JPH08330593A - Manufacture of thin film transistor - Google Patents

Abstract

PURPOSE: To ensure the stability of a process accompanying thinning a semicon ductor film for improving OFF-characteristics, prevent the increase of source.drain resistance, and maintain high drive capability. CONSTITUTION: The manufacturing method of a thin film transistor formed on an insulating substrate 1 on the surface of which a base coat film 2 is formed consists of the following: a process for forming a recessed part 3 on the base coat film 2 in a source.drain region 9 of the thin film transistor, a process for forming a conducting film or a semiconductor film 4 on the base coat film 2, and a process for eliminating the conducting film or the semiconductor film 4 except the recessed part 3 by etching back the whole part of the conducting film or the semiconductor film 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor (hereinafter referred to as a TFT) provided on an insulating substrate such as glass, and more particularly to a method of manufacturing a thin film transistor which can be used in an active matrix type image display device, an image sensor and the like. It is about.

[0002]

2. Description of the Related Art As a semiconductor device having a TFT on an insulating substrate such as glass, an active matrix type liquid crystal display device and an image sensor using the TFT as a pixel switching element are known. A thin film silicon semiconductor is generally used for the semiconductor layer (active layer) of the TFT. The silicon semiconductor is roughly classified into two types, that is, an amorphous silicon semiconductor (a-Si) and a crystalline silicon semiconductor.

Among the above-mentioned thin film silicon semiconductors, the amorphous silicon semiconductor is most commonly used because it has a low film forming temperature, can be relatively easily manufactured by the chemical vapor deposition method, and has high mass productivity. However, the physical properties such as conductivity are inferior to those of crystalline silicon semiconductors. Therefore, in the future, in order to obtain higher speed characteristics, establishment of a method for manufacturing a TFT made of a crystalline silicon semiconductor is strongly demanded. As the crystalline silicon semiconductor, there are known polycrystalline silicon, microcrystalline silicon, amorphous silicon containing a crystalline component, semi-amorphous silicon having an intermediate state between crystalline and amorphous.

As a method for obtaining these thin film silicon semiconductors having crystallinity, a film having crystallinity is directly formed at the time of film formation, or heat energy is applied after forming an amorphous semiconductor film. Accordingly, a method of improving crystallinity or a method of forming an amorphous semiconductor film and then improving crystallinity by energy of laser light is used.

Next, a conventional method for manufacturing a top gate type TFT will be described. 2A and 2B are manufacturing process diagrams of a conventional top gate type TFT. In FIG. 2A, after cleaning the insulating substrate (eg, glass substrate) 21,
Silicon dioxide (SiO ₂ ) is used as a base coat film 22 on the surface of the insulating substrate 21 by chemical vapor deposition (hereinafter,
Thickness of 30 using CVD method) or sputtering method
Deposit about 0 nm.

Next, an amorphous silicon film having a thickness of 30 is formed on the base coat film 22 by the CVD method or the sputtering method.
Then, the amorphous silicon film is changed to a polycrystalline silicon film by a solid phase growth method or a laser annealing method. After forming the island-shaped semiconductor layer 26 by photolithography and etching of the polycrystalline silicon film, a gate insulating film 27 and a gate electrode material are deposited, and a gate electrode 28 is patterned by photolithography and etching. Next, impurities are implanted into the source / drain regions 29 by the ion doping method, and the source / drain regions 29 are
Is activated by a laser annealing method or a thermal diffusion method, and an interlayer insulating film 30 is further deposited on the region of the insulating substrate 21.

Next, a contact hole is formed in the source / drain region 29 by photolithography and etching to manufacture a top gate type TFT.

[0008]

As a future technique, it is desired to simultaneously form high-speed TFTs on the same substrate so as to form, for example, a peripheral driving circuit of an active matrix type liquid crystal display device. However, in the conventional technique, a leak current is generated at the grain boundary of the crystal, and it is difficult to obtain good off characteristics.

It is known that reducing the thickness of the semiconductor layer 26 is effective as one of the methods for obtaining good off characteristics, but in this method, the semiconductor layer 26 is used.
2 at the time of forming a contact hole 31 for connecting the source / drain region 29 of FIG.
As shown in (b), there is a problem that the semiconductor layer 26 is over-etched and the contact resistance is increased. Further, by thinning the semiconductor layer 26, the source / drain resistance becomes high, and the drive frequency of the peripheral drive circuit that requires high-speed operation is limited by the contact resistance and the source / drain resistance. It was

The method of manufacturing a thin film transistor according to the present invention solves the above problems, and secures the stability of the process associated with the thinning of the semiconductor layer of the TFT for improving the off-characteristic, and the source / drain. It is an object of the present invention to provide a method of manufacturing a thin film transistor that can prevent an increase in resistance and maintain a high driving capability.

[0011]

In order to achieve the above object, the invention according to claim 1 is a method of manufacturing a thin film transistor formed on a substrate having an insulating film formed as a base coat on the surface thereof. A step of forming a recess on the insulating film in the drain region,
It is a manufacturing method including a step of forming a conductive film or a semiconductor film on the insulating film, and a step of removing the conductive film or the semiconductor film other than the concave portion.

According to a second aspect of the invention, in the first aspect of the invention, the conductive film is a semiconductor doped with a refractory metal or impurities.

[0013]

As described above, according to the present invention, after the insulating film is formed as the base coat on the surface of the substrate, the recess is formed on the insulating film in the source / drain region of the TFT, and the conductive film is formed on the insulating film. Alternatively, a TFT is formed by forming a semiconductor film and removing the conductive film or the semiconductor film other than the above-mentioned recess.
Even if overetching occurs when the contact hole is formed, which is a problem when the thickness of the semiconductor layer is thinned, the lower layer of the TFT source / drain region is electrically connected to the conductive film. Therefore, it is possible to fabricate a top-gate TFT having good off characteristics without causing an increase in contact resistance and source / drain resistance.

In addition, a high performance T film with a crystalline silicon thin film is formed on a large substrate, for example, a 300 mm square glass substrate.
If the FT can be formed, it becomes easy to incorporate not only the pixel switching elements of the active matrix type image display device as in the past, but also the peripheral drive circuit, which reduces the cost of the product and the size of the module.
It is possible to simplify the mounting process.

Further, a system-on-panel in which many functions such as a display, a CPU, a memory, an image sensor, and a touch operation are mounted on a single substrate can be realized.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method of manufacturing a thin film transistor of the present invention will be described below with reference to FIG. 1 (a)-(d)
Shows a manufacturing process diagram of the top gate type TFT of the present invention.
In FIG. 1A, after cleaning an insulating substrate (for example, a glass substrate) 1 having a size of about 300 mm □, silicon dioxide having a thickness of 300 nm is formed as a base coat film 2 on the surface of the insulating substrate 1 by a CVD method or a sputtering method. Deposit to a degree.

Next, a photosensitive photoresist (not shown) is applied on the base coat film 2, and light is applied to the entire surface through a photomask (not shown) to write the mask pattern on the photoresist. (Photolithography). Then, excess photoresist is removed to form a base coat film 2 in which a contact hole 11 described later is formed.
A recessed portion 3 having a depth of 150 nm is formed in the region of by etching, and a conductive film such as polysilicon doped with refractory metal such as Ta (tantalum), Mo (molybdenum) or W (tungsten) or phosphorus is used. The semiconductor film 4 is deposited by sputtering or CVD to a thickness of about 500 nm to 1 μm.

Further, a flattening film 5 is formed on the conductive film or the semiconductor film 4. As a generally known method, an organic film such as a resist or a polyimide film is formed by a spin coating method, or a silicon dioxide film is formed by coating and baking a solution of a silicon compound dissolved in an organic solvent. It is effective to form a film.

Next, in FIG. 1B, the recess 3 formed by etching back is performed under the condition that the flattening film 5 and the conductive film 4 have the same etching rate.
The conductive film or the semiconductor film 4 in the regions other than the above is removed, but since the flatness is obtained, the conductive film or the semiconductor film 4 in the formed recess 3 remains without being etched.

Thereafter, the top gate type TF is formed by a known method.
T is manufactured as described below. In FIG. 1C, an amorphous silicon film is deposited to a thickness of about 30 nm by using the CVD method or the sputtering method, and the amorphous silicon film is changed into a polycrystalline silicon film by the solid phase growth method or the laser annealing method. . A semiconductor layer 6 having an island structure is formed on the polycrystalline silicon film by photolithography and etching, a gate insulating film 7 and a gate electrode material are deposited, and a gate electrode 8 is patterned by photolithography and etching. Next, impurities are implanted into the source / drain regions 9 by the ion doping method, the source / drain regions 9 are activated by the laser annealing method or the thermal diffusion method, and the interlayer insulating film 10 is formed on the region of the insulating substrate 1. accumulate.

Next, in FIG. 1D, the source / drain regions 9 are formed by photolithography and etching.
A contact hole 11 is formed in. At this time, if the thickness of the semiconductor layer 6 which is the active layer is set to 30 nm or less in order to obtain good off characteristics, as shown in FIG. There is a risk that the semiconductor layer 6 may not be penetrated and a sufficient ohmic contact may not be obtained. Display size, especially to obtain aperture ratio in the future,
It is indispensable to use dry etching in order to miniaturize the processing size, and when the selection ratio between the interlayer insulating film 10 and the semiconductor layer 6 becomes difficult to obtain, it is important to solve this problem. . However, in the present invention, since the conductive film or the semiconductor film 4 is buried under the source / drain region 9 of the semiconductor layer 6, the contact hole 1
Even if over-etching occurs when forming 1, the sufficient ohmic contact can be obtained through the conductive film or the semiconductor film 4.

[0022]

Since the thin film transistor of the present invention is manufactured by the above-described manufacturing method, it is necessary to increase the T
Even if overetching at the time of contact etching, which is a problem when trying to thin the semiconductor layer of FT, occurs, the semiconductor layer of the TFT is electrically connected to the conductive film or the semiconductor film. A sufficient ohmic contact can be obtained.

Further, since the semiconductor layer of the TFT can be thinned, it is possible to manufacture a TFT having high performance and excellent off characteristics. Particularly, in a liquid crystal display device, a high definition and large area active matrix substrate is required. Not only can the off characteristics of the pixel switching TFT be reduced and a driver monolithic active substrate that constitutes the peripheral drive circuit section can be realized, but thin-film integrated circuits such as CPUs can also be manufactured on the same substrate, making the module compact, Higher performance, lower cost, and system-on-panel can be achieved.

[Brief description of drawings]

1A to 1D are manufacturing process diagrams showing an embodiment of a method of manufacturing a thin film transistor according to the present invention.

2 (a) and 2 (b) are manufacturing process diagrams showing an example of a conventional method of manufacturing a thin film transistor.

[Explanation of symbols]

 1, 21 Insulating substrate 2, 22 Base coat film 3 Recess 4 Conductive film or semiconductor film 5 Planarizing film 6, 26 Semiconductor layer 7, 27 Gate insulating film 8, 28 Gate electrode 9, 29 Source / drain region 10, 30 Interlayer insulation film 11, 31 Contact hole

Claims (2)

[Claims] 1. A method of manufacturing a thin film transistor formed on a substrate having an insulating film formed as a base coat on the surface thereof, comprising the steps of forming recesses on the insulating film in a source / drain region of the thin film transistor, A method of manufacturing a thin film transistor, comprising: a step of forming a conductive film or a semiconductor film on the film; and a step of removing the conductor film or the semiconductor film other than the recess. 2. The method for manufacturing a thin film transistor according to claim 1, wherein the conductive film is a refractory metal or a semiconductor doped with impurities.