CN104009093B - A kind of preparation method of high k dielectric layer aqueous indium oxide film transistor - Google Patents

Abstract

The invention belongs to the technical field of semiconductor thin film transistor preparation, and relates to a method for preparing a water-based indium oxide thin film transistor with a high-k dielectric layer. Firstly, zirconium acetylacetonate is dissolved in dimethylformamide, and an equivalent molar amount of zirconium acetylacetonate is added at the same time. ethanolamine is used as a stabilizer to form a precursor solution; then the precursor solution is spin-coated on the cleaned low-resistance silicon substrate to obtain a sample, and the sample is placed under a high-pressure mercury lamp for ultraviolet light treatment to obtain a photo-annealed sample; then The sample after photoannealing is annealed to obtain a thin film sample; then the In ₂ O ₃ aqueous solution is spin-coated on the surface of the obtained thin film sample to obtain an In ₂ O ₃ channel layer; finally, the source and drain electrodes are prepared on the In ₂ O ₃ channel layer , that is, a thin film transistor is obtained; the overall implementation scheme is low in cost, simple in process, reliable in principle, good in product performance, friendly in preparation environment, and broad in application prospect, providing a feasible solution for large-area preparation of high-performance thin film transistors.

Description

A kind of preparation method of water-based indium oxide thin film transistor with high-k dielectric layer

Technical field:

The invention belongs to the technical field of semiconductor thin film transistor preparation, and relates to a method for preparing a water-based indium oxide thin film transistor with a high-k dielectric layer, in particular to a method using water-based indium oxide (In ₂ O ₃ ) as the channel layer and ultra-thin oxide A method for preparing a thin film transistor with zirconium (ZrO _x , 1<x<2) as a high-k dielectric layer.

Background technique:

In recent years, thin film transistors (Thin Film Transistor, TFT) have played an important role in active matrix liquid crystal display devices (Active Matrix Liquid Crystal Display, AMLCD). From low-temperature amorphous silicon TFT to high-temperature polysilicon TFT, the technology is becoming more and more mature, and the application object has also developed from only driving LCD (Liquid Crystal Display) to driving both LCD and OLED (Organic Light Emitting Display), and even electronic paper. With the continuous improvement of the semiconductor process level, the pixel size is continuously reduced, and the resolution of the display screen is getting higher and higher. TFT is used as a switch for driving pixels in liquid crystal displays (TFT-LCD) and other display devices. The gate dielectric material The size of the forbidden band determines the size of the leakage current, and its relative permittivity determines the size of the subthreshold swing of the device (ie, the size of energy consumption). With the development of large-scale integrated circuits, the feature size of metal-oxide-semiconductor transistors, which are the core devices of silicon-based integrated circuits, has been continuously reduced, and the law of reduction follows Moore's law. The current lithography size has reached 28nm, the equivalent oxide thickness of the CMOS gate is reduced to less than 1nm, and the thickness of the gate oxide layer is close to the atomic distance (IEEE Electron Device Lett.2004,25(6):408-410). The reduction of the equivalent oxide thickness causes the tunneling effect. Studies have shown that when the thickness of silicon dioxide (SiO ₂ ) is reduced from 3.5nm to 1.5nm, the gate leakage current increases from 10 ^-12 A/cm ² to 10A/cm ² (IEEE Electron Device Lett. 1997, 18(5):209-211). A large leakage current will cause high power consumption and corresponding heat dissipation problems, which will have a negative impact on device integration, reliability, and life. Therefore, it is urgent to develop new high-dielectric materials to replace traditional SiO ₂ . At present, high dielectric constant (high-k) gate dielectric is widely used in MOS integrated circuit technology to increase capacitance density and reduce gate leakage current. Because of its large dielectric constant, high-k materials have the same properties as SiO ₂ In the case of the equivalent gate oxide thickness (EOT), its actual thickness is much larger than that of SiO ₂ , thus solving the quantum tunneling effect of SiO ₂ due to its proximity to the physical thickness limit.

New high-k dielectric materials that have become research hotspots include ATO (Advanced Material, 24, 2945, 2012), Al ₂ O ₃ (Nature, 489, 128, 2012), ZrO ₂ (Advanced Material, 23, 971, 2011), WO ₃ (Applied Physics Letters, 102, 052905, 2013) and Ta ₂ O ₅ (Applied Physics Letters, 101, 261112, 2012), etc. TFT devices are thin-film structures, and the dielectric constant, density and thickness of the gate dielectric layer have a great influence on the performance of the transistor. Among many SiO ₂ gate dielectric substitutes, zirconia (ZrO _x ) is used as a high-k The dielectric material has good reliability, it has a large dielectric constant (20-30), a wide band gap (5.8eV) (Advanced Material, 23, 971, 2011), and is more suitable for electrons and holes. The channel barrier height (greater than 1eV), has a good lattice match with the Si surface, and is compatible with the traditional CMOS process. Therefore, ZrO _x is expected to replace traditional gate dielectric materials and become a strong candidate for a new generation of TFT high-k gate dielectric materials. Moreover, considering the new direction of the development of microelectronic devices in the future - printing electronic devices, it will be a good choice to use sol-gel technology to prepare thin films. It has been widely used in the preparation process of the compound, and it has its unique advantages: the mixing of the components in the reaction is carried out between molecules, so the particle size of the product is small and the uniformity is high; the reaction process is easy to control, and some can be obtained by other methods. Products that are difficult to obtain, and the reaction is carried out at low temperature, which avoids the appearance of high-temperature impurity phases, making the product of high purity. Therefore, the sol-gel technology is used to prepare ZrO _x high-k dielectric films, and a method of combining ultraviolet light decomposition and low temperature (300°C) thermal decomposition to decompose the organic components in ZrO _x films is proposed. The principle of ultraviolet light decomposition Yes: Use UVC (200-275nm) and UVD bands (100-200nm) of ultraviolet rays to react with oxygen in the air to generate active oxygen. Active oxygen with strong oxidative properties can react with C and N elements in the film at room temperature to form Co _x , NO _x gases are detached from the film; at the same time, the ultraviolet light decomposition method can improve the surface state of the film sample (Applied Physics Letters, 102, 192101, 2013), making the sample surface more dense and smooth, and the surface of the gate dielectric layer is less rough The degree is conducive to the migration of carriers on the surface, and improves the carrier mobility and switching response speed of TFT devices. In addition, the follow-up low-temperature pyrolysis treatment of ZrO _x thin film can effectively avoid the interlayer miscibility phenomenon caused by the low-temperature annealing (<300°C) process of the semiconductor channel layer; in the preparation process of the channel layer, distilled water is used instead of traditional organic Solution (ethylene glycol methyl ether, etc.) is used as a solvent to form a new type of aqueous solution. Compared with conventional organic solutions, aqueous solutions have the advantages of non-toxicity, environmental protection, and low cost; in addition, due to the electrostatic combination between solute cations and water molecules in aqueous solutions , Compared with the organic solution, the covalent bonding method has weaker binding energy, so the film spin-coated by the aqueous solution method has a lower decomposition temperature, and the aqueous solution technology is used to prepare high reliability, good repeatability, and low-temperature decomposition. Semiconductor thin films are becoming a technical field that is being intensively studied by industry and scientific research circles.

At present, the preparation and application technology of using amorphous oxide indium zinc oxide (IZO), indium gallium zinc oxide (IGZO), and indium oxide (In ₂ O ₃ ) materials as the channel layer of thin film transistors has been published. countries have done a lot of research. In ₂ O ₃ has become a strong candidate for semiconductor channel layer materials due to its high mobility (>100cm ² /V·s) and high transmittance (visible light>80%) (IEEE Electron Device Lett. 31, 567, 2010). Through the review of relevant patents and literature, there are few reports on the preparation of TFT channel layer by aqueous solution method, and no one has set foot in aqueous In ₂ O ₃ TFT based on ultra-thin ZrO _x high-k dielectric layer. Considering the low temperature requirements of the future "flexible display device" in the thin film preparation process, we ensure that the temperature in the TFT preparation process is lower than 300°C. The TFT device with In ₂ O ₃ /ZrO _x structure prepared by the above process not only has high carrier mobility, but also has the characteristics of high transparency (the transmittance in the visible light band is greater than 80%), and its TFT is used as the pixel of AMLCD The switch will greatly increase the aperture ratio of the active matrix, increase the brightness, and reduce power consumption; in addition, its full solution preparation process does not rely on expensive vacuum coating equipment, which further reduces the production cost. These advantages make it possible for future transparent electronic displays There is a very broad potential market in the field of devices.

Invention content:

The purpose of the present invention is to overcome the shortcomings of the prior art, to design and provide a high-k dielectric layer with ultra-thin zirconia (ZrO _x ) and water-based indium oxide (In ₂ O ₃ ) as the channel layer. The preparation method of high-performance thin-film transistors first selects low-resistance silicon as the substrate and gate electrode, and prepares an ultra-thin ZrO _x (<10nm) gate dielectric layer by combining sol-gel technology, photoannealing and low-temperature thermal annealing; Then, an aqueous solution method is used to prepare an In ₂ O ₃ semiconductor channel layer with high transmittance and high mobility at low temperature, thereby preparing a high-performance thin-film transistor whose electrical performance fully meets the requirements of the display for a thin-film transistor (TFT).

In order to achieve the above object, the present invention specifically comprises the following process steps:

(1), preparation of precursor solution: dissolving zirconium acetylacetonate Zr(C ₅ H ₇ O ₂ ) ₄ in dimethylformamide, and simultaneously adding ethanolamine in an equimolar amount to zirconium acetylacetonate as a stabilizer, zirconium The molar content [Zr ⁴⁺ ] is 0.01-0.9; the volume ratio of ethanolamine to dimethylformamide is 1:1-10; magnetically stirred at 20-100°C for 1-24 hours to form a clear and transparent precursor solution, wherein The concentration of the zirconia precursor solution is 0.01-0.5M;

(2) Preparation of thin film samples: the surface of the low-resistance silicon substrate is cleaned by plasma cleaning method, and the precursor prepared in step (1) is spin-coated on the cleaned low-resistance silicon substrate by conventional sol-gel technology Solution to get the sample, after the spin coating, put the sample under the high-pressure mercury lamp for ultraviolet light treatment to obtain the photoannealed sample, so that the sample can achieve the purpose of photolysis and curing; then the photoannealed sample is annealed at 300 ° C 1-3 hours, to avoid the interlayer mutual dissolution phenomenon caused by the low-temperature annealing process of the semiconductor channel layer, and obtain thin film samples;

(3) Preparation of In ₂ O ₃ channel layer: Dissolve indium nitrate In(NO ₃ ) ₃ in distilled water and stir at room temperature for 1-24 hours to form clear and transparent In with a concentration of 0.1-0.3mol/L ₂ O ₃ water-based solution; then use the sol-gel technique to adopt commercially available glue leveler to spin-coat In ₂ O ₃ water-based solution on the film sample surface that step (2) obtains, first under 400-600 rpm 4-8 seconds, then uniform glue at 2000-4000 rpm for 15-30 seconds, the number of spin coatings is 1-3 times, and the thickness of each spin coating is 5-10nm; put the spin-coated film sample at 120- 150°C scorching table for curing treatment, then put it into a muffle furnace for low-temperature annealing treatment at 200-300°C for _1-3 hours, and obtain an _{In 2 O 3} film with a thickness of 5-30nm, that is, In ₂ O ₃ channel layer;

(4) Preparation of source and drain electrodes: use a conventional vacuum thermal evaporation method to prepare source and drain electrodes on the In ₂ O ₃ channel layer with a stainless steel mask, and obtain a high-k dielectric layer based on ultra-thin ZrO _x Aqueous In ₂ O ₃ thin film transistors.

The plasma cleaning method involved in the step (2) of the present invention adopts oxygen or argon as the cleaning gas, its power is 20-60Watt, the cleaning time is 20-200s, and the intake of working gas is 20-50 SCCM; When preparing film samples, use a homogenizer to spin coat, first homogenize the glue at 400-600 rpm for 4-8 seconds, and then homogenize the glue at 3000-6000 rpm for 15-25 seconds; the number of spin coatings is 1-5 The film thickness of each spin coating is 4-8nm; the power of the high-pressure mercury lamp is 1-2KW, the main wavelength of ultraviolet light is 365nm, the illumination time is 20-40 minutes, and the distance between the high-pressure mercury lamp light source and the sample surface is 5-100cm .

The electrode channel aspect ratio of the thin film transistor prepared by the step (4) of the present invention is 1:4-20, and the thermal evaporation current is 30-50A; The source and drain electrodes prepared are metal Al or Au electrodes, and the electrode thickness is 50-50A. 200nm.

Compared with the prior art, the present invention has the following advantages: First, the semiconductor channel layer and the high-k dielectric layer in the thin film transistor are prepared by chemical solution method, the chemical solution system is very cheap, and the preparation process does not require high vacuum The environment can be carried out in the air to reduce the cost; the reaction can be carried out at low temperature, which can reduce the cost and avoid the appearance of high-temperature impurity phases; the second is to use plasma to clean the substrate surface and increase the precursor solution during spin coating. The adhesion of the substrate makes the surface of the spin-coated thin film sample more uniform and flat; the third is to use a combination of ultraviolet light annealing and low-temperature thermal annealing to obtain a dense and new type of new gate dielectric material ZrO _x , avoiding the traditional sol- The requirement of high temperature (>500°C) for the gel film forming process enables the prepared ZrO _x dielectric layer to be prepared on a plastic substrate, laying an important foundation for the application of flexible and transparent display devices; the fourth is that the prepared ZrO _x The physical thickness of the high-k gate dielectric layer is only 10nm, and at the same time, the low leakage current well meets the requirements of microelectronics integration for device size; the ZrO _x film itself has high transmittance (visible light band is close to 90%) , in line with the requirements of transparent electronic devices for the material itself; the prepared ZrO _x thin film is amorphous, which can realize large-area industrial preparation; fifth, the semiconductor channel layer in the thin film transistor is prepared by an aqueous solution method. Using distilled water as a solvent has the advantages of non-toxicity and environmental protection compared with traditional organic solvents; at the same time, the aqueous solution does not require high environmental humidity, so the preparation cost is further reduced; finally, because distilled water is not corrosive, when dropped on the ZrO _x grid When it is on the dielectric layer, it will not erode the ZrO _x surface, so it is beneficial to form a clearer interface, which is very important for the high-performance electrical properties of TFT devices; the sixth is that the use of aqueous solutions to prepare In ₂ O ₃ semiconductor films has high The transmittance (more than 80% in the visible light band) meets the requirements of transparent electronic devices; at the same time, its low-temperature (<300°C) preparation conditions are compatible with the low-temperature manufacturing technology required by flat panel display technology; its overall implementation cost is low, and the process is simple. The principle is reliable, the product performance is good, the preparation environment is friendly, and the application prospect is broad, which provides a feasible solution for the large-area preparation of high-performance thin film transistors.

Description of drawings:

Fig. 1 is a schematic diagram of the structure and principle of the aqueous In ₂ O ₃ thin film transistor based on the ZrO _x high-k dielectric layer prepared by the present invention.

Fig. 2 is the output characteristic curve of the thin film transistor prepared by the present invention at different In ₂ O ₃ annealing temperatures, wherein the gate bias voltage V _GS = 1.5V, the In ₂ O ₃ annealing temperature of curve a is 200°C; curve b The annealing temperature of In ₂ O ₃ in curve c is 230°C; the annealing temperature of In ₂ O ₃ in curve c is In ₂ O ₃ -250°C; the annealing temperature of In ₂ O ₃ in curve d is In ₂ O ₃ -270°C.

Fig. 3 is the transition characteristic curve of the thin film transistor prepared by the present invention at different In ₂ O ₃ annealing temperatures, wherein the source-drain voltage V _DS =1.0V, the In ₂ O ₃ annealing temperature of curve a is 200°C; The annealing temperature of In ₂ O ₃ is 230°C; the annealing temperature of In ₂ O ₃ in curve c is In ₂ O ₃ -250°C; the annealing temperature of In ₂ O ₃ in curve d is In ₂ O ₃ -270°C.

detailed description:

The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

Example:

The zirconium acetylacetonate and indium nitrate powders, dimethylformamide, and ethanolamine organic solvents in this example were all purchased from Aladdin Company, and the purity was greater than 98%; the bottom gate structure was ultra-thin zirconia (ZrO _x ) The preparation process of the dielectric layer and the thin film transistor with the water-based indium oxide (In ₂ O ₃ ) film as the channel layer is as follows:

(1) First use sol-gel technology to prepare ultra-thin ZrO _x high-k dielectric film:

Step 1: Select commercially purchased single-sided polished low-resistance silicon as the substrate (ρ<0.0015Ω·cm) and the gate electrode, and the low-resistance silicon substrate is ultrasonically cleaned with hydrofluoric acid, acetone, and alcohol for 10 minutes each. After repeated washing with deionized water, blow dry with high-purity nitrogen;

Step 2: Prepare a mixed solution of dimethylformamide and ethanolamine at a molar ratio of 2:1, dissolve zirconium acetylacetonate at 0.1M in the mixed solution, weigh 10 mL of the mixed solution, and weigh 0.48 g of zirconium acetylacetonate, After mixing, stir in a water bath at 70°C for 3 hours under the action of magnetic stirring to form a clear and transparent precursor liquid;

Step 3: Put the clean low-resistance silicon substrate into the plasma cleaning chamber. After the chamber is pumped to 0.5Pa, inject high-purity (99.99%) oxygen, control its power to 30Watt, and clean it for 120s. The inflow of oxygen is 30SCCM;

Step 4: Prepare ZrO _x samples: Spin-coat the precursor solution prepared in step 2 on the cleaned low-resistance silicon substrate, the number of spin coatings is 1 to 5 times, and the parameters of the homogenizer when spin-coating the precursor solution The setting is: first spread the glue at 500 rpm for 5 seconds, and then spread the glue at 5000 rpm for 25 seconds; after the spin coating is completed, put the sample under a high-pressure mercury lamp for UV curing treatment, and the power of the high-pressure mercury lamp is 1KW , the main wavelengths are UVC and UVD, the ultraviolet exposure time is 30 minutes, the mercury lamp light source is 10cm away from the sample surface, and the cured ZrO _x sample is placed in a muffle furnace for low-temperature annealing treatment, the annealing temperature is 300 ° C, and the annealing time is 1 Hour, obtain ZrO _x sample;

(2) Preparation of In ₂ O ₃ channel layer by spin coating with In ₂ O ₃ aqueous solution:

Step 1: Dissolve indium nitrate powder in distilled water with an indium ion concentration of 0.1M; in this experiment, weigh 10mL of distilled water, weigh 0.3g of indium nitrate, mix and stir at room temperature for 12 hours under the action of magnetic stirring to form Clear and transparent In ₂ O ₃ aqueous solution;

Step 2: prepare In ₂ O ₃ channel layer: the In ₂ O ₃ aqueous solution of preparation in step 1 is spin-coated on the ZrO _x sample that has been processed, and the parameter setting of homogenizer during spin-coating is: first at 500 rpm Homogenize the glue for 5 seconds, then homogenize the glue at 3000 rpm for 25 seconds. After the spin coating is completed, put the sample into the muffle furnace for low-temperature annealing treatment. Hour;

(3) Preparation of source and drain metal electrodes by vacuum thermal evaporation method:

By means of thermal evaporation, a 100nm-thick metal Al was prepared on the In ₂ O ₃ channel layer with a stainless steel mask with a width-to-length ratio of 1000/100 μm as the source and drain electrodes. The thermal evaporation current was 40A, and the Al/ Thin film transistors with In ₂ O ₃ /ZrO _x /Si structure;

(4) Test the thin film transistor of the Al/In ₂ O ₃ /ZrO _x /Si structure (Fig. 1); the output characteristic curve of the thin film transistor under different In ₂ O ₃ annealing temperature conditions uses Keithley 2634B semiconductor source Table test (Figure 2); the corresponding transfer characteristic curve (Figure 3) of the prepared thin film transistor is also obtained by Keithley 2634B semiconductor source meter test, in which In ₂ O ₃ annealed at 200, 230, 250, 270 °C is used as the channel The transfer characteristic curves of the channel layer TFT correspond to a, b, c, and d in Fig. 3 respectively.

Claims (3)

1. a preparation method for high k dielectric layer aqueous indium oxide film transistor, its feature It is to specifically include following processing step:

(1), the preparation of precursor solution: by acetylacetone,2,4-pentanedione zirconium Zr (C₅H₇O₂)₄It is dissolved in dimethyl In Methanamide, it is simultaneously introduced ethanolamine with acetylacetone,2,4-pentanedione zirconium equimolar amounts as stabilizer, At 20-100 DEG C, magnetic agitation 1-24 hour forms the precursor solution of clear, wherein oxygen Changing zirconium precursor liquid solution concentration is 0.01-0.5M, zirconium Zr⁴⁺Molar content be 0.01-0.9； Ethanolamine is 1:(1-10 with the volume ratio of dimethylformamide)；

(2), the preparation of film sample: using plasma cleaning method cleans low-resistance silicon substrate Surface, low-resistance silicon substrate after cleaning uses the sol-gel technique spin-coating step of routine (1) precursor solution prepared obtains sample, after spin coating terminates, sample is put into high-pressure mercury Carry out ultraviolet lighting under lamp and process the sample after obtaining photo-annealing, it is achieved the photodissociation of sample is with solid Change；The sample after photo-annealing is carried out 300 DEG C of process annealings 1-3 hour again, it is to avoid quasiconductor The interlayer that channel layer process annealing process is brought dissolves each other phenomenon, obtains ZrO_xFilm sample；

(3)、In₂O₃The preparation of channel layer: by indium nitrate In (NO₃)₃It is dissolved in distilled water, It is stirred at room temperature the In that concentration is 0.1-0.3mol/L forming clear for 1-24 hour₂O₃ Aqueous solution；Then the ZrO obtained in step (2)_xFilm sample surface utilizes sol-gel Technology uses commercially available sol evenning machine spin coating In₂O₃Aqueous solution, the evenest under 400-600 rev/min The glue 4-8 second, then 2000-4000 rev/min of lower spin coating 15-30 second, spin coating number of times is 1-3 Secondary, each spin coating thickness 5-10nm；By the ZrO after spin coating_xFilm sample is put into 120-150 DEG C Burned carry out cured after put into and Muffle furnace carries out 200-300 DEG C of process annealing process 1-3 hour, prepare In₂O₃Thickness is the In of 5-30nm₂O₃Thin film, i.e. prepares In₂O₃ Channel layer；

(4), the preparation of source, drain electrode: utilize conventional Vacuum sublimation to utilize rustless steel Mask plate is at In₂O₃Channel layer source prepared above, drain electrode, i.e. obtain based on ZrO_xHigh k is situated between Aqueous In of electric layer₂O₃Thin film transistor (TFT).

High k dielectric layer aqueous indium oxide film transistor the most according to claim 1 Preparation method, it is characterised in that the plasma clean method related in step (2) uses oxygen Or argon is as purge gas, its power is 20-60Watt, and scavenging period is 20-200s, The intake of working gas is 20-50SCCM；Sol evenning machine spin coating is used when preparing film sample, First 400-600 rev/min of lower spin coating 4-8 second, then at 3000-6000 rev/min of lower spin coating 15-25 Second；Spin coating number of times is 1-5 time, and the film thickness of each spin coating is 4-8nm；High voltage mercury lamp Power be 1-2KW, the dominant wavelength of ultraviolet light is 365nm, and light application time is that 20-40 divides Clock, high voltage mercury lamp light source distance sample surfaces 5-100cm.

High k dielectric layer aqueous indium oxide film transistor the most according to claim 1 Preparation method, it is characterised in that the electrode raceway groove length and width of thin film transistor (TFT) prepared by step (4) Ratio is 1:(4-20), thermal evaporation electric current is 30-50A；Prepare source, leak electricity extremely metal Al or Au electrode, thickness of electrode is 50-200nm.