CMOS circuit analysis with luminescence measurements and simulations

Transcription

1 ESSERC, 8th European Sold-State evce Reearch Conference, Florence (Italy), -6 Sep.. CMOS crcut analy wth lumnecence meaurement and mulaton F. Stellar IBM T.J. Waton Reearch Center Yorktown Heght, NY 1598 (USA) emal: A. To, F. Zappa, and S. Cova Poltecnco d Mlano EI P. L. da Vnc, Mlano (Italy) emal: cova@elet.polm.t Abtract Hot-carrer n MOSFET are reponble for tmedependent near-nfrared emon, ynchronou wth the wtchng tranton n CMOS crcut. Fat electrcal waveform propagatng through ntegrated crcut can be effectvely meaured by mean of hgh entvty old-tate photodetector wth harp tme-reoluton. Thank to a tme jtter of le than 3p, we obtaned an equvalent analog bandwdth of about 3GHz. We developed a photoemon model n SPICE n order to mulate the lumnecence waveform. By comparng meaured and mulated optcal waveform, n-depth nght of crcut behavor reported, leadng to a powerful dentfcaton of defect and falure. 1. Non-nvave tetng Moore Law predct a progreve decreae n ze and pacng of actve and pave tructure (uch a trantor and ther nterconnecton), accompaned by an ncreae n chp complexty, ze and peed of operaton [1]. Such evoluton, bede the ntroducton of flp-chp technology, make t ncreangly dffcult the debuggng of new generaton of IC []. In the lat year, new tetng technque have been ntroduced for optcally acceng actve devce wthn IC from the backde of the wafer [3,]. In partcular, Pcoecond Imagng Crcut Analy (PICA) [3] a very powerful tool for dentfyng wtchng tranton and meaurng propagaton delay and kew by mean of the hot-carrer lumnecence emtted by CMOS trantor n aturaton. The recent ntroducton of nnovatve ngle-photon detector wth harp tme reoluton allow the recontructon of analog waveform wth an equvalent bandwdth of ~3GHz [5]. However, the non-lnear relatonhp between MOSFET ba condton and emon ntenty [6] lmt the drect etmaton of electrcal waveform from optcal meaurement. Such problem can be olved wth the help of approprate electro-optcal mulaton of IC. Indeed, a compact model of lumnecence [6] can be nerted n a SPICElke mulator n order to foreee the emon ntenty of each trantor. In th paper, we dcu the combned ue of lumnecence meaurement and crcut mulaton n order to analye the gnal propagatng through analog CMOS crcut. The mulated waveform are drectly compared wth dynamc meaurement, thu confrmng ther matchng, but alo dentfyng defectve behavour of the crcut under tet. Moreover, the tme ntegral of meaured lumnecence, overlad to crcut layout, allow a mple localzaton of falure when t compared wth tatc meaurement of the emon.. evce under tet The devce under tet a mxed analog/dgtal crcut degned for dcrmnatng the arrval tme of very fat (nanoecond repone) pule appled to t nput. Fg. 1 how a chematc of the crcut degned n a BCMOS technology, wth mnmum channel-length of.8µm and typcal breakdown voltage of 13V. The crcut work at a nomnal voltage of 1V. The current nput gnal unk from retor R1 (Fg. 1), thu producng a voltage drop on t. The crcut quckly lower the nput voltage to zero a oon a the nput pule trgger P1 and then N1, connected n a potve feedback loop. The monotable ubcrcut (Fg. ) reet the nput by wtchng PU1 and P1 on, thu rang the voltage back to 1V. IN R1 N1 PM1 NM1 C M R PU1 P1 NM3 NM P1 PM PM3 monotable PO1 OUT NO1 Fgure 1. Schematc of the crcut under tet

2 ESSERC, 8th European Sold-State evce Reearch Conference, Florence (Italy), -6 Sep.. IN P N P3 N3 urng normal operatng condton, the crcut n tandby tatu for mot of the tme, watng for the arrval of an nput current. urng crcut tetng, the nput wa trggered at a rate of 1MHz. 3. Lumnecence meaurement The IC tetng begn wth a prelmnary tatc characterzaton of the lumnecence emon followed by dynamc waveform recontructon and, fnally, by a comparon wth electro-optcal mulaton. Fg. 3 depct the expermental et-up for optcal acquton. The mcrocope collect lght emtted by the devce under tet and focue t onto two detector: a CC camera [7] for tatc mage and a Sngle-Photon Avalanche ode (SPA) [8] for waveform recontructon. The total CC feld of vew can be vared from le then 1µm to few mllmetre by mply changng the magnfcaton M of the collectng objectve from 1X to 5X, whle the SPA can be focued on a ngle pxel of the CC. N 1V P P7 C RE OUT RE1 Fgure. Monotable ubcrcut compoed by a varable retor and a capactor. Fg. how a 1-acquton taken wth a X objectve magnfcaton. By overlayng lumnecence peak to crcut layout (Fg. 5), t poble to dentfy the emttng trantor. The net of Fg. how a zoom of trantor RE1 folded nto three fnger. Fg. 6 how a -acquton obtaned wth a hgher magnfcaton (5X), leadng to better patal reoluton and emon detal. We calculated trantor lumnecence ntenty by ntegratng the photon emtted by each MOSFET n Fg. 6. Then, all ntente were normalzed by trantor channel wdth and reported a N n Tab. 1. Although mot of the trantor emt mlar amount of photon, RE1, P1 and N are gnfcantly brghter. Such dfference n lumnecence are due to larger electrc feld or longer wtchng tranton [5]. A better undertandng of uch behavour can be acheved only by analyng crcut mulaton. By lowerng the frequency of the nput gnal from 1Mhz to 35kHz, the emon N kh z of each trantor reduce by the ame amount (.e. ~36 tme), thu howng that the crcut not gnfcantly affected by hgh nput rate. Only two MOSFET, N and NM1, preent a much tronger reducton: 5 and 65 tme, repectvely. Thee trantor are the mallet one n the IC and both drve large capactance (NM1 drve alo CM=pF). Th a clear gnature that, at hgh nput rate, thoe MOSFET do not work properly. In fact, f upply voltage raed toward technology breakdown voltage, the frt trantor that burn NM1, thu confrmng t hgh tre condton Statc acquton wth CC camera Statc acquton were performed by mean of a hgh-entve CC camera [7] n order to quckly localze the emttng trantor n the crcut layout. Moreover, the hgh quantum effcency and the capablty of multaneouly montorng many trantor make the dentfcaton of defect and falure very eay. CC Semtraparent Mrror MICROSCOPE Collectng Objectve UT etecton effcency, η Wavelength, λ [µm] SPA Focalzng Objectve SPA AQC START STOP CC TAC Fgure 3. Expermental etup for optcal acquton. MCA Fgure. Label dentfy trantor wth enble lumnecence emon n a CC meaurement. Fgure 5. Layout of the crcut under tet

3 ESSERC, 8th European Sold-State evce Reearch Conference, Florence (Italy), -6 Sep... Lumnecence and electrcal mulaton Fgure 6. Lumnecence ntenty. 3.. ynamc acquton wth SPA Snce CC provde only tatc mage, the fat optcal waveform were recontructed by mean of a SPA [8], n the tandard tme-correlated ngle-photon countng apparatu hown n Fg. 3. The old-tate detector provde an output pule for each detected photon wth very harp tme reoluton, better than 3p- FWHM (Full-Wdth at Half Maxmum) [1]. Optcal waveform are obtaned by collectng a htogram of photon arrval tme, meaured wth repect to a ynchronzaton gnal from the IC (.e. output pule of the crcut under tet). The acquton tme, and the number of detected photon, mut be large enough to guarantee a uffcent gnal-to-noe rato. An expoure tme of only 3mn wa enough for explotng the feature of the waveform hown n Fg. 7. ue to the.8µm-channel length of trantor, wtchng tranton are nor very fat. Therefore, the FWHM of the emtted pule gnfcantly larger than the ntrnc tme reoluton of the detector (~3p- FWHM), thu guaranteeng accurate recontructon of the waveform wth no need of any numercal deconvoluton wth the detector repone. Table 1. Comparon of meaured and mulated lumnecence emon ntenty MOS W [µm] N N khz [cp/µm] [cp/µm] m RE %. NM % 8.9 P % 7.1 N % 6.5% N % 89.7% N % 1.5 N % 6.1 NM %. The meaured optcal waveform acqured wth the SPA provde very ueful nght nto crcut behavour thank to ther trct relatonhp wth trantor operatng condton. However, t ha been proved [6] that lumnecence ntenty ha a non-lnear dependence on MOSFET gate and dran voltage, thu makng more challengng the extracton of electrcal waveform from optcal meaurement. Such problem can be olved by mean of approprate electro-optcal mulaton. In fact, by nertng lumnecence equaton nto a SPICE model [6], we were able to etmate the emon ntenty of each trantor of the IC at each ntant n tme. The drect comparon between meaurement and mulaton mplfe the verfcaton of hypothe concernng fault caue. For etmatng the number of emtted photon, we ued the equaton preented n [6]: I β PH NPH = α PH exp at q VS V, (1) S where N PH the rate of emtted photon, I the dran current, q the electron charge, V S the dran-ource at voltage, V S the aturaton dran voltage. The two coeffcent α PH and β PH depend on many proce parameter, bede the optcal effcency of the et-up. In order to compare optcal mulaton wth tatc CC mage, we computed the ntegral of mulated waveform ( N ). However, the latter cannot be drectly compared wth the meaured emon ntenty, N, becaue of the unknown optcal collecton effcency. Therefore both N and have been N MHz normalzed to the total meaured/mulated emon ntenty ( tot N = N ) obtanng the relatve ntenty m/ m/ of each trantor: Nm m = and N tot = tot Nm N. () Tab. 1 how an excellent agreement between meaured,, and mulated,, relatve ntente m for mot of the trantor, thu confrmng that the lumnecence model accurate enough to decrbe the emon phenomenon. However, the dcrepance extng for N1 and N ugget an napproprate etmaton of the workng condton for thee trantor. SPA dynamc meaurement were hence employed to better undertand uch effect. Fg. 7 compare the optcal waveform collected wth the SPA wth the electro-optcal mulaton obtaned from Eq. (1). It nteretng to oberve that the frt wtchng tranton of RE1, whch correpond to the end of crcut reet, late wth repect of mulaton. Such delay repreent a crtcal condton becaue a new nput gnal can arrve before the reet of the crcut ha

4 ESSERC, 8th European Sold-State evce Reearch Conference, Florence (Italy), -6 Sep.. been completed. On the contrary, N3, N and NM1 hghlght that the nterventon of the potve feedback take place earler than what mulaton ugget. Optcal meaurement how alo that N1 and N emt lght pule durng the trggerng of nput gnal, whch are not predcted by mulaton. Such tranton are caued by a current mpule n the old-tate detector at the nput. Fg. 7 how alo that the FWHM of NM1 and NM3 pule gnfcantly larger than predcted by mulaton,.e. wtchng tranton are abnormally low. The 6n-delay n the nterventon of NM3 concur n uggetng that C M capactance probably bgger than what ha been uppoed durng mulaton. Optcal meaurement can alo be effectvely ued for extractng quanttatve nformaton regardng crcut behavor. For example, V S of N follow an exponental decay due to the RC dcharge of capactance C n Fg.. By mean of Eq. (1) and approprate hypothe, the tme contant RC can be calculated tartng from N optcal data n Fg. 7. Fg. 8 how the good agreement between calculated (contnuou lne) and mulated (dahed lne) RC contant. 5. Concluon In th paper we dcued on the combned ue of optcal npecton of electrcal gnal propagatng through CMOS ntegrated crcut wth optcal mulaton of the hot-carrer tme-dependent lumnecence emon. Such compoton offer a very powerful and veratle method for localzng, dentfyng and olvng unexpected defect and falure n modern IC. Reference [1] R.R. Schaller, Moore' law: pat, preent and future, IEEE Spectrum, vol. 3, 1997, pp [] Y. Taur and T.H. Nng, Fundamental of modern VLSI devce, Cambrdge Unverty Pre, [3] J.C. Tang, J.A. Kah and.p. Vallett, Tmereolved optcal characterzaton of electrcal actvty n ntegrated crcut, IEEE Proceedng, vol. 88,, pp [] T.M. Ele et al., Optcal nterferometrc probng of advanced mcroproceor, Proc. ITC, 1, pp [5] F. Stellar, F. Zappa, S. Cova, C. Porta and J.C. Tang, Hgh-Speed CMOS Crcut Tetng by 5p Tme-Reolved Lumnecence Meaurement, IEEE Tran. on Electron ev., vol. 8, 1, pp [6] F. Stellar, F. Zappa, S. Cova and L. Vendrame, Tool for Non-Invave Optcal Characterzaton of CMOS Crcut, IEM Tech. g., 1999, pp [7] C88-1 uer manual, Hamamatu Photonc K.K., Japan. [8] S. Cova, M. Ghon, A.L. Lacata, C. Samor and F. Zappa, Avalanche photodode and quenchng crcut N N N N RC dcharge 6 NM NM RE1 Tme [n] Fgure 7. SPA meaurement (contnuou lne) compared to optcal mulaton (dahed lne). RC [n] Smulated RC Optcally extracted RC Tme [n] Fgure 8. Smulated (dahed lne) and optcally extracted (contnuou lne) tme contant

5 ESSERC, 8th European Sold-State evce Reearch Conference, Florence (Italy), -6 Sep.. for ngle-photon detecton, Appl. Opt., vol. 35, 1996, pp