Porous Low-Dielectric-Constant Material for Semiconductor Microelectronics

To provide high speed, low dynamic power dissipation, and low cross-talk noise for microelectronic circuits, low-dielectric-constant (low-k) materials are required as the inter- and intra-level dielectric (ILD) insulator of the back-end-of-line interconnects. Porous low-k materials have low-polarizability chemical compositions and the introducing porosity in the film. Integration of porous low-k materials into microelectronic circuits, however, poses a number of challenges because the composition and porosity affected the resistance to damage during integration processing and reduced the mechanical strength, thereby degrading the properties and reliability. These issues arising from porous low-k materials are the subject of the present chapter

Copper Metal for Semiconductor Interconnects

Resistance-capacitance (RC) delay produced by the interconnects limits the speed of the integrated circuits from 0.25 mm technology node. Copper (Cu) had been used to replace aluminum (Al) as an interconnecting conductor in order to reduce the resistance. In this chapter, the deposition method of Cu films and the interconnect fabrication with Cu metallization are introduced. The resulting integration and reliability challenges are addressed as well

Development of plasma enhanced chemical vapor deposition (PECVD) gate dielectrics for TFT applications

This study investigated a variety of electrically insulating materials for potential use as a gate dielectric in thin-film transistor applications. The materials that were investigated include silicon dioxide and oxynitride films deposited using PECVD and LPCVD techniques. Silicon source materials included tetraethylorthosilicate (TEOS) and silane (SiH4). Oxygen sources included diatomic oxygen (O2) and nitrous oxide (N2O). The optical, electrical, and material properties of the dielectrics were analyzed using Variable Angle Spectroscopic Ellipsometry (VASE), Fourier Transform Infrared Spectroscopy (FTIR), Capacitance-Voltage (C-V) analysis and current-voltage (I-V) analysis. Transistors were also fabricated at low temperatures with different gate dielectrics to investigate the impact on device performance. While a deposited gate dielectric is intrinsically inferior to a thermally grown SiO2 layer, an objective of this study was to create a high quality gate dielectric with low levels of bulk and interface charge (Qit & Qot~1x1010 cm2); this was achieved

Plasma Damage on Low-k Dielectric Materials

Low dielectric constant (low-k) materials as an interconnecting insulator in integrated circuits are essential for resistance-capacitance (RC) time delay reduction. Plasma technology is widely used for the fabrication of the interconnects, such as dielectric etching, resisting ashing or stripping, barrier metal deposition, and surface treatment. During these processes, low-k dielectric materials may be exposed to the plasma environments. The generated reactive species from the plasma react with the low-k dielectric materials. The reaction involves physical and chemical effects, causing degradations for low-k dielectric materials. This is called “plasma damage” on low-k dielectric materials. Therefore, this chapter is an attempt to provide an overview of plasma damage on the low-k dielectric materials

Mechanistic Study Of Plasma Damage Of Low k Dielectric Surfaces

Plasma damage to low k dielectric materials was investigated from a mechanistic point of view. Low k dielectric films were treated by plasma Ar, O-2, N-2/H-2, N-2 and H-2 in a standard RIE chamber and the damage was characterized by Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS), X-Ray Reflectivity (XRR), Fourier Transform Infrared Spectroscopy (FTIR) and Contact Angle measurements. Both carbon depletion and surface densification were observed on the top surface of damaged low k materials while the bulk remained largely unaffected. Plasma damage was found to be a complicated phenomenon involving both chemical and physical effects, depending on chemical reactivity and the energy and mass of the plasma species. A downstream hybrid plasma source with separate ions and atomic radicals was employed to study their respective roles in the plasma damage process. Ions were found to play a more important role in the plasma damage process. The dielectric constant of low k materials can increase up to 20% due to plasma damage and we attributed this to the removal of the methyl group making the low k surface hydrophilic. Annealing was generally effective in mitigating moisture uptake to restore the k value but the recovery was less complete for higher energy plasmas. Quantum chemistry calculation confirmed that physisorbed water in low k materials induces the largest increase of dipole moments in comparison with changes of surface bonding configurations, and is primarily responsible for the dielectric constant increase.Microelectronics Research Cente

High-K dielectric sulfur-selenium alloys.

Upcoming advancements in flexible technology require mechanically compliant dielectric materials. Current dielectrics have either high dielectric constant, K (e.g., metal oxides) or good flexibility (e.g., polymers). Here, we achieve a golden mean of these properties and obtain a lightweight, viscoelastic, high-K dielectric material by combining two nonpolar, brittle constituents, namely, sulfur (S) and selenium (Se). This S-Se alloy retains polymer-like mechanical flexibility along with a dielectric strength (40 kV/mm) and a high dielectric constant (K = 74 at 1 MHz) similar to those of established metal oxides. Our theoretical model suggests that the principal reason is the strong dipole moment generated due to the unique structural orientation between S and Se atoms. The S-Se alloys can bridge the chasm between mechanically soft and high-K dielectric materials toward several flexible device applications

Interaction between plasma and low-k dielectric materials

textWith the scaling of devices, integration of porous ultra low-κ dielectric materials into Cu interconnect becomes necessary. Low-k dielectric materials usually consist of a certain number of methyl groups and pores incorporated into a SiO₂ backbone structure to reduce the dielectric constant. They are frequently exposed to various plasmas, since plasma is widely used in VLSI semiconductor fabrication such as etching, ashing and deposition. This dissertation is aimed at exploring the interaction between plasma and low-κ dielectric surfaces. First, plasma assisted the atomic layer deposition (ALD) of Ta-based Cu barriers. Atomic layer deposition of Ta barriers is a self-limited surface reaction, determined by the function groups on the low-κ dielectric surface. But it was found TaCl₅ precursor could not nucleate on the organosilicate low-κ surface that was terminated with methyl groups. Radical NH[subscript x] beam, generated by a microwave plasma source, could activate the surface through exchanging with the methyl groups on the low-κ surface and providing active Si-NH[subscript x] nucleation sites for TaCl₅ precursors. Results from Monte Carlo simulation of the atomic layer deposition demonstrated that substrate chemistry was critical in controlling the film morphology. Second, the properties of low-κ dielectric materials tended to degrade under plasma exposure. In this dissertation, plasma damage of low-κ dielectric surface was investigated from a mechanistic point of view. Both carbon depletion and surface densification were observed on the top surface of damaged low-κ materials while the bulk remained largely uninfluenced. Plasma damage was found to be a complicated phenomenon involving both chemical and physical effects, depending on chemical reactivity and the energy and mass of the plasma species. With a downstream plasma source capable of separating ions from the plasma beam and an in-situ x-ray photoelectron spectroscopy (XPS) monitoring of the damage process, it was clear that ions played a more important role in the plasma damage process. Increase of dielectric constant after plasma damage was mainly attributed to moisture uptake and was confirmed with quantum chemistry calculation. Annealing was found to be effective in mitigating moisture uptake and thus restoring κ value. Finally, oxygen plasma damage to blanket and patterned low-κ dielectrics was studied in detail. Energetic ions in oxygen plasma contributed much to the loss of film hydrophobicity and dielectric constant through the formation of C=O and Si-OH. Based on results from residual gas analyses (RGA), three possible reaction paths leading to carbon depletion were proposed. This was followed by analytical solution of the evolution of carbon concentration during O₂ plasma damage. O₂ plasma damage to patterned CDO film was studied by TEM/EELS. And the damage behavior was simulated with Monte Carlo method. It was found that the charging potential distribution induced by plasma was important in determining the carbon loss in patterned low-k films. The charging potential distribution was mainly related to the geometry of low-k trench structures. To recover the dielectric constant, several recovery techniques were tried and briefly discussed.Physic