A leading provider of engineering solutions used to produce new chips and advanced display equipment, made a strategic decision to overhaul its suite of mask lithography tools. The wholesale upgrade would include replacing all electronics, lasers, and environmental control units (ECU). The company approached Air Innovations for a custom ECU that could meet stringent temperature and humidity requirements needed to preserve expensive instruments and highly sensitive processes for years to come.
There are several challenges inherent in protecting lithography tools in the semiconductor industry and this project presented many of them. First, since the tools were comprised of several different types of metals of various thicknesses, the rate at which they expanded and contracted was different. The ECU would need to maintain extremely tight temperature tolerances to prevent the metals from moving and disrupting the process of transferring circuits onto the masks.
Second, the lithography tools utilized interferometry to track the distance between a laser and a substrate, and this distance was always changing. If the temperature within the tool fluctuated too much, light beams would be unable to accurately calculate the distance to the substrate, disrupting the circuit writing process. Since accuracy between the laser and plate was calculated at the nanometer level, precision was mandatory. Specifically, in order properly calculate, the lithography tool could not experience more than a +/-0.03C temperature variation.
In addition to temperature changes, the light beams were also sensitive to moisture which can negatively impact interferometry. The ECU needed to control relative humidity (RH) so that the lithography tool would not experience more than a +/- 1% RH variation.
Additionally, as this was a retrofit of an existing design, the ECU would need to be mounted within the exact dimensions available inside the electrical cabinet.
Finally, as there are very specific cleanliness and off-gassing requirements in the semiconductor industry, particular attention was needed to be given to the materials of construction to limit any risk of the ECU contaminating the lithography process.
Air Innovations engineered, manufactured, and tested a custom ECU for the semiconductor company that would maintain a temperature of 20℃ within ±0.03℃ with 40% RH with ±1% RH. The system included an electric reheater and hot-gas bypass refrigeration control to maintain the tight-tolerance temperature control. The semiconductor control equipment included an ultrasonic DI (deionized water) humidifier to maintain precise RH conditions.
Given the sensitive nature of lithography tools, Air Innovations included various alarms and sensors to fully monitor the operating characteristics of the ECU. All the critical points were transmitted to the customer’s control system for remote monitoring. The ECU included various safeties such as the ability to close valves, shut down, and sound an alarm in the presence of a leak.
The final ECU for the lithography tool was customized to fit a precise footprint of 32” x 25”x 75”, constructed of powder-coated aluminum, and suited with Poron® microcellular closed-cell insulation. The unit was designed to meet S2 and S8 SEMI standards and meets or exceed UL standards.
The semiconductor lithography company was then able to deliver upgrade kits with essential components—including electrical boxes, lasers, and ECUs—to its chip manufacturers. These modules can be retrofitted into existing lithography tools being used in facilities around the world.
The environmental control unit included the following:
- Set point range adjustable 20℃ to 26℃
- Set point range adjustable 40-50% RH
- 1650 CFM design airflow
- 80 CFM make-up air from surrounding class 10 controlled environment
- 75” external static pressure
- Incoming power 208V/3P at 50 or 60 Hz
- Hot gas bypass refrigeration control
- Electric reheater
- Water-cooled refrigeration system
- Auto-tuning PID loop controllers for temperature and humidity
- Powder coated aluminum and stainless-steel construction
- Poron® insulation to minimize outgassing
- Nominal 1.5 ton R-134a Scroll Compressor
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