The platform for Gigaphoton's twin-chamber system is common to its four generations. From the first generation of twin-chamber system, the GT40A
(4 kHz/45 W/0.5 pm), through the fourth generation, the GT62A (6 kHz/90 W/0.35 pm), the required performance can be obtained simply by upgrading their major modules. Formerly, the platform of the excimer laser system had to be changed every time the repetition rate changed. This imposed a heavy burden on excimer laser manufacturers in terms of cost, time, and manpower for development. Users, meanwhile, needed to re-check reliability every time a new model was released and sometimes suffered initial failures associated with a new model. A twin-chamber system with a common platform, on the other hand, has several advantages: (1) only the major modules need to be developed for every new model, thus allowing timely and speedy new model releases; (2) the reliability achieved by the current model is inherited by the next-generation model; and (3) new technologies developed for the next-generation model can be smoothly introduced backwards into the current model. These advantages, specific to our twin-chamber system, are detailed as follows:
Figure 1. GTA Common Platform Configuration
Development of Major Modules
Module development is outlined as follows, identifying the new technologies introduced for each model:
- Introduction of injection-locking technology (For details, see here)
- Flexible platform usable for next-generation model
- Development of new chamber associated with increase in repetition rate:
A damper is introduced to suppress the influence of acoustic waves in a chamber (because the influence of acoustic waves increases as the repetition rate increases). Also, products generated by the discharge between the electrodes need to be moved away from the discharge area before the next discharge. The increase in the repetition rate causes the time between discharges to be shortened, so therefore the flow rate of the laser gas needs to be increased. To solve this problem, an increase in the CFF (cross-flow fan) motor output is effective, but this directly causes an increase in the power capacity. Therefore, an increase in the motor output is minimized by optimizing the flow channels in the chamber.
- Increased power associated with increase in repetition rate to 6 kHz:
The power supply capacity is increased in association with the increase in the repetition rate to 6 kHz. At the same time, the power increase is minimized by enhancing the efficiency for extracting pulse energy from the chamber.
Figure 2. Technologies Newly Developed for GT60A
- Development of line-narrowing module (LNM) to improve spectral bandwidth:
In order to achieve a spectral bandwidth (E95%) of less than 0.35 pm, a new technology has been introduced to increase the wavelength resolution of the LNM as well as to minimize the thermal impact on the LNM caused by the laser operating conditions.
- Increased power:
Improvement of the spectral bandwidth causes a reduction in pulse energy. Thus, the power (of the power supply) is increased to make up for the pulse energy reduction caused by improvement of the spectral bandwidth.
- Bandwidth Control Module (BCM) provided as standard feature:
The BCM will be detailed in the next update of this technology column.
Figure 3. Spectral Bandwidth Improvement by Introducing High-Resolution LNM
- Development of highly durable optics:
Since the energy per pulse has been increased from 10 mJ to 15 mJ, the optics must be highly durable. Accelerated durability tests have proved that the new optics are sufficiently durable for laser operation at 15 mJ.
Figure 4. Durability of New Optics Checked by Accelerated Test
Two hundred ninety-eight units of the twin-chamber system (GT40A/GT60A) were operating in the field as of the 1st quarter of 2012. At present, the average uptime of these units is 99.7%, and they have made a great contribution to stabilized mass production. This high reliability is inherited by our latest models, GT61A and GT62A (90 W), so that they can be smoothly introduced to a mass-production environment immediately after installation.
Introduction of New Technologies to Current Models
The technologies developed for new models (to increase the life of each module and reduce down time) can be introduced to the current models. Therefore, even users of the current models are able to leverage these advantages.