Effect of Hydrogen-Ion-Implantation on Self-Separation of Free-Standing Gallium Nitride Wafers Grown By Hvpe
Authors: Park Jin-Seong , Shim Jae-Hyoung , Lee Jae-Eon , Shim Tae-Hun , Park Jea-Gun 
Published: February 2020

In recent years, free-standing Gallium Nitride (FS-GaN) wafers were utilized as substrates for high-brightness light-emitting-diodes (HB-LED), LASER diodes (LD) and power devices due to their characteristics, such as 3 times higher thermal conductivity than sapphire substrates and higher breakdown voltage than conventional Si substrates. The FS-GaN wafers grown by hydride vapor phase epitaxy (HVPE) demonstrated lower dislocation density (DD) than that of GaN wafers grown by metal-organic chemical vapor deposition (MOCVD) on sapphire substrates (template GaN wafer). However, one of big challenges for their commercializing is the crack free FS-GaN wafers during the HVPE GaN growth, which resulted in lowering the productivity and increasing the fabrication cost. The main cause of the cracking is the stress induced by the differences in thermal expansion coefficients (TEC) and lattice constants of sapphire and GaN. To overcome this issue, the design of GaN growth process with self-separation is the key technology. The self-separation technique consists of two key points, one is separation enhancement and the other is blocking edge-poly-GaN growth. In this study, we investigated the effect of hydrogen-ion-implantation on self-separation of FS-GaN wafers. In addition, the blocking effect of edge grinding of template GaN wafers was also investigated.
Two-inch-diameter template GaN wafers with the GaN layer thickness of 5 μm were prepared and the hydrogen-ions were implanted with various dose conditions to enhance self-separation of FS-GaN wafers from the sapphires. The edges of the implanted template GaN wafers were then ground to eliminate the polished edge surfaces to deter the poly-GaN growth. 800-μm-thick GaN layers were grown by HVPE on the template GaN wafers, and the FS-GaN wafers were successfully self-separated during the cool-down process.
Fig. 1 shows the edge images of the GaN on sapphire substrates after 300-μm-thick GaN layer was grown on the template GaN substrates. When the edge-grinding was utilized to template GaN substrate, the poly-GaN was grown less than that of the substrate without edge-grinding. Also, the poly-GaN was easily removed at the edge of the substrate by edge-grinding without additional process.
Fig. 2 shows the hydrogen-ion-band inside the MOCVD-GaN layer with three different hydrogen-ion dose conditions. The sample with hydrogen-ion dose of 2.25 E17 H+/cm2 showed larger size of the hydrogen cavity than the samples with hydrogen-ion dose of 1.75 E17 and 2.0 E17 H+/cm2.
Fig. 3 shows the wafer images after 800-μm-thick GaN grown on the edge-ground template GaN with three different hydrogen-ion-implantation conditions. The FS-GaN wafers with hydrogen-ion dose of 1.75 E17 and 2.0 E17 H+/cm2 were successfully self-separated from the sapphire substrates, while the sample with hydrogen-ion-dose of 2.25 E17 H+/cm2 was self-separated around 63% of the area.
In our presentation, we will report how we achieved the self-separation of FS-GaN wafers without cracking by hydrogen-ion-implantation into the template GaN substrates, and discuss about the crystal quality of the grown FS-GaN samples.
* This work was financially supported by the Brain Korea 21 Plus Program in 2018.

Figure 1