We report an inexpensive and rapid method to measure the reflectance of dielectrics in the vacuum ultraviolet (VUV) range of the spectrum using synchrotron radiation. Porous low-k organosilicate (SiCOH) dielectrics deposited on silicon were irradiated with VUV photons of various energies. Reflectance is calculated from ratio of the measured reflected photon flux to the measured incident photon flux. A 90% transmitting nickel mesh connected to a picoammeter was used to measure the incident and reflected photon flux. When the sample is absent from the path of the VUV photons, a photon dump is used to minimize any possible reflectance. Thus, the net photon flux incident on the nickel mesh is the synchrotron flux. Under these circumstances the reading from the picoammeter is proportional to the synchrotron flux. When the sample is present some of the photons are reflected from the sample. Since the sample is placed normal to the VUV photon flux, the reflected photons can travel back to the nickel mesh. Thus, under these conditions, the nickel mesh current is sum of the incident synchrotron photon flux and the reflected photon flux. The reflectance is calculated from the two current measurements. The reflectances of SiCOH of different porosities were compared. By using the Kramers-Kronig algorithm, [1] the index of refraction and the extinction coefficient as a function of energy can be obtained from the reflectance. We also find that during VUV irradiation, the reflectance of a dielectric and the substrate current are inversely correlated. Thus, the reflectance can be obtained from the substrate current and vice versa. We conclude that reflectance or substrate current measurements can determine which photon energies are more likely to be absorbed and can therefore cause dielectric damage during processing. [2] Reducing the flux of deleterious photon energies in processing systems can minimize dielectric damage.

 

This work has been supported by the Semiconductor Research Corporation under Contact 2008-KJ-1871 and by IBM Research. The UW-Madison Synchrotron is funded by NSF under Grant DMR-0084402.

[1] D. M. Roessler, Brit. J. Appl. Phys. 16, 1119 (1965).

 

[2] G. S. Upadhyaya, J. B. Kruger, and J. L. Shohet, J. Appl. Phys. 105, 053308 (2009)