Metal friendly integration sequence to generate high-performance air-gap structures
Publication Date: 2010-Oct-13
The IP.com Prior Art Database
Disclosed is an improved integration sequence for the formulation of air-gap back-end-of-line (BEOL) structures. The sequence incorporates a self-aligned scheme where the copper is protected during reactive ion etch and wet etch. With the metal protected, the invention provides a more reliable and cost-effective method of generating high-performance air-gap structures.
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Metal friendly integration sequence to generate high -performance air-gap structures
In prior approaches for the formation of air-gap back-end-of-line (BEOL) structures, the copper (Cu) is exposed to reactive ion etch (RIE) and wet etch. This may lead to damage to the Cu by sputtering, oxidation, or dissolution mechanisms. The associated Cu loss as well as deterioration in the surface quality of the Cu is highly undesirable. In addition, with such approaches the cap/Cu interface is highly susceptible to irreparable chemical attack, which causes reliability issues.
Known solutions to the problem include use of an additional lithography step, either self-aligned schemes (1) or through using a mask.
The drawbacks of self-aligned lithography schemes include:
• Resist has to be deposited on developed diblock
• Block out mask resist has to be deposited over the self-aligned resist without dissolving resist and avoiding exposure of the self-aligned resist. This poses integration challenges.
• Specific reflectance modulations are required between the Cu regions and the inter-layer dielectric (ILD) regions between the copper. It is difficult to achieve this with additional intermediate layers such as the developed diblock with holes and the perforated SiNXCYHZ (nBLok) if present.
Mask-based lithography techniques have the drawbacks of being expensive (due to the requirement of a high resolution mask) and having the possibility of misalignment and exposure the metal lines.
The disclosed novel solution is a metal-friendly integration sequence that generates high-performance air-gap structures. (Figure) The sequence is as follows: (Starting stack: post polish wafer)
• Recess Cu (2)
• Deposit a thick cap layer
• Timed polish to planarize the cap layer
• Followed by previously developed sequences
Figure: 'metal friendly' air-gap structure
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