Porous dielectric materials offer lower capacitances that reduce RC time delays in integrated circuits. Typical porous low dielectric (low-k) materials include SiOCH—silicon dioxide with carbon groups, principally –CH3, lining the pores. Fluorocarbon plasmas are often used to etch such low-k materials. These processes leave a fluorocarbon polymer on the SiOCH surface that must be removed, often with oxygen or hydrogen containing plasmas. Pores open to the surface and that are internally connected provide pathways for reactive species to enter into the porous network and produce damage. For example, during cleaning using O2 containing plasmas, reactions of O atoms with –CH3 groups can increase the k-value by removing C atoms. Vacuum ultraviolet (VUV) photons produced by the plasma and that penetrate into the material can scission –Si–CH3bonds and accelerate the removal of –CH3 groups. This paper reports on results from a computational investigation of Ar/O2 and He/H2plasma cleaning of porous SiOCH when including the effects of VUV photons. The authors found that He/H2 plasmas are able to clean CFx polymers deposited during etching while producing milder damage to underlying –CH3 sites compared to O2plasmas due to the lower reactivity of H atoms and the shorter penetration distance of photons produced in He/H2plasmas.
Porous dielectric materials offer lower capacitances that reduce RC time delays in integrated circuits. Typical porous low dielectric (low-k) materials include SiOCH-silicon dioxide with carbon groups, principally-CH 3 , lining the pores. Fluorocarbon plasmas are often used to etch such low-k materials. These processes leave a fluorocarbon polymer on the SiOCH surface that must be removed, often with oxygen or hydrogen containing plasmas. Pores open to the surface and that are internally connected provide pathways for reactive species to enter into the porous network and produce damage. For example, during cleaning using O 2 containing plasmas, reactions of O atoms with-CH 3 groups can increase the k-value by removing C atoms. Vacuum ultraviolet (VUV) photons produced by the plasma and that penetrate into the material can scission-Si-CH 3 bonds and accelerate the removal of-CH 3 groups. This paper reports on results from a computational investigation of Ar/O 2 and He/H 2 plasma cleaning of porous SiOCH when including the effects of VUV photons. The authors found that He/H 2 plasmas are able to clean CF x polymers deposited during etching while producing milder damage to underlying-CH 3 sites compared to O 2 plasmas due to the lower reactivity of H atoms and the shorter penetration distance of photons produced in He/H 2 plasmas. V
Porous dielectric materials, such as SiOCH, are used as the insulator in interconnect wiring in microelectronics devices to lower the dielectric constant and so decrease the RC time delay. Sealing of the pores (up to a few nm in diameter) is necessary to prevent degradation of the low-k properties during subsequent processing steps by diffusion of reactants through the pores into the material. Sequential treatment of porous SiOCH by He and NH 3 plasmas is potentially a means of sealing pores while maintaining the low-k of the dielectric. The He plasma activates surface sites to accelerate the reactions responsible for pore sealing. NH 3 plasma treatment completes the sealing through one of two mechanisms resulting from the adsorption of NH x radicals -catalyzing the formation of a densified surface layer or formation of Si-N, C-N and N-N bonds to bridge over the pore. In this paper, we discuss mechanisms for pore sealing bridging bonds based on results from an integrated computational investigation of the etching, cleaning, activation and sealing of porous SiOCH in sequential Ar/C 4 F 8 /O 2 , Ar/O 2 , He and Ar/NH 3 plasmas. The authors found that pores in excess of 1 nm in radius are difficult to seal due to the inability of N-bonding to bridge the pore opening. Factors affecting the sealing efficiency, such as treatment time, average pore radius and aspect ratio are discussed.
Articles you may be interested inComparison of the effects of downstream H2-and O2-based plasmas on the removal of photoresist, silicon, and silicon nitride Effect of high-frequency variation on the etch characteristics of ArF photoresist and silicon nitride layers in dual frequency superimposed capacitively coupled plasmaa) Plasma enhanced chemical vapor deposition Si-rich silicon oxynitride films for advanced self-aligned contact oxide etching in sub-0.25 μm ultralarge scale integration technology and beyondTo minimize leakage currents resulting from the thinning of the insulator in the gate stack of field effect transistors, high-dielectric constant ͑high-k͒ metal oxides, and HfO 2 in particular, are being implemented as a replacement for SiO 2 . To speed the rate of processing, it is desirable to etch the gate stack ͑e.g., metal gate, antireflection layers, and dielectric͒ in a single process while having selectivity to the underlying Si. Plasma etching using Ar/ BCl 3 / Cl 2 mixtures effectively etches HfO 2 while having good selectivity to Si. In this article, results from integrated reactor and feature scale modeling of gate-stack etching in Ar/ BCl 3 / Cl 2 plasmas, preceded by photoresist trimming in Ar/ O 2 plasmas, are discussed. It was found that BCl n species react with HfO 2 , which under ion impact, form volatile etch products such as B m OCl n and HfCl n . Selectivity to Si is achieved by creating Si-B bonding as a precursor to the deposition of a BCl n polymer which slows the etch rate relative to HfO 2 . The low ion energies required to achieve this selectivity then challenge one to obtain highly anisotropic profiles in the metal gate portion of the stack. Validation was performed with data from literature. The effect of bias voltage and key reactant probabilities on etch rate, selectivity, and profile are discussed.
The low dielectric constant (low-k) and low capacitance of porous materials used for the inter-layer dielectric reduces signal propagation delays in integrated circuits. Ty pical low k materials include Si02 with methyl groups (CH3) lining the pores -SiOCH. Generally, fluorocarbon plasmas are used to etch porous SiOCH, a process that deposits CFx polymers on the sidewalls of features and inside pores. The CFx polymer must be cleaned as these fluorocarbon compounds cause compatibility issues in future process steps. O2 plasmas may be used for such cleaning due to the efficiency of oxidation of the polymer. However, O2 plasma cleans can also remove hydrophobic methyl groups in the SiOCH, replacing them with hydrophilic groups (such as -OH) that increases the di electric constant.[I] Photons (777 nm and 130 nm) produced by plasma can also break Si-C bonds and speed the C deple tion rate. It has been reported that the low-k SiOCH is rela tively stable when H2 plasmas are used for cleaning.[2] The addition of He to the H2 plasma also aids in preconditioning the surface to improve pore sealing in subsequent treatment using NH3 containing plasmas.In this paper, we discuss results from a computational comparison of cleaning of porous SiOCH using Ar/02 and HeIH2 plasmas. The Hybrid Plasma Equipment Model was used to obtain the ion energy and angle distributions of reac tive fluxes from inductively and capacitively coupled plas mas. These were used as input to the Monte Carlo Feature Profile Model to predict profiles and composition of the low k materials. Damage of the porous SiOCH was characterized by the depth at which removal of -CH3 is observed. For pores which are not in the line-of-sight to the plasma, diffusion of reactive species into the porous SiOCH is required for damage to occur. Results will be discussed, including valida tion, for the cleaning of pores as a function of treatment time, pore radius, interconnectivity and plasma power. Surface reaction mechanisms in Ar/02 and He/H2 plasmas and pho ton generation (130 nm and 77 nm) in Ar/02 plasmas will be discussed.
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