Thin film stress measurement systemUsed for detecting residual stress or dynamic stress within thin films (with thicknesses ranging from nanometer to micrometer), widely used in fields such as semiconductor chips, flexible electronics, and optical coatings. The physical properties of different material films, such as high hardness of metal films, low elastic modulus of polymer films, and brittleness of semiconductor films, vary greatly. Therefore, a collaborative design of "principle matching fixed adaptation parameter calibration environment adjustment" is needed to achieve precise adaptation and avoid measurement errors caused by mismatched material properties (target error ≤ 5%).

1、 Measurement principle selection: matching core methods based on material characteristics

Choosing the appropriate stress measurement principle based on the mechanical and physical properties of the material is the foundation of accurate measurement

The bending method is suitable for rigid materials such as metal thin films (such as aluminum films, copper films), semiconductor thin films (such as silicon-based thin films), etc. (elastic modulus ≥ 100GPa). Laser bending method is preferred - by measuring the bending curvature change of the substrate before and after film deposition (accuracy ≤ 0.1m ⁻¹), combined with Stoney's formula to calculate stress. This type of material is not easily deformed, has stable bending signals, and can accurately reflect stress changes; For example, when measuring metalized thin films on silicon wafers, the laser spot diameter can be set to 50 μ m to ensure spatial resolution of curvature measurement.

Optical interferometry is suitable for flexible/transparent materials such as polymer films (such as PI films, PET films), transparent optical films (such as ITO films), etc. (elastic modulus ≤ 10GPa, transmittance ≥ 80%), and is suitable for white light interferometry or phase-shifting interferometry. By detecting the optical phase change caused by film stress (accuracy ≤ 0.01 π), avoid damage to flexible materials by contact measurement; For example, when measuring the PI substrate film of flexible OLED, a non-contact interference optical path is used to prevent substrate deformation from affecting the measurement results.

Raman spectroscopy is suitable for brittle/high-temperature materials such as ceramic thin films (such as Al ₂ O3 films), high-temperature alloy thin films, and other brittle or high-temperature resistant materials (temperature resistance ≥ 500 ℃). Raman spectroscopy is used to analyze the Raman peak shift caused by stress (wave number accuracy ≤ 0.1cm ⁻¹) and calculate the stress distribution. This type of material is prone to rupture due to external forces, and the non-contact, micro area measurement (spot diameter ≤ 1 μ m) characteristics of Raman spectroscopy can avoid damage, while also adapting to high temperature environments (requiring a high temperature sample stage).

2、 Sample fixation adaptation: Design a fixation scheme according to the material form

Design suitable fixing devices for different substrate shapes of thin films (such as rigid substrates, flexible substrates, sheet/roll shapes) to ensure sample stability during measurement

Rigid substrate fixation: Thin films on rigid substrates such as silicon wafers and glass are fixed using vacuum adsorption (adsorption pressure 0.05-0.08MPa) to avoid additional stress caused by mechanical clamping; For example, when measuring a silicon nitride film on a 6-inch silicon wafer, the diameter of the vacuum suction cup should match the silicon wafer (6 inches) to ensure that the substrate is uniformly stressed and there is no local bending.

Flexible substrate fixation: A thin film (such as a rolled PI film) on a flexible polymer substrate is fixed using tension controlled fixation - a constant tension (0.1-1N, adjusted according to the thickness of the film) is applied through tension rollers at both ends to maintain the substrate flat and without additional stress; The tension fluctuation during measurement should be ≤ 5% to avoid misjudging tension changes as stress signals. For example, when detecting ultra-thin PI films used for flexible screens, the tension should be set to 0.3N to balance flatness and stress free requirements.

3、 Parameter calibration optimization: Adjust the calculation model according to material parameters

Calibrate based on mechanical parameters such as elastic modulus and Poisson's ratio of the materialThin film stress measurement systemThe calculation model eliminates errors caused by differences in material properties:

Mechanical parameter input calibration: Before measurement, the elastic modulus of the material (such as aluminum film 70GPa, PI film 2.5GPa) and Poisson's ratio (such as silicon film 0.28, polymer film 0.4) need to be accurately input into the system to correct core calculation models such as Stoney formula and Raman peak displacement stress conversion coefficient. For example, when measuring different metal thin films, if the input deviation of the elastic modulus of the aluminum film is 10%, it will result in a stress calculation error of over 8%. It is necessary to verify and correct the parameters through a standard sample (such as a calibration film with known stress).

Measurement range adaptation: Adjust the system range according to the stress range of the material - the residual stress of the metal film is usually 10-500MPa, and the range can be set to 0-1000MPa; The stress of polymer film is mostly 1-50MPa, and the range is set to 0-100MPa to avoid insufficient measurement accuracy of low stress due to excessive range (if measuring 10MPa stress with a range of 1000MPa, the error may exceed 10%).

4、 Environmental compensation adjustment: Adapt to the measurement environment based on material stability

To address the sensitivity of materials to temperature, humidity, and vibration, adjust the measurement environment parameters to ensure measurement stability:

Temperature and humidity compensation: Polymer films (such as PET films) are sensitive to temperature and humidity (stress changes may exceed 10MPa for every 1 ℃ temperature change), and need to be measured in a constant temperature and humidity environment (temperature control 23 ± 0.5 ℃, humidity 50 ± 5% RH), and the stress deviation caused by temperature and humidity should be compensated in real time through environmental sensors; For example, when measuring PI film for flexible electronics, the system has a built-in temperature and humidity compensation algorithm that automatically corrects measurement errors caused by environmental factors.

Anti vibration and electromagnetic shielding: Semiconductor thin films (such as photoresist films) and magnetic thin films are sensitive to vibration (vibration amplitudes exceeding 1 μ m can affect optical measurements) and electromagnetic interference. The measurement system requires the installation of a shock absorber (vibration attenuation rate ≥ 90%) and the use of an electromagnetic shielding cover (shielding effect ≥ 30dB) to avoid external interference affecting signal acquisition. For example, when measuring photoresist thin films in a semiconductor clean room, the shock absorber can control the vibration within 0.1 μ m.

Through the above adaptation scheme,Thin film stress measurement systemIt can cover the measurement needs of various materials such as metals, semiconductors, polymers, ceramics, etc., ensuring that the stress measurement accuracy under different materials can meet the requirements of application scenarios (such as semiconductor chip thin film measurement error ≤ 3%, flexible electronic thin film error ≤ 5%), providing data support for the performance optimization of thin film materials and the improvement of device reliability.