oxide film formed by the low pressure CVD method has a relatively high quality and is called HTO. Furthermore,
In order to modify the interface between the semiconductor thin film 32 and the gate insulating film 33, heat treatment is performed at a temperature higher than the film forming temperature of the gate insulating film 33. By performing this thermal annealing in a nitrogen atmosphere or an argon atmosphere, the surface of the semiconductor thin film 32 is thermally oxidized and a silicon oxide film having a thickness of about 10 nm can be formed. Note that this thermal annealing may be performed in an oxygen atmosphere to promote thermal oxidation. This thermal oxidation may be performed before forming the gate insulating film 33 by the CVD method.

Next, after forming the gate insulating film 33, a material for the gate electrode is grown by the CVD method or the sputtering method. The film thickness is set to about 200 nm to 400 nm, and low resistance polysilicon, metal such as Al, Mo, W, or metal silicide or metal silicide is used as the gate material. Considering the high performance of the thin film transistor 22, a two-layer structure of silicide and metal is ideal. After that, the formed gate material is patterned by the photoresist method and the etching method to form the gate electrode 34. Then, impurities are implanted into the semiconductor thin film 32 by the ion implantation method using the gate electrode 34 as a mask. When forming the N-channel type thin film transistor 22, arsenic or phosphorus is used as an impurity. When forming the P-channel type thin film transistor 22, boron is used as an impurity. By this ion implantation, the source region S and the drain region D of the thin film transistor 22 are formed. Next, the impurities implanted in the semiconductor thin film 32 are activated. Activation is performed by heat treatment, instantaneous annealing with lamp light, or laser irradiation.

Subsequently, SiO ₂ or PSG is formed by a CVD method to provide an interlayer insulating film 35. This interlayer insulating film 35
A contact hole communicating with the source region S and the drain region D is opened by etching. A metal such as aluminum (Al) is formed on the interlayer insulating film 35 by a sputtering method, and the wiring electrode 3 is formed by a photoresist method and an etching method.
Process to 6. One wiring electrode 36 is electrically connected to the source region S through a contact hole, and the other wiring electrode 3
Similarly, 6 is electrically connected to the drain region D through the contact hole. An insulating film 37 made of SiN or the like is formed by plasma CVD so as to cover these wiring electrodes 36. In this state, heat treatment at about 400 ° C. is performed to improve the contact state of the contact portion, and at the same time, the semiconductor thin film 3
Hydrogenate 2. By this hydrogenation treatment, the interlayer insulating film 35
Hydrogen contained in or above the insulating film 37 is introduced into the semiconductor thin film 32 made of polycrystalline silicon or the like, and the film quality can be improved. As described above, the thin film transistor 2
2 is completed. After that, a flattening film 38 made of acrylic resin or the like is formed for flattening the surface of the pixel array portion. After forming a contact hole in the flattening film 38, a transparent conductive film made of ITO or the like is formed. The transparent conductive film is patterned by the photoresist method and the etching method to form the pixel electrode 21. The pixel electrode 21 is electrically connected to the wiring electrode 36 on the drain region D side through a contact hole opened in the flattening film 38.

[0016]

As described above, according to the present invention,
A laser beam shaped into a band with a predetermined width is step-irradiated along the boundary of the section, and the semiconductor thin film belonging to the peripheral region in the section adjacent to the boundary is efficiently converted from non-single crystalline to polycrystalline. There is. Therefore, the semiconductor thin film belonging to the peripheral region can be processed to integrally form a semiconductor thin film for high-performance circuit elements, and a drive circuit for a display thin film semiconductor device can be provided.

[Brief description of drawings]

FIG. 1 is a schematic plan view showing a method of manufacturing a display thin film semiconductor device according to the present invention.

FIG. 2 is a schematic view showing an example of an irradiation step performed in the method of manufacturing a display thin film semiconductor device according to the present invention.

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

FIG. 4 is a schematic partial cross-sectional view showing a specific structural example of a display thin-film semiconductor device manufactured according to the present invention.

[Explanation of symbols]

1 ... Wafer, 2 ... Partition, 3 ... Central area, 4 ... Pixel array, 5 ... Peripheral area, 6 ... Driving circuit, 7 ... Laser beam,
8 ... Thin film semiconductor device for display, 15 ... Vertical scanning circuit, 16
... horizontal scanning circuit, 21 ... pixel electrode, 22 ... thin film transistor

Claims (5)

(57) [Claims] 1. A plurality of sections are defined along a surface of a planar substrate made of an insulator, the sections being separated from each other by vertical and horizontal boundaries, a pixel array is formed in a central area of each section, and a driving circuit is formed in a peripheral area. A method of manufacturing a thin film semiconductor device for display, comprising: a film forming step of forming a non-single-crystal semiconductor thin film on the entire surface of the flat substrate; and a laser beam preliminarily shaped into a band with a predetermined width. And selectively irradiating the semiconductor thin film belonging to the peripheral region in each partition adjacent to each boundary with a non-single-crystal state to a polycrystalline state. A first processing step in which a semiconductor thin film belonging to the central region is integrated to form a thin film transistor for a circuit element and a drive circuit is provided; and a semiconductor thin film belonging to the central region is processed to form a thin film transistor for a switching element in an integrated manner. A second processing step in which pixel electrodes connected to these are integrally formed to provide a pixel array; and a cutting step in which the flat substrate is cut along the boundary and the display thin film semiconductor devices formed in each section are individually separated. The irradiation step includes
Sufficient width to illuminate the surrounding areas on both sides at once
A method of manufacturing a thin film semiconductor device for display, comprising using a laser beam having 2. In the irradiation step, a semiconductor thin film belonging to a peripheral region which is vertically and horizontally arranged along at least two sides of each section is irradiated with a laser beam along both vertical and horizontal boundaries to have non-single crystallinity. 2. The method for manufacturing a thin film semiconductor device for display according to claim 1, wherein the film is converted to polycrystalline. 3. The irradiation step includes the step of collectively irradiating a central region included in each section with a laser beam shaped like a plane, and the semiconductor thin film belonging to the central region is changed from non-single crystalline to polycrystalline. The method for manufacturing a thin film semiconductor device for display according to claim 1, wherein the method is the same. 4. The irradiation step includes a step of scanning and irradiating a central region included in each section with a linearly shaped laser beam while partially overlapping the central region, and the semiconductor thin film belonging to the central region is also a non-single crystal. 2. The method of manufacturing a thin film semiconductor device for display according to claim 1, wherein the property is changed to polycrystalline. 5. The flat substrate is heated to 400 ° C. or more in the irradiation step.
The method for manufacturing a thin film semiconductor device for display according to claim 1, wherein the laser beam is irradiated while heating in a temperature range of 800 ° C.