Lecture#20 Ion Implant for ULSI

Transcription

1 EMCR632/702 - Silicon Processes Catalog: EMCR632 Silicon Processes EMCR702 Microelectronics II Lecture#20 Ion Imlant for ULSI Prof. K.D. Hirschman 1/30/02 K.D. Hirschman Silicon Processes: Ion Imlantation 1 Ion Imlant - Lecture#20 Toics: Motivation: Advanced CMOS device structure Ion imlant Pearson distribution Ion Channeling Imlant Damage 1/30/02 HW#4 due Friday K.D. Hirschman Silicon Processes: Ion Imlantation 2

2 Advanced CMOS Technology Side wall Sacer Silicide Gate Low Doed Drain (LDD) Source Drain Sto STI STI Punch Through Imlant Retrograde Well K.D. Hirschman Silicon Processes: Ion Imlantation 3 EMCR632/702 Silicon Processes Ion Imlant Ref: Cambell chater 5 Wolf & Tauber Vol I - chater 9 K.D. Hirschman Silicon Processes: Ion Imlantation 4

3 Random interactions with target atoms Ion, dose, energy R R K.D. Hirschman Silicon Processes: Ion Imlantation 5 Pearson-IV Distribution If an analytical solution is used, a higher-moment distribution is needed which can more accurately describe the imlanted imurity rofile Parameters adjusted to fit Monte Carlo simulations (using ion stoing theory) or actual measured rofiles (SIMS). Gaussian skewness Kurtosis Pearson-IV Distribution I. Mean (R) II. St.Dev. ( R) III. Skewness (γ) - asymmetry of the dist. IV. Kurtosis (β) - distortion of eak - larger value if flatter to K.D. Hirschman Silicon Processes: Ion Imlantation 6

4 4-Moment Distribution 1) Projected Range (mean) 2) Straggle (standard deviation) 3) skewness 4) kurtosis R R γ = β = 1 = Φ = 1 Φ ( x R ( x R xn( x) dx ( x R ) ) 3 Φ R 4 Φ R K.D. Hirschman Silicon Processes: Ion Imlantation ) 2 N ( x) dx N( x) dx N( x) dx Ion Channeling Pearson-IV distribution works well for imlants into amorhous silicon, or if ion channeling is suressed. Otherwise an adjustment must be made to correct for tilt/rotation deendence. Fig from W & T K.D. Hirschman Silicon Processes: Ion Imlantation 8

5 Channeling Effects K.D. Hirschman Silicon Processes: Ion Imlantation 9 Channeling Effects normalized rofiles low-dose high-dose self-amorhization K.D. Hirschman Silicon Processes: Ion Imlantation 10

6 Methods to avoid channeling Tilt & Twist Screen Oxide - amorhous surface layer Å is thick enough Pre-amorhization imlant - silicon imlant to re-amorhize lattice - 2-stage BF 2 & B 11 imlant Self-amorhization - arsenic (heavy ions), high dose K.D. Hirschman Silicon Processes: Ion Imlantation 11 BF 2+ molecular ion imlants Used for shallow + junctions Used for re-amorhization for boron (B11) imlants to reduce channeling effects and avoid buried amorhous regions Some issues with excess fluorine at high doses BF 2 molecule dissociates uon imact some electrical activity defect cluster formation BF 2 + F B F Si Kinetic Energy associated with boron atom: KE = ½(m)v 2 E B = E BF2 (M B /M BF2 ) = E BF2 (11/49) ex: BF 100KeV ~ B 20KeV K.D. Hirschman Silicon Processes: Ion Imlantation 12

7 LSS Theory of Ion Stoing LSS: Linhard, Scharff & Schiott R Nuclear Stoing: Coulombic Scattering Electronic Stoing m1 v 1 m1 m1 v m2 0 + m2 v 2 K.D. Hirschman Silicon Processes: Ion Imlantation 13 Nuclear Stoing Energy loss er distance traveled as a function of energy: deends on incident ion and target atom nuclear charge (Z = # rotons) and atomic masses (M) S n ( E) de = dx Energy loss due to interactions with atomic nuclei is basically a decreasing function of energy. At high kinetic energy (ion velocity) there is a very short interaction time for any absortion of energy by target atoms. S n (E) S n E Aroximate nuclear stoing near max of S n (E): 2 de π 2 Z1Z2M1 = Sn = N e a dx( n) 2 M + M where N is the atomic density (atoms/volume) -2 a ~1.4x10 nm, subscrits1and 2 refer to ion and target resectively, Z is atomic number and M is mass number 1 K.D. Hirschman Silicon Processes: Ion Imlantation 14 2 n

8 Electronic Stoing Due to interactions with electrons in the target material - like a drag force that is roortional to the ion velocity Ion velocity α (Energy) 1/2 S de ( k E 1/ 2 e E) = E = dx e e 1/ 2 where k e is relatively indeendent of the incident ion For silicon: k e ~ 10 7 (ev) 1/2 /cm Total rate of energy loss = de/dx = S n (E) + S e (E) K.D. Hirschman Silicon Processes: Ion Imlantation 15 LSS Calculations ε & ρ are dimensionless arameters ε α energy ρ α range (R) (distance variable) like de/dx K.D. Hirschman Silicon Processes: Ion Imlantation 16

9 Range & Straggle From LSS Theory: R R M 1 + T 3M i R 2R Mi M 3 M + M i T T K.D. Hirschman Silicon Processes: Ion Imlantation 17 Nuclear & Electronic Stoing Electronic stoing dominates: Light ions and high energies Nuclear stoing dominates: Heavy ions and low energies Imlant damage occurs due to nuclear interactions. The extent of damage deends on S n (E). * K.D. Hirschman Silicon Processes: Ion Imlantation 18