Improvement of Uniformity and Reliability of Scaled-Down Cu Interconnects with Carbon-Rich Low-k Films

Abstract

Highly selective dry-etching processes are developed for conventional via-first (VF) pattering sequences to fabricate reliable Cu dual-damascene interconnects (DDI) in carbon-rich low-k films, such as a molecular-pore-stack (MPS) SiOCH film (k = 2.55). The carbon-rich MPS film, which had excellent endurance against plasma-processes, acted as etching stopper during hard-mask (HM)-etching on it, and the high selectivity of trench-HM etching reduced variability of over-etching depth in the MPS film. This effect reduced variability in trench-depth in the MPS film, or interconnect characteristics such as capacitance–resistance (C–R) time delay. The via yield and reliability were influenced also by via-etch selectivity of MPS against SiCN cap underlain. We found that the SiCN thickness remained after the via etch should be greater than 10 nm to prevent Cu from oxidation by O2 ashing step followed. Chemical-reaction-enhanced gas chemistry in N2–CF X –Ar system, i.e., high N2/Ar ratio under limited CF X supply, increased the etching selectivity of MPS to keep enough thickness of SiCN. Early-failure-mode in electro-migration test was suppressed by the high selective via-etch. Precise selectivity control for robust carbon-rich low-k films was very important to achieve the low variability and high reliability of scaled-down Cu interconnects.

Low-k SiCxNyFilms Prepared by Plasma-Enhanced Chemical Vapor Deposition Using 1,3,5-trimethyl-1,3,5-trivinylcyclotrisilazane Precursor

“…It is proposed that the use of a single source precursor and low plasma power density can alleviate or eliminate the resist poisoning, which required further experimental validation. Moreover, high etch selectivity can be achieved for our SiC x N y films deposited at 100-300 • C (C/Si = 0.72-0.81), and even higher for SiC x N y film deposited at 400 • C (C/Si = 0.29) if a low-k ILD with a high carbon content (C/Si ratio = 2.7) in Kume et al's study 35 is assumed.…”

“…34,35 In the via etch process, highly selective etching of the low-k ILD against the underlying etch-stop layer, such as SiC x N y in our case, is required. This is to ensure sufficient thickness of SiC x N y film to protect the underlying copper layer from plasma induced damage and oxidation due to diffusion of oxygen.…”

“…The etch selectivity requirement becomes more challenging as the low-k ILD is reduced to k < 2.6, which is achieved by incorporating high carbon content. Recently Kume et al 35 reported that a high etch selectivity (∼10) can be achieved for a low-k ILD with high carbon content (C/Si = 2.7 for k = 2.55) against a SiC x N y etch-stop layer with C/Si = 0.9 using N 2 -Ar-CF x etching gas chemistry. In our study, as shown in Table II, a wide range of C/Si ratio from 0.29 to 1.82 was obtained with decreasing deposition temperature from 400 • C to 25 • C. We can infer that high etch selectivity can be achieved for our SiC x N y films deposited at 100-300 • C (C/Si = 0.72-0.81), and even higher for SiC x N y film deposited at 400 • C (C/Si = 0.29) if a low-k ILD with a high carbon content (C/Si ratio = 2.7) in Kume et al's study 35 is assumed.…”

“…Recently Kume et al 35 reported that a high etch selectivity (∼10) can be achieved for a low-k ILD with high carbon content (C/Si = 2.7 for k = 2.55) against a SiC x N y etch-stop layer with C/Si = 0.9 using N 2 -Ar-CF x etching gas chemistry. In our study, as shown in Table II, a wide range of C/Si ratio from 0.29 to 1.82 was obtained with decreasing deposition temperature from 400 • C to 25 • C. We can infer that high etch selectivity can be achieved for our SiC x N y films deposited at 100-300 • C (C/Si = 0.72-0.81), and even higher for SiC x N y film deposited at 400 • C (C/Si = 0.29) if a low-k ILD with a high carbon content (C/Si ratio = 2.7) in Kume et al's study 35 is assumed. Even for SiC x N y film deposited at room temperature (C/Si ratio = 1.82), a high selectivity is still possible by designing the etching gas chemistry to enhance their difference in etch rates of ILD and etch-stop layer with specific carbon contents.…”

Review of methods for the mitigation of plasma‐induced damage to low‐dielectric‐constant interlayer dielectrics used for semiconductor logic device interconnects

“…In the integration scheme, the low‐k films face etch gas chemistry containing fluorine. Hayashi et al applied etching plasma from an Ar/N 2 /CF 4 /O 2 gas mixture to a stack of oxygen‐rich SiOC (k = 2.7) and porous SiOCH (k = 2.5). The large hydrocarbons attached to hexagonal silica backbones in molecular‐pore‐stacked SiOCH prevent the oxidation of Si‐CH 3 during the O 2 plasma ash process, reducing the C‐depleted damage area at the sidewalls of via holes and trench lines.…”