JP4066564B2 - Thin film semiconductor manufacturing apparatus and thin film semiconductor manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a manufacturing apparatus for manufacturing a thin film transistor formed on an insulator, a display pixel of a liquid crystal display device, or a thin film transistor used as a constituent element of a liquid crystal driving circuit.
[0002]
[Prior art]
Semiconductor films such as polycrystalline silicon are widely used for thin film transistors (hereinafter referred to as TFTs in the present specification) and solar cells. In particular, polycrystalline silicon (poly-Si) TFTs can be made on a transparent and insulating substrate such as a glass substrate while being capable of high mobility, making it possible to make liquid crystal display devices (LCD) and liquid crystal projectors. It is widely used as a component of light modulation elements such as built-in drivers for driving liquid crystals, and has succeeded in creating new markets.
[0003]
As a method for producing a high-performance TFT on a glass substrate, a manufacturing method called a high-temperature process has already been put into practical use. A process using a high temperature with a maximum process temperature of about 1000 ° C. as a TFT manufacturing method is generally called a high temperature process. The characteristics of the high-temperature process are that a relatively high-quality poly-Si can be produced by solid phase growth of silicon, a high-quality gate insulating film (generally silicon dioxide) and a clean poly-Si and gate by thermal oxidation. That is, the interface of the insulating film can be formed. Due to these characteristics, a high-performance TFT having high mobility and high reliability can be stably manufactured in a high-temperature process. However, in order to use a high temperature process, it is necessary that the substrate on which the TFT is formed can withstand a high temperature heat process of 1000 ° C. or higher. The only transparent substrate that satisfies this condition is currently quartz glass. For this reason, poly-Si TFTs of recent years are all manufactured on a small and expensive quartz glass substrate, and are not suitable for enlargement due to cost problems. In addition, the solid phase growth method requires a heat treatment for a long time of ten and several hours, and there is a problem that productivity is extremely low. In addition, this method has caused a problem that the thermal deformation of the substrate becomes a big problem due to the whole substrate being heated for a long time, and it is impossible to use a substantially inexpensive large glass substrate. This also hinders cost reduction.
[0004]
On the other hand, a technique called a low-temperature process is intended to solve the above-mentioned drawbacks of a high-temperature process and to realize a poly-Si TFT with high mobility. In order to use a relatively inexpensive heat-resistant glass substrate, a poly-Si TFT manufacturing process having a maximum process temperature of approximately 600 ° C. or lower is generally called a low-temperature process. In a low temperature process, a technique for crystallizing a silicon film using a pulse laser having an extremely short oscillation time is widely used. Laser crystallization is a technology that utilizes the property of crystallizing in the process of solidifying instantaneously by irradiating an amorphous silicon film on a glass substrate with high-power pulsed laser light. Recently, a technique for forming a poly-Si film having a large area by scanning an amorphous silicon film on a glass substrate while repeatedly irradiating it with an excimer laser beam has been widely used. In addition, a relatively high quality silicon dioxide (SiO 2) film can be formed by a film forming method using plasma CVD as the gate insulating film, and the prospect for practical use is obtained. With these technologies, poly-Si TFTs can be created on a large glass substrate that is currently several tens of centimeters on a side.
[0005]
However, a problem in this low-temperature process is that the polycrystal-Si film crystallized by laser has a high defect density and becomes a factor that greatly affects the mobility of the TFT. The density of defects generated by laser crystallization particularly depends strongly on the control of the laser irradiation method during laser crystallization. In recent laser crystallization apparatuses for large substrates, a method of shaping a laser beam in a line shape as shown in FIG. 4 and irradiating a semiconductor thin film with a laser is becoming common. This emphasizes the practicality for forming a poly-Si film on a large area substrate such as a liquid crystal display device in a short tact time. In particular, in this case, in order to ensure the length 201 of the long direction of the laser beam that can generate only limited pulse energy, the beam width 202 in the short axis direction is almost as small as several tens μm to several hundreds μm. A method of irradiating pulses while moving the line beam as indicated by an arrow (203) in FIG. 4 is employed. However, since there should be no boundary in the irradiation area of each pulse, the irradiation area for each pulse is usually scanned and laser irradiation is performed while overlapping each other by about 90%. For this reason, the laser crystallization apparatus crystallizes the entire surface of the substrate while shifting the position of the semiconductor thin film on the substrate and the laser beam focused on the line with a high accuracy of several microns to several tens of microns for each laser irradiation pulse. To do.
[0006]
Laser crystallization utilizes the property that a silicon thin film is heated with a pulsed laser for a very short time, and the thin film melts above its melting point, and then crystallizes in the cooling process. Usually, this laser crystallization is performed in vacuum for the purpose of preventing impurities from being mixed into the film and controlling the surface state. However, since the silicon film reaches the melting point as described above, the film temperature is 1000 ° C. That's more than that. When such treatment is performed in a vacuum, silicon atoms and clusters having thermal energy are desorbed from the film surface. Since the melting time is a few hundred nanoseconds at most, the amount of desorbed silicon is very small. However, as described above, in a mass production apparatus that crystallizes a large-area silicon thin film by multiple laser irradiations with a high overlap rate, a laser is used. There is a problem that the above-described thermally desorbed silicon adheres to the light introduction window and the transmittance of the laser light gradually changes. Even if a small amount of silicon adheres to the window, the optical effect on the ultraviolet light is enormous. For example, when about 10 substrates having an outer size of 400 mm × 400 mm are processed, the transmittance is reduced by nearly 10%. Since the optimum energy condition for laser crystallization is only in the range of 3 to 5%, the film quality of the laser crystallization poly-Si changes with time. In order to avoid this problem, there is JP-A-11-26393 as a conventional technique. As shown in FIG. 5, the treatment is performed while gas is blown onto the laser beam introduction window, thereby preventing the adhesion of silicon particles. However, as described above, particles flying at a thermal speed pass through a distance of about 10 cm to a window in a normal apparatus structure in just a few μsec, and the collision probability is extremely low under reduced pressure as long as the gas is blown by pressure. The effect is hardly expected.
[0007]
For this reason, the effective energy of the irradiation laser light changes with time, resulting in variations in the quality of the crystallized film, which causes a decrease in yield. Moreover, the time required for the maintenance of the apparatus is required, and the operating rate is lowered and the cost of the product is increased.
[0008]
[Problems to be solved by the invention]
Therefore, in view of the above-described problems, the present invention prevents a change in transmittance of a light introduction window, which is a problem in a semiconductor manufacturing apparatus that performs heat treatment using light in a vacuum, and in particular, variation in a laser crystallized poly-Si film. Can be reduced, and a semiconductor manufacturing apparatus and a thin film semiconductor manufacturing method having a high operation rate can be provided.
[0009]
[Means for Solving the Problems]
According to an aspect of the present invention, a thin film semiconductor manufacturing apparatus includes a decompression container, and performs heat treatment by irradiating a thin film semiconductor in the decompression container with a laser beam through a light introduction window. The decompression vessel includes a light introduction chamber having the light introduction window, a light irradiation chamber for holding a semiconductor substrate to be processed, a gate valve capable of separating the light introduction chamber and the light irradiation chamber, and the light A plasma discharge electrode for generating plasma in the introduction chamber, and the plasma is generated in the light introduction chamber when the light introduction chamber and the light irradiation chamber are separated by the gate valve. The light introduction window is heated. Here, the light introduction window is a window that transmits the laser light applied to the semiconductor. Therefore, it is formed of a material having a relatively high transmittance at the wavelength of the laser beam to be irradiated.
[0010]
In order to solve the above-mentioned problems, the invention according to claim 2 is the semiconductor manufacturing apparatus according to claim 1, wherein the volume of the light introducing chamber is not more than one fifth of the volume of the light irradiation chamber. To do.
[0011]
The invention of claim 3, wherein in order to solve the above problems, a semiconductor manufacturing apparatus according to claim 1 or 2, wherein the light introducing chamber is characterized by comprising the plasma discharge electrode.
[0012]
In order to solve the above problems, a fourth aspect of the present invention is the semiconductor manufacturing apparatus according to the third aspect, wherein the plasma discharge electrode is a movable electrode. Here, the movable type means that the thin film semiconductor is not on the optical path when irradiating light to the thin film semiconductor but moves near the light introduction window when performing the discharge treatment.
[0013]
Wherein the fifth aspect of the present invention to solve the above problems, a semiconductor manufacturing apparatus according to claim 3, wherein the plasma discharge electrode is inductively coupled discharge electrode located outside of the light introducing chamber And
[0014]
According to an aspect of the present invention, a method of manufacturing a thin film semiconductor includes a light introduction chamber having a light introduction window, a light irradiation chamber, and a gate valve that separates the light introduction chamber and the light irradiation chamber. By holding a semiconductor substrate on which a thin film semiconductor is formed on the surface in the light irradiation chamber of the vacuum container provided, opening the gate valve, and irradiating the thin film semiconductor with the laser light through the light introduction window When the first step of performing heat treatment, the second step of separating the light introduction chamber and the light irradiation chamber by closing the gate valve, and the light introduction chamber and the light irradiation chamber are separated, And a third step of performing plasma discharge in the light introduction chamber while heating the light introduction window.
[0015]
In order to solve the above-mentioned problems, a seventh aspect of the invention is characterized in that in the semiconductor manufacturing apparatus of the sixth aspect, the plasma discharge is performed using an etching gas for the thin film semiconductor.
[0016]
In order to solve the above-mentioned problems, the invention according to claim 8 is the method of manufacturing a thin film semiconductor according to claim 6 or 7, wherein the thin film semiconductor is silicon and the etching gas is sulfur hexafluoride. And
[0017]
In order to solve the above-mentioned problem, the invention according to claim 9 is the thin film semiconductor manufacturing method according to claim 6, 7 or 8, wherein plasma discharge is performed in the light introducing chamber and at the same time the light irradiation chamber is covered. The processing semiconductor substrate is transported.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an embodiment according to the present invention will be described in detail with reference to FIG.
[0019]
First, the semiconductor thin film (403) will be described. As a semiconductor film to which the present invention is applied, in addition to a single group IV semiconductor film such as silicon (Si) or germanium (Ge), silicon germanium (Si _x Ge _1-x : 0 <x <1) or silicon A semiconductor film of a quaternary element complex such as carbide (Si _x C _1-x : 0 <x <1) or germanium carbide (Ge _x C _1-x : 0 <x <1), gallium arsenide (GaAs ) And indium antimony (InSb), etc., a compound compound semiconductor film of a group 3 element and a group 5 element, or a compound compound semiconductor film of a group 2 element, such as cadmium selenium (CdSe), and a group 6 element, etc. is there. Alternatively, further compound compound semiconductor films such as silicon, germanium, gallium, and arsenic (Si _x Ge _y Ga _z As _z : x + y + z = 1) and these semiconductor films include phosphorus (P), arsenic (As), and antimony (Sb The present invention also applies to an N-type semiconductor film to which a donor element such as) is added, or a P-type semiconductor film to which an acceptor element such as boron (B), aluminum (Al), gallium (Ga), or indium (In) is added. Is adaptable. These semiconductor films are formed by a CVD method such as an APCVD method, an LPCVD method, or a PECVD method, or a PVD method such as a sputtering method or a vapor deposition method. In the case of using a silicon film as the semiconductor film, LPCVD can be deposited using disilane (Si ₂ H ₆ ) or the like as a substrate at a substrate temperature of about 400 ° C. to 700 ° C. In the PECVD method, deposition can be performed at a substrate temperature of about 100 ° C. to about 500 ° C. using monosilane (SiH ₄ ) or the like as a raw material. When using the sputtering method, the substrate temperature is about room temperature to 400 ° C. There are various states, such as amorphous, mixed crystal, microcrystalline, and polycrystalline, as the initial state (as-deposited state) of the semiconductor film deposited in this way. May be in any state. In the present specification, not only amorphous crystallization but also polycrystalline and microcrystalline recrystallization are all called crystallization. The thickness of the semiconductor film is suitably about 20 nm to 100 nm when it is used for a TFT.
[0020]
After forming the base insulating film (402) and the semiconductor film (403), the semiconductor film is crystallized by laser irradiation. Usually, a silicon film surface deposited by a CVD method such as an LPCVD method or a PECVD method is often covered with a natural oxide film. Therefore, it is necessary to remove this natural oxide film before irradiating the laser beam. For this purpose, there are a method of wet etching by immersing in a hydrofluoric acid solution, dry etching in a plasma containing fluorine gas, and the like.
[0021]
Next, the substrate with the semiconductor film is set in a laser irradiation chamber (405). A part of the laser irradiation chamber is formed by a quartz window (406) (light introduction window), and after the chamber is evacuated to vacuum, laser light is irradiated from the quartz window.
[0022]
Here, laser light will be described. It is desirable that the laser light is strongly absorbed on the surface of the semiconductor thin film (403) and hardly absorbed by the insulating film (402) immediately below the laser light. Therefore, excimer laser, argon ion laser, YAG laser harmonic, etc. having a wavelength in the ultraviolet region or the vicinity thereof are preferable as this laser light. Further, in order to heat the semiconductor thin film to a high temperature and simultaneously prevent damage to the substrate, it is necessary to have a pulse output with a large output and a very short time. Therefore, among the above laser beams, excimer lasers such as a xenon chloride (XeCl) laser (wavelength 308 nm) and a krypton fluoride (KrF) laser (wavelength 248 nm) are most suitable. Next, the laser light irradiation method will be described with reference to FIG. The half width of the intensity of the laser pulse is an extremely short time of about 10 ns to about 500 ns. Laser irradiation is performed in a vacuum in which the substrate (300) is between room temperature (25 ° C.) and 400 ° C. and the background vacuum is about 10 ⁻⁴ Torr to 10 ⁻⁹ Torr. As shown in FIG. 2, the irradiation region shape may be a line shape (301) having a width of about 100 μm (302) or more and a length of several tens of centimeters or more, and the crystallization may be advanced by scanning this line laser beam. In this case, the overlap in the beam width direction for each irradiation (the overlap between 303 and 304) is about 5% to 95% of the beam width (302). If the beam width is 100 μm and the overlap amount for each beam is 90%, the beam advances 10 μm for each irradiation, so that the same point receives 10 laser irradiations. Usually, in order to crystallize the semiconductor film uniformly over the entire substrate, at least about 5 times of laser irradiation is desired. Therefore, the overlap amount of the beam for each irradiation is required to be about 80% or more. In order to reliably obtain a highly crystalline polycrystalline film, it is preferable to adjust the overlap amount from about 90% to about 97% so that the same point is irradiated about 10 to 30 times.
[0023]
In the semiconductor manufacturing apparatus of the present invention, the vacuum vessel (405) is provided by the gate valve (441) in the light introduction chamber so that the light transmittance of the light introduction window (406) does not decrease even when laser irradiation is repeated at such a high overlap rate. (442) and a light irradiation chamber (443). Laser irradiation is performed on the silicon film (403) on the substrate (401) placed in a vacuum with the gate valve opened. In the state where the crystallization of the entire surface of the substrate is completed, silicon is slightly attached to the light introduction window, but there is a portion that is not completely attached but not a complete film. The transmittance drop at this point is still slight. In this state, the gate valve (441) is closed and the light introduction chamber is separated from the light irradiation chamber. Thereafter, the movable discharge electrode (420) is moved directly under the laser introduction window (406). While controlling the gas flow rate by the mass flow controller (423), an AC voltage is applied to the discharge electrode by the high frequency power source (421) to perform discharge. This discharge method is a capacitive coupling type discharge, but the discharge may be performed by a DC voltage. As the gas (427), H ₂ , SF ₆ , CF ₄ or the like can be used. These gases are adjusted to a pressure of about 1 Torr and discharge is performed to etch the silicon adhering to the inside of the laser introduction window. Since a very small amount of silicon is deposited by laser irradiation, such dry etching can be completely removed from 1 second to at most 10 seconds. It is also effective to heat the light introduction window in order to increase the etching rate. In the conventional example, it was difficult to always keep the transmittance of the laser irradiation window constant. However, when the quartz window is used according to the method of the present invention, the transmittance can always be maintained at a value of 94% or more and stable. Laser irradiation is possible. Also, since the dry etching time is very short, this etching can be completed within the substrate transfer time, and the throughput of the apparatus is not reduced. Immediately after the etching, gas exhaustion is started. The gate valve (441) is opened to keep the whole vacuum chamber in a vacuum again, and the next substrate is laser crystallized. At this time, the light irradiation chamber serves as a buffer for evacuating the light introduction chamber (that is, a role for allowing the entire chamber to reach high vacuum again in a short time). For this reason, the volume of the light introduction chamber is preferably smaller than the volume of the light irradiation chamber. A volume of 1/5 or less is desirable. Further, the discharge electrode may be installed outside the vacuum vessel as shown in FIG. Particularly in this case, an inductively coupled discharge electrode (521) in which the discharge electrode has a ring shape and the tip is brought into contact with the vacuum vessel is effective. With such an electrode structure, the electrode can be produced with a structure that surrounds the laser light path and does not block the laser light path, and the electrode can be installed in the atmosphere, eliminating the need for a complicated structure such as a movable electrode, and reducing the cost. The device can be manufactured with. In addition, if inductive coupling type discharge is used, a high-density plasma can be generated at a low pressure. Therefore, a high vacuum can be reached immediately after performing the deposit etching process on the laser irradiation window in a very short time.
[0024]
In this way, even when laser crystallization is performed on a large number of large substrates, the transmittance of the laser introduction window can always be kept constant. Moreover, since the etching can be performed in parallel with the substrate transport, the throughput of the apparatus is not lowered at all.
[0025]
【Example】
An embodiment of the present invention will be described with reference to FIG. Although the substrate and the base protective film used in the present invention are in accordance with the above description, a square general-purpose non-alkali glass 501 having an outer size of 300 mm × 300 mm is used here as an example of the substrate. First, a silicon oxide film (502) having a thickness of about 200 nm is deposited on the substrate (501) by ECR-PECVD at a substrate temperature of 150 ° C. Next, using a high vacuum type LPCVD apparatus, disilane (Si ₂ H ₆ ), which is a raw material gas, is flowed at 200 SCCM, and an amorphous silicon film (503) is deposited at a deposition temperature of 425 ° C. by 50 nm. Next, the substrate is irradiated with excimer laser light (506) for crystallization. This laser crystallization apparatus has an XY stage (507) in a vacuum vessel (505), and a substrate holder (506) on top of this. The above-mentioned substrate (501) is installed in this substrate holder. The XY stage (507) is moved by rotation of the ball screw (508), and this ball screw is driven by a pulse motor (509). The laser introduction window (520) is fixed on a ceramic support base (524), and an inductive coupling type discharge electrode (523) is installed around the support base in a coil shape. This electrode is a matching box (522). ) To the AC power source (521). The substrate (501) is moved while laser irradiation is performed in a vacuum of 1 × 10 ⁻⁴ Pa to crystallize the silicon thin film on the entire surface of the substrate. As soon as the crystallization is completed, the gate valve (544) is closed, and the crystallized substrate is immediately transferred to another vacuum container by the vacuum robot. At the same time as the gate valve is closed, SF ₆ gas is allowed to flow from the gas inlet at 80 sccm, and the pressure in the chamber is adjusted to 1.3 Pa. Thereafter, an AC voltage is applied to the discharge electrode with a power of 500 W to cause discharge, and the silicon adhering to the inside of the laser introduction window (520) is etched. Although it takes time for the gas pressure to stabilize, the discharge may start immediately. When the semiconductor to be crystallized is silicon, SF ₆ gas has a high etching rate and is particularly efficient. Silicon deposited on the laser introduction window is completely etched in just 5 seconds by the inductively coupled high-density plasma, and when the next substrate is laser crystallized, the transmittance of the laser introduction window (520) is completely the same. It is true. Thereafter, the gate valve (544) is opened and the light introduction chamber is evacuated. At this time, a new substrate is transported and set, and the next laser irradiation can be performed without wasting time. As a result, the change in laser crystallization conditions with time can be completely eliminated, and a crystalline silicon film having stable characteristics can be obtained. Moreover, the throughput of the apparatus is not different from that of the conventional apparatus.
[0026]
In the prior art, the crystal film characteristics vary due to changes in the transmittance of the laser introduction window, and low throughput due to a decrease in the apparatus operating rate has been a problem. However, as described above, by using the semiconductor manufacturing apparatus and thin film semiconductor manufacturing method of the present invention, the transmittance of the laser introduction window can be maintained constant, and the uniformity of the characteristics of the crystal film can be dramatically improved. In addition to improvement, it is possible to realize a manufacturing apparatus having high throughput by improving the operation rate of the apparatus.
[Brief description of the drawings]
FIG. 1 shows a semiconductor manufacturing apparatus according to the present invention.
FIG. 2 is a diagram showing a line laser beam irradiation method during laser crystallization.
FIG. 3 shows a semiconductor manufacturing apparatus according to the present invention.
FIG. 4 shows a laser beam at the time of laser crystallization.
FIG. 5 is a view showing a conventional semiconductor manufacturing apparatus.
[Explanation of symbols]
101. . . Substrate 102. . . Underlying insulating film 103. . . Semiconductor film 104. . . Insulating film 106. . . Quartz window 107. . . Laser light 110. . . Crystallized semiconductor film 111. . . Oxygen gas or oxygen radical 109. . . Exhaust pipe 113. . . Gate insulating film 114. . . Gate electrode 115. . . Source and drain regions 116. . . Interlayer insulating film 117. . . Source and drain electrodes

Claims (9)

In a thin film semiconductor manufacturing apparatus that includes a decompression vessel and performs heat treatment by irradiating the thin film semiconductor in the decompression vessel with a laser beam through a light introduction window,
The decompression vessel includes a light introduction chamber having the light introduction window, a light irradiation chamber for holding a semiconductor substrate to be processed, a gate valve capable of separating the light introduction chamber and the light irradiation chamber, and the light introduction chamber. A plasma discharge electrode for generating plasma,
The light introduction window is heated when the light introduction chamber and the light irradiation chamber are separated by the gate valve and the plasma is generated in the light introduction chamber. Thin film semiconductor manufacturing equipment.   2. The thin film semiconductor manufacturing apparatus according to claim 1, wherein the volume of the light introducing chamber is 1/5 or less of the volume of the light irradiation chamber. A thin film semiconductor manufacturing apparatus according to claim 1 or 2, wherein said light introducing chamber is characterized by comprising the plasma discharge electrode.   4. The thin film semiconductor manufacturing apparatus according to claim 3, wherein the plasma discharge electrode is a movable electrode. The plasma discharge electrode is a thin film semiconductor manufacturing apparatus according to claim 3, wherein it is installed inductive coupling type discharge electrodes to the outside of the light introducing chamber. A thin film semiconductor is formed on the surface of the light irradiation chamber of the decompression vessel including a light introduction chamber having a light introduction window, a light irradiation chamber, and a gate valve for separating the light introduction chamber and the light irradiation chamber. A first step of holding the processed semiconductor substrate, opening the gate valve, and performing heat treatment by irradiating the thin film semiconductor with laser light through the light introduction window;
A second step of separating the light introduction chamber and the light irradiation chamber by closing the gate valve;
A third step of performing plasma discharge in the light introduction chamber while heating the light introduction window when the light introduction chamber and the light irradiation chamber are separated;
A method for producing a thin film semiconductor, comprising:   The method of manufacturing a thin film semiconductor according to claim 6, wherein the plasma discharge is performed using an etching gas for the thin film semiconductor.   8. The method of manufacturing a thin film semiconductor according to claim 7, wherein the thin film semiconductor is silicon and the etching gas is sulfur hexafluoride. 9. The method for manufacturing a thin film semiconductor according to claim 6, 7 or 8, wherein a plasma discharge is performed in the light introducing chamber and simultaneously the transfer of the semiconductor substrate to be processed in the light irradiation chamber is performed.

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