Polycrystalline inclusion-free growth of thick, lattice-matched SiGeC with high substitutional Carbon concentrations up to 2%
Authors: Frauenrath Marvin , Vives Jeremy , Devaux Matteo , Blondel Claudel , Aybeke Ece , Obeid Baydaa , Duru Romain , Levert Theo , Printemps Tony , Verdier Stephane , Deprat Fabien 
Published: December 2024

State of the art semiconductor manufacturing seeks to expand its range of Si-based materials with novel properties, boosting performance to comply with customer demands. These materials mostly comprise of large lattice parameter materials like Ge-rich or group III/V alloys. To reduce costs, heteroepitaxy of these materials on Si substrates is desired. Buffer solutions like SiGe [1] or Ge Virtual Substrates [2] or III/V patterned Superlattices [3] usually do not result in threading dislocations densities below 106 cm-2, which affects device performance and process robustness.

The incorporation of Carbon into SiGe allows to tailor SiGe’s lattice parameter, theoretically enabling to match the Si substrate’s lattice parameter. This allows the strain-free growth of a few hundred nanometers up to several micrometers thick SiGeC on a Si substrate without the formation of dislocations.

The growth of SiGeC was performed in a 300 mm industrial standard Reduced Pressure-Chemical Vapor Deposition (RP-CVD) reactor. Si2H6, GeH4 and SiH3CH3 were used as precursors with constant flows at 550°C, 10 Torr. Interstitial (C
Int) and substitutional Carbon (C
Sub) concentrations were determined by XPS. [4]

For a 50 nm SiGeC layer with C
Int~0.4% and C
Sub=2.0%, smooth surfaces were observed by top view Scanning Electron Microscopy (SEM) (Fig. 1 (a)) and confirmed by Atomic Force Microscopy (AFM) (Fig. 1 (b)) with a RMS of 0.23 nm. X-Ray Diffraction measurements showed the growth of SiGeC lattice matched to the Si substrate (Fig. 1 (c)). Above ~250 nm, islands are visible on the surface by top-view SEM (Fig. 2 (a)) with the island’s diameter increasing as the SiGeC layer thickness increased. Transmission Electron Microscopy showed a dislocation free growth and that the islands/clusters were polycrystalline, originating from several hundred nanometers below the surface (Fig. 2 (b)).

Growing SiGeC of the same thickness range under the same growth conditions with lower SiH3CH3 flow, resulted in fully substitutional incorporated Carbon with C
Sub~1.0% and C
Int below the detection limit. No islands/clusters were observed by SEM and AFM (Fig. 2 (c)). The elimination of C
Int allowed to suppress the formation of polycrystalline SiGeC inclusions. The starting point of these defects should be due to point defects formed by C
int clusters.

Even if the reduction of SiH3CH3 flow resulted in defect free growth of thick SiGeC on Si substrates, other approaches are mandatory to incorporate higher C
Sub into the SiGeC layer to achieve the desired novel properties. Dhayalan et al. [5] showed in the literature the growth of SiC with 2% of Carbon (C
Sub=1.6%) without the formation of islands/clusters by introducing HCl during a Cylic Deposition Etch (CDE) process. These results are based on the preferential etching of C
int point defects, which are preferentially etched by HCl, reducing the amount of C
Int and preventing the formation of islands/clusters. Meanwhile, the C
Sub was not significantly affected by HCl etching.

The impact of HCl on the growth of SiGeC was evaluated by performing co-flow (simultaneous growth and etching) and CDE (separate growth and etching steps) with various small HCl flows, preventing aggressive etching of monocrystalline SiGeC, and varying the duration of the CDE etch step. The introduction of HCl during a co-flow process changed the C and Ge incorporation. The C
Sub concentration varied between 2.0% and 1.9% (Tab. 1), while the interstitial Carbon concentration varied between 0.7% and 0.3%, which is the lower detection limit of the XPS measurement. The Germanium concentration increased from 20% to 25% (Tab. 1). The growth of SiGeC without Chlorine showed the transition to a polycrystalline material at the same Carbon composition for higher Ge concentrations. XRD profiles (Fig. 3) showed a good crystalline quality, well-defined SiGeC peak, outlining a reduction of C
Int thanks to the HCl etching. The CDE process did not result in significant compositional changes. To gain further understanding a wider range of HCl flows and thicker layers will be investigated in the future.

The growth of dislocation free, high crystalline quality SiGeC with high C
Sub was demonstrated. It was outlined that interstitial Carbon was likely to create point defects which lead to polycrystalline islands/cluster formation for thick films. HCl was shown to reduce interstitial Carbon incorporation. Other materials with large lattice parameters could benefit from the knowledge gained on defect reduction and lattice matched growth.

[1] Y. Bogumilowicz et al., J. Cryst.
Growth, vol. 283, no. 3, 2005.

[2] J. M. Hartmann, J. Cryst. Growth, 2018.

[3] J.-S. Park, M. Tang, S. Chen, and H. Liu, Crystals, vol. 10, no. 12, 2020.

[4] J. Vives, J Mater Chem C, 2023.

[5] S. K. Dhayalan et al., ECS J3ST, p. 6, 2017.

Figure 1