Influence of the additives argon, O2, C4F8, H2, N2 and CO on plasma conditions and process results during the etch of SiCOH in CF4 plasma

Reactive ion etch processes for modern interlevel dielectrics become more and more complex, especially for further scaling of interconnect dimensions. The materials will be damaged within such processes with the result of an increase in their dielectric constants. The capability of selected additives to minimize the low-k sidewall damage during reactive ion etching (RIE) of SiCOH materials in fluorocarbon plasmas was shown in different works in the past. Most of the investigated additive gases alter the fluorine to carbon ratio as well as the dissociation of the parent gas inside the etch plasma. The result is a changed etch rate, a modified polymerization behavior and other characteristics of the process induced SiCOH damage. Heavy inert ions like argon will be accelerated to the sample surface in the cathode dark space and enhance therewith the sputter yield on the SiCOH network [1]. In this paper the additives Ar, O₂, C₄F₈, H₂, N₂ and CO were added to a conventional CF₄ etch plasma. We try to provoke different changes in the plasma conditions and therewith in the process results. Contact angle measurements, spectroscopic ellipsometry, Hg-probe analysis, FTIR measurements and SEM cross-sections were used to overview the additive induced modifications. To understand the influences of the additives gases more exactly, changes in the physical and chemical plasma behavior must be analyzed. Therefore quadrupole mass spectrometry (QMS) and quantum cascade laser absorption spectroscopy (QCLAS) were used.     

DMCPS/CHF3制备的F-SiCOH低k薄膜结构与沉积速率研究

以十甲基环五硅氧烷(DMCPS)和三氟甲烷(CHF3)作为反应气体,采用电子回旋共振等离子体化学气相沉积(ECR-CVD)方法,制备了氟掺杂的SiCOH低介电常数薄膜。研究发现:随着CHF3/DMCPS流量比的增大,薄膜的沉积速率呈"N"型变化。根据薄膜结构和成分的傅立叶变换红外光谱仪(FTIR)、X射线光电子能谱(XPS)以及放电等离子体中基团分步的光强度标定的发射光谱(OES)分析可知:薄膜沉积速率的变化是由于CHF3进气量的增加导致薄膜生长从以沉积F-SiCOH薄膜为主过渡到以沉积氟化非晶碳(a-C:F:H)薄膜为主的结果。     

Repair of plasma-damaged p-SiOCH dielectric films in supercritical CO2

The silylation of plasma-damaged p-SiOCH low-k dielectric films was investigated with trimethychlorosilane (TMCS), hexamethyldisilazane (HMDS) and dimethyldichlorosilane (DMDCS) dissolved in supercritical CO₂ (scCO₂) and the effect of thermal pre-treatment on the repair performance was also studied. The surface hydrophobicity was rapidly recovered by silylation and the order of recovery efficiency was HMDS (85.4°) > DMDCS (83.4°) > TMCS (75.0°). The FTIR analyses revealed that the restoration to the original state was not achieved over various reaction conditions (up to 31 MPa, 85 °C, and 3 h reaction time). After pre-treatment in a vacuum cell at 250 °C, the Si-O-Si peak intensity increased slightly, and the surface hydrophobicity was partially recovered to 54.4° due to the removal of physically adsorbed H₂O molecules as well as some extent of dehydration of neighboring surface silanol groups. The hydrophobicity increased to 84.4° after subsequent treatment with HMDS in scCO₂. From DSIMS, the carbon concentration did not increase in bulk region after silylation of thermally pre-treated low-k films.     

Analysis of the impact of different additives during etch processes of dense and porous low-k with OES and QMS

The focus of this paper is the impact of CF₄ based plasma etch processes with the additives argon and C₄F₈ on material properties and geometrical parameters of etched trenches using dense and porous SiCOH. Argon and C₄F₈ were added to change the radical to ion composition and to shift the carbon to fluorine ratio, respectively. With several techniques, FTIR, spectral ellipsometry and contact angle measurements, modifications in the structure of the materials and their surface conditions were analyzed. To understand the influences of the additives on the plasma conditions, optical emission spectroscopy (OES) and quadrupole mass spectrometry (QMS) were used to estimate the composition of the plasma insitu.For the additive argon, a slightly enhanced etch rate and an increased refractive index due to serious plasma damage for porous SiCOH was observed. At higher Ar flow rates peaks of Si₂O₄H_x clusters in the QMS spectra and increased CO and O lines, measured with OES, indicate a higher sputter yield on the SiCOH network. SEM cross-sections show, that argon has no effect on the sidewall geometry of etched trenches. A higher CH/CN line in the OES spectra indicates an enhanced sputter effect of the SiCN films in via bottoms.For C₄F₈ addition results of spectral ellipsometry show a decreased etch rate and refractive index. Using FTIR the formation of a polymer film on the surface was observed. Higher C₂ lines in the OES spectra are indications of enhanced polymerization efficiency. Finally, the addition of C₄F₈ decreases the etch rate in the trench sidewalls and therewith assumedly the sidewall damage.     

Reducing Cu diffusion in SiCOH low-k films by O2 plasma treatment

This work investigates the Cu diffusion in SiCOH low dielectric constant films treated by O₂ plasma. By capacitance–voltage and current-voltage measurement, and thermal stress analysis, it is found that the O₂ plasma surface treatment of SiCOH films can lead to the decrease of flatband voltage shift ΔV_FB, the increase of activation energy E_a, and the decrease of leakage current. The small ΔV_FB and lower leakage current indicate the weak Cu diffusion. The increase of active energy means the reducing of fast Cu ions surface diffusion through the interconnected pores structure of the film. Hence, the Cu diffusion in SiCOH films can be reduced by O₂ plasma treatment. By FTIR and AFM analysis on the bonding configuration and microstructure, the reduce of Cu diffusion is related to the increase of Si-O cages and networks, which makes more open pores sealed at the surface of SiCOH films.     

紫外辐照对超低介电常数SiCOH薄膜组成与机械性能的影响

采用紫外光辐照超低介电常数多孔SiCOH薄膜,研究不同照射时间对薄膜结构和性能的影响。采用动态纳米压入技术测量薄膜的力学性能,发现随照射时间增加,薄膜的模量（Er）和硬度（H）不断提高。当辐照时间增至6h时,薄膜力学强度分别达到Er约7.4GPa,H约1.0GPa。傅里叶变换红外光谱（FT-IR）、X射线光电子能谱（XPS）分析表明紫外辐照处理能够使薄膜样品中发生键的断裂与重新结合,从而改变了薄膜骨架的交联密度和刚性,进而提高力学性能。但介电性能并未受到明显影响,紫外辐照6h后,k值仅从2.0增至2.2。     

Properties of low-k SiCOH films prepared by plasma-enhanced chemical vapor deposition using trimethylsilane

The properties of low-k SiCOH film deposited by plasma-enhanced chemical vapor deposition using trimethylsilane are reported here. The deposition process was performed at different temperatures from 200 to 400 °C. The influence of deposition temperature on the films were characterized using Fourier transform infrared spectroscopy (FTIR) to understand its impact on the studied properties. The films were annealed at ∼450 °C in an inert ambient after deposition in all the cases. The deposition rate decreases with increase in deposition temperature. The refractive index of the films increases as a function of deposition temperature. From FTIR spectra, OH-related bonds were not detected in films even when deposited at 200 °C. The Si-CH₃ bonds were detected in all the films and decreased monotonically from 200 to 400 °C. All deposition conditions studied resulted in films with dielectric constant less than 3, the lowest being ∼2.7 when deposited at 200 °C. All films exhibited good thermal stability.     

Effect of Si-OH group on characteristics of SiCOH films prepared by decamethylcyclopentasiloxane electron cyclotron resonance plasma

This paper investigates the effect of Si-OH group on dielectric property and leakage current of the SiCOH low dielectric constant films deposited by decamethylcyclopentasiloxane electron cyclotron resonance plasma. The results show that the increasing of Si-OH content in the films can lead to the increasing of dielectric constant k, decreasing of leakage current and stronger dielectric dispersion. Due to the strong polarization of Si-OH group, it leads to the increase of k value of the SiCOH films. The decreasing of leakage current at high Si-OH content is due to the low connecting probability p of networks because the networks break at the terminal Si-OH groups. At the case of high ionization degree of precursor, more Si-OH groups break and form Si-O-Si linkages by condensation chemistry occurring between proximal Si-OH groups. As a result, the k value of SiCOH films can be further reduced.     

Effect of high-frequency on etching of SiCOH films in CHF3 dual-frequency capacitively coupled plasmas

The effect of high-frequency (HF) frequency on etching characteristics of SiCOH films in a CHF₃ dual-frequency capacitively couple plasma driven by 13.56 MHz/2 MHz, 27.12 MHz/2 MHz or 60 MHz/2 MHz sources was investigated in this work. The surface structure of the films after etching and the CHF₃ discharge plasma were characterized. The increase of HF frequency reduced the critical HF power for the etching, suppressed the C:F deposition at the surface of etched films, and improved the etching of SiCOH films. The improvement of etching was attributed to the increase of ions energy and F concentration at high HF frequency.     

Plasma ash processing solutions for advanced interconnect technology

A mechanism for the modification of porous ultra low-k (ULK) and extreme ultra low-k (EULK) SiCOH-based materials is proposed. This is achieved by correlating film damage on a patterned structure measured by angular resolved x-ray photoelectron spectroscopy (ARXPS) with corresponding changes in reactive species radical density and ion current in the plasma measured by optical emission spectroscopy (OES), rare gas actinometry, and modeling. Line-to-line electrical leakage and capacitance data of nested line structures exposed to downstream ash plasmas suggest that other etching steps during back-end-of-the-line (BEOL) dual damascene processing are also critical for the overall modification induced to these materials.