AU2020104175A4

AU2020104175A4 - Method for preparing c-axis aligned crystalline igzo thin film at low temperature

Info

Publication number: AU2020104175A4
Application number: AU2020104175A
Authority: AU
Inventors: Chang Liu; Yiming Liu; Mingxin Lu; Chong PENG; Houyun QIN; Song WEI; Yi Zhao
Original assignee: Jilin University
Current assignee: Jilin University
Priority date: 2020-09-27
Filing date: 2020-12-18
Publication date: 2021-03-04
Anticipated expiration: 2028-12-18
Also published as: CN112126896A

Abstract

The disclosure provides a method for preparing C-axis aligned crystalline IGZO thin film at low temperature, belonging to the field of liquid crystal display technology. The method of the disclosure includes the following steps: Under a mixed atmosphere of inert gases and reactant gases, target materials are magnetron sputtered on the surface of the substrate and simultaneously an in-situ plasma treatment is applied on the surface of the substrate, to get a C axis aligned crystalline IGZO thin film; the target materials for the magnetron sputtering are oxides of indium, gallium and zinc; the temperature of the substrate is maintained at 25100°C. The disclosure prepares the C-axis aligned crystalline IGZO thin film by in-situ plasma assisted magnetron sputtering, in which the heat needed to form the crystal is replaced by the energy of plasma partially, to achieve the deposition of C-axis aligned crystalline IGZO at a low temperature of 25~100°C, thus extending the application of C-axis aligned crystalline IGZO thin film in flexible display.

Description

METHOD FOR PREPARING C-AXIS ALIGNED CRYSTALLINE IGZO THIN FILM AT LOW TEMPERATURE TECHNICAL FIELD

10001] The disclosure pertains to the field of liquid crystal display technology, and specifically pertains to a method for preparing C-axis aligned crystalline IGZO thin film at low temperature.

BACKGROUD

10002] Metal oxide thin film transistors are widely used in the display field owing to their high mobility, good large area uniformity, and compatibility with flexible processes. Amorphous metal oxide IGZO is an N-type semiconductor material composed of In203, Ga2O3 and ZnO, with a forbidden band width of about 3.5 eV. The C-axis aligned crystalline IGZO (CAAC-IGZO) has a low defect density of states, making the electrical properties of thin film transistors less dependent on the channel length, and maintaining a higher stability at small sizes, thus it is the optimal choice for high resolution display. In addition, due to its low off-state current, the static power consumption can be reduced greatly, thus effectively extending the battery life of the equipment.

10003] In general, C-axis aligned crystalline IGZO thin film is deposited by sputtering, mainly in two ways: one is heating the substrate during the deposition of the thin film with keeping the temperature at 0 °C35 0 °C; the other is without heating the substrate, annealing at a temperature of 400°C-750°C after the IGZO thin film has deposited to a certain thickness to get the IGZO thin film with a C-axis aligned crystalline structure. However, the heating temperatures for the two methods are both high. If flexible substrates are used, most flexible substrate may be damaged irreversibly at such temperatures, thus limiting their applications in flexible display.

SUMMARY

10004] In view of this, an objective of the disclosure is to provide a method for preparing C-axis aligned

crystalline IGZO thin film at low temperature. The preparation of C-axis aligned crystalline IGZO thin

film can be achieved under low temperature conditions by the method of the disclosure.

10005] To realize the above objective, the disclosure provides the following technical scheme:

10006] The disclosure provides a method for preparing C-axis aligned crystalline IGZO thin film

at low temperature, comprising the following steps:

10007] Under a mixed atmosphere of inert gases and reactant gases, target materials are

magnetron sputtered on the surface of the substrate and simultaneously an in-situ plasma

treatment is applied on the surface of the substrate, to get a C-axis aligned crystalline IGZO thin

film;

10008] The target materials for the magnetron sputtering are oxides of indium, gallium and zinc;

10009] The temperature of the substrate is maintained at 25-100°C.

10010] Preferably, the inert gases are argon and/or helium, and the reactant gases are oxygen

and/or nitrogen;

10011] The flow rate of the inert gases is 1-1000 sccm; the flow rate of the reactant gases is

1-1000 sccm; in the mixed atmosphere, the concentration of the reactant gases is 0.01-20wt%.

10012] Preferably, the substrate includes, from top to bottom in turn, an insulating layer, an

electrode layer and a substrate base, and target materials are magnetron sputtered on the surface

of the insulating layer;

10013] The insulating layer is made of one of insulating metal oxide, insulating non-metal oxide

and insulating organic material; the insulating metal oxide is A1 20 3 and/or HfO 2, the insulating

non-metal oxide is one or more of SiO 2, Si 3N 4 and SiON, and the insulating organic material is

PMMA and/or pp-HMDSO;

10014] The electrode layer is made of one or more of metal, metal oxide or metalnitride.

10015] Preferably, the substrate is a flexible substrate or a non-flexible substrate; when the

substrate is a flexible substrate, the substrate base is made of one or more of polyethylene,

polypropylene, polystyrene, polyethylene terephthalate and polyimide; when the substrate is a non-flexible substrate, the substrate base is made of one or more of glass, silicon oxide, aluminum oxide, silicon nitride and silicon carbide.

10016] Preferably, the in-situ plasma treatment is applied by a method comprising the following steps:

10017] The inert gases and reactant gases on the surface of the substrate are ionized, to get the

plasma.

10018] Preferably, the power of the radio-frequency (RF) source used in the ionization is 1-2000 W, and the frequency of the RF source is 13.56 MHz or 4 MHz; the method for ionization is capacitive coupling or inductive coupling.

10019] Preferably, the oxides of indium, gallium and zinc are ZnO, In203 and Ga2 0 3 ;

or GaZnO and InZnO;

or InGaZnO.

10020] Preferably, the magnetron sputtering is DC magnetron sputtering or RF magnetron sputtering; the power density applied on the surface of the target materials by the magnetron sputtering is 0.1-100 W/cm 2 , the magnetron sputtering time is 0.1-100 min, and the vacuum degree is 0.1-20 mTorr.

10021] Preferably, during the magnetron sputtering, it further comprises rotating the surface of the substrate; and the rotating speed is 1-1000 rpm.

10022] The disclosure provides a method for preparing C-axis aligned crystalline IGZO thin film

at low temperature, comprising the following steps: Under a mixed atmosphere of inert gases and reactant gases, target materials are magnetron sputtered on the surface of the substrate and simultaneously an in-situ plasma treatment is applied on the surface of the substrate, to get a C axis aligned crystalline IGZO thin film; The target materials for the magnetron sputtering are oxides of indium, gallium and zinc; The temperature of the substrate is maintained at 25-100°C. The disclosure prepares the C-axis aligned crystalline IGZO thin film by in-situ plasma assisted magnetron sputtering, in which the heat needed to form the crystal is replaced by the energy of plasma partially, to achieve the deposition of C-axis aligned crystalline IGZO at a low temperature of 25~100°C, thus extending the application of C-axis aligned crystalline IGZO thin film in flexible display. Moreover, the C-axis aligned crystalline IGZO thin film obtained by the method of the disclosure has high mobility and stability when used as the channel layer of a thin film transistor.

BRIEF DESCRIPTION OF THE DRAWINGS

10023] Fig. 1 is a schematic diagram showing the preparation of a C-axis aligned crystalline IGZO thin film at low temperature according to the disclosure;

10024] Fig. 2 is an X-ray diffraction diagram of the C-axis aligned crystalline IGZO thin film obtained in embodiment 1;

10025] Fig. 3 shows the transfer characteristic curve of the C-axis aligned crystalline IGZO thin film obtained in embodiment 2 as the thinfilm transistor.

DESCRIPTION OF THE EMBODIMENTS

10026] The disclosure provides a method for preparing C-axis aligned crystalline IGZO thin film

at low temperature, comprising the following steps:

10027] Under a mixed atmosphere of inert gases and reactant gases, target materials are magnetron sputtered on the surface of the substrate and simultaneously an in-situ plasma

film;

10028] The target materials for the magnetron sputtering are oxides of indium, gallium and zinc;

10029] The temperature of the substrate is maintained at 25-100°C.

10030] According to the disclosure, under a mixed atmosphere of inert gases and reactant gases, target materials are magnetron sputtered on the surface of the substrate and simultaneously an in

situ plasma treatment is applied on the surface of the substrate, to get a C-axis aligned crystalline

IGZO thin film. In the disclosure, the inert gases are preferably argon and/or helium, and the

reactant gases are preferably oxygen and/or nitrogen; in the disclosure, the flow rate of the inert

gases is preferably 1-1000 secm, more preferably 40-500 secm; the flow rate of the reactant

gases is preferably 1-1000 secm, more preferably 5-200 secm; in the disclosure, the

concentration of the reactant gases in the mixed atmosphere is preferably 0-20 wt%, more

preferably 5-15 wt%.

10031] In the disclosure, the substrate preferably includes, from top to bottom in turn, an insulating layer, an electrode layer and a substrate base, and target materials are magnetron

sputtered on the surface of the insulating layer. In the disclosure, the insulating layer is

preferably made of one of insulating metal oxide, insulating non-metal oxide and insulating

organic material; the insulating metal oxide is preferably aluminum oxide (Al 20 3 ) and/or

hafnium oxide (HfO2 ); the insulating non-metal oxide is preferably one or more of silicon oxide

(SiO2 ), silicon nitride (Si 3 N 4 ) and silicon oxynitride (SiON); and the insulating organic material is preferably polymethyl methacrylate (PMMA) and/or polyhexamethyl disiloxane (pp

HMDSO). In the disclosure, the electrode layer is preferably made of one or more of metal,

metal oxide or metalnitride. In the disclosure, the metal is preferably one of aluminum, gold,

silver and molybdenum; the metal oxide is preferably indium tin oxide; and the metal nitride is

preferably titanium nitride.

10032] The disclosure has no special requirements on the thicknesses of the insulating layer, the

electrode layer and the substrate base, and the thicknesses familiar to technicians in this field can

be used.

10033] In the disclosure, the substrate is preferably a flexible substrate or a non-flexible substrate, more preferably a flexible substrate. In the disclosure, when the substrate is a flexible substrate,

the substrate base is preferably made of one or more of polyethylene, polypropylene,

polystyrene, polyethylene terephthalate and polyimide; when the substrate is a non-flexible substrate, the substrate base is preferably made of one or more of glass, silicon oxide, aluminum oxide, silicon nitride and silicon carbide.

10034] As a specific embodiment of the disclosure, the substrate is a PET/ITO/PMMA substrate, of which the flexible substrate is made of PET, the gate-electrode layer is made of ITO with a thickness of 100 nm, and the insulating layer is made of PMMA with a thickness of 1000 nm.

10035] The disclosure has no special requirements on the preparation method of the substrate, and the preparation methods of the substrate familiar to technicians in this field can be used. As a specific embodiment of the disclosure, the preparation method of the substrate includes the following steps: 100 nm indium tin oxide ITO is firstly deposited on the flexible PET substrate as the electrode layer, and then a PMMA insulating layer of 1000 nm is spin coated by a spin coating method.

10036] Before magnetron sputtering, the disclosure further includes rinsing the substrate preferably; in the disclosure, the detergents for rinsing are preferably one or more of acetone, ethanol and deionized water. The disclosure has no special requirements on the rinsing way, and the rinsing ways familiar to technicians in this field can be used. The disclosure employs rinsing to remove stains on the surface of the substrate.

10037] In the disclosure, the method for applying an in-situ plasma treatment preferably includes the following steps:

10038] The inert gases and reactant gases on the surface of the substrate are ionized, to get the plasma.

10039] The disclosure preferably employs a RF source for ionization, the power of the RF source during ionization is preferably 1-2000 W independently, and the frequency of the RF source is preferably 13.56 MHz or 4 MHz.

10040] In the disclosure, the method for ionization is preferably capacitive coupling or inductive

coupling. In the disclosure, when the method for ionization is capacitive coupling, it preferably includes the following steps:

10041] The substrate is placed at the anode of the RF source, the magnetron sputtering cavity is grounded, and the RF source is initiated to ionize the inert gases and the reactant gases on the

surface of the substrate, to get the plasma.

10042] In the disclosure, when the method for ionization is inductive coupling, it preferably includes the following steps:

10043] The substrate is placed near the inductive coupling coil in the vacuum cavity, and the RF source is initiated to ionize the inert gases and the reactant gases around the substrate, to get the

plasma.

10044] In the disclosure, the magnetron sputtering is preferably DC magnetron sputtering or RF magnetron sputtering; Target materials for the magnetron sputtering are oxides of indium,

gallium and zinc; the oxides of indium, gallium and zinc are preferably ZnO, In203 and Ga20 3 ;

or preferably GaZnO and InZnO; or preferably InGaZnO.

10045] In the disclosure, when target materials for the magnetron sputtering are ZnO, In203 and

Ga2 0 3 , the magnetron sputtering is three-target co-sputtering; when target materials for the

magnetron sputtering are GaZnO and InZnO, the magnetron sputtering is two-target co

sputtering; when target material for the magnetron sputtering is InGaZnO, the magnetron

sputtering is single target sputtering.

10046] In the disclosure, before magnetron sputtering, the vacuum degree in the magnetron sputtering cavity is preferably reduced to below 5x10-6 mTorr; during the magnetron sputtering,

inert gases and reactant gases are charged into the magnetron sputtering cavity, and the vacuum

degree in magnetron sputtering is preferably 0.1-20 mTorr, more preferably 5-15mTorr. In the

disclosure, the power density applied on the surface of target materials by magnetron sputtering

is preferably 0.1~100 W/cm 2 , more preferably 10-50 W/cm 2; in the disclosure, the magnetron

sputtering time is preferably 0.1~100 min, preferably 5-50 min, more preferably 10-30 min. In

the disclosure, the thickness of the C-axis aligned crystalline IGZO thin film obtained after

magnetron sputtering is preferably 1-200 nm, preferably 50~100 nm.

10047] In the disclosure, during magnetron sputtering, the temperature of the substrate is maintained at 25-100°C, preferably 40-60°C. In the disclosure, the substrate is insulated

preferably by making the back of the substrate contact with a cold plate, wherein the back of the

substrate is the side on which IGZO thin film does not deposited. The disclosure has no special

requirements on the cold plate, and the cold plates familiar to technicians in this field can be

used. In the disclosure, the cold plate is cooled preferably by water cooling, air cooling or

semiconductor refrigeration cooling.

10048] During magnetron sputtering, the disclosure further includes rotating the surface of the substrate; the rotating speed is preferably 1~1000 rpm, more preferably 50-500 rpm. In the

disclosure, target materials for magnetron sputtering are uniformly deposited on the surface of

the substrate by rotating.

10049] In the disclosure, the schematic diagram showing the preparation of a C-axis aligned crystalline IGZO thin film at low temperature is shown in Fig. 1.

10050] An in-situ plasma assisted sputtering is employed in the disclosure, in which while the IGZO thin film is sputtered, an in-situ plasma treatment is applied onto the surface of the

deposited thin film, meanwhile the substrate is kept at a constant temperature of 25-100°C, so as

to replace the heating process at 250°C-350°C generally required for the deposition of C-axis

aligned crystalline IGZO, solving the problem of substrate damages caused by the high

temperature during the deposition when the C-axis aligned crystalline IGZO is applied on a

flexible substrate, thus allowing the application of C-axis aligned crystalline IGZO on more

inexpensive flexible substrates.

10051] The method for preparing C-axis aligned crystalline IGZO thin film at low temperature

provided in the disclosure will be illustrated in detail below in combination with the following

embodiments, but they should not be construed as the limitation to the protection scope of the

disclosure.

Embodiment 1

10052] SiO2 glass is used as the substrate base. The surface of the substrate base is treated with acetone, ethanol, and deionized water to remove stains on the surface, and an electrode layer and

an insulating layer are then deposited. The substrate is then placed into the magnetron sputtering

cavity, and the cold plate is at the back of the substrate. The cavity is evacuated to 5x10-6 mTorr,

and then charged with a mixed gas of 40 seem argon and 5 seem oxygen. After the vacuum

degree in the cavity is maintained at 5 mTorr, ZnO, In203 and Ga2 03 target materials are used for

RF magnetron sputtering, wherein the power density for sputtering is 10 W/cm2 , meanwhile the

substrate is rotated at a rate of 5 rpm to ensure the uniformity of deposition. At the same time,

the RF source is initiated to ionize argon and oxygen on the surface of the substrate to get the

plasma, wherein the power density of the RF source is 5 W/cm 2 . The cold plate at the back of the

substrate is cooled with external cold circulating water, keeping the temperature of the substrate

at 25°C. After deposition for 10 min, a C-axis aligned crystalline IGZO thin film with a

thickness of 30 nm is formed on the surface of the substrate.

10053] The resulting C-axis aligned crystalline IGZO thin film is characterized by X-ray

diffraction using an X-ray diffractometer, with the images obtained shown in Fig. 1. It can be

seen from Fig. 1 that, there is an obvious diffraction peak near 31, which is the characteristic

peak of C-axis aligned crystalline IGZO.

Embodiment 2

10054] Firstly, on a flexible PET substrate base is deposited 100 nm indium tin oxide ITO as the

gate-electrode, and then a PMMA insulating layer of 1000 nm is spin coated by a spin coating

method. The PET/ITO/PMMA thin film is placed into the in-situ plasma assisted magnetron

sputtering equipment. The magnetron sputtering cavity is then evacuated to 5x10-6 mTorr, and

then charged with a mixed gas of 40 seem argon and 5 seem oxygen. After the vacuum degree in

the cavity is maintained at 5 mTorr, GaZnO and InZnO target materials are used for RF

magnetron sputtering, wherein the sputtering power is 150 W, meanwhile the substrate is rotated

at a rate of 5 rpm to ensure the uniformity of deposition. At the same time, the plasma source is

initiated to ionize argon and oxygen on the surface of the substrate, wherein the power density of

the plasma source is 5 W/cm 2 . The substrate is cooled with external cold circulating water, keeping the temperature of the substrate at 25°C. After deposition for 10 min, a C-axis aligned crystalline IGZO thin film with a thickness of 30 nm is formed on the surface of the substrate.

10055] Source-drain electrode region is defined by photolithography. Then an aluminum electrode of 40 nm is deposited on the surface of the etched C-axis aligned crystalline IGZO thin

film by evaporation, to produce a thin film transistor with the C-axis aligned crystalline IGZO as

the channel layer. Its transfer characteristic curve is shown in Fig. 2. It can be seen from Fig. 2

that, the prepared transistor has good transfer characteristics, including a mobility of about 10

cm 2/vs, an off-state current as low as a magnitude of 10-11, as well as an on-state current at a

magnitude of 10-4.

Embodiment 3

Firstly, on a flexible polyimide (PI) substrate is deposited 100 nm fluorine-doped SnO2

conductive glass (SnO2 :F, FTO) as the gate-electrode, and then a PMMA insulating layer of

1000 nm is spin coated by a spin coating method. The PET/FTO/PMMA thin film is placed into

the in-situ plasma assisted magnetron sputtering equipment. The magnetron sputtering cavity is

then evacuated to 5x10-6 mTorr, and then charged with a mixed gas of 40 seem argon and 5 seem

oxygen. After the vacuum degree in the cavity is maintained at 5 mTorr, GaZnO and InZnO

target materials are used for RF magnetron sputtering, wherein the power density for sputtering

is 8 W/cm 2 , meanwhile the substrate is rotated at a rate of 5 rpm to ensure the uniformity of

deposition. At the same time, the plasma source is initiated to ionize argon and oxygen on the

surface of the substrate, wherein the power density of the plasma source is 5 W/cm2 . The

at 25°C. After deposition for 40 min, a C-axis aligned crystalline IGZO thin film with a

thickness of 30 nm is formed on the surface of the substrate.

10056] Source-drain electrode region is defined by photolithography. Then a molybdenum electrode of 40 nm is deposited on the surface of the etched C-axis aligned crystalline IGZO thin

the channel layer.

Embodiment 4

2 0 3 is used as the substrate base. The surface of the substrate base is treated 10057] A1 with

acetone, ethanol, and deionized water to remove stains on the surface, and an electrode layer and

and then charged with a mixed gas of 40 seem argon and 8 seem oxygen. After the vacuum

RF magnetron sputtering, wherein the sputtering power is 95 W, meanwhile the substrate is

rotated at a rate of 5 rpm to ensure the uniformity of deposition. At the same time, the RF source

is initiated to ionize argon and oxygen on the surface of the substrate to get the plasma, wherein

the power density of the RF source is 5 W/cm 2 . The cold plate at the back of the substrate is

cooled with external cold circulating water, keeping the temperature of the substrate at 25°C.

After deposition for 15 min, a C-axis aligned crystalline IGZO thin film with a thickness of 60

nm is formed on the surface of the substrate.

10058] The foregoing are only the preferred embodiments of the disclosure. It should be noted

that, several improvements and modifications can be made by those of ordinary skill in the art

without deviating from the principle of the disclosure, which are all should be covered within the

protection scope of the disclosure.

Claims

Claims WHAT IS CLAIMED IS:

1. A method for preparing C-axis aligned crystalline IGZO thin film at low temperature, comprising the following steps:

Under a mixed atmosphere of inert gases and reactant gases, target materials are magnetron

sputtered on the surface of the substrate and simultaneously an in-situ plasma treatment is

applied on the surface of the substrate, to get a C-axis aligned crystalline IGZO thin film;

The target materials for the magnetron sputtering are oxides of indium, gallium and zinc;

The temperature of the substrate is maintained at 25-100°C.

2. The method according to claim 1, wherein, the inert gases are argon and/or helium, and

the reactant gases are oxygen and/or nitrogen;

The flow rate of the inert gases is 1-1000 secm; the flow rate of the reactant gases is

1-1000 secm; in the mixed atmosphere, the concentration of the reactant gases is 0.01-20wt%.

3. The method according to claim 1, wherein, the substrate comprises, from top to bottom in

turn, an insulating layer, an electrode layer and a substrate base, and target materials are

magnetron sputtered on the surface of the insulating layer;

The insulating layer is made of one of insulating metal oxide, insulating non-metal oxide

and insulating organic material; the insulating metal oxide is A1 2 0 3 and/or HfO 2 , the insulating

non-metal oxide is one or more of SiO 2 , Si 3 N 4 and SiON, and the insulating organic material is

PMMA and/or pp-HMDSO;

The electrode layer is made of one or more of metal, metal oxide or metalnitride;

wherein, the substrate is a flexible substrate or a non-flexible substrate; when the substrate

is a flexible substrate, the substrate base is made of one or more of polyethylene, polypropylene,

polystyrene, polyethylene terephthalate and polyimide; when the substrate is a non-flexible substrate, the substrate base is made of one or more of glass, silicon oxide, aluminum oxide, silicon nitride and silicon carbide.

4. The method according to claim 1, wherein, the in-situ plasma treatment is applied by a method comprising the following steps:

The inert gases and the reactant gases on the surface of the substrate are ionized, to get the plasma;

wherein, the power of the radio-frequency (RF) source used in the ionization is 1-2000 W, and the frequency of the RF source is 13.56 MHz or 4 MHz; the method for ionization is capacitive coupling or inductive coupling.

5. The method according to claim 1, wherein, the oxides of indium, gallium and zinc are ZnO, In203 and Ga2 0 3 ;

or GaZnO and InZnO;

or InGaZnO;

wherein, the magnetron sputtering is DC magnetron sputtering or RF magnetron sputtering; the power density applied on the surface of the target materials by the magnetron sputtering is 0.1-100 W/cm 2 , the magnetron sputtering time is 0.1-100 min, and the vacuum degree is 0.1-20

mTorr;

wherein, during the magnetron sputtering, it further comprises rotating the surface of the substrate; and the rotating speed is 1-1000 rpm.

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