Ionized Metal Physical Vapor Deposition Research Articles

Numerical analysis of geometry effects for target re-deposition during low pressure hollow cathode magnetron sputtering

During low pressure ionized metal physical vapor deposition (PVD) of Cu seed layer for microprocessor interconnects, the re-deposited Cu film on the hollow cathode magnetron (HCM) target may fall off and damage the Cu film on the wafer. An analytical view factor model based on the analogy between metal sputtering and diffuse thermal radiation was used to obtain re-deposition profiles for HCM targets in low pressure (below 0.1 Pa) Cu ionized PVD. The model predictions indicate that there is an inherent non-uniformity in the re-deposition profile even for uniform sputtering over the entire HCM target. The predicted re-deposition profile agrees with experimental observations. Subsequent target redesign studies found that the non-uniformity in the re-deposition profile could be mitigated by using a conical sidewall between the top disk and the cylindrical sidewall or reducing the length of the cylindrical sidewall.

Modeling film uniformity and symmetry in ionized metal physical vapor deposition with cylindrical targets

Severe asymmetry of the metal deposits on the trench sidewalls occurs near the wafer edge during low pressure ionized metal physical vapor deposition of Cu seed layer for microprocessor interconnects. To investigate this process and mitigate the asymmetry, an analytical view factor model based on the analogy between metal sputtering and diffuse thermal radiation was constructed to investigate deposition uniformity and symmetry for cylindrical target sputtering in low pressure (below 0.1 Pa) ionized Cu physical vapor deposition. The model predictions indicate that as the distance from the cylindrical target to wafer increases, the metal film thickness becomes more uniform across the wafer and the asymmetry of the metal deposits at the wafer edge increases significantly. These trends are similar to those for planar targets. To minimize the asymmetry, the height of the cylindrical target should be kept at a minimum. For cylindrical targets, the outward-facing sidewall of the trench could receive more direct Cu fluxes than the inward-facing one when the target to wafer distance is short. The predictions also indicate that increasing the diameter of the cylindrical target could significantly reduce the asymmetry in metal deposits at the wafer edge and make the film thickness more uniform across the wafer.

Scaling of hollow cathode magnetrons for ionized metal physical vapor deposition

Ionized metal physical vapor deposition is being increasingly used to deposit diffusion barriers and Cu seed layers into high aspect ratio trenches for microelectronics fabrication. Hollow cathode magnetrons (HCMs) represent a technology capable of depositing metal over large areas at pressures of a few millitorrs. The fundamental mechanisms of these devices are not well understood and so their optimization is difficult. In this article, results from a two-dimensional computational investigation of HCMs are discussed to illuminate scaling issues. The hybrid model incorporates algorithms whereby transport coefficients for use in fluid equations are derived using a kinetic simulation. The goal is to enable the fluid algorithms in the model to be able to more accurately represent low pressure operation. The consequences of power, pressure, and magnitude and orientation of applied magnetic fields were investigated. The authors found that the magnetic field configuration significantly affects the magnitude and distribution of fluxes incident on the substrate. A study of the Cu seed layer deposition process, carried out using a feature scale model, correlates changes in plasma properties with conformal deposition into trenches.

Magnetron target designs to improve wafer edge trench filling in ionized metal physical vapor deposition

Severe asymmetry of the metal deposits on the trench sidewalls occurs near the wafer edge during low pressure ionized metal physical vapor deposition of Cu seed layer for microprocessor interconnects. To investigate this process and mitigate the asymmetry, an analytical view factor model based on the analogy between metal sputtering and diffuse thermal radiation was constructed. The model was validated based on the agreement between the model predictions and the reported experimental values for the asymmetric metal deposition at trench sidewalls near the wafer edge for a 200 mm wafer. This model could predict the thickness of the metal deposits across the wafer, the symmetry of the deposits on the trench sidewalls at any wafer location, and the angular distributions of the metal fluxes arriving at any wafer location. The model predictions for the 300 mm wafer indicate that as the target-to-wafer distance is shortened, the deposit thickness increases and the asymmetry decreases, however the overall uniformity decreases. Up to reasonable limits, increasing the target size and the sputtering intensity for the outer target portion significantly improves the uniformity across the wafer and the symmetry on the trench sidewalls near the wafer edge.

Integrated feature scale modeling of plasma processing of porous and solid SiO2. II. Residual fluorocarbon polymer stripping and barrier layer deposition

The adoption of low dielectric constant materials as inter-level dielectrics in microelectronics fabrication will ultimately depend on process integration. Porous SiO2 (PS) is one candidate material. Cleaning of residual polymer from trenches following etching using fluorocarbon plasmas and the deposition of a continuous barrier layer are critical processes for integration of PS as inter-level dielectrics. To investigate these issues, reactions mechanisms for plasma stripping of fluorocarbon polymer using oxygen containing plasmas and deposition of metal barrier coatings into PS trenches were developed, and incorporated into a feature profile model. The reaction mechanism was validated by comparison to experiments for blanket plasma etching of polytetrafluoroethylene using Ar–O2 chemistries. Plasma stripping of fluorocarbon polymers from solid SiO2 (SS) trenches was found to be less efficient at higher aspect ratios. Stripping was also less efficient from PS trenches having large average pore radius and high interconnectivity. Cu ionized metal physical vapor deposition was investigated as a surrogate for barrier coating in SS and PS trenches. Compared to SS, thin film deposition was less conformal for PS having closed pore networks. Thicker films were required for interconnected PS to avoid pin-hole formation.

Trench filling by ionized metal physical vapor deposition

Ionized metal physical vapor deposition (IMPVD) is a process in which sputtered metal atoms from a magnetron target are ionized by a secondary plasma, accelerated into the substrate, and deposited with moderately anisotropic fluxes. To investigate these processes, an integrated plasma equipment and feature scale model was developed to simulate the sputtering of metal atoms, their transport in IMPVD reactors, and their deposition into trenches. The model self-consistently predicts the magnitude and distributions (energy and angle) of the depositing metal flux and the profiles of metal deposits in trenches. The predicted profiles agree with experimentally observed trends. The results indicate that the ionization fraction of the depositing metal flux is the critical factor in trench filling. Formation of voids occurs when the ionization fraction of the depositing metal flux is too low or the aspect ratio of the trench is too large. As the aspect ratio of the trench increases, the ionization fraction required for complete trench filling also increases. To increase the ionization fraction, high pressure, low magnetron power and high inductively coupled plasma power are the desired operating conditions. To the degree that the ionization fraction and the ion flux angular distribution vary as a function of radius on the substrate, so will the trench filling properties. This is particularly true near the edge of the wafer where fluxes may be asymmetric.

Inflight electron impact excitation in ionized metal physical vapor deposition

Ionized metal physical vapor deposition (IMPVD) is a process in which sputtered metal atoms from a magnetron target are ionized by a secondary plasma before depositing onto the substrate. The sputtered metal atoms and neutralized ions reflected from the target have higher kinetic energies than the buffer gas and so are not in thermal equilibrium. These nonthermal (inflight) species can dominate the total metal species density at low pressures (<5 mTorr). As a result, electron impact of the inflight species may significantly contribute to excitation and ionization. To investigate these processes, a model was developed to include the inflight electron impact excitation (IEIE) of sputtered species during IMPVD. Results for Cu IMPVD indicate that the predicted Cu+ density at low pressure (2 mTorr) significantly increased when IEIE was taken into account. As the pressure increases, the rate of thermalization increases and the importance of IEIE decreases.

Effect of sputter heating in ionized metal physical vapor deposition reactors

Ionized metal physical vapor deposition (IMPVD) is a process in which sputtered metal atoms from a magnetron target are ionized by a secondary plasma, accelerated into the substrate, and deposited with moderately anisotropic fluxes. The momentum and energy transfer from the sputtered metal atoms and ion-produced reflected neutrals to the background gas, sputter heating, produces rarefaction which influences the operating characteristics of the discharge. To address these processes, a model was developed to simulate the sputtering of metal atoms and their transport in IMPVD reactors. The model accounts for the ion-energy-dependent yield and kinetic energy of the sputtered and reflected atoms, and for sputter heating. The model was validated by comparing its results to experimentally measured metal atom densities and the ionization fraction of the deposition flux. Sputter heating as a function of auxiliary ionization and magnetron power in an inductively coupled plasma IMPVD reactor for Al deposition was then investigated. Sputter heating produces rarefaction of the buffer gas which results in a redistribution of Al species in the reactor compared to the absence of sputter heating. Consequently, the ionization fraction of the depositing metal flux decreases, while the magnitude of the flux increases. The minimum Ar density due to sputter heating is regulated by heat transfer to the target. The electron density increases significantly with the addition of a small amount of metal atoms to the plasma.

Design issues in ionized metal physical vapor deposition of copper

The filling of deep vias and trenches with metal for interconnect layers in microelectronic devices requires anisotropic deposition techniques to avoid formation of voids. Ionized metal physical vapor deposition (IMPVD) is a process which is being developed to address this need. In IMPVD, a magnetron sputter deposition source is augmented with a secondary plasma source with the goal of ionizing a large fraction of the metal atoms. Application of a bias to the substrate results in an anisotropic flux of metal ions for deposition. The ion flux also contributes to “sputter back” of metal deposits on the lip of the via which could lead to void formation. In this article, we describe and present results from a two-dimensional plasma model for IMPVD using a dc magnetron and an inductively coupled auxiliary ionization source. The scaling of copper IMPVD is discussed as a function of buffer gas pressure, sputter source, and source geometry. We show that the deposition rate of metal on the substrate will be reduced as pressure increases due to the increase in diffusive losses. We also show that the sputtering of the auxiliary coils can be a significant issue in IMPVD systems, which must be addressed in tool design.