J. Swerts

Atomic Layer Deposition of Strontium Titanate Films Using Sr ( #2#1Cp ) 2 and Ti ( OMe ) 4

Strontium titanate (STO) is a promising candidate as a high-k dielectric for dynamic random access memory application. STO thin films are deposited by atomic layer deposition using Sr( t Bu 3 Cp) 2 , Ti(OMe) 4 , and H 2 O as precursors. Growth and saturation behavior of STO and binary oxides are evaluated by ellipsometry thickness measurements. The precursor pulse ratio controls the amount of Sr and Ti incorporated in STO films. Stoichiometric SrTiO 3 is characterized by the lowest crystallization temperature and largest refractive index, density, and dielectric constant. An excess of Ti or Sr results in an increase in the crystallization onset temperature and contraction or expansion of the cubic cell constant of perovskite SrTiO 3 . Incorporation of more Sr in STO reduces the leakage current density but also increases the capacitance-equivalent thickness.

Achieving Conduction Band-Edge Effective Work Functions by

Conduction band-edge effective work functions (phi_m,eff) are demonstrated with TaC_x and TiN by means of La₂O₃ capping of HfSiO_x in a gate-first process flow with CMOS-compatible thermal budget. With TaC_x, a 10- Aring-thick La₂O₃ cap results in a phi _m,eff of 3.9 eV with a low equivalent oxide thickness (EOT) increase (1-2 Aring) and unaffected electron mobility. With TiN, non-nitrided La₂O₃ capping results in a smaller phi_m,eff reduction at a larger EOT increase, while with post-cap nitridation, the TiN phi_m,eff is lower at a smaller EOT increase. Results show that the choice of metal and nitridation conditions have significant effects on La₂O₃ capped stacks

\hbox{La}_{2}\hbox{O}_{3}

Hf-based dielectrics are currently being introduced into complementary metal oxide semiconductor transistors as replacement for SiON to limit gate leakage current densities. Alternative materials such as rare earth based dielectrics are of interest to obtain proper threshold voltages as well as to engineer a material with a high thermal stability. The authors have studied rare earth based dielectrics such as Dy2O3, DyHfOx, DyScOx, La2O3, HfLaOx, and LaAlOx by means of ellipsometry, time of flight secondary ion mass spectroscopy x-ray diffraction, and x-ray photoelectron spectroscopy. The authors show that ellipsometry is an easy and powerful tool to study silicate formation. For ternary rare earth oxides, this behavior is heavily dependent on the composition of the deposited layer and demonstrates a nonlinear dependence. The system evolves to a stable composition that is controlled by the thermal budget and the rare earth content of the layer. It is shown that silicate formation can lead to a severe overe...

Capping of Hafnium Silicates

Gd x Hf 1-x O y thin films were deposited by atomic layer deposition (ALD) using tris(isopropyl-cyclopentadienyl) gadolinium [Gd( i PrCp) 3 ] and HfCl 4 in combination with H 2 0 as an oxidizer. Growth curves showed a nearly ideal ALD behavior. The growth per individual Gd( i PrCp) 3 /H 2 O or HfCl 4 /H 2 O cycle was 0.55 A, independent of the Gd/(Gd + Hf) composition x in the studied range. This indicates that the amount of HfO 2 deposited during a HfCl 4 /H 2 O cycle was essentially identical to the amount of Gd 2 O 3 deposited during a Gd( i PrCp) 3 /H 2 O cycle, assuming identical atomic densities of the films independent of composition. The crystallization of Gd x Hf 1-x O y , with Gd/(Gd + Hf) contents x between 7 and 30% was studied. Films with x ≳ 10% crystallized into a cubic/tetragonal HfO 2 -like phase during spike or laser annealing up to 1300°C, demonstrating that the cubic/tetragonal phase is thermally stable in this temperature range. A maximum dielectric constant of K ~ 36 was found for a Gd/(Gd + Hf) concentration of x ~ 11%.

Silicate formation and thermal stability of ternary rare earth oxides as high-k dielectrics

Metal-insulator-metal capacitors with SrxTiyOz (STO) dielectric films on TiN, Ru, and RuOx bottom electrodes with TiN top electrodes were studied. Metastable perovskite STO films with compositions in the Sr/(Sr+Ti)∼54–64 at. % range were obtained by crystallization at 600 °C in N2 of dielectric stacks grown by atomic layer deposition consisting of Sr-rich STO films [Sr/(Sr+Ti)∼64 at. %] on thin interfacial TiOx layers. The significant decrease in equivalent oxide thickness (EOT) and STO lattice parameter observed with increasing TiOx thickness indicates full intermixing of the TiOx and STO layers during the crystallization anneal, which results in the formation of an STO layer with higher Ti content and higher dielectric constant. The Sr-rich STO on TiOx stacks crystallize with small grain size, favorable for low leakage (JG). A significant improvement in JG for e-injection from the bottom electrode is obtained when using RuOx, as compared to TiN or Ru. A milder JG improvement with RuOx bottom electrode i...

Atomic Layer Deposition of Gd-Doped HfO2 Thin Films

Perpendicularly magnetized MgO-based tunnel junctions are envisaged for future generation spin-torque transfer magnetoresistive random access memory devices. Achieving a high tunnel magneto resistance and preserving it together with the perpendicular magnetic anisotropy during BEOL CMOS processing are key challenges to overcome. The industry standard technique to deposit the CoFeB/MgO/CoFeB tunnel junctions is physical vapor deposition. In this letter, we report on the use of an ultrathin Mg layer as free layer cap to protect the CoFeB free layer from sputtering induced damage during the Ta electrode deposition. When Ta is deposited directly on CoFeB, a fraction of the surface of the CoFeB is sputtered even when Ta is deposited with very low deposition rates. When depositing a thin Mg layer prior to Ta deposition, the sputtering of CoFeB is prevented. The ultra-thin Mg layer is sputtered completely after Ta deposition. Therefore, the Mg acts as a sacrificial layer that protects the CoFeB from sputter-indu...

Impact of bottom electrode and SrxTiyOz film formation on physical and electrical properties of metal-insulator-metal capacitors

Metastable perovskite SrxTiyOz (STO) films were formed over a wide composition range by crystallization of layers grown by atomic layer deposition. An expansion of the lattice, decrease in permittivity and mild increase in band gap are observed with increasing Sr content. Sr-rich films [Sr/(Sr+Ti)∼62 at. %] show significant improvement in leakage current at low equivalent oxide thicknesses (EOT) as compared to stoichiometric films (Sr/(Sr+Ti) ∼50 at. %). TiN/STO/TiN capacitors with leakage ∼10−6 A/cm2 at 1 V were obtained at 0.6 nm EOT for crystalline Sr-rich STO. The difference in leakage behavior was found to correlate with different microstructures developed during crystallization.

BEOL compatible high tunnel magneto resistance perpendicular magnetic tunnel junctions using a sacrificial Mg layer as CoFeB free layer cap

Excellent tunnel magneto resistance (TMR) values of 143% at resistance-area products (RA) of 4.7 Ωμm2 from 11nm thin Co/Ni based perpendicular magnetic tunnel junctions (p-MTJ) was achieved. Engineered wetting layer (WL), seed layer (SL) and the introduction of newly designed inner synthetic anti-ferromagnetic (iSAF) pinned layer in combination with ultra-smooth bottom electrode (roughness 0.5 Å) was yielded to vertically scaled 11nm thick Co/Ni p-MTJ stack with excellent magnetic properties. The introduction of iSAF layer demonstrates for the 1st time the free layer offset field controllability (<; 100 Oe) of the spin-transfer-torque (STT) magnetic random access memory (MRAM) device down to 12 nm in diameter.

Impact of crystallization behavior of SrxTiyOz films on electrical properties of metal-insulator-metal capacitors with TiN electrodes

Improved metal-insulator-metal capacitor (MIMCAP) stacks with strontium titanate (STO) as dielectric sandwiched between Ru as top and bottom electrode are shown. The Ru/STO/Ru stack demonstrates clearly its potential to reach sub-20 nm technology nodes for dynamic random access memory. Downscaling of the equivalent oxide thickness, leakage current density (Jg) of the MIMCAPs, and physical thickness of the STO have been realized by control of the Sr/Ti ratio and grain size using a heterogeneous TiO2/STO based nanolaminate stack deposition and a two-step crystallization anneal. Replacement of TiN with Ru as both top and bottom electrodes reduces the amount of electrically active defects and is essential to achieve a low leakage current in the MIM capacitor.

Co/Ni based p-MTJ stack for sub-20nm high density stand alone and high performance embedded memory application

Atomic layer deposition of Hf-Si-O and Hf O2 using Hf Cl4, Si Cl4, and H2 O was studied. The growth per cycle and composition of Hf-Si-O films were analyzed as a function of the growth temperature, the pulse sequence, and the precursor doses. The growth of Hf-Si-O from Hf Cl4 Si Cl4 H2 O appeared to be determined not only by the -OH density but also by the -OH bonding mode. The Hf Cl4 Si Cl4 H2 O chemistry results in carbon-free films with low chlorine impurity content. The Hf-Si-O films of Hf-rich composition are meeting the leakage-current requirements for 45 nm technology node and below.