Multilayer CdHgTe-based infrared detector: 2D/3D microtomography, synchrotron emission and finite element modelling with stress distribution at room temperature and 100 K

Abstract

The mechanical behaviour of a CdHgTe-based infrared detector was evaluated after processing at several temperatures to determine the impact of thermomechanical loading on residual stress and reliability. The architecture of the detector was first entirely characterized, relying on SEM, X-ray microtomography and diffraction analysis, in order to get the nature, the morphology and the crystallographic orientation of all the constitutive layers, and in particular the indium solder bumps. The results notably showed the unexpected single crystal aspect of the indium bumps with a repeatable truncated cone geometry. To obtain the thermomechanical response of the structure after processing and in the range of operating temperatures (from 430 K to 100 K), a 3D Finite Element model was then developed. As expected, the numerical results showed a stress gradient evolution in the structure from high to low temperatures, with high loca njvvl stress around 30 MPa in the CdHgTe at 100 K, mainly due to the thermal expansion coefficient mismatch between the different layers. They highlighted the significant influence of the geometry and the single crystal nature of the bumps as well as the behaviour law of the different materials.

Simulation and measurement of residual stress and warpage in a HgCdTe-based infrared detector at 100 K

“…For the stress results in HgCdTe, the value obtained with the nominal FEM model is 49 MPa: it is thus less influenced by elastic assumption and geometry simplification than warpage (even equation (10) led to a value only 9% higher). As expected from the analytical models, (apart from edge effects and stress concentration), the stress in HgCdTe is biaxial and homogeneous in x and y directions (Fig.…”

“…Some XRD stress measurements in HgCdTe have already been published in literature, considering a simple epitaxial layer on a CdZnTe substrate [7,8] and an achieved IR detector [9,10]. For the epitaxy process, biaxial stress values were measured, mainly induced by imperfect lattice match between Hg 1-x Cd x Te and Cd 1-y Zn y Te.…”

“…Considering the IR detector, biaxial stresses (compressive at room temperature and tensile at low temperature) were also highlighted and the corresponding values were in good agreement with the above-mentioned difference in CTE between HgCdTe and silicon. A gradient between the center and the edges of the samples was reported [9], but the origin remains to be clearly identified, even with Finite Element Method (FEM) [10]. The warpage evolution with temperature for such detectors does not seem to have ever been studied before, but numerical simulations have been performed on InSb-based detectors [11,12] without any measurements at low temperature.…”

“…Thermomechanical issues in such detectors also exist at the micrometric scale, such as stress gradient in HgCdTe at the pixel scale [10] and other phenomena which impact reliability of interconnections in all flip-chip devices. From what we know, both scales are important, but neither experimental nor simulation methods enable to study both of them at the same time.…”

In-situ mapping of local orientation and strain in a fully operable infrared sensor

“…It is known that In bumps with tetragonal crystal structure are highly anisotropic in their thermomechanical behavior [27][28][29] . Lebaudy et al showed that the thermomechanical response of IR detector can yield notable variations due to random crystallographic orientations of the In bumps [30] .…”