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Vol. 32, No. 6 Journal of Semiconductors June 2011Study of hybrid orientation structure waferTan Kaizhou 谭开洲 1; , Zhang Jing张静 1, Xu Shiliu 徐世六 1, Zhang Zhengfan 张正璠 1,Yang Yonghui 杨永晖 2 , Chen Jun陈俊 2 , and Liang Tao梁涛 21 National Laboratory of Analog Integrated Circuits, Chongqing 400060, China2 Sichuan Institute of Solid-State Circuits, Chongqing 400060, ChinaAbstract Two types of 5 m thick hybrid orientation structure wafers, which were integrated by 110 or 100orientation silicon wafers as the substrate, have been investigated for 15– 40V voltage ICs and MEMS sensorapplications. They have been obtained mainly by SOI wafer bonding and a non-selective epitaxy technique, andhave been presented in China for the first time. The thickness of BOX SiO2 buried in wafer is 220 nm. It has beenfound that the quality of hybrid orientation structure with 100 wafer substrate is better than that with 110 wafersubstrate by “ Sirtldefect etching of HOSW”.Key words HOT; SOI; 110 crystal orientation; 15– 40V ICs; MEMS sensorDOI 10.1088/1674-4926/32/6/063002 PACC 7340T EEACC 25001. IntroductionIt is well know that CMOS ICs are usually made from100 crystal orientation silicon wafer, and NMOS carrier mo-bility is about 2–3 times greater than PMOS carrier mobility,but most people might forget that hole mobility in 110 orien-tation silicon wafer is about 2 times larger than that in 100wafer, which was found by Sato et al.1 in 1969. Many newtechnologies, such as strained silicon, have been developedas the design rule in CMOS technology scales down to the45 nm node and beyond, and high hole mobility in 110 ori-entation wafer have been recognized again. Then, hybrid ori-entation technology HOT, where NMOS transistors are fab-ricated on 100 wafer but PMOS transistors are fabricated on110 wafer, was exploited 2 9 . HOT improves PMOS transis-tor performance, maintains NMOS transistor performance and,in the meantime, reduces the mismatch of PMOS and NMOStransistor characteristics. In addition, 110 wafer has a largerpiezoresistive coefficient than 111 and 100 wafer, which iswidely used for MEMS sensors. Most of the HOT active layerthickness is usually much thinner 45 – 100nm and was usedin 90 nm CMOS node or less outside China3; 7 , which is dif-ferent from the thickness that we use.2. Process flowThe process flow of the hybrid orientation structure waferHOSW experiment is shown in Fig. 1. Both 110 and 100wafers are 100 mm in diameter. The 110 wafer is n-type,whose resistivity is 10– 20 cm, whereas 100 wafer is alson-type, whose resistivity is 7– 10 cm.First, we must obtain hybrid orientation SOI wafer. TheseSOI wafers are made by a conventional wafer bonding, grind-ing and SOI polishing process flow, and the wafer is differentfrom the top Si layer in orientation. The 110 and 100 waferswere used as a handle wafer or a top Si layer, respectively. Theburied BOX thermal SiO2 is about 220 nm thick and the topSi layer thickness is about 3.3 – 3.62 m Fig. 1a. A micro-graph of hybrid orientation SOI wafer is shown in Fig. 2. ThereFig. 1. HOSW processflow. a Formation of 110/100 or 100/110hybrid orientation SOI. b A part of the top Si layer and BOX SiO2etching. c Non-selective epitaxy. d Silicon epitaxial layer CMP.* Project supported by the National Basic ResearchProgram of China No. 61398 and the National Laboratory of Analog Integrated CircuitsFoundation of China No. YZ0808.Corresponding author. Email tkz123163.comReceived 14 September2010, revised manuscript received 18 January 2011 c 2011 Chinese Institute of Electronics063002-1J. Semicond. 2011, 326 Tan Kaizhou et al.Fig. 2. Photo of hybrid orientation SOI wafer. The left SOI handlewafer orientation is 110 and the top Si layer is 100, and the rightone is 100 and 110, respectively.Fig. 3. Cross section of 110 HOSW.is no defect in the upper left corner of the left-hand SOI waferin Fig. 2 but there is a mirror reflection pattern.Second, after the photolithographic process, a part of thetop Si layer and BOX SiO2 was etched, as shown in Fig. 1b.Then a 7.5 m thick non-selective epitaxial layer was de-posited Fig. 1 c.Third, a roughly 5 m thick silicon epitaxial layer wasremoved from the epitaxial wafer by CMP Fig. 1 d. ThenHOSW was carried out.3. Results and discussion3.1. Cross section of hybrid orientation structureFigure 3 shows a cross section of the hybrid orientationstructure with 110 handle wafer 110 HOSW, and Figure 4is a cross section of the hybrid orientation structure with 100handle wafer 100 HOSW. From Fig. 4, it can be seen thatthere is no distinct step across 110/100 on wafer surface.The top Si layer on BOX SiO 2 is about 5 m thick and BOXSiO 2 thickness is about 0.22 m.3.2. Surface shape and defect indicationBoth 110 and 100 handle wafer hybrid orientationstructures had a thermal oxide, which formed in 950 C vaporambience, the oxide on the 100 surface is 98 nm thick, and theFig. 4. Cross section of 100 HOSW.Fig. 5. Micrograph of HOSW surface.oxide on the 110 surface is 136 nm thick. Figure 5 shows ami-crograph of the hybrid orientation structure surface. In Fig. 5,the top left image is a 110 handle wafer hybrid orientationstructure, where orientations inside and outside the rectangularpattern area are 110 and 100, respectively. However, the topright image is 100 handle wafer, where the orientations in andout of the rectangular pattern are100 and 110, respectively.It can be seenclearly that there are many special sharp-angledcorners shown asdashedcircles in the bottom image of Fig. 5on 100 HOSW, but there are no such corners on 110 HOSW.A photolithographic layout schematic on wafer is shownin Fig. 6. All of the patterns in the layout are rectangular.To know what the surface quality of HOSW looks like, thewafer has been smashed by natural cleavage fracture. We puta suitable sized fragment into “ Sirtl ”etching solution CrO 3 H2O HF 50 g 100 mL 100 mL for about 2 min andthen took it out to take a micrograph. It was found that 110HOSW had some different behavior from 100 HOSW. First,the cleavage plane angle was about 60 in 110 HOSW seeFig. 7, but it was 90 in 100 HOSW see Fig. 8.Second, there were some line defects on the surface of110 HOSW, indicated by dashed ellipses in Fig. 7. There werealmost no defects on 100 HOSW except for some along theedgeof the fragment, asshown on the right part of Fig. 8. These063002-2J. Semicond. 2011, 326 Tan Kaizhou et al.Fig. 6. Layout schematic on wafer.Fig. 7. Surface micrograph after 110 HOSW cleavage.defects along the edge were probably caused by cleavage frac-ture mechanical stress.4. ConclusionsTwo types of 5 m thick hybrid orientation structures wererealized mainly by SOI wafer bonding, non-selective epitaxyand CMP, and they have been presented in China for the firsttime. “ Sirtldefect etching ”of HOSW indicated that the qual-ity of hybrid orientation structure with 100 wafer substrate isbetter than that with 110 substrate.AcknowledgmentsThe authors would like to thank Li Zhilang, Wang Bing,Chen Guangbing, Wang Jianan, Xu Xueliang, Li Kaicheng andFig. 8. Surface micrograph after 100 HOSW cleavage.Cao Yang for their support and helpful discussions.References[1] SatoT, Takeishi Y, Hara H. 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