SEL EXHIBIT NO. 2010
`INNOLUX CORP. v. PATENT OF SEMICONDUCTOR ENERGY
`LABORATORY CO., LTD.
`
`IPR2013-00064
`
`

`

`tREE ELF.CTRON DEVICE LETEERS. VSI.. 17. 50.9, SEPTEMBER 199E
`
`437
`
`High Field-Effect-Mobility a-Si:H TFT Based
`on High Deposition-Rate PECVD Materials
`
`Churt-ying Chen and Jerzy Kanicki
`
`Abstrseet-The hydrogenated amorphous silicon (a-Si:tfr thin-
`111m transistors (TI7T's) hosing a field-effect mobility of 1.45
`± 0.05 cm4/V s and threshold voltage of 2.0 ± 0.2 V bave
`been fabricateol Irons the high deposition-rate plasma-enhanced
`chemtcal vapor deposited (PECVD) materials. For this 1Ff, the
`deposition rates of a-StaB and N-rich hydrogenated amorphous
`siticon nitride (a-SiNs s:H) are about SO and 190 um/min respec-
`tively. The TFT bas a very high ON/OFF-current rallo (of more
`than ioi, sharp snbthreshold slope (0.3 ± 0.03 V/decade), and
`very low source-drain current activation energy (50 ± S meV).
`All these parameters are consistent ssith a high mobility value
`obtained for our a-SitU TIlT structures. To our best knowledge,
`this is the highest field-effect mobility ever reported for an a-Si:H
`TFF fabricated from higls deposition-rate PECVD materials.
`
`To improve the productivity and lower the cost of active-
`
`matrix liquid crystal displays (AMLCD's), there is a
`need fur eahancement of the throughpal and operation up
`time uf existing plasma-enhauced chemical vapor deposi-
`tion (PECVD) tools osed in the fabrication of hydrogenated
`amorphous silicon (a-Si:}-l) thin-film teansisturs (TFT's). This
`should be achieved without sacrificing the a-Si:H TNT elec-
`tricot performance. Ose melhod to increase the AMLCI)
`production throoghput is by increasing the depositioo rate of
`the FECVO materials used in fubricaliuu uf a-Si:H It-I's.
`Different methods such as very high-frequency plasma [t],
`high-pulsed KF power density [2], helium dilution [3], and
`unique design of electrodes for efficient ionization is the multi-
`chamber system for cust-effcctive manufacturing [4], [5] have
`beco developed to produce a-Si:ll film with a high deposition
`rate. Among these different technologies, only a very high
`frequency (60 MHZ) PECVD [6] and a multi-chamber FlIC VO
`[4], [5] systems have been used is the prodactino of a-Si:H
`It- l's. For a very high frequency (60 MHz) PECVD, it has
`been reported [6] that a-Si:H TNT having a high field-effect
`mnbilily (lIFE) (1.1 cm2/Vs) can be fabricated from Itigh
`deposition-rule materials. Hosvever, in another higls frequency
`(40 MHz) PECVD system of a similar design u slightly lower
`mobility (0.7 cm2/Vs) has been obtained [7]. At the same
`time, a-Si:H TFT's uxhibitiag lIFE m 0.8 cm2/Vs were
`fabricated from u high growth rate materials [8] produced in a
`multi-chamber AKT 1600 PECVD system mentioned above.
`
`MssascpIrsasivcd Apsit 3, 1996; revised loss4. 1996.
`Thu sathcn use wilh Ors Depanrcrss ut Elsaniaal EsOisuosiso usd Cow-
`pases asieses, Ceso, rs, Dispiny Tuchaslogy asd Massraurosisn, tisivrrsisy
`ut Michinas, Ass AsSur, Mt 41109 USA.
`Pabtishor Item tdustiOee 5 0741-3 loO(o6)n6i74-7.
`
`In this letter, we repart high field-effect mobility a-Si:H
`161's which have been fabricated from high deposition-rate
`materials deposited at 320 5C in a 13.6 MHz AKT 1600 mutti-
`chamber FECVD system. Back-channel etched a-Si:H TFF's
`were fabricated acd tested during this study. The a-Si:H in
`AKT 1600 PECVD system was deposited under the followiag
`conditions: silane 110w is 250-500 seem; hydrogen flow is
`2000 seem; preasore is 2-4 ton; KF power is 150 W. Based
`on our preliminary data the micruslructnre of oar high-rate
`trcvo
`materials is similar to the one obtained for low-rate
`Olms [9]. The thicknesses of N-rich hydrogenated amorphous
`silicon nitride (a-SiNtu:H), intrinsic u-Si:l-1, F-doped (n6)
`a-Si:H are 240, 200, and 50 cm, respectively. The channel
`length was defined by using the source/drum metal (300-nm-
`thick Mo) as a mask. The channel svidth and length of typical
`TFT's are 116 and 32 pam, respectively. All these geometry pa-
`rameters were measured by bath scanning eteetmn microscope
`(SEM) and Dektuk profiler. The materials used in our TF'l"s
`have the following properties: (a) a-Si:H deposition ente is
`50 nut/min. dwk conductivity is about 2,81<10_lt ('r' em',
`activation energy is 0.94 eV, Taue Optical bandgap is 1.78 eV,
`and hydrogen content is abeot 3 x 1021 cm3; (b) a-SiNu n:li
`growth rate is 190 nmlmin, etching rate in oxide etch solution
`is 61 nm/mm, Taue optical bandgup is 5.0 eV. dielectric
`constant is 7.0 (measared at 1 MHz frequency), and hydrogen
`content is about 1.0 x 102a cm3; (e) n a-Si:H growth rule
`is 60 nm/mm, film resistivity is 41 fi cm, activation energy
`is 0.2 eV, Taue optical baudgap is 1.74 eV, and tvto/u<
`a-Si:H contact resistance (Rç) is 0.25 ft cm2. Mure detailed
`iufocnsatíoa about a-SiNt :Fl film used in oor a-Si:H TFT is
`reported elsewhere [9].
`Fig. t shows the drain-source earreat (fas) versas drain
`voltage (V00) characteristics fur varions gate voltages (V05).
`At small drain vottugen (below 2 V), the curacas crowding
`effect is absent, which indicates a gund electrical/ohmic quality
`of sonree/druin contacts in oar TIlT. Fig. 2 shows Ihn TIlT
`transfer characteristics for varions V05. For V05
`10 V,
`the drain current changes from 10_12 to to-u A as the gate
`bias sweeps from -5 to 20 V. Thus ON-OFF-current ratio
`Exceeds tO7 and the OFF-current is tess thon 10_12 A; 1hz
`gate leakage caracol was below Ihn detection limit of HP4145.
`This TIlT with tow OFF-current satistles the requirement of
`low leakage caracul needed fnr AMLCD's. In linear regiou
`(V05 = 0.1 V) the sabthreOhald slope (S) measured from
`V05 = O to 0.6 V is about 0.30 ± 0.03 V/decade. This slope
`is much sharper than any other slopes ranging from 0.5 to
`
`n741-3109/96305.00 o tsss tEEE
`
`EXHIBIT 'Jx\
`
`ÓC\\Qi
`
`

`

`438
`
`IEEE ELECTRON DEVICE LEITERS, VOL. II. NO. 9, SE
`
`tuER 1996
`
`- W/L=1l6/32
`linear region
`: V05Oj V
`
`: 't2
`
`V.r=t9 V
`
`5
`
`4
`
`o
`
`0.15
`
`0.1
`
`0.05
`
`0
`
`5
`
`10
`V (V)
`US
`
`15
`
`20
`
`0.00
`O
`
`Vig. 1. Room temperature drain-source current (los) versus drain-source
`voltage (VDS) characteristics for various gate biases (V05).
`
`saturation region - 2 9
`
`o
`
`cm2JVs
`V =2.0 V
`
`o
`
`20
`
`5
`
`IS
`lO
`V0 (V)
`
`(s)
`
`- Vna.lv
`/ tesar region
`
`1ss'treo U(L*ÔL)
`1.6 on2/Ve
`6tI4 tain
`
`1.8
`
`1.6
`
`1.4
`
`g
`Ea
`
`.0
`.5
`
`ti
`
` LO
`a
`a
`
`0.8
`
`o
`
`20
`
`40
`
`60
`
`lO
`
`lOO
`
`channel lIngOt (rim)
`
`(b)
`
`(a) Room temperature TDS and
`Fig. 3.
`versus V05 characteristics
`in linear and saturation region, respectively. (b) The variation or linear and
`saturation mebilities as a ftsnction of channel length. The linear mobility is
`fitted to UbE = #epso(L/L + ÖL), whcre ¿'pEo it the active channel
`fleld-cfftct mobility and (L + IL) is Ihe effective channrl length f161.
`
`1.0
`
`-
`
`-
`
`-
`
`-
`
`0.0
`
`O
`
`pJT-flJ3
`.r I .5 cm2IVs
`I V =2.0 V
`
`saturation region(V = V0) -
`
`linearrcgion(V=0.IV)
`
`5
`
`lO
`V0 I»
`
`IS
`
`20
`
`Fig. 4. The evolution of drain-source cuneta activation energy as a function
`of gate hies in saturation region. The values for linear region (-) are also
`given in this figure.
`
`approximation equations [14]
`
`'OS =
`
`=
`
`2L
`
`L
`
`(V05
`
`VT)2
`
`(saturation region)
`
`(V05 - VT) . VJ5
`
`(linear region)
`
`(2)
`
`(3)
`
`t0-
`
`10-8
`
`fi
`
`to_to
`
`-
`
`.2
`
`.
`
`IO-I2
`
`lois
`-5
`
`-
`
`-
`0
`
`W/L=1t6/32
`S0.3 V/decade
`tfl4248om
`usan.0
`
`IS
`
`20
`
`5
`lO
`VI»)
`
`Fig. 2. Room temperature drain-source current ('Dg) versus gate-source
`voltage (Vos) characteristics at different V5.
`
`2.5 V/dec reported in the literature [10}-[12] for a-Sï:H TFT.
`The shaap subthreshold slope implies a low density of deep-
`gap states localized at or near the a-SiN:I-1/a-Si:H interface.
`Assuming that the distribution of deep-gap states is energy
`independent and using the followiog relationship [10]
`
`kT [ +
`qlosr(c) [
`
`ei
`
`+
`
`(1)
`
`where e1 and e are the a-SiN:H and a-Si:H dielectric con-
`stants, respectively; d is a-SiN15:H thickness; q is electron
`charge; k is J3oltzmann constant; N65 is deep-gap bulk states;
`N55 is interface states; and T is temperature, the maximum
`possible value for AÇ5 (iv5, = 0) is on the order of 8 x
`iO11 cm2 eV'. This N,5 density is lower than any other
`values ranging from I 7x1012 to 5x1012 cm-2 eVt reported
`in the literature for a-Si:H TFT s [10], [13].
`The equivalent transfer characteristics, l'S versus V05 in
`the linear region (V05 = 0.1 V) and
`versus V05 in the
`saturation region (VDS = V05), are shown in Fig. 3(a). The
`mobility and threshold voltage (VT) in linear and saturation
`regions 'vere extracted by a least-squares fit, between 20
`and 80% of the total drain current, to the gradual channel
`
`

`

`CElEN AND KANICKI: HIGH FIELD-EFFEa-MOBILITY a-Si:H TF BASED ON tItOlI DEPOSITION-RATE PECVD MATERIALS
`
`439
`
`where G1 is gate insulator capacitance per unit area: L is
`channel length; and 14'
`is channel width. The field-effect
`mobilities extracted from Fig. 3(a) are 1.45 ± 0.05 cm2/Vs
`and 1j5 x 0.05 cm2/Vs in the saturation and linear regions,
`respectively. The extracted field-effect mobility has a channel
`length dependence, Fig. 3(b), similar to the one described in
`the literature [151, [16]. Following analysis described in these
`references we have obtained a similar active channel field-
`effect mobility value for the linear and saturation regions,
`which is about 1.60 ± 0.02 cm2/Vs. This high-mobility value
`is in agreement with a low density of the interface states
`deduced from Fig.2. The threshold voltages obtained from
`Fig. 3 are 2.0 ± 0.2 V and 1.9 ± 0.2 V in the saturation
`and linear regions, respectively. This low 14 indicates that
`the interface states and fixed charges localized at or near a-
`SiH/a-SiN1:H interface are small. To confirm our high pp
`we have investigated the temperature dependence of 1DS
`VGS characteristics. From this temperature dependence, the
`evolution of 'DS activation energy as a function of V05 in
`the saturation region have been obtained, Fig. 4. An activation
`energy on the order of 50 ± 5 meV at V05 = 20 V has been
`deduced in the saturation region indicated in this figure. A
`similar value has also heen obtained in the linear region of
`TFF characteristics. Based on our previous a-Si:H TFI' two
`dimensional simulation [17] this activation energy value will
`correspond to a Fermi level position of about 20 ± 5 meV
`below the conduction band-edge, and a slope of conduction
`band-tail states (Ec) nf about 27 ± i meV. For this Ec and
`taking lic = 0.25 Q cm2, we will expect that PEE should be
`on the order of 1.4 ± 0.1 cm2/Vs [181. This theoretical PEE
`value is very close to the experimental value obtained for our
`a-Si:H TFT structures.
`In conclusion, a high mobility (1.45 ± 0.05 cm2/V . s)
`a-Si:H TV]' s have been fabricated using a high deposition-
`rate PECVD materials. We speculate that this high mobility is
`due to a low density of deep-gap states and a steep slope of
`conduction band-tail states for a-Si:H channel region.
`
`ACKNOWLEDGMENT
`The a-Si:H TFT s were designed and processed at the
`University of Michigan, Ann Arbor. High deposition-rate
`PECVI) materials were developed in collaboration with Opti-
`cal Imaging System Inc.. The authors would like to thank the
`following people who have contributed to this project: C. T.
`Malone, Optical Imaging System Inc., and T. Li, University
`of Michigan.
`
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`