| AVS 55th International Symposium & Exhibition | |
| Applied Surface Science | Tuesday Sessions |
| Session AS-TuA |
| Session: | Practical Surface Analysis |
| Presenter: | V. Fernandez, IMN-CNRS, France |
| Authors: | C. Cardinaud, IMN-CNRS, France S. Bouchoule, LPN-CNRS, France V. Fernandez, IMN-CNRS, France |
| Correspondent: | Click to Email |
Angular X-ray Photoelectron Spectroscopy (XPS) is usually a well suited technique to obtain and discriminate chemical information from the bottom and the sidewall of periodic patterns, such as an array of ridges.1,2,3 In most commercial XPS systems, the direction of analysis is vertical, i.e. normal to the sample surface, while the x-rays strike the surface with an angle of incidence (α) usually close to the magic angle (54.7°). And the tilt axis is perpendicular to the plane defined by the x-rays and the analyser. Assuming the x-rays are not significantly absorbed by the sample as it is the case for silicon, resists or dielectric materials, this setting allows to analyse the bottom of the pattern (as well as the top of the ridges). Tilting the sample towards the x-ray source to an angle θ, allows to shadow the bottom and observe photoelectrons coming from the ridges sidewall (and the top of the ridges). Obviously the suitable value for θ is given as atan(space width / ridge height). Problems arise whenever the ridges are sufficiently wide to absorb significantly the x-rays. This may occur for III-Vs materials such as InP or GaAs widely used in photonics. For example InP ridges having a width of 1.8µm will absorb 99% of AlKα, under 60° angle of incidence. Then for θ=0 the bottom is irradiated only in part, and very weakly or even not at all if α>atan(space width / ridge height). In the same way, at angle θ to obtain full irradiation of the sidewall that comes in the analyser line of sight requires that θ>α. However this may not be satisfying with regards to the pattern dimension. Taking advantage of the absorption of the x-rays, an alternative angular configuration exists: it consists in tilting the sample opposite to the x-ray source until the bottom is totally screened. Simultaneously, this brings the sidewall that is irradiated in the analyser line of sight. In the present communication we expose and discuss in detail the advantages, drawbacks and limits of these two configurations. The XPS system used here is a Kratos Axis Ultra, several operating modes are experienced for the surface analysis of etched InP patterns.
1C.S. Fadley, Prog.Surf.Sci. 16(1984)275
2G.S. Oehrlein, J.Appl.Phys. 64(1988)2399
3 E. Pargon, J.Vac.Sci.Technol. 23(2005)1913.