JP2007043140A - p-CHANNEL THIN-FILM TRANSISTOR, METHOD OF MANUFACTURING THE p-CHANNEL THIN-FILM TRANSISTOR, AND DISPLAY DEVICE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin-film transistor with which a TFT having higher mobility of electrons (or holes) can be manufactured, a method of manufacturing the thin-film transistor, and a display device. <P>SOLUTION: The thin-film transistor 1 has a source region S, a channel region C and a drain region D which are provided on a semiconductor thin film 4a that is crystal-grown in a lateral direction; and a gate insulation film 11 and a gate electrode 12 which are provided on the top of the channel region C. An end of the drain 10 on the channel region C side of the drain region D is formed so as to be positioned near the finish position 8 of the crystal growth. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a p-channel thin film transistor, a method for manufacturing a p-channel thin film transistor, and a display device.

  Conventionally, for example, a thin-film transistor (TFT) used as a switching element for controlling a voltage applied to a pixel of a liquid crystal display (LCD), a control circuit of the liquid crystal display, or the like As the semiconductor thin film used to form the thin film transistor used, an amorphous-silicon thin film or a poly-silicon thin film has been used.

  A TFT using the polycrystalline silicon thin film as a semiconductor thin film generally has a higher mobility of electrons or holes moving in the channel region than a TFT using an amorphous silicon thin film as a semiconductor thin film. Therefore, a transistor using a polycrystalline silicon thin film has a higher switching speed and can operate at a higher speed than a transistor using an amorphous silicon thin film. Therefore, an LCD pixel selection circuit and a peripheral drive circuit for driving the LCD can be formed using TFTs on the same substrate as the pixel control thin film transistor. Furthermore, there is an advantage that the design margin of other parts can be expanded. In addition, peripheral driver circuits such as a driver circuit and a DAC can be reduced in cost, increased in definition, and reduced in size by being incorporated in a display portion including a pixel control thin film transistor.

The applicant of the present invention has developed an industrialization technique for stably producing a crystallized region having a large grain size in a non-single crystal semiconductor thin film formed on an insulating substrate. As a method for forming the large grain crystallization region, for example, the crystallization methods described in Non-Patent Document-1 and Non-Patent Document-2 below have been proposed. If industrialization of the large grain size crystallization region is realized, the liquid crystal display device will be able to manufacture not only switching switching transistors for each pixel but also memory circuits such as DRAM and SRAM, and logical operation circuits on a glass substrate. Thus, power saving and downsizing of the liquid crystal display device and the like can be achieved.
(1) “Method of forming a giant grain Si film using an excimer laser” Matsumura, M., Surface Science, Vol. 21, No. 5 pp.278-287, 2000 (2) “Method of forming a giant grain Si film by excimer laser irradiation” Masayoshi Matsumura, Applied Physics, Vol. 71, No. 5 pp.543-547, 2000

  The present inventors have developed a manufacturing technique for forming a higher performance TFT for obtaining optimum practical transistor characteristics in this large grain size crystallization region. For example, the surface of single crystal silicon grown to a large grain size by heat treatment of an amorphous silicon thin film is different from a single crystal silicon wafer formed by slicing a single crystal rod formed by a normal pulling method, It is not a microscopically flat thin film, or a crystal grain boundary generated during crystal growth is complicated, and if a TFT is simply formed at an arbitrary position in a crystallization region, a desired S value characteristic cannot be obtained. understood.

  An object of the present invention is to provide a p-channel thin film transistor, a p-channel thin film transistor manufacturing method, and a display device that can manufacture a p-channel TFT having optimum S-value characteristics.

  The present invention is configured as follows to achieve the above object. The thin film transistor of the present invention has a source region, a channel region, and a drain region in a semiconductor thin film having a crystallized region grown in the lateral direction, and a p-channel type having a gate insulating film and a gate electrode on the channel region. The channel region side end of the drain region or the source region is a position from 1.0 μm to 2.5 μm and a crystal growth start position from the crystal growth start position or the vertical growth start position. Alternatively, it is provided in a crystallization region at a position from 3.0 μm to 4.7 μm from the vertical growth start position. The thin film transistor thus configured can be formed as a TFT having higher electron (or hole) mobility than a conventional TFT.

  The thin film transistor of the present invention has a source region, a channel region, and a drain region in a semiconductor thin film having a crystallized region of an inclined surface that grows in the lateral direction and rises in the crystal growth end direction, and has a gate insulation on the channel region. A p-channel thin film transistor having a film and a gate electrode, wherein the drain region or the source region has an end on the channel region side from a position from 1.0 μm to 2.5 μm and a start position or longitudinal position of crystal growth It is characterized in that it is provided in a crystallization region at a position from 3.0 μm to 4.7 μm from the direction growth start position. The thin film transistor thus configured can be formed in the crystallization region as a TFT having higher electron (or hole) mobility.

  The crystallized region of the thin film transistor of the present invention is formed by irradiating a non-single-crystal semiconductor film with a laser beam having a reverse peak light intensity distribution by a pulse laser beam through a homogenizer by a phase shifter. It can be characterized by being a single crystal region. The thin film transistor thus configured can be formed in the crystallization region as a TFT having higher electron (or hole) mobility.

  The thin film transistor manufacturing method of the present invention includes a step of irradiating a non-single-crystal semiconductor film with laser light having a reverse peak light intensity distribution to crystallize an irradiation region to form a crystallization region; The position from 1.0 μm to 2.5 μm from the start position of crystal growth or the vertical growth start position and the position from 3.0 μm to 4.7 μm from the start position of crystal growth or the vertical growth start position Forming a thin film transistor by positioning a side end of the drain region or the source region with respect to the channel region in the crystallization region. In this thin film transistor manufacturing method, a TFT having higher electron (or hole) mobility can be manufactured in the crystallization region.

  The display device of the present invention relates to a display device in which the p-channel thin film transistor is provided in a peripheral circuit portion that requires high-speed operation such as a signal line driver circuit or a scanning line driver circuit.

  By using the thin film transistor, this display device can be realized as a system display in which active elements such as a peripheral circuit portion and a memory circuit portion are formed on the same substrate.

  According to the present invention, it is possible to obtain a p-channel TFT having an optimum S value characteristic, a method for manufacturing the p-channel TFT, and a display device.

  The present inventor has developed a technique for manufacturing a p-channel TFT by aligning a drain end or a source end in the vicinity of a crystal growth end position as a means for obtaining optimum transistor characteristics in a crystallized region in which a crystal is grown in a lateral direction. Developed and filed. The present inventor has made extensive studies on transistor characteristics in the crystallization region in the vicinity of the crystal growth start position in order to form as many TFTs as possible in the crystallization region having a large grain size that has been crystallized in the lateral direction. It was found that there was a region for obtaining transistor characteristics.

  That is, in this embodiment, when a TFT is formed in a crystallized region that is crystal-grown in the lateral direction, the drain region of the TFT or the end of the source region on the channel region side is positioned at the crystal growth start position or in the vertical direction. A crystallization region excluding the vicinity of the start position, for example, a position from 1.0 μm to 2.5 μm from the start position of crystal growth or the vertical growth start position, and a position of 3.0 μm from the start position of crystal growth or the start of vertical growth This is an example in which optimum transistor characteristics are obtained by forming a TFT in accordance with the position of the crystallized region from the position to 4.7 μm.

  Next, an embodiment of a thin film transistor according to the present invention will be described with reference to FIG. FIG. 1 is an enlarged sectional view showing a region where a thin film transistor is formed. This embodiment has the following characteristics.

  A crystallized region (5, ie, (7-SCD-8)) crystallized laterally in the irradiated region of the non-single-crystal semiconductor layer is horizontal from the crystal growth start position 7. The crystal grows up to the maximum at the crystal growth end position 8. That is, a non-single crystal semiconductor layer, for example, an amorphous silicon film is irradiated with light and crystallized in the lateral direction, and crystallized region 5 is a silicon film that grows from the crystal growth start position 7 in the crystal growth direction. It has an inclined surface whose film thickness increases toward the crystal growth end position 8. In such a crystallized region 5, the mobility (μmax) of electrons or holes in the channel region increases in the direction of crystal growth of the TFT, and increases remarkably in the vicinity of the crystal growth end portion.

  In the vicinity of the crystal growth start position 7, there is a portion where a large number of fine crystal grains are distributed, and it has been found that it is not desirable to form a TFT by aligning the drain end of the TFT with this portion. That is, forming the TFT by aligning the drain end of the TFT in the vicinity of the crystal growth start position 7 is undesirable in the S value characteristic of the transistor characteristics. The TFT of this embodiment is to use this characteristic.

  Further, the crystallized region in which the light irradiated region of the non-single crystal semiconductor layer is crystallized in the horizontal direction has a crystal growth in the horizontal direction from the crystal growth start position 7 and has an inclined surface protruding in the direction of the crystal growth end position 8. It is also a semiconductor thin film. The reason is not clear, but the end of the raised portion has a large laser fluence, and the end of the crystallized region 5 grown from the right side of FIG. 1 and the end of the crystallized region 5 grown from the left side of FIG. Since crystals collide with each other, the film stress increases and ablation occurs, which is considered to be a region where characteristics such as mobility deteriorate. The end of the drain region or source region on the channel region side is disposed in a crystallization region that avoids the vicinity of the crystal growth start position 7. Furthermore, the crystallized region in which the non-single-crystal semiconductor layer is crystallized in the lateral direction is a semiconductor thin film having an inclined surface whose thickness monotonously increases in the horizontal direction from the crystal growth start position. On the crystal growth end position side, the end of the drain region or source region on the channel region side is arranged near the apex of the inclined surface where the film thickness increases monotonously. Examples of the non-single-crystal semiconductor film include a polycrystalline semiconductor film and an amorphous semiconductor film.

  Next, a specific configuration example of a TFT for driving the liquid crystal display device will be described with reference to FIG. The TFT 1 in FIG. 1 has a top gate type thin film transistor structure. The substrate 2 may be an insulator or a semiconductor substrate or a metal substrate with an insulating film formed on the surface. An insulating film such as a silicon oxide film 3 is provided on the insulating substrate such as a glass substrate 2. The silicon oxide film 3 is, for example, a CVD film or a thermal oxide film, and is formed to a thickness of, for example, 1 μm. On this silicon oxide film 3, a non-single crystal semiconductor film, for example, an amorphous silicon film 4 is provided. The amorphous silicon film 4 has a thickness of 30 nm to 300 nm, for example, 200 nm, and is formed by film formation such as plasma CVD.

  A crystallization region 5 is provided on the entire surface of the amorphous silicon film 4 or a predetermined region. The crystallized region 5 has a light intensity distribution having an inverse peak pattern as shown by L in FIG. 6B, and has a light beam having an energy for melting the amorphous silicon film 4, for example, KrF excimer laser light. The crystallized region 5 is crystallized by irradiation.

  The crystallized region 5 crystallized by a laser beam having a plurality of reverse peak pattern-like light intensity distributions grows in the order of the film thickness in the horizontal direction from the crystal growth start position 7, and near the crystal growth end position 8. The single crystal silicon film crystallized in FIG. In the crystallization region 5 crystallized by a laser beam having a plurality of reverse peak pattern light intensity distributions, the crystal growth end positions 8 crystallized in adjacent positive peak portions collide with each other and the silicon film is raised. The shape is to have a cross-sectional shape. The film in which the predetermined position is crystallized in this way is defined as a semiconductor thin film 4a in this specification. The length from the crystal growth start position 7 to the crystal growth end position 8 is determined by the pulse width of the reverse peak light intensity distribution in FIG. 6B.

  In this embodiment, the drain end or the source end of the channel region C of the TFT 1 is positioned from the crystallization region avoiding the vicinity of the crystal growth start position 7 or the vertical growth start, for example, the crystal growth start position 7. Thus, the TFT 1 is formed. For example, the drain end 10 (side end portion 10) of the channel region C of the TFT 1 is located at a position from 1.0 μm to 2.5 μm from the crystal growth start position or the vertical growth start position and the crystal growth start position or vertical position. A p-channel TFT 1 is provided in a crystallization region at a position from 3.0 μm to 4.7 μm from the direction growth start position, for example, a crystallization region 1.5 μm away from the crystal growth start position 7. A channel region C and a source region S are provided continuously to the drain region D.

  On the channel region C, a gate insulating film 11 such as a silicon oxide film is provided in alignment with the channel region C. This silicon oxide film is an oxide film of a low-temperature process of direct oxidation by microwave CVD at a temperature of 300 to 400 degrees Celsius, for example, 350 degrees Celsius. Further, a gate electrode 12 is provided on the gate insulating film 11 so as to be aligned with the channel region C. In this way, the TFT 1 is manufactured. In this specification, a TFT is an element having a TFT structure, and includes not only those used as transistors but also those used for applications such as memories, capacitors and resistors.

  Next, an example of a manufacturing method of the TFT 1 will be described with reference to the process chart of FIG. Constituent elements having the same contents as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted because it is duplicated.

  First, a crystallization substrate is manufactured. For example, a quartz substrate or a glass substrate 2 made of non-alkali glass or the like is transported and positioned and installed at a predetermined position in the plasma CVD apparatus chamber (step-1). A base insulating film such as a silicon oxide film 3 is vapor-phase grown on the glass substrate 2 by plasma CVD (step-2). This plasma CVD is performed, for example, under conditions of a substrate temperature of 500 ° C. and a deposition time of 40 minutes. Next, a non-single-crystal semiconductor film made of amorphous silicon or polycrystalline silicon to be crystallized, for example, an amorphous silicon film 4 having a thickness of 30 nm to 300 nm (for example, about 200 nm) is formed on the silicon oxide film 3. Then, vapor phase growth is performed by plasma CVD (step-3).

The amorphous silicon film 4 is deposited on the silicon oxide film 3 by, for example, LP-CVD (Low Pressure CVD). The amorphous silicon film 4 is an amorphous silicon film (a-Si) having a thickness of, for example, 200 nm. The LP-CVD process is performed under the conditions of, for example, an Si ₂ H ₆ atmosphere, a flow rate of 150 sccm, a pressure of 8 Pa, a substrate temperature of 450 ° C., and a deposition time of 35 minutes. Although the LP-CVD method is used here, for example, a PE-CVD (low temperature plasma CVD) method may also be used.

As the non-single crystal semiconductor thin film, a thin film such as Ge or SiGe can be used in addition to the amorphous silicon film 4 (Si). The formation of the non-single-crystal semiconductor film is not limited to the CVD method, and may be formed by, for example, a sputtering apparatus.

  Next, a cap film, such as a silicon oxide film, that is transparent to incident light to form a large grain crystallized region on the amorphous silicon film 4 is formed by plasma CVD to a film thickness of 10 nm to 100 nm, for example. A film is formed to 10 nm. The silicon oxide film can be deposited on the amorphous silicon film 4 by a LP-CVD method, for example, at a substrate temperature of 500 ° C. and a deposition time of 10 minutes. The cap film is made of an insulating film and has a heat storage effect, and is a film for relaxing the temperature drop rate of the non-single-crystal semiconductor thin film 2 when crystallizing by laser irradiation in the next step. In this way, the crystallization cap film is manufactured (step-4).

Next, crystallization steps 5 to 6 are performed. The crystallization substrate is placed in alignment with a predetermined position of the crystallization apparatus. Excimer laser light having a reverse peak pattern-like light intensity distribution as shown in FIG. 9B is irradiated in a pulsed manner to a predetermined crystallization position of the crystallization substrate conveyed to the crystallization apparatus. The region is melted at a high temperature (step-5). This temperature distribution is stored in the cap film. When the excimer laser beam is interrupted, the temperature is lowered by the temperature gradient of the light intensity distribution as shown in FIG. In this temperature lowering process, since the cap film stores heat, the temperature is slowly decreased, and crystal growth is performed along the temperature gradient to form a crystallized region having a large grain size (step-6). The excimer laser light is, for example, a KrF excimer laser and has an energy density of 350 mJ / cm ² . Position information for crystallization is stored in advance in a computer. This computer automatically moves the substrate sequentially to the crystallization position in the crystallization substrate, positions it, irradiates the laser beam for crystallization, performs crystallization, and completes the crystallization steps 5 to 6 To do.

  That is, in the crystallization steps 5 to 6, an excimer pulse having a reverse peak light intensity distribution R (see FIG. 6B) on the surface of the cap film by using a phase modulation excimer laser crystallization method which will be described in detail later. Irradiate with laser light. The irradiated region of the amorphous silicon film 4 is melted by laser irradiation with pulsed laser light. The melting region is cooled during the interruption period of the pulse laser beam, the solidification position moves in the lateral direction (horizontal direction), and crystal grows to form a crystallization region 5. In the crystallization region 5, as shown in FIG. 1, the distance from the crystal growth start position 7 to the crystal growth end position 8 in the horizontal direction is 5.0 μm, for example. As a result, the amorphous silicon film 4 is converted into a semiconductor thin film 4a that is partially or entirely crystallized. The pulse laser beam irradiation may be performed once, but may be performed a plurality of times, or pulse laser beam irradiation and flash lamp light irradiation may be combined.

  The crystallization region 5 thus formed has a shape that grows in the horizontal direction from the crystal growth start position 7 and rises at the crystal growth end position 8 as shown in FIG.

Next, the silicon oxide film of the cap film formed to form the TFT 1 in the large grain size crystallization region is removed (step-7). The method for removing the silicon oxide film can be performed by dry etching. This dry etching process can be performed using, for example, BCl ₃ and CH ₄ as an etching gas.

  Next, a TFT manufacturing process is performed on the glass substrate 2 after the crystallization process. The feature of this embodiment is that the formation of the TFT in the crystallized region crystallized through the process as described above is, for example, 1.5 μm away from the crystal growth start position or the vertical growth start position of the crystallized region. Manufacturing is performed so that the drain region or source region of the TFT is aligned with the channel region side end of the TFT in the crystallization region.

  In this specification, the crystal growth start position or the vertical growth start position is the crystal growth start position 7 of the crystallized single crystal region in FIG. The crystal growth start position 7 is a growth start position of a single crystal region excluding this fine crystal grain portion, where a portion where fine crystal grains are gathered is generated at the crystal growth start portion. The channel region side end of the drain region or source region of the TFT is a boundary position with the drain region or source region in contact with the channel region.

  First, the glass substrate 2 is transported to a predetermined position of plasma CVD, positioned and installed. In plasma CVD, a silicon oxide film for forming the gate insulating film 11 is formed on the exposed semiconductor thin film surface of the transferred glass substrate 1 (step-8).

  Next, the glass substrate 2 on which the gate insulating film 11 is formed is transferred to a sputtering apparatus for forming a conductor film for forming a gate electrode, and is aligned. Thereafter, for example, aluminum (Al) is deposited as a gate electrode (step-9). Next, it is transferred to a plasma etching apparatus and plasma etching is performed to form the gate electrode 12 (step-9).

  Impurity ions for forming a source region and a drain region are ion-implanted at a high concentration into the crystallization region using the formed gate electrode 12 as a mask. As the impurity ions, for example, phosphorus is ion-implanted in the case of an N-channel transistor, and boron is ion-implanted in the case of a P-channel transistor. Thereafter, annealing is performed in a nitrogen atmosphere (for example, at 600 ° C. for 1 hour) to activate the impurities and form the source region S and the drain region D in the crystallized region as shown in FIG. As a result, a channel region C in which carriers move is formed between the source region S and the drain region D (step-10).

  Next, an interlayer insulating layer (not shown) is formed on the gate insulating layer 11 and the gate electrode 12. Contact holes for connection between the source and drain electrodes and the source / drain regions S and D are formed in the interlayer insulating layer (not shown).

  Next, each contact hole is filled with a metal layer, for example, aluminum, which becomes a gate electrode, a source, and a drain electrode, and a film is also formed on the interlayer insulating layer (not shown). The metal layer formed on the interlayer insulating layer is etched into a predetermined pattern using a photolithography technique to form a source electrode and a drain electrode, and the n-channel thin film transistor 1 is manufactured (process) ―11). The gate length of the TFT 1 is, for example, 1 μm.

  As is apparent from the above manufacturing process, the side edge of the source region S or drain region D with respect to the channel region C is aligned with the crystallization region excluding the vicinity of the crystal growth start position 7 to form a TFT. That is, it is positioned by the gate electrode 12. Accordingly, the installation position of the gate electrode 12 is positioned and formed on the crystallization region excluding the vicinity of the crystal growth start position 7.

  The result of measuring the transistor characteristics of the TFT manufactured in this way will be described with reference to FIG.

  FIG. 3 is a characteristic curve diagram showing the relationship between the S value characteristic of the p-channel TFT 1 and the drain-in end position when the TFT 1 is formed in the crystallized region 5 crystallized as described above. FIG. 3 shows the S-value characteristics when the source-drain electrode voltage is Vds = 0.1 V and the source-date electrode voltage is Vgs = −5V.

S-value characteristics Position from 1.0 μm to 2.5 μm from start position of crystal growth or longitudinal growth start position, and position from 3.0 μm to position of 3.0 μm from start position of crystal growth or longitudinal growth start position The TFT 1 in which the drain region or the source region end on the channel region side is formed in the crystallization region up to the above position has the minimum S value and the optimum characteristics can be obtained. Further, a position within 0.8 μm from the crystal growth start position or the vertical growth start position, a position from 2.7 μm to 3.0 μm from the crystal growth start position or the vertical growth start position, and a crystal growth start position or The p-channel TFT 1 in which the drain region or the source region side end of the source region is formed in the crystallized region from a position of 4.7 μm to 5.0 μm from the vertical growth start position has an increased S value. It is unsuitable.

  Next, an embodiment of a crystallization apparatus that forms a crystal in the horizontal (lateral) direction from a crystal growth start position 7 where a large number of fine crystal grains exist and forms a raised shape at the crystal growth end position 8 will be described with reference to FIGS. It demonstrates concretely with reference to. The crystallization apparatus includes an illumination system 15, a phase modulation element 16 provided on the optical axis of the illumination system 15, an imaging optical system 17 provided on the optical axis of the phase modulation element 16, and this connection. It comprises a stage 19 that supports a crystallized substrate 18 provided on the optical axis of the image optical system 17.

  The illumination system 15 is an optical system shown in FIG. 4 and in detail in FIG. 5, and includes a light source 21 and a homogenizer 22, for example. As the light source 21, for example, a KrF excimer laser light source 21 that supplies light having a wavelength of 248 nm can be used. As the light source 21, an excimer laser such as an XeCl excimer laser light source that emits pulsed light having a wavelength of 308 nm, a KrF excimer laser that emits pulsed light with a wavelength of 248 nm, or an ArF laser that emits pulsed light with a wavelength of 193 nm is used. Can be used. The light source 21 may be a YAG laser light source. The light source 21 may be another appropriate light source that outputs energy for melting the non-single crystal semiconductor film, for example, the amorphous silicon film 4. A homogenizer 22 is provided on the optical axis of the laser light emitted from the light source 21.

  The homogenizer 22 equalizes the light intensity of the laser light emitted from the light source 21 and the incident angle to the phase modulation element 16 within the cross section of the light beam. The homogenizer 22 includes, for example, a beam expander 23, a first fly-eye lens 24, a first condenser optical system 25, a second fly-eye lens 26, and a second condenser optical on the optical axis of the laser light from the light source 21. A system 27 is provided.

  That is, in the illumination system 15, the laser light incident from the light source 21 is magnified through the beam expander 23 and then enters the first fly-eye lens 24. A plurality of light sources are formed on the rear focal plane of the first fly-eye lens 24, and light beams from the plurality of light sources pass through the incident surface of the second fly-eye lens 26 via the first condenser optical system 25. Illuminate in a superimposed manner. As a result, a larger number of light sources are formed on the rear focal plane of the second fly-eye lens 26 than on the rear focal plane of the first fly-eye lens 24. Light beams from a number of light sources formed on the rear focal plane of the second fly-eye lens 26 are incident on the phase modulation element 16 via the second condenser optical system 27 and are illuminated in a superimposed manner.

  As a result, the first fly-eye lens 24 and the first condenser optical system 25 of the homogenizer 22 constitute a first homogenizer, and perform a uniform process on the incident angle of the laser light incident on the phase modulation element 16. The second fly-eye lens 24 and the second condenser optical system 27 constitute a second homogenizer, and the laser light whose incident angle from the first homogenizer is uniformized by the second homogenizer on the phase modulation element 16. The light intensity at each position in the plane is made uniform. Thus, the illumination system 22 forms laser light having a substantially uniform light intensity distribution, and this laser light irradiates the phase modulation element 16.

  The phase modulation element 16, for example, a phase shifter is an optical element that emits a laser beam with a reverse peak-shaped light intensity minimum distribution as shown in FIG. 6B by phase-modulating the light emitted from the homogenizer 22. FIG. 6B shows an enlarged part of the reverse peak-shaped light intensity minimum distribution. In FIG. 6B, the horizontal axis is the place (position on the irradiated surface), and the vertical axis is the light intensity (energy).

  The phase shifter 16 used as a phase modulation element has a step on a transparent body, for example, a quartz substrate, causes laser beam diffraction and interference at the step boundary, and gives a periodic spatial distribution to the laser beam intensity. It is. The phase shifter is, for example, a case where a phase difference of 180 ° is given on the left and right with the stepped portion x = 0 as a boundary. In general, when the wavelength of laser light is λ, a transparent medium having a refractive index n is formed on a transparent base material and given a phase difference of 180 °, the film thickness difference t of the transparent medium is t = λ / 2 ( n-1). If the refractive index of the quartz base material is 1.46, the wavelength of the XeC1 excimer laser light is 308 nm. Therefore, in order to add a phase difference of 180 °, a step of 334.8 nm is formed by a method such as etching.

In addition, when forming a step portion by forming the step portion by PECVD, LPCVD or the like using the SiN _x film as a transparent medium, if the refractive index of the SiN _x film is 2.0, the SiN _x film is formed on the quartz substrate at 154 nm. Etching can be used to provide a step. The intensity of the laser beam that has passed through the phase shifter with a phase of 180 ° shows a pattern of periodic strength.

  In this embodiment, the mask in which the steps themselves are formed periodically is a periodic phase shifter. In this embodiment, both the width of the phase shift pattern and the distance between patterns are 3 μm, for example. The phase difference does not necessarily need to be 180 °, and may be any phase difference that can realize strength and weakness suitable for crystallization in the laser light.

  The laser light phase-modulated by the phase modulation element 16 is incident on a crystallized substrate 18 such as an amorphous silicon film via an imaging optical system 17 shown in FIG. Here, the imaging optical system 17 is disposed so that the pattern surface of the phase modulation element 16 and the crystallized substrate 18 are in an optically conjugate position. In other words, the height position of the stage 19 is set so that the crystallized substrate 18 is set to a surface optically conjugate with the pattern surface of the phase modulation element 16 (image surface of the imaging optical system 17). It is corrected. The imaging optical system 17 includes an aperture stop 33 between the positive lens group 31 and the positive lens group 32. The imaging optical system 17 can be an optical lens that forms an image on the crystallized substrate 18 by equalizing or reducing the image of the phase modulation element 16 to, for example, 1/5.

  The aperture stop 33 shown in FIG. 4 has a plurality of aperture stops having different sizes of openings (light transmission portions). The plurality of aperture stops 33 may be configured to be replaceable with respect to the optical path. Alternatively, the aperture stop 33 may have an iris stop that can continuously change the size of the opening. In any case, the size of the aperture of the aperture stop 33 (and consequently the image-side numerical aperture NA of the imaging optical system 4) is a required light intensity distribution on the semiconductor film of the crystallized substrate 18, as will be described later. Is set to generate. The imaging optical system 17 may be a refractive optical system, a reflective optical system, or a refractive / reflective optical system.

Further, as shown in FIG. 6A, the crystallized substrate 18 is formed, for example, on the liquid crystal display plate glass 2 by a chemical vapor deposition method (CVD method) or a sputtering method as a base insulating film. The amorphous silicon film 4 and the cap film 35 are sequentially formed. The base insulating film is formed, for example, with a SiO ₂ film thickness of 500 to 1000 nm. The base insulating film 3 prevents the amorphous silicon film 4 and the glass substrate 2 from being in direct contact with each other and foreign matters such as Na deposited from the substrate 2 are prevented from entering the amorphous silicon film 4. Further, during the crystallization process of the amorphous silicon film 4, the amount of heat of fusion is prevented from being directly transferred to the glass substrate 2, and the effect of accumulating the heat of fusion suppresses the rate of temperature decrease and crystallizes a large grain size. Contribute to.

The amorphous silicon film 4 is a film to be crystallized, and the film thickness can be, for example, 30 to 250 nm. The cap film 35 stores heat generated when the amorphous silicon film 4 is melted during the crystallization process, and this heat storage action contributes to the formation of a crystallized region having a large grain size. The cap film 35 is an insulating film such as a silicon oxide film (SiO ₂ ), and can have a film thickness of 100 nm to 400 nm, for example, 300 nm.

  The substrate 18 to be crystallized is automatically transferred onto a stage 19 of a crystallization apparatus as shown in FIG. 4 and is positioned and placed at a predetermined position. Retained.

  Next, the crystallization process will be described with reference to FIGS. The pulsed laser light emitted from the laser light source 21 shown in FIG. 5 is incident on the homogenizer 22 to make the light intensity of the laser light uniform and make the incident angle to the phase modulation element 16 uniform. That is, the homogenizer 22 spreads the laser beam incident from the light source 21 in the horizontal direction to form a linear (for example, a line length of 200 mm) laser beam, and further makes the light intensity distribution uniform. For example, a plurality of X direction cylindrical lenses are arranged in the Y direction to form a plurality of light beams arranged in the Y direction, each light beam is redistributed by another X direction cylindrical lens, and similarly, a plurality of Y direction cylindrical lenses are A plurality of light beams arranged in the direction and in the X direction are formed, and each light beam is redistributed by another Y-direction cylindrical lens.

  The laser beam is a XeCl excimer laser beam with a wavelength of 308 nm, and the pulse duration of one shot is 20 to 200 ns. When the phase modulation element 16 is irradiated with pulsed laser light under the above conditions, the pulsed laser light incident on the periodically formed phase modulation element 16 causes diffraction and interference at the stepped portion. As a result, the phase modulation element 16 generates a strong and weak light intensity distribution in a reverse peak pattern as shown in FIG.

  The light intensity distribution in the reverse peak pattern desirably outputs a laser light intensity sufficient to melt the amorphous silicon film 4 between the minimum light intensity part L and the maximum light intensity part P. The pulse laser beam that has passed through the phase modulation element 16 is incident on the amorphous silicon film 4 so as to be focused on the surface of the crystallized substrate 18 by the imaging optical system 17.

  The incident pulsed laser light is almost transmitted through the cap film 35 and absorbed by the amorphous silicon film 4. As a result, the irradiated region of the amorphous silicon film 4 is heated and melted. The heat at the time of melting is stored by the presence of the cap film 35 and the silicon oxide film 3.

  When the irradiation of the pulsed laser beam is in the cut-off period, the irradiated region tries to cool down at a high speed, but the cooling rate is reduced by the heat stored in the cap film 35 and the silicon oxide film 3 provided on the front and back surfaces. It becomes very gentle. At this time, the temperature of the irradiated region is decreased according to the light intensity distribution of the reverse peak pattern generated by the phase modulation element 16, and sequentially crystallized in the horizontal direction from the minimum light intensity portion L toward the maximum light intensity portion P. grow up.

  In other words, the solidification position in the molten region within the irradiated region sequentially moves from the low temperature side to the high temperature side. That is, as shown in FIGS. 6C and 6D, the crystal grows from the crystal growth start position 7 toward the crystal growth end position 8. At this time, a slight bulge occurs in the vicinity of the crystal growth end position 8 in the irradiated region as shown in FIG. FIG. 6C is a plan view for explaining the shape of the crystallization region 5 in the amorphous silicon film 4 after the cap film 35 is peeled off. FIG. 6C shows a form in which the crystal grows laterally from the crystal growth start position 7 to the crystal growth end position 8.

  FIG. 6D is a cross-sectional view of FIG. In FIG. 6D, the thickness of the semiconductor thin film 4a increases from the crystal growth start position 7 in the direction of the crystal growth end position 8, and has an inclined surface that becomes the apex at the crystal growth end position 8, and has a peak in the cross-sectional shape. A state of being crystallized into a shape is shown. FIG. 6D shows the case where there are a plurality of reverse peak light intensity distribution patterns as shown in FIG. In the case of a single reverse peak light intensity distribution pattern, a film thickness distribution changed into a pair of peaks is formed, and only a pair of raised portions are formed.

  In this way, the crystallization process with one pulse laser beam is completed. The crystallized region thus crystal-grown is large enough to accommodate one or more functional elements. 6B, 6C, and 6D show the mutual relationship with dotted lines. That is, in FIGS. 6B, 6C, and 6D, crystal growth starts at the reverse peak portion L of the reverse peak light intensity distribution of FIG. 6B (crystal growth start position 7), and the positive peak. In the portion P, the crystal growth end point position (crystal growth end position 8) is reached, and the single crystal silicon film thickness gradually increases from the crystal growth start position 7 to the crystal growth end position 8 and rises in the vicinity of the end position 8. Has been.

  In the crystallization apparatus 20 shown in FIG. 4, control is performed so as to automatically irradiate the next crystallized region of the amorphous silicon film 4 with pulsed laser light by a program stored in advance in a control device (not shown). Is done. In the movement to the next crystallization region, for example, the irradiation position can be selected by moving the stage 19. Of course, the movement of the crystallization position can be selected by relatively moving the crystallized substrate 18 and the light source 21.

  When a region to be crystallized is selected and alignment is completed, the next pulse laser beam is emitted. By repeating such shots of laser light, the crystallized substrate 18 can be crystallized over a wide range. In this way, the crystallization process for the entire substrate is completed. As shown in FIG. 6D, the amorphous silicon film 4 in which the crystallized region is formed in this way is defined as a semiconductor thin film 4a.

  Next, with reference to FIG. 7 and FIG. 8, an example of the TFT manufacturing process after Step-8 shown in FIG. 2 will be described for the substrate after the crystallization process. The same parts as those in FIGS. 1 to 6 are denoted by the same reference numerals, and detailed description thereof is omitted.

  On the surface of the substrate on which the crystallization process has been completed, a SiO2 film as a cap film 35 is formed. This SiO2 film can also be used as a gate insulating film of a TFT. However, if there is a possibility that foreign matter is mixed due to ablation from the amorphous silicon film 4 during the crystallization process, the SiO2 film is preferably removed by etching. In this embodiment, the SiO2 film is removed.

  On the semiconductor thin film 4a that is the surface of the substrate from which the cap film 35 has been removed, as shown in FIG. The gate insulating film 11 is an 80 nm thick silicon oxide film deposited on the semiconductor thin film 4a by, for example, LP-CVD. LP-CVD is performed, for example, under conditions of a substrate temperature of 500 ° C. and a deposition time of 45 minutes.

  Next, a step of forming the gate electrode 12 is performed. That is, as shown in FIG. 7B, a gate electrode layer, for example, an aluminum layer 40 is formed on the gate insulating film 11. The aluminum layer 40 is deposited on the silicon oxide film (SiO2 film) of the gate insulating film 11 by a thickness of, for example, 100 nm by, for example, sputtering. The sputtering conditions are, for example, a substrate temperature of 100 ° C. and a deposition time of 10 minutes.

  A resist pattern 41 is formed on the aluminum layer 40 in order to selectively etch the aluminum layer 40 to form the gate electrode 12 at a predetermined position. The resist pattern 41 is formed by applying a resist film on the aluminum layer 40, selectively exposing the resist film using a photomask, and removing the resist film leaving a gate electrode mask region. A resist pattern 41 is formed as shown in FIG. The position of the resist pattern 41 for forming the gate electrode 12 is important. The resist pattern 41 is formed in alignment with the crystallization region excluding the vicinity of the crystal growth start position 7.

Next, the aluminum layer 40 is removed using the resist pattern 41 as a mask, for example, by dry etching, thereby forming the gate electrode 12 as shown in FIG. In this dry etching process, for example, BCl ₃ and CH ₄ are used as an etching gas. Subsequently, as shown in FIG. 8E, the resist pattern 41 on the gate electrode 12 is removed.

  Next, as shown in FIG. 8F, an impurity is added to the semiconductor thin film 4a using the gate electrode 12 as a mask. As for the impurity, boron is ion-implanted into the semiconductor thin film 4a when the TFT 1 is of a p-channel type. For example, a logic circuit such as a CMOS inverter is configured by a combination of an n-channel TFT 1 and a p-channel TFT 1. For this reason, the ion implantation for forming either the n-channel TFT 1 or the p-channel TFT 1 is performed in a state where the semiconductor thin film 4a of the other TFT is covered with a mask of resist or the like that prevents undesired ion implantation. Done in When the TFT 1 is an n-channel type, phosphorus is ion-implanted into the semiconductor thin film 4a.

  After ion implantation for each of the p-channel TFTs 1, impurities such as phosphorus and boron implanted into the semiconductor thin film 4a are activated by annealing. The annealing treatment can be performed by a heat treatment at a substrate temperature, for example, 600 ° C. for 3 hours in a nitrogen atmosphere. As a result, as shown in FIG. 8G, the high impurity concentration source region S and drain region D are formed on the semiconductor thin film 4 a on both sides of the gate electrode 12.

  As a result, the side end portion 10 of the source region S or the drain region D with respect to the channel region C is formed in alignment with the vicinity of the crystal growth end position 8 as shown in FIG.

  Next, an interlayer insulating film (not shown) is formed on the gate insulating film 11 and the gate electrode 12. The process of forming a source electrode, a drain electrode, a gate electrode (not shown), etc. through a through hole (not shown) formed in the interlayer insulating film is a well-known process. The TFT 1 can be formed by such a method.

  A cross-sectional structure of the TFT 1 manufactured in this way is shown in FIG. FIG. 9 is a photomicrograph showing that the side end portion 10 of the drain region D with respect to the lower channel region C of the gate electrode 12 is provided near the crystal growth end position 8 in the crystallization region. Furthermore, it can be seen that in the source region S and the drain region D of the TFT 1, stacking faults S1 and D1 that run from the deep direction to the shallow direction of the semiconductor thin film 4a are generated. Furthermore, it can be clearly seen that the gate electrode 12 is inclined.

  FIG. 10 is a plan view of FIG. 9 and shows a state in which a side end portion 10 of the drain region D with respect to the channel region C is provided in the vicinity of the crystal growth end position 8. In FIG. 11 and FIG. 13 according to another embodiment, n is a value corresponding to the position of the drain side end 10 of the thin film transistor in which the side end 10 of the drain region D and the channel region C is formed near the crystal growth end position 8. The relationship with the mobility μ of electrons or holes of the type TFT is shown.

As shown in FIGS. 11 and 13, the mobility of the TFT 1 provided with the end 10 with respect to the channel region C of the drain region D within the vicinity of 1.5 μm from the crystal growth end position 8 is 150 cm ² / v. The characteristic more than s is acquired. In particular, the TFT 1 in which the end portion 10 of the drain region D with respect to the channel region C is formed within 0.05 to 0.2 μm from the crystal growth end position 8 has a mobility of 300 cm ² / v. Excellent characteristics over s are obtained.

  11 and 13 plot the mobility characteristics of a number of n-type TFTs. This characteristic indicates that the end of crystal growth at the drain end position (the end of the drain area D on the channel area side) of the n-type TFT is terminated. This is a mobility characteristic of a TFT formed within a vicinity of 1.5 μm from the position 8. Furthermore, the characteristics plotted by the squares are the mobility characteristics of TFTs formed with the source end position of the n-type TFT (the end of the source region S on the channel region side) within the vicinity of 1.5 μm from the crystal growth end position 8. is there. This mobility characteristic is obtained from a characteristic curve diagram of drain current (vertical axis) with respect to gate voltage (horizontal axis). Within the vicinity of 1.5 μm from the crystal growth end position 8, the TFTs having the drain end position and the TFTs having the source end position have substantially the same characteristics.

  In FIGS. 11 and 13, the data plotted out of the crystal growth end position 8 (near the adjacent crystallization region end position 8) are TFT characteristics formed so that the channel region straddles the crystal growth end position 8. is there. The characteristics shown in FIG. 11 are those of an n-type TFT, but similar characteristics can be obtained with a p-type TFT. Furthermore, the direction of the current flowing through the TFT 1 of this embodiment is parallel to the growth direction grown in the lateral direction, and it is optimal to flow the current in the crystal growth direction.

  Next, an embodiment in which the TFT according to the present invention is applied to a transistor circuit of a display device such as a liquid crystal display device will be described with reference to FIG. The same parts as those in FIGS. 1 to 11 are denoted by the same reference numerals, and detailed description thereof is omitted. FIG. 12 shows an example of the display unit of the active matrix liquid crystal display device 50. The liquid crystal display device 50 includes a transparent substrate 52, a pixel electrode 53, a scanning line 54, a signal line 55, a counter electrode 56, a TFT 1, a scanning line driving circuit 57, a signal line driving circuit 58, a liquid crystal controller 59, and the like. .

  In other words, peripheral circuit portions such as the scanning line driving circuit 57 and the signal line driving circuit 58 that are required to operate at high speed are configured by the thin film transistors. This display device can realize a system display including active elements such as a peripheral circuit section and a memory circuit section.

The TFT 1 is formed in the structure as described with reference to FIG. 1 and constitutes a peripheral circuit portion that is required to operate at high speed, such as a scanning line driving circuit 57 and a signal line driving circuit 58. Peripheral circuit portions such as the scanning line driving circuit 57 and the signal line driving circuit 58 form the source end position of the source region S or the drain end position of the drain region D within 0.05 to 0.2 μm from the crystal growth end position 8. It is desirable that the TFT is constructed. By forming such a TFT, the peripheral circuit can be formed of a TFT having excellent characteristics with a mobility (μmax) of 300 cm ² / V · s or more.

  The display device manufactured in this manner can realize a system display including active elements such as peripheral circuits and memory circuits. This display device is also effective in reducing the size and weight.

  The thin film transistor 1 of each circuit and the memory, capacitor, resistor, and the like that are replaced by the thin film transistor can be formed by the thin film transistor of FIG. That is, in this specification, the thin film transistor includes a thin film transistor which can be configured by the thin film transistor shown in FIG.

  The thin film transistor 26 manufactured in this way can be applied to a driving circuit such as a liquid crystal display device (display) or an EL (electroluminescence) display, an integrated circuit such as a memory (SRAM or DRAM) or a CPU in each pixel circuit. .

  As described above, according to the above embodiment, a TFT having a high electron or hole mobility can be obtained. A TFT capable of obtaining such high mobility can be applied to peripheral circuit portions such as the scanning line driver circuit 57 and the signal line driver circuit 58.

FIG. 3 is a partially cutaway cross-sectional view for explaining a configuration of a thin film transistor of the present invention. FIG. 2 is a process diagram for explaining a manufacturing process of the TFT of FIG. 1 in order of processes. FIG. 2 is a characteristic diagram showing S value characteristics with respect to a drain end position of the p-channel thin film transistor of FIG. It is a block diagram of the crystallization apparatus for demonstrating the crystallization process of FIG. It is a block diagram for demonstrating the illumination optical system of FIG. 4 concretely. It is a figure for demonstrating the board | substrate structure at the time of crystallizing by the crystallization process of FIG. 2, and the shape of the crystallized semiconductor thin film. FIG. 3 is a cross-sectional view for explaining an example of the TFT manufacturing process of FIG. 2 in the order of steps. FIG. 8 is a cross-sectional view for explaining a subsequent process of the TFT manufacturing process of FIG. 7 in order of processes. It is a cross-sectional photograph of FIG. It is the photograph seen from the plane of FIG. FIG. 9 is a characteristic diagram showing a comparison of mobility characteristics of a large number of TFTs obtained by the steps of FIGS. 7 and 8. It is a circuit block diagram for demonstrating the Example which applied the thin-film transistor of FIG. 1 to the liquid crystal display device. FIG. 9 is a characteristic diagram showing a comparison of mobility characteristics of a number of TFTs according to another embodiment obtained by the steps of FIGS. 7 and 8.

Explanation of symbols

    1: TFT, 2: glass substrate, 3: silicon oxide film, 4: amorphous silicon film, 4a: semiconductor thin film, 5: crystallization region, 7: crystal growth start position, 8: crystal growth end position, 10: Drain end (side end), 11: gate insulating film, 12: gate electrode, 15: illumination system, 16: phase modulation element, 17: imaging optical system, 18: substrate to be crystallized, 19: stage, 20: Crystallizer, 21: light source, 22: homogenizer, 23: beam expander, 24: first fly-eye lens, 25: first condenser optical system, 26: second fly-eye lens, 27: second condenser optical system, 33: aperture stop, 35: cap film, 40: aluminum layer, 41: resist pattern, 50: liquid crystal display device 52: transparent electrode, 53: pixel electrode, 54: scanning line, 55: signal line, 56: counter electrode, 57: scanning line driving circuit, 58: signal line driving circuit, 59: liquid crystal controller.

Claims (5)

A p-channel type thin film transistor having a source region, a channel region, and a drain region in a semiconductor thin film having a crystallized region crystallized in a lateral direction, and having a gate insulating film and a gate electrode on the channel region;
The end of the drain region or the source region on the channel region side is a position from 1.0 μm to 2.5 μm from the crystal growth start position or vertical growth start position, and the crystal growth start position or vertical growth start. A p-channel thin film transistor, which is provided in a crystallization region at a position from a position of 3.0 μm to a position of 4.7 μm from the position. A semiconductor thin film having a crystallized region with an inclined surface that grows in the lateral direction and rises in the crystal growth end direction has a source region, a channel region, and a drain region, and has a gate insulating film and a gate electrode on the channel region. a p-channel thin film transistor,
The end of the drain region or the source region on the channel region side is a position from 1.0 μm to 2.5 μm and a position from a crystal growth start position or a vertical growth start position to a position from 3.0 μm to 4.7 μm. A p-channel thin film transistor, which is provided in a crystallization region at a position up to. The crystallized region is a single crystal region formed by irradiating a non-single crystal semiconductor film with a laser beam having a reverse peak light intensity distribution by a phase shifter through a homogenizer. The p-channel thin film transistor according to claim 1 or 2, wherein the p-channel thin film transistor is provided. Irradiating a non-single crystal semiconductor film with laser light having a reverse peak light intensity distribution to crystallize the irradiated region to form a crystallized region;
A position from 1.0 μm to 2.5 μm from the crystal growth start position or vertical growth start position of the crystallized region and a position from 3.0 μm to 4.0 μm from the crystal growth start position or vertical growth start position. Forming a thin film transistor by positioning a side end of the drain region or the source region with respect to the channel region in the crystallized region at a position of up to 7 μm. Manufacturing method. 4. A display device in which the p-channel thin film transistor according to claim 1 is provided in a peripheral circuit portion that requires high-speed operation such as a signal line driver circuit or a scanning line driver circuit.

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