Characteristic properties of macroporous silicon sintering in an argon atmosphere

The temperature and time dependences of the sintering of macroporous silicon in Ar or Ar + 3% H$_2$ are studied. The contribution of various mechanisms governing this process is determined. The specific features of the sintering of macroporous silicon are examined by means of isochronous and isothermal annealing of the samples with ordered and random macropores in the temperature range 1000–1225$^\circ$C. It is found that the sintering of macroporous silicon under atmospheric pressure in an inert gas flow containing 2 $\times$ 10$^{-4}$% O$_2$ is greatly affected by thermal etching. Thermal etching competes with the substance-transfer processes characteristic of sintering and hinders the formation of a defect-free surface crust. The reason for etching consists in that gaseous silicon monoxide is generated and then carried away by the gas flow. The etching effect is dominant in the low-temperature range and is independent of whether H$_2$ is added. The values obtained for the activation energy of the silicon diffusion coefficient, $E_a$ = 2.57 eV, and for the exponent $n$ = 3.31–3.74 in the time dependence of the pore radius, $r\sim t^{1/n}$ are indicative of a mixed substance-transfer mechanism via the surface and volume diffusion of silicon atoms.