TWI389848B - Method for preparation of zno films - Google Patents

Description

Method for preparing zinc oxide film

The invention relates to a method for preparing a zinc oxide film, in particular to a method for preparing a zinc oxide film which has better electrical properties, is inexpensive to manufacture, and is advantageous for large-area coating, and can be mass-produced.

With the development and advancement of flat panel displays, Transparent Conducting Oxide (TCO) plays an important role. There are many ways to form TCO films, such as magnetron sputtering, thermal evaporation, pulsed laser deposition, spray pyrolysis, and sol-gel methods. However, only the magnetron sputtering method and the sol-gel method are suitable for mass production and industrialization, especially the former.

Indium Tin Oxide (ITO), which is currently produced by magnetron sputtering, is still the primary choice for transparent electrode materials for flat panel displays. However, since indium tin oxide transparent conductive films are mostly obtained by sputtering methods which are expensive to manufacture, the demand for indium tin oxide transparent conductive films for flat displays and other optoelectronic products has increased year by year, and indium tin oxide is produced in the long run. The transparent conductive film inevitably suffers from the problem that the manufacturing cost of the device is too high.

In addition, in the conventional sol-gel process, the organic substance is evaporated using a high-temperature furnace or a heating plate at a temperature of 400-700 ° C for 10-30 min, and then a plurality of high-temperature furnaces are placed and vacuumed for heat. annealing. Although the manufacturing cost of this technology is relatively low, the use of a high-temperature furnace or a heating plate requires a long process time and the quality of the film to be produced needs to be strengthened.

The main object of the present invention is to provide a method for preparing a zinc oxide film, which can make the zinc oxide film have better electrical properties, is relatively inexpensive to manufacture, and is advantageous for large-area coating, and can be mass-produced. By.

In order to achieve the above object, the present invention provides a method for preparing a zinc oxide film by first adding methanol to zinc acetate (ZnAc, Merck) and stirring it with aluminum nitrate (Al(NO ₃ ) ₂ .9H ₂ O, Merck). Aluminum doping, and finally add ethanolamine [MEA] to prepare the desired coating solution; after pickling the substrate, then rinse the substrate with deionized water, after washing, use high pressure nitrogen to dry the surface of the water, Subsequently, the preparation of the transparent conductive film is carried out; the film is placed in a heating furnace equipped with an infrared heating device for pre-heat treatment, and finally subjected to post-heat treatment under vacuum (~1 mtorr) to obtain a zinc oxide film.

Preferably, the pre-heat treatment heats the temperature of the heating furnace to 600 ° C, the time is 50 s, the temperature is 10 min, and the step is repeated 10-15 times.

Wherein, the substrate is a germanium wafer or a glass substrate, preferably Corning glass 1737.

For a more complete and clear disclosure of the technical means, objects and effects of the present invention, the following is a detailed description of the method for preparing a zinc oxide film according to the present invention, wherein the coating solution on the substrate has an absorption peak in the near-infrared band. Therefore, the substrate is subjected to heat treatment by infrared rays, so that the coating solution absorbs infrared rays to generate heat to quickly remove H ₂ O, R-PH residues and -OR, -OH groups, so that the substrate rapidly heats up. A zinc oxide film having a low sheet resistance is obtained.

Please refer to the first and second figures, which are schematic diagrams of the steps of the first and second preparation methods of the zinc oxide film of the present invention. The methanol was first stirred at room temperature, and then added with zinc acetate (ZnAc, Merck) for about 15 minutes to completely disperse until the solution was completely clear and transparent, and formulated into a 0.3 M solution and a 0.5 M solution. Aluminum nitrate (Al(NO ₃ ) ₂ .9 H ₂ O, Merck) was used as the source of aluminum doping so that the atomic ratio of Al/Zn was 1 at.%, and finally ethanolamine [MEA] was added to prepare the desired a coating solution; wherein, if it is prepared without adding ethanolamine [MEA], its pH is 6.3; when ethanolamine: zinc acetate [MEA:ZnAc] molar ratio is 1:1, pH is 7.4; when ethanolamine : Zinc acetate [MEA: ZnAc] The molar ratio is 4:1, and the pH is 10.5.

In addition, the substrate is pickled, the pickling solution is sulfuric acid plus phosphoric acid, the ratio is 1:3, heated at 75 ° C, 10 minutes, after washing, rinsed with deionized water, and finally high pressure nitrogen is used to wet the surface of the substrate. Blow dry. The coating solution was applied to the substrate by dip coating at a pulling rate of 10 cm/min and spin coating at a rotation speed of 3000 rpm for 20 s, respectively, since the gel obtained by the polymerization reaction was crystalline, The transparent film of H ₃ O, R-OH and -OR, -OH groups are contained, and the residues and organic groups are removed by heat treatment which is sufficiently dried to obtain the transparent film of zinc oxide.

The heat treatment is divided into two parts: pre-heat treatment and post-heat treatment. The pre-heat treatment is related to crystal growth and is heated in the atmosphere; the post-heat treatment is heated under vacuum. In the present invention, two heat treatment methods are used: <Process 1>: coating the substrate with a thin film After the film, pre-bake at 50 ° C for 5 minutes, pre-heat treatment to 600 ° C, 1 h, repeat this step 5 times and then post-heat treatment under vacuum (~1 mtorr). <Process 2>: After placing the film on the substrate, place it in a rapid heating furnace, heat it to 600 ° C for 50 s, constant temperature for 10 min, repeat this step 10-15 times and then under vacuum (~1 mtorr) Post heat treatment at 600 ° C for 1 h.

The Rigaku D/MAX2500 film diffractometer is used for low-grain diffraction of the polycrystalline film. The K α ray excited by the copper target is used as the incident light source (λ=1.5418A), the incident angle is 1°, and the scanning range is 30°~65°. The relationship between the X-ray diffraction broadening effect and the grain size can be expressed by the Scherrer equation [eg, equation (2)], where D is the grain size, λ is the X-ray wavelength, and β is the diffraction peak half-height, θ For the diffraction angle, K is a constant of about 0.9. The main crystal faces of zinc oxide polycrystals are known by JCPDS as (100), (002) and (101). In order to compare the difference in (002) intensity, the following formula is defined as the basis for strength judgment: D = Kλ / β cos θ (2)

When the substrate is a germanium wafer and the process 1 is used, the X-ray diffraction pattern of the solution of different pH values can be seen from the third figure, and the peak of the (002) diffraction will increase as the pH value of the solution increases. The pH value affects the peak size of the AZO (002) direction, and the higher pH value contributes to the growth of the grain in the (002) direction. From the X-ray diffraction pattern, the relative intensity of AZO(002) highest point [peak] can be calculated [see Table 1].

Please refer to the fourth figure, which is when the substrate is a germanium wafer and the process 2 is used. The X-ray diffraction pattern of the pH solution; as can be seen from the fourth figure, the addition of MEA to different pH solutions (6.3, 7.4, 10.5), in addition to making the (002) direction better, [Table 2], also let (103) The direction intensity is much larger than the (002) direction intensity, and the (002) diffraction peak will increase with the pH value of the solution. If compared with the process, the relative intensity of the (002) highest point of the process 2 is much larger than Process 1; the main reason is that the second process is to irradiate infrared rays on the substrate to rapidly heat the substrate, and the growth property of the c-axis growth is preferably oriented during the growth of the film.

The fifth picture shows the X-ray diffraction pattern using Corning Glass 1737 as the substrate and using Process 2 and different pH solutions (6.3, 7.4, 10.5); comparing the fourth and fifth figures, which are shown in Corning Glass 1737. A preferred preferred orientation is obtained with the tantalum wafer, especially at a pH of 10.5, and the substrate is selected from Corning glass 1737, and even the highest relative strength of (002) of 0.84 is obtained.

The UV-Vis-NIR (Jasco, V670) spectrometer was used to measure the light transmittance of the film, and the reflectance of the film produced by different heating methods was investigated. It is found from the experimental results that the use of the process to produce 4 or 5 layers of zinc oxide film can reveal a reflectance of 10 to 30% below the wavelength of 1000 nm, especially at a wavelength of 400 nm, as shown in the sixth figure. 6, 2, and 15 layers of zinc oxide film were prepared using Process 2, and the pH of the solution was 6.3, 7.4, and 10.5, respectively, and it was found that the reflectance was only about 1-2% below the wavelength of 1000 nm, as shown in FIG. Therefore, the difference between the deposition film of Process 1 and Process 2 can be analyzed, because the process-heating method is 10 ° C / min, which results in a disordered grain distribution and a large reflectance after the multilayer film is coated, so that the transparency is lowered. In the second aspect of the process, since the heating method is 12 ° C / s and the substrate is heated upward, The solvent such as the organic substance is quickly removed, so that the crystal grains are arranged in a uniform manner and the transmittance is better. That is, the zinc oxide film is grown by using a rapid heating furnace equipped with an infrared heating device to obtain a better film quality.

A zinc oxide doped aluminum film was fabricated on a Corning glass 1737 using a rapid heating furnace equipped with an infrared heating device. As shown in the eighth figure, all film samples at pH 6.3, 7.4 and 10.5 were transparent in the visible light range. The characteristic (the transmittance is 90% at a wavelength of 550 nm), and as the wavelength of the incident light falls to a certain range, the transmittance of the film drops sharply, which is the optical absorption limit (wavelength is about 380 nm). In terms of light absorption limit, as the number of coating layers increases, the near-ultraviolet light absorption limit has a tendency to move toward long wavelengths, but as the number of coating layers increases, it becomes closer to the wavelength at 380 nm. This phenomenon has not expanded to the visible range.

Following the Xe lamp source, the excitation wavelength was 325 nm, and the scanning band was 350 nm to 550 nm in this experiment. It is found from the experimental results that the crystal microstructure of the film has different changes after annealing at different pH values; the photoluminescence characteristics of the zinc oxide film are affected by the crystal microstructure inside the film to obtain the characteristic luminescence of different bands. As shown in the ninth figure, the photoluminescence spectrum is obtained, and it can be found that the luminescence wavelength of the zinc oxide film is about 380 nm. In terms of excitation peak intensity, the process of measuring a zinc oxide film by a fluorescence spectrometer, its peak intensity is much larger than the zinc oxide film produced by Process 2, but the peak half-height width does not narrow with the increase of strength [Please And refer to the tenth and eleventh figures and Tables 4 and 5], and there is a significant peak generation between the wavelengths of 450-500 nm, which is caused by film defects. The photo-luminescence spectrum of the luminescence spectrometer of the zinc oxide film is prepared by using the ruthenium wafer as the substrate and the ruthenium wafer as the substrate. The pH values of 7.4 and 10.5 are similar to the peak half-height and width, while the pH 6.3 peak intensity and full width at half maximum are smaller than the rest of the pH; therefore, the film quality pH values of 7.4 and 10.5 are better than the pH value of 6.3. In the eleventh figure, the photoluminescence spectrum of the zinc oxide film is made by using Corning Glass 1737 as the substrate, and the peak width at half maximum is small and the peak intensity is strong at pH 7.4. As shown in Table 5. Therefore, the use of pH 7.4 to produce zinc oxide has a better film quality, and a significant peak appears at a wavelength of 450-500 nm, indicating that the film has more lattice defects, such as zinc ion gap or oxygen vacancy.

The carrier concentration and carrier mobility of the film were analyzed using an Ecopia HMS-3000 Hall Effect Meter. In order to increase the conductivity of the film, the present invention is doped with 1 at.% aluminum and the pH is adjusted by adding MEA to understand the effect of pH on film growth and electrical properties. The experimental results show [please refer to the twelfth figure], using the solution pH values of 7.4 and 10.5 respectively, the substrate is a germanium wafer, and the process one produces a zinc oxide film, which can distinguish the pH value and the electricity by the carrier mobility. The relationship between the two, because the solution pH value of 10.5 carrier mobility is greater than the solution pH of 7.4, but the resistance value is not significantly reduced, it can be understood that the film with a pH of 10.5 has more scattering, which hinders electron transfer, so that The resistivity cannot be reduced. As for the use of the process-making method for the production of zinc oxide film, the film has a reflectance of 20-30% in the visible light and ultraviolet light range due to the excessive stretching speed (10 cm/min) and the heating method of the high-temperature furnace [refer to the sixth figure]. The film quality and relative density are deteriorated and the resistivity cannot be lowered.

It is known from the thirteenth and fourteenth figures that the second process is also used, but the AZO plating on different substrates will also give different results; among them, the thirteenth picture is selected from the silicon wafer. For the substrate, the fourteenth figure is selected from Corning Glass 1737. The use of Corning Glass 1737 as a substrate for film production has a lower resistivity due to the carrier concentration. That is, the concentration of the carrier plated on the crucible wafer is only 2.7×10 19 cm −3 and the concentration of the 1737 carrier on the Corning glass is 1.5×10 20 cm −3 , so that the resistivity is greatly reduced, and the sheet resistance is decreased from 318 Ω/□ to 64 Ω/□. Comparing the electrical properties of pH 7.4 with pH 10.5 can be seen from the fourteenth graph, and the resistivity at pH 7.4 is better than that at pH 10.5.

From the above description, it is understood that the present invention has the following advantages: (1) The present invention prepares a transparent conductive film by a sol-gel method, which has low equipment cost and low material cost compared to sputtering or other methods. The advantages.

(2) The invention has a 15 layer coating film, a solution concentration of 0.3 M, Al/Zn = 1 at.%, a pH of 7.4, a temperature of 760 ° C in the atmosphere, and a vacuum heat treatment at 600 ° C to obtain a sheet resistance of 64 Ω / □, The resistivity is 2.89×10-3 Ω. Cm, a transparent conductive film with a transmittance of more than 85%, has reached the value of making transparent electrodes for solar wafers.

In summary, the embodiments of the present invention can achieve the expected use efficiency, and the specific structure disclosed therein has not been seen in similar products, nor has it been disclosed before the application, and has completely complied with the provisions of the Patent Law. And the request, the application for the invention of a patent in accordance with the law, please forgive the review, and grant the patent, it is really sensible.

The first picture: the flow chart of the film forming technology of the dipping method and the high temperature furnace heating (process 1)

The second picture: flow chart of spin coating method and rapid heating furnace film forming process (process 2)

The third picture: the substrate is a germanium wafer, pH 7.4, 10.5, X-ray diffraction pattern of the process one, four, five layers of film

The fourth picture: the substrate is a germanium wafer, pH 6.3, 7.4, 10.5, X-ray diffraction pattern of the second, sixth, ten, and fifteen layers of the film

Figure 5: The substrate is Corning Glass 1737, pH 6.3, 7.4, 10.5, X-ray diffraction pattern of the second, sixth, ten, and fifteen layers of the film

Figure 6: Using a process 4, 5 layer film reflectivity

Figure 7: 4, 5 layer film reflectance using process 2

Figure 8: Film penetration of 6, 10, 15 layers with (MEA: ZnAc) = 1:1 and pH 7.4

The ninth picture: the substrate is a germanium wafer, the pH of the solution is 7.4, 10.5, the fluorescence spectrum, process one

Figure 10: The substrate is a germanium wafer, the pH of the solution is 6.3, 7.4, 10.5, the fluorescence spectrum, process 2

Figure 11: The substrate is Corning Glass 1737, the pH of the solution is 6.3, 7.4, 10.5, fluorescence spectrum, process 2

Twelfth picture: 0.5M, the substrate is a germanium wafer, the solution is pH 7.4 and 10.5, the carrier concentration of the sample, the carrier mobility and the resistivity, process one

Thirteenth figure: 0.3M, the substrate is a germanium wafer, the pH of the solution is 7.4, the carrier concentration of the sample, the carrier mobility and the resistivity, and the process 2

Figure 14: 0.3M, the substrate is Corning glass 1737, the pH of the solution is 7.4, 10.5, the carrier concentration of the sample, the mobility of the carrier and the resistivity, process 2

Claims (10)

A method for preparing a zinc oxide film is to first prepare a coating solution, and pickle the substrate, the acid pickling solution is sulfuric acid and phosphoric acid, the ratio is 1:3, heating at 75 ° C for 10 minutes, and then washing with deionized water. The substrate is further dried with high-pressure nitrogen gas to be coated with a transparent conductive film, and then the film is preheated in the atmosphere by infrared rays, and then subjected to vacuum (~1 mtorr). Heat treatment, so that a zinc oxide film can be obtained. The method for preparing a zinc oxide thin film according to the first aspect of the invention, wherein the coating solution is prepared by adding zinc acetate to methanol, doping with aluminum nitrate as aluminum, and finally adding ethanolamine. A method for producing a zinc oxide thin film according to the second aspect of the invention, wherein the Al/Zn atomic ratio is 1 at.%. A method for preparing a zinc oxide film according to the second aspect of the invention, wherein the coating solution has an ethanolamine:zinc acetate [MEA:ZnAc] molar ratio of 1:1, and a pH of 7.4. A method for preparing a zinc oxide film according to the second aspect of the invention, wherein the coating solution has an ethanolamine:zinc acetate [MEA:ZnAc] molar ratio of 4:1, and the pH is 10.5. The method for preparing a zinc oxide thin film according to the first aspect of the invention, wherein the coating solution is obtained by adding zinc acetate to methanol and doping with aluminum nitrate as aluminum. A method of preparing a zinc oxide thin film according to claim 6, wherein the coating solution has a pH of 6.3. The method for preparing a zinc oxide film according to the first aspect of the invention, wherein the preheating treatment is 600 ° C, 1 h, and the step is repeated 5 times. The method for preparing a zinc oxide film according to the first aspect of the invention, wherein the preheating treatment is performed by heating to 600 ° C for 50 s, constant temperature for 10 min, and repeating the step 10-15 times. A method of preparing a zinc oxide thin film according to the first aspect of the invention, wherein the post heat treatment is 600 ° C for 1 h.