Amplification and surface topography in synchrotron radiation induced dry etching of Si with XeF2

Abstract

The topography of Si͑100͒ surfaces is investigated by scanning electron microscopy after generating replicas using photoinduced dry etching with radiation predominantly in the wavelength range between 105 and 122 nm. XeF 2 and Ar mixtures provide high selectivity with a structural resolution of about 100 nm. Pores and grains indicate that single photons initiate chain reactions with an amplification of 3ϫ10 5 . The overall quantum efficiency of removed Si atoms per incident photon above unity leads to a probability for stimulation of a reaction per incident photon of 6ϫ10 Ϫ5 . Addition of O 2 increases the amplification factor, reduces the excitation probability, and causes a reduced selectivity at high irradiation intensity.

Reactions of halogens with surfaces stimulated by VUV light

“…Such a structure could be separated from smaller steps due to inhomogeneities on the surface. Inspection of the transition area between etched and shaded parts in Si/XeF 2 indeed revealed these pitches with a density distribution as expected from the light intensity distribution [18] in SEM (scanning electron microscopy) pictures. The pitch size appeared also as a roughness in those parts which where etched much deeper than a single pitch diameter.…”

“…They represent the reservoir to be stimulated by light for a reaction. A fluorosilyl layer with a tree-like structure of Si-F bonds plays this role in the Si case [18]. Efficient light induced etching requires gas pressures of XeF 2 and Cl 2 of the order of 10 −2 and 1 mbar respectively.…”

“…In addition they have strong electronic transitions in the spectral range from 150 to 50 nm and it is expected that the reactivity can be enhanced further by stimulating these excited states with light. The reactions are induced on Cu plates [11][12][13][14][15] and films [16] and on single-crystalline Si(100) [17][18][19][20][21][22][23] and GaAs(100) [24][25][26][27] surfaces in order to cover relevant metallic and semiconductor systems. Due to the high reactivity of halogens it is necessary in a first step to separate the reaction of ground state atoms, which is independent from irradiation and therefore called dark reaction, from the light induced reactions.…”

Microstructuring of Si(100) by light induced dry etching in the VUV

“…The efficiencies above unity demand complex amplification processes. A better understanding of the processes contributing to etching and especially to quantum efficiencies larger than unity follows from the details of the topography of the etched replica [12]. It is necessary to distinguish between the overall absolute quantum efficiency q which represents the number of etched atoms per incident photon and the efficiencies of the different processes involved in etching.…”

“…From the size of the pores etched by single photons, values of the order of 10 5 were estimated for q reac [12]. This means that one photon initiates a chain reaction with an amplification given by q reac .…”