CN106977179B

CN106977179B - Method for preparing high-density ITO target by two-step staged sintering method

Info

Publication number: CN106977179B
Application number: CN201710224509.8A
Authority: CN
Inventors: 许亚利; 方宏; 刘冠鹏; 崔晓芳
Original assignee: 725th Research Institute of CSIC
Current assignee: 725th Research Institute of CSIC
Priority date: 2017-04-07
Filing date: 2017-04-07
Publication date: 2021-06-04
Anticipated expiration: 2037-04-07
Also published as: CN106977179A

Abstract

A method for preparing a high-density ITO target by a two-step staged sintering method comprises the steps of preparing raw materials into a biscuit, preserving heat and degreasing the biscuit in the air atmosphere, directly heating the biscuit to 800-1300 ℃ in the air atmosphere after degreasing, preserving heat for 5-30 hours to carry out first-step presintering, placing the presintering blank on a burning plate, heating the biscuit to 1500-1600 ℃ in the oxygen atmosphere, preserving heat for 5-30 hours to carry out second-step sintering, stopping introducing oxygen 1-5 hours before sintering is finished, and then cooling the biscuit along with a furnace to obtain an ITO target sintered body. The presintering is carried out in the air atmosphere, so that the sintering time in the oxygen atmosphere can be shortened, and the production energy consumption is greatly reduced. The degreasing and presintering processes are integrated, the total sintering time is saved, particles in the blank are further homogenized by presintering, abnormal grain growth is avoided, the microscopic uniformity of the target is improved, the improvement of the strength and the thermal shock resistance is facilitated, and the density of the prepared ITO target reaches above 7.128g/cm for thin film transistor thin.

Description

Method for preparing high-density ITO target by two-step staged sintering method

Technical Field

The invention relates to a preparation method of an ITO target material, in particular to a method for preparing a high-density ITO target material by a sintering method.

Background

An ITO (Tin-doped Indium Oxide) target belongs to Indium-Tin composite Oxide ceramics, is often used as a magnetron sputtering target to prepare a transparent conductive film on a substrate material such as glass, plastic and the like, and is used for producing flat panel display equipment such as a liquid crystal display, a touch screen and the like. The ITO target material sintering methods which are published at present comprise oxygen pressure sintering, pressureless sintering, SPS sintering, hot pressure sintering, hot isostatic pressing sintering, microwave sintering and the like. Most of the sintering technologies of the ITO target have one or more problems of high sintering temperature, long sintering time, high powder treatment requirement, difficult slurry preparation, addition of a sintering aid or special equipment requirement and the like. In addition, in order to ensure the compactness of the ITO target, the target biscuit is immediately converted into an oxygen atmosphere for sintering after degreasing, and the volatilization of target components in a high-temperature environment is inhibited by utilizing the oxygen partial pressure. The oxygen atmosphere sintering needs to be carried out in an oxygen furnace, the energy consumption of the oxygen furnace is much larger than that of a common air furnace, the conventional production process consumes much energy due to the long-time oxygen atmosphere sintering, and the cost is increased along with the energy consumption.

For example, the patent application CN 102167597 a proposes a method for preparing a highly dense ITO target by pressureless multistage sintering: the density of the product is improved by controlling the oxygen partial pressure in the sintering atmosphere in a segmented manner, the degreased biscuit is sintered to 1000 ℃ under the oxygen atmosphere in a non-pressure manner, the temperature is kept for 10 hours, then the temperature is increased to 1200 ℃ and kept for 6 hours, then the temperature is increased to 1450 ℃, the temperature is kept for 4 hours, and finally the temperature is kept for 60 hours at 1600 ℃. During which the oxygen flow and the rate of temperature rise are strictly controlled. The method has the advantages of multiple sintering processes, multiple fine control of oxygen flow, long heat preservation time and high energy consumption.

CN 105669186A addition of Nb₂O₅And Bi₂O₃The sintering aid is sintered into an indium tin oxide target with high relative density and low resistivity at low temperature (1450 ℃), the resistivity of the target is still at a high level although the sintering temperature is reduced, and the method introduces new doping impurities which can have adverse effects on the coating.

CN 102491741A adds a large amount of organic monomers, cross-linking agents and other organic matters into the mixed slurry, then directly heats the degreased blank to the sintering temperature by single-step sintering, and keeps the temperature to obtain the target material. The organic matters added into the mixed slurry account for more than 15 percent of the mass of the slurry suspension, which causes great difficulty in degreasing and great pressure on the environment.

CN 102718499A is prepared by adding dispersing agent, binder, humectant, defoaming agent and other auxiliary agents and water ball grinding slurry after heat treatment of nanometer powder, and then grouting to obtain a blank. Drying and degreasing, preserving the temperature for a period of time between 1250 and 1450 ℃ in an oxygen atmosphere, and sintering at a sintering temperature of 1500 to 1650 ℃ to obtain the target material with the final density of more than 99.7 percent. The method needs to control and adjust a plurality of parameters such as the specific surface area of the nano powder, the pH value of the slurry, the viscosity and the like, and has the advantages of long drying and degreasing time of the blank, high requirements on the pulping process, difficult operation, low yield and easy generation of pinhole defects, thereby increasing the nodules in the film coating process.

CN 103232234A discloses a microwave doping sintering method, wherein additives such as ZnO, TiN, etc. are added, so that more impurities are introduced, and the coating performance of the target material is affected. And although the microwave sintering temperature is lower, the internal microstructure is not uniform due to the microwave sintering, the phenomena of deformation, cracking and the like are easily generated in the sintering process, the yield is not large due to the limitation of equipment under normal pressure, and the equipment cost is high.

Aiming at the problems in the prior art, a simple and energy-saving preparation method is needed in the sintering of large-size ITO target materials, and the final target material has uniform micro and macro structures, high density purity and high strength and can meet the film coating requirements of TFT.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, shorten the sintering time of an oxygen atmosphere and provide a method for preparing a high-density ITO target material, which has low energy consumption and is easy to operate.

The technical scheme adopted by the invention for solving the technical problems is as follows: a method for preparing a high-density ITO target by a two-step staged sintering method comprises the steps of preparing raw materials into a biscuit, preserving heat and degreasing the biscuit in the air atmosphere, directly heating the biscuit to 800-1300 ℃ in the air atmosphere after degreasing, preserving heat for 5-30 hours to carry out first-step presintering, placing the presintering blank on a burning plate, heating the biscuit to 1500-1600 ℃ in the oxygen atmosphere, preserving heat for 5-30 hours to carry out second-step sintering, stopping introducing oxygen 1-5 hours before sintering is finished, and then cooling the biscuit along with a furnace to obtain an ITO target sintered body.

Further, the heat preservation degreasing method comprises the following steps: the raw materials are made into biscuit and then are degreased in air atmosphere at 400-600 ℃ for 15-30 hours.

Further, the temperature rise rate of the first pre-sintering after degreasing is 80-120 ℃/h.

Further, after the first step of pre-sintering, the green body is firstly cooled along with the furnace, and then the second step of sintering is carried out.

Furthermore, the oxygen gas introduction flow rate of the oxygen gas atmosphere in the second sintering step is 5-60L/min, and the oxygen pressure is kept at 0.1 MPa.

Further, after the second step of sintering, the mixture is firstly cooled to 1400-1450 ℃ along with the furnace, then the temperature is preserved for 1-20 hours, and then the mixture is cooled to room temperature along with the furnace.

Further, the preparation method of the biscuit comprises the following steps: the preparation method comprises the steps of taking nanoscale indium oxide and tin oxide as raw materials, adding water, a dispersing agent and a binder, mixing, and carrying out ball milling to prepare a biscuit.

Furthermore, the dispersing agent is one of ammonium polyacrylate, ammonia water and polyethylene glycol, the addition amount is 0.8-2.0% of the weight of the raw materials, the binder is one or more of polyvinyl alcohol, polyvinyl butyral, polyethylene glycol and acrylic emulsion, and the addition amount is 1-3% of the weight of the raw materials.

Further, the slurry after mixing and ball milling is sprayed and dried to prepare granulation powder, and then the granulation powder is put into a die to be preformed under the pressure of 16-40 MPa and then is isostatic-pressed under the pressure of 250-300 MPa to prepare a biscuit.

The invention has the beneficial effects that: after degreasing, the biscuit is directly subjected to first-step presintering in an air atmosphere, and after presintering, the sintering time in an oxygen atmosphere can be shortened, so that the production energy consumption is greatly reduced. According to the above, the temperature and time of the first pre-sintering step are controlled within a reasonable range, so that the density of the ITO target is not greatly influenced, the density of the finally prepared ITO target can still reach more than 7.128g/cm and more than 99.7% of relative density (theoretical density of 7.15 g/cm) through thin film epitaxy, and the sintering time in the oxygen atmosphere can be shortened to less than 30 hours. In the method, the degreasing process and the presintering process are integrated, so that the total sintering time is saved. The pre-sintering further realizes the homogenization of the particles in the blank, avoids the abnormal grain growth, improves the microscopic uniformity of the target material, and is beneficial to the improvement of the strength and the thermal shock resistance of the target material. Degreasing and the first step of presintering are carried out in the air atmosphere, equipment and sintering environment do not need to be replaced, and the operation is convenient and can be carried out continuously. In the process, degreasing and heat preservation can be used as a preheating stage of the first pre-sintering step, so that the biscuit gradually enters a high-temperature environment, internal microcosmic components and tissues are gradually refined uniformly, and cracking is avoided. After the first-step pre-sintering, the blank has certain strength, the temperature is directly raised to the sintering temperature at a certain speed without adopting sectional control and gradual raising as in the prior art in the second-step sintering stage, and the heat-preservation sintering time is effectively shortened on the premise of ensuring the uniformity of the strength and microstructure of the target.

Detailed Description

The following examples are provided to specifically describe embodiments of the present invention.

In order to shorten the sintering time of the ITO target blank in the oxygen atmosphere, the blank is pre-sintered in the air atmosphere before the sintering in the oxygen atmosphere, the pre-sintering temperature is lower than the temperature of formal sintering, under the condition of avoiding volatilization of components as much as possible, the microcosmic components and tissues in the blank are changed, the strength is improved to a certain degree, and then the sintering is carried out in the normal-pressure oxygen atmosphere. Before the first pre-sintering, the blank is required to be heated to a certain temperature for degreasing treatment, and the heat preservation process of degreasing is also used as the preheating stage of the first pre-sintering, so that the biscuit gradually enters a high-temperature environment.

The blank can be manufactured by adopting a mould pressing or slip casting method, for example, nano-scale indium oxide and tin oxide can be used as raw materials, the raw materials are weighed according to the mass ratio of indium oxide to tin oxide =90:10, and according to the weight of raw material powder, proper amount of water, 0.8% -2.0% of dispersing agent and 1-3% of binder are added, mixed and then ball-milled uniformly, so that slurry with the mass percentage concentration of about 45-55% is prepared. The dispersant can be one of ammonium polyacrylate, ammonia water and polyethylene glycol. The binder is one or more of polyvinyl alcohol, polyvinyl butyral, polyethylene glycol and acrylic emulsion. Mixing the slurry after ball milling, carrying out spray drying to prepare granulating powder, then placing the granulating powder into a mould, preforming at the pressure of 16-40 MPa, and carrying out isostatic pressing at the pressure of 250-300 MPa to prepare a biscuit.

The prepared biscuit needs to be degreased at 400-600 ℃ under the air atmosphere by keeping the temperature for 15-30 hours, the specific time and temperature are determined according to the specific conditions such as the size of the target material, and the temperature is generally kept for 20 hours at 500 ℃. After degreasing, the temperature was raised directly to perform calcination, and the calcination was performed in the same manner as in the air atmosphere. The pre-burning and degreasing can be carried out in an air furnace, the middle part does not need to be replaced, and the temperature can be adjusted. The presintering temperature can be selected to be 800-1300 ℃ and the time is 5-30 hours, which is determined according to specific conditions. The heating rate from the degreasing temperature to the pre-sintering temperature can be selected to be 80-120 ℃/h, and is generally selected to be 100 ℃/h.

After the pre-sintering, the second step of high-temperature sintering is carried out, the sintering is carried out in an oxygen atmosphere, the temperature is about 1500-1600 ℃, the heat preservation time is determined between 5-30 hours, and the temperature rise rate has no special requirement. The sintering temperature in the second step is higher, and the green body is placed on a high-temperature-resistant and oxidation-resistant setter plate (any one of corundum, corundum-mullite and silicon carbide). The second sintering step can be carried out in an oxygen furnace, the oxygen flow is controlled to be 5-60L/min, the oxygen pressure is kept at about 0.1MPa, and the oxygen atmosphere of the second sintering step is formed. Stopping introducing oxygen 1-5 hours before the heat preservation sintering is finished, and cooling along with the furnace after the heat preservation is finished to obtain the ITO target sintered body. Preferably, after the heat preservation is carried out for a certain time at the high temperature of 1500-1600 ℃, the oxygen is stopped to be introduced, the temperature is preserved and sintered, then the furnace is cooled to 1400-1450 ℃ and then the temperature is preserved for a certain time, the specific time can be determined between 1-20 hours, and then the temperature is cooled to the room temperature. The method can properly reduce the heat preservation time of the high-temperature section of 1500-1600 ℃ and simultaneously reduce the introduction time of oxygen.

After the first step of pre-sintering and before the second step of sintering, the temperature of the green body can be reduced along with furnace cooling, and then the sintering atmosphere environment is switched. But also is beneficial to the stable structure of the blank body.

The following description will be made by way of specific examples

Example 1: weighing indium oxide with the average particle size of 200nm and tin oxide with the average diameter of 100nm according to the mass ratio of 90:10, and adding a certain amount of water to prepare slurry with the mass percentage concentration of 45%. Then adding 0.8% of dispersant ammonium polyacrylate powder by mass percentage to ball mill for 8 hours, then adding 2% of binder polyvinyl alcohol by mass percentage to ball mill for 3 hours. After ball milling is carried out uniformly, the slurry is sprayed and granulated to prepare granulation powder. Taking a proper amount of granulated powder under the pressure of 30MPa, pressing the granulated powder into a blank under a steel mould, and carrying out isostatic pressing under the pressure of 250MPa to obtain a biscuit. Degreasing the biscuit at 500 ℃ for 20h in air atmosphere, heating to 1000 ℃ at the speed of 100 ℃/h, preserving heat for 10h, and cooling along with a furnace to finish the first-step presintering. And (3) taking the prefabricated body sintered in the first step, adopting an oxygen atmosphere, selecting a corundum-mullite setter plate, sintering at 1580 ℃ for 10 hours, and controlling the oxygen flow to be 40L/min. And stopping oxygen introduction 1h before the heat preservation is finished. And naturally reducing the temperature to 1450 ℃, preserving the temperature for 5 hours, and cooling along with the furnace to obtain the final target material. The target resistivity was measured to be 1.6×10^-4Omega cm, target density of 7.141g/cm³The grain size is 4-8 microns, and the bending strength reaches 180 +/-13 MPa.

Example 2: weighing indium oxide with the average particle size of 100nm and tin oxide with the average particle size of 70nm according to the mass ratio of 90:10, adding a certain amount of water to prepare slurry with the mass percentage of 50%, adding dispersing agent ammonia water with the mass percentage of 2% of powder, carrying out ball milling for 8 hours, adding binder polyethylene glycol with the mass percentage of 1% of powder, carrying out ball milling for 2 hours, and carrying out spray granulation on the slurry to obtain granulated powder. Then taking a proper amount of granulating powder, pressing the granulating powder into a blank under the pressure of 16MPa under a steel mould, and carrying out isostatic pressing under the pressure of 300MPa to obtain a biscuit. Degreasing the biscuit at 500 ℃ for 20h in air atmosphere, heating to 1100 ℃ at the speed of 100 ℃/h, preserving the heat for 20h, and cooling along with the furnace to finish the first-step presintering. And placing the pre-sintered blank into an oxygen atmosphere sintering furnace, selecting a corundum firing bearing plate, carrying out heat preservation sintering at 1550 ℃ for 30 hours, and controlling the oxygen flow to be 30L/min. And stopping oxygen introduction 5 hours before the heat preservation is finished. And then cooling along with the furnace to obtain the final target material. The target density was found to be 7.132g/cm³Resistivity of 1.7X 10^-4Omega cm, bending strength of 146 plus or minus 15 MPa.

Example 3: indium oxide with the average particle size of 200nm and tin oxide with the average particle size of 70nm are taken, and certain water is added according to the mass ratio of 90:10 to prepare slurry with the mass percentage concentration of 50%. Adding 1.5% of dispersant ammonium polyacrylate in percentage by mass of powder, ball-milling for 10h, adding 2.5% of binder polyvinyl butyral in percentage by mass of powder, ball-milling for 3h, and then carrying out spray granulation to obtain granulated powder. And pressing the granulated powder in a 36MPa steel die to obtain a blank, and performing isostatic pressing at 280MPa to obtain the final blank. Degreasing the blank body in an air furnace at 500 ℃ for 20h, heating to 800 ℃ at the speed of 100 ℃/h, preserving heat for 30h, cooling along with the furnace, and finishing the first-step presintering. And placing the pre-sintered blank into an oxygen atmosphere sintering furnace, selecting a corundum-mullite setter plate, carrying out heat preservation sintering at 1590 ℃ for 30 hours, and controlling the oxygen flow to be 20L/min. And stopping oxygen introduction 3 hours before the heat preservation is finished. And cooling the sintered target material to 1450 ℃ along with the furnace, and then preserving the heat for 20 hours to obtain the final target material. The target density was found to be 7.145g/cm³Resistivity of 1.6X 10^-4Omega cm, bending strength of 156 +/-18 MPa.

Example 4: taking indium oxide with the average particle size of 200nm and tin oxide with the average particle size of 70nm, adding certain water according to the mass ratio of 90:10 to prepare slurry with the mass percentage of 55%, adding a dispersant polyethylene glycol with the mass percentage of 1.0% of powder, carrying out ball milling for 8 hours, then adding a binder polyvinyl butyral with the mass percentage of 1% of powder, carrying out ball milling for 2 hours, and then carrying out spray granulation and drying. And pressing the granulated powder in a 40MPa steel die to obtain a blank, and performing isostatic pressing at 280MPa to obtain the final blank. Degreasing the blank body in an air furnace at 500 ℃ for 30h, heating to 1300 ℃ at the speed of 100 ℃/h, preserving heat for 10h, cooling along with the furnace, and finishing the first-step presintering. And placing the pre-sintered blank into an oxygen atmosphere sintering furnace, selecting a corundum-mullite burning bearing plate, carrying out heat preservation sintering at 1600 ℃ for 10 hours, and controlling the oxygen flow to be 60L/min. And stopping oxygen introduction 2 hours before the heat preservation is finished. And then cooling along with the furnace to obtain the final target material. The target density was found to be 7.128g/cm³Resistivity of 2.0X 10^-4Omega cm, the strength reaches 130 +/-15 MPa.

Example 5: taking 150nm indium oxide and 80nm tin oxide, adding water according to a mass ratio of 90:10 to prepare 50% slurry, adding 0.8% of powder by mass of dispersant polyethylene glycol, ball-milling for 8 hours, adding 1% of powder by mass of binder polyethylene glycol, ball-milling for 2 hours, and then spray-granulating and drying. And pressing the granulated powder in a 40MPa steel die to obtain a blank, and performing isostatic pressing at 300MPa to obtain the final blank. Degreasing the blank body in an air furnace at 600 ℃ for 15h, heating to 1180 ℃ at the speed of 80 ℃/h, preserving heat for 5h, cooling along with the furnace, and finishing the first-step presintering. And (3) converting the pre-sintered blank into an oxygen atmosphere, carrying out heat preservation sintering at 1500 ℃ for 30h, and controlling the oxygen flow to be 20L/min. And stopping oxygen introduction 2 hours before the heat preservation and sintering are finished. And cooling the sintered target material to 1400 ℃ along with the furnace, and continuously preserving the heat for 1 hour to obtain the final target material. The target density was found to be 7.139g/cm³Resistivity of 1.7X 10^-4Omega cm, the strength reaches 148 +/-15 MPa.

Example 6: taking indium oxide with the average grain diameter of 200nm and tin oxide with the average grain diameter of 70nm, adding water according to the mass ratio of 90:10 to prepare slurry with the mass percentage of 45 percent, and adding 1.5 percent of powder according to the mass percentageBall milling is carried out on powder polyethylene glycol for 8h, then adding 1% of binder polyethylene glycol in percentage by mass of the powder, ball milling is carried out for 2h, and then spray granulation is carried out for drying. Pressing the granulated powder in a steel die with the pressure of 30MPa to form a blank, and performing isostatic pressing at the pressure of 280MPa to obtain the final blank. Degreasing the blank body in an air furnace at 400 ℃ for 18h, heating to 1000 ℃ at the speed of 120 ℃/h, preserving heat for 20h, cooling along with the furnace, and finishing the first-step presintering. And (3) converting the pre-sintered blank into an oxygen atmosphere, carrying out heat preservation sintering at 1550 ℃ for 5h, and controlling the oxygen flow to be 5L/min. And stopping oxygen introduction 1h before the heat preservation sintering is finished, cooling to 1450 ℃ along with the furnace after the sintering, and continuing to preserve heat for 10 hours to obtain the final target material. The target density was found to be 7.141g/cm³Resistivity of 1.6X 10^-4Omega cm, the strength reaches 146 plus or minus 15 MPa.

Claims

1. A method for preparing high-density ITO target material by two-step staged sintering method, which comprises the steps of preparing raw materials into biscuit, and then degreasing the biscuit in air atmosphere at 400-600 ℃ for 15-30 hours, and is characterized in that: after degreasing, directly heating to 800-1300 ℃ in air atmosphere, preserving heat for 5-30 hours, carrying out first-step presintering, cooling the presintered blank along with a furnace, then placing the cooled blank on a burning bearing plate, heating to 1500-1600 ℃ in oxygen atmosphere, preserving heat for 5-30 hours, carrying out second-step sintering, wherein the oxygen introduction flow in the oxygen atmosphere in the second-step sintering process is 5-60L/min, and keeping the oxygen pressure at 0.1 MPa; stopping introducing oxygen 1-5 hours before sintering, cooling to 1400-1450 ℃ along with the furnace after the second step of sintering, then preserving heat for 1-20 hours, and then cooling to room temperature along with the furnace to obtain the ITO target sintered body.

2. The method for preparing the high-density ITO target material by the two-step staged sintering method according to claim 1, which is characterized in that: the heating rate of the first step of pre-sintering after degreasing is 80-120 ℃/h.

3. The method for preparing the high-density ITO target material by the two-step staged sintering method according to claim 1, which is characterized in that: the preparation method comprises the steps of taking nanoscale indium oxide and tin oxide as raw materials, adding water, a dispersing agent and a binder, mixing, and carrying out ball milling to prepare a biscuit.

4. The method for preparing the high-density ITO target material by the two-step staged sintering method according to claim 3, which is characterized in that: the dispersing agent is one of ammonium polyacrylate, ammonia water and polyethylene glycol, the addition amount is 0.8-2.0% of the weight of the raw materials, the binder is one or more of polyvinyl alcohol, polyvinyl butyral, polyethylene glycol and acrylic emulsion, and the addition amount is 1-3% of the weight of the raw materials.

5. The method for preparing the high-density ITO target material by the two-step staged sintering method according to claim 3, which is characterized in that: and (3) carrying out spray drying on the slurry after mixing and ball milling to prepare granulation powder, then placing the granulation powder into a mould, preforming at the pressure of 16-40 MPa, and carrying out isostatic pressing at the pressure of 250-300 MPa to prepare a biscuit.