《Microelectronics Process》lecture5

Oxidation of si Why spend a whole lecture on oxidation of Si? Ge has high ue, Wh, Ge stable but no oxide GaAs has high ue and direct band Why sio? Sio, is stable down to 10 9 Torr. T>900C Sio can be etched with hf which leaves si unaffected Sio, is a diffusion barrier for B. p. as SiO, is good insulator, p>106 Q2cm, E. 8 eV Sio, has high dielectric breakdown field, 500 V/um SiO2 growth on Si= clean Si/ Sio, interface Oxide because DSi through Sio,<< DOxy through Sio2 Sept.19,2003 3.155J/6.152J

Oxidation of Si Why spend a whole lecture on oxidation of Si? Ge has high me, mh , Ge stable… … but no oxide GaAs has high m and direct band… … no oxide e Why SiO2? SiO2 is stable down to 10-9 Torr , T > 900°C SiO2 can be etched with HF which leaves Si unaffected SiO2 is a diffusion barrier for B, P, As SiO2 is good insulator, r > 1016 Wcm, Eg = 8 eV! O2 SiO2 has high dielectric breakdown field, 500 V/mm SiO2 growth on Si fi clean Si / SiO2 interface because DSi through SiO2 << DOxy through SiO2 SiO2 Si dtOxide Sept. 19, 2003 3.155J/6.152J 1

So Sio2 growth occurs at inside surface Oxide Si+O2→S02 Si+ 2H20=Si02+ 2H wth, more porous, lower quality Unsaturated Bond 0262nm 0.162nm Oxyge con Oxygen Silicon Sept19,2003 3.155J6.152J

2 So SiO2 growth occurs at inside surface Si + O2 Æ SiO2 or Si + 2H2O = SiO2 + 2H2 (faster growth, more porous, lower quality) O2 SiO2 Si dtOxide Sept. 19, 2003 3.155J/6.152J

ata Extra free volume in dangling bonds of amor phous SiO, Implications different for field vs patterned oxide 3.155J/6.152

O2 SiO2 Si dtOxide in dangling bonds of => Extra free volume amorphous SiO2 Implications different for field vs. patterned oxide. Sept. 19, 2003 3.155J/6.152J 3

Cleaning station for removing organic contaminants and native oxide(by HF-dip) from si wafers Oxidation furnaces for controlled growth oxide layer on Si 1050 C and steam for field oxide Sept.19,2003 3.155J/6.152J

Cleaning station for removing organic contaminants and native oxide (by HF-dip) from Si wafers. Oxidation furnaces for controlled growth of oxide layer on Si: 1050 C and steam for field oxide. Sept. 19, 2003 3.155J/6.152J 4

Probably safe to say that entire course of semiconductor industry would be different without Sio 2 Device fabrication, especially mOs more difficult Depositing Sio2 or ALO3 is not clean Sept.19,2003 3.155J/6.152J

Probably safe to say that entire course of semiconductor industry would be different without SiO2. Device fabrication, especially MOS, more difficult. Depositing SiO2 or Al2O3 is not clean. Sept. 19, 2003 3.155J/6.152J 5

It's no accident that the world leader in Si chip technology, Intel, has been led by the flamboyant hungarian, andy Grove as a young researcher at fairchild Semiconductor. he wrote the book on Sio2 growth: the Deal-Grove model Sept.19,2003 3.155J6.152

It’s no accident that the world leader in Si chip technology, Intel, has been led by the flamboyant Hungarian, Andy Grove. As a young researcher at Fairchild Semiconductor, he wrote the book on SiO 2 growth: the Deal-Grove model. Sept. 19, 2003 3.155J/6.152J 6

Deal-Grove model of silicon oxidation Sio, growth occurs at si/ sio interface because D(Sio, )>>D'(Sio, Growth Process limited by 1. P(O2)=Pg a Cg Concentration layer: Sio, Si 2. Transport O, to Sio, surface across dead layer J 3. Adhesion of C(O ) at SiO, surface Co c 4. Diffusion O, through Sio2 J2 5. Chemical reaction rate J Sept.19,2003 3.155J/6.152J

Deal-Grove model of silicon oxidation SiO2 Si SiO O2 2 growth occurs at Si / SiO2 interface because DO2 (SiO2) >> DSi(SiO2) Growth Process limited by O2 1. P(O2) = Pg µ Cg 2. Transport O2 to SiO2 surface across dead layer J1 3. Adhesion of Cs(O2) at SiO2 surface C0 4. Diffusion O2 through SiO2 J2 Concentration SiO2 Si Cg Cs Co Ci dead layer J1 J2 J3 x 5. Chemical reaction rate J3 Sept. 19, 2003 3.155J/6.152J 7

Deal-Grove model of silicon oxidation Oxide growth rate Ideal gas law: PV=NkT dead Concentration layer/ Sio, Si kT Co= HP= HkRTC SdsC Henry' s law dead laver Turbulence→> 2=D(Si02 )C- Co X J J1=h(Cn·C rate constant Diffusion(D cm/s) k,(cm/s Equate ideal gas J Equate J2+ Henry to J3 to J2+ Henry →C=fP,1,H,D,xh,k Sept.19,2003 3.155J6

Cg J 2 C 0 - Ci J1 (C - Cs ) N V Deal-Grove model of silicon oxidation Oxide growth rate Ideal gas law: PgV = NkT O2 Concentration = C = g C0 = HP = Hk s B TCs (C gg - C )s J Henry’s law 1 > D tdead layer SiO 2 Si dead layer Ci C o J3 3 Cs J1 J1 Cg 2 J2 = J = J C -C0 J1 g(C g - Cs = h ) Turbulence => J2 = D O2 (SiO 2 ) s xox x J3 = k i Ci rate constant Diffusion ( D cm 2/s) Pg kT ki (cm/s) Equate ideal gas + J1 Equate J2 + Henry to J3 Sept. 19, 2003 to J2 + Henry 3.155J/6.152J fi Ci = fn Pg ,hg ,H,D O2 , xoxide ,k ( ) i 8

Deal-Grove model of silicon oxidation J1=J2=J dead Si ayer:SiO Concentration Si =Ci=f(PR,h, H, D, roxide, k i C C HP/k h h h DOck mass transport Diffusion Reaction ( i=ke in text) J2 Slowest process controls concentration of oxygen at interface Sept.19,2003 3.155J/6.152J

Deal-Grove model of silicon oxidation J1 = J2 = J3 O2 Concentration fi Ci = fn (Pg ,hg ,H,DO2 , xoxide ,ki ) hg h = x SiO2 Si Cg Cs Co Ci dead layer J2 J3 J1 HkT Ci = HPg /ki 1 h + xox DO2 + 1 ki mass (ki = k in text) Diffusion Reaction s transport J2 J3 J1 Slowest process controls concentration of oxygen at interface… Sept. 19, 2003 3.155J/6.152J 9

HP/k +-0+ k;L H]T very large/ h Limits: Growth mass diffusion reaction limited by: transpo Reaction-rate limited Diffusion limited k i <h, Do2/x Do2/.<kh G G C HP DO C=HP CaC C≈0 C年 Oxide Silicon Gas Oxide Silicon Sept 19,2003 Slower process controls concentration of oxygen at interface which in turn controls growth rate

† 2 Limits: Growth limited by: Ci = HPg /ki 1 h + xox DO2 + 1 ki mass transport diffusion reactionReaction-rate limited: Diffusion limited: ki < hg, DO2/xox hg h = very large HkT Ci = HPg DO2/xox < ki, hg, Ci = gDO2 kixox HP Sept. 19, 2003 Slower process controls concentration of oxygen at interface, which in turn controls growth rate…