Method for detecting indium, gallium and zinc in glass substrate indium gallium zinc oxide film

Abstract

This invention relates to the field of thin film material analysis and testing technology, and provides a method for detecting indium, gallium, and zinc in glass-based indium gallium zinc oxide (IGZO) thin films. It utilizes the rapid dissolution characteristics of IGZO oxide films in warm aqua regia, and the kinetic difference between this and the extremely low dissolution rate (<0.1 mg / cm²·h) of the glass substrate at 90℃–110℃. By controlling the digestion time (20–40 min), the method ensures complete dissolution of the IGZO film while keeping the amount of Si introduced into the glass substrate within an acceptable range (typically <5 mg / L), without affecting the accurate determination of In, Ga, and Zn. The open digestion using a room-temperature hot plate is conducted under normal pressure and low temperature conditions, keeping the glass substrate intact and preventing excessive dissolution and cracking. This method is particularly suitable for online testing and factory inspection of commercial IGZO thin film products using soda-lime glass, alkali-free glass, or high-strain-point glass as substrates.

Description

Technical Field

[0001] This invention relates to the field of thin film material analysis and testing technology, and in particular to a method for detecting indium, gallium, and zinc in glass-based indium gallium zinc oxide thin films. Background Technology

[0002] IGZO (In-Ga-Zn-O) thin film is an amorphous oxide semiconductor thin film composed of indium (In), gallium (Ga), zinc (Zn), and oxygen (O). It is the core material of the channel layer in thin-film transistors (TFTs) and is widely used in the driving circuits of TFT-LCD and OLED display panels. In actual production, IGZO thin films are deposited on glass substrates (such as soda lime glass, alkali-free borosilicate glass, and high strain point glass) using magnetron sputtering. Precise control of the stoichiometry of the IGZO thin film directly determines the electrical performance of the TFT device. Deviations in sputtering process parameters (such as oxygen partial pressure, substrate temperature, and power) can cause the film composition to deviate from the design values, leading to failure problems such as decreased electron mobility, threshold voltage drift, and increased leakage current. Therefore, accurate quantitative analysis of the main elements in the finished IGZO thin film on the glass substrate is a crucial step in thin film process quality control and product inspection before shipment.

[0003] Compared with IGZO target or powder samples, glass-substrate IGZO thin film samples have the following unique characteristics:

[0004] (1) Extremely small sample size: The thickness of a typical IGZO film is 30 nm to 200 nm, and the mass of the film on a 10 cm × 10 cm glass substrate is only tens to hundreds of micrograms, which is far lower than the sample weight for conventional analysis.

[0005] (2) Complex interference from glass substrate: IGZO thin films are deposited on glass substrates. Glass (with SiO2 content usually >70%, and also contains network modifiers and external oxides such as Na2O, CaO, Al2O3, and MgO) can slowly dissolve under acidic conditions. The dissolved Si, Na, Ca, Al and other elements may cause spectral interference or matrix effects on the determination of In, Ga and Zn by ICP-AES.

[0006] (3) High dissolution selectivity: An ideal dissolution method should be able to completely dissolve the IGZO oxide layer in the film while maintaining the integrity of the glass substrate to the maximum extent and avoiding matrix interference caused by the dissolution of a large amount of substrate.

[0007] Existing methods for analyzing the composition of IGZO thin films on glass substrates have the following limitations:

[0008] (1) X-ray photoelectron spectroscopy (XPS): It can only analyze the composition of the very shallow layer (within about 5 nm) of the film surface, and the quantitative accuracy of stoichiometry is limited by the scarcity of standard materials, and cannot provide absolute content data of the whole film.

[0009] (2) Rutherford backscattering spectroscopy (RBS): The equipment is expensive and the analysis cycle is long, making it unsuitable for routine quality control.

[0010] (3) X-ray fluorescence spectroscopy (XRF): The signal is extremely weak for ultrathin films, and the absorption enhancement effect of glass substrate (light substrate) on In and Ga is difficult to be accurately corrected, resulting in insufficient accuracy;

[0011] (4) Microwave digestion-ICP method: The microwave digestion system has a high heating temperature (>180℃). Under sealed high pressure conditions, the glass substrate (SiO2 content>70%) will dissolve in large quantities, resulting in high concentration of Si matrix interference, which seriously affects the accurate determination of In, Ga and Zn. At the same time, for ultrathin film samples, the integrity of the sample is difficult to guarantee in the sealed high pressure environment, and there is a risk of loss.

[0012] (5) Acid dissolution at room temperature (shaking at room temperature): At room temperature and pressure, the HCl / HNO3 mixed acid dissolves the IGZO film slowly. If the dissolution time is too long (several hours), the slow erosion of the glass substrate is inevitable, resulting in the introduction of a large amount of substrate elements such as Si, Na, and Ca.

[0013] In summary, existing technologies cannot simultaneously meet the comprehensive requirements of complete dissolution of IGZO thin film samples on glass substrates, suppression of substrate interference, and analytical efficiency. Therefore, developing a simple, efficient, and accurate main element detection method specifically for IGZO thin films on glass substrates has significant application value. Summary of the Invention

[0014] In view of this, the purpose of this invention is to provide a method for detecting indium, gallium, and zinc in glass-based indium gallium zinc oxide thin films, thereby solving the problems in the prior art.

[0015] To achieve the above objectives, the present invention provides a method for detecting indium, gallium, and zinc in an indium gallium zinc oxide thin film on a glass substrate, characterized by comprising the following steps:

[0016] Step 1, Thin film sample preparation: First, measure the effective size of the thin film, then weigh the sample, and finally place the sample in a clean 100 mL polytetrafluoroethylene (PTFE) digestion cup with the thin film side facing up.

[0017] Step 2: Digestion on a hot plate at room temperature: First, add acid to the digestion vessel, then let it stand for pretreatment, then place the digestion vessel on a hot plate for heating and digestion, then evaporate and concentrate, and finally make up to a fixed volume;

[0018] Step 3: Online addition of internal standard solution: Prepare a 1.0 mg / L rhodium internal standard working solution using 2% HNO3 as the matrix. Add the internal standard working solution to the test solution to make the concentration of Rh in the final injection solution 0.1 mg / L.

[0019] Step 4: Preparation of standard working curve: Using 1000 mg / L certified standard solutions of indium, gallium and zinc, GBW(E) series as stock solution, prepare mixed standard solution with 2% HNO3. Rh internal standard is added to the standard solution simultaneously to a concentration of 0.1 mg / L. 2% HNO3 solution is used as matrix, and the acidity is consistent with the solution to be tested.

[0020] Step 5, ICP-AES determination: The determination was performed using an inductively coupled plasma atomic emission spectrometer;

[0021] Step Six: Data Processing and Result Calculation

[0022] (1) Establish a linear regression working curve with the intensity ratio of each element to the internal standard Rh as the ordinate and the corresponding standard solution concentration as the abscissa. The required Rh value is... 2 ≥0.9999;

[0023] (2) Subtracting the glass substrate blank: ci(net) = ci(measured) − ci(blank)

[0024] (3) Calculate the area content (μg / cm²) of each element in the thin film:

[0025] ρi(μg / cm2)=ci(net)×V / A

[0026] Where: ci is the net concentration (μg / mL), V is the volume of the film (mL), and A is the film area (cm²).

[0027] (4) Calculate the oxide molar ratio:

[0028] .

[0029] Preferably, step one specifically includes: (1) Measuring the effective size of the film: using a vernier caliper to accurately measure the size of the glass substrate on which the IGZO film is deposited, and calculating the effective area A (cm²) of the film.

[0030] (2) Sample weighing: The mass of the sample with film and the pure glass substrate without film were weighed separately using a microbalance with an accuracy of 0.01 mg. The difference is the mass of the film.

[0031] (3) Place the sample in a clean 100 mL polytetrafluoroethylene digestion cup with the membrane side facing up. Avoid touching the membrane surface with your fingers or metal tools during the operation to prevent contamination.

[0032] Preferably, step two specifically includes: (1) adding acid: slowly adding 5 mL of hydrochloric acid along the edge of the glass substrate into the digestion cup. The hydrochloric acid is of analytical grade and has a density of ρ=1.18 g / mL. Then add 2 mL of nitric acid. The nitric acid is of analytical grade and has a density of ρ=1.40 g / mL. The total acid volume is 7 mL. The ratio of hydrochloric acid to nitric acid is approximately 2.5:1, so that the surface of the mixed acid solution covers the surface of the substrate film.

[0033] (2) Standing pretreatment: Let stand at room temperature for 5 min to 10 min and observe whether bubbles or color changes appear on the surface of the film. If the reaction is violent, wait until the reaction is stable before heating.

[0034] (3) Digestion by heating with an electric hot plate: Place the digestion cup on the electric hot plate, set the temperature to 90℃~110℃, and heat for 20min~40min; observe the state of the film surface every 5min during the digestion process, and judge according to the following criteria:

[0035] During digestion: the film changes from translucent to transparent, and the digestion front can be seen gradually shrinking towards the center;

[0036] Digestion complete: The film color has completely disappeared visually, the glass substrate surface is smooth and transparent, and the digestion solution is pale yellow to colorless and transparent.

[0037] For glass substrate samples, once the film digestion is confirmed to be complete, the digestion cup should be transferred and cooled immediately to avoid prolonged immersion of the glass substrate in hot acid, which could lead to the leaching of large amounts of Si, Na, and Ca.

[0038] Preferably, in step four, the following series of mixed standard solutions are prepared using 2% HNO3 solution;

[0039] .

[0040] Preferably, the parameters measured in step five are: radio frequency power 1200 W, plasma gas (Ar) flow rate 15 L / min, auxiliary gas flow rate 0.3 L / min, nebulizing gas flow rate 0.65 L / min, peristaltic pump injection rate 1.5 mL / min, integration time 10 s, and the average value of three measurements.

[0041] Preferably, in a blank experiment with a glass substrate of the same specification and batch without a thin film, the measured values ​​of indium, gallium, and zinc should all be lower than 10 ng / mL.

[0042] Preferably, two glass substrate thin film samples of the same size and prepared by the same process from the same batch are digested and measured independently, and the relative deviation of each element does not exceed 3%; the digested thin film sample solution is then mixed with known amounts of In, Ga, and Zn standards and measured again, and the recovery rate of each element should be in the range of 90% to 110%.

[0043] Preferably, two glass substrate thin film samples of the same size and prepared by the same process from the same batch are independently digested and measured, and the relative deviation of each element does not exceed 3%.

[0044] Preferably, after digestion, the glass substrate surface should be visually inspected to ensure there are no residual IGZO traces or green / blue spots. If necessary, it should be confirmed under a microscope at 10x magnification.

[0045] The beneficial effects of this invention are:

[0046] Selective dissolution of thin films is achieved through open digestion with an electric heating plate: This invention utilizes the rapid dissolution characteristics of IGZO oxide thin films in warm aqua regia and the kinetic difference between the rapid dissolution of IGZO oxide thin films and the extremely low dissolution rate (<0.1 mg / cm²·h) of glass substrates at 90℃~110℃. By controlling the digestion time (20~40 min), the amount of Si introduced into the glass substrate is controlled within an acceptable range (usually <5 mg / L) while ensuring complete dissolution of the IGZO thin film, without affecting the accurate determination of In, Ga, and Zn.

[0047] Open-type digestion avoids damage to the glass substrate caused by microwave sealed systems: Compared with microwave sealed digestion (>180℃, high pressure), room-temperature hot plate open-type digestion is carried out under normal pressure and low temperature conditions, keeping the glass substrate intact and preventing extensive dissolution and cracking. It is especially suitable for online testing and factory inspection of commercial IGZO thin film products (such as TFT panel diced wafers) with soda lime glass, alkali-free glass, or high strain point glass as substrates.

[0048] Highly sensitive ICP-AES detection with ultra-low sample volume: The mass of IGZO thin films is only tens of micrograms, and after being dissolved in 25 mL of solution, the concentrations of each element are low (typically In is 1–50 mg / L, Ga is 0.1–10 mg / L, and Zn is 0.2–20 mg / L). ICP-AES detection sensitivity can reach the mg / L level, effectively covering the analytical concentration range of ultra-thin film samples.

[0049] Rh internal standard effectively compensates for matrix differences introduced by glass substrate digestion: The matrix composition of the solution after digestion of different batches of glass substrate samples may vary slightly due to the type of glass (soda lime, borosilicate, etc.) and degree of dissolution. Online correction of Rh internal standard can eliminate signal fluctuations caused by matrix ionization interference, making the batch repeatability RSD better than 3%.

[0050] The method is simple to operate and has low equipment requirements: This invention only requires conventional laboratory equipment such as hot plates and PTFE beakers, without the need for microwave digestion systems or expensive surface analysis instruments, which lowers the barrier to entry for the method and makes it suitable for routine component analysis of glass substrate IGZO thin film products by various testing institutions and panel manufacturers. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0052] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0053] Example 1: Major element detection of IGZO thin films on soda lime glass substrate

[0054] Sample: IGZO thin film for TFT panel, deposited on soda lime glass substrate, film thickness approximately 100 nm, substrate size 5.0 cm × 5.0 cm;

[0055] operate:

[0056] The effective area of ​​the film is A = 25.0 cm²;

[0057] Add acid: 5 mL HCl + 2 mL HNO3, let stand at room temperature for 5 min, then heat on a hot plate at 100℃;

[0058] Digestion time: approximately 25 minutes, until the film color disappears and the solution becomes clear;

[0059] Once digestion is complete, immediately transfer the digestion vessel to cool it down.

[0060] Evaporate and concentrate to approximately 0.5 mL, then bring the volume up to 25 mL.

[0061] The measurement results are shown in the table below:

[0062] .

[0063] Substrate blank confirmation: After the same digestion, the soda lime glass substrates of the same specification and batch without thin film had In<0.01 mg / L, Ga<0.005 mg / L, and Zn<0.01 mg / L, and the influence of the substrate was negligible.

[0064] Molar ratio calculation:

[0065] ;

[0066] Normalized (with Ga2O3 as 1): n(In2O3):n(Ga2O3):n(ZnO) = 2.35:1.00:4.09.

[0067] (Actual values ​​may vary depending on process conditions; this is just an example.)

[0068] Spike recovery: Add In 2.0 mg / L, Ga 0.5 mg / L, and Zn 1.0 mg / L to the digestion solution.

[0069] In: 102.3%; Ga: 98.7%; Zn: 101.5%; all within the range of 90% to 110%, indicating the method is reliable.

[0070] Example 2: Major element detection of IGZO thin films on alkali-free glass, i.e., borosilicate substrates.

[0071] Sample: IGZO thin film for OLED panels, deposited on an alkali-free glass (Corning Eagle XG) substrate, with a film thickness of approximately 50 nm and a substrate size of 3.0 cm × 3.0 cm;

[0072] operate:

[0073] The effective area of ​​the film is A = 9.0 cm²;

[0074] Add acid: 4 mL HCl + 1 mL HNO3, let stand at room temperature for 5 min, then heat on a hot plate at 90°C;

[0075] Digestion time: approximately 20 minutes, until the film color disappears and the solution becomes clear;

[0076] Once digestion is complete, immediately transfer the digestion vessel to cool it down.

[0077] Evaporate and concentrate to approximately 0.3 mL, then bring the volume to 25 mL.

[0078] The measurement results are shown in the table below:

[0079] .

[0080] Substrate blank confirmation: After the same digestion process, the EAGLE XG glass of the same batch without thin film showed In < 0.005 mg / L, Ga < 0.003 mg / L, and Zn < 0.005 mg / L. The Si leaching amount of alkali-free glass is lower than that of soda lime glass, and the impact on the substrate is smaller.

[0081] Molar ratio calculation:

[0082] ;

[0083] Parallel measurement verification:

[0084]

[0085] The results of parallel measurements were stable, with RSDs all well below 3%.

[0086] Example 3: Glass substrate digestion time control experiment

[0087] Objective: To verify the effect of different digestion times on the degree of dissolution of soda lime glass substrate and the determination results of In, Ga, and Zn under the conditions of 90℃ to 110℃, and to determine the optimal digestion time window.

[0088] Procedure: Take a 5 cm × 5 cm thin-film soda lime glass slide and digest it in a 5 mL HCl + 2 mL HNO3 system for 20 min, 40 min, and 60 min respectively, and determine the Si, Na, and Ca contents in the solution; take another glass slide of the same specification containing an IGZO thin film, digest it under the same conditions and determine the In, Ga, and Zn contents, and examine the degree of interference of substrate dissolution on the elements to be measured.

[0089] Substrate dissolution data:

[0090]

[0091] Verification of the effect on the determination of In, Ga, and Zn:

[0092]

[0093] in conclusion:

[0094] (1) When the digestion time is no more than 40 min, the Si introduced by the dissolution of the glass substrate is less than 4 mg / L, and Na and Ca are both less than 1 mg / L. It has been confirmed that it does not affect the accuracy of the determination of In (230.606 nm), Ga (294.364 nm) and Zn (213.857 nm), and the spiked recovery rate is in the range of 95% to 105%.

[0095] (2) When the digestion time exceeds 60 min, the Si concentration increases significantly to 5.73 mg / L, which may cause slight spectral interference of Ga (294.364 nm). At the same time, the recovery rates of Ga and Zn show a low trend, which should be avoided.

[0096] (3) Therefore, the recommended digestion time window for glass substrate IGZO film is 20 min to 40 min, with the best being around 30 min, to suppress substrate interference to the maximum extent while ensuring complete dissolution of the film.

[0097] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and many other variations of different aspects of the invention as described above exist, which are not provided in detail for the sake of brevity. Any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A method for detecting indium, gallium, and zinc in a glass-based indium gallium zinc oxide thin film, characterized in that, It includes the following steps: Step 1, Thin film sample preparation: First, measure the effective size of the thin film, then weigh the sample, and finally place the sample in a clean 100 mL polytetrafluoroethylene (PTFE) digestion cup with the thin film side facing up. Step 2: Digestion on a hot plate at room temperature: First, add acid to the digestion vessel, then let it stand for pretreatment, then place the digestion vessel on a hot plate for heating and digestion, then evaporate and concentrate, and finally make up to a fixed volume; Step 3: Online addition of internal standard solution: Prepare a 1.0 mg / L rhodium internal standard working solution using 2% HNO3 as the matrix. Add the internal standard working solution to the test solution to make the concentration of Rh in the final injection solution 0.1 mg / L. Step 4: Preparation of standard working curve: Using 1000 mg / L certified standard solutions of indium, gallium and zinc, GBW(E) series as stock solution, prepare mixed standard solution with 2% HNO3. Rh internal standard is added to the standard solution simultaneously to a concentration of 0.1 mg / L. 2% HNO3 solution is used as matrix, and the acidity is consistent with the solution to be tested. Step 5, ICP-AES determination: The determination was performed using an inductively coupled plasma atomic emission spectrometer; Step Six: Data Processing and Result Calculation (1) Establish a linear regression working curve with the intensity ratio of each element to the internal standard Rh as the ordinate and the corresponding standard solution concentration as the abscissa, requiring R²≥0.9999; (2) Subtracting the blank from the glass substrate: ci(net) = ci(measured) - ci(blank) (3) Calculate the area content (μg / cm²) of each element in the thin film: ρi(μg / cm2)=ci(net)×V / A Where: ci is the net concentration (μg / mL), V is the volume of the film (mL), and A is the film area (cm²). (4) Calculate the oxide molar ratio: 。 2. The method for detecting indium, gallium, and zinc in a glass-based indium gallium zinc oxide thin film according to claim 1, characterized in that, The first step is specifically: (1) Measure the effective size of the film: Use a vernier caliper to accurately measure the size of the glass substrate on which the IGZO film is deposited, and calculate the effective area A (cm²) of the film. (2) Sample weighing: The mass of the sample with film and the pure glass substrate without film were weighed separately using a microbalance with an accuracy of 0.01 mg. The difference is the mass of the film. (3) Place the sample in a clean 100 mL polytetrafluoroethylene digestion cup with the membrane side facing up. Avoid touching the membrane surface with your fingers or metal tools during the operation to prevent contamination.

3. The method for detecting indium, gallium, and zinc in a glass-based indium gallium zinc oxide thin film according to claim 2, characterized in that, The second step is as follows: (1) Adding acid: Slowly add 5 mL of hydrochloric acid along the edge of the glass substrate into the digestion cup. The hydrochloric acid is of superior purity and ρ=1.18 g / mL. Then add 2 mL of nitric acid. The nitric acid is of superior purity and ρ=1.40 g / mL. The total acid volume is 7 mL. The ratio of hydrochloric acid to nitric acid is approximately 2.5:

1. The mixed acid solution covers the surface of the substrate film. (2) Standing pretreatment: Let stand at room temperature for 5 min to 10 min and observe whether bubbles or color changes appear on the surface of the film. If the reaction is violent, wait until the reaction is stable before heating. (3) Digestion by heating with an electric hot plate: Place the digestion cup on the electric hot plate, set the temperature to 90℃~110℃, and heat for 20 min~40 min; observe the surface state of the film every 5 min during the digestion process, and judge according to the following criteria: During digestion: the film changes from translucent to transparent, and the digestion front can be seen gradually shrinking towards the center; Digestion complete: Visually, the film color has completely disappeared, the glass substrate surface is smooth and transparent, and the digestion solution is pale yellow to colorless and transparent; For glass substrate samples, once the film digestion is confirmed to be complete, the digestion vessel should be immediately transferred and cooled to avoid prolonged immersion of the glass substrate in hot acid, which could lead to the leaching of large amounts of Si, Na, and Ca.

4. The method for detecting indium, gallium, and zinc in a glass-based indium gallium zinc oxide thin film according to claim 3, characterized in that, In step four, the following series of mixed standard solutions are prepared using 2% HNO3 solution. 。 5. The method for detecting indium, gallium, and zinc in a glass-based indium gallium zinc oxide thin film according to claim 4, characterized in that, The parameters for step five are as follows: radio frequency power 1200 W, plasma gas (Ar) flow rate 15 L / min, auxiliary gas flow rate 0.3 L / min, nebulizing gas flow rate 0.65 L / min, peristaltic pump injection rate 1.5 mL / min, integration time 10 s, and three measurements taken as the average value.

6. The method for detecting indium, gallium, and zinc in a glass-substrate indium gallium zinc oxide thin film according to claim 1, characterized in that, During the testing process, parallel blank tests were conducted simultaneously on blank glass substrates of the same specifications and batch without IGZO films. The measured values ​​of indium, gallium, and zinc should all be lower than 10 ng / mL.

7. The method for detecting indium, gallium, and zinc in a glass-based indium gallium zinc oxide thin film according to claim 6, characterized in that, Method validation is also required, which includes precision testing and spike recovery testing. Precision testing was conducted by independently digesting and measuring two glass substrate thin film samples of the same size and prepared by the same process from the same batch, with the relative deviation of each element not exceeding 3%. The spiked recovery test is as follows: Add known amounts of a mixed standard of In, Ga, and Zn to the digested thin film sample solution, and re-determine the recovery rate of each element. The recovery rate of each element should be in the range of 90% to 110%.

8. The method for detecting indium, gallium, and zinc in a glass-based indium gallium zinc oxide thin film according to claim 7, characterized in that, Two glass substrate thin film samples of the same size and prepared by the same process from the same batch were independently digested and measured, and the relative deviation of each element did not exceed 3%.

9. The method for detecting indium, gallium, and zinc in a glass-based indium gallium zinc oxide thin film according to claim 6, characterized in that, After digestion, the glass substrate surface should be visually inspected to ensure there are no residual IGZO traces or green / blue spots. If necessary, confirm under a microscope at 10x magnification.

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