**2.3. Plasma damage mechanism**

a lower-*k* value. In the subtractive method, the films are deposited as a dual-phase material, using a mixture of a SiCOH skeleton precursor with an organic porogen precursor. The popularly used skeleton precursor is diethoxymethylsilane (DEMS). The used organic porogen precursor must have sufficient volatility for easy removal. The used molecules are

to remove the labile organic fraction in the as-deposited films, curing process has to be done after the deposition [8, 10, 27]. By this way, a porous film can be formed. Thermal curing, electron beam, or ultraviolet (UV) irradiation can be used to achieve this work. Generally, UV-assisted curing for the fabrication of porous SiCOH dielectrics is widely adopted by the semiconductor industry because it can also rearrange the film's structure and enhance the cross-linking of the skeleton. This provides a big help to improve the mechanical strength for

The *k* value of porous SiCOH dielectrics can be scaling down by increasing the porosity and pore size simultaneously. However, this makes materials to become softer. Moreover, both the dielectric breakdown field and leakage current are degraded. Furthermore, as the porosity or pore size increases to a critical value, the pores can be connected each other to form socalled open pores. The open pores can be served as the easier penetration path into the bulk of the low-*k* material for active reactants [28]. Thus, more challenges will be addressed as porous

In a vacuum system, plasma can be produced by introducing the process gas and applying the power. The process gas can be underwent ionization, excitation/relaxation, and dissociation under the power. Therefore, energetic ions, electrons, light (from deep vacuum ultraviolet (VUV) to infrared (IR)), and highly reactive radicals are produced in the plasma [29, 30]. In semiconductor processing, plasma technology can be used for ion implantation, etching, and deposition. The ion implantation processing is achieved by the energetic ions. The etching processing involves both physical and chemical reactions, which are related to the energetic ions and the highly reactive radicals, respectively. The deposition processing only relies on

To produce the plasma, three main reactors are used: capacitively coupled plasma (CCP), inductively coupled plasma (ICP), and remote or downstream plasma (RP or DSP) [31]. The energy transfers are through capacitive coupling by parallel electrodes, inductive coupling by a coil, and microwaves for CCP, ICP, and RP systems, respectively. In the CCP and ICP systems, light from VUV to IR, energetic ions, electrons, and highly reactive radicals are presented. In the RP reactors, however, the plasma generation region is usually separated from the processing region. Additionally, a grid between the plasma and the substrate is used for charge neutralization, and a special measure is designed to minimize the photon flux. As a result, only reactive radicals or dissociated molecules or atoms can reach the surface of the wafer. This minimizes the damage from light and/or high-energy species. Due to the absence

H16). Hence, in order

alpha-terpinene (ATRP), bicycloheptadiene (BCHD), or cyclooctane (C8

294 Plasma Science and Technology - Basic Fundamentals and Modern Applications

SiCOH dielectrics are integrated in the advanced technology nodes.

the highly reactive radicals for chemical reaction.

of ions, the RP reactors cannot provide patterning etching.

porous SiCOH dielectrics.

**2.2. Plasma**

The plasma-induced damage on the low-*k* dielectrics is a complex phenomenon involving both physical and chemical effects. Ion bombardment on the low-*k* dielectrics represents the physical effect. This effect depends on the energy distribution and flux for each ionic species. The chemical effect involves photochemistry induced by the UV radiation and chemical reaction between the radicals and low-*k* constituents. Under physical and chemical reactions in the plasma, the surface of low-*k* dielectrics is modified. The modification depth is related to the ion energy, diffusion of active radicals (O, H, F, etc.), and porosity and constituents in the low-*k* material [32, 33].

The plasma damage on low-*k* dielectrics makes the increase of the dielectric constant, the changes in bonding configuration, the formation of carbon-depleted layer, film shrinkage, and surface densification.

The depletion of carbon is mainly caused by active radicals through chemical reactions. Due to the loss of hydrophobic CH3 groups, the surface of low-*k* dielectrics becomes hydrophilic and adsorbs moisture. Therefore, a drastically increase in the *k* value and leakage current and a degradation in the dielectric breakdown were detected for plasma-treated low-*k* dielectrics.
