PhD Position in Dual-color ultrafast laser welding of semiconductors (M/F)

Job Description

Thesis Subject

Transmission ultrafast laser micro-welding is an emerging manufacturing technology with growing applications across photonics, microelectronics, and advanced materials. By focusing ultrashort laser pulses at the interface between two transparent materials, localized melting and mixing can be achieved, enabling strong, precise bonding upon resolidification.
While this technique has been successfully demonstrated for glasses, ceramics, and polymers, extending it to semiconductors—particularly silicon—remains a major scientific and technological challenge. Silicon's high refractive index (n ≈ 3.5) and narrow bandgap (~1.12 eV) lead to strong optical limitations, including beam delocalization, nonlinear propagation, and plasma screening. These effects significantly hinder energy delivery at the interface and limit reliable welding.
Recent breakthroughs in our group have demonstrated, for the first time, transmission laser welding of silicon using nanosecond pulses, achieving shear strengths exceeding 10 MPa for both similar and dissimilar semiconductor assemblies (e.g., Si and GaAs). However, fundamental barriers remain—most notably the strong reflectivity at the interface, which restricts energy transmission, especially when the interfacial gap is comparable to or larger than the laser wavelength. In such cases, the interface behaves as a Fabry–Perot cavity, severely limiting coupling efficiency.
This PhD project aims to overcome these limitations through an innovative dual-color laser strategy. The core idea is to employ two synchronized laser beams at different wavelengths (λ₁ and λ₂), engineered such that one compensates for the reflection of the other (e.g., λ₂ offset by λ/4 multiples). This approach ensures that, even under unfavorable interference conditions, at least one wavelength efficiently transmits through the interface to enable welding.
The candidate (M/F) will:
• Design and implement a dual-wavelength ultrafast laser system (femtosecond laser, optical parametric amplifier).
• Investigate light–matter interaction mechanisms in semiconductors under dual-color excitation.
• Develop analytical and numerical models to understand energy coupling at interfaces.
• Perform laser irradiation experiments with in situ diagnostics and microscopy.
• Characterize welded interfaces using advanced material analysis techniques.
• Extend the approach to non-ideal and non-uniform interfaces, moving toward real-world applications.
This project offers a unique opportunity to contribute to a cutting-edge solution in laser processing of semiconductors, with strong potential impact in microelectronics packaging and photonic device integration.

Your Work Environment

The PhD will be carried out in the LP3 laboratory (Marseille) and enrolled at Aix-Marseille Université (AMU) under la supervision of P. Sopeña and D. Grojo.
LP3 Laboratory is a Joint Research Unit (UMR 7341) of AMU and CNRS. LP3 conducts original research on the physics of pulsed laser-matter interactions and the development of new laser-based processes.
The laboratory is a major national and international player in many fields of pulsed laser-matter interaction, including ablation and plasma diagnostics, LIBS spectroscopy, laser plasma X-ray source generation and in the development of innovative processes and laser-based procedures for the functionalization and transformation of matter. Recent achievements encompass 3D laser writing in silicon, 3D (sub)-micrometric additive printing, laser-synthesis of nanoparticles and development of diagnostics processes, and (sub)micro-structuration of dielectrics materials. The laboratory operates two high-tech laser platforms ASUR (Applications of Ultra-Fast Sources) and LaMP (Lasers for Micro-Processes). The
This PhD is funded within the framework of the PROSECO project (ANR-24-EXLU-0012) of the PEPR LUMA, a collaboration between INPHYNI (Nice, France), FEMTO-ST (Besançon, France), and LP3. The project will be carried out in LP3, in an international environment with multiple PhD students, postdoc, master students, researchers, professors, and engineers. Mobility opportunities to the project partner labs are envisioned, as well as participation in national and international conferences and training events.

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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