JPH04299534A - Manufacture of thin film transistor - Google Patents

Abstract

PURPOSE:To perform simultaneously two kinds of laser emissions of different energy densities, that is, a laser emission for turning an amorphous silicon film into a polysilicon film and a laser emission for activating phosphorus ions, by a laser emission of one time. CONSTITUTION:An amount-of-a-laser beam adjusting film 4 consisting of SiO2 and a a make 5 for impurity implantation use consisting of a photoresist are formed on a channel formation region 3 in an amorphous silicon film 2 and phosphorus ions 6 are implanted to form impurity-implanted regions 7. After this, the make 5 is removed and when a laser emission is performed in an energy density of 220mJ/cm<2> in this state, a laser beam is reflected by about 40% at a region, where the film 4 exists, of the film 2 and is reflected by about 50% at regions, where the film 4 does not exist, of the film 2. For this, the density of an energy which is substantially incided in the film 2 is set so as to become an energy density of 110mJ/cm<2> at the region 3 and so as to become an energy density of about 130mJ/cm<2> at the regions 7.

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 thin film transistors.

0002

[Prior Art] A method for manufacturing a thin film transistor involves forming an amorphous silicon film on the upper surface of an insulating substrate such as a glass substrate, and converting the amorphous silicon film into a polysilicon film by irradiating the amorphous silicon film with an excimer laser. , phosphorus ions (impurity) are implanted into the polysilicon film except for the channel formation region,
There is a method in which the implanted phosphorus ions are irradiated with excimer laser again to activate them, and a thin film transistor is formed through predetermined steps. In this case, the laser irradiation process for converting amorphous silicon into polysilicon is divided into three stages:
with an energy density of J/cm2, then 220 mJ/cm
Laser irradiation was performed at an energy density of 2, and finally at an energy density of 260 mJ/cm2. At this time, approximately 50% of the laser beam is reflected, so the energy density substantially incident on the amorphous silicon film is 260×0.
．． 5=130mJ/cm2. On the other hand, in the laser irradiation process for activating phosphorus ions, the melting point of polysilicon decreases when phosphorus ions are implanted, and therefore, if the energy density is too high, film destruction will occur.To avoid this, Laser irradiation is performed at a low energy density of 220 mJ/cm2. At this time, approximately 50% of the laser beam is also reflected, so the energy density actually incident on the polysilicon film is 220 x 0.5 = 1
It becomes 10mJ/cm2.

0003

[Problems to be Solved by the Invention] However, in the conventional manufacturing method of such a thin film transistor, laser irradiation is performed twice: one to convert amorphous silicon into polysilicon, and the other to activate phosphorus ions. Therefore, when the number of manufacturing steps is large and the area of the insulating substrate is large, the spot size of the excimer laser is quite small, ranging from several mm to 10 mm, so laser irradiation is performed by scanning. Therefore, there are problems in that it takes time, has poor productivity, and increases costs. Note that it is conceivable to perform laser irradiation for converting amorphous silicon into polysilicon and laser irradiation for activating phosphorus ions at the same time in one laser irradiation. However, in this case, as explained above, in order to turn amorphous silicon into polysilicon, laser irradiation is ultimately performed at an energy density of 260 mJ/cm2, so the melting point of polysilicon decreases due to the implantation of phosphorus ions. The phosphorus ion (
There is a problem in that the energy density is too high in the region where impurities are implanted, resulting in film destruction. An object of the present invention is to provide a method for manufacturing a thin film transistor that can simultaneously perform polysiliconization and activation with one laser irradiation without causing film destruction in an impurity implanted region.

0004

[Means for Solving the Problems] The present invention provides a method for forming an amorphous silicon film, covering a channel forming region of the amorphous silicon film with a beam amount adjustment film and an impurity implantation mask, and implanting an impurity. By irradiating the laser beam with the beam amount adjustment film left in place, the channel forming region of the amorphous silicon film is made into polysilicon and the impurities are activated.

[0005]

[Operation] According to the present invention, the channel formation region of the amorphous silicon film is covered with the beam amount adjustment film and the mask for impurity implantation, and the laser beam is irradiated after the impurity is implanted. Accordingly, the laser beam reflectance in the channel forming region can be made appropriately smaller than that in the impurity implanted region. For this reason,
For example, the laser beam reflectance in the channel forming region is approximately 4
When the impurity implantation region is set to 0%, the impurity implantation region is set to approximately 50%, and laser irradiation is performed at an energy density of 220 mJ/cm2, the energy density substantially incident on the amorphous silicon film is 220× in the channel formation region. 0.6=
It is about 130 mJ/cm2, and 220 mJ/cm2 in the impurity implanted region.
×0.5=110 mJ/cm2. Therefore, polysiliconization of the channel formation region and activation of the impurity can be simultaneously performed by one laser irradiation without causing film breakdown in the impurity implanted region.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 to 3 each show the manufacturing steps of 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 figures in order.

First, as shown in FIG. 1, an amorphous silicon film 2 with a thickness of about 500 Å is formed on the upper surface of an insulating substrate 1 made of a glass substrate or the like by plasma CVD. Next, a beam amount adjusting film 4 made of SiO2 is formed to a thickness of about 530 Å on the upper surface of the channel forming region 3 of the amorphous silicon film 2 by sputtering. Next, an impurity implantation mask 5 made of photoresist is formed on the upper surface of the beam amount adjustment film 4 by photolithography. In this state, phosphorus (P) ions (impurity) 6 are implanted into the amorphous silicon film 2 on both sides of the impurity implantation mask 5 using an ion implantation device to form an impurity implantation region 7. After this, the impurity implantation mask 5
Remove by etching.

Next, as shown in FIG.
XeCl excimer laser with energy density of 220 m
Laser irradiation is performed at J/cm2. Then, about 50% of the laser beam is reflected in the region where the beam amount adjustment film 4 is not present, that is, the impurity implantation region 7, and about 40% is reflected in the region where the beam amount adjustment film 4 is present, that is, the channel forming region 3. Therefore, the energy density substantially incident on the amorphous silicon film 2 is 220×0 in the impurity implantation region 7.
．． 5 = 110 mJ/cm2, and the channel forming region 3
Therefore, 220×0.6=approximately 130 mJ/cm2. Therefore, by one laser irradiation, the channel formation region 3 of the amorphous silicon film 2 can be made into polysilicon, and the phosphorus ions 5 can be activated without causing film breakdown in the impurity implantation region 7. Note that changing the thickness of the beam amount adjustment film 4 changes the reflectance of the laser beam, so even if laser irradiation is performed at a constant energy density, the energy density that is substantially incident on the Si in the channel forming region 3 will be changed. It can be changed arbitrarily.

Next, the beam amount adjustment film 4 is removed by etching. Next, as shown in FIG. 3, a gate insulating film 8 made of SiO2 with a thickness of 1500 Å is deposited on the entire surface by sputtering.
Form to a certain thickness. Next, a photoresist film (not shown) is patterned on the upper surface of the gate insulating film 8 by photolithography, and using this photoresist film as a mask, two predetermined locations of the gate insulating film 8 are etched and removed. Two contact holes 9 are formed. next,
A metal layer made of Al is formed to a thickness of about 3000 Å on the upper surface of the gate insulating film 8 by sputtering, and unnecessary parts of this metal layer are removed by etching to form the gate electrode 10 and the two source/drain electrodes 11. At the same time, source/drain electrodes 11 are connected to impurity implanted regions 7 via contact holes 9. A thin film transistor is thus formed.

In the above embodiments, the present invention is applied to a coplanar type thin film transistor, but the present invention is not limited to this, but can also be applied to an inverted coplanar type, staggered type, or inverted staggered type thin film transistor.

[0011]

[Effects of the Invention] As explained above, according to the present invention, the channel formation region of the amorphous silicon film is covered with a beam amount adjustment film and an impurity implantation mask, and after the impurity is implanted, a laser beam is irradiated. Therefore, depending on the presence or absence of the beam amount adjustment film, the laser beam reflectance in the channel formation region can be appropriately made smaller than that in the impurity implantation region. Therefore, one laser irradiation can form a channel in the amorphous silicon film. In addition to making the region polysilicon, it is also possible to activate the impurity without causing film breakdown in the impurity implanted region, thus reducing the number of manufacturing steps, improving productivity and reducing costs. be able to.

[Brief explanation of drawings]

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

FIG. 2 is a cross-sectional view of the thin film transistor irradiated with excimer laser during manufacturing.

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

[Explanation of symbols]

1 Insulating substrate 2 Amorphous silicon film 3 Channel formation region 4 Beam amount adjustment film 5. Mask for impurity implantation 6 Phosphorus ion (impurity) 7 Impurity implantation region

Claims (3)

[Claims] 1. After forming an amorphous silicon film, a channel formation region of this amorphous silicon film is covered with a beam amount adjustment film and an impurity implantation mask, and after implanting impurities, a state is formed in which at least the beam amount adjustment film remains. A method for manufacturing a thin film transistor, characterized in that the channel formation region of the amorphous silicon film is made into polysilicon and the impurities are activated by irradiating the amorphous silicon film with a laser. 2. The method of manufacturing a thin film transistor according to claim 1, wherein the beam amount adjustment film is made of SiO2. 3. The method of manufacturing a thin film transistor according to claim 1, wherein the impurity implantation mask is made of photoresist.