As the feature size of devices becomes smaller, there are many issues and challenges in nanotechnology. Among the many problems found, gate oxide damage during tungsten silicide gate etching process and plasma strip damage, which causes RC delay time in BEOL, have been studied for improvements in bo...
As the feature size of devices becomes smaller, there are many issues and challenges in nanotechnology. Among the many problems found, gate oxide damage during tungsten silicide gate etching process and plasma strip damage, which causes RC delay time in BEOL, have been studied for improvements in both processes. The tests focused on understanding the mechanisms and minimizing plasma damage. During the tungsten silicide etching process, inductively coupled plasma (ICP) was used to eliminate oxide damage and to correctly detect endpoint. Capacitance coupled plasma (CCP) was used to introduce new gas chemistry to minimize plasma strip damage. Scanning electron spectroscopy (SEM) was used to observe gate oxide pitting, and optical emission spectroscopy (OES) was used to detect the exact endpoint of each thin film. Also, X-ray Photoelectron Spectroscopy (XPS) was used for qualified analysis, and ellipsometry was used to measure the thickness and the selectivity of the thin films. To reduce gate oxide pitting damage in 90nm technology, O₂ and N₂ chemistries have been introduced to main etch chemistry, NF₃/Cl₂, for the first time in the WSix etching process. When NF₃/Cl₂/O₂/N₂ plasma etches away the WSix film and the poly-Si film is exposed, the added O₂/N₂ gas chemistries form a layer of SiO, SiN, or SiON on the surface of the poly-Si layer. This can increase the selectivity between the WSix and the poly-Si layer. Also, this gas chemistry minimizes the micro-loading loading effect between dense and isolated patterns and prevents damage to the gate oxide which lies under the poly-Si. When poly-Si etching is complete, plasma damage is minimized and gate oxide pitting can be prevented, even if the gate oxide layer is exposed to plasma due to high selectivity. Therefore, a high selectivity and low micro-loading process can be improved by using O₂ and N₂ added chemistries during WSix film etching. Also, during WSix etching, the Optical Emission Spectroscopy (OES) is used as an endpoint detector. However, when developing a next generation device, an endpoint time delay can occur in WSix gate etching. During this time delay, damage takes place on the gate oxide. Tests have been conducted to improve these time delays. Copper, which shows lower resistivity than aluminum materials and low-k materials, has been introduced to the BEOL process. While the conventional dielectric materials have dielectric constants higher than 4, the low-k materials have dielectric constants lower than 3.5. The dielectric constant k for these low-k materials is changed during plasma strip tests when they react with the O₂, N₂, and H₂ chemistries. In order to improve this change in k value, N₂O gas has been newly introduced and showed minimum damage on ultra low-k material during the plasma strip test.
As the feature size of devices becomes smaller, there are many issues and challenges in nanotechnology. Among the many problems found, gate oxide damage during tungsten silicide gate etching process and plasma strip damage, which causes RC delay time in BEOL, have been studied for improvements in both processes. The tests focused on understanding the mechanisms and minimizing plasma damage. During the tungsten silicide etching process, inductively coupled plasma (ICP) was used to eliminate oxide damage and to correctly detect endpoint. Capacitance coupled plasma (CCP) was used to introduce new gas chemistry to minimize plasma strip damage. Scanning electron spectroscopy (SEM) was used to observe gate oxide pitting, and optical emission spectroscopy (OES) was used to detect the exact endpoint of each thin film. Also, X-ray Photoelectron Spectroscopy (XPS) was used for qualified analysis, and ellipsometry was used to measure the thickness and the selectivity of the thin films. To reduce gate oxide pitting damage in 90nm technology, O₂ and N₂ chemistries have been introduced to main etch chemistry, NF₃/Cl₂, for the first time in the WSix etching process. When NF₃/Cl₂/O₂/N₂ plasma etches away the WSix film and the poly-Si film is exposed, the added O₂/N₂ gas chemistries form a layer of SiO, SiN, or SiON on the surface of the poly-Si layer. This can increase the selectivity between the WSix and the poly-Si layer. Also, this gas chemistry minimizes the micro-loading loading effect between dense and isolated patterns and prevents damage to the gate oxide which lies under the poly-Si. When poly-Si etching is complete, plasma damage is minimized and gate oxide pitting can be prevented, even if the gate oxide layer is exposed to plasma due to high selectivity. Therefore, a high selectivity and low micro-loading process can be improved by using O₂ and N₂ added chemistries during WSix film etching. Also, during WSix etching, the Optical Emission Spectroscopy (OES) is used as an endpoint detector. However, when developing a next generation device, an endpoint time delay can occur in WSix gate etching. During this time delay, damage takes place on the gate oxide. Tests have been conducted to improve these time delays. Copper, which shows lower resistivity than aluminum materials and low-k materials, has been introduced to the BEOL process. While the conventional dielectric materials have dielectric constants higher than 4, the low-k materials have dielectric constants lower than 3.5. The dielectric constant k for these low-k materials is changed during plasma strip tests when they react with the O₂, N₂, and H₂ chemistries. In order to improve this change in k value, N₂O gas has been newly introduced and showed minimum damage on ultra low-k material during the plasma strip test.
Keyword
#plasma etching
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