Client: Semiconductor Equipment Manufacturer
Application requirements:
- A high vacuum UHV viewport for UV emitting, plasma-process vessel.
- UV must be blocked while simultaneously allowing the transmission of visible light, both states at high efficiency.
Critical Issues:
- Personnel eye protection and safe viewing into process vessel.
- Protective filter outside the process envelope to prevent alteration of transmission properties.
- Clear but unobtrusive markings to indicate window is safe for viewing.
Design Basis:
- UV light is electromagnetic radiation with wavelengths between soft x-rays and visible violet light. It is often divided into three regions: UVA (315-400nm), UVB (280-315nm) and UVC (100-280nm).
- Long-pass, UV blocking edge filters protect against UV exposure primarily by reflecting short wave radiation.
- Eye protection standard ANSI Z80.3 mandates that both UVA and UVB be blocked at >99%
- Visible transmission required >90%
- Edge filtered with OD>2 (99% efficiency) meeting the 90% transmission requirement.
Results:
MPF designed a tamper-proof adapter which mounts a long- pass, edge-filter as a cover for a sapphire window. The filter-coating is sandwiched between filter substrate and window such that the coating is protected from inadvertent contact and potential damage. Further, the window is indelibly marked with text indicating the blocked UV wavelengths, ensuring that only safe UHV viewports, thusly marked, are used for viewing the active plasma.
A wide range of band-pass, short-pass and long-pass filters are available for special applications. Filters can be of the coated variety or made of filter glass. Optical densities up to OD>5 (>99.999%) are available with high transmission in the visible.
For more information regarding specific optical filter applications, see Optical Filters by Blue Ridge Optics.
