Methods for testing twin defects in protolamellae after thermal oxidation using a particle testing machine

Abstract

This invention relates to a method for testing twin defects in pre-oxidized wafers using a particle testing machine, belonging to the field of semiconductor wafer defect detection technology. The method includes the following steps: Step 1: Thermal oxidation preparation; the grown oxide film is obtained through wet oxidation in an oxidation furnace, and the wafer is cleaned using a final cleaning machine. Step 2: Particle testing method optimization and film establishment. Step 3: Result comparison and verification; by establishing an Oxide Film model, the signal processing algorithm of the particle testing machine can distinguish between particle signals and twin signals, thereby achieving synchronous capture. Step 4: By optimizing the particle testing machine method, twin defect detection of the pre-oxidized wafer is successfully completed simultaneously during particle testing. By optimizing the particle testing machine method, synchronous detection of particle testing and twin defects is achieved, thereby improving detection efficiency, shortening the process, and maintaining the integrity of the sample.

Description

Technical Field

[0001] This invention relates to the field of semiconductor wafer defect detection technology, and specifically to a method for testing twin defects in pre-embedded wafers after thermal oxidation using a particle testing machine. Background Technology

[0002] In the manufacturing process of semiconductor silicon wafers, especially in the pulling of single-crystal silicon and subsequent thermal processing, a crystal defect called "twins" is easily generated. Twins refer to two groups of atoms in a crystal lattice forming a symmetrical arrangement with a specific twin plane as a mirror image. For semiconductor devices, twins are a serious lattice structure defect that disrupts the integrity of the crystal structure, leading to decreased carrier mobility, increased leakage current, and even direct chip failure. Therefore, accurate detection and monitoring of twin defects in the front-end processes of wafer manufacturing (such as thermal oxidation) are crucial for improving yield.

[0003] Currently, the detection of wafer defects is mainly divided into the following categories, but all of them have certain limitations: Particle testing equipment is the most commonly used equipment on the production line, primarily used to detect physical particles and scratches on the wafer surface. However, these devices are typically calibrated for "bare wafers" or standard wafers with specific film thicknesses. Their signal processing algorithms are mainly based on the principle of light scattering, which often makes it difficult to distinguish between particle signals caused by minute surface irregularities and twin signals caused by lattice distortion. Especially after thermal oxidation, when an oxide film grows on the wafer surface, if the "Film Curve" model used for polished wafers is still applied, the optical interference effect of the oxide film will mask or distort the characteristic signals of twins, leading to missed detections.

[0004] Destructive physical testing, specifically selective etching, is the traditional gold standard for detecting twins. It involves etching the wafer surface with a specific etching solution to expose the twins, which are then observed under a microscope. However, this method is not only time-consuming and costly, but also destructive, rendering the tested wafer unusable for production and preventing online full inspection.

[0005] Stress testing (PSI): Although it can detect crystal stress, the equipment is expensive, the testing speed is slow, and it is not usually used in routine particle scanning steps.

[0006] Pre-test wafers, also known as control wafers or companion wafers, are test wafers used to monitor the quality of the oxidation process. In evaluating crystal defects in pre-test wafers, after the thermal oxidation process in the oxidation furnace, the wafers need to undergo SP7 particle inspection and microscopic testing. They may also require PSI stress testing or, more advanced, selective etching followed by microscopic examination for crystal defects. However, stress testing, PSI, and microscopic examination after selective etching all cause some damage to the wafers, rendering them unusable after testing. Furthermore, the increased testing time and time required to obtain results place a burden on testing efficiency and wafer integrity. Summary of the Invention

[0007] This invention addresses the shortcomings of existing technologies by providing a method for testing twin defects in pre-embedded wafers after thermal oxidation using a particle testing machine. By optimizing the particle testing machine, it achieves simultaneous detection of particle testing and twin defects, thereby improving detection efficiency, shortening the process, and maintaining the integrity of the sample.

[0008] The above-mentioned technical problems of the present invention are mainly solved by the following technical solutions: A method for testing twin defects in pre-oxidized lamellar structures using a particle testing machine includes the following steps: Step 1: Thermal oxidation preparation; The oxide film grown by wet oxidation in an oxidation furnace has a thickness of 840 Å to 860 Å; After oxidation, the wafer is cleaned using a final cleaning machine.

[0009] Step 2: Optimization of particle testing methods and establishment of film layer; a new Oxide Film model is established in the system based on the measured oxide film thickness, refractive index n, and extinction coefficient k.

[0010] The third step is result comparison and verification. By establishing an Oxide Film model, the signal processing algorithm of the particle testing machine can distinguish between particle signals and twin signals, thereby achieving synchronous capture.

[0011] The reference group was tested simultaneously with the experimental group using the preferred etching method and PSI stress test on the particle testing machine, and twin defects were captured in both cases.

[0012] Step 4: By optimizing the particle testing equipment, twinning defect detection of the thermally oxidized precursor wafer was successfully completed simultaneously during particle testing.

[0013] Preferably, the gas flow rate is set to 3L of oxygen and 3L of hydrogen; the heating temperature is 950℃; and the time is 16 minutes for oxide film growth.

[0014] As a preferred option, the parameters are input and adjusted. The actual thickness of 850Å is entered in the thickness field, and the key parameters of laser power and layout or scanning layout are optimized and adjusted. When the thermal oxidation precursor particle test is performed after optimization, the twinning defect is detected simultaneously.

[0015] Preferably, the refractive index n is 1.46 to 1.50 and the extinction coefficient k is 0; in the particle testing method, the original polished sheet "Film Curve" is replaced with the newly created "Oxide Film".

[0016] As a preferred method, the result comparison and verification steps specifically include observing twin defects under a microscope after etching using the preferred etching method, and capturing twin defects using PSI stress testing; the detection results of the preferred etching method and PSI stress testing are superimposed and compared with the defect patterns captured by the particle testing machine in the experimental group to confirm that the defects detected by the particle testing machine are twin defects.

[0017] The present invention can achieve the following effects: This invention provides a method for testing twin defects in pre-oxidized wafers using a particle testing machine. Compared with existing technologies, this method significantly improves defect detection efficiency and shortens the overall testing process while ensuring the accuracy of the test results. It also avoids destructive testing and effectively preserves the integrity of the pre-oxidized wafer. Without changing the hardware, through innovation in software algorithms and optical models, the functional boundaries of existing equipment are successfully expanded, solving the technical challenge of online, rapid, and non-destructive detection of twin defects in wafers after thermal oxidation. This invention demonstrates significant inventiveness.

[0018] Typical particle testing equipment is designed for polished wafers and cannot distinguish or identify wafer defects after thermal oxidation, especially lattice-structured "twin" defects.

[0019] Film modeling: A specific “Oxide Film” model is established based on the actual optical parameters (n, k, thickness n, k, thickness) after thermal oxidation, replacing the general “Film Curve”.

[0020] Algorithm differentiation: Through specific model and laser / scanning parameter optimization, the machine's algorithm can distinguish the different signal characteristics of foreign particles and lattice twins.

[0021] Verification: The accuracy of the pellet mill test results was verified by using destructive preferential corrosion method and physical stress test method as the "gold standard".

[0022] Those skilled in the art typically believe that particle testing equipment is limited to detecting physical foreign objects, and the default models built into these equipment, such as the film curve, are generally considered universal and require no modification. This invention breaks with this conventional thinking, creatively proposing to explore the potential of particle testing equipment in detecting "crystal structure defects" by reconstructing the oxide film model and utilizing the interaction between specific oxide film thickness and laser signals. This method of adjusting the optical model to distinguish between defects of different physical mechanisms (particles vs. twins) has significant substantive characteristics. Detailed Implementation

[0023] The technical solution of the invention will be further described in detail below through examples.

[0024] Example: A method for testing twin defects in pre-oxidized lamellar structures using a particle testing machine, comprising the following steps: Step 1: Thermal oxidation preparation; The oxide film with a thickness of 850 Å is grown by wet oxidation in an oxidation furnace; The gas flow rate is set to 3L of oxygen and 3L of hydrogen; The heating temperature is 950℃; The oxide film growth time is 16 minutes.

[0025] After oxidation is complete, the wafer is cleaned using a final cleaning machine.

[0026] Step 2: Optimization of particle testing method and establishment of film layer; Based on the measured oxide film thickness, refractive index n, and extinction coefficient k, a new Oxide Film model is established in the system. The refractive index n is 1.4997, and the extinction coefficient k is 0; In the particle testing method, the original polished sheet "Film Curve" is replaced with the newly created "Oxide Film".

[0027] Input and adjust the parameters, enter the actual thickness of 850Å in the thickness column, and optimize and adjust the key parameters of laser power and layout or scanning layout; when performing thermal oxidation pre-sheet particle testing after optimization, twin defects are detected simultaneously.

[0028] The third step is result comparison and verification. By establishing an Oxide Film model, the signal processing algorithm of the particle testing machine can distinguish between particle signals and twin signals, thereby achieving synchronous capture.

[0029] The reference group was tested simultaneously with the experimental group using the preferred etching method and PSI stress test on the particle testing machine, and twin defects were captured in both cases.

[0030] The specific steps for result comparison and verification include observing twin defects under a microscope after etching using the preferred etching method, and capturing twin defects using PSI stress testing; the detection results of the preferred etching method and PSI stress testing are superimposed and compared with the defect patterns captured by the particle testing machine in the experimental group to confirm that the defects detected by the particle testing machine are indeed twin defects.

[0031] Step 4: By optimizing the particle testing equipment, twinning defect detection of the thermally oxidized precursor wafer was successfully completed simultaneously during particle testing.

[0032] In summary, this method for testing twin defects in pre-embedded wafers after thermal oxidation using a particle testing machine optimizes the particle testing machine to achieve simultaneous detection of particle testing and twin defects, thereby improving detection efficiency, shortening the process, and maintaining the integrity of the sample.

[0033] This technology enables non-destructive online synchronous inspection by optimizing the algorithms and models of particle testing equipment. This allows devices originally designed for surface particle detection to simultaneously identify twin defects within the wafer. This means that crystal quality monitoring is achieved without adding expensive additional testing equipment or damaging the wafer, significantly improving inspection efficiency and cost-effectiveness.

[0034] The accuracy of defect identification is significantly improved by establishing a specific "OxideFilm" model for the 850Å oxide film in the system, setting the refractive index n=1.4997 and the extinction coefficient k=0; and replacing the original polishing sheet "Film Curve". This adjustment eliminates optical signal errors caused by film layer mismatch, enabling the instrument's signal processing algorithm to accurately distinguish between "particle signals" and "twin signals", effectively solving the problem of twin signals being submerged or misjudged in traditional testing.

[0035] Precise matching and optimization of process parameters were performed for a specific thermal oxidation process: 950℃, wet oxidation, 3L each of O2 and H2, growth for 16 minutes. The resulting 850Å film thickness was then precisely calculated using optimized parameters, including the 850Å thickness, laser power, and scanning layout. This highly customized parameter setting ensured optimal matching of the test signals, guaranteeing the sensitivity and repeatability of the detection results.

[0036] The scientific validity of the method was verified by introducing the preferred corrosion method and PSI stress test as reference groups, and comparing the results with the patterns captured by the pellet mill, thus establishing a rigorous verification process. This not only confirmed the accuracy of the pellet mill's test results but also provided data support for the continuous optimization of the subsequent mill model.

[0037] Improving process monitoring capabilities and immediately detecting wafer twinning anomalies after the thermal oxidation process helps engineers quickly identify abnormalities in process parameters such as oxidation furnace temperature and gas flow rate, thereby adjusting the process in a timely manner and preventing batch quality accidents.

[0038] The above description is only a specific embodiment of the present invention, but the structural features of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for testing twin defects in pre-oxidized lamellar structures using a particle testing machine, characterized in that... The following steps are included: Step 1: Thermal oxidation preparation; The oxide film grown by wet oxidation in an oxidation furnace has a thickness of 840 Å to 860 Å; After oxidation, the wafer is cleaned using a final cleaning machine; Step 2: Optimization of particle testing methods and establishment of film layer; a new oxide film model is established in the system based on the measured oxide film thickness, refractive index n, and extinction coefficient k. Step 3: Result comparison and verification. By establishing the Oxide Film model, the signal processing algorithm of the particle testing machine can distinguish between particle signals and twin signals, thereby achieving synchronous capture. The reference group was tested simultaneously with the experimental group using the preferred etching method and PSI stress test on the particle testing machine, and twin defects were captured in both cases. Step 4: By optimizing the particle testing equipment, twinning defect detection of the thermally oxidized precursor wafer was successfully completed simultaneously during particle testing.

2. The method for testing twin defects in pre-oxidized lamellar structures using a particle testing machine according to claim 1, characterized in that: The gas flow rate was set to 3L of oxygen and 3L of hydrogen; the heating temperature was 950℃; and the duration was 16 minutes for oxide film growth.

3. The method for testing twin defects in pre-oxidized lamellar structures using a particle testing machine according to claim 1, characterized in that: Input and adjust the parameters, enter the actual thickness of 850Å in the thickness column, and optimize and adjust the key parameters of laser power and layout or scanning layout; when performing thermal oxidation pre-sheet particle testing after optimization, twin defects are detected simultaneously.

4. The method for testing twin defects in pre-oxidized lamellar structures using a particle testing machine according to claim 3, characterized in that: The refractive index n is 1.46 to 1.50, and the extinction coefficient k is 0. In the particle testing method, the original polished sheet "Film Curve" is replaced with the newly created "Oxide Film".

5. The method for testing twin defects in pre-oxidized lamellar structures using a particle testing machine according to claim 1, characterized in that: The specific steps for result comparison and verification include observing twin defects under a microscope after etching using the preferred etching method, and capturing twin defects using PSI stress testing; the detection results of the preferred etching method and PSI stress testing are superimposed and compared with the defect patterns captured by the particle testing machine in the experimental group to confirm that the defects detected by the particle testing machine are indeed twin defects.