JP2021136299A - Manufacturing method of flexible display panel - Google Patents

Abstract

To provide a manufacturing method for a flexible display panel that can be manufactured at low temperature and low cost with respect to small to large panels on which pixel-driving LTPS-TFTs are mounted, such as organic EL displays and liquid crystal displays.SOLUTION: In a manufacturing method for a flexible panel according to the present invention, in a semiconductor layer on a flexible substrate including a pixel portion and a driving portion, only a peripheral part excluding the pixel portion is irradiated with an energy beam with a wavelength of 180 to 500 nm. Thus, only the semiconductor layer in the peripheral part excluding the pixel portion is dehydrogenated and crystallized continuously by the same laser annealing processing apparatus.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a flexible display panel capable of manufacturing a small to large area panel such as an organic EL display (OLED) or a liquid crystal display (LCD) at a low temperature and at a low cost.

Conventionally, liquid crystal displays (LCDs) have been the mainstream of flat panel displays (FPDs), and especially for thin film transistors (TFTs) that control liquid crystals in medium to large area panels, hydrogenation that can be produced at a temperature of about 500 ° C or less. Amorphous silicon TFTs have been mainly used.
On the other hand, as flexible panels made of glass or plastic equipped with driver ICs are required to have higher definition quality, low-temperature polysilicon that can be manufactured mainly on medium to small LCDs and resin substrates with low heat resistance temperature. Demand for silicon TFTs (LTPS-TFTs) is increasing.

This trend of increasing demand for LTPS-TFT is the same for organic EL displays (OLEDs) that require higher current drive capability, and in addition to being able to be equipped with high mobility and CMOS drive, it has less deterioration over time than amorphous silicon TFTs. Therefore, LTPS-TFT is becoming mainstream mainly for small and medium-sized panels.
As the area of the panel (board) increases, a high-power laser oscillator that can anneal the entire surface of the board is required, but the excimer laser annealing device that can irradiate ultraviolet beam light achieves both high energy and high repetition for each pulse. Therefore, there is a limit to the improvement of throughput, and in order to manufacture a large panel equipped with LTPS-TFT, it is necessary to invest appropriate laser equipment, and there is a problem that the manufacturing cost becomes high.

Further, in excimer laser annealing (ELA), it is generally difficult to control the particle size, and at present, it is difficult to obtain uniform TFT characteristics with little variation, and flat and uniform small particle size crystal grains. In order to obtain this, dehydrogenation treatment at a slightly high temperature (around 500 ° C.) must be performed after silicon deposition by the PECVD method (before ELA), so that there is a problem that the processing temperature in the manufacturing process becomes high.
Therefore, especially polyimide (PI), which has heat resistance of only about 500 ° C, has temperature restrictions, and is more inexpensive polycarbonate (PC), polyethylene naphthalate (PEN), polyether sulfone (PES), and cycloolefin polymer. Flexible resins such as (COP) cannot be used for substrates due to the problem of high processing temperature.

Therefore, the inventor of the present application can realize a high-performance TFT having a small particle size that allows a uniform current to flow without dehydrogenation by laser annealing (BLDA) using a blue semiconductor laser, and the crystallization processing temperature. Invented a technique capable of lowering the temperature (300 ° C. or lower) (Patent Document 1).
Laser annealing by the BLDA method by continuous (CW) scanning takes longer than ELA to heat the semiconductor film, but can be shorter than RTA, and local heating and temperature control of the semiconductor film and its lower layer are possible, so dehydrogenation is possible. It can be crystallized without treatment and can also be used for flexible resin substrates.

However, for example, since a peripheral scanning circuit requires a high mobility TFT that can obtain a high drive current, high power irradiation that can obtain higher crystallinity is advantageous, and in the case of film formation by PECVD, dehydrogenation is performed. It is more desirable to perform the treatment, but as the area of the panel (board) increases, it takes a long time to crystallize the entire surface of the substrate, and there is a limit to the improvement of the throughput.

Japanese Unexamined Patent Publication No. 2012-74675

Therefore, in view of the above problems, the present invention is manufactured at low temperature and at low cost for small to large area panels equipped with LTPS-TFT for pixel driving such as organic EL display (OLED) and liquid crystal display (LCD). It is an object of the present invention to provide a method for manufacturing a flexible display panel capable of being capable of manufacturing.

The method for manufacturing a flexible display panel according to the present invention is as follows.
On a flexible substrate consisting of a pixel part and a peripheral scanning circuit part,
The process of depositing a hydrogenated amorphous silicon film to form an amorphous semiconductor layer,
With respect to the semiconductor layer
Only in the peripheral scanning circuit part excluding the pixel part
An energy beam with a wavelength of 180 to 500 nm,
By irradiating with a scanning speed of 300 mm / s or more, ^{a laser output of 6.5 × 10 5} W / cm ^{2 to} 2.4 × 10 ⁶ W / cm ² , and continuous oscillation (CW) mode.
A step of simultaneously performing dehydrogenation and crystallization of only the semiconductor layer of the peripheral scanning circuit part excluding the pixel part by the same laser annealing treatment device is included.
It is characterized by that.

The flexible substrate in the present invention includes the present invention and the following inventions, in addition to glass, polyimide (PI), polycarbonate (PC), polyethylene naphthalate (PEN), and poly which have heat resistance only about 500 ° C. A substrate made of a flexible resin such as ether sulfone (PES) or cycloolefin polymer (COP) (hereinafter referred to as "flexible substrate").
Further, the scanning circuit unit in the present invention means a horizontal scanning unit and a vertical scanning unit provided around the substrate.

Normally, the pulse energy beam in ELA is irradiated in a band shape with respect to the irradiation direction, and is reciprocated many times on the substrate so as to cause overlap to crystallize the hydride amorphous silicon film of the entire substrate. If the portion is limited to the peripheral portion of the substrate, particularly the CMOS vertical scanning circuit portion, it is not necessary to reciprocate the substrate many times, and the crystallization processing time can be shortened.
In addition, since the temperature rise due to irradiation can be prevented, the substrate does not warp or crack due to the shrinkage of the molten silicon thin film, and stable quality and cost reduction can be realized.

Further, if the energy beam is locally irradiated only to the scanning circuit portion around the scanning circuit, polysilicon TFTs and amorphous silicon TFTs can be simultaneously produced on the same substrate.
As a result, in the LCD panel, a hydride amorphous silicon TFT that requires low leakage characteristics can be made in the pixel part, while in the OLED panel, a polysilicon TFT with a small particle size can be made in the pixel part. A silicon thin-film optical sensor of the same thickness can be mounted on the panel, and a polysilicon TFT with a large particle size (and also an optical sensor) that can obtain a high drive current can be mounted on other peripheral scanning circuits. Can be made.

To increase the drive current, make the channel direction of the transistor in the peripheral scanning circuit part the same as the scanning direction of the laser beam (direction in which the carrier flows), and to suppress the leakage current, the channel of the transistor is in the pixel part in the panel. It is necessary to make the direction and the scanning direction of the laser beam perpendicular to each other and scan-anneal with a lower power than the surrounding scanning circuit section. However, the area irradiated with the laser is the entire horizontal scanning section as shown in the shaded area in FIG. , Or a part of it (the side closer to the pixel) and all of the vertical scanning unit.

The same laser annealing processing device performs the dehydrogenation annealing process for releasing hydrogen from the film and the annealing process for crystallization by scanning and annealing the peripheral scanning circuit part excluding the pixel part with a large power. Since it can be performed at the same time, the process can be simplified.

As the energy beam, a blue laser (BLDA) or a UV laser in continuous oscillation (CW) mode can be used.
Irradiation conditions are wavelength 180 to 500 nm, scanning speed 300 mm / s or more, 6.5 x 10 ⁵ W / cm ^{2 to} 2.4 x 10 ⁶ W / cm ² , and continuous oscillation (CW) mode.
Preferably, the wavelength is 445 nm, the scanning speed is 300 mm / s, 6.5 × 10 ⁵ W / cm ² , and the continuous oscillation (CW) mode is used.

Be irradiated under the condition of lower laser power density (e.g., ^{6.5 × 10 5 W / cm 2} ) and the scanning speed 300~2000mm / s, as compared to the channel dimensions, the polysilicon film is obtained a more uniform fine particle size , Transistors with small variation in characteristics can be manufactured.
In addition, by irradiating under the conditions of high laser power density (for example, 2.4 × 10 ⁶ W / cm ² ) and scanning speed of 300 to 2000 mm / s, a polysilicon film with a large particle size can be obtained, and a transistor capable of high-speed operation can be obtained. Can be manufactured.

If fine micropolysilicon or amorphous silicon can be used for the pixel part and silicon with a large particle size or silicon with a long particle size can be used for the peripheral scanning circuit part, silicon having each characteristic (characteristic). TFTs can be mounted on the same surface.

The method for manufacturing a flexible display panel according to the present invention is as follows.
On a flexible substrate consisting of a pixel part and a peripheral scanning circuit part,
The process of depositing a hydrogenated amorphous silicon film to form an amorphous semiconductor layer,
With respect to the semiconductor layer
Only in the peripheral scanning circuit part excluding the pixel part
Blue laser (BLDA) or UV laser,
After irradiating in pulse (1 or more shots) or continuous oscillation (CW) mode to dehydrogenate
A blue laser (BLDA) or UV laser with a wavelength of 180-500 nm,
By irradiating once at a scanning speed of 500 mm / s or less, 6.5 × 10 ⁵ W / cm ^{2 to} 3.2 × 10 ⁶ W / cm ^2.
A step of continuously dehydrogenating and crystallization of only the peripheral semiconductor layer excluding the pixel portion by the same laser annealing treatment apparatus is included.
It is characterized by that.

The present invention can reduce costs by using pulses with a blue laser (BLDA) using a semiconductor laser diode or a semiconductor UV laser instead of an excimer laser (ELA), resulting in miniaturization, stabilization, and CW scanning. This has the advantage of improving flatness.

First, scan with a power that does not crystallize, release hydrogen from the film, perform dehydrogenation, and then scan-anneal with a power higher than the first time, dehydrogenation annealing process and crystallization annealing process. And can be performed continuously by the same laser annealing treatment device, so that the process can be simplified.

The method for manufacturing a flexible display panel according to the present invention is carried out through the following steps.
1. 1. Film formation process A film is formed on a flexible substrate by the PECVD method (60 nm thickness or less, preferably 50 nm or less).
2. Dehydrogenation process Only the peripheral semiconductor layer excluding the pixel part of the flexible substrate is 4.5 × 10 ⁵ W / cm ^{2 to} 1.6 × 10 ⁶ W / cm ² , 445 nm semiconductor laser (BLDA) or 375 nm (UVLDA: Ultra-). Violet Laser Diode Annealing) is irradiated.
3. 3. ^{Crystallization process 6.5 × 10 5} W / cm ^{2 to} 3.2 × 10 ⁶ W / cm ² , 445 nm semiconductor laser (BLDA) or 375 nm (UVLDA: Ultra-) only on the peripheral semiconductor layer excluding the pixel part of the flexible substrate. Violet Laser Diode Annealing) is irradiated.
4. Patterning 5. Gate oxide film formation (CVD or sputtering method)
6. Source drain formation, contact hole formation, patterning 7. Metal source / drain region formation by vacuum deposition method without using ion implantation method (By using titanium for the source / drain region, electrons can easily move from titanium to silicon, and n-type operation TFTs can be obtained. By using Au etc., a TFT with p-type operation can be obtained.)
8. Liquid crystal process

If the crystal grain size of the polysilicon that constitutes the silicon layer is uniform with a small particle size, the field effect mobility in the silicon layer that constitutes the channel layer of the semiconductor device is further improved as compared with the case of the large particle size silicon film. , The BLDA method is superior in flatness as compared with the case of crystallization by the ELA method, and the current driving ability of the semiconductor device is improved.
As a result, for example, when using TFT for pixel drive, especially in the case of OLED (organic EL) drive, it may be possible to reduce the number of TFTs used per pixel, and the product cost can be reduced. ..

By irradiating the amorphous silicon thin film with a laser beam under this condition and repeating the operation of performing polycrystalline silicon a plurality of times, it is possible to form a higher quality polycrystalline silicon thin film.
Further, in the present invention, a patterning step of patterning the amorphous silicon thin film formed on the pixel portion and the polycrystalline silicon thin film formed on the peripheral scanning circuit portion to form the amorphous silicon thin film pattern and the polycrystalline silicon pattern, respectively. As a result, at least a part of the hydrided amorphous silicon thin film pattern can be used as the TFT channel part of the pixel part, and at least a part of the polycrystalline silicon pattern can be used as the TFT channel part of the scanning circuit part.

According to the present invention, the crystallization processing time can be shortened by limiting the irradiation portion of the energy beam to only the semiconductor layer of the peripheral scanning circuit portion excluding the pixel portion.
In addition, since the temperature rise due to irradiation can be prevented, the substrate does not warp or crack due to the shrinkage of the molten silicon thin film, and stable quality and cost reduction can be realized.
Further, by locally irradiating only the peripheral scanning circuit portion with the energy beam, polysilicon TFTs and amorphous silicon TFTs can be simultaneously produced on the same substrate.

As a result, in both the OLED panel and the LCD panel, amorphous silicon or polysilicon TFTs with a small particle size and optical sensors, which require low leakage characteristics, are applied to the pixel part, and a high drive current is applied to the scanning circuit part around them. It is possible to make a polysilicon TFT with a large particle size (and an optical sensor on the panel).
Furthermore, since it can be applied to flexible substrates and can produce versatile TFTs, it becomes possible to manufacture bendable display panels.

By performing the dehydrogenation annealing treatment step and the crystallization annealing treatment step simultaneously or continuously by the same laser annealing treatment apparatus, the steps can be simplified and the product cost can be reduced.

It is a circuit diagram which showed the region which irradiates a laser to a flexible display panel. It is explanatory drawing which showed one execution procedure of manufacturing of a flexible display panel.

The present invention can manufacture small to large area panels such as organic EL displays (OLEDs) and liquid crystal displays (LCDs) at low temperature and low cost while mounting polysilicon TFTs and amorphous silicon TFTs on the same substrate. This is a method for manufacturing a flexible display panel.

As shown in FIG. 1, the flexible display panel according to this embodiment is composed of a pixel unit 1, a horizontal scanning unit 2 and a vertical scanning unit 3 which are scanning circuit units around the pixel unit 1, and these are on the same flexible substrate. Is formed in.

As the flexible substrate in this embodiment, a resin material can be used in addition to glass, and the heat resistant temperature of polyimide, polyamideimide, polysiliceskioxane, polyethylene terephthalate, polycarbonate, polyethylene naphthalate, polyether sulfone, cycloolefin polymer, etc. can be used. Low materials can also be used.

The TFT formed in the pixel portion 1 and the TFT formed in the horizontal scanning portion 2 and the vertical scanning portion 3 are formed on the same flexible substrate.

A film (underlayer) made of SiN (silicon nitride) and SiO _{2 (silicon oxide) is formed on the flexible substrate.}
A channel portion and a source / drain portion made of a hydrogenated amorphous silicon thin film are formed in the pixel portion 1 above the base layer, and a polycrystalline silicon thin film is formed in the horizontal scanning portion 2 and the vertical scanning portion 3. A channel part and a source / drain part are formed.

The channel portion and the source / drain portion are both hydrogenated amorphous silicon thin films formed by the same process.
A gate insulating film is formed on the channel portion and the source / drain portion, and a gate electrode is formed on the portion of the gate insulating film that covers the channel portion.
The TFT of the pixel unit 1, the horizontal scanning unit 2, and the vertical scanning unit 3 is configured by the channel unit, the source / drain unit, the gate insulating film, and the gate electrode.

The flexible display panel according to this embodiment is manufactured by the following method.
_{An underlayer made of SiO 2} is deposited on the entire surface of the flexible substrate by the plasma CVD method, and further, by the plasma CVD method, for example, a hydrogen concentration of 40 to 120 nm and a hydrogen concentration of 5-30% is deposited on the entire surface of the underlayer. A hydride amorphous silicon thin film is deposited.
By this step, a base layer and a hydrogenated amorphous silicon thin film are formed on all of the pixel portion 1, the horizontal scanning portion 2, and the vertical scanning portion 3 on the flexible substrate.

Next, among the hydrogenated amorphous silicon thin films formed on the flexible substrate, the hydrogenated amorphous silicon thin film formed on the pixel portion 1 was not irradiated, and as shown in the shaded area in FIG. 1, the horizontal scanning portion 2 An energy beam is applied to all or part of (the side closer to the pixel) and all of the vertical scanning unit 3 at a scanning speed of 300 mm / s, 6.5 × 10 ⁵ W / cm ^{2 to} 2.4 × 10 ⁶ W / cm. ^{Irradiate in 2} laser output, continuous oscillation (CW) mode.

A dehydrogenation annealing process for releasing hydrogen from the film and an annealing process for crystallization can be performed by scanning and annealing the horizontal scanning unit 2 and the vertical scanning unit 3 around the periphery excluding the pixel portion with a large power. Since it can be performed simultaneously by the same laser annealing treatment device, the process can be simplified.

As the energy beam, a blue laser (BLDA) or a UV laser in continuous oscillation (CW) mode can be used.

Be irradiated under the condition of lower laser power density (e.g., ^{6.5 × 10 5 W / cm 2} ) and the scanning speed 300~2000mm / s, as compared to the channel dimensions, the polysilicon film is obtained a more uniform fine particle size , Transistors with small variation in characteristics can be manufactured.
Irradiation under the conditions of high laser power density (for example, 2.4 × 10 ⁶ W / cm ² ) and scanning speed of 300 to 2000 mm / s can obtain a polysilicon film with a large particle size, and a transistor capable of high-speed operation can be manufactured. ..

Further, the irradiation of the energy beam can be performed continuously with the dehydrogenation step of releasing hydrogen from the hydrogenated amorphous silicon thin film.
In other words, after the dehydrogenation process of releasing hydrogen from the hydrided amorphous silicon thin film is completed, the intensity of the energy beam emitted from the laser oscillator is changed without removing the flexible substrate from the chamber, and the amorphous silicon thin film is continuously formed. A crystallization step can be performed.
By continuously performing the dehydrogenation annealing treatment step and the crystallization annealing treatment step by the same laser annealing treatment apparatus, the steps can be simplified.

When the amorphous silicon thin film contains a large amount of hydrogen, when the energy beam is irradiated, hydrogen bumps occur before the amorphous silicon thin film melts, and after the amorphous silicon thin film melts, it is more violently contained in the thin film. Hydrogen is released and pinholes are formed in the film, and damage such as peeling of the film from the flexible substrate occurs.
The occurrence of damage due to the release of hydrogen in the amorphous silicon thin film is affected by the rate of temperature rise of the amorphous silicon thin film.

Therefore, it is irradiated with a blue laser (BLDA) or UV laser in pulse (1 or more shots) or continuous oscillation (CW) mode to release hydrogen atoms contained in the amorphous silicon thin film, and then dehydrogenated. By crystallization treatment of the amorphous silicon thin film, a polycrystalline silicon thin film without damage can be produced.
By repeating the operation of crystallization of the amorphous silicon thin film a plurality of times, the amorphous silicon thin film can be changed into a polycrystalline silicon thin film.
If the energy beam in the crystallization annealing process after dehydrogenation is a blue laser (BLDA) or UV laser with a wavelength of 180 to 500 nm, one irradiation (6.5 x 10 ⁵ W / cm ^{2 to} 3.2 x 10 ⁶ W) It can be crystallized at / cm ² , 445 nm, 500 mm / s).

For example, the first laser irradiation is performed at a scanning speed of 300 mm / s, ^{a laser output of 4.5 × 10 5} W / cm ^{2 to} 1.6 × 10 ⁶ W / cm ² , and a continuous oscillation (CW) mode.
In this case, hydrogen contained in the hydrogenated amorphous silicon thin film formed in the horizontal scanning unit 2 and the vertical scanning unit 3 is released, and the film changes to an amorphous silicon thin film containing almost no hydrogen (5% or less).
Therefore, the second laser irradiation is further irradiated with a wavelength of 405 nm, a scanning speed of 300 mm / s, ^{a laser output of 6.5 × 10 5} W / cm ^{2 to} 3.2 × 10 ⁶ W / cm ² , and a continuous oscillation (CW) mode. do.

First, scan with a power that does not crystallize, release hydrogen from the film to perform dehydrogenation, and then scan-anneal with a power higher than the first time, the dehydrogenation annealing process and the crystallization annealing process. Can be continuously performed by the same laser annealing processing apparatus, so that the process can be simplified.
When the second laser irradiation (crystallization step) is performed under ^{the conditions of a laser output of 4.5 × 10 5} W / cm ² and a scanning speed of 300 to 2000 mm / s, a polysilicon film having a fine particle size can be obtained. Transistors with small variation can be manufactured.
Further, if the second laser irradiation (crystallization step) is performed under ^{the conditions of a laser output of 1.6 × 10 6} W / cm ² and a scanning speed of 300 to 2000 mm / s, a polysilicon film having a large particle size can be obtained. , Can manufacture transistors that can operate at high speed.

Through the above steps, the amorphous silicon thin film formed in the horizontal scanning unit 2 and the vertical scanning unit 3 crystallizes and changes into a polycrystalline silicon thin film.
At this time, the energy beam is not applied to the hydrogenated amorphous silicon thin film formed in the pixel portion 1.

As described above, in the flexible display panel obtained by the present embodiment, the TFT channel portion provided in the pixel portion 1 and the TFT channel portion provided in the horizontal scanning unit 2 and the vertical scanning unit 3 are the same. Since it is manufactured from the hydride amorphous silicon thin film formed by the process, there are many steps in which the TFT can be manufactured in common. Can be produced.
On the other hand, even in the case of an OLED panel, a semiconductor film having a silicon film crystal structure having a uniform particle size can be obtained by micropolysiliconizing the pixel silicon film by BLDA.

Further, according to the present embodiment, the hydrided amorphous silicon thin film formed in the horizontal scanning section 2 and the vertical scanning section 3 is dehydroaned to release hydrogen contained in the hydrided amorphous silicon thin film, and the amorphous silicon thin film is formed. Since the amorphous silicon thin film is changed to the polycrystalline silicon thin film by the crystallization annealing treatment after the change to the above, a polycrystalline silicon thin film having excellent film quality can be produced.

Moreover, according to this embodiment, since the energy beam is not applied to the hydride amorphous silicon thin film formed in the pixel portion 1, hydrogen is released from the hydride amorphous silicon thin film formed in the pixel portion 1. Therefore, the unbonded hands of the hydrogenated amorphous silicon thin film formed in the pixel portion 1 can be suppressed to a small extent, so that the film quality of the hydrogenated amorphous silicon thin film formed in the pixel portion 1 is also ensured to be excellent.

In this embodiment, the hydrogenated amorphous silicon thin film formed in the pixel portion 1 is not irradiated with the energy beam, but the dehydrogenation annealing treatment step and the crystallization annealing treatment step are performed by the same laser annealing treatment device. The pixel portion 1 may be included in the area to be irradiated with the laser as long as the continuity of the laser annealing treatment steps performed at the same time is not impaired.

Claims (2)

On a flexible substrate consisting of a pixel unit and a drive unit,
The process of depositing a hydrogenated amorphous silicon film to form an amorphous semiconductor layer,
With respect to the semiconductor layer
Only in the peripheral part excluding the pixel part,
An energy beam with a wavelength of 180 to 500 nm,
By irradiating with a scanning speed of 300 mm / s or more, ^{a laser output of 6.5 × 10 5} W / cm ^{2 to} 2.4 × 10 ⁶ W / cm ² , and continuous oscillation (CW) mode.
A step of continuously dehydrogenating and crystallization of only the peripheral semiconductor layer excluding the pixel portion by the same laser annealing treatment apparatus is included.
A method for manufacturing a flexible panel, which is characterized in that. On a flexible substrate consisting of a pixel unit and a drive unit,
The process of depositing a hydrogenated amorphous silicon film to form an amorphous semiconductor layer,
With respect to the semiconductor layer
Only in the peripheral part excluding the pixel part,
Blue laser (BLDA) or UV laser,
After irradiating in pulse (1 or more shots) or continuous oscillation (CW) mode to dehydrogenate
A blue laser (BLDA) or UV laser with a wavelength of 180-500 nm,
By irradiating once at a scanning speed of 500 mm / s or less, 6.5 × 10 ⁵ W / cm ^{2 to} 3.2 × 10 ⁶ W / cm ^2.
A step of continuously dehydrogenating and crystallization of only the peripheral semiconductor layer excluding the pixel portion by the same laser annealing treatment apparatus is included.
A method for manufacturing a flexible panel, which is characterized in that.

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