| For a long time,my country has been in a relatively backward position in the field of wafer manufacturing and inspection.With the rapid development of high-tech industries such as the Internet of Things and 5G,the demand for chips is becoming stronger and stronger,and the problem of insufficient chip production capacity has further magnified China's backward state in this field.In the field of wafer stress testing equipment,related foreign companies started early and have strong technology,which opened a big gap with us.In addition,due to the impact of Sino-US trade,the import of thin-film stress measuring instruments has also become difficult,resulting in many companies in China without instruments available.Finally,the research and development of the domestic wafer thin film stress meter is at a relatively low level,and the accuracy and repeatability of the stress measurement are difficult to expect from the imported equipment.At present,the methods of improving the thin film stress meter are mainly divided into three categories:(1)Change the mechanical structure or optical path structure of the measuring instrument.The main plans include adding laser beams,changing vertical measurement to horizontal measurement,adding rotating trays,etc.The mechanical structure of these schemes is relatively complicated,but will increase the instability of the measurement results,making the measurement process uncontrollable and unreliable.(2)Using the optical properties of the film,the film stress meter was redesigned by the stress birefringence method and the X-ray diffraction method.The instrument based on this scheme can further improve the measurement accuracy and stability,but the cost is relatively high,the development cycle is long,and the later maintenance is difficult.(3)The traditional thin film stress meter has been upgraded in software and hardware,the hardware has been updated,the software has been optimized,and the measurement process has been redesigned.This type of solution has low cost,quick results,significant performance improvement,and simple maintenance.This article combines the third type of improvement plan,selects more advanced electronic components and other structural modules,and optimizes the algorithm to enhance the hardware performance.From the software level to further reduce or even eliminate the noise of the hardware itself and the vibration of the mechanical platform,an error compensation formula is proposed to compensate for the inaccuracy of the measurement results caused by the inherent error of the platform,and to improve the stability,repeatability and accuracy of the measurement results.First,use a more precise and stable stepper motor in the moving element module,and use a onedimensional position-sensitive sensor with a higher resolution and a higher stray light elimination rate in the data sampling module.Then,the trapezoidal acceleration and deceleration algorithm is used to optimize the control of the moving components to ensure accurate and smooth movement.Redesign the operational amplifier circuit for the position-sensitive sensor to improve the sampling accuracy.Finally,an error compensation algorithm is proposed to adjust the measurement results.The main contributions and innovations of this article are as follows:(1)Designed and realized the precise and stable control of the moving components of the thin film stress meter.Aiming at the problem of out-of-step or vibration of the moving components of the traditional thin film stress meter,this paper re-selects the high-precision stepper motor,optimizes the stepper motor control through the acceleration and deceleration algorithm,and effectively reduces the interference to the sampling result during the measurement process.(2)Designed and realized the high-fidelity sampling of the position-sensitive sensor in the thin film stress meter.This article redesigns the operational amplifier circuit according to the high-resolution position-sensitive sensor and measurement requirements,customizes the magnification and manual zero adjustment.Further ensure the accuracy of sensor data acquisition.(3)Propose an error compensation formula.This paper analyzes the average fitted radius of curvature of the optical film before and after wafer coating relative to the theoretical value,compares the error law between the two,and proposes an error compensation formula,and gives the method of solving the compensation coefficient and the calibration process in practical application.The error compensation formula effectively improves the accuracy and repeatability of the measurement results,and the compensation coefficient solution method effectively improves the work efficiency,avoiding repeated testing and adjustment when calibration is required.(4)The unity of all optical sheet materials for measuring the radius of curvature or stress based on the substrate deformation method is realized.In addition to the main application for the detection of the radius of curvature,bending and stress of the wafer before and after coating,it is also suitable for testing the radius of curvature and bending of the non-coated surface of any rigid material substrate that can reflect laser.It is also suitable for testing the radius of curvature of the coating surface of any rigid material substrate that can reflect the laser,the bending test and the residual profit test of the film,such as titanium alloy substrates,polished stainless steel substrates,etc.The research results of this article have applied for an invention patent(The patent numbers are 202111154932.8 and 202110612472.2 respectively)and two software copyrights.The film stress prototype realized in this paper has been handed over to cooperative enterprises for productization and commercialization upgrade.With the joint efforts of both parties,the intention order has been reached with several semiconductor companies,and the next step is to commit to the comprehensive achievement transformation and commercial promotion of this thin-film stress meter. |
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