What process is used to produce precision thin film resistors?

The production process of precision thin film resistors is a high-precision and cutting-edge technology in the field of electronic manufacturing. Its core lies in achieving high-precision (± 0.01%) resistance values, low temperature coefficient (± 1ppm/℃), and long-term stability through nanoscale material control, precision machining, and strict testing. The production overview of precision thin film resistors is systematically analyzed from three aspects: process flow, key technologies, and quality control
1、 Process flow
1. Substrate preparation
Material selection:
Ceramic substrate: mainly made of 96% aluminum oxide (Al ₂ O ∝) or aluminum nitride (AlN), requiring thermal conductivity>20W/m · K and bending strength>300MPa.
Metal substrate: such as copper molybdenum copper (Cu/Mo/Cu) composite material, with a coefficient of thermal expansion (CTE) matched with silicon chips (CTE ≈ 4ppm/℃).
Precision machining:
Laser cutting: Using femtosecond laser, the cutting accuracy reaches ± 5 μ m, ensuring substrate size tolerance.
Grinding and polishing: By using chemical mechanical polishing (CMP) technology, the surface roughness Ra is reduced to less than 0.05 μ m, providing a mirror substrate for thin film deposition.
2. Thin film deposition
Physical Vapor Deposition (PVD):
Magnetron sputtering: Deposition of nickel chromium (NiCr) alloy film with a thickness control accuracy of ± 0.1nm. The stress of the film layer is optimized by adjusting the power (500~2000W) and gas pressure (0.1~1Pa).
Electron beam evaporation: suitable for high melting point materials (such as tantalum nitride TaN), with an evaporation rate of 0.1-1nm/s, to achieve low stress film layers.
Chemical Vapor Deposition (CVD):
Deposition of a protective layer of silicon carbide (SiC) or silicon nitride (Si ∝ N ₄) with a thickness of 0.1~1 μ m to enhance moisture resistance and wear resistance.
3. Photolithography patterning
Photoresist coating:
Rotating glue coating, with a speed of 3000-6000rpm, a film thickness of 0.5-2 μ m, and a uniformity of ± 2%.
Exposure and development:
We use an i-line stepper lithography machine with a resolution of 0.8 μ m and a etching accuracy of ± 0.5 μ m.
The precision of developing time control is ± 1s, avoiding overexposure (resulting in line width loss) or underexposure (residual photoresist).
Etching:
Wet etching: using a mixture of phosphoric acid and nitric acid, with an etching rate of 50-100nm/min and selectivity greater than 10:1.
Dry etching: using inductively coupled plasma (ICP) etching, with sidewall perpendicularity>85 °, suitable for high aspect ratio structures.
4. Laser resistance adjustment
Equipment requirements:
Picosecond/femtosecond laser, pulse width<10ps, heat affected zone<0.5 μ m, to avoid film damage.
Resistance adjustment algorithm:
Real time measurement of resistance based on the four terminal method, and control of laser energy (1-10 μ J) and scanning path through PID algorithm.
Resistance adjustment accuracy: ± 0.01%, can achieve wide range adjustment from milliohms to megaohms, and the resistance distribution after resistance adjustment is σ<0.005%.
5. Packaging and Testing
Packaging process:
Airtight packaging: using metal ceramic sealing, helium leakage rate<1 × 10 ⁻⁹ Pa · m ³/s, suitable for aerospace scenes.
Surface mount packaging: such as 0402/0603 packaging, reflow soldering is carried out in a nitrogen atmosphere with a peak temperature of 245 ± 5 ℃ to prevent oxidation.
Electrical performance testing:
Resistance measurement: Using the four terminal method, with an accuracy of ± 0.001% and a testing frequency of 1kHz.
Temperature coefficient (TCR) test: Within the range of -55 ℃~150 ℃, TCR fluctuation is less than ± 1ppm/℃, and it is measured by combining a constant temperature bath with an LCR meter.
Reliability testing:
High temperature aging: Working continuously for 1000 hours at 150 ℃, the resistance change rate is less than 0.01%.
Temperature cycle: -65 ℃~150 ℃, no cracking or resistance drift after 1000 cycles.
Vibration test: frequency 10-2000Hz, acceleration 100g, continuous for 4 hours, normal function.
2、 Key technologies
1. Nano scale film thickness control
Challenge: A 1nm fluctuation in film thickness can cause a 0.1% change in resistance.
Plan:
Introducing atomic layer deposition (ALD) technology to achieve single atomic layer accuracy (0.1nm/cycle).
Using an elliptical polarization spectrometer (SE) for online monitoring of film thickness and feedback control of deposition parameters.
2. Preparation of low stress thin films
Challenge: Membrane stress can cause substrate bending or cracking.
Plan:
Optimize sedimentation process parameters (such as temperature, pressure, power) to control membrane stress within ± 50MPa.
Adopting gradient material design, such as NiCr/TaN composite film, to alleviate thermal stress.
3. High precision resistance adjustment algorithm
Challenge: Laser impedance adjustment needs to balance speed and accuracy.
Plan:
Develop an adaptive PID algorithm to dynamically adjust laser parameters based on real-time resistance feedback.
Introducing a machine vision system to automatically identify the position of resistance adjustment and avoid human error.
3、 Quality control
1. Statistical Process Control (SPC)
Implementation: Deploy SPC in key processes such as thin film deposition, photolithography, and resistance adjustment to monitor parameters such as film thickness, line width, and resistance.
Goal: Process Capability Index (CpK)>1.67 to ensure product consistency.
2. Failure Analysis (FA)
Tools: Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), focused ion beam (FIB) and other technologies are used.
Process: Dissect and analyze the failed sample, locate the failure mode (such as film peeling, etching residue), and provide feedback to process optimization.
3. Reliability acceleration test
method:
High temperature and high humidity bias test (H3TRB): 85 ℃/85% RH/1000V, 1000 hours, failure rate<0.1%.
Thermal shock test: -65 ℃~150 ℃, 1000 cycles, resistance change rate<0.05%.
4、 Technological Trends and Innovation
Material Innovation:
Graphene resistance: a two-dimensional material with a resistivity as low as 10 Ω· cm and a temperature coefficient close to zero, suitable for ultra precision scenarios such as quantum computing.
Carbon nanotube (CNT) resistance: Good flexibility, capable of three-dimensional integration, with a power density of up to 100W/cm ².
Technological breakthrough:
Extreme Ultraviolet Photolithography (EUV): Resolution<10nm, suitable for the next generation of ultra small precision resistors.
Self assembly technology: forming nanoscale resistance patterns through molecular self-assembly, with a line width control accuracy of ± 1nm.
Intelligent production:
Digital Twin: Establish a digital twin model for the production line, optimize process parameters in real-time, and improve yield.
AI visual inspection: using deep learning algorithms, defect detection rate>99.9%, false positive rate<0.1%.
The production process of precision thin film resistors is a deep integration of material science, precision machining, and intelligent control. Its core lies in achieving high precision and long-term stability of resistance values through nanoscale film thickness control, low stress thin film preparation, high-precision resistance adjustment algorithms, and strict quality control. With the rapid development of 5G, quantum computing, aerospace and other fields, the production technology of precision thin film resistors is evolving towards higher precision, stronger reliability, and more intelligence, providing key basic component support for high-end electronic devices. The production process of precision thin film resistors is a high-precision and cutting-edge technology in the field of electronic manufacturing. Its core lies in achieving high-precision (± 0.01%) resistance values, low temperature coefficient (± 1ppm/℃), and long-term stability through nanoscale material control, precision machining, and strict testing. The production overview of precision thin film resistors is systematically analyzed from three aspects: process flow, key technologies, and quality control
1、 Process flow
1. Substrate preparation
Material selection:
Ceramic substrate: mainly made of 96% aluminum oxide (Al ₂ O ∝) or aluminum nitride (AlN), requiring thermal conductivity>20W/m · K and bending strength>300MPa.
Metal substrate: such as copper molybdenum copper (Cu/Mo/Cu) composite material, with a coefficient of thermal expansion (CTE) matched with silicon chips (CTE ≈ 4ppm/℃).
Precision machining:
Laser cutting: Using femtosecond laser, the cutting accuracy reaches ± 5 μ m, ensuring substrate size tolerance.
Grinding and polishing: By using chemical mechanical polishing (CMP) technology, the surface roughness Ra is reduced to less than 0.05 μ m, providing a mirror substrate for thin film deposition.
2. Thin film deposition
Physical Vapor Deposition (PVD):
Magnetron sputtering: Deposition of nickel chromium (NiCr) alloy film with a thickness control accuracy of ± 0.1nm. The stress of the film layer is optimized by adjusting the power (500~2000W) and gas pressure (0.1~1Pa).
Electron beam evaporation: suitable for high melting point materials (such as tantalum nitride TaN), with an evaporation rate of 0.1-1nm/s, to achieve low stress film layers.
Chemical Vapor Deposition (CVD):
Deposition of a protective layer of silicon carbide (SiC) or silicon nitride (Si ∝ N ₄) with a thickness of 0.1~1 μ m to enhance moisture resistance and wear resistance.
3. Photolithography patterning
Photoresist coating:
Rotating glue coating, with a speed of 3000-6000rpm, a film thickness of 0.5-2 μ m, and a uniformity of ± 2%.
Exposure and development:
We use an i-line stepper lithography machine with a resolution of 0.8 μ m and a etching accuracy of ± 0.5 μ m.
The precision of developing time control is ± 1s, avoiding overexposure (resulting in line width loss) or underexposure (residual photoresist).
Etching:
Wet etching: using a mixture of phosphoric acid and nitric acid, with an etching rate of 50-100nm/min and selectivity greater than 10:1.
Dry etching: using inductively coupled plasma (ICP) etching, with sidewall perpendicularity>85 °, suitable for high aspect ratio structures.
4. Laser resistance adjustment
Equipment requirements:
Picosecond/femtosecond laser, pulse width<10ps, heat affected zone<0.5 μ m, to avoid film damage.
Resistance adjustment algorithm:
Real time measurement of resistance based on the four terminal method, and control of laser energy (1-10 μ J) and scanning path through PID algorithm.
Resistance adjustment accuracy: ± 0.01%, can achieve wide range adjustment from milliohms to megaohms, and the resistance distribution after resistance adjustment is σ<0.005%.
5. Packaging and Testing
Packaging process:
Airtight packaging: using metal ceramic sealing, helium leakage rate<1 × 10 ⁻⁹ Pa · m ³/s, suitable for aerospace scenes.
Surface mount packaging: such as 0402/0603 packaging, reflow soldering is carried out in a nitrogen atmosphere with a peak temperature of 245 ± 5 ℃ to prevent oxidation.
Electrical performance testing:
Resistance measurement: Using the four terminal method, with an accuracy of ± 0.001% and a testing frequency of 1kHz.
Temperature coefficient (TCR) test: Within the range of -55 ℃~150 ℃, TCR fluctuation is less than ± 1ppm/℃, and it is measured by combining a constant temperature bath with an LCR meter.
Reliability testing:
High temperature aging: Working continuously for 1000 hours at 150 ℃, the resistance change rate is less than 0.01%.
Temperature cycle: -65 ℃~150 ℃, no cracking or resistance drift after 1000 cycles.
Vibration test: frequency 10-2000Hz, acceleration 100g, continuous for 4 hours, normal function.
2、 Key technologies
1. Nano scale film thickness control
Challenge: A 1nm fluctuation in film thickness can cause a 0.1% change in resistance.
Plan:
Introducing atomic layer deposition (ALD) technology to achieve single atomic layer accuracy (0.1nm/cycle).
Using an elliptical polarization spectrometer (SE) for online monitoring of film thickness and feedback control of deposition parameters.
2. Preparation of low stress thin films
Challenge: Membrane stress can cause substrate bending or cracking.
Plan:
Optimize sedimentation process parameters (such as temperature, pressure, power) to control membrane stress within ± 50MPa.
Adopting gradient material design, such as NiCr/TaN composite film, to alleviate thermal stress.
3. High precision resistance adjustment algorithm
Challenge: Laser impedance adjustment needs to balance speed and accuracy.
Plan:
Develop an adaptive PID algorithm to dynamically adjust laser parameters based on real-time resistance feedback.
Introducing a machine vision system to automatically identify the position of resistance adjustment and avoid human error.
3、 Quality control
1. Statistical Process Control (SPC)
Implementation: Deploy SPC in key processes such as thin film deposition, photolithography, and resistance adjustment to monitor parameters such as film thickness, line width, and resistance.
Goal: Process Capability Index (CpK)>1.67 to ensure product consistency.
2. Failure Analysis (FA)
Tools: Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), focused ion beam (FIB) and other technologies are used.
Process: Dissect and analyze the failed sample, locate the failure mode (such as film peeling, etching residue), and provide feedback to process optimization.
3. Reliability acceleration test
method:
High temperature and high humidity bias test (H3TRB): 85 ℃/85% RH/1000V, 1000 hours, failure rate<0.1%.
Thermal shock test: -65 ℃~150 ℃, 1000 cycles, resistance change rate<0.05%.
4、 Technological Trends and Innovation
Material Innovation:
Graphene resistance: a two-dimensional material with a resistivity as low as 10 Ω· cm and a temperature coefficient close to zero, suitable for ultra precision scenarios such as quantum computing.
Carbon nanotube (CNT) resistance: Good flexibility, capable of three-dimensional integration, with a power density of up to 100W/cm ².
Technological breakthrough:
Extreme Ultraviolet Photolithography (EUV): Resolution<10nm, suitable for the next generation of ultra small precision resistors.
Self assembly technology: forming nanoscale resistance patterns through molecular self-assembly, with a line width control accuracy of ± 1nm.
Intelligent production:
Digital Twin: Establish a digital twin model for the production line, optimize process parameters in real-time, and improve yield.
AI visual inspection: using deep learning algorithms, defect detection rate>99.9%, false positive rate<0.1%.
The production process of precision thin film resistors is a deep integration of material science, precision machining, and intelligent control. Its core lies in achieving high precision and long-term stability of resistance values through nanoscale film thickness control, low stress thin film preparation, high-precision resistance adjustment algorithms, and strict quality control. With the rapid development of 5G, quantum computing, aerospace and other fields, the production technology of precision thin film resistors is evolving towards higher precision, stronger reliability, and more intelligence, providing key basic component support for high-end electronic devices.