JP2001308337A - Method of manufacturing low-temperature polysilicon tft - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a simple, excellent, low- temperature polysilicon TFT(thin film transistor) by avoiding increase in the number of mask steps in forming an LDD structure for use in the method. SOLUTION: Isotropic etching after transistor gate patterning causes formation of a metallic film on electrodes larger in area than a gate electrode, into which implantation of E and P is carried out. Consequently, a method for manufacturing a simple, excellent, low-temperature polysilicon TFT can be obtained wherein a single implantation enables formation of a transistor of an LDD structure.

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 low-temperature polysilicon TFT used for a pixel portion or a peripheral circuit portion for driving a liquid crystal in a liquid crystal panel, for example.

[0002]

2. Description of the Related Art A conventional low-temperature polysilicon manufacturing method will be described below.

FIG. 2 shows a conventional method for manufacturing a low-temperature polysilicon TFT. In FIG. 2A, 1 is glass, 2 is SiO ₂ , and 3 is a polysilicon layer.

First, in FIG. 2B, a gate insulating film 4 is deposited on the polysilicon layer 3, a metal oxide film 5 is further deposited on the gate insulating film 4, and a gate electrode is formed on the metal oxide film 5. The metal film 6 is deposited. Further, FIG.
2, after the metal film 6 is etched using the patterned resist 7, the metal oxide film 5 is etched using a resist mask as shown in FIG. . In FIG. 2E, a high-concentration impurity layer 8 and a low-concentration impurity layer 9 are simultaneously formed by implanting P from above to form an LDD structure (Lightly Doped Drain).

[0005]

However, in the structure of the above-mentioned conventional example, since the metal oxide film 5 and the metal film 6 are formed using different masks, a mask step is required twice and the cost is increased. In addition, there is a problem that the transistor characteristics are deteriorated due to a mask shift because two mask steps are required.

[0006]

According to a first aspect of the present invention, there is provided a method of manufacturing a low-temperature polysilicon TFT, comprising: depositing a gate insulating film on a polysilicon layer formed on an upper surface of a substrate; A step of depositing one metal film, a step of depositing a second metal film of a material different from the first metal film on the first metal film, and the second metal film using a patterned resist A step of patterning a film with a transistor gate; a step of isotropically etching the first metal film so that both the length and width are smaller than the second metal film; and Using a structure smaller than the second metal film as a mask to implant source and drain impurity atoms to form an LDD transistor.

According to the method of manufacturing a low-temperature polysilicon TFT according to the first aspect, a structure is formed in which a metal film having a length and a width larger than the gate electrode is mounted on the gate electrode.
Impurity implantation for forming a source / drain is performed on the structure, and a TFT having an LDD structure is formed in a low concentration impurity region formed through the metal film simultaneously with the formation of the source / drain. For this reason, the LDD structure can be formed only by one mask process, so that T
Deterioration of FT characteristics can be suppressed, and masks can be reduced. Further, since a transistor having an LDD structure can be formed by one implantation, an excellent low-temperature polysilicon TFT can be realized in which cost can be reduced and transistor characteristics do not deteriorate due to mask shift.

According to a second aspect of the present invention, there is provided a method for manufacturing a low-temperature polysilicon TFT according to the first aspect, further comprising the step of selectively etching and removing the second metal film after implanting impurity atoms of source and drain.

According to the method of manufacturing a low-temperature polysilicon TFT according to the second aspect, the same effect as that of the first aspect is obtained.

According to a third aspect of the present invention, in the method of manufacturing a low-temperature polysilicon TFT according to the first or second aspect, the impurity atoms are boron or phosphorus.

According to the method of manufacturing a low-temperature polysilicon TFT according to the third aspect, the same effect as that of the first or second aspect can be obtained.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.

In FIG. 1A, reference numeral 11 denotes glass, 12
Is a SiO ₂ layer, and 13 is a polysilicon layer, which becomes a substrate.

First, in FIG. 1B, a gate insulating film 14 is deposited on the polysilicon layer 13 and a first metal film 15 including a metal oxide film as a gate electrode is formed on the gate insulating film 14. Then, a second metal film 16 of a material different from that of the first metal film 15 is deposited on the first metal film 15 as a mask material for ion doping. Further, FIG.
In FIG. 1C, after the second metal film 16 is etched using the patterned resist 17, FIG.
In the above, by performing isotropic etching using the second metal film 16 as a mask, the first metal film 15 as the gate electrode is formed in a structure in which both the length and the width are smaller than the second metal film 16. In FIG. 1 (E), through this structure, B (boron) which is an impurity atom of a source / drain
Alternatively, high-concentration impurity layers 18 and low-concentration impurity layers 19 are simultaneously formed by injecting P (phosphorus), and FIG.
In (F), an LDD structure is formed by selectively removing the second metal film 16 by etching.

As described above, according to this embodiment, the impurity is implanted through the second metal film 16 on the gate electrode formed by isotropic etching, so that the LDD structure can be implanted by one implantation. Transistors can be formed. This allows self-aligned LD
Since a TFT having a D structure can be manufactured, good Tr characteristics without mask misalignment can be obtained, and the number of steps can be reduced. Further, since only an impurity having the same concentration as that of the low-concentration impurity layer is implanted into the gate electrode, an increase in specific resistance due to the introduction of the impurity can be suppressed.

[0016]

The low-temperature polysilicon TFT according to claim 1
According to the manufacturing method of (1), a structure in which a metal film having a length and width larger than the gate electrode is mounted on the gate electrode is formed, and an impurity is implanted into the structure to form a source / drain. LDD structure TFT with low concentration impurity region formed through the metal film at the same time as the formation
To form For this reason, LDD is performed only by one mask process.
Since the structure can be formed, deterioration of the TFT characteristics due to misalignment of the mask can be suppressed, and the number of masks can be reduced. Further, since a transistor having an LDD structure can be formed by one implantation, an excellent low-temperature polysilicon TFT can be realized in which cost can be reduced and transistor characteristics do not deteriorate due to mask shift.

According to the method of manufacturing a low-temperature polysilicon TFT according to the second aspect, the same effect as that of the first aspect is obtained.

According to the method of manufacturing a low-temperature polysilicon TFT according to the third aspect, the same effects as those of the first or second aspect can be obtained.

[Brief description of the drawings]

FIG. 1 is a process explanatory view of a method for manufacturing a low-temperature polysilicon TFT according to an embodiment of the present invention.

FIG. 2 is a process explanatory view of a conventional low-temperature polysilicon TFT manufacturing method.

[Explanation of symbols]

11 glass 12 SiO ₂ 13 polysilicon layer 14 gate insulating film 15 first metal film 16 a second metal film 17 resist 18 high concentration impurity layer 19 lightly doped layer

Claims (3)

[Claims] A step of depositing a gate insulating film on a polysilicon layer formed on an upper surface of a substrate; a step of depositing a first metal film on the gate insulating film; Depositing a second metal film of a different material from the first metal film, transistor gate patterning the second metal film using a patterned resist, and forming the first metal film on the first metal film. A step of isotropically etching such that both the length and width are smaller than the second metal film,
Using a structure in which the first metal film is smaller than the second metal film as a mask to implant a source / drain impurity atom to form a transistor having an LDD structure. 2. The method of manufacturing a low-temperature polysilicon TFT according to claim 1, further comprising the step of selectively etching and removing the second metal film after implanting source / drain impurity atoms. 3. The method according to claim 1, wherein the impurity atoms are boron or phosphorus.