A novel Al-reflow process using surface modification by the ECR plasma treatment and its application to the 256 Mbit DRAM

Abstract

A novel AI-reflow process with the electron cyclotron resonance (ECR) plasma treatment for the modification of linderlayers was developed in a vacuum isolated sputtering equipment. The key feature of this technology is the introduction of the in-situ ECR plasma treatment for the modification of the surface characteristics such as surface morphology and stoichiometry of the TiN wettingharrier layer. High wettability of the A1 film was obtained on the ECR-treated TiN surface, producing a conformal AI film on the sidewall of the contact hole before the reflow process. Consequently, complete filling of contact holes with A1 was achieved in deep sub-micron contact holes with a high aspect ratio. This study has demonstrated that the AI-reflow process can be extended to the process of the devices of 256Mbit DRAM generation and beyond. In trod iictionIt has been verified that the AI-reflow p r o c e s~( ' *~-~) is effective for mass production due to its relative simplicity in process and low cost-of-ownership. However, it is generally believed that the Al-reflow process cannot be applied to small contact holes with a high aspect ratio. For the void-free filling of contact holes with AI, it is necessary i) to have a conformal deposition of the AI film by increasing the wettability betwecn AI and the underlying layer and ii) not to have a reaction between A1 and the underlayer which hinders the reflow process.Conformal deposition of A I is dependent on the underlying layer bccause of the difference in wettabilities of AI with materials. Titanium is well known to show good wetting characteristics for the sputter-deposited AI film.However, the Ti film reacts with A1 forming AlxTi and migration of AI atoms is hindered by the formation of the AlxTi phase because atomic mobility of AlxTi is lower than that of Al. The TIN film was investigated as an alternative to the Ti film since the TiN film does not react with AI. However, compared to Ti, TiN does not show satisfactory wetting characteristics.In this study, we introduced the ECR treatment of the TiN surface to improve wetting characteristics of Al. ExperimentalDiffusion barrier Ti and TiN films, 30nm and 40nm thick, respectively, were deposited by the collimated sputtering. Surface of the underlying TiN film was modified in an ECR soft-clean chamber utilizing a vacuum isolated sputtering equipment. The nucleation characteristics of A1 films on the contact holes were evaluated on Ti, TiN, and ECR-treated TiN underlayers. The ECR-treatment conditions were 1kW of 2.45 GHz microwave and -50 volts of bias voltage by Ar ECR. A layer of 2nm TiN was removed during the Ar ECR plasma process at 0.9mTorr. The AI-Si-Cu film was deposited at 25°C to a thickness of 60nm on contact holes in order to study the early stage of A1 grain growth. Filling characteristics for contact holes with the 500nm-thick AI-Si-Cu film for three underlayers were evaluated by applying the AI-reflow process at 580°C. 2x 10-'Torr for 90 seconds. The actual temperature of the wafer measured by the fiberToptic me...

The sprint process of Al interconnects with low-temperature PVD via filling

“…As tight pitch wiring with steep tapered vias is required, the two-step cold/hot Al PVD with Ti liner is necessary to improve filling capability. In general, the cold/hot Al PVD processes, referred to as "Al-reflow filling," have been developed for filling of contact holes on Si or filling of dual-damascene grooves on W bit lines [2,3]. In these cases, the hot Al deposition is permitted to be performed at higher than 450 • C. However, upper metal levels in Al multilevel interconnects require less than 400 • C filling to suppress via hillocks.…”