What is the process of quality inspection in the quality control system of silicon wafer manufacturers?

In the quality control system of silicon wafer manufacturers, the quality inspection process usually includes raw material inspection, semi-finished product inspection during the production process, and finished product inspection, as follows:

Raw material inspection

Supplier supply inspection: When raw materials arrive, first verify the delivery note, quality certification documents, etc. provided by the supplier to ensure that the goods are consistent with the order and are accompanied by necessary quality inspection reports.

Visual inspection: Conduct visual inspection on raw materials to check if there are any obvious defects in raw materials such as silicon materials and quartz crucibles, such as surface impurities and cracks in silicon materials, and damage or deformation of quartz crucibles.

Dimensional specification measurement: Use professional measuring tools, such as calipers and micrometers, to measure the key dimensional parameters of raw materials to ensure they comply with the specified tolerance range. For example, check whether the diameter and length of the silicon rod are within the allowable error range.

Chemical composition analysis: By using methods such as spectral analysis and chemical titration, the chemical composition of raw materials is detected to determine whether the purity of silicon and the content of impurities meet the requirements. For instance, test whether the content of impurity elements such as boron and phosphorus in the silicon material exceeds the standard.

Physical property testing: For some raw materials, physical property testing is also required. For instance, the resistivity of silicon material is tested to ensure that it meets the requirements for the electrical properties of the material in subsequent production processes. Only raw materials with all qualified indicators can enter the warehouse and be put into production use.

Semi-finished product inspection

Post-cutting inspection of silicon wafers: After silicon rods are cut into silicon wafers through the cutting process, the first step is to conduct an appearance inspection to check if there are any defects such as cutting marks, chipped edges, or missing corners on the surface of the silicon wafers. Then, use a thickness gauge to measure the thickness of the silicon wafer to ensure it meets the product specification requirements, and the thickness deviation is controlled within the specified range. Meanwhile, the surface flatness of the silicon wafers is inspected through a flatness tester to ensure that the surface undulation of the silicon wafers is within the allowable tolerance range.

Post-cleaning inspection: After the silicon wafer cleaning process is completed, check the cleanliness of the silicon wafer surface to confirm whether there are any residual cleaning solutions, stains or particle impurities. Microscopic inspection can be carried out using an optical microscope or an electron microscope to ensure that the surface of the silicon wafer meets the cleanliness standards required by the production process. In addition, the surface roughness of the silicon wafers needs to be tested to ensure that it meets the requirements of the subsequent processes.

Post-diffusion inspection: After the silicon wafer undergoes a diffusion process to form a PN junction, the block resistance of the silicon wafer needs to be measured. The block resistance at different positions on the surface of the silicon wafer is detected by equipment such as the four-probe tester to ensure that its uniformity meets the requirements, so as to guarantee the consistency of the electrical performance of the silicon wafer. Meanwhile, infrared spectrometers and other equipment are used to detect the depth of impurity diffusion in silicon wafers to confirm whether the diffusion process has achieved the expected effect.

Post-etching inspection: After the etching process is completed, check the integrity of the silicon wafer's edges to see if there are any issues such as uneven etching or edge damage. Use equipment such as scanning electron microscopes to observe the microstructure of the silicon wafer surface, ensuring that the etching process precisely removes the silicon material to be removed without causing damage to the effective areas of the silicon wafer. Meanwhile, test the reflectivity of the silicon wafers to ensure that they meet the optical performance requirements of the product.

Finished product inspection

Full appearance inspection: Conduct a comprehensive appearance inspection of the silicon wafers, using optical inspection equipment or manual visual inspection to check if there are any minor defects on the surface of the silicon wafers, such as pinholes, color spots, scratches, etc. At the same time, check whether the edges of the silicon wafers are smooth and regular, without issues such as chipping or burrs.

Dimensional accuracy measurement: Measure the various dimensional parameters of the silicon wafer again precisely, including length, width, thickness, diagonal, etc., to ensure that all dimensions are within the tolerance range specified in the product specifications. For high-precision silicon wafer products, it may be necessary to use high-precision measurement equipment such as laser interferometers for measurement.

Electrical performance testing: Through professional electrical testing equipment, such as semiconductor parameter testers, key electrical performance indicators of silicon wafers, such as resistivity, minority carrier lifetime, and breakdown voltage, are measured. These indicators directly affect the application performance of silicon wafers in solar cells or other semiconductor devices and must meet strict standard requirements.

Optical performance testing: For silicon wafers used in optical applications such as solar cells, it is necessary to test their optical performance indicators such as optical transmittance and reflectance. Use spectrometers and other equipment to measure the optical characteristics of silicon wafers at different wavelengths to ensure that they meet the optical performance requirements of silicon wafers for products such as solar cells, so as to improve the photoelectric conversion efficiency.

Pre-packaging inspection: Before packaging the silicon wafers, recheck the surface cleanliness and appearance quality of the wafers to ensure they have not been contaminated or damaged during transportation or storage. At the same time, check whether the packaging materials meet the requirements, such as whether the packaging box is intact and whether the desiccant is in sufficient quantity, to ensure that the quality of the silicon wafers is not affected during transportation and storage.

After going through the above comprehensive and strict quality inspection process, only silicon wafers with all indicators meeting the quality standards can be delivered to customers as qualified products.