Roughness control in the processing of 2-inch polycrystalline diamond films on 4H-SiC wafers
September1, 2024
Diamond is an essential material for the manufacture of semiconductors devices, infrared optical windows, heat dissipation and other fields.
The applications have put forward a practical demand that the diamond substrates have an ultra-smooth surface and are free of structural damage. However, precision polishing of diamond is challenging due to the extreme hardness and chemical inertness. A recent study is to prepare nanoscale smooth polycrystalline diamond films with roughness Ra down to 0.1 nm using chemical and mechanical synergies. After processing, the surface roughness and quality of CVD diamond film were characterized, and a material removal mechanism was proposed. The graphitization process is accelerated when diamond contacts the transition metal Fe in the mechanical polishing process. In chemical mechanical polishing process, the polished surface of diamond C is transformed into deformed diamond C* under friction.
A relatively soft polishing pad is used to increase the contact area with the diamond, which is transformed into a softer, easy-to-remove structure under the action of potassium permanganate oxidant, and then the reaction layer is removed again by mechanical friction.
CVD diamond films
Polycrystalline diamond films were deposited on single-crystal 4H-SiC substrates with a diameter of 2 inches using a UP-206 (2.45 GHz) MPCVD machine. The specific growth parameters for growing diamond on 4H-SiC substrates are provided in Table 1. Deposition on the 4H-SiC substrate was carried out at a deposition rate of 6.53 μm/h and an input power of 4 kW for 60 h. The plasma gas used was a mixture of hydrogen (H2) and oxygen (O2), and the source gas was methane (CH4).
Surface morphology and roughness evolution
The main purpose of polishing is to achieve fast, smooth surface finishes over large areas with ultra-low subsurface/surface damage. It is of direct significance to understand the surface morphology changes in the polishing process .
Conclusions
Non-damaged and smooth PCD films are obtained, and the roughness Ra is reduced to 0.1 nm (selected 10 × 10 μm2 region) using the multi-step processing process with chemical and mechanical synergism. CMP is combined with traditional MP to achieve high quality and efficiency. In the MP process, two stages of pre-polishing are performed using W20 and W7 diamond powder, respectively, which accelerate the graphitization process when the diamond contacts the transition metal Fe.
Nanoscale smooth PCD films with roughness <0.2 nm (or even 0.1 nm) were efficiently achieved using a multi-step process, taking advantage of synergistic chemical and mechanical effects. The surface quality and polishing removal efficiency of diamond polishing were further evaluated using three-dimensional laser confocal microscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM). The surface quality of diamond was verified by Raman spectroscopy. The X-ray photoelectron spectroscopy (XPS) of the polished diamond surface further illustrated the removal mechanism of the material.
Diamond semiconductor researching cente
