JPH0567786A - Manufacture of thin film transistor - Google Patents

Abstract

PURPOSE:To eliminate the need for blocking insulating film and to reduce manufacturing cost by preventing an i-type semiconductor layer from being damaged in a manufacturing process even if a blocking insulating film is not formed in advance on a channel region of the i-type semiconductor layer. CONSTITUTION:After a gate electrode 12 is formed on a substrate 11, a gate insulating film 13, an i-type semiconductor layer 14, an n-type semiconductor layer 15 and a metallic film 16 are formed one by one on the substrate 11. After a source electrode 16S and a drain electrode 16D are formed by patterning the metallic film 16, a part between the source electrode 16S and the drain electrode 160 of the n-type semiconductor layer 15 is anodized all over its thickness and the n-type semiconductor layer 15 is electrically isolated in a channel region.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art As a thin film transistor used in, for example, an active element of an active matrix liquid crystal display element, a gate insulating film is formed on a gate electrode formed on a substrate, and an i-type semiconductor layer is formed on the gate insulating film. There is a structure in which a source electrode and a drain electrode are formed on both sides of this i-type semiconductor layer with an n-type semiconductor layer interposed therebetween while being formed. This structure is generally called an inverted stagger structure.

The thin film transistor having the inverted stagger structure is conventionally manufactured by the following manufacturing method.

FIG. 2 is a manufacturing process diagram of a conventional thin film transistor, showing a manufacturing process of a thin film transistor formed as an active element of a pixel electrode on one transparent substrate of an active matrix liquid crystal display element.

[Step 1] First, as shown in FIG. 2A, a gate electrode 2 and a wiring portion (scanning line) (not shown) connected to the gate electrode 2 are formed on a transparent insulating substrate 1 made of glass or the like. After forming, the gate insulating film 3, the i-type semiconductor layer 4, and the blocking insulating film 7 for protecting the i-type semiconductor layer 4 are sequentially formed on the substrate 1.

The gate electrode 2 and its wiring portion are formed by depositing a metal such as Ta, Ta-Mo alloy, Cr on the substrate 1 by a sputtering method or a plating method.
This metal film is formed by patterning by a photolithography method.

Further, in general, the gate insulating film 3 is made of Si.
The i-type semiconductor layer 4 is made of N (silicon nitride) or the like, and is a
-Si (amorphous silicon), and the blocking insulating film 7 has the same insulating material (S) as the gate insulating film 3 described above.
iN, etc.), and these are continuously formed by the plasma CVD method.

[Step 2] Next, as shown in FIG. 2B, the blocking insulating film 7 is patterned by photolithography into a shape corresponding to the channel region of the i-type semiconductor layer 4, and then the i-type semiconductor. The layer 4 is patterned into a predetermined shape by photolithography.

[Step 3] Next, as shown in FIG. 2C, the n-type semiconductor layer 5 is formed on the substrate 1 by the plasma CVD method, and the metal film 6 for the source and drain electrodes is formed thereon. A film is formed by the sputtering method. The n-type semiconductor layer 5 is formed of impurity-doped a-Si, and the source / drain electrode metal film 6 is formed of Cr or the like.

[Step 4] Next, as shown in FIG. 2D, the source / drain electrode metal film 6 is patterned by photolithography to form the source electrode 6S.
And a drain electrode 6D and a wiring portion (data line) (not shown) connected to the drain electrode 6D are formed, and the n-type semiconductor layer 5 is further used as a source / drain electrode 6
By etching while leaving S and 6D underneath,
The n-type semiconductor layer 5 is separated in the channel region to complete the thin film transistor.

In this case, if the n-type semiconductor layer 5 is in direct contact with the channel region of the i-type semiconductor layer 4, the channel region of the i-type semiconductor layer 4 is etched when the n-type semiconductor layer 5 is etched. Although the surface is also etched and the i-type semiconductor layer 4 is damaged, the characteristics of the manufactured thin film transistor are deteriorated. However, in the above manufacturing method, the blocking insulating film 7 is formed on the channel region of the i-type semiconductor layer 4. Therefore, when the n-type semiconductor layer 5 is etched, i
It is possible to prevent the type semiconductor layer 4 from being etched and to manufacture a thin film transistor having excellent characteristics.

2E shows a state in which the pixel electrode 8 is formed on the substrate 1 on which the thin film transistor is formed, and the pixel electrode 8 is formed on the gate insulating film 3. .. The pixel electrode 8 is formed by a method of forming a transparent conductive film made of ITO or the like and patterning the transparent conductive film. The pixel electrode 8 is formed by overlapping one end thereof on the source electrode 6S of the thin film transistor. By doing so, it is connected to the source electrode 6S.

[0013]

However, in the above-mentioned conventional method for manufacturing a thin film transistor, the n-type semiconductor layer 5 is etched to separate the n-type semiconductor layer 5 in the channel region. In order to prevent the i-type semiconductor layer 4 from being etched and damaged when the layer 5 is etched, it is necessary to form the blocking insulating film 7 on the channel region of the i-type semiconductor layer 4.

Therefore, in the conventional manufacturing method, as described above, after the blocking insulating film 7 is formed on the i-type semiconductor layer 4 and patterned, the n-type semiconductor layer 5 and the source / drain are formed. Since the electrode metal film 6 must be formed, the number of manufacturing steps of the thin film transistor is large and the manufacturing cost is high.

Moreover, since the blocking insulating film 7 is generally formed of the same insulating material (SiN or the like) as the gate insulating film 3, if the i-type semiconductor layer 4 has a pinhole, the blocking insulating film 7 is formed. At the time of patterning, the etching solution of the blocking insulating film 7 reaches the gate insulating film 3 through the pinholes of the i-type semiconductor layer 4,
Will also be etched.

Therefore, in the conventional manufacturing method, a pinhole defect is generated in the gate insulating film 3 in the manufacturing process of the thin film transistor (patterning process of the blocking insulating film 7),
In this portion, the gate electrode 2 and the source / drain electrode 6
There was also a problem that S and 6D would be short-circuited.

An object of the present invention is to separate the n-type semiconductor layer in the channel region without damaging the i-type semiconductor layer without forming a blocking insulating film on the channel region of the i-type semiconductor layer. I was able to do it,
The manufacturing cost of the thin film transistor is reduced by eliminating the step of forming the blocking insulating film, and it is possible to prevent short circuit between the gate electrode and the source / drain electrode due to pinholes in the gate insulating film during the manufacturing process. Another object of the present invention is to provide a method of manufacturing a thin film transistor, which can improve the manufacturing yield of

[0018]

According to the method of manufacturing a thin film transistor of the present invention, after a gate electrode is formed on an insulating substrate, a gate insulating film, an i-type semiconductor layer, an n-type semiconductor layer and a metal are formed on the substrate. A film and a metal film are sequentially formed, a source electrode and a drain electrode are formed by patterning the metal film, and then a portion between the source and drain electrodes of the n-type semiconductor layer is anodized over its entire thickness. To do.

[0019]

That is, in the method of manufacturing a thin film transistor of the present invention, the separation in the channel region of the n-type semiconductor layer is performed by anodic oxidation instead of etching.
When the type semiconductor is anodized, the n-type semiconductor becomes an insulator. Therefore, if the portion between the source and drain electrodes of the n-type semiconductor layer is anodized over its entire thickness as described above,
The n-type semiconductor layer is electrically isolated in the channel region.

Since this manufacturing method electrically separates the n-type semiconductor layer in the channel region without etching, it is formed on the channel region of the i-type semiconductor layer like the conventional manufacturing method. Even if the blocking insulating film is not formed, the i-type semiconductor layer is not damaged during the manufacturing process, and thus the blocking insulating film is unnecessary.

Further, in this manufacturing method, it is not necessary to form a blocking insulating film, and therefore, unlike the conventional manufacturing method, pinholes are not generated in the gate insulating film during the manufacturing process.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to the manufacturing process chart of FIG. 1 by taking as an example the manufacture of a thin film transistor formed as an active element of a pixel electrode on one transparent substrate of an active matrix liquid crystal display element. I will explain.

[Step 1] First, as shown in FIG. 1A, a gate electrode 12 and a wiring portion (scan line) (not shown) connected to the gate electrode 12 are formed on a transparent insulating substrate 11 made of glass or the like. And then the substrate 11
A gate insulating film 13 made of Si N or the like and a-Si
And an i-type semiconductor layer 14 made of a
An n-type semiconductor layer 15 made of Si is successively formed by a plasma CVD method, and a metal film 16 for source and drain electrodes made of Cr or the like is further formed thereon by a sputtering method.

The n-type semiconductor layer 15 has a thickness of about 25-1.
The metal film 16 for source / drain electrodes is formed to a film thickness of 00 nm, and is formed to a film thickness of about 200 to 500 nm. In addition, the gate electrode 12 and its wiring portion are
A metal such as Ta, Ta-Mo alloy, or Cr is deposited thereon by sputtering or plating, and this metal film is patterned by photolithography.

[Step 2] Next, as shown in FIG. 1B, the source / drain electrode metal film 16 is patterned by photolithography to form the source electrode 16S.
And the drain electrode 16D and this drain electrode 16D
A wiring portion (data line) (not shown) connected to is formed. Then, the n-type semiconductor layer 15 and the i-type semiconductor layer 14 thereunder are connected to the portions below the source / drain electrodes 16S, 16D and the source / drain electrodes 16S, Etching is performed while leaving a portion serving as a channel region between 16D.

In etching the n-type semiconductor layer 15 and the i-type semiconductor layer 14, a resist mask (not shown) is formed on the portion of the n-type semiconductor layer 15 between the source and drain electrodes 16S and 16D. The resist mask and the source / drain electrodes 16S and 16D are used as etching masks.

[Step 3] Next, the resist mask on the n-type semiconductor layer 15 is removed, and thereafter, as shown in FIG. 1C, the source / drain electrode 1 of the n-type semiconductor layer 15 is removed.
A portion between 6S and 16D, that is, a portion corresponding to the channel region of the i-type semiconductor layer 14 is anodized over its entire thickness, and the n-type semiconductor layer 15 is electrically separated in the channel region to complete a thin film transistor. To do.

For the anodic oxidation of the n-type semiconductor layer 15, the terminal portion of the wiring portion (hereinafter referred to as a data line) of the drain electrode 16D is connected to the anode of the DC power source by a clip-type connector or the like, and the substrate 11 is filled with an electrolytic solution (for example, an electrolyte solution). Ammonium borate solution) so that the substrate 11 faces the counter electrode (cathode) arranged in the electrolytic solution, and in this state, the n-type semiconductor layer 15 is energized via the data line and the drain electrode 16D. By doing so, a voltage is applied between the n-type semiconductor layer 15 and the counter electrode. The anodic oxidation is performed by covering the pixel electrode connecting portion of the source electrode 16S with the resist mask M.

Thus, when a voltage is applied between the n-type semiconductor layer 15 and the counter electrode in the electrolytic solution, the portion (source, source, of the n-type semiconductor layer 15 serving as the anode, which is in contact with the electrolytic solution.
The portion between the drain electrodes 16S and 16D) undergoes a chemical conversion reaction and is anodized from the surface side thereof, and this portion becomes the oxide insulating layer 15a, and the n-type semiconductor layer 15 is electrically separated in the channel region. To be done.

That is, when anodizing an n-type semiconductor,
Since the n-type semiconductor serves as an insulator, if the portion between the source and drain electrodes of the n-type semiconductor layer 15 is anodized over its entire thickness as described above, the n-type semiconductor layer 15 will be electrically conductive in the channel region. Is separated into

In this case, when the n-type semiconductor layer 15 is anodized from the surface side, the unoxidized layer of the n-type semiconductor layer 15, that is, the conductive layer, becomes thin as the oxide insulating layer 15a grows. However, since a current flows through the n-type semiconductor layer 15 until the oxide insulating layer 15a reaches the interface with the i-type semiconductor layer 14, if the applied voltage is set sufficiently high (for example, the n-type semiconductor layer 15). Of about 50 V when the film thickness is 25 nm), the source and drain electrodes 1 of the n-type semiconductor layer 15
The n-type semiconductor layer 15 can be electrically isolated in the channel region by anodizing the portion between 6S and 16D over its entire thickness, that is, until no current flows at the interface with the i-type semiconductor layer 14. ..

Further, in this embodiment, the n-type semiconductor layer 15 is used.
Anodization of the data line and drain electrode 16D
Since the n-type semiconductor layer 15 is energized via the electrode, the surface of the data line and the drain electrode 16D also undergoes a chemical conversion reaction in the electrolytic solution to be anodized from the surface side thereof, and the source electrode 16S. Also the n-type semiconductor layer 1
A current flows through the source electrode 16S and the source electrode 16S is also anodized from the surface side thereof.
The surfaces of 6S and 16D also become the oxide insulating layer 16a as shown in FIG.

Since the metal oxidizes faster than the n-type semiconductor, the thickness of the oxide insulating layer 16a formed on the surface of the drain electrode 16S and the data line while the n-type semiconductor layer 15 is oxidized over its entire thickness is n. The thickness is somewhat thicker than that of the type semiconductor layer 15. However, the voltage applied to the source electrode 16S is a voltage dropped in the n-type semiconductor layer 15, and when the n-type semiconductor layer 15 is electrically separated in the channel region, the voltage is applied to the source electrode 16S. Since it disappears, the oxide insulating layer 16a formed on the surface of the source electrode 16S is thinner than the oxide insulating layer 16a formed on the surface of the drain electrode 16S and the data line.

However, in this embodiment, as described above,
Since the source / drain electrodes 16S, 16D are formed to a thickness (about 200-500 nm) sufficiently thicker than the film thickness of the n-type semiconductor layer 15 (about 25-100 nm), the surface of the source / drain electrodes 16S, 16D. Is an oxide insulation layer 1
6a, the source and drain electrodes 16S, 1
The conductivity of the source / drain electrodes 16S and 16D can be sufficiently ensured by leaving a conductive layer having a sufficient thickness under the 6D oxide insulating layer 16a.

Further, the thin film transistor is an active element of an active matrix liquid crystal display element, and since the pixel electrode is connected to the source electrode 16S thereof, the surface of the pixel electrode connecting portion of the source electrode 16S is also anodized. , The electrical connection with the pixel electrode is lost.

Therefore, in this embodiment, the source electrode 16
The pixel electrode connection portion of S is covered with the resist mask M, and the above anodic oxidation is performed. With this configuration, the pixel electrode connecting portion of the source electrode 16S is not anodized because it does not come into contact with the electrolytic solution, so that the surface of the pixel electrode connecting portion of the source electrode 16S is left as a conductive surface and the pixel electrode has good conductivity. You can connect with sex.

FIG. 1D shows a state in which the pixel electrode 18 is formed on the substrate 11 on which the thin film transistor is formed. The pixel electrode 18 is formed on the gate insulating film 13 and one end thereof is a thin film transistor. Source electrode 16S
Are formed on top of each other. The pixel electrode 18 is formed by removing the resist mask M covering the pixel electrode connection portion of the source electrode 16S, forming a transparent conductive film made of ITO or the like, and patterning the transparent conductive film.

That is, according to the method of manufacturing the thin film transistor, the separation in the channel region of the n-type semiconductor layer 15 is
This is performed by anodic oxidation instead of etching. When the n-type semiconductor 15 is anodized, the n-type semiconductor 15 becomes an insulator.
If the portion between the source and drain electrodes 16S and 16D of 5 is anodized over its entire thickness, the n-type semiconductor layer 1
5 are electrically isolated in the channel region.

Since this manufacturing method electrically separates the n-type semiconductor layer 15 in the channel region without etching, the n-type semiconductor layer 15 is formed on the channel region of the i-type semiconductor layer as in the conventional manufacturing method. Even if a blocking insulating film is not formed on the i-type semiconductor layer 1 during the manufacturing process.
4 is not damaged, and therefore the blocking insulating film is not necessary, the manufacturing cost of the thin film transistor can be reduced by eliminating the step of forming the blocking insulating film.

Further, in this manufacturing method, since it is not necessary to form the blocking insulating film, a pinhole is generated in the gate insulating film in the manufacturing process (patterning step of the blocking insulating film) unlike the conventional manufacturing method. Therefore, it is possible to prevent short-circuiting between the gate electrode and the source / drain electrodes due to the occurrence of pinholes in the gate insulating film during the manufacturing process, and it is possible to improve the manufacturing yield of the thin film transistor.

In the above embodiment, the n-type semiconductor layer 15 is used.
The surface of the source / drain electrodes 16S, 16D is also oxidized during the anodic oxidation of
If S and 16D are covered with a resist mask and anodization of the n-type semiconductor layer 15 is performed, only the n-type semiconductor layer 15 can be anodized without oxidizing the surfaces of the source and drain electrodes 16S and 16D. it can.

Further, in the above-mentioned embodiment, the manufacture of the thin film transistor formed as the active element of the pixel electrode on one transparent substrate of the active matrix liquid crystal display element has been described, but the present invention is applicable to other thin film transistors. It can also be applied to manufacturing.

[0043]

According to the method of manufacturing a thin film transistor of the present invention, the n-type semiconductor layer is separated in the channel region by anodic oxidation, not by etching.
Even if the blocking insulating film is not formed on the channel region of the i-type semiconductor layer, the n-type semiconductor layer can be separated in the channel region without damaging the i-type semiconductor layer. The manufacturing cost of the thin film transistor is reduced by eliminating the step of forming the film, and it is also possible to prevent a short circuit between the gate electrode and the source / drain electrodes due to pinholes in the gate insulating film during the manufacturing process. The yield can be improved.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram of a thin film transistor showing an embodiment of the present invention.

FIG. 2 is a manufacturing process diagram showing a conventional method of manufacturing a thin film transistor.

[Explanation of symbols]

11 ... Substrate, 12 ... Gate electrode, 13 ... Gate insulating film,
14 ... i-type semiconductor layer, 15 ... n-type semiconductor layer, 15a ... Oxidation insulating layer, 16 ... Metal film for source and drain electrodes, 16
S ... Source electrode, 16D ... Drain electrode, 16a ... Oxidation insulating layer, M ... Resist mask, 18 ... Pixel electrode.

Claims (1)

[Claims] 1. After forming a gate electrode on an insulating substrate,
A gate insulating film, an i-type semiconductor layer, an n-type semiconductor layer, and a metal film are sequentially formed on this substrate, the metal film is patterned to form a source electrode and a drain electrode, and then the n-type semiconductor layer is formed. A method of manufacturing a thin film transistor, characterized in that a portion between the source and drain electrodes of is anodized over its entire thickness.