多晶硅栅耗尽导致的SRAM单比特位失效分析_英文_

多晶硅栅耗尽导致的SRAM单比特位失效分析_英文_ 2008年 10月 JOURNAL O F FUNCT IONAL MA TER IAL S AND D EV ICES O c t. , 2008 ( ) 文章编号 : 1007 - 4252 2008 05 - 0923 - 04 Ana ly s is of SRAM s in g le b it fa ilure due to loca l po ly dep le t ion 1 , 2 , 3 1 , 2 , 3 3 3 L I R u i, WAN G J un, KON G W e i2ran, MA H u i2p ing, 3 3 3PU X iao2dong, X IN H a i2we i, WAN G Ch ing2dong ( 1. Shangha i In stitu te of M ic ro system and Info rm a tion Techno logy, Ch ine se A cadem y of Sc ience s, Shangha i 200050 , Ch ina; 2. Gradua te Schoo l of Ch ine se A cadem y of Sc ience s, )B e ijing 100049 , Ch ina; 3. Grace Sem iconduc to r M anufac tu ring Co rpo ra tion, Shangha i 201203 , Ch ina A b stra c t:A SRAM single b it fa ilu re a t w rite mode wa s ca refu lly ana lyzed. B y nano - p rob ing the fa iled b it, it wa s found tha t a weak acce ss - NMO S d isab led the w rite - op e ra tion of tha t p a rticu la r b it. A TEM check showed tha t the fa iled b it ha s la rge po ly gra in size a s comp a red to a no rm a l b it, wh ich cau se s the ga te wo rk func tion to change and lowe r the loca l a rsen ic concen tra tion. It is then ve rified by SP ICE sim u2 la tion tha t the loca l po ly dep le tion is the o rigin of the acce ss - NMO S conduc tib ility degrada tion. Key word s: SRAM ; single b it fa ilu re; po ly dep le tion CL C: 7340 G, 7300 , 7360J , 7340Q D ocum en t code: A 多晶硅栅耗尽导致的 SRAM 单比特位失效分析 1, 2 , 3 1, 2 , 3 3 3 3 3 3 李睿 , 王俊 , 孔蔚然 , 马惠平 , 浦晓栋 , 莘海维 , 王庆东 ( 1. 中国科学院上海微系统与信息技术研究所 ,上海 200050; 2. 中国科学院研究生院 ,北京 100049; )3. 宏力半导体制造有限公司 ,上海 201203 摘要 :本文分析了一种静态随机存储器单比特位失效的机理 。通过纳米探针测量 ,发现该比特位写 操作失败是由负责存取的 N 型晶体管的驱动力较弱导致 。 TEM 分析显示该晶体管的多晶硅栅中 晶粒尺寸较大 ,这有可能导致栅的功函数变化以及靠近栅介质层区域的掺杂较轻 。我们用 SP ICE 模拟证实了晶体管驱动力变弱的原因是局域的多晶栅耗尽 。 关键词 :静态随机存储器 ;单比特位失效 ;多晶硅栅耗尽 ( ) SRAM ha s becom e a p reva len t em bedded m emo ry in 0 In troduc t ion [ 1 ] m any app lica tion s . The dem and fo r qua lity and p e r2 W ith the advan tage s of h igh acce ss - sp eed, un2 fo rm ance of h igh den sity SRAM w ill p u sh fo r tigh te r lim ited read - w rite endu rance and fu ll comp a tib ility de sign ru le s and sm a lle r fea tu re size, wh ich w ill be w ith CMO S p roce ss, sta tic random acce ss m emo ry Rece ived da te: 2007 - 09 - 10; M od if ied da te: 2007 - 12 - 21 ( ) ( B iogra phy: L i R u i 1981 - , gradua te studen t. H e is engaged in advanced sem iconduc to r p roce ss and device p hysic s E - m a il: rayli ) @ gsm c thw. com . 924 功能材料与器件学报 14卷 mo re sen sitive to p roce ss va ria tion. The refo re, SRAM is frequen tly u sed a s a qua lifica tion veh ic le fo r p roce ss deve lopm en t. A s a re su lt, fa ilu re ana lysis of SRAM is no t on ly fo r troub le - shoo ting, bu t a lso fo r a ssu rance [ 2 ] of on - tim e de live ry to m a rke t . In conven tiona l m emo ry fa ilu re ana lysis, the fa iled b it is de tec ted by a logic te ste r and then a scan2 ( ) n ing e lec tron m ic ro scop e SEM and /o r a tran sm ission ( ) e lec tron m ic ro scop e TEM a re u sed to p hysica lly ob2 [ 3 ] se rve and de te rm ine the roo t cau se of the fa ilu re . Howeve r, the SEM and TEM on ly a llow one to exam ine one po in t among seve ra l po ssib le fa ilu re loca tion s. Fu r2 F ig. 1 6T SRAM ce ll layou t the rmo re, the p hysica l ob se rva tion canno t d irec tly re2 The fa ilu re occu rred in the read op e ra tion. The flec t the fa ilu re mode. R ecen t advance s in nano - den sity of the fa ilu re b its is app roxim a te ly 0. 001 % , p robe rs, wh ich enab le the p rob ing of extrem e ly sm a ll wh ich a re random ly d istribu ted w ith in d ie s and wafe rs. line w id th s, p e rm it the e lec trica l cha rac te riza tion of in2 ( ) E lec trica l fa ilu re ana lysis EFA confirm ed tha t the d ividua l device s w ith in an in tegra ted c ircu it. fa ilu re b its d istribu tion is a lmo st indep enden t on the Th is p ap e r de sc ribe s the de ta iled ana lysis of ran2 powe r supp ly vo ltage and the op e ra tion frequency. dom SRAM single b it fa ilu re, wh ich cau se s seve re p ro2 duc tion yie ld lo ss. U sing the nano - p robe r techn ique, MO S cha rac te ristic s of fa ilu re b it we re m ea su red d irec t2 2 FA ILUR E ANAL YS IS ly. Then, a TEM ana lysis of the MO S device w ith a2 The po ssib le single b it fa ilu re m echan ism s of the nom a lou s e lec trica l cha rac te ristic s wa s imp lem en ted. 6 T SRAM ce ll inc lude in suffic ien t sta tic no ise m a rgin The fa ilu re mode wa s iden tified, ba sed on the se two ( ) SNM and weak acce ss tran sisto r / strong load tran2 [ 4 ] ana lytica l step s. sisto r . SRAM ce lls becom e un stab le when lack of SNM. SNM can be dec rea sed by reduc ing supp ly vo lt2 ( age, dec rea sing be ta ra tio ra tio of the d rive cap ab ili2 1 侢 EXPER IM EN T tie s be tween the d rive - NMO S and the acce ss - ( ) F ig. 1 show s the 6 - tran sisto r 6 TSRAM ce ll ) ) ( NMO S, and dec rea sing V of th re sho ld vo ltage th μlayou t u sed fo r 0. 15 m gene ra tion logic p roduc tion. [ 5 ] 2 ce ll tran sisto rs . A s m en tioned above, the fa ilu re μ The ce ll size is 1. 96 ×1. 44 = 3. 43m,2 and the m in i b its d istribu tion is indep enden t on the powe r supp ly. μm um ga te length in the ce ll is 0. 15 m.The ch ip wa s The refo re , the lack of SNM is no t the fa ilu re mode. O n ( ) fab rica ted on 100 p - typ e silicon sub stra te. A fte r the o the r hand, if the conduc tib ility of the acce ss - ( ) the sha llow trench iso la tion ST Ifo rm a tion, a 2. 5 nm NMO S is sm a lle r than tha t of the load - PMO S, the ga te oxide wa s grown, fo llowed by a 180 nm po ly - Si h igh vo ltage node canno t be p u lled down in the w rite film depo sition a t 620 ? by low - p re ssu re chem ica l va2 mode. () po r depo sition L PCVD . A fte r ga te p a tte rn ing, rap id In o rde r to iden tify the fa ilu re m echan ism , a ll the ( ) the rm a l annea l R TA wa s p e rfo rm ed to hea l any dam 2 six tran sisto rs of the fa iled b it we re m ea su red d irec tly age a t the ga te edge du ring the p la sm a e tch p roce ss. u sing the nano - p robe r techn ique. A fte r m echan ica lly ( ) N ext, sou rce d ra in exten sion SD Eion s we re imp lan2 po lish ing the ch ip to expo se the W - p lug, the device ted fo r N and P region s. A fte r L - shap e sp ace r cha rac te ristic s can be m ea su red by p rob ing the W - p roce ss, N + and P + ion s we re imp lan ted and fo l2 ( ) p lugs. A s shown in F ig. 2 do ts, it is found tha t one lowed by R TA fo r dop an t ac tiva tion. L I R u i, et a l: A na lysis of SRAM single b it fa ilu re due to loca l po ly dep le tion 925 5期 the fa ilu re. Fu rthe rmo re, it wa s confirm ed the e lec tri2 and lowe rof the acce ss - NMO S ha s m uch h ighe r V th ( ) m axim um tran s - conduc tance The sub - ca l cha rac te ristic s of the anom a lou s acce ss - NMO S is g. m _m ax sou rce / d ra in symm e tric. A n inc rea se of effec tive ga te th re sho ld sw ing degrade s from 84 mV / dec to 98 mV / ( ) dec. The sa tu ra tion d ra in cu rren t Id rop s from 60 oxide th ickne ss cou ld po ssib ly exp la in a ll the m ea su red d sa t μμre su lts. A to 13 A. The d rive - NMO S, load - PMO S and ano the r acce ss - NMO S cha rac te ristic s of the fa ilu re b it The TEM im age s of the acce ss - NMO S in bo th a re sam e a s tha t of a no rm a l b it. The conduc tib ility of fa iled b it and no rm a l b it a re shown in F ig. 3. The ga te oxide wa s ca refu lly checked and no th ing abno rm a l wa s the weak acce ss - NMO S is too weak to p u ll down the ( found. Howeve r, the re exists a la rge gra in , 0. 2 h igh node du ring the w rite mode and the refo re cau se s μ) m in the po ly ga te of the fa iled b it, wh ile the gra in size of the no rm a l one is m uch sm a lle r and mo re un i2 fo rm. It is we ll known tha t ion s d iffu sion is fa st in po ly - Si a long the gra in bounda rie s, the refo re is dep enden t F ig. 2 E lec trica l cha rac te ristic comp a rison s of the acce ss - ( ) F ig. 3 TEM im age s of acce ss - NMO S in a the no rm a l b it ( ) NMO S in the no rm a l b it and the fa iled b it: alinea r Id - V g; ( ) and bthe fa iled b it. ( ) ( ) bloga rithm ic Id - V g; cGm - V g. 926 功能材料与器件学报 14卷 fu lly ana lyzed. B y nano - p rob ing the fa iled b it, it wa s found tha t a weak acce ss - NMO S d isab led the w rite - op e ra tion of tha t p a rticu la r b it. A TEM check showed tha t the fa iled b it ha s la rge po ly gra in size a s comp a red to a no rm a l b it, wh ich cau se s the ga te wo rk func tion to change and lowe r the loca l a rsen ic concen tra tion. It is then ve rified by SP ICE sim u la tion tha t the loca l po ly dep le tion is the o rigin of acce ss - NMO S conduc tib ility degrada tion. A s a re su lt, po ly dep le tion is a con tinu2 ou s cha llenge fo r SRAM of sm a lle r d im en sion. F ig. 4 Sim u la tion of a rsen ic concen tra tion in po ly - Si w ith d if2 Referen ce s: fe ren t gra in size. [ 1 ] Sa llago ity P, J uge M , D iop O , et a l. Ga te m a te ria l p rop e r2 [ 6 ] on gra in size . Th is can be confirm ed u sing p roce ss μtie s induced 0. 25m SRAM m a rgina lity [ A ]. P roc of thesim u la to r TSU PR EM - 4. A s shown in F ig. 4 , the a rse2 32nd Eu rop ean So lid - Sta te D evice R e sea rch Confe rence [ C ]. 2002. 575 - 578. n ic d iffu sion is re ta rded when the ave rage gra in size [ 2 ] J ung S M , Uom J S, Cho W S, et a l. A study of fo rm a tion μwa s se t to 0. 2m. The ligh t concen tra tion nea r the in2 and fa ilu re m echan ism of CM P sc ra tch induced defec ts on te rface of po ly - Si and oxide m ay re su lt in po ly dep le2 ILD in a W - dam a scene in te rconnec t SRAM ce ll [ A ]. tion effec t and fla t band sh ift due to the change of po ly 39 th A nnua l In te rna tiona l R e liab ility Physic s Sympo sium ga te wo rk func tion, and con sequen tia l gdegrada2 m _m ax [ C ]. 2001. 42 - 47. tion and V sh ift. A ll the se sugge st tha t loca l po ly de2 th [ 3 ] Q in W T, Vo lin sky A , R ice L , et a l. App lica tion of F IB / p le tion of the acce ss - NMO S is one po ssib le exp lana2 SEM and TEM to b it fa ilu re ana lysis in SRAM a rrays[ A ]. tion of the fa iled b it. M a t Re s Soc Sym p Proc, 2004. 325 - 330. W e u sed SP ICE sim u la tion to va lida te the imp ac t [ 4 ] Ikeda S, Yo sh ida Y, Ish iba sh i K, et a l. Fa ilu re ana lysis of of la rge gra in size on device e lec trica l p e rfo rm ance. 6 T SRAM on low - vo ltage and h igh - frequency op e ra tion ( ) () [ J ]. IEEE Tran s E lec tron D ev ice s, 2003 , 50 5 : 1270 F irstly, a B S IM 3 mode l M _no rm a lwa s deve lop ed to - 1276. de sc ribe the acce ss - NMO S cha rac te ristic of a no rm a l [ 5 ] Seevinck E, L ist F J , Loh stroh J. Sta tic - no ise m a rgin a2 b it. The line in F ig. 2 , wh ich is the sim u la ted re su lt na lysis of MO S SRAM ce lls[ J ]. IEEE J of So l id - S ta te show s good fitting w ith the m ea su red da ta. Two p a ram 2 ( ) C ircu its, 1987, 22 5: 748 - 754. e te rs in M _no rm a l we re ad ju sted to ob ta in the fa iled b it [ 6 ] B ane rjee S, D unham S T. Two stream mode l fo r dop an t d if2 () ( ) mode l M _fa ilu re: 1 vth0 wa s changed from 0. 61 fu sion in po lysilicon inco rpo ra ting effec ts of gra in grow th V to 0. 72 V to rep re sen t the mod ified wo rk func tion ( ) [ J ]. E lec trochem Soc Proc, 1996 , 96 4 : 92 - 101. ( ) and the inc rea sed effec tive oxide th ickne ss; 2 tox wa s changed from 3. 6 nm to 8. 5 nm to rep re sen t the po ly dep le tion effec t. The da sh line in F ig. 2 show s tha t bo th the Id - V g and gm cu rve can be we ll fitted by the M _ fa ilu re. F rom the se re su lts, we conc luded tha t the single b it fa ilu re o rigina ted from the loca l po ly dep le tion induced weak acce ss - NMO S. 3 CONCLU S ION A SRAM single b it fa ilu re a t w rite mode wa s ca re2