JP3063207B2 - Method for manufacturing thin film transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thin film transistor.

[0002]

2. Description of the Related Art In a method of manufacturing a thin film transistor, an amorphous silicon film is formed on an upper surface of an insulating substrate such as a glass substrate and the amorphous silicon film is irradiated with an excimer laser to convert the amorphous silicon film into a polysilicon film. Implanting phosphorus ions (impurities) into the polysilicon film except for the channel formation region,
There is a method in which an excimer laser is irradiated again to activate the implanted phosphorus ions, and a thin film transistor is formed through a predetermined process. In this case, in the laser irradiation step for converting amorphous silicon into polysilicon, in order to prevent the surface from becoming uneven due to rapid escape of hydrogen, the laser irradiation step is divided into three steps, that is, 180 steps.
at an energy density of mJ / cm ² , then 220 mJ / c
Laser irradiation is performed at an energy density of 260 mJ / cm ^{2 at} an energy density of m ² . At this time, since about 50% of the laser beam is reflected, the energy density substantially incident on the amorphous silicon film is 260 ×
0.5 = 130 mJ / cm ² . On the other hand, in the laser irradiation step for activating phosphorous ions, the melting point of polysilicon decreases when phosphorous ions are implanted, and if the energy density is too high, film destruction occurs. Laser irradiation is performed at a low energy density of 220 mJ / cm ² . At this time, since about 50% of the laser beam is also reflected, the energy density substantially incident on the polysilicon film is 220 × 0.5 =
It becomes 110 mJ / cm ² .

[0003]

However, in such a conventional method of manufacturing a thin film transistor, two laser irradiations of laser irradiation for converting amorphous silicon into polysilicon and laser irradiation for activating phosphorus ions are performed. Since the number of manufacturing steps is large and the area of the insulating substrate is large, since the spot size of the excimer laser is as small as several mm to 10 mm, scanning is performed and laser irradiation is performed. Therefore, there is a problem that it takes a long time, the productivity is low, and the cost is high. It is conceivable that laser irradiation for converting amorphous silicon into polysilicon and laser irradiation for activating phosphorus ions are simultaneously performed by one laser irradiation. However, in this case, as described above, in order to convert amorphous silicon into polysilicon, laser irradiation is finally performed at an energy density of 260 mJ / cm ² , so that the melting point of polysilicon is lowered by phosphorus ion implantation. In the phosphorus ion (impurity) implanted region, there is a problem that the energy density is too high and the film is destroyed. The purpose of this invention is
It is an object of the present invention to provide a method of manufacturing a thin film transistor which can simultaneously perform polysilicon conversion and activation by one laser irradiation without causing film destruction in an impurity implantation region.

[0004]

According to the present invention, after an amorphous silicon film is formed, a channel forming region of the amorphous silicon film is covered with a beam amount adjusting film and an impurity implantation mask. By irradiating a laser beam with the beam amount adjusting film left, the impurity injection of the amorphous silicon film is performed.
Energy density incident on the entrance region to the channel formation region
The energy density is made lower than the incident energy density to convert the channel formation region of the amorphous silicon film into polysilicon and activate the impurity.

[0005]

According to the present invention, the channel forming region of the amorphous silicon film is covered with the beam amount adjusting film and the impurity implantation mask, and after the impurity is implanted, the laser beam is irradiated. Thereby, the laser beam reflectivity in the channel formation region can be appropriately made smaller than that in the impurity implantation region. For this reason,
For example, the laser beam reflectivity in the channel formation region is set to about 4
When the laser irradiation is performed at an energy density of 220 mJ / cm ² , the energy density substantially incident on the amorphous silicon film becomes 220% in the channel formation region. × 0.6 =
About 130 mJ / cm ² , and 220
× 0.5 = 110 mJ / cm ² . Therefore, the polysilicon formation in the channel formation region and the activation of the impurity can be performed simultaneously by one laser irradiation without causing the film breakdown in the impurity implantation region.

[0006]

1 to 3 show the steps of manufacturing a thin film transistor according to an embodiment of the present invention. Therefore, a method for manufacturing a thin film transistor will be described with reference to these drawings in order.

First, as shown in FIG. 1, an amorphous silicon film 2 is formed on an upper surface of an insulating substrate 1 made of a glass substrate or the like to a thickness of about 500 ° by a plasma CVD method. Next, a beam amount adjusting film 4 made of SiO ₂ is formed on the upper surface of the channel forming region 3 of the amorphous silicon film 2 by sputtering to a thickness of about 530 °. Next, an impurity implantation mask 5 made of photoresist is formed on the upper surface of the beam amount adjustment film 4 by photolithography. Then, in this state, the impurity implantation mask 5 is formed.
Of phosphorus (P) ions (impurities) 6 are implanted into the amorphous silicon film 2 on both sides by an ion implanter to form an impurity implanted region 7. Thereafter, the impurity implantation mask 5 is removed by etching.

Next, as shown in FIG.
Energy density 220m by XeCl excimer laser
Laser irradiation at J / cm ² . Then, the laser beam is reflected by about 50% in a region where the beam amount adjustment film 4 does not exist, that is, in the impurity-implanted region 7, and is reflected by approximately 40% in a region where the beam amount adjustment film 4 exists, that is, the channel forming region 3. Therefore, the energy density substantially incident on the amorphous silicon film 2 is 220 × in the impurity implantation region 7.
0.5 = 110 mJ / cm ^2, and 220 × 0.6 = about 130 mJ / cm ^{2 in} the channel formation region 3. Therefore, by one laser irradiation, the channel formation region 3 of the amorphous silicon film 2 can be converted to polysilicon, and the phosphorus ions 5 can be activated without causing film destruction in the impurity implantation region 7.
When the thickness of the beam amount adjusting film 4 is changed, the reflectivity of the laser beam changes. Therefore, even if the laser beam is irradiated at a constant energy density, the energy density substantially incident on Si in the channel formation region 3 is reduced. It can be changed arbitrarily.

Next, the beam amount adjusting film 4 is removed by etching. Next, as shown in FIG. 3, a gate insulating film 8 made of SiO ₂ is formed on the entire surface by sputtering at 1500 ° C.
It is formed to a thickness of about. Next, a photoresist film (not shown) is formed in a pattern on the upper surface of the gate insulating film 8 by a photolithography method, and two predetermined gate insulating films 8 are removed by etching using the photoresist film as a mask. Two contact holes 9 are formed. next,
A metal layer made of Al is formed to a thickness of about 3000 ° on the upper surface of the gate insulating film 8 by a sputtering method, and unnecessary portions of the metal layer are removed by etching, and a gate electrode 10 and two source / drain electrodes 11 are formed. Is formed, and the source / drain electrodes 11 are connected to the impurity-implanted regions 7 via the contact holes 9. Thus, a thin film transistor is formed.

In the above embodiment, the case where the present invention is applied to a coplanar thin film transistor has been described.

[0011]

As described above, according to the present invention, the channel forming region of the amorphous silicon film is covered with the beam amount adjusting film and the impurity implantation mask, and after the impurity is implanted, the laser beam is irradiated. Therefore, depending on the presence or absence of the beam amount adjustment film, the reflectivity of the laser beam in the channel formation region can be made appropriately smaller than that in the impurity-implanted region. The region can be made of polysilicon, and the impurity can be activated without causing film destruction in the impurity implanted region.
Therefore, the number of manufacturing steps can be reduced, thereby improving productivity and reducing costs.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a state in which phosphorus ions are implanted into a portion excluding a channel formation region of an amorphous silicon film formed on an upper surface of an insulating substrate in manufacturing a thin film transistor according to one embodiment of the present invention.

FIG. 2 is a cross-sectional view of a state where an excimer laser is irradiated in manufacturing the thin film transistor.

FIG. 3 is a cross-sectional view showing a state in which a gate electrode and a source / drain electrode are finally formed in manufacturing the thin film transistor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 2 Amorphous silicon film 3 Channel formation region 4 Beam amount adjustment film 5 Impurity implantation mask 6 Phosphorus ion (impurity) 7 Impurity implantation region

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 29/786 H01L 21/336 H01L 21/20 H01L 21/268

Claims (3)

(57) [Claims] 1. After forming an amorphous silicon film,
Covering the channel forming region of the amorphous silicon film with a beam amount adjusting film and the impurity implantation mask, after implanting impurity by irradiating a laser while leaving at least the beam amount adjusting film, the amorphous sheet
The energy density incident on the impurity implantation region of the recon film
Lower than the energy density incident on the channel formation region
And forming the channel formation region of the amorphous silicon film into polysilicon and activating the impurity. 2. The beam amount adjusting film is made of SiO _2.
The reflectance of the laser irradiation light is
2. The method according to claim 1, wherein the thin film is smaller than a silicon film . 3. The method according to claim 1, wherein the impurity implantation mask is made of a photoresist.