Overhaul Report for the Mex-L2 Technolas 193nm Excimer Laser

Introduction

This report systematically documents a comprehensive in-depth maintenance and performance optimization process for a Mex-L2 Technolas 193nm ArF excimer laser. The purpose of this maintenance was to address core issues such as output energy attenuation and stability degradation caused by long-term high-load operation. The maintenance scope covered key subsystems including the optical cavity, discharge system, gas circuit, electrical control, and cooling air path.

Through thorough cleaning, refurbishment of key components, replacement of aged and damaged parts, and precise calibration, the equipment performance was excellently restored. Final tests showed that the laser's maximum single-pulse energy reached 153.6 mJ (@27kV), and the energy stability (relative standard deviation) was better than 1.4% (@10Hz). All key parameters significantly exceeded 80% of the original factory specifications, far surpassing the contractually stipulated acceptance criteria (>100 mJ). This report concludes by providing long-term maintenance strategies and recommendations aimed at extending the equipment's service life and ensuring stable operation in the future.

Maintenance Background and Detailed Work Content

This in-depth maintenance primarily included the following detailed tasks:

1. Laser Cavity Opening and Comprehensive Maintenance

Operation: The laser cavity was opened strictly according to operating procedures in a clean environment.

Optical Component Handling: The fully reflective mirror and output coupling mirror of the resonant cavity were non-destructively cleaned using specialized lint-free paper and high-purity solvents. A He-Ne laser was used to assist in checking the optical path alignment before and after cleaning.

Mechanical Check: All optical component mounts were checked for tightness and stability to ensure no looseness, guaranteeing long-term stability of the optical path.

2. Discharge Electrode and Pre-ionization System Cleaning

Problem Diagnosis: After opening the cavity, it was found that the surface of the main discharge electrodes was covered with uneven black sputter and small amounts of metal fluoride; the ceramic shell of the pre-ionization structure showed signs of arc erosion.

Processing Technique: The electrodes were finely hand-polished using specialized polishing paste and cloth to restore their mirror finish and improve discharge uniformity. The pre-ionization assembly was disassembled, cleaned, and aged insulating ceramic parts were replaced. This step was the most critical part of restoring laser efficiency and energy stability.

3. Gas Circulation Drive Power Supply Repair

Fault Localization: Testing revealed distorted output waveforms from the power module, causing abnormal drive voltage for the fan motor, resulting in unusual noise and speed fluctuations.

Repair Measures: Damaged drive devices and filter capacitors were replaced, solder joints were re-soldered, and output parameters were recalibrated. After repair, the fan operated smoothly and noise returned to normal, ensuring uniformity of laser gas mixture.

4. Cavity Circulation Air Path System Cleaning and Refurbishment

Operation: The circulation air ducts were completely disassembled, and accumulated powder and other contaminants inside were removed using isopropyl alcohol and a high-pressure air gun.

Updated Components: Aged duct seals and the electrostatic precipitator (used to adsorb impurities and by-products in the laser gas) were replaced to ensure gas purity and circulation efficiency.

5. Laser Cavity Gas Tightness Restoration

Standard Operation: Cavity seals were replaced and leak testing was performed again.

Inspection: A high-precision helium mass spectrometer leak detector was used to check the cavity for leaks. The final leak rate was better than 5x10⁻⁷ Pa·m³/s, far exceeding operational requirements, ensuring long life of the working gas (Ar /F₂ /Ne mixture) and energy stability during prolonged operation.

6. Full System Integration and Testing

After assembling all components, vacuum pumping, purging with high-purity nitrogen, and final filling with working gas were performed.

An external high-precision energy meter, spectrometer, and oscilloscope were connected for comprehensive performance testing and data acquisition.

3. Contractual Requirement Specifications

According to the contract, the post-maintenance equipment must meet:

• Overall laser performance restored to over 80% of original factory specifications;

• Maximum single-pulse energy >100 mJ (193nm);

• Extended service life, ensuring long-term stable operation.

Maintenance Test Results

1. Wavelength Verification

Test Equipment: Spectrometer.

Result: The central wavelength was stably locked at 193.3 nm, with a full width at half maximum (FWHM) < 0.5 nm, consistent with ArF excimer laser characteristics. No other stray peaks were observed, indicating good condition of the optical cavity mirrors and correct gas mixture ratio.

Image Description:

The horizontal axis is wavelength (unit: nm), and the vertical axis is intensity (relative units). The chart shows a sharp and symmetrical peak centered at 193.3nm, confirming the accuracy and purity of the output wavelength, meeting the standard ultraviolet output of excimer lasers.

2. Pulse Energy and Stability

Test Equipment: Energy meter.

Result Analysis: As shown in the table above, the energy output shows a good linear relationship with the high voltage. At the contractually required 27kV, the maximum single-pulse energy reached 153.6 mJ (@27kV), far exceeding the >100 mJ standard. Crucially, the energy stability (measured by relative standard deviation RSD%) remained better than 1.8% even at 10Hz operation, demonstrating excellent condition of the discharge uniformity and gas circulation system. The slightly lower energy at high repetition rates is due to the thermal lens effect, which is normal.

3. Beam Profile Analysis

Test Method: Using UV-sensitive burn paper.

Result: The beam profile was a regular rectangle, approximately 15mm x 5mm in size, with uniform energy distribution, sharp edges, and no significant distortion or hollowing. This indicates precise resonator alignment and uniform electrode discharge.

Image Description:

The burn pattern on the paper shows a bright, uniform rectangular spot, with dimensions meeting specifications and overall uniform energy distribution, proving excellent beam quality suitable for precision material processing applications.

4. Pulse Waveform Measurement

Test Equipment: Fast-response photodiode and high-speed oscilloscope.

Result: The pulse width (FWHM) was approximately 18 ns, with a steep rising edge and no significant double peaks or shoulders, indicating sufficient pre-ionization and a fast, well-synchronized main discharge process.

Image Description:

The oscilloscope screenshot shows a typical excimer laser pulse waveform. The horizontal axis is time (unit: ns), and the vertical axis is intensity (relative units). The measured pulse FWHM is 18 ns, with a clean waveform, indicating excellent condition of the discharge circuit.

5. Test Site Record

Video Description:

Laser unit operating status. Shows the overall appearance of the laser after maintenance, with equipment doors closed, control panel indicators displaying normally, and in normal operation.

Video Description:

Data acquisition and monitoring interface. Close-up shows the data monitoring screen during operation, including real-time energy readings, high voltage setting, repetition rate, and other parameters, as well as the acquisition instrument interface for ongoing energy acquisition.

Comprehensive Conclusion and Improvement Suggestions

Conclusion:

This in-depth maintenance was completely successful. The equipment performance was not only fully restored but its output energy and stability even exceeded expectations. This indicates that the core components of this laser (such as the Blumlein circuit, optical substrates) are still in good condition with high remaining value. This maintenance effectively avoided the high cost of purchasing new equipment and extended the service life by at least 3-5 years.

Long-term Improvement Suggestions:

Regular Maintenance: Recommend inspecting the gas circulation system every 6-12 months.
Electrode Monitoring: Check electrode surface condition after every 1 million discharges to avoid excessive sputter accumulation.
Environmental Control: The operating environment should be kept low in dust to prevent airborne particles from entering the cavity and affecting optical components.
Intelligent Monitoring: Introduce an online monitoring system (energy, current, voltage) to promptly detect abnormalities.
Lifetime Management: Establish a complete lifetime record by logging gas replacement cycles and electrode maintenance times.

FAQ

Q1: Why does an excimer laser require regular maintenance?

A: Long-term operation leads to: deposition and corrosion on electrode surfaces due to discharge, which can cause energy drop; contamination of optical windows, leading to uneven beam profiles; attenuation of gas composition, causing pulse energy fluctuations; aging of seals, leading to gas leaks affecting lifetime. Therefore, regular maintenance restores performance and extends equipment life.

Q2: How long will the post-maintenance performance last? When is the next major overhaul expected?

A: The duration of performance retention is directly related to workload and the quality of routine maintenance. Under a recommended preventive maintenance schedule, core performance is expected to remain stable for 12-18 months. Afterwards, energy will slowly decline due to gas aging and slight electrode corrosion, which can be partially restored by replacing the working gas. The next major overhaul of similar scale is anticipated in 3 to 4 years, or should be considered after cumulative operation exceeds 150 million pulses.

Q3: Why is energy stability (RSD%) so important?

A: Energy stability directly determines the consistency of processing results and yield rate. Especially in micro-processing, a 1% energy fluctuation can cause defects such as uneven processing depth, failure to cut through, or over-burning. The post-repair stability of below 1.8% (at 10Hz) is excellent industrial-grade performance, sufficient for most precision application needs.

Q4: If a sudden energy drop occurs in the future, what should we do first?

A: First, perform a "gas refill" operation. Over 90% of sudden energy drops are caused by gas aging or minor leaks. If the problem persists after refill, please record the energy readings and any alarm messages, then contact our technical support for remote diagnosis. Do not open the cavity yourself.

Q5: Can the output energy be further increased?

A: This unit has already output 156 mJ at 28kV, very close to its design limit. Long-term operation above 27.5kV is not recommended, as it significantly accelerates electrode and gas aging, shortens maintenance intervals, and even risks shutdown. The 153 mJ energy already fully meets the original design application requirements.