Introduction to Silvaco ATHENA Tool and Basic Concepts in Process Modeling Part - 1. Instructor: Dragica Vasileska

Transcription

1 Introduction to Silvaco ATHENA Tool and Basic Concets in Process Modeling Part - 1 Instructor: Dragica Vasileska Deartment of Electrical Engineering Arizona State University

2 1. Introduction to Process Simulation The farication rocess of an integrated circuit consists of the following main stes: ❶ Eitaxial growth ❷ oxidation, assivation of the silicon surface ❸ Photolithograhy ❹ diffusion ❺ metalization A schematic descrition of a lanar rocess for the farication of a n-junction, consists of the following stes: 1. Eitaxial growth: Eitaxial n-layer -sustrate High-temerature rocess (~1000 C) The amount of doant atoms determines the conductivity of the layer

3 . Oxidation and Photolithograhy Eitaxial n-layer -sustrate oxidation SiO Eitaxial n-layer -sustrate hotolithograhy Diffusion window Thermal oxidation leads to formation of oxide layer for surface assivation Photolithograhy allows roer formation of the diffusion window 3. Diffusion and Metalization stes n-layer -sustrate diffusion n-layer -sustrate metalization The diffusion rocess gives rise to the n-junction (takes lace at ~1000 C) Electrical contacts are formed via the metalization rocess

4 The sequence of events that lead to successful farication of the device structure are the following: otimization Faricate device structure Simulation relacing exerimental stes: ATHENA Process simulation tool Perform electrical characterization ATLAS Device simulation tool no yes Design condition met?

5 Physically-ased rocess simulation redicts the structure that results from secified rocess sequence Accomlished y solving systems of equations that descrie the hysics and chemistry of semiconductor rocesses Physically-ased rocess simulation rovides three major advantages: ❶ it is redictive ❷ it rovides insight ❸ catures theoretical knowledge in a way that makes the knowledge availale to non-exerts Factors that make hysically-ased rocess simulation imortant: ❶ quicker and cheaer than exeriments ❷ rovides information that is difficult to measure

6 The rocessing stes that one needs to follow, for examle, for faricating a 0.1 µm MOSFET device, include (in random order): ❶ Ion imlantation rocess ❷ Diffusion rocess ❸ Oxidation rocess ❹ Etching models ❺ Deosition models In the following set of slides, each of this rocess is descried in more details with the aroriate statements and arameter secification.

7 Some historical dates: - Biolar transistor: DTL - technology Monocrystal germanium: TTL - technology First good BJT: ECL - technology Monocrystal silicon: MOS integrated circuit Oxide mask, - CMOS 1963 Commercial silicon BJT: Linear integrated circuit Transistor with diffused - MSI circuits 1966 ase: MOS memories Integrated circuit: LSI circuits Planar transistor: MOS rocessor Planar integrated circuit: Microrocessor Eitaxial transistor: I L MOS FET: VLSI circuits Schottky diode: Comuters using - Commercial integrated VLSI technology 1977 circuit (RTL):

8 . Descrition of the Ion Imlantation Process Ion imlantation is the most-frequently alied doing technique in the farication of Si devices, articularly integrated circuits. Two models are frequently used to descrie the ion imlantation rocess: ❶ Analytical models: do not contriute to hysical understanding can e adequate for many engineering alications ecause of its simlicity ❷ Statistical (Monte Carlo technique): first rinciles calculation (time consuming) can descrie arasitic effects such as: - lattice disorder and defects - ack scattering and target suttering - channeling (imortant in crystalline mater.)

9 (A) Analytical Models For all of the analytical models, the real ion distriution in 1D is given the following functional form: C ( x) = Df ( x) D total imlanted dose er unit area f(x) roaility density function, frequency function - descried with the following four characteristic quantities: ❶ Projected range R : ❷ Standard deviation R P : = + R xf x) dx ( R = ( x R ) ❸ Skewness γ: ❹ Excess or kurtosis β: γ = + ( x R ) 3 ( R ) 3 f ( x) dx β = + + ( x R ) 4 ( R ) 4 f ( x) dx f ( x) dx 1/

10 Analytical distriutions most frequently used for descriing doing rofiles are: ❶ Simle Gaussian or normal distriution ❷ Joined half-gaussian distriution ❸ Pearson tye IV distriution Simle Gaussian or normal distriution 1D model Makes use of the rojected range R and the standard deviation R : ( ) D x R ( ) C( x) = ex π R R Has γ=0 and β=3. The aroximation of the true rofile is only correct u to first order, since it gives symmetric rofiles around the eak of the distriution. Range arameters R and R for all the imuritymaterial cominations are stored in the ATHENAIMP file.

11 The model is activated via the GAUSS arameter on the IMPLANT statement; R (RANGE) and R (STD.DEV) Other arameter that has to e secified is the dose D (via the arameter DOSE on the IMPLANT statement) Pearson distriution 1D model This is a standard model in SSUPREM4, and is used for generating asymmetrical doing rofiles. The family of Pearson distriution functions is otained as a solution of a differential equation: ( ) ( ) ( ) ( ) = + + = / arctan 4 / ex ) ( ) ( ) ( R x a R x R x K x f x x x f a x dx x df

12 The tye of the Pearson distriution deends uon the sign of the term: D = Only the Pearson IV (D>0) distriution has the roer shae and a single maximum. The constants a, 0, 1 and are related to the moments of f(x) in the following manner: R a = γ β 3γ = A ( ) ( ) β + 3 R 4β 3γ A, 6, The vertical doant concentration is then roortional to the ion dose: C ( x) = Df ( x) This simle model can fail in the case when channeling effects are imortant (dual Pearson model has to e used) 0 = A A = 10β 1γ 8, 1 = a

13 The model is activated via the PEARSON arameter on the IMPLANT statement. Other arameters that can e secified in conjunction with the model choice include: ❶ Lattice structure tye: CRYSTAL or AMORPHOUS ❷ Imlant material tye: ARSENIC, BORON, etc. ❸ Imlant energy in kev via ENERGY arameter ❹ For dual-pearson model, another arameter is imortant and descries the screen oxide (S.OXIDE) through which ion imlantation rocess takes lace

14 Two-dimensional imlant rofiles D analytical imlant models are quite rudimentary and usually ased on a simle convolution of a quasi-one dimensional rofile C(x, t mask (y)) with a Gaussian distriution in the y-direction: MASK IONS C( x, y) = 1 πσ y + C( x, t mask ( y'))ex ( y y' ) σ y - indeendent of deth (rolem) dy' In the case of an infinitely high mask extending to the oint y = a, the convolution can e erformed analytically, to give: σ 0 y < a C( x, tmask( y)) = C( x) y a a y = C( x, y) 1 C( x) erfc ; erfc( x) = e σ y π x y y (lateral) x (deth) t dt

15 Additional Parameters that need to e secified for D ion-imlantation rofiles are: ❶ Tilt angle: TILT ❷ Angle of rotation of the imlant: ROTATION ❸ Imlant erformed atall rotation angles: FULLROTATIO ❹ Print moments used for all ion/material cominations: PRINT.MOM ❺ Secification of a factor y which all lateral standard deviations for the first and second Pearson distriution are multilied: LAT.RATIO1 and LAT.RATIO

16 (B) Monte Carlo Models Analytical models can give very good results when alied to ion-imlantation in simle lanar structures. For non-lanar structures, more sohisticated models are required. SSUPREM4 contains two models for Monte Carlo simulation: ❶ Amorhous material model ❷ crystaline material model The Monte Carlo model can also deal with the rolem of ion imlantation damage: Damage tyes: Frankel airs (Interstitial and Vacancy rofiles), <311> clusters, Dislocation loos Two models exist for ion imlantation damage modeling: ❶ Kinchin-Pease model (for amorhous material) ❷ Crystalline materials model

17 (C) Some examles for analytical models Imlant of hoshorus with a dose of cm - and Gaussian model used for the distriution function. The range and standard deviation are secified in microns instead of using tale values. IMPLANT PHOS DOSE=1E14 RANGE=0.1 STD.DEV=0.0 GAUSS 100 kev imlant of hoshorus done with a dose of cm - and a tilt angle of 15 to the surface normal. Pearson model is used for the distriution function. IMPLANT PHOSPH DOSE=1E14 ENERGY=100 TILT=15 60 kev imlant of oron is done with a dose of cm -, tilt angle of 0 and rotation of 0. Pearson model for the distriution function is used that takes into account channeling effect via the secification of the CRYSTAL arameter. IMPLANT BORON DOSE=4.0E1 ENERGY=60 PEARSON \ TILT=0 ROTATION=0 CRYSTAL

18 (D) Characteristic values for the ion-imlantation rocess Dose: 10 1 to atoms/cm Current: 1 µa/cm to 1 A/cm Voltage-energy: 10 to 300 kv After the fact annealing: 500 to 800 C Advantages of the ion imlantation rocess: Relatively low-temerature rocess that can e used at aritrary time instants during the farication sequence.