JP2005032831A - Crystallization method, crystallization equipment, tft, and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crystallization method wherein laser beam having intensity and distribution which are optimized on a plane of incidence of a substrate is designed, and desired crystallization organization can be formed while restraining generation of the other organization region which is not desirable, and to provide crystallization equipment, a TFT and a display device. <P>SOLUTION: When a non-single crystal semiconductor thin film is irradiated with laser beam and crystallized, irradiation light to the non-single crystal semiconductor thin film has intensity distribution which repeats monotonous increase and monotonous falloff periodically, and has intensity by which the non-single crystal semiconductor thin film is melted. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for manufacturing a field effect transistor on a surface layer portion of a polycrystalline semiconductor thin film, a single crystal and polycrystalline semiconductor thin film substrate for manufacturing the field effect transistor, and a liquid crystal display device and an information processing apparatus incorporating the field effect transistor. The present invention relates to a crystallization method, a crystallization device, a thin film transistor, and a display device suitable for manufacturing an electronic device such as the above.
[0002]
[Prior art]
As a display method of the current liquid crystal display, there is an active matrix method in which individual pixels are switched. As the pixel switching element, an amorphous silicon thin film transistor (a-Si TFT) is mainly used.
[0003]
In the technical development of the liquid crystal display (LCD), intensive research is being conducted with the aim of (1) high definition, (2) high aperture ratio, (3) light weight, and (4) cost reduction. In order to realize these performances, a technique using a polycrystalline semiconductor thin film transistor (poly-Si TFT) has attracted attention. Poly-Si TFTs have a mobility that is two orders of magnitude higher than a-Si TFTs, so the device size can be reduced and integrated circuits can be formed. It is possible to do.
[0004]
A method of manufacturing a polycrystalline semiconductor thin film transistor by an excimer laser crystallization method according to the prior art will be described with reference to FIG. As shown in FIG. 12A, a base protective film (for example, SiO 2) is formed on the glass substrate 101. ₂ Films, SiN films, and SiN / SiO ₂ A laminated film 102) and an amorphous silicon thin film 103 are deposited. Next, as shown in FIG. 12B, when the surface of the amorphous silicon thin film is irradiated with an excimer laser (XeCl, KrF, etc.) 104 which has been shaped into a square shape or a long shape by an optical system, The crystalline silicon thin film 103 is converted from an amorphous structure to a polycrystalline structure through a melting and solidifying process in an extremely short time of 50 to 100 nanoseconds by irradiation and heating of the excimer laser 104. When the entire surface of the amorphous silicon film 103 is scanned and heated by the excimer laser 104 in the direction of the arrow 105, a polycrystalline silicon thin film 106 as shown in FIG. 12C is formed.
[0005]
The above process is called an excimer laser crystallization technique (hereinafter referred to as ELA method). The ELA method is used when a high-quality polycrystalline silicon thin film is formed on a substrate made of a low melting point material such as glass. Regarding these, for example, see Non-Patent Document 1.
[0006]
A thin film transistor shown in FIG. 12D is manufactured using the polycrystalline silicon thin film 106 in FIG. On top of the polycrystalline silicon thin film 106 of this TFT, SiO 2 is formed by film formation. ₂ A gate insulating film 107 such as a film is provided. Further, a source impurity implantation region 108 and a drain impurity implantation region 109 are provided. A gate electrode 110 is provided over the source and drain regions and the gate insulating film, a protective film 111 is formed, and a source electrode 113 and a drain electrode 114 are formed. Thus, a TFT capable of controlling the current between the source and the drain by the voltage of the gate electrode is completed.
[0007]
Furthermore, in order to improve the performance of the TFT, a “phase modulation excimer laser crystallization method”, which is a technique for crystallizing polycrystalline silicon, has been reported as a method developed from the ELA method. In the phase modulation excimer laser crystallization method, the position-controlled laterally grown Si crystal grains r1 are controlled by controlling the beam profile A shown in FIG. 2A and the beam profile B shown in FIG. It is possible to form crystal grains r2. Non-patent document 2 is an example of a paper on such a phase modulation excimer laser crystallization method. In the phase modulation excimer laser crystallization method, formation of laterally grown Si crystal grains is promoted using a controlled beam profile. In the conventional ELA method, for example, Non-Patent Document 3 relates to the correlation between the beam profile and the crystallized structure, but there is a great difference because the beam profile is not controlled.
[0008]
[Non-Patent Document 1]
Nikkei Microdevices separate volume flat panel display 1999 (Nikkei BP, 1998, pp. 132-139)
[0009]
[Non-Patent Document 2]
The Ninth International Display Worksshop (IDW'02) Proceedings pp. 263-266
[0010]
[Non-Patent Document 3]
Journal of Applied Physics Vol. 88 No9 1Nov 2000 pp. 4994-4999
[0011]
[Problems to be solved by the invention]
However, when the silicon film is crystallized by using the conventional phase modulation excimer laser crystallization method, polycrystalline silicon grains r3 are formed at the periphery in addition to the laterally grown Si crystal grains r2, as shown in FIG. In some cases, a fine crystal grain r4 is generated at the center, and further a crystal grain breaking region r5 is generated. This is because the light intensity distribution is not optimized.
[0012]
When the structure crystallized by the phase modulation excimer laser crystallization method is actually observed, a single crystallized region r2 having a large grain size is formed, but other undesirable structures r4 and r5 are simultaneously generated. It was.
[0013]
Similarly, when a structure crystallized by the phase modulation laser crystallization method is observed, a single crystal silicon region r2 having a large grain size is formed, but a crystal grain breakdown region r5 and a microcrystal region r4 are formed around the single crystal silicon region r2. It has occurred.
[0014]
The present invention has been made in order to solve the above-described problems, and designed a laser beam having an optimized light intensity and distribution on the incident surface of the substrate to suppress the generation of other undesirable tissue regions. It is another object of the present invention to provide a crystallization method, a crystallization apparatus, a thin film transistor, and a display device that can form a desired crystallized structure.
[0015]
[Means for Solving the Problems]
In order to achieve this object, the present invention is configured as follows. In advance, the laser beam intensity JL for starting the lateral growth and the light intensity JB that can be input are respectively examined. A beam profile is measured on the same plane as the substrate surface, and the beam profile is set to a waveform that monotonously increases and monotonously decreases, for example, a triangular wave, with a minimum laser intensity of JL or more and a maximum laser light intensity of less than JB. At this time, since the position where JL is the crystallization start position, the crystal position can be defined.
[0016]
In the crystallization method according to the present invention, when the non-single crystal semiconductor thin film is irradiated with laser light having a light intensity distribution that periodically repeats monotonous increase and monotone decrease at predetermined intervals in the irradiation region of the non-single crystal semiconductor thin film. The light intensity distribution is such that the light intensity equal to or exceeding the light intensity obtained by melting the non-single crystal semiconductor thin film and growing in the lateral direction is minimized, and the laterally grown crystal grains are broken. The light intensity lower than the light intensity is set to the maximum value. By irradiating a laser beam having such a light intensity distribution, the crystal grains grow stably in a lateral direction (lateral) without being broken, resulting in a large grain structure having a uniform size suitable for a thin film transistor (see FIG. 3) 3).
[0017]
The minimum value of the light intensity distribution is characterized in that the non-single crystal semiconductor thin film is melted. By irradiating laser light having such a light intensity distribution, the entire structure of the non-single-crystal semiconductor thin film is crystallized into a polycrystalline structure (region 2 in FIG. 3).
In addition, the maximum value of the light intensity distribution is in the light intensity range below the light intensity that causes breakage in the laterally grown crystal grains, and the minimum value of the light intensity distribution is below the light intensity at which the non-single crystal semiconductor thin film melts. And By irradiating laser light having such a light intensity distribution, the ratio of the polycrystalline structure to the amorphous structure can be freely changed (region 1 and region 2 in FIG. 3).
[0018]
The maximum value and the minimum value of light intensity are set according to at least the film thickness and temperature conditions of the non-single-crystal semiconductor thin film. For example, under the condition of the substrate temperature of 500 ° C., the beam profile BP shown in FIG. 9B can be set. The beam profile BP shown in FIG. 9B is a dimensionless index in which the light intensity on the vertical axis is normalized. This normalized light intensity index is the actual unit (J / cm ² ) Can be converted into a laser fluence. For example, the average laser fluence (J / cm ² ), The laser fluence at each position (J / cm ² ).
[0019]
A crystallization apparatus according to the present invention is an apparatus for crystallizing a non-single-crystal semiconductor thin film by irradiating a laser beam, a laser light source, and a mounting table on which a substrate having the non-single-crystal semiconductor thin film is placed; A spatial intensity modulation optical element that is inserted between the laser light source and the substrate and modulates the light intensity distribution on the incident surface of the substrate, and measures the intensity and distribution of the laser light on the incident surface of the substrate using laser light (Beam profile measuring machine) means to set the target laser light intensity and distribution in advance, and periodically repeat monotonously increasing and decreasing monotonically at a predetermined interval in the irradiation area, and A means for designing a light intensity distribution in which the minimum value is a value that exceeds the light intensity at which the non-single crystal semiconductor thin film melts, and the light intensity that is lower than the light intensity that causes breakage in the laterally grown crystal grains is the maximum value. As distribution and the measured light intensity coincides with the set target, characterized by comprising, a means for guiding the laser light modulated by the spatial intensity modulation optical element on the incident surface of the substrate.
[0020]
It is desirable that the measuring unit has a fluorescent plate on an incident surface on which the reference light is incident, and the fluorescent plate is arranged in substantially the same plane as the incident surface of the substrate.
[0021]
The spatial intensity modulation optical element is preferably a uniform optical system including a phase shifter. The homogenizing optical system is composed of optical components such as a homogenizer having a pair of small lenses and a plurality of sets of condenser lenses. Note that a phase shift mask used for exposure in a photolithography process of a semiconductor device may be used as the spatial intensity modulation optical element.
[0022]
Here, “laser fluence” refers to a measure of light intensity that represents the energy density of a laser, and refers to an integral of the amount of energy per unit area per unit time.
[0023]
The “beam profile” refers to a two-dimensional light intensity distribution of laser light incident on the crystallization target film. The reference light incident on the profiler (beam profile measurement unit) is the same as the light source used for laser annealing, but it does not have to be the same as the light intensity of the laser incident on the film to be crystallized. The light intensity required to do so may be used.
[0024]
In addition, “predetermined target light intensity and distribution” means that an amorphous semiconductor thin film melts and lateral crystal grows by a verification test described later, and a crystallized film is not destroyed by thermal contraction. The confirmed intensity (laser fluence) and distribution (beam profile) of the laser beam shall be said.
[0025]
FIG. 3 is a state diagram showing the qualitative relationship of the temperature / light intensity / structure of a semiconductor (for example, silicon) by making the vertical axis and the horizontal axis dimensionless. In the figure, the characteristic line JC indicates a boundary (crystallization boundary) whether or not an amorphous film (or a mixed film in which amorphous and fine crystal grains are mixed) is crystallized (recrystallization). The characteristic line JL is the boundary whether or not the crystal grain grows in the lateral direction (lateral growth boundary), and the characteristic line JB is the boundary whether or not the grown crystal grain is finally broken (boundary for crystal grain destruction). Respectively.
[0026]
In the region 1 below the characteristic line JC, the physical state of the amorphous film or the mixed film in which fine crystal grains are mixed in the amorphous material does not change.
In the region 2 between the characteristic lines JC-JL, the amorphous film crystallizes (the mixed film recrystallizes) but does not grow laterally.
In the region 3 between the characteristic lines JL-JB, the crystal grains stably grow laterally without breaking.
In the region 4 above the characteristic line JB, the film (crystal structure) is destroyed (film destruction region) by receiving various stresses during or after the growth of crystal grains.
[0027]
Here, “film breakdown” means that the regular structure (film structure) constituting the film is broken in a broad sense, and in a narrow sense, the cap film is caused by stress generated when the crystal grains laterally grow laterally. The film to be crystallized is broken by the stress generated during lateral growth, or cracks in the crystal grains or the grain boundaries due to hydrogen contained in the cap film or the film to be crystallized, etc. It shall mean that the above defect is produced.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0029]
FIG. 1 shows a schematic diagram of a laser crystallization apparatus embodying the present invention. In the laser crystallization apparatus, an attenuator (attenuator) 2 and a beam profile modulator 3 are arranged at the beginning of the optical axis a of the laser light source 1, and a semiconductor substrate 5 is installed at the end via a mirror 4. In addition, the beam profile measuring unit 6 is arranged in parallel on the semiconductor substrate 5, and the semiconductor substrate 5 and the beam profile measuring unit 6 are fixed to the moving stage 7.
[0030]
Further, a control personal computer 8 is installed, the beam profile measuring unit 6 is connected to the input side, and the control system of the attenuator 2, the beam profile modulating unit 3, and the moving stage 7 is connected to the output side.
[0031]
The attenuator 2 optically modulates the intensity (power) of laser light by adjusting the angle of the dielectric multilayer coating filter, and includes a sensor, a motor, and a control system (not shown).
[0032]
The beam profile modulation unit 3 modulates the spatial intensity distribution of the laser light, and includes a phase shifter 31 and a uniformizing optical system 32. For example, the phase shifter 31 generates a reverse peak pattern in which the light intensity is minimized in the phase shift unit by alternately shifting the phase of the light passing through the mask pattern to 0 and π. 5, the first solidified region (crystal nucleus) is controlled in position, and then a crystal is laterally grown from there (lateral growth), thereby providing a crystal grain having a large grain size at a designated position. At this time, a desired beam profile is set according to the shape of the phase shifter, the distance from the semiconductor substrate 5, the angular distribution of the laser light, and the like. The phase shifter 31 also includes a sensor, an actuator, and a control system (not shown) for exchanging mask patterns and aligning in the optical axis direction.
[0033]
The homogenizing optical system 32 is disclosed in detail in the specification of Japanese Patent Application No. 2003-110861 filed earlier by the present inventors, and is an optical component such as a homogenizer having a pair of small lenses and a plurality of condenser lenses. It is configured. The semiconductor substrate 5 is held at a position defocused from the focal position of the uniformizing optical system 32 and the laser beam 50 is irradiated. The shape and width of the reverse peak pattern are controlled by the mask pattern and the defocus amount at this time. The width of the reverse peak pattern increases in proportion to the 1/2 power of the gap d between the phase shifter 31 and the semiconductor substrate 5.
[0034]
The beam profile measuring unit 6 receives an ultraviolet excimer laser on the fluorescent plate 61 and converts it into visible light, and the visible light reflected on the mirror 62 is received on the CCD 63 and simultaneously measures the intensity and beam profile of the laser light. You may measure the intensity | strength of a laser beam separately using a semiconductor lower meter etc. FIG. Alternatively, an ultraviolet excimer laser may be directly received by the CCD 63.
[0035]
The fluorescent plate 61 is placed on a plane parallel to the center on the same plane as the semiconductor substrate 5. When the fluorescent plate 61 is installed on a parallel plane with a step, the movable stage 7 is moved up and down to position the fluorescent plate 61 at the same height as the semiconductor substrate 5 and perform measurement. Thereby, the beam profile of the laser beam on the substrate surface can be measured under the same conditions as in actual irradiation.
[0036]
The image received by the CCD 63 is input to the computer 8 and sliced by an arbitrary scanning line, and the intensity of the laser beam and the beam profile are measured from the intensity distribution of the image signal.
[0037]
Then, the manipulated variable is calculated by comparing the measured intensity with a preset target intensity, and the angle of the attenuator 2 is adjusted while feeding back the measured intensity to the target intensity by outputting an operation signal to the attenuator 2. Adjust.
[0038]
Further, an operation amount is calculated by comparing the measured beam profile with a preset target beam profile, and an operation signal is output to the beam profile modulation unit 3 and the moving stage 7 so that the measured beam profile becomes the target beam profile. The position of the phase shifter 31 and the height of the moving stage 7 are adjusted with feedback.
[0039]
The moving stage 7 can move in the front-rear, left-right, and upper-lower three-dimensional directions, and includes sensors, actuators, and a control system (not shown) for alignment in the in-plane direction and the optical axis direction. The beam profile measuring unit 6 is moved to and positioned at the laser beam irradiation position by the moving stage 7, and the intensity and beam profile of the laser beam are measured in advance before the laser beam is irradiated onto the substrate.
[0040]
The laser crystallization apparatus embodying the present invention is configured as described above. In the laser crystallization process, first, the moving stage 7 is moved in the in-plane direction, and the tip of the optical axis a of the laser light source 1 is set as a beam profile measuring unit. 6 is positioned on the fluorescent plate 61 and irradiated with laser light to measure its intensity and beam profile.
[0041]
Next, the angle of the attenuator 2, the position of the phase shifter 31, and the height of the moving stage 7 are aligned so that the measured intensity and beam profile coincide with a preset target. Next, the moving stage 7 is moved in the in-plane direction, this time the tip of the optical axis a is positioned in a predetermined crystal region of the semiconductor substrate 5, set to a gap d, and laser light having a preset intensity and beam profile is set. Irradiate.
[0042]
By repeating the above measurement, alignment, and irradiation, crystal regions having different average sizes Na of the number of crystal grain boundaries crossing the current direction in the channel region but having different TFT sizes are formed simultaneously. Measurement, alignment, and irradiation are not performed alternately in this way. First, all measurements are performed to determine the amount of operation necessary for alignment, and then alignment and irradiation are performed in parallel for each crystal region. You may do it.
[0043]
【Example】
First, as shown in FIG. 4A, as a substrate preparation, a first thin film 102 (for example, tetraethylorthosilicate (TEOS) is formed on the surface of an insulator substrate 5 (for example, Corning 1737 glass, fused silica, sapphire, plastic, polyimide, etc.). ), And O ₂ 300 nm-thickness SiO 2 deposited by plasma chemical vapor deposition ₂ Film or SiN / SiO ₂ (A laminated film alumina, mica, etc.), on the surface of the first thin film 102, a second thin film amorphous semiconductor thin film 103 (for example, 200 nm thick amorphous Si, amorphous SiGe, etc. by plasma chemical vapor deposition) Is deposited. On top of that, tetraethyl orthosilicate (TEOS) and O ₂ For example, SiO film having a film thickness of 200 nm is formed as a gate insulating film by plasma chemical vapor deposition. ₂ A film 107 is formed. Next, dehydrogenation treatment of the thin film is performed (for example, heat treatment at 600 ° C. for 1 hour in a nitrogen atmosphere). The following points are investigated on this crystallization substrate and adjusted so as to obtain a suitable beam profile.
[0044]
(I) The laser beam intensity JL at which lateral growth occurs on the crystallization substrate to be used is investigated.
[0045]
(Ii) Investigate the laser beam intensity JB at which crystal grain breakage occurs in the crystallization substrate to be used.
[0046]
(Iii) The distribution of the laser beam intensity is such that the laser beam intensity J at the position desired to be the crystallization start point is JB> J ≧ JL, and the laser intensity distribution monotonously increases toward the maximum laser beam intensity.
[0047]
The maximum laser beam intensity is set to be less than JB. By performing crystallization that satisfies this requirement, it is possible to perform crystallization without generating a crystal grain breakdown region and a microcrystalline region.
[0048]
(Verification test)
When a specific experiment was performed using the above substrate, results as shown in FIG. 6 were obtained. FIG. 6 is a state diagram showing the results of examining the quantitative relationship of temperature / light intensity / structure in a silicon thin film with the substrate temperature (° C.) on the horizontal axis and the laser fluence (relative value) on the vertical axis. is there. As is apparent from the figure, at 500 ° C., for example, the lateral growth starting strength JL is 20-30% (for example, 0.4-0.6 J / cm) as a relative value. ² The film breaking occurrence strength JB is 20 to 60% (for example, 0.8 to 1.2 J / cm) as a relative value. ² Equivalent to the converted intensity). Therefore, it has been clarified that the laser light intensity in the mesh region should be set under the condition (iii) (JB and JL are the laser light intensity inside the mesh) at each substrate temperature.
[0049]
Next, laser crystallization is performed using the laser crystallization apparatus of FIG. The laser light source 1 uses a pulsed high energy laser such as a KrF excimer laser.
[0050]
The laser light emitted from the laser light source 1 passes through the attenuator 2 and the beam profile modulation unit 3 that can modulate the power and the beam profile. As a result, the power and beam profile are modulated. Thereafter, the mobile stage 7 is reached. A semiconductor substrate 5 is disposed on the moving stage 7. Laser crystallization is performed by irradiating the semiconductor substrate 5 with modulated laser light. The moving stage 7 is provided with a beam profile measuring unit 6 that can measure a beam profile and can also be used as a power meter. This apparatus is linked with a personal computer 8 for measurement, and parameters of an optical system (for example, angle of the attenuator 2 and phase shifter) that can modulate the moving stage 7 height z, power, and beam profile so as to have a suitable bee beam profile. 31 position, gap d, etc.) are set.
[0051]
The beam profile BP of FIG. 9B is a beam profile that can form a large crystal grain region. The beam profile BP is set with a system linked to the above-described measurement personal computer 8. A scanning electron micrograph of the resulting tissue is shown in FIG. In this case, the profile necessary for manufacturing the TFT is that the gap d = 60 μm and the average laser light intensity J is 0.8 J / cm. ² , JL = 0.5J / cm ² , JB = 0.9J / cm ² It became clear that this should be done.
[0052]
The crystal region manufactured by these methods is subjected to patterning and the following process is performed.
As shown in FIG. 4B, a gate electrode 110 (for example, high-concentration Lindo polysilicon, W, TiW, WSi is formed on the gate insulating film 107. ₂ , MoSi ₂ ). Using the gate electrode 110 as a mask, ion implantation is performed to form a source region 103b and a drain region 103c, respectively. For example, if ion implantation is an N-type TFT, p + is set to 10 ¹⁵ cm ^-2 Implanted on the order, BF in p-type TFT ²⁺ 10 ¹⁵ cm ^-2 Inject on order. Thereafter, annealing is performed for about 1 hour at 500 to 600 ° C. using nitrogen as a carrier gas in an electric furnace to activate the impurities. Moreover, you may make it heat only by 700 degreeC x 1 minute by rapid thermal annealing (RTA). Between the source region 103b and the drain region 103c is a channel region 103a crystallized by the above-described method.
[0053]
Finally, an interlayer insulating film 111 is formed, contact holes are formed, the contact holes are filled with metal by a metal CVD film forming method, and a source electrode 113 and a drain electrode 114 are formed. For example, Al / TIN is used as the material of the source electrode 113 and the drain electrode 114.
[0054]
In FIG. 7A, the horizontal axis is the distance (μm) from the laser optical axis a, and the vertical axis is the normalized laser intensity index (no unit), and the profile created by the multi-beam by the homogenizer is shown. FIG. The normalized strength index on the vertical axis is a parameter that serves as a guide for crystallization, and when these are averaged, they converge to 1.0. In FIG. 7A, when the strength index is 1.0, 0.2 J / cm. ² Is equivalent to a laser fluence of 0.19 J / cm, which is a critical light intensity of polycrystallizing when this is multiplied by a coefficient of 0.95. ² Is obtained.
[0055]
In the figure, a characteristic line E (thin line) indicates a simulation result, and a characteristic line F (thick line) indicates an actual measurement result. The measured results and the simulation results were in good agreement except for the high spatial frequency components caused by a finite number of beams.
[0056]
FIG. 7B shows a film morphology crystallized under a low average light intensity condition. The sample is 300 nm thick at a substrate temperature of 500 ° C. ₂ Cap film / 200 nm thick a-Si film / 1000 nm thick SiO ₂ Film / Si structure. A portion where the polycrystallization occurs (low portion) is a local high light intensity portion, and a local low light intensity portion (black portion) is a region where crystallization has not occurred. The black part is 0.19 J / cm on the characteristic line E in FIG. ² It was in good agreement with the position below the line indicated by (intensity index 0.95). The critical light intensity at which polycrystallization occurs is about 0.19 J / cm ² This value was the same as in the case of uniform irradiation. Note that the critical light intensity at which lateral crystallization starts and film failure occurs from experiments with a high average light intensity is 0.5 J / cm, respectively. ² 0.9J / cm ² It turned out to be. It has also been found that the distance that can be grown in a single shot is about 7 microns.
[0057]
In FIG. 8A, the horizontal axis indicates the distance (μm) from the laser optical axis a, and the vertical axis indicates the normalized laser intensity index (unitless), so that crystallized Si grows laterally. FIG. 5 is a characteristic diagram showing a relationship with laser fluence regarding whether or not a laterally grown crystal film breaks due to excessive contraction force. A characteristic line P in the figure is a critical line for lateral growth, and the Si crystal grows laterally in the region above this, and does not grow laterally in the region below this. The characteristic line Q is a critical line for film destruction. In the region above this, the Si crystal film is destroyed by excessive shrinkage, and in the region below this, the Si crystal film is not destroyed. The laser fluence conversion value obtained by multiplying the index of both characteristic lines P and Q by a coefficient is about 0.5 J / cm, respectively. ² And about 0.9 J / cm ² Met. The characteristic line R is the beam profile of the laser light intensity. When the characteristic line R is in a region sandwiched between both characteristic lines P and Q, the lateral growth is stably performed without causing film destruction.
[0058]
FIG. 8B is an SEM image of the Si thin film in the lateral growth process. A laterally grown Si crystal can be seen from the laser optical axis a to a range of less than 10 μm on one side. However, in the region of 10 μm or more from the laser optical axis a, the laser intensity varies greatly, and a film-breaking structure (white lump scattered in the figure) is observed. In addition, the region near the laser optical axis a is not crystallized due to insufficient laser fluence intensity and remains amorphous, and this region is not laterally grown.
[0059]
Using the above experimental results, an optical system capable of forming large crystal grains (average diameter 5 microns) with a high filling rate was obtained. The obtained light intensity distribution and film morphology are shown in FIGS. 9B and 9C, respectively. The vertical axis of (b) in FIG. 9 indicates the normalized laser intensity (unitless), which is a parameter that serves as a standard for crystallization. When these are averaged, they converge to 1.0. In the beam profile BP of FIG. 9B, the maximum value of the light intensity is set to 1.4, the minimum value of the light intensity is set to 0.7, and a pattern in which the decrease and increase are monotonically repeated at equal pitch intervals of 5 μm. .
[0060]
FIG. 9C shows laser irradiation (J = 0.76 mJ / cm ² ) Is an SEM image (20 μm × 20 μm) showing an enlarged part of the repetitive pattern in the region. It was observed that Si crystal grains were stably laterally grown from the laser optical axis a to 5 μm on one side. From this, large crystal grains of about 5 μm with a high filling rate could be uniformly formed on the entire irradiation region (0.24 mm × 0.24 mm).
[0061]
In addition to the sinusoidal waveform shown in FIG. 5A and the triangular waveform shown in FIG. 9C, various waveforms can be adopted for the beam profile BP of the present invention. For example, it may be a continuous wave of a mountain wave shown in FIG. 10 (a), a continuous waveform of a valley wave shown in FIG. 10 (b), a sawtooth waveform shown in FIG. 10 (c), or FIG. 10 (d). A mixed triangular waveform in which a large triangular waveform with a relatively large amplitude and a small triangular waveform with a relatively small amplitude shown in FIG. 10 are alternately repeated may be used, and a jagged shape is formed along a mountain-shaped envelope shown in FIG. A waveform in which triangular waves are superimposed may be used, or a twin peak waveform having two peaks shown in FIG. As described above, the beam profile BP of the present invention can use various modified waveforms as long as it is a continuous wave of a V-shaped wave portion or a U-shaped wave having a monotonously increasing waveform portion and a monotone decreasing waveform.
[0062]
In addition, the sine wave waveform shown in FIG. 5A, the triangular waveform shown in FIG. 9C, the continuous wave of the mountain wave shown in FIG. 10A, and the continuous wave of the valley wave shown in FIG. A wave or the like is irradiation light that monotonously increases and monotonously decreases with the same amplitude and the same period. Also, a sinusoidal waveform shown in FIG. 5 (a), a triangular waveform shown in FIG. 9 (c), a continuous wave of a mountain wave shown in FIG. 10 (a), and a continuous wave of a valley wave shown in FIG. 10 (b). Waves and the like are symmetrical waveforms.
[0063]
The waveform of the triangular wave shown in FIG. 9 (c), the monotonically increasing and monotonically decreasing light intensity distributions of the waveforms shown in FIGS. 10 (c), (d), (e), and (f) are linear, It is triangular.
[0064]
In order to obtain large-sized crystallized grains, the switching portion between the monotonically increasing waveform and the monotonically decreasing waveform may be a waveform having a gradient in both the V-shaped wave and the U-shaped continuous wave. is important. If a flat waveform exists in the switching portion, the crystal grains are broken or the crystallization in the lateral direction is stopped at that portion. Further, in order to obtain a crystallized grain having a large grain size, the switching portion between the monotonically decreasing waveform and the monotonically increasing waveform is a waveform having a gradient in both the V-shaped wave and the U-shaped continuous wave. This is very important. If a flat waveform is present in the switching portion, a polycrystalline grain region is generated in that portion, or lateral crystallization is insufficient.
[0065]
The fact that there is a slope in the switching portion between the monotonically increasing waveform and the monotonically decreasing waveform and the switching portion between the monotonically decreasing waveform and the monotonically increasing waveform means that there is no flat waveform in the switching portion.
[0066]
The properties of excimer laser light were extracted by high resolution beam profiler. As a result, the light intensity distribution on the sample surface can be designed. Furthermore, by evaluating various critical light intensities and combining these results, an optical system for growing large crystal grains with a high filling rate was designed. This effectiveness was confirmed by experiments.
[0067]
FIG. 11 illustrates an example of an active matrix display device using a thin film transistor. The thin film transistor 112 is manufactured through the steps shown in FIG. As shown in the figure, the display device 120 has a panel structure including a pair of insulating substrates 121 and 122 and an electro-optical material 123 held therebetween. As the electro-optical substance 123, a liquid crystal material is widely used. A pixel array portion 124 and a drive circuit portion are integrated on the lower insulating substrate 121. The drive circuit section is divided into a vertical drive circuit 125 and a horizontal drive circuit 126.
[0068]
Further, a terminal portion 127 for external connection is formed at the upper end of the peripheral portion of the insulating substrate 121. The terminal portion 127 is connected to the vertical drive circuit 125 and the horizontal drive circuit 126 through the wiring 128. In the pixel array portion 124, row-shaped gate wirings 129 and column-shaped signal wirings 130 are formed. A pixel electrode 131 and a thin film transistor 112 for driving the pixel electrode 131 are formed at the intersection of both wirings. The thin film transistor 112 is manufactured using the above-described method (see FIG. 4). The gate electrode 110 of the thin film transistor 112 is connected to the corresponding gate wiring 129, the drain region 103 c is connected to the corresponding pixel electrode 131, and the source region 103 b is connected to the corresponding signal wiring 130. The gate wiring 129 is connected to the vertical driving circuit 125, while the signal wiring 130 is connected to the horizontal driving circuit 126.
[0069]
The thin film transistor 112 for switching and driving the pixel electrode 131 and the thin film transistor included in the vertical drive circuit 125 and the horizontal drive circuit 126 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.
[0070]
Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.
[0071]
【The invention's effect】
As described above, according to the present invention, a laser beam having an optimized light intensity and distribution is designed on the incident surface of the substrate, while suppressing generation of other undesirable tissue regions such as film breakage. A desired crystallized structure can be formed. That is, the crystal grains are stably laterally grown without being broken, and a large grain structure having a uniform size suitable for a thin film transistor is obtained (region 3 in FIG. 3).
[0072]
Further, according to the present invention, the light intensity distribution is set to a light intensity equal to or exceeding the light intensity for crystallizing the structure of the non-single crystal semiconductor thin film, and the crystallized crystal grains are laterally aligned. By setting the light intensity lower than the light intensity to be grown to the maximum value, the structure of the non-single-crystal semiconductor thin film can be crystallized into a polycrystalline structure (region 2 in FIG. 3).
[0073]
Furthermore, according to the present invention, the light intensity distribution is equal to or higher than the light intensity for crystallizing the structure of the non-single-crystal semiconductor thin film in a light intensity range that is lower than the light intensity that causes destruction in the laterally grown crystal grains. By setting the light intensity to the maximum value and the light intensity below the light intensity for crystallizing the structure of the non-single crystal semiconductor thin film to the minimum value, the ratio between the polycrystalline structure and the amorphous structure can be freely changed. (Region 1 and region 2 in FIG. 3).
[Brief description of the drawings]
FIG. 1 is a structural block diagram showing a crystallization apparatus of the present invention.
2A is a diagram showing a beam profile A, FIG. 2B is a plan view schematically showing a crystallized structure formed by laser beam irradiation of the beam profile A, and FIG. 2C is a beam profile B; FIG. 4D is a plan view schematically showing a crystallized structure formed by laser irradiation of the beam profile B. FIG.
FIG. 3 is a state diagram showing a qualitative relationship of temperature / light intensity / tissue.
FIGS. 4A and 4B are schematic cross-sectional views for explaining a process for manufacturing a semiconductor element according to the present invention. FIGS.
5A is a diagram showing a beam profile C, and FIG. 5B is a plan view schematically showing a crystallized structure formed by laser beam irradiation of the beam profile C;
FIG. 6 is a state diagram showing a quantitative relationship of substrate temperature / laser fluence / tissue.
7A is a beam profile characteristic diagram showing a simulation result and an actual result relating to crystallization, and FIG. 7B is an SEM image showing amorphous Si and crystalline Si in a laser irradiation region.
8A is a characteristic diagram showing the relationship between lateral growth / film destruction and laser fluence, and FIG. 8B is an SEM image of a Si thin film during the lateral growth process.
9A is a cross-sectional view schematically showing a part of the phase shifter, FIG. 9B is a beam profile characteristic diagram formed using the phase shifter of FIG. 9A, and FIG. The SEM image which shows the repetitive pattern of the crystallized structure laterally grown by laser beam irradiation with a profile.
FIGS. 10A to 10F are diagrams showing modifications of beam profiles, respectively.
FIG. 11 is a schematic perspective view of a display device.
12A to 12D are schematic cross-sectional views for explaining a process for manufacturing a semiconductor element.
[Explanation of symbols]
1 ... laser light source, 2 ... attenuator,
3. Light intensity pattern adjustment unit,
31 ... Phase shifter (spatial intensity modulation optical element), 32 ... Uniform optical system,
4 ... mirror, 5 ... semiconductor substrate,
6 ... Profiler (light intensity pattern measurement unit),
61 ... Fluorescent screen, 62 ... Mirror, 63 ... CCD,
7 ... Movement stage, 8 ... Computer,
101 ... Substrate, 102 ... Base protective film, 103 ... Amorphous silicon thin film,
103a ... channel region, 103b ... source region, 103c ... drain region,
104 ... excimer laser, 105 ... arrow indicating scanning heating direction,
106 ... polycrystalline silicon thin film (channel region),
107: Gate insulating film, 108: Source region, 109: Drain region,
110 ... Gate electrode, 111 ... Protective film,
112 ... Thin film transistor,
113 ... Source electrode, 114 ... Drain electrode,
r1 ... small crystal grain size region, r2 ... large crystal grain size region,
r3 ... polycrystalline grain region, r4 ... microcrystalline grain region, r5 ... crystal grain breaking region.

Claims (18)

When the non-single crystal semiconductor thin film is crystallized by irradiating the non-single crystal semiconductor thin film, the irradiation light to the non-single crystal semiconductor thin film has a light intensity distribution that periodically repeats monotonic increase and monotonic decrease, A crystallization method characterized by light intensity for melting a semiconductor thin film. The crystallization method according to claim 1, wherein the maximum value of the light intensity is lower than the light intensity at which the crystal grains irradiated and crystallized are broken. The maximum value of the light intensity is a light intensity range that is lower than the light intensity that causes the crystal grains that have been irradiated and crystallized to break, and the minimum value of the light intensity is equal to the light intensity that melts the non-single-crystal semiconductor thin film. A crystallization method characterized in that it exceeds or exceeds that. The crystallization method according to claim 1, wherein the light intensity distribution is irradiation light that monotonously increases and monotonously decreases with the same amplitude and the same period. The crystallization method according to any one of claims 1 to 4, wherein a distance of one period of the light intensity distribution in which the monotonous increase and the monotonic decrease are periodically repeated is 0.001 mm to 1 mm. . The light intensity distribution in which the monotonous increase and the monotonous decrease are periodically repeated increases linearly and decreases linearly in one cycle. Crystallization method. 6. The crystallization method according to claim 1, wherein the light intensity distribution in which the monotonous increase and the monotonic decrease are periodically repeated is a waveform that is symmetrical in one cycle. The crystallization method according to any one of claims 1 to 7, wherein the monotonously increasing and monotonically decreasing light intensity distribution is a triangular waveform. 9. The crystallization according to claim 1, wherein the monotonously increasing and monotonically decreasing light intensity distribution has a gradient at a switching portion between the monotonically increasing waveform and the monotonically decreasing waveform. Method. 10. The crystallization according to claim 1, wherein the monotonously increasing and monotonically decreasing light intensity distribution has a gradient at a switching portion between the monotonically decreasing waveform and the monotonically increasing waveform. Method. A crystallization apparatus for crystallizing a non-single crystal semiconductor thin film by irradiating a laser beam with a laser beam, wherein the non-single crystal semiconductor thin film has a light intensity distribution that periodically repeats monotonic increase and decrease, A crystallization apparatus comprising irradiation means for irradiating light having light intensity for melting a single crystal semiconductor thin film. A crystallization apparatus for crystallization by irradiating a non-single crystal semiconductor thin film with laser light,
Irradiation means for irradiating the non-single crystal semiconductor thin film with a light intensity distribution that periodically repeats monotonic increase and monotonic decrease, and irradiating light of light intensity that melts the non-single crystal semiconductor thin film;
A beam profile measuring instrument provided for measuring the light intensity distribution of the irradiation light;
A crystallization apparatus comprising: The crystallization apparatus according to claim 11, wherein the laser beam is a homogenized laser beam. Irradiation means for irradiating the non-single crystal semiconductor thin film with a light intensity distribution that periodically repeats monotonic increase and monotonic decrease, and irradiating light of light intensity that melts the non-single crystal semiconductor thin film is a space The crystallization apparatus according to claim 11, wherein the crystallization apparatus is an intensity modulation optical element. 15. The apparatus according to claim 14, wherein the spatial intensity modulation optical element is a homogenization optical system including a phase shifter that phase-modulates the incident laser beam. A semiconductor thin film including source, drain, and channel regions formed on an insulating substrate, a gate insulating film provided on the semiconductor thin film, and a gate provided on the semiconductor thin film through the gate insulating film A top gate type thin film transistor comprising an electrode,
The semiconductor thin film is
A thin film transistor characterized in that it is crystallized by irradiation with laser light having a light intensity distribution that periodically monotonously increases and decreases monotonically in an irradiation region and melts a non-single-crystal semiconductor thin film. A gate electrode formed on an insulating substrate; a gate insulating film provided on the gate electrode; a source, a drain, and a channel region; provided to cover the gate electrode through the gate insulating film A bottom gate type thin film transistor comprising a semiconductor thin film,
The semiconductor thin film is
A thin film transistor characterized in that it is crystallized by irradiation with laser light having a light intensity distribution that periodically monotonously increases and decreases monotonically in an irradiation region and melts a non-single-crystal semiconductor thin film. It has a pair of substrates bonded to each other through a predetermined gap and an electro-optic material held in the gap. One substrate is formed with a counter electrode, and the other substrate is driven with a pixel electrode. A display device formed of a semiconductor thin film,
The semiconductor thin film is
A display device characterized in that it is crystallized by irradiation with laser light having a light intensity distribution that periodically repeats monotonous increase and monotonic decrease in an irradiation region and melts the semiconductor thin film.

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