We succeeded in measuring the density and direction of the edge component of threading dislocations (TDs) in c-plane (0001) GaN by micro-Raman spectroscopy mapping. In the micro-Raman spectroscopy mapping of the E2H peak shift between 567.85 and 567.75 cm−1, six different contrast images are observed toward directions of . By comparing X-ray topography and etch pit images, the E2H peak shift is observed where the edge component of TDs exists. In contrast, the E2H peak is not observed where the screw component of TDs exists.

This paper describes an advanced Si-deep etching process achieving a high aspect ratio with excellent verticality by the improvement of the O 2 plasma source condition in the oxygen plasma irradiation inserted deep reactive ion etching (OP-DRIE) process that we have developed. The conventional DRIE process which we call the Bosch process has a trade-off relation between the high aspect ratio and verticality in the trench profile. Our developed process technique, repeating the conventional DRIE and the O 2 plasma irradiation process alternately, can achieve the vertical trench profile with a higher aspect ratio than that of the conventional DRIE process. In order to maximize an advantage of the developed process, a thickness of the SiO 2 layer formed by irradiation of O 2 plasma should be large enough as a protection layer. However, because of insufficient SiO 2 thickness formed by O 2 plasma, the aspect ratio has been limited in previous work. Furthermore, mask material (SiO 2 ) erosion which is another limitation factor of the aspect ratio is increased by the insertion of O 2 plasma irradiation. In this paper, we have investigated optimum O 2 plasma source conditions that allow an increase in SiO 2 thickness with a high oxidation rate, and at the same time, with less mask erosion on the top of the wafer. We have clarified the effects of frequency and pulsed/CW modes of the plasma source on the effectiveness in SiO 2 formation. From the obtained oxygen plasma source condition, we achieved the etched Si trench having an aspect ratio of over 70 with excellent verticality (uniform trench width).

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In this study, we have developed a new reactive ion etching (RIE)-lag reduction technique in Si deep etching. The conventional RIE-lag reduction technique has a dependence of polymeric layer deposition thickness on mask opening width in the deep reactive ion etching (DRIE) process (Bosch process). However, in our experiment, when the RIE-lag was suppressed, the polymeric layer on the wider trench bottom remained and caused Black Si under typical process condition. Even if the Black Si is suppressed by optimization of process parameters, it appears when the trench becomes deeper. Therefore, the remaining of the polymeric layer is considered to determine the depth range for the RIE-lag reduction. In order to avoid this limitation, we have developed a new RIE-lag reduction technique that forms a double protection layer consisting of polymer and SiO 2 on the trench bottom before the etching step in the DRIE process. The SiO 2 layer formed by O 2 plasma irradiation under polymeric layer has higher ability for removal than that of the polymeric layer and it can be removed clearly without Black Si phenomenon. Experimental result shows that this technique can obtain RIE-lag free region up to an aspect ratio of 13. Within this aspect ratio range, the RIE-lag free effect is considered to be applicable not only to trench pattern but also to other two-dimensional mask patterns except hall pattern. 