EUV mirror based absolute incident flux detector

Details EUV mirror based absolute incident flux detector EUV mirror based absolute incident flux detector

2001-09-18

2004-03-23

Hannaher, Constantine (Department: 2878)

Radiant energy

Invisible radiant energy responsive electric signalling

Ultraviolet light responsive means

C250S365000

Reexamination Certificate

active

06710351

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a flux detector device and more particularly to an absolute incident extreme-ultraviolet radiation detector for in-situ monitoring.
BACKGROUND OF THE INVENTION
In general lithography refers to processes for pattern transfer between various media. Projection lithography is a powerful and essential tool for microelectronics processing.
FIG. 2
schematically depicts an apparatus for extreme-ultraviolet (EUV) lithography that comprises a radiation source
11
, such as a synchrotron or a laser plasma source, that emits EUV radiation
12
into condenser
13
which in turn emits beam of light
14
that illuminates a portion of reticle or mask
15
. The emerging patterned beam is introduced into the imaging optics
16
which projects an image of mask
15
, shown mounted on mask stage
17
, onto wafer
18
which is mounted on stage
19
. Element
20
, an x-y scanner, scans mask
15
and wafer
18
in such direction and at such relative speed as to accommodate the desired mask-to-image reduction.
Measuring and regulating the EUV radiation flux through the lithography system is critical to maximizing performance. Prior art techniques for measuring the flux typically employed devices with EUV-sensitive vacuum photodiodes, which were difficult to calibrate to an absolute standard. One reason is that the electronic work function of the surface on which the EUV radiation impinged was influenced by environmental conditions. This phenomenon is commonly known in the art to as “band bending.” For instance, surface contamination caused the work function to vary. Since the detector's response changed with environmental conditions, it was necessary to continuously recalibrate the devices. The art is in need of a reliable, cost effective EUV radiation flux detector whose calibration.
SUMMARY OF THE INVENTION
The invention is based in part on the recognition that an EUV mirror based, absolute flux detector can be fabricated by embedding an integral EUV photodiode beneath a multilayer reflection stack. This detector exploits the fact that a multilayer reflection stack can be designed to selectively transmit a desired amount of radiation through the stack. For example, a 40 bi-layer molybdenum/silicon EUV multilayer reflection stack allows the transmission of approximately 0.7% of the mirror's programmed peak wavelength through the stack. Since the intensities typically incident on the multilayer are quite high (approximately 10
9
-10
13
photons/cm
2
shot), the signal generated on the photodiode after the 1:1000 attenuation will be quite high. Given that the detector has a multilayer reflection stack as the radiation incident surface, and that the diode detector does not respond to the photoelectric current originating from the surface of the detector (the way a vacuum photodiode operates), the response of this detector will not substantially change with time and/or environmental conditions.
In one embodiment, the invention is directed to an extreme ultraviolet (EUV) radiation flux detector that includes:
a photodiode with an EUV sensitive region;
a planarizing layer positioned on the EUV sensitive region of the photodiode; and
multilayer film positioned on the planarizing layer wherein the multilayer film is exposed to EUV radiation.


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