Mask Contamination Monitoring System "MCM400"

Along with the pursuit for ever-finer design rule, the wavelength of the light source used in lithography is becoming shorter and shorter. There have been cases that photomasks are contaminated during wafer exposure in the conventional KrF lithography and the causes for these contaminations are due to the effect of residual ions and so on, as the result of insufficient cleaning in many cases. At the same time, energy of light used in ArF lithography is larger than bond energies of chemical substances and multiple gaseous substances can be the cause of contamination, accordingly. At the moment, application of ArF lithography to mass production is vigorously promoted at many semiconductor device makers and the issue of photomask contamination is becoming more and more obvious, as the result of long hour usage of photomasks in the production lines in their start-up procedures. The cause for this kind of contamination is considered to originate in pellicle itself, adhesive materials used in pellicles, and organic gases in ambient atmosphere of lithography operation environment. However, the conventional evaluation techniques do not easily provide determination of the cause for contamination or ways to manage contamination.

The conventional contamination management has relied on mask pattern inspection tools and this method has had such a limitation that contamination is detected only in those cases that the contamination grows into foreign particles of certain size that surpasses the maximum inspection sensitivity of the mask pattern inspection tools. For this limitation, the conventional contamination management has had severe difficulty in obtaining quantitative evaluation and also has needed a long period of time in developing contamination prevention technologies.

In contrast to the conventional method, our new product, the Mask Contamination monitor MCM400, has capability of quantitatively measuring thickness of contamination at the stage of mono molecular layer level, which is far before deposited contamination layer grows to foreign particles. As this monolayer measurement capability provides quantitative contamination evaluation with far shorter a time after mask exposure than the conventional methods provide, contamination prevention technologies can be developed very quickly by performing experiments with shorter cycles. Also, there is always a possibility that contamination occurs by emergent accident in the stage of applying new lithography process to device production. For this kind of accidental contamination issue that could lead to a very serious trouble, our new product, MCM400, provides a solution because regular monitoring of masks by MCM400 will find out contamination well before the contamination grows to foreign particles that could be transferred on wafers as defects.

• The first mask contamination monitor system, in the industry, that measures contamination quantity on photomask used in semiconductor device manufacturing
• The system measures one molecular layer level contamination by non-contact optical method.
• The system is most suitable for the development of contamination prevention technology because the system has capability of quantitative contamination measurement.
• The system is also most suitable for contamination management in device production.
• The system provides not only the measurement of contaminant layer of constant thickness, but also the measurement of localized thickness distribution that may originate to aggregation process of contaminant.
• The system price is as low as just a fraction of the mask inspection system price.

• Laser beams are irradiated on chromium pattern and aperture pattern simultaneously from the glass substrate side and the phase difference of the two reflected beams from each pattern is measured.
• The measurement result is highly stable because this method utilizes the reflected light from interfaces, which are isolated from ambient condition, of the chromium pattern and the glass pattern as the reference wave front.
• Maintainability is good because the system uses a solid state laser.
• Measurement of a minute area with high S/N ratio is available due to utilization of laser confocal optics.
• Automated measurement is available by the image recognition function of measured patterns.
• Mask is handled automatically because mask cassettes such as RSP can be equipped.
• Measurement is easy because the system operationality is high.

Main body and control unit

Standard measurement resolution : 0.5nm*
* The detailed value is defined by a refractive index of contamination material at the measurement wavelength.

Measurement speed : ~ 10 seconds per measuring point
Mask Size : 6025
Outer dimension : Main body W:1080 D:1530 H:1850 mm
Control unit W:800 D:705 H:1750 mm
Weight : About 1t

Please review product page for any further information.