AVS 59th Annual International Symposium and Exhibition
    Applied Surface Science Monday Sessions
       Session AS-MoM

Paper AS-MoM4
XPS Characterisation of InP Features Etched in Cl2-Ar and Cl2-H2 Inductively Coupled Plasmas

Monday, October 29, 2012, 9:20 am, Room 20

Session: Quantitative Surface Chemical Analysis, Technique Development, and Data Interpretation - Part 1
Presenter: C. Cardinaud, CNRS, France
Authors: C. Cardinaud, CNRS, France
R. Chanson, CNRS-IMN, France
S. Bouchoule, CNRS-LPN, France
A. Rhallabi, Université de Nantes, France
M.-C. Fernandez, Université de Nantes, France
Correspondent: Click to Email
High-aspect-ratio etching of InP-based heterostructures is a critical building block for photonic device fabrication. This study is focused on the chemical characterisation of the bottom and sidewall surfaces of InP ridge patterns etched with Cl2-Ar and Cl2-H2 plasmas using a SiNx mask. Each sample contains five arrays combining various ridge widths (1.5 to 4µm) and space widths (5 to 16µm) plus four InP and mask open areas. Experiments are carried out in a Kratos-Axis-Ultra. 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 = 60°. The sample can be rotated in azimuth to align precisely the arrays, either parallel to or perpendicular to the plane defined by the x-source and the analyser. The first arrangement enables the analysis of the bottom (as well as the top of the ridge), whereas the second arrangement allows the analysis of the sidewall after tilting the sample. In this latter case two configurations are used. Taking advantage of the absorption of the x-rays by the InP ridges (1.8µm of InP absorbs 99% of AlKα under 60° of angle of incidence), the first configuration 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. Tilting the sample towards the x-ray source to an angle θ = atan(space width / ridge height) allows to shadow the bottom and observe photoelectrons coming from the sidewall (and the top of the ridges), in this case θ needs to be larger than α to obtain full irradiation of the sidewall that comes in the analyser line of sight.

For each array, the intensity of the In, P, N and Si core levels, normalised with respect to that measured on the mask and InP open spaces, are compared to the corresponding ratio calculated from the geometry of the array and the analysis arrangement or configuration. Modelling takes into account the contribution of the various surfaces (mask, InP) in the line of sight of the analyser, and the rate of irradiation according to the geometry of the array and the nature of the materials (InP ridge, mask) the x-rays pass through. This comparison points out the relation between the intensity emitted from the bottom and the aspect ratio of the array. A good agreement is obtained when including the analyser acceptance angle to the model. Concerning the sidewall the discrepancy between experiment and simulation corroborates the presence of a passivation layer. The presentation will discuss in detail the influence of the plasma chemistry on the quantitative composition of the sidewall and the bottom.