JPH0772821B2 - Liquid crystal display manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a liquid crystal display device including a thin film transistor.

[Prior Art] Conventionally, a display panel using an active matrix has attracted attention as a method capable of realizing a large-sized panel having a large number of dots because its matrix size can be made extremely large as compared with the dynamic method.

In particular, a light-receiving element such as a liquid crystal has a limited drive duty in a dynamic system, and an active matrix application is considered for a television display and the like.

FIG. 1 shows one cell of a conventional active matrix.

The address line X is input to the gate of the transistor 2, and the transistor is turned on to store the signal on the data line Y in the holding capacitor 3 as electric charge. Until the data is written again, it is held by this capacitor 3 and simultaneously drives the liquid crystal 4.

Where VC is the common electrode signal. Since the liquid crystal leaks very little, it is sufficient for holding charges for a short time. The manufacturing method of transistors and capacitors here is exactly the same as the process of normal IC.

FIG. 2 is an example in which the cell of FIG. 1 is produced by a silicon gate process.

Transistor 10 and capacitor on single crystal silicon wafer
10 are composed. Address line X and capacitor upper electrode 11
Is polycrystalline silicon (polysilicon), and the data line Y and the liquid crystal drive electrode 13 are made of Al.
The substrate and Al are connected to each other by 8, 9 and the polysilicon and Al are connected to each other.

However, since such a structure has a problem that the process is complicated and the yield is difficult to control, a display body in which a thin film transistor is formed on a transparent substrate has been considered.
When such a thin film transistor is used, amorphous silicon, polysilicon, etc. have been used as a semiconductor thin film.

[Problems and Objectives to be Solved by the Invention] Generally, in a MOS transistor, when a semiconductor substrate made of single crystal silicon is used, P-type
An N type substrate is used for the mold substrate and the P channel. In such a structure, the OFF leakage current between the source and the drain is reduced by utilizing the PN junction.

However, in a thin film transistor made of amorphous silicon or polysilicon (hereinafter referred to as non-single-crystal silicon) provided on a glass substrate, a high-quality PN cannot be formed due to the property of the non-single-crystal silicon thin film, and the transistor There was a problem that a leak current was generated when it was turned off.

In order to solve such a problem, an attempt has been made to reduce the leak current when the transistor is turned off by making the channel portion of the thin film transistor an intrinsic semiconductor.
Keeping the channel authentic has never been easier.

The present invention overcomes such problems, and an object of the present invention is to provide a method of manufacturing a thin film transistor capable of ensuring that the channel portion of the thin film transistor is an intrinsic region.

[Means for Solving Problems] According to the present invention, a liquid crystal is sealed between a pair of glass substrates, and the pixel electrodes are arranged in a matrix on one of the pair of glass substrates. In the method of manufacturing an inverted staggered thin film transistor connected to an electrode, a liquid crystal display device having a storage capacitor having the pixel electrode as one electrode, a step of forming an insulating film having good adhesion on the one glass substrate Forming a gate electrode and the other electrode of the storage capacitor made of the same material on the insulating film, oxidizing the other electrode of the gate electrode and the storage capacitor, and the upper surface and side surface of the gate electrode and the other electrode Forming an insulating film on the surface of the electrode of the gate electrode, and a channel formed of an intrinsic non-single crystal silicon semiconductor layer not doped with impurities on the gate oxide film of the gate electrode. It is characterized in that it comprises a step of forming a channel region and a step of connecting to the channel region and forming source and drain regions made of a non-single-crystal silicon thin film doped with impurities.

[Example] FIG. 3 shows a matrix cell used in the present invention.

The only difference from FIG. 1 is that a GND wiring for the capacitor is newly provided, and the basic circuit is the same. In this case, the GND potential means a constant bias, and the bias level does not matter.

FIG. 4 shows an example of the cell structure.

(A) is a plan view, and the address line 26 serves as the gate of the channel 28 of the transistor having the data line 25, the drive electrode and the electrode 29 of the capacitor as the source / drain. or
The GND line 27 is formed at the same time as the address line 26 and forms a capacitance with the electrode 29. Figure 4 (B) is AB of (A).
It shows a cross section along a line.

Explaining one example of the manufacturing process, polysilicon is used as a silicon thin film on a high melting point glass substrate 31 such as quartz.
Grow 3000 Å, then implant P ions on the entire surface to N
Use as a mold. However, in some cases to improve adhesion,
Thin SiO ₂ may be formed in advance.

Further, by photo etching, the gate 26 and the capacitor electrode
After forming 27, a SiO ₂ film 30 of about 1500 Å is grown by thermal oxidation as a gate insulating film and a dielectric film of a capacitor. After that, a second layer of polysilicon is applied to form a pattern by photo-etching, and then P ions are implanted again in a region other than the channel portion 28 by a resist mask to form a liquid crystal that also serves as a source / drain electrode, a data line wiring portion, and a capacitor electrode. Drive electrodes are formed.

Locally on this channel portion 28 or evenly over the entire substrate,
Laser is applied to melt polysilicon in a short time.
By solidifying and growing grains, it is possible to improve the performance such as threshold value and conductance. This is what is called laser annealing.

In the structure shown in FIG. 4, an electrode that transmits light is used, but an Al electrode may be further provided thereon.

FIG. 5 shows a simple cross section of a liquid crystal display device using the matrix substrate of the present invention.

A liquid crystal body 38 is sandwiched between a quartz substrate 35 on which a polysilicon electrode 37 is placed and a glass 36 on which a common electrode 39 made of a Nesa film is placed. Furthermore, after sandwiching with the polarizing plates 32 and 33, the reflecting plate 34 is attached to the lower side. In this way, most of the light incident from above passes through the polysilicon electrode 37, is reflected by the reflector 34, and is sensed by the human eye. Since this method can use normal FE type liquid crystal, it has high contrast and wide viewing angle.

FIG. 6 shows a cross section of a cell formed on a normal glass substrate as another example of the present invention. A polysilicon film is formed on the glass substrate 40 by a low temperature film forming method such as sputtering or plasma CVD, and P ions or B ions are implanted on the entire surface. Next, the gate 43 and the capacitor electrode 42 are formed by photoetching. Further, the insulating film 44 is formed. Again, SiO ₂ or the like grown by low temperature is used.

Further, the second layer polysilicon, which also serves as the source / drain of the transistor and the capacitor and the drive electrode, is formed at a low temperature.

The polysilicon is either undoped at all or implanted with a sufficient amount of B ions to enhance the darkness.

After that, the laser beam is locally or entirely irradiated and annealed. A part of the laser beam is absorbed by the polysilicon of the first layer, but it is transmitted through the glass substrate 40. Therefore, the activation of the ion-implanted impurities in the first layer of polysilicon and the growth of the second layer of polysilicon grains (particularly the channel portion 48) are carried out at an appropriate beam energy for an appropriate time (pulse laser). If so, it can be annealed within a range that has almost no effect on the glass substrate by performing a pulse interval or a scanning speed for a CW laser).

The feature of this method is that the laser annealing can significantly reduce the influence on the glass substrate with respect to the conventional thermal annealing, so that it is possible to use the glass at a low cost.
The laser annealing is capable of simultaneously improving the characteristics (particularly the mobility) of the transistor by growing the polysilicon grains in the channel portion together with the activation of the impurities.

Then, Al is applied and photoetching is performed to form source / drain electrodes 46 and 47. Since Al and polysilicon are difficult to make contact with each other as they are, they may be heat-treated a little or irradiated with a weak laser beam.

[Effect] With the invention as described above, the following effects can be obtained.

That is, (a) since the inverted stagger type thin film transistor is formed via the insulating film, the film can be continuously formed without breaking the vacuum state. Therefore, impurities are not mixed between the films, and a boundary surface having good electrical characteristics can be obtained.

(B) After the gate insulating film is formed on the gate electrode formed on the substrate, a channel portion made of an intrinsic semiconductor that is not doped with impurities can be formed continuously, so that impurities are not formed at the MOS interface between the intrinsic semiconductor and the insulating film. A thin film transistor that does not remain can be formed.

(C) Since the insulating film having good adhesion is formed on the glass substrate, the adhesion between the glass substrate and the thin film transistor is improved.

(D) Since the thin film transistor is an inverted stagger type, and since the insulating film is formed on the glass substrate, it is possible to prevent impurities from the glass substrate from diffusing into the channel region of the thin film transistor. Stabilize.

(E) Since the gate insulating film can be formed by oxidizing the gate electrode itself, the contact between the gate electrode and the gate insulating film can be improved, and a dense insulating film without defects can be formed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a cell used in a conventional active matrix. FIG. 2 is a plan view of a cell using bulk silicon. FIG. 3 is a cell diagram of the present invention. 4 (A) and 4 (B) are a plan view and a sectional view of the implementation example. FIG. 5 is a sectional view when the substrate of the present invention is mounted on a panel. FIG. 6 is a diagram showing another embodiment of the present invention. 7,8,9 …… Contact hole 10 …… Polysilicon gate 11 …… Polysilicon upper electrode of capacitor 3 ………… Al driving electrode 26,27 …… First layer polysilicon 25,29 …… 2 Layer polysilicon 28 …… Channel 31 …… Quartz substrate 32,33 …… Polarizer 34 …… Reflector 35,36 …… Transparent substrate 39 …… Nesa film 37 …… Polysilicon drive electrode 38 …… Liquid crystal body 40 …… Glass substrate 42,43 …… First layer polysilicon 45 …… Second layer polysilicon 46,47 …… Al 48 …… Channel

Claims (1)

[Claims] 1. A pixel electrode formed by enclosing a liquid crystal between a pair of glass substrates, arranged in a matrix on one glass substrate of the pair of glass substrates, and an inverted stagger type connected to the pixel electrodes. In the method of manufacturing a liquid crystal display device having a thin film transistor and a storage capacitor having the pixel electrode as one electrode, a step of forming an insulating film having good adhesion on the one glass substrate, the same material being formed on the insulating film. Forming a gate electrode and the other electrode of the storage capacitor, wherein the gate electrode and the other electrode of the storage capacitor are oxidized to form an insulating film on the upper surface and the side surface of the gate electrode and the surface of the other electrode. A step of forming a channel region made of an intrinsic non-single-crystal silicon semiconductor layer in which impurities are not doped on the gate oxide film of the gate electrode, Method of manufacturing a liquid crystal display device impurities are connected to the channel region to the source of non-single-crystal silicon thin film doped, characterized in that it comprises the step of forming a drain region.