An Indian Patent – A NOVEL ABRASIVE FREE CHEMICAL MECHANICAL PLANARIZATION (AFCMP) OF NON-POLAR AND SEMI POLAR III-V NITRIDE SURFACES has been granted to Dr. Dibakar Das and his team members from University of Hyderabad (UoH) and Tata Institute of Fundamental Research (TIFR), Mumbai for a period of Twenty years.
III-V nitride semiconductors (such as GaN, AlN, AlGaN, InN, InP, InGaN etc), in particular, are ideally suited for a wide range of electronic and optoelectronic applications especially for visible and UV-light emitting devices (LED) and for high-temperature and high-frequency applications in unfriendly environment. Nitride semiconductors have mostly been used in optoelectronics such as blue/green LEDs for various display applications. Recently it has been used for RF and microwave power electronics for applications in wireless communications. III-V nitride semiconductors are formed mostly in wurtzite crystal structure, where the polar planes, with Miller indices (0001 or 000-1), are formed by one type of atoms, such as Ga or N in GaN, for example. Non-polar planes, with Miller indices (11-20, 10-10 etc), which are perpendicular to the polar planes and semi-polar planes, with Miller indices (11-22, 10-11 etc), which are inclined to the polar plane at an angle q < 900, contain both type of atoms, Ga and N in GaN, for example. III-V nitrides with non-polar orientation, such as (11-20) and semi-polar orientation, such as (11-22) are better alternative than polar orientations, such as (0001) or (000-1) for laser diode, visible and ultra-violet LEDs and high power electronic devices applications because of the absence of or large reduction in built-in electric field resulting from spontaneous and piezoelectric polarization. Device applications require a smooth and flat semiconductor surface. However, most non-polar and semi-polar epitaxial layers are grown heteroepitaxially on miscut sapphire substrates, where the anisotropic nature of the growth surface results in a rough surface morphology. Growth of high quality homoepitaxial layer on the bulk crystal is also challenging because of the presence of damaged sub-surface layer in the final mechanically-polished bulk wafer after grinding and lapping. Therefore, very smooth and atomically flat surface (rms roughness £ 0.5 nm) with no sub-surface damage is a pre-requisite for growth of high quality epitaxial device layer. Removal of the surface defects and improvement in surface roughness (rms roughness < 0.5 nm) is done by a process called chemical mechanical planarization (CMP). The current invention on abrasive free chemical mechanical planarization (AFCMP) technology is a significant step towards development of high quality device layer for fabrication of electronic devices based on III-V nitride semiconductors.
Dibakar Das, S Vijayalakshmi, Khushnuma Asghar (UoH)
Arnab Bhattacharya, A Azizur Rahaman, Nirupan Hatui (TIFR, Mumbai)
Indian Patent No. : 396483 granted for 20 years from the 1st day of August 2013 in accordance with the provisions of the Patents Act, 1970.