Gravure en plasma dense fluorocarboné de matériaux organosiliciés à faible constante diélectrique (SiOCH, SiOCH poreux). Etude d'un procédé de polarisation pulsée.

摘要

In microelectronics, the performance of integrated circuit is limited by increasing interconnections delays. One solution is to replace the standard interlevel dielectric (SiO2) by a low dielectric constant material (low-k). This study deals with low-k SiOCH and porous SiOCH etching, as well as SiO2 and SiCH etching used as hard mask or etch stop layer. The aim is to obtain a high etch rate for porous SiOCH with a high selectivity versus SiCH and SiO2. Moreover, the etch step should not alter the low-k, and modify its dielectric constant. Then, etching of features has to be anisotropic. To reach these goals, a better etching control and a better etching mechanisms understanding is required. Etch is performed in an inductively coupled reactor using fluorocarbon gases (CHF3, CHF3/Ar, CHF3/H2), where the substrate is negatively biased. This etching process has been modified : the bias voltage, and so the ion energy, is pulsed. The influence of pulsed conditions, frequency and duty cycle (TON/T), is studied. Indeed, by decreasing the duty cycle, this process provides excellent results concerning porous SiOCH selectivity with respect to SiCH or SiO2. To understand etch mechanisms of Si, SiCH, SiO2, SiOCH, and porous SiOCH in continuous and pulsed modes, material analyses (XPS, spectroscopic ellipsometry, SEM) are coupled to plasma analyses (mass spectrometry, optical emission spectroscopy, Langmuir and planar probes). In particular, the development of the planar probe diagnostic has been part of my work. It enables an accurate measurement of the ion flux towards the substrate. Ion fluxes are then successfully measured in real time in polymerising, electronegative, and unstable plasmas. Comparing those different diagnostics, we conclude that etch mechanisms in pulsed mode are similar to those in continuous mode. However, the etching process is different. To understand that, a model describing etch rates when a pulsed bias voltage is applied has been developed. In summary, when no bias voltage is applied (phase OFF), a fluorocarbon film is deposited onto material surfaces. Then, when a bias is applied (phase ON), a higher ion energy than in continuous mode is needed to etch this film and hence to etch the material. Moreover, with a pulsed bias voltage, materials are etched through a fluorine rich fluorocarbon film. Thereby, the model clarifies the pulsed etching process and is useful to understand etch rates evolution with a pulsed bias voltage.