International Radiation Detectors, Inc.

SXUV Responsivity Stability

It is known that the UV photon exposure induced instability of common silicon photodiodes is caused by the front silicon dioxide window. The PtSi window in the SXUV series diodes replaces this SiO₂ window eliminating the XUV exposure induced instability problem.

Stability tests performed at NIST and LBL showed that quantum efficiency of these devices did not change after exposure to 10 eV 10¹⁶ photons/cm² and 100 eV 10²² photons/cm² fluences respectively. This suggests a radiation hardness of hundreds of Gigarads (Si).

Stability tests performed on the SXUV diodes with a 244 nm CW laser with 8.5 W/cm² power density (1.5 mm diameter spot, 150 mW beam power) show about 4.5% increase in the 244 nm responsivity after 4 days of exposure (total energy received 2.94 MJ/cm²). As this increased responsivity did not decrease after 5 months of storage in nitrogen, it is presumed that the increased responsivity is caused by surface cleaning effects due to the high intensity laser beam.

Figure 1 shows the responsivity stability of SXUV series diodes after exposure to intense radiation at 193 nm from an ArF excimer laser with 100 Hz pulse repetition rate and an energy density of 200 mJ/cm² (3.9W at 100 Hz).

Fig. 1: Stability of SXUV diodes compared to UVG series and p-on-n diodes when exposed to 193nm radiation

Figure 2 shows responsivity stability of SXUV diodes after exposure to billion pulses of 193 and 157 nm radiation with 100uJ/cm² pulse energy density.

Fig. 2: Responsivity stability of SXUV series photodiodes after exposure to 193 and 157nm excimer laser:
-193nm, -157nm

Figure 3 shows the responsivity stability of the SXUV-100 diode compared to the AXUV-100G diode when exposed to 100 eV photons with 3x10¹⁴ photons/sec/cm² flux. After receiving a total fluence of 1.8x10¹⁸ photons, the AXUV-100G diode showed approximately 28 % decrease in response while the SXUV-100 diode showed virtually no change after the same exposure. Further exposure indicated that no change in the SXUV-100 diode responsivity is noticed after receiving a total fluence of 10²² photons.

Figure 3 also shows the responsivity stability of the SXUV-100 and AXUV-100G diodes when exposed to 10 eV photons with 5x10¹³ photons/sec/cm2 flux. Again, virtually no change in the SXUV-100 diode responsivity was noticed after several hours of this exposure.

Fig. 3: Relative responsivity of SXUV and AXUV series photodiodes when exposed to
10 eV and 100 eV photons.

The SXUV-100 photodiodes are currently in the field and are being used in the feedback loop to control the energy of excimer laser pulses. They are guaranteed to have less than 3% variation in response when exposed to 1.6x10⁵ J/cm² total fluence of 157 nm pulses.

The SXUV photodiodes are also guaranteed to have less than 3% variation in response when exposed to 1.6x10⁵ J/cm² total fluence of 157 nm pulses with 100 mJ/cm² pulse energy density.  

Figure 4 shows a scan of the SXUV-100 photodiode surface before and after exposure to 100 eV photons with a fluence in excess of 10²² photons/cm². The arrow indicates the position where the detector was exposed to the synchrotron radiation beam for several hours. The beam sized used was 0.1 mm x 0.5 mm. Taking into account the measurement uncertainty, it may be concluded that there is no change in the diode response after receiving the above fluence. Note also that uniformity of the SXUV-100 diodes is within a couple of percent when scanned with 0.1 mm x 0.5 mm beam.

Fig. 4: Line scan of the SXUV-100 diode with 12.4 nm beam before and after exposure to 10²² photons/cm² 100 eV photons

Figure 5 shows a SXUV-100 with Si/Zr filter after exposure to 16 mW of 60-110 eV photons for 13 hours. The irradiating beam spot size was 0.3mm x 0.05 mm, for a total deposited energy of 0.75 J or 5 kJ/cm² or approximately 4 x 10²⁰ photons/cm². In general, addition of front metal filters does not significantly impact stability of the SXUV-100 devices. A selection of SXUV diodes with directly deposited filters is available on the SXUV filtered diode page.

Fig. 5: Line scan of the SXUV-100 Si/Zr diode with 13.5 nm beam
before and after exposure to 4 x 10²⁰ 60-110 eV photons

Figure 6 shows the responsivity stability of UVG20B, SXUV20A and SXUVPS4C series diodes after irradiation by a 6.53 mW/cm² 185 nm lamp. Total energy deposited totals 16.9 kJ/cm². At this exposure level, degradation was 25% over the course of one month (720 hours). SXUVPS4C and SXUV20A diodes at the same intensity did not show any significant change in responsivity over 1 month of exposure.