JP4974416B2 - Laser annealing equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser annealing method and apparatus for growing a crystal grain by heating a silicon film on a substrate by laser irradiation.
[0002]
[Prior art]
The excimer laser is a high-power pulse laser used in the ultraviolet region. As one application of such an excimer laser, annealing to a thin film transistor (TFT) used in a liquid crystal display (LCD) has attracted attention. For example, Japanese Patent Application Laid-Open No. 4-37144 irradiates an excimer laser with characteristics. “A method for manufacturing a thin film transistor” is disclosed.
[0003]
FIG. 6 is a cross-sectional structure diagram of a low-temperature polysilicon TFT annealed with an excimer laser. In general, the thickness of silicon is 25 to 100 nm, the insulating film is silicon dioxide or silicon nitride, the thickness is 50 to 300 nm, the gate electrode is aluminum, tungsten, or the like.
[0004]
Excimer laser annealing is used to form a polysilicon film and activate a contact layer. The silicon film is melted and crystallized by laser irradiation to become polysilicon. A high quality film is formed because it undergoes a melting process once. Since the excimer laser is an ultraviolet light pulse laser, the laser energy is absorbed by the film surface. Moreover, since the pulse width is about several tens of ns, the melting time of silicon is about several hundreds of ns, and there is almost no influence on the underlying glass substrate. In addition, other low temperature forming methods such as “Infrared annealing method” disclosed in Japanese Patent Application Laid-Open No. 61-32419 require annealing for a long time at a high temperature of about 1000 to 1200 ° C. for polysilicon formation and activation. However, according to excimer laser annealing, formation at a maximum temperature of 400 ° C. is possible, and there is no such problem.
[0005]
The operating speed of the TFT is represented by mobility (unit: cm ² / V · s). The mobility of the polysilicon TFT is 10 to 600 cm ² / V · s. The mobility is wide because it depends on both the grain size and the grain boundary. In order to obtain high mobility, it is necessary to have few intragranular defects and be close to a single crystal, and to form grain boundaries with low defects. In general, the larger the particle size and the fewer the defects at the grain boundaries, the higher the mobility.
[0006]
FIG. 7 is a configuration diagram of a conventional excimer laser annealing apparatus. The excimer laser used is XeCl, ArF, KrF, XeF or the like. The laser beam is introduced into the chamber through an optical system centered on a beam homogenizer. The inside of the chamber is controlled to a vacuum or a gas atmosphere by a pump system and a gas system. The beam is scanned by moving the stage or the optical system.
[0007]
[Problems to be solved by the invention]
FIG. 8 schematically shows a manufacturing process of a low-temperature polysilicon TFT. In this figure, (1) forms amorphous silicon (a-Si) on the surface of the glass substrate, (2) converts a-Si to polysilicon (poly-Si), and dry-etches (3 The surface is covered with an insulating coating (SiO ₂ ), an electrode film is formed in (4), and doping is performed in (5).
In the excimer laser annealing, poly-Si is heated in the above (2) and (5), the crystal grain size is increased, and impurities implanted by doping are diffused to increase the bond with silicon. Used to obtain mobility.
[0008]
However, in the above-described conventional excimer laser activation process, as shown in FIG. 8 (5), an electrode film is formed on the polysilicon, so that the electrode is formed by irradiation from the TFT side. There is a problem that the polysilicon in the existing part cannot be activated because it is not irradiated with laser. Therefore, the activity of silicon after doping cannot be maximized.
[0009]
Furthermore, in order to improve this, when the activation process with a heater is performed, heating for a long time in a high-temperature furnace that can be heated in a nitrogen atmosphere is required, and the processing time is long and complicated, and the glass substrate is distorted or impurities The problem of excessive diffusion occurs.
[0010]
The present invention has been made to solve such problems. That is, even if an electrode film is formed on polysilicon, the object of the present invention is to reliably activate the polysilicon in the portion where the electrode is formed. It is an object of the present invention to provide a laser annealing method and apparatus capable of maximizing the activity of silicon, maximizing the processing time, and reducing the risk of substrate distortion.
[0011]
[Means for Solving the Problems]
According to the present invention, the thin film transistor (2) formed on the substrate (1) is irradiated with laser light (10) that can be transmitted through the substrate from the substrate side to activate the polysilicon (3) constituting the thin film transistor. A laser annealing method is provided. According to a preferred embodiment of the present invention, the substrate (1) is a glass substrate, a plastic substrate or a quartz substrate, and the wavelength of the laser beam (10) is not less than 300 nm and not more than 900 nm.
[0012]
Further, a transfer device (12) for horizontally transferring a substrate (1) having a thin film transistor (2) formed on the surface thereof, and a laser beam that can be transmitted from the substrate side to the polysilicon (3) constituting the thin film transistor (3). And a laser apparatus (14) for irradiating 10), and activates the polysilicon constituting the thin film transistor. According to a preferred embodiment of the present invention, the substrate (1) is a glass substrate, a plastic substrate or a quartz substrate, and the wavelength of the laser beam (10) is not less than 300 nm and not more than 900 nm.
[0013]
According to the method and apparatus of the present invention, since the laser beam (10) is a visible laser having a wavelength of 300 nm or more and 900 nm or less, all of the TFTs (thin film transistors) can be irradiated through the substrate from the substrate side. The polysilicon (3) can be annealed.
[0014]
According to a preferred embodiment of the present invention, the laser beam (10) includes an excimer laser having a wavelength of 308 nm, a YAG laser having a wavelength of 532 nm, a YLF laser having a wavelength of 527 nm, an Ar laser having a wavelength of 488 nm or 514.2 nm, and a wavelength of 532 nm. YVO ₄ laser or HeNe laser with a wavelength of 543.5 nm.
By using these laser beams (10), a laser beam having a wavelength of 300 nm or more and 900 nm or less can be irradiated through the substrate with high output and high efficiency.
[0015]
It is preferable that the transport device (12) has a gas slider device (15) that transports the substrate by floating the gas.
[0016]
With this configuration, a thin (1 to 2 mm) substrate can be supported without contact, and laser light can be irradiated from the substrate side to the entire surface of the substrate, and all the polysilicon (3) constituting the TFT (Thin Film Transistor) is annealed. can do.
[0017]
Further, the transport device (12) has a gas bearing (16) for adjusting the flying height of the substrate by simultaneously blowing and sucking gas to the substrate in the vicinity of the irradiation position of the laser beam (10). .
With this gas bearing (16), the horizontal accuracy of the substrate can be adjusted by the gas flow rate, and the flying height of the substrate at the irradiation position of the laser beam (10) can be adjusted precisely.
[0018]
Furthermore, it is preferable to provide a lamp heating device (17) for preheating the substrate before irradiating the laser beam (10). The required output of the laser beam (10) can be reduced by preheating the substrate with the lamp heating device (17).
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the common part in each figure, and the overlapping description is abbreviate | omitted.
[0020]
1A and 1B are schematic views of a laser annealing apparatus of the present invention, in which FIG. 1A is a side view and FIG. 1B is an AA arrow view thereof. In this figure, the laser annealing apparatus of the present invention includes a transfer device 12 and a laser device 14.
[0021]
The transport device 12 transports the substrate 1 having a thin film transistor 2 (not shown: see FIG. 8) formed on the surface thereof in a horizontal manner by floating with a gas. At this time, the thin film transistor 2 on the substrate 1 is formed on the upper surface as shown in FIG. The substrate 1 may be a glass substrate, a plastic substrate, or a quartz substrate. Hereinafter, a case where the substrate 1 is a glass substrate will be described.
Further, the laser device 14 irradiates the polysilicon 3 (not shown: see FIG. 8) constituting the thin film transistor 2 with the laser beam 10 having a wavelength of 300 nm or more and 900 nm or less from the glass substrate side (lower side in the figure). It has become.
[0022]
The laser beam 10 is preferably an excimer laser with a wavelength of 308 nm, a YAG laser with a wavelength of 532 nm, a YLF laser with a wavelength of 527 nm, an Ar laser with a wavelength of 488 nm or 514.2 nm, a YVO ₄ laser with a wavelength of 532 nm, or a HeNe with a wavelength of 543.5 nm. It is a laser.
[0023]
The laser beam 10 is generated by the laser device 14 a, passes through the optical system 14 b and the beam homogenizer 14 c, is reflected upward by the mirror 14 d, and is irradiated onto the lower surface of the glass substrate 1 through the opening 12 a provided in the transport device 12. The In this example, the scanning of the laser beam 10 is performed by swinging the mirror 14d, but may be performed by other means such as movement of the optical system 14b.
[0024]
FIG. 2 is a plan view of the conveying apparatus of FIG. 1, and FIG. 3 is an enlarged view of a main part of FIG. As shown in FIGS. 2 and 3, the transport device 12 includes a gas slider device 15 and a gas bearing 16. The gas slider device 15 blows gas (air, nitrogen, etc.) upward, and the glass substrate 1 is floated and transported by this gas. In this conveyance, for example, the glass substrate 1 is moved horizontally by a clamping device (not shown) provided in the traveling carriage 18 traveling on the rail 18a.
[0025]
The gas bearing 16 adjusts the flying height of the glass substrate by simultaneously blowing and sucking the gas to the glass substrate 1 in the vicinity of the irradiation position of the laser beam 10.
[0026]
The lamp heating device 17 is, for example, a plurality of infrared lamps, and preheats the glass substrate 1 before being irradiated with the laser light 10 to reduce the required output of the laser light 10.
[0027]
Using the apparatus described above, according to the method of the present invention, the thin film transistor 2 formed on the glass substrate 1 is irradiated with the laser beam 10 having a wavelength of 300 nm or more and 900 nm or less from the glass substrate side, thereby forming polysilicon forming the thin film transistor 3 is activated.
[0028]
FIG. 4 is a relationship diagram of the wavelength and transmittance of a glass substrate having a thickness of 0.7 mm. From this figure, the excimer laser (ArF: 194 nm, KrF: 248 nm) having an oscillation wavelength of less than 300 nm has a low transmittance of several percent or less and can hardly be transmitted through the TFT glass substrate. This shows that the TFT cannot be activated.
[0029]
On the other hand, in the method and apparatus of the present invention, the laser beam 10 having a wavelength of 300 nm or more and 900 nm or less, specifically, an excimer laser having a wavelength of 308 nm, a YAG laser having a wavelength of 532 nm, a YLF laser having a wavelength of 527 nm, or a wavelength of 488 nm. Or, since an Ar laser with a wavelength of 514.2 nm, a YVO ₄ laser with a wavelength of 532 nm, or a HeNe laser with a wavelength of 543.5 nm is used, as shown by the double arrow in the figure, about 40% or more in the case of an excimer laser with a wavelength of 308 nm, etc. With this laser light, a transmittance of about 90% or more can be obtained, and the polysilicon 3 constituting the thin film transistor can be activated efficiently from the substrate side.
[0030]
FIG. 5 is a relationship diagram between the wavelength of silicon and the absorption coefficient. In this figure, a-Si is amorphous silicon, c-Si is crystalline silicon, and polysilicon (poly-Si) has an intermediate absorption coefficient.
From this figure, it can be seen that when the wavelength exceeds 900 nm, the absorption coefficient significantly decreases, but in the optimum range of wavelengths of 300 nm to 900 nm, polysilicon (poly-Si) has a sufficiently high absorption coefficient.
[0031]
According to the above-described method and apparatus of the present invention, since the laser beam 10 is a visible laser having a wavelength of 300 nm or more and 900 nm or less, all the polysilicon 3 constituting the TFT (thin film transistor) can be irradiated from the glass substrate side. Can be annealed.
[0032]
Also, by using an excimer laser with a wavelength of 308 nm, a YAG laser with a wavelength of 532 nm, a YLF laser with a wavelength of 527 nm, an Ar laser with a wavelength of 488 nm or 514.2 nm, a YVO ₄ laser with a wavelength of 532 nm, or a HeNe laser with a wavelength of 543.5 nm, Laser light having a wavelength of 300 nm or more and 900 nm or less can be irradiated through the substrate with high output and high efficiency.
[0033]
Furthermore, the gas slider device 15 supports a thin (1 to 2 mm) glass substrate in a non-contact manner, and the entire surface thereof can be irradiated with laser light from the glass substrate side through the glass substrate. Further, the horizontal precision of the glass substrate 1 can be adjusted by the gas flow rate by the gas bearing 16, and the flying height of the glass substrate at the irradiation position of the laser beam 10 can be precisely adjusted.
[0034]
In addition, this invention is not limited to the Example and embodiment mentioned above, Of course, it can change variously in the range which does not deviate from the summary of this invention. For example, although the glass substrate has been described in detail in the above description, the present invention can be similarly applied to a plastic substrate or a quartz substrate.
[0035]
【Effect of the invention】
As described above, the laser annealing method and apparatus of the present invention can reliably activate the polysilicon in the portion where the electrode is formed even when the electrode film is formed on the polysilicon. Thus, the activity of silicon after doping can be maximized, and the processing time is short, and there is an excellent effect such that there is little risk of distortion of the substrate.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a laser annealing apparatus of the present invention.
FIG. 2 is a plan view of the transport device of FIG.
FIG. 3 is an enlarged view of a main part of FIG. 2;
FIG. 4 is a graph showing the relationship between the wavelength and transmittance of a glass substrate.
FIG. 5 is a graph showing the relationship between the wavelength of silicon and the absorption coefficient.
FIG. 6 is a cross-sectional structure diagram of a low-temperature polysilicon TFT annealed with an excimer laser.
FIG. 7 is a configuration diagram of a conventional excimer laser annealing apparatus.
FIG. 8 is a manufacturing process diagram of a low-temperature polysilicon TFT.
[Explanation of symbols]
1 Substrate (glass substrate)
2 Thin film transistor (TFT)
3 Polysilicon 10 Laser beam 12 Conveying device 14 Laser device 15 Gas slider device 16 Gas bearing 17 Lamp heating device

Claims (3)

A laser annealing device having a gas slider device and a conveying device including a gas bearing, and a laser device,
The transfer device is provided with an opening,
The gas slider device has a function of levitating a substrate irradiated with laser light from the laser device through the opening by blowing gas,
The gas bearing has a function of adjusting the flying height of the substrate at the laser light irradiation position by simultaneously performing gas blowing and suction and adjusting the gas flow rate. Laser annealing equipment. In claim 1,
The laser annealing apparatus, wherein the laser beam is applied to a surface of the substrate on which the gas is blown. In claim 1 or 2 ,
A laser annealing apparatus having an infrared lamp.

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