JP2005039259A - Crystallization method, crystallization equipment, thin-film transistor (tft), and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crystallization method, crystallization equipment, a thin-film transistor, and a display device that can minutely form crystal grains with a large grain diameter over a film and can meet low-temperature treatment requirements. <P>SOLUTION: As an insulating film, at least a silicon oxide film and a silicon nitride film are laminated, in the order to a laser beam incidence plane of a non-single-crystalline semiconductor film up to a prescribed thickness, and a uniform laser beam that is phase-modulated to a specific light intensity distribution is irradiated to the non-single-crystalline semiconductor film from the insulating film side. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a thin film transistor and a display device used for a display device such as a liquid crystal or an organic EL, and more particularly to a crystallization method and a crystallization device used for them.

  A driving circuit of a display device such as a liquid crystal display device is formed on an amorphous semiconductor film formed on a glass substrate. Since information handled by the expansion of the IT market is digitized and speeded up, display devices are also required to have high image quality. As means for satisfying this requirement, for example, by forming a switching transistor for switching each pixel in the crystal region, the switching speed is increased, and the image quality can be improved.

An excimer laser annealing method (ELA method) is known as a means for crystallizing an amorphous silicon layer formed on a glass substrate. However, the grain size of crystals obtained by this ELA method is about 0.1 μm, and when a thin film transistor (TFT) is formed in this crystallized region, a large number of crystal grains are formed in the channel region of one thin film transistor. would contain the field, mobility 200 cm ² / Vs, the on-off current ratio and extent ^107, inferior considerably when compared to MOS transistor formed in the single crystal Si.

  The present inventors have developed a technique for forming crystal grains that are large enough to form at least one thin film transistor by irradiating the amorphous silicon layer with laser light. By forming a TFT in a single crystal grain, there is no adverse effect of crystal grain boundaries, TFT characteristics are greatly improved, and functional elements such as a processor, a memory, and a sensor can be formed. As such a crystallization method, for example, there are crystallization methods described in Non-Patent Document 1 and Non-Patent Document 2.

In the former Non-Patent Document 1, the amorphous silicon film is irradiated with 0.8 mJ / cm ² fluence phase-modulated laser light through the SiON / SiO ₂ cap layer or the SiO ₂ cap layer to A method is described in which crystal grains are laterally grown in parallel directions to crystallize an amorphous silicon film.

In the latter non-patent document 2, the amorphous silicon film is irradiated in a lateral direction by irradiating the amorphous silicon film with a homogenized and phase-modulated laser beam through the SiO ₂ cap layer under substrate heating. A method for crystal growth is described.

W. Yeh and M. Matsumura Jpn. Appl. Phys. Vol. 41 (2002) 1909.

Proceedings of the 63rd JSAP Autumn Meeting 2002, p779, 26a-G-2. Masato Hiramatsu et al.

  However, in the method of Non-Patent Document 1, although a crystal grain having a large grain size of 10 μm or more can be obtained, a fine crystal grain having a small grain size is generated in the vicinity of the enlarged crystal grain. However, there is a problem that the film structure as a whole cannot be formed relatively uniformly (that is, densely) by arranging crystal grains having a large grain size.

  Further, in the methods of Non-Patent Documents 1 and 2, there is a problem that the substrate needs to be heated to a high temperature region in order to increase the crystal grain size, and the requirement for low temperature processing cannot be sufficiently satisfied. . For example, in the conventional crystallization apparatus 100 shown in FIG. 8, the laser beam 50 is irradiated while heating the substrate to be processed 5 to a high temperature region by the heater 101 built in the mounting table 6. The heater 101 is supplied with power from the power source 102 controlled by the controller 103 and has a capability of heating the substrate 5 to a temperature range of 300 to 750 ° C.

  Since the substrate heating temperature may exceed 500 ° C., for example, general-purpose glass (for example, soda glass) and plastic are likely to be altered or deformed by heating, and in order to employ these as substrates for liquid crystal display devices (LCD). Low temperature processing is an essential condition. In addition, there is a strong demand for weight reduction in large-screen LCDs, so there is a tendency to reduce the thickness of the substrate, which tends to cause deformation by heating, and low-temperature processing is an indispensable condition to ensure flatness of thin substrates. .

  The present invention has been made in order to solve the above-mentioned problems. A crystallization method and a crystal that can form large-sized crystal grains densely over the entire film and satisfy the requirements for low-temperature treatment. It is an object to provide a display device, a thin film transistor, and a display device.

  As a result of diligent research on the formation of crystal grains that are large enough to form at least one thin film transistor, the present inventors have found that crystal grains are not irradiated with conventional parallel pulsed laser light (laser light that has not been homogenized). In other words, it was found that the particle size could not be increased. The cause of this is not clarified in a strict sense, but the following can be presumed.

  FIG. 9 shows the light intensity distribution after the parallel pulse laser beam has passed through the phase shifter 4. In this light intensity distribution, the component that can contribute to the crystal growth in the lateral direction is from the first reverse peak wave 91 to the next peak wave 92. On the other hand, since the higher-order waves 93 (vibration; interference fringes) outside this do not contribute to the crystal growth in the lateral direction, each reverse peak wave 93 of higher-order vibrations other than the main reverse peak wave 91 contributing to the lateral growth. From the results, it was found that the crystal grains grew for a very short time to produce fine crystal grains, and the entire film could not be uniformly and densely enlarged. That is, it has been found that light obtained by phase-modulating parallel pulse laser light (light that has not been homogenized) includes high-order vibrations 93, so that crystal grains having a large grain size cannot be formed.

  In the crystallization of the present invention, the homogenized pulsed laser light is incident on the amorphous semiconductor film through the phase modulation optical system and the insulating film having the light absorption characteristic, thereby arranging the crystal grains having a large particle size in a dense manner. Can be formed. In other words, by irradiating the amorphous semiconductor film with pulsed laser light having a light intensity distribution as shown in FIG. 1B that does not include the high-order vibration 93 of FIG. Crystal grains can be formed in a dense (uniform) arrangement. The light intensity distribution BP shown in FIG. 1B is a light intensity distribution of a V-shaped groove as shown in FIG. This light intensity distribution BP has a plurality of peak patterns having an inverted triangular cross section. The light intensity distribution of each inverted triangular peak pattern has the same amplitude PH and the same pitch interval PW.

  The insulating film having the light absorption characteristic needs to have a thickness that has a function of absorbing a part of the incident homogenized pulse laser beam and storing the generated heat. The heat storage period is a period during which crystal grains can grow greatly.

  The crystallization method of the present invention is a crystallization method in which a non-single crystal semiconductor film is crystallized by irradiating a laser beam, and at least a silicon oxide film and an oxynitride are formed on the laser light incident surface of the non-single crystal semiconductor film. A silicon film is provided, and the laser beam is a laser beam having a light intensity distribution having a plurality of cross-section inverted triangular peak patterns.

  The crystallization apparatus of the present invention is a crystallization apparatus for crystallization by irradiating a non-single crystal semiconductor film with laser light, and a laser light source, a mounting table on which a substrate having the non-single crystal semiconductor film is mounted, A homogenizer provided between the mounting table and the laser light source, having a plurality of incident angles with respect to the substrate having the non-single crystal semiconductor film, and homogenizing the laser light with respect to a light intensity distribution, and the homogenizer And a phase shifter provided between the mounting table and phase-modulating the laser beam made uniform by the homogenizer.

  In the present invention, the pulse laser beam with the optimized light intensity distribution, that is, the pulse laser beam from which the influence of the higher-order vibration 93 shown in FIG. 9 is removed is crystallized through the SiON film as the light absorption film. Irradiation to a semiconductor film (amorphous film or polycrystalline film). As a result, the SiON film absorbs part of the irradiated laser light, generates heat over the entire film, stores heat in the SiON film for a predetermined period, and most of the remainder enters the non-single-crystal semiconductor film 52, and the irradiation Only the part is melted. The heat energy from the heat-stored SiON film heats the non-single crystal semiconductor film over the heat storage period. By heating from the SiON film, lateral growth of the non-single-crystal semiconductor film is promoted, and as a result, crystal grains can be formed relatively uniformly (that is, densely).

  That is, according to the method of the present invention, the heating effect of directly supplying heat energy from the light-absorbing exothermic insulating film in contact with the semiconductor film does not cause the substrate to be heated to a high temperature region as in the conventional method, and is simply Crystals having a large grain size close to or close to crystals can be obtained.

  The film thickness of the silicon oxynitride (SiON) film is preferably in the range of 100 to 1000 nm from the light absorption characteristics and the heat storage characteristics. When the film thickness is less than 100 nm, the total heat storage amount becomes insufficient, so that large crystal grains having a desired size cannot be obtained. On the other hand, if the film thickness exceeds 1000 nm, the amount of transmitted light decreases due to the light absorption of the cap film, and it becomes difficult for a sufficient fluence pulse laser beam to reach the non-single crystal semiconductor film to be crystallized. The objective of crystallization cannot be fully achieved.

  Further, the pulse laser beam is made uniform in terms of light intensity by the first fly-eye lens and the first condenser optical system as the homogenizer optical system (homogenizer), and further by the second fly-eye lens and the second condenser optical system. It is desirable that When the laser light that has been made uniform with respect to the light intensity passes through the phase shifter 4 in FIG. 1A, the ideal light repeats monotonously increasing and decreasing as shown in FIG. 1B. It becomes intensity distribution BP. The light intensity distribution BP in FIG. 1B has an inverted triangular cross section, the maximum peak value and the minimum peak value are projecting, and have no flat portion. Moreover, it has an equal amplitude PH and an equal pitch interval PW. That is, since the phase-modulated homogenized laser beam does not contain a high-order vibration component, when a crystallized film is irradiated with this, theoretically, large crystal grains having a size corresponding to the pitch interval PW of the beam profile are laterally generated. It becomes possible to grow. At this time, heat energy is replenished to the film to be crystallized by the heat generation effect and heat storage effect due to the light absorption of the insulating layer. Become. In the light intensity distribution BP of FIG. 1 (b), when the peak portion angle θ becomes sharp, film breakage is likely to occur. Therefore, the light intensity distribution BP is set so that the peak portion angle θ is as gentle as possible. It is desirable.

  In this specification, “non-single-crystal semiconductor film” refers to a thin film to be crystallized, such as an amorphous semiconductor (eg, an amorphous silicon film), a polycrystalline semiconductor (eg, a polysilicon film), and a mixed structure thereof. Say.

  In this specification, “crystallization” refers to crystal growth starting from a crystal nucleus in the process of melting and solidifying a film to be crystallized.

  In this specification, “lateral growth” means that the growth of crystal grains proceeds laterally along the film surface in the process of melting and solidifying the film to be crystallized.

  In this specification, “laser fluence” is a scale representing the energy density of laser light, which is obtained by integrating the amount of energy per unit area over time, and specifically measured in a light source or an irradiation region (irradiation field). This means the average light intensity of the laser beam.

  In this specification, “irradiation laser fluence” refers to the laser fluence of the homogenized laser light before being modulated by the phase shifter.

  In this specification, the “phase shifter” is an example of a phase modulation optical system, refers to a spatial intensity modulation optical element for modulating the phase of laser light, and is used in an exposure process of a photolithography process. It is distinguished from a shift mask. The phase shifter is, for example, a step formed on a quartz substrate as a transparent body. The step of the phase shifter is formed by a process such as etching so that incident light is phase-modulated to a predetermined phase angle, for example, 180 °.

As described above, according to the present invention, since large crystal grains can be formed side by side over the entire film, it is possible to manufacture a TFT that operates fast and has little threshold voltage variation. Become.
Further, according to the present invention, since it can be processed at a low temperature, it is possible to employ a thinner glass plate or plastic plate than the conventional one as the substrate.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  As shown in FIG. 2, the crystallization apparatus 10 irradiates the target substrate 5 on the mounting table 6 with the pulsed laser light 50 oscillated from the KrF excimer laser apparatus 1 through the optical systems 2a, 2b, 3 and 4. To do. The power supply circuit of the KrF excimer laser device 1 is connected to the output unit of the controller 8 so that the oscillation timing, pulse interval, output magnitude, etc. of the laser beam 50 are controlled. The mounting table 6 incorporates a heater 101. The power source 102 of the heater 101 is connected to the output unit of the controller 8 so that the amount of power supplied to the heater 101 is controlled.

  The optical systems 2a, 2b, 3 and 4 of this apparatus are configured such that, for example, a concave lens 2a, a convex lens 2b, a homogenizer 3, a phase shifter 4 and the like are arranged on the same optical axis.

  The homogenizer 3 has a function of leveling the pulse laser beam 50 in the irradiation region. That is, the light intensity of the pulsed laser light 50 that has passed through the homogenizer 3 is homogenized. The homogenizer 3 is an optical system for homogenizing (homogenizing) the pulse laser beam 50 with respect to the light intensity.

  Further, the homogenized pulse laser beam 50 is phase-modulated by the phase shifter 4. The phase shifter 4 is made of a transparent body, has a plurality of linear steps 4a arranged in parallel, and causes a phase difference in the pulse laser beam 50 at the steps 4a. Due to this phase difference, phase modulation occurs in the pulse laser beam 50. As a result, as shown in FIG. 1B, a light intensity distribution BP having a repeating pattern that repeats monotonous increase and monotonous decrease is formed in the irradiated portion. In the present embodiment, the interval W between the steps 4a to 4a of the phase shifter 4 is set to 20 μm.

  A SiON film 54 as a light absorption layer is provided on the upper surface of the substrate 5. The distance between the SiON film 54 and the phase shifter 4 is set to an interval of 500 μm or less, for example.

  The mounting table 6 is mounted on an XYZθ stage 7, is movable in the X-axis and Y-axis directions in the horizontal plane, is movable in the Z-axis direction orthogonal to the horizontal plane, and is rotatable about the Z-axis. is there. The power supply circuit of the XYZθ stage 7 is connected to the output unit of the controller 8 so that the X-axis drive mechanism, the Y-axis drive mechanism, the Z-axis drive mechanism, and the θ-rotation drive mechanism are controlled. In the above-described embodiment, the proximity method in which the phase shifter 4 is disposed close to the substrate 5 has been described. However, the present invention is not limited to this method, and may be applied to a projection method (projection method). Can do.

Next, a crystallization method by the crystallization apparatus 10 will be described. A pulse laser beam 50 having a pulse width of, for example, 30 nsec and an irradiation laser fluence of, for example, 1 J / cm ² is emitted from the pulse laser light source 1. The pulse laser beam 50 is diverged and converged by the concave lens 2 a and the convex lens 2 b and is incident on the homogenizer 3. The homogenizer 3 homogenizes the light intensity of the incident pulse laser beam 50.

  The homogenizer 3 causes the uniformed pulsed laser beam 50 to enter the phase shifter 4, and the phase shifter 4 emits the pulsed laser beam 50 having a light intensity distribution with a reverse peak pattern. A part of the pulsed laser light 50 having a light intensity distribution with a reverse peak pattern is absorbed by the light absorption film 54 provided on the pulsed laser light incident surface of the non-single crystal semiconductor film. Most of the remaining portion is incident on the non-single crystal semiconductor film 52 and only the irradiated portion is melted. The non-single crystal semiconductor film 52 immediately melts in the thickness direction, starts to solidify (crystallization) starting from the reverse peak point at which the fluence is minimized, and crystallizes in the lateral direction (direction perpendicular to the thickness of the film 52). Grain grows. Since the lateral growth of the crystal grains is promoted by the heat storage effect of the light absorption film 54, the size of the crystal grains after the final solidification is increased, and a wide range of single crystallization is realized in the irradiated portion.

  Such a crystallization step is performed over a predetermined entire surface of the non-single-crystal semiconductor film 52. The means for performing the crystallization process over the entire surface can be performed by moving the stage 7 relative to the irradiation position by the pulse laser light source 1.

Next, the optical system will be specifically described with reference to FIG.
The optical systems 2 and 3 of the apparatus of the present invention include a KrF excimer laser light source 1 that emits an excimer pulse laser beam having a wavelength of 248 nm, for example, as a pulse laser light source. As the light source 1, another light source such as a XeCl excimer laser light source or a YAG laser light source can be used. The laser light emitted from the light source 1 is incident on the first flyer lens 33 after being expanded through the optical systems 2a and 2b formed of a beam expander.

  A plurality of light sources are formed on the rear focal plane of the first fly-eye lens 33, and light beams from the plurality of light sources enter the second fly-eye lens 35 via the first condenser optical system 34. Illuminate the surface in a superimposed manner. As a result, more light sources are formed on the rear focal plane of the second flyer lens 35 than on the rear focal plane of the first fly-eye lens 33. The light flux from the light source formed on the rear focal plane of the second fly-eye lens 35 illuminates the phase modulation element 4 (phase shifter) in a superimposed manner via the second condenser optical system 36.

  Here, the first fly-eye lens 33 and the first condenser optical system 34 constitute a first homogenizer, and the second fly-eye lens 35 and the second condenser optical system 36 constitute a second homogenizer. Constitute. By these two homogenizers, the light intensity (laser fluence) at each position in the plane on the phase shifter 4 is made uniform. In this way, the illumination system irradiates the phase shifter 4 with light having a substantially uniform light intensity distribution (light intensity distribution).

The amorphous semiconductor film was crystallized by irradiating the substrate with light obtained by phase-modulating the homogenized pulse laser beam using the above-described apparatus. The substrate 5 to be processed includes a base protective film 51, a non-single crystal semiconductor film such as an amorphous semiconductor film 52, a first cap insulating film 53, and a second cap on a base made of an insulator or a semiconductor such as a silicon substrate 48. In this structure, insulating films 54 are sequentially stacked. The base protective film 51 is a material that prevents impurities from penetrating from the silicon substrate 48 and stores heat generated during the crystallization process of amorphous silicon. For example, the base protective film 51 is made of insulating SiO ₂ having a thickness of 1000 nm. Become. The amorphous semiconductor film 52 is a film to be crystallized and is made of amorphous silicon having a thickness of 50 nm to 200 nm. The first cap insulating film 53 is made of insulating SiO ₂ having a thickness of 30 nm. The second cap insulating film 54 is a light absorbing film that generates heat by absorbing part of the laser light 50, and is made of a SiON film having a thickness of 500 nm.

  A method for manufacturing the substrate to be processed having the double cap insulating films 53 and 54 will be described more specifically.

  As shown in FIG. 4B, the substrate 5 to be processed is obtained by forming an insulating layer as a base protective film 51 on an insulating substrate made of, for example, a glass substrate. As the insulating substrate, in addition to an insulating substrate such as a glass substrate, a quartz substrate, or a plastic substrate, a metal substrate, a silicon substrate, a ceramic substrate, or the like having an insulating film formed on a surface thereof can be used. As the glass substrate, it is desirable to use a low alkali glass substrate, for example, represented by Corning # 1737 substrate.

  An amorphous silicon film 52 (for example, an amorphous Si film having a thickness of 200 nm formed by plasma chemical vapor deposition) is formed on the base protective film 51.

A SiO ₂ film (for example, a 30 nm-thick SiO ₂ film formed by a plasma chemical vapor deposition method of SiH ₄ and N ₂ O) is formed thereon as a cap layer 53, and a light absorption layer 54 is further formed thereon. A SiON film (for example, a 500 nm thick SiON film formed by plasma chemical vapor deposition of NH ₃ , SiH _4, and N ₂ O) was formed. Next, dehydrogenation treatment of the thin films 51 to 54 formed on the substrate was performed (for example, heat treatment at 570 ° C. × 2 hours in a nitrogen atmosphere).

  A substrate having such double cap insulating films 53 and 54 is irradiated with a phase-modulated pulse laser beam 50 that is homogenized using the crystallization apparatus 10 shown in FIGS. The silicon film was crystallized and laterally grown.

  The mounting table 6 was moved in the X axis, Y axis, Z axis, and θ rotation axis directions by the XYZθ stage 7, and the substrate 5 to be processed was aligned with respect to the optical axis with high accuracy.

After heating the substrate, the pulsed laser beam 50 was emitted from the light source 1 while controlling the irradiation laser fluence to 620 mJ / cm ² . The pulse laser beam 50 is expanded by the beam expander 2, homogenized with respect to the light intensity by the homogenizer 3, further phase-modulated by the phase shifter 4 having the step 4 a, and then incident on the SiON cap film 54 on the substrate 5 to be processed. . As a result, the amorphous silicon film 52 grew in the lateral direction, and as a result, large crystal grains having an average crystal grain size of about 8 μm were obtained as shown in FIG.

  FIG. 5 is an SEM image of a Si thin film crystallized by the method of the present invention. As is apparent from the observation of the SEM image, it was confirmed that a Si crystal having a large particle size was formed by lateral growth in the range of 8 to 9 μm on one side from the laser optical axis (the center of the photograph). Further, it was confirmed that the laterally grown Si crystals extended very well in the lateral direction starting from the crystal nucleus in the vicinity of the center, and were aligned closely.

  After irradiating the pulse laser beam for one shot, the substrate was translated by a predetermined pitch distance, and the substrate was irradiated with the pulse laser beam of the next shot to obtain a Si crystal having a large particle size by lateral growth. By repeating the same operation, the element formation region of the amorphous silicon film was crystallized one after another.

In FIG. 6, the horizontal axis represents the substrate temperature (° C.), the vertical axis represents the lateral growth distance (μm), and the substrate temperature was varied for various samples, and the effect of the cap film and the lateral growth distance depended on the substrate temperature. It is a characteristic diagram which shows the result of having investigated property. In the figure, the characteristic line A is the result of the example sample having the SiON / SiO ₂ double cap film shown in FIG. 4A, and the characteristic line B is the comparative example having the SiO ₂ cap film having a film thickness of 300 nm. Sample results are shown respectively. The example sample and the comparative example sample had the same configuration and crystallization conditions except for the cap film. Moreover, the lateral growth distance calculated | required the average value.

  As is apparent from the figure, in the example samples, a lateral growth distance of about 4 μm at the longest was obtained even when the substrate temperature was room temperature (15 ° C. to 28 ° C.). As the substrate temperature was raised, the lateral growth distance became longer, the lateral growth distance when the substrate temperature was 300 ° C. increased to nearly 8 μm, and the lateral growth distance when the substrate temperature was 500 ° C. exceeded 8 μm. On the other hand, the lateral growth distance of the comparative sample was 1 μm at room temperature, slightly over 1 μm at 300 ° C., and less than 3 μm at 500 ° C.

  From the above, it was confirmed that it was possible to laterally grow large crystal grains (average crystal grain size of 4 to 8 microns) with a high filling rate by using the method of the present invention.

  Next, the configuration of the thin film transistor (TFT) of the present invention and the manufacturing method thereof will be described with reference to FIG. A thin film transistor was manufactured using a substrate having a semiconductor film having a large particle size by the crystallization method described above.

In addition to an insulating substrate such as a glass substrate 49, a quartz substrate, or a plastic substrate, a metal substrate, a silicon substrate, a ceramic substrate, or the like having an insulating film formed on the surface is applied to a base made of an insulator or a semiconductor. Is possible. As the glass substrate 49, it is desirable to use a low alkali glass substrate, for example, represented by a # 1737 substrate manufactured by Corning. The base protective film 51 is an insulating film containing silicon oxide (SiO ₂ ) or silicon nitride as a main component, for example, a silicon oxide film having a thickness of 300 nm, and is preferably formed in close contact with the glass substrate 49. The base protective film 51 is a film that acts to prevent impurities from diffusing from a base, for example, a glass substrate 49, into the non-single crystal semiconductor film.

  An amorphous semiconductor film or a non-single crystal semiconductor such as an amorphous silicon film 52 (for example, an amorphous Si film having a thickness of 200 nm formed by plasma chemical vapor deposition) is formed on the base protective film 51.

  After the cap films 53 and 54 are formed on the amorphous silicon film 52, a dehydrogenation process is performed to form the substrate 40 to be processed. The substrate to be processed 40 is subjected to a crystallization process by using a laser beam 50 that is phase-modulated by making the pulse laser beam homogenized by the optical system shown in FIG.

  After the crystallization process, the cap insulating films 53 and 54 are removed from the crystallized semiconductor film by etching. Next, a semiconductor circuit, for example, a thin film transistor shown in FIG. 4B is manufactured as follows in alignment with the crystallized region of the amorphous silicon film 52. First, in order to define the shape of the active region, patterning was performed using photolithography, and Si islands having a predetermined pattern substantially corresponding to each of the channel region 52a, the source region 52b, and the drain region 52c were formed in the planar field of view. At this time, the channel region 52a causes the non-single-crystal semiconductor film 52 to be lateralized by reaching the light obtained by phase-modulating the pulsed laser light 50 homogenized to the non-single-crystal semiconductor film 52 via the cap insulating films 53 and 54. This is a region where the crystal is grown in the direction.

Next, a gate insulating film 59 is formed over the channel region 52a, the source region 52b, and the drain region 52c. The gate insulating film 59 is a material mainly composed of silicon oxide (SiO ₂ ) or silicon oxynitride (SiON) and has a thickness of 10 to 200 nm. For example, a silicon oxide film using SiH ₄ and N ₂ O as raw materials is formed by a plasma CVD method to a thickness of 50 nm to form the gate insulating film 59.

  Next, a conductive layer for forming the gate electrode 55 was formed over the gate insulating layer 59. The conductive layer was formed using a material mainly composed of elements such as Ta, Ti, W, Mo, and Al by a known film formation method such as a sputtering method or a vacuum evaporation method. For example, an Al—Ti alloy was used. The gate electrode metal layer was patterned using photolithography to form a gate electrode 55 having a predetermined pattern.

Next, the source region 52b and the drain region 52c were formed by implanting impurities using the gate electrode 55 as a mask. For example, when forming a p-channel TFT, a p-type impurity such as boron ion is implanted using an ion implantation method. The boron concentration in this region was set to, for example, 1.5 × 10 ^{20 to} 3 × 10 ²¹ . In this way, high-concentration p-type impurity regions constituting the source region and drain region of the p-channel TFT are formed. At this time, it goes without saying that an n-channel TFT is formed if n-type impurities are implanted.

  Next, a heat treatment step is performed to activate the impurity element implanted by the ion implantation method. This step can be performed by methods such as furnace annealing, laser annealing, and rapid thermal annealing. In the present embodiment, the activation process is performed by furnace annealing. The heat treatment is desirably performed in a temperature range of 300 to 650 ° C. in a nitrogen atmosphere. In this example, heat treatment was performed at 500 ° C. for 4 hours.

  Next, an interlayer insulating film 56 was formed on the gate electrode 55 and the gate insulating film 59. The interlayer insulating film 56 may be formed of a silicon nitride film, a silicon oxide film, a silicon nitride oxide film, or a stacked film that combines them. The film thickness may be 200 to 600 nm, and is 400 nm in this embodiment.

  Next, a contact hole is opened at a predetermined position in the interlayer insulating film 56. Then, a conductive layer is formed inside the contact hole and on the surface of the interlayer insulating layer 56 and patterned into a predetermined shape. In this embodiment, the source / drain electrodes 57 and 58 are formed as a laminated film having a three-layer structure in which a Ti film is 100 nm, an aluminum film containing Ti is 300 nm, and a Ti film is 150 nm continuously formed by sputtering.

  Thus, the thin film transistor shown in FIG. 4B was obtained.

  Hereinafter, an example in which the thin film transistor obtained in the above-described embodiment is actually applied to an active matrix liquid crystal display device will be described.

  FIG. 7 is a diagram illustrating an example of an active matrix display device using thin film transistors. The display device 70 has a panel structure including a pair of insulating substrates 71 and 72 and an electro-optical material 73 held between the substrates. A liquid crystal material is widely used as the electro-optical material 73. A pixel array unit 74 and a drive circuit unit are integrated on the lower insulating substrate 71. The drive circuit section is divided into a vertical drive circuit 75 and a horizontal drive circuit 76.

  Further, a terminal portion 77 for external connection is formed at the upper end of the peripheral portion of the insulating substrate 71. The terminal portion 77 is connected to the vertical drive circuit 75 and the horizontal drive circuit 76 via the wiring 78. In the pixel array portion 74, row-shaped gate wirings 79 and column-shaped signal wirings 80 are formed. A pixel electrode 81 and a thin film transistor 82 for driving the pixel electrode 81 are formed at the intersection of both wirings. The gate electrode of the thin film transistor 82 is connected to the corresponding gate wiring 79, the drain region is connected to the corresponding pixel electrode 81, and the source region is connected to the corresponding signal wiring 80. The gate wiring 79 is connected to the vertical driving circuit 75, while the signal wiring 80 is connected to the horizontal driving circuit 76.

  The thin film transistor 82 for switching and driving the pixel electrode 81 and the thin film transistor included in the vertical drive circuit 75 and the horizontal drive circuit 76 are manufactured according to the present invention and have higher mobility than the conventional one. Therefore, not only the drive circuit but also a higher-performance processing circuit can be integrated.

  As described above, according to the above embodiment, the non-single-crystal semiconductor film is irradiated with the pulsed laser light that is modulated so that the light intensity has a repeated pattern of light intensity distribution that repeats monotonous increase and monotonous decrease. The next vibration component is reduced, and the appearance of small grain crystals due to the vibration component is effectively suppressed, and further, the pulsed laser light is incident from the light-absorbing heat-generating film, and the light-absorbing heat-generating property. As the temperature of the semiconductor film to be crystallized is raised due to the effect of the pseudo substrate heating of the film, lateral growth of the crystal grains is greatly promoted, and as a result, the lateral growth distance becomes longer, and the large-grain crystal grains are densely packed. Can be formed.

  Further, in a crystallization step, crystallization with a large particle size can be performed even at a low temperature such as room temperature and a temperature range in the vicinity thereof (for example, 5 ° C. to 50 ° C.). Furthermore, the laser light energy can be reduced to a low fluence.

(A) is a diagram showing the phase shifter and the substrate, (b) is a diagram showing the light intensity distribution of the homogenized pulse laser beam that has passed through the phase shifter, and (c) is a three-dimensional illustration of the light intensity distribution of the pulse laser beam. FIG. 1 is a configuration block diagram showing an outline of a crystallization apparatus of the present invention. The internal see-through block diagram showing the optical system of the device of the present invention. (A) is a cross-sectional schematic diagram explaining the manufacturing process of the to-be-processed substrate of this invention, (b) is a cross-sectional schematic diagram which shows the thin-film transistor of this invention. The SEM image which shows the effect of this invention. The characteristic diagram which shows the effect of this invention. The perspective view which shows the outline | summary of the display apparatus which concerns on embodiment of this invention. The block diagram which shows the outline | summary of a conventional apparatus. (A) is a figure which shows a phase shifter and a board | substrate, (b) is a figure which shows light intensity distribution after a parallel pulse laser beam passes a phase shifter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Excimer laser apparatus, 2a, 2b ... Optical lens,
3 ... Homogenizer (illumination system) 33, 35 ... Fly eye lens,
34, 36 ... condenser optical system, 4 ... phase shifter (spatial intensity modulation optical element),
48 ... Silicon substrate, 49 ... Glass substrate,
5 ... Substrate to be processed, 50 ... Laser light, 51 ... Base protective film,
52 ... Amorphous silicon film (non-single crystal semiconductor film) 52a ... Channel region,
52b ... source region, 52c ... drain region,
53... Cap layer (SiO ₂ film, first cap insulating film),
54 ... Light absorption layer (SiON film, second cap insulating film),
55 ... Gate electrode, 56 ... Interlayer insulating film,
57 ... Source electrode, 58 ... Drain electrode, 59 ... Gate insulating film,
6 ... mounting table, 7 ... X, Y, Z, θ stage,
10: Crystallizer.

Claims (8)

A crystallization method for crystallizing a non-single crystal semiconductor film by irradiating a laser beam,
At least a silicon oxide film and a silicon oxynitride film are provided on the laser light incident surface of the non-single-crystal semiconductor film,
The crystallization method, wherein the laser beam is a laser beam having a light intensity distribution having a plurality of cross-section inverted triangular peak patterns. The method according to claim 1, wherein at least one layer of the insulating film is a film exhibiting absorption characteristics with respect to a wavelength of the laser beam. The method according to claim 1, wherein the silicon oxynitride film has a thickness of 100 to 1000 nm. 4. The laser beam according to claim 1, wherein the laser beam is a pulsed laser beam modulated using a phase shifter so that the light intensity has a repeated pattern of light intensity distribution that repeats monotonous increase and monotonous decrease. The method according to claim 1. The method according to claim 1, wherein the laser light is light that is made uniform with respect to light intensity. A crystallization apparatus for crystallizing a non-single crystal semiconductor film by irradiating a laser beam,
A laser light source;
A mounting table on which a substrate having a non-single crystal semiconductor film is mounted;
A homogenizer provided between the mounting table and the laser light source, for homogenizing the laser light with respect to light intensity;
A phase shifter that is provided between the homogenizer and the mounting table and that modulates the phase of the laser beam that has been uniformized by the homogenizer;
A crystallization apparatus comprising: A pixel of a display device and a thin film transistor for driving the pixel,
An insulating substrate;
A SiO ₂ film is formed as a cap layer on the non-single-crystal semiconductor film formed on the substrate, and a SiON film is further formed as a light absorption layer on the SiO ₂ film. Incident light from the SiON film causes the SiON film to generate heat by absorption of the homogenized pulse laser light, and the homogenized pulse laser light to the non-single-crystal semiconductor film via the SiON film and the SiO ₂ film. A channel region formed in a crystal grain having a large grain size formed by laterally crystallizing the non-single crystal semiconductor film,
A source region and a drain region which are provided so as to sandwich the channel region and are doped with a predetermined impurity;
A gate insulating film formed on the channel region;
A gate electrode formed on the gate insulating film;
An interlayer insulating film covering the gate electrode;
A source electrode conducting from the interlayer insulating film side to the source region;
A drain electrode conducting from the interlayer insulating film side to the drain region;
A thin film transistor comprising: A pair of substrates bonded to each other through a predetermined gap and an electro-optic material held in the gap, a counter electrode is formed on one substrate, and a pixel and this are driven on the other substrate A display device formed of a thin film transistor,
The thin film transistor
An insulating substrate;
A SiO ₂ film is formed as a cap layer on the non-single-crystal semiconductor film formed on the substrate, and a SiON film is further formed as a light absorption layer on the SiO ₂ film. Incident light from the SiON film causes the SiON film to generate heat by absorption of the homogenized pulse laser light, and the homogenized pulse laser light to the non-single-crystal semiconductor film via the SiON film and the SiO ₂ film. A channel region formed in a crystal grain having a large grain size formed by laterally crystallizing the non-single crystal semiconductor film,
A source region and a drain region which are provided so as to sandwich the channel region and are doped with a predetermined impurity;
A gate insulating film formed on the channel region;
A gate electrode formed on the gate insulating film;
An interlayer insulating film covering the gate electrode;
A source electrode conducting from the interlayer insulating film side to the source region;
A drain electrode conducting from the interlayer insulating film side to the drain region;
A display device comprising:

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