Huagen Peng

Process integration compatibility of low-k and ultra-low-k dielectrics

Damage of plasma-enhanced chemical vapor deposited SiOCH films on exposure to typical plasma etch, plasma ash and wet clean processes are investigated. Dielectrics of k=3.0, 2.5, and 2.2 show little film damage with standard fluorine chemistry plasma etch, but experience severe film degradation on exposure to a typical oxygen plasma ash, used to remove photoresist. Effects of film damage on exposure to oxidative plasma ash include film densification, Si-OH formation, water adsorption, and dielectric constant increases. Theses effects are found to be more severe for the higher porosity, lower-k films, and are unrecoverable with thermal anneal.

Damage of Low-k and Ultralow-k Dielectrics from Reductive Plasma Discharges Used for Photoresist Removal

Hydrogen-containing plasma discharges, used to remove photoresist in integrated circuit manufacturing, are compared for their damaging effect on porous ultralow-k dielectrics. Such reductive ash processes studied are (A) a low- pressure N 2 /H 2 chemistry, reactive ion etch (RIE)-type discharge; (B) a high-pressure NH 3 chemistry, RIE-type discharge; and (C) a high-pressure H 5 /He remotely generated discharge. Two porous SiOCH dielectrics of differing porosity and k values 2.5 and 2.2 are used in this comparative study. Diagnostic methods used for film analysis include Fourier transform infrared spectroscopy, thermal desorption spectroscopy, density, and k-value measurements. Both RIE ash processes (A) and (B) were found to cause significant dielectric damage through film densification, -CH 3 loss, water gain, and dielectric constant increases. Film damage is noted to be more severe for the higher porosity k = 2.2 film. In contrast, all measured parameters for both dielectric films showed low damage with use of the remotely generated discharge. Positronium annihilation lifetime spectroscopy is employed in this work to show pore collapse and surface densification with use of either RIE reductive ash.

Revealing hidden pore structure in nanoporous thin films using positronium annihilation lifetime spectroscopy

The highly inhomogeneous pore morphology of a plasma-enhanced-chemical-vapor-deposited ultralow-k dielectric film (k=2.2) has been revealed using depth-profiled positronium annihilation lifetime spectroscopy (PALS) combined with progressive etch back of the film surface. The film is found to have a dense surface layer, an intermediate layer of 1.8nm diameter mesopores, and a deep region of ∼3nm diameter mesopores. After successively etching of the sealing layer and the isolated 1.8nm pore region, PALS reveals that the underlying large pores are highly interconnected. This inhomogeneous pore structure is proposed to account for observed difficulties in film integration.

Effects of pore morphology on the diffusive properties of a porous low-κ dielectric

Porous methylsilsesquioxane-based spin-on films with pore sizes of 1.5–2nm and porosities ranging from 0% to 32% have been exposed to a variety of processing environments such as fluorocarbon or oxygen containing plasmas and TaN atomic layer deposition to determine the integratability of the films. The porosity of the low-κ films was found to decrease during processing due to tantalum and fluorine indiffusion (fluorine potentially depositing as fluorocarbon film in the pores) while oxygen indiffusion depleted carbon (possibly by forming volatile CO and CO2). Carbon removal from the low-κ film alters the film’s dielectric constant and refractive index. The depth of the indiffusion appears to be independent of diffusant (fluorocarbon, oxygen, or tantalum), ranging from 40to150nm, and to correlate directly to the pore structure. It was also found that water (moisture) in these films significantly affects the measured porosity as well as can be used to reduce the indiffusion of fluorine containing molecules b...

Additive-loaded EUV photoresists: performance enhancement and the underlying physics

A series of molecular glasses (MGs) protected with multiple tert-butoxylcarbonylmethyl (tBCM) groups are employed as additives to enhance extreme ultra violet (EUV) photolithographic performance of a hydroxystyrene based Environmentally Stable Chemically Amplified Photoresist (ESCAP). The tBCM groups deprotect to form carboxylic acids that are capable of hydrogen bonding with chain segments of the polymer resist. This approach enables a systematic study of the governing physics underlying the improved lithographic performance. While MGs inhibit solubility in all cases, we find that differences in the structure of the MGs can significantly affect the photoacid diffusivity. In our ongoing optimization of the structure and loading of MGs, photoacid generators (PAGs), and base quenchers, 25 nm to 30 nm resolution has been achieved. The structure-property relationships and the synergistic effects of employing small, multi-functional additives in the polymeric photoresists are studied using various characterizations.

Porosity characteristics of ultra-low dielectric insulator films directly patterned by nano-imprint lithography

Direct patterning of low-dielectric constant (low-k) materials via nanoimprint lithography (NIL) has the potential to simplify fabrication processes and significantly reduce the manufacturing costs for semiconductor devices. We report direct imprinting of sub-100 nm features into a high modulus methylsilsesquioxane-based organosilicate glass (OSG) material. An excellent fidelity of the pattern transfer process is quantified with nm precision using critical dimension small angle X-ray scattering (CD-SAXS) and specular X-ray reflectivity (SXR). X-ray porosimetry (XRP) and positron annihilation lifetime spectroscopy (PALS) measurements indicate that imprinting increases the inherent microporosity of the methylsilsequioxane-based OSG material. When a porogen (pore generating material) is added, imprinting decreases the population of mesopores associated with the porogen while retaining the enhanced microporosity. The net effect is a decrease the pore interconnectivity. There is also evidence for a sealing effect that is interpreted as an imprint induced dense skin at the surface of the porous pattern.