Front-End Technologies for nano-scale MOSFETs

Transcription

1 Front-End Technologies or nano-scale s Kentaro Shibahara Research Center or Nanodevices and Systems, Hiroshima University 1-4-2, Kagamiyama, Higashihiroshima, Japan Phone , FAX: , ksshiba@hiroshima-u.ac.jp 1. Introduction We are working or development o ront-end process and device technologies o nano-scale s. Our COE project aims development o 3DCSS system. Highperormance mixed-signal device technologies are demanded or such a system. The major our research targets are shallow junction ormation and metal-gate workunction tuning. These are standard development or CMOS logic application., in addition, helpul or improvement o RF device perormance. Low resistive shallow junction ormation is indispensable to improve T that is degraded by parasitic series resistance. Gate resistance reduction by replacing poly-si gate with metal gate is eective or MAX improvement. In this abstract, these research activities are briely introduced. 2. Metalgate tecnology The most undamental motivation or development o metal gate s is solving the gate depletion problem. The gate depletion is unavoidable or a poly-si gate structure and is the origin o penalty or eective gate oxide thickness. By replacing semiconductor, that is poly-si, with metal the gate depletion problem can be removed. However, it also means losing the beneit o workucntion tuning by doping. A dual gate structure that utilizes high and low workunction or p- and n-mos threshold voltage adjustment and that is indispensable or CMOS devices (Fig. 1). Thereore, one o the most important development target o metalgate is metal workucntion tuning technology. We have working on workunction tuning o Mo and silicides. As shown in Fig.2, metal workunction o a Mo MOS structure can be varied by nitrogen pileup ormation at Mo/SiO 2 interace [1,2]. Electric dipole ormed by high concentration impurity at the metal/insulator interace (Fig.3) is considered to be origin o the workunction shit [3,4]. We have abricated s with the Mo gate and ound nitrogen redistribution during additional thermal treatment process or FET abrication [5,6]. Thus, metalgate workunction tuning technology must be conirmed through integration to the device abrication. Fully silicided (FUSI) gate is also another candidate or workunction tunable metalgate. Though combination o ploy-si gate and silicide is already integrated into commercially available devices as polycide gate or salicide gate, FUSI dose not remain poly-si by reaction process o poly-si and metal deposited on the poly-si. Workunction o a FUSI MOS structure is also tunable by pileup ormation o impurities at the interace o silicide and SiO 2. We have investigated the relationship between silicidation condition o NiSi FUSI gate and its workunction [7,8]. NiSi is the most popular material or the FUSI gate. Details o obtained results are shown in another paper o this workshop [9]. We are also working on Pd 2 Si as an alternative candidate o FUSI gate material [10]. 3. Shallow Jucntion ormation by laser annealing Currently RTP based annealing technologies are used or source and drain (S/D) ormation o leading edge device mass production. New annealing technologies that is suitable or shallower S/D are demanded or urther scaling o CMOS devices. Melt laser annealing (LA) is one o such technologies. Though LA has long development history, melt LA currently stands or LA that utilizes melting point dierence between crystalline Si and amorphous Si. Selective melting o a thin amorphous Si layer that has lower melting point prevents over-melt to crystalline Si and leads to high activation due to non-equilibrium re-crystallization. Amorphous layer can be ormed heavy ion, such as Ge +, implantation prior to dopant implantation. We used two laser source shown in Fig. 4. One is KrF excimer laser and another is all-solid-state green laser. Both lasers provides nanosecond order pulse. We have proposed the combination o substrate heating and LA, that is heatassisted LA (HALA) [11-13]. This method was applicable to ultra-shallow junctions shallower than 20 nm and sheet resistance lower than 1 kω/sq. was easily obtained. Based on heat-assisted LA, we have proposed a new LA scheme, partial-melt LA (). This scheme utilizes solid-phase regrowth o amorphous-si during preparation heating or HALA. By stopping appropriate timing, amorphous layer thinner than initial thickness can be obtained. This provides separation o juncntion depth and amorphous layer thickness, which means increase in process design reedom. We have demonstrated with 10 nm junction ormation [14,15]. Sheet resistance about 700Ω/sq. was obtained or 10 nm junctions with negligible diusion, as shown in Fig. 6. Green laser has deep penetration depth compared with KrF excimer laser. This leads to increase in laser power, in other words diiculties or development o production equipments. To compensate this problem, we are working on green laser annealing with light absorber. We have discussed selection o light absorber materials and their layered structures based on both experimental and simulation results [16-19]. 4. Summary Our activities on ront-end device abrication

2 technologies beneicial or mixed-signal application like 3D-CSS was introduced. We are currently working integration o these technologies or abrication to demonstrate their useulness. Acknowledgements Our research activities were partly supported by STARC and NEDO/MIRAI Project. The research achivement shown here is a result o cooperative work with co-authors or publications listed below. Reerences 1. T. Amada et al., MRS Proc., 716 (2002) p K. Shibahara, Abst. o 1st. Hiroshima Int. Workshop on NTIP, 2003, p. 38. Metal Gate (Mo, FUSI NiSi, Pd2Si...) 3. M. Hino et al., Ext. Abst. SSDM 2003, p K. Sano et al., Abst. o 2nd. Hiroshima Int. Workshop on NTIP, 2004, p T. Hosoi et al., Abst. o MRS 2005 spring meeting, pp H. Sunami, presented at this workshop. 7. K. Sano et al., Ext. Abst. SSDM 2004, p K. Sano et al., Jpn. J. Appl. Phys. 44, p (2005). 9. T. Hosoi et al., Proc. o 3rd Hiroshima Int. Workshop on NTIP, 2004, p K. Sano et al., Proc. 13th Int. RTP Con., to be presented. 11. K. Kurobe et al., Ext. Abst. IWJT, 2002, p K. Kurobe et al., Proc. o 3rd Hiroshima Int. Workshop on NTIP, 2004, p K. Kurobe et al., Jpn. J. Appl. Phys. accepted or publication. 14. K. Shibahara et al., Ext. Abst. IMFEDK, 2005, p K. Shibahara, Ext. Abst. IWJT, 2005, p E. Takii et al., Abst.o Int. Con. on Ion Implantation Tech., 2004, p E. Takii et al., Jpn. J. Appl. Phys. Part 2. Letter, 44, p. L756 (2005). 18. A. Matsuno et al., Nucl. Instr. and Meth. B (NIM-B), 237, p. 136 (2005). 19. A. Matsuno et al., presented at SSDM KrF Excimer Laser Green Laser Green Laser Impurity pileup low Φ M high Φ M Fig. 1 Schematic model o ingle-metal dual-workunction CMOS. By orming impurity pileup at the metal/gate insulator interace, metal workucntion can be tuned. Nitrogen [cm -3 ] TiN/Mo Diode Proc. FET Proc. Mo SiO 2 Si N O - + Dipole [nm] Interace Mo SiO 2 O Si O N + Imp. Fig. 2 Nitrogen back-side SIMS proiles in a Mo/SiO 2 /Si MOS structure. Nitrogen pileup was ormed ater adequate annealing. Fig. 3 A model to explain Mo workunction shit. By the dierence o electron negativity, electric dioples are ormed at the Mo/SiO 2 interace. < 20 nm 927 nm as Implanted Dopant Ge: Channeling tail supressor without Ge PAI Channeling tail as Implanted Amorphized depth ~ melt depth Light Absorber Penetration in Si Gree Laser (532 nm): 927 nm KrF Excimer Laser: 5.5 nm Ater Melt LA Redistribution in Melt Phase Si Sub. Fig. 4 Penetration depth o KrF excimer laser and green laser light. As Implanted Conventional Melt Amorphized by Ge PAI Sheet Resistance R s [ sq.] with Ge PAI B 0.3 kev +Ge 3 kev X j ~ 10 nm Sb 3.5 kev +Ge 3keV X j ~ 9 nm 450 o C Sb 10 kev X j ~ 21 nm as Implanted melt depth Laser Energy Density E L [mj/cm 2 ] ater Partially-Melt LA Solid-phase Regrowth Fig. 5 Relationships between dopant proiles and amorphized layer depth beore and ater melt laser annealing. Fig. 6 Sheet resistance o ultra-shallow jucntions ormed with.

3 Front-End Technologies or Nanoscale s 3DCSS System multi-chip inormation processing with wireless Interconnect Kentaro Shibahara Research Center or Nanodevices and Systems, Hiroshima Univ. 1 Tera-bit processing high RF perormance devices T max = g m = 2πC gs 8πC T gd R Parasitic series resistance should be low Low resistive junction ormation Laser Annealing g Gate resistance should be low Metal gate 2 Mo Gate Workunction Tuning by Nitrogen-Dope Mo gate with Nitrogen pileup ormation: Nitrogen ion implantation - suicient workunction shit, ΔΦ Mo = -1 ev ( P. Ranade et al., MRS2000, 611, C.3.2.1) but - increases in interace state & leakage current ( T. Amada et al., MRS2002, 716, 299 ) 4.05eV E c E I 5.17eV E v 4.03eV 4.60eV N-SPD 5.10eV This poster NiSi FUSI: visit poster P-26 Pd 2 Si FUSI: coming next time Nitrogen solid-phase diusion (N-SPD) - ΔΦ Mo = -0.5 ev - No degradation ( R.J.P. Lander et al., MRS2002, 716, 253 ) ( M. Hino et al., SSDM2003, 494 ) Fabrication o Mo Gate with N-SPD 3 4 Nitrogen Solid-Phase Diusion into Mo Gate Nitrogen Redistribution by S/D Activation Annealing p-si (100) LOCOS ormation Gate oxidation (5 nm) Mo & TiN sputter (50 & 30 nm) Nitrogen Solid-Phase Diusion (800 C, 1min) TiN removal Gate ormation S/D implantation ( As : 5x10 15 cm -2, 30 kev ) S/D activation annealing (900 C, 1min) Al wiring and PMA I d (A) w/o N-SPD expected () V g (V) V d : 0.05 V L/W : 1/10 μm T ox : 5 nm ΔΦ Mo ev -0.1 ev M.Hino et al., SSDM2003, Nitrogen (cm -3 ) back-side SIMS Mo SiO 2 Si Relative (nm) Mo-gate Reduction o N concentration at Mo/SiO 2 interace (N out-diusion) Reversible workunction shit (-0.46 ev -0.1 ev) Modiication in abrication process

4 Nitrogen Redistribution in Mo Gate (Oxide-cover) Device Characteristics o Oxide-cover & TiN-cap just ater N-SPD N pileup at Mo/SiO 2 interace was ormed ater S/D activation annealing Modiied Device Structures Oxide-cover TiN-cap I D (A) oxide-cover TiN-cap w/o N-SPD L g : 1 μm W g : 10 μm T ox : 5 nm N pileup at bottom Mo/SiO 2 Interace redistributes toward top and two side interaces Oxide-cover : ΔV th = -0.1 ev - same as standard process V g (V) small V th shit 7 TiN-cap : ΔV th = ev - enlarge V th shit (still smaller than MOS case) 8 Basic Ideas o Schemes Proposal o New Scheme Pre-amorphization Implantation o n Solid Phase Regrowth Laser Irradiation Partial Melt Laser Annealing : melt(good activation) + non-melt(diusion less) 9 10 Time Sequence Advantage o Substrate Temperature (T sub ): o C Laser Energy Density (E L ) : mj/cm 2 FWHM o Laser Pulse: 38 ns, Pulse Number: 1 Pulse X j ~t a melt LA t a: Amorphized layer thickness t a X j T sub Heating Up Temperature Proile Laser Irradiations (E L ) Cooling Down Time [min] : Amorphization depth is ree rom junction depth 11 12

5 XTEM beore and Ater Laser Irradiation Ater LA Beore LA Ge + Implantation non-melt heat-assistedla Sb [cm -3 ] nm Junction Formation with Sb and B 2.5 nm/dec No irradiation 360 mj/cm Ω/sq. X J : 10.5 nm [nm] Temperature Improved Sequence o Fast ramp-up with lamp heating a-si c-si ~500 o C Slow down LA X j dye-by-dye Laser irradition ~450 o C Time For more details: Publication List Mo gates 1. T. Amada et al., MRS Proc., 716 (2002) p K. Shibahara, Abst. o 1st. Hiroshima Int. Workshop on NTIP, 2003, p M. Hino et al., Ext. Abst. SSDM 2003, p K. Sano et al., Abst. o 2nd. Hiroshima Int. Workshop on NTIP, 2004, p T. Hosoi et al., Abst. o MRS 2005 spring meeting, pp H. Sunami, presented at this workshop. NiSi FUSI 7. K. Sano et al., Ext. Abst. SSDM 2004, p K. Sano et al., Jpn. J. Appl. Phys. 44, p (2005). 9. T. Hosoi et al., Proc. o 3rd Hiroshima Int. Workshop on NTIP, 2004, p. 70. Pd 2 Si FUSI 10. K. Sano et al., Proc. 13th Int. RTP Con., to be presented. KrF Excimer Laser Annaling 11. K. Kurobe et al., Ext. Abst. IWJT, 2002, p K. Kurobe et al., Proc. o 3rd Hiroshima Int. Workshop on NTIP, 2004, p K. Kurobe et al., Jpn. J. Appl. Phys. accepted or publication. 14. K. Shibahara et al., Ext. Abst. IMFEDK, 2005, p K. Shibahara, Ext. Abst. IWJT, 2005, p. 53. Green Laser Annealing with Light Absorber 16. E. Takii et al., Abst.o Int. Con. on Ion Implantation Tech., 2004, p E. Takii et al., Jpn. J. Appl. Phys. Part 2. Letter, 44, p. L756 (2005). 18. A. Matsuno et al., Nucl. Instr. and Meth. B (NIM-B), 237, p. 136 (2005). 19. A. Matsuno et al., Ext. Abst. SSDM 2005, p