COOL PLASMA ACTIVATED SURFACE IN SILICON WAFER DIRECT BONDING TECHNOLOGY

Transcription

1 COOL PLASMA ACTIVATED SURFACE IN SILICON WAFER DIRECT BONDING TECHNOLOGY G.-L. Sun, J. Zhan, Q.-Y. Tong, S.-J. Xie, Y.-M. Cai, S.-J. Lu To cite this version: G.-L. Sun, J. Zhan, Q.-Y. Tong, S.-J. Xie, Y.-M. Cai, et al.. COOL PLASMA ACTIVATED SURFACE IN SILICON WAFER DIRECT BONDING TECHNOLOGY. Journal de Physique Colloques, 1988, 49 (C4), pp.c4-79-c4-82. < /jphyscol: >. <jpa > HAL Id: jpa Submitted on 1 Jan 1988 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2 JOURNAL DE PHYSIQUE Colloque C4, supplgment au n09, Tome 49, septembre 1988 COOL PLASMA ACTIVATED SURFACE IN SILICON WAFER DIRECT BONDING TECHNOLOGY G.-L. SUN, J. ZHAN, Q.-Y. TONG, S.-J. XIE, Y.-M. CAI and S.-J. LU Microelectronics Center, Nanjing Institute Of Technology, Nanjing , China Abstract--A novel cool plasma surface activation method has been developed for high quality SOI/SDB (Silicon wafer Direct Bonding) preparation. The activation effectiveness of different plasma gases, espetially of 02 plsma gases were investigated. The measurements of H.V-PMOS and L.V.-NMOS devices made on the SOI/SDB and on a bulk Silicon indicate that ratios of electron and hole mobility of SO1 to those of bulk Silicon are 0.92 and 0.88,respectively.It was proved that our SO1 substrate produced by SDB is of device level quality. SO1 material has been the subject of an intense and challenging research over past few decads, because it has the poqential to provide the ideal substrate for ultra-high speed,high voltage,high temperature and high radiation-hardness VLSI systems.recently,soi produced by Silicon wafer Direct Bonding (SDB) technology has attracted much attention because of its high quality'high flexibility and low cost(l),(2),(3).however,sucessful bonding depends in large extend on the surface treatment.in this paper we report a novel cool plasma surface activation method for SOI/SDB preparation. 2.EXPERIMENTS AND DISCUSSION The bonding process adopted in this work is shown in Fig.l.Tow polished wafers were oxidized thermally, and the surface activation of tow wafers were performed before the prebonding process which was carried out in clean air condition.the bonding was then processed in N2 or 02 ambient at about 1000 "C for a few hours. It has been found that the surface activation and subsequent absorption of OH groups are key process steps for suceessful prebonding.the surface treatment in this work is as follows:(a) Radical atoms/moleculars (02,N2,NH3, etc.)produced by R.F.plasma activate the surface for 6 minutes.(b)silicon wafers are immersed in a molecular type surface activation solvent for about 1 hours in order that the surface absorbs large amounts of OH groups.(c)wafers are cleanned by standard IC wafer 'cleanning procedures. Article published online by EDP Sciences and available at

3 C4-80 JOURNAL DE PHYSIQUE The infrared t.ransmittance curves (0, N, A and V) in Fig.2 show broad and split dips between cm-1 owing to absorption of OH groups on the surface.the sym~bols O,N,A and V refer to samples treated at 850 " C for 6 minutes in 02,N2,NH3.and vacuum plasma respectively,and 9 is original sample. It was found that the sample 0 in Fig.3 is deactivated after being heated at C for 0.5 hour and then being passed steps (b) and (c).the broad and split dips no longer apper in the curve.it furthur confirms that plasma treatment activates the surface and enhances the absorption of OH groups. The investigation of the influence of temperature and time on O2 plasma activation process was carried out.fig.4 show that temp. less than 850'~ is better than 900 "C in terms of OH groups absorption.but there is almost no difference between IR transmittance spectra curves of O2 plasma treatment for 6 minutes and 60 minutes at 850 c in Fig.5.It is assumed that there is a critical temperature value above which deactivation dominates in O2 plasma treatment. The fracture strength of.the bonded silicon wafer is kg/cm2, which is close to the values of silicon wafers used. SEM microphotograph,in Fig.6 shows the cross-section of resulted bonding wafer. The high voltage PMOS device, as shown in Fig.7 was designed.it was fabricated with standard voltage NMOS device both on the SOI/SDB substrate and bulk Si using Al-gate CMOS process to assess the electrical properties of the SO1 1ayer.The SOI/SDB substrate has 4 pm thickness with resietivity of 20 fi*cm.fig.8 is I-V characteristic of 100V.H.V.PMOS device.the measurements indicate that ratios of electron and hole mobility on SO1 layer to those of bulk Silicon are 0.92 and 0.88 respectively.it shows that our SOI/SDB is of device level quality. 3. CONCLUTION A cool plasma can activate the SiOZ of a Si wafer and helps the bonding process.activation effectiveness of different plasma was compared and we found no sigificant difference among various plasma gases.the temperature during activation of O2 plasma below 850 C is nessary to avoid deactivation.the devices made on SO1 layer show that SOI/SDB subsrtrate is suitable to IC application. This work was supported by Chinese Natural Science Foundation ( ). REFERENCE (1) J.B. Laskey, S.R. Stiffler. F.R.White and J.R.Abernathey,Tech. Dig. IEDM pp (2) Semicondutor World,6,1986. (Japan) (3) Li Hui, Sun Guo-Liang,Zhan Juan, and Tong Bin-Yi, Applied Surface Science 30, PP ,1987. Fig.1 SDB process sequence

4 Fig.2 IR transmittance spectras Fig.4 Temp.influence on IR spectras a: at 300 C, b: at 700 C c: at 850 c, d: at 900 C Fig.3 IR spectra of heated sample Fig.5 Time influencee on IR spectras e: 6 minutes f: 60 minutes

5 C4-82 JOURNAL DE PHYSIQUE Fig.6 SEM cross-section microphotograph of SOI/SDB - Fig.7 H.V.-PMOS structure Fig.8 I-V characteristic of H.V.PMOS Horizantal axis,vc~.20v/div;vertica~ axis,id,500ua/div;gate volt.,2v/div