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Method for an etch process to improve the structural strength in air gap integration

IP.com Disclosure Number: IPCOM000032361D
Publication Date: 2004-Nov-02
Document File: 8 page(s) / 90K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for an etch process to improve the structural strength in air gap integration. Benefits include improved performance and improved ease of implementation.

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Method for an etch process to improve the structural strength in air gap integration

Disclosed is a method for an etch process to improve the structural strength in air gap integration. Benefits include improved performance and improved ease of implementation.

Background

              Low dielectric constant (low-k) materials have been investigated for use in interlayer dielectrics (ILD) layers in semiconductor devices to reduce resistance capacitance (RC) delay and improve device performance. As device size continues to shrink, the dielectric constant of the material between metal lines must decrease to maintain the improvement. The eventual limit for the dielectric constant is k = 1, which is the value for a vacuum. This value can only be obtained by producing void space between metal lines, which is the equivalent to creating an air gap. Air has a dielectric constant very near 1.

      One of the major challenges of creating air gaps and building multiple air-gap layers is structural weakness. By substituting air for the conventional ILD layer, the only structural supports between layers are trenches and vias filled with barrier layers and copper (Cu).

      These via and trenches should not only support electrical connection between layers but also supply mechanical support to withstand mechanically harsh process conditions, such as chemical mechanical planarization (CMP) or packaging processes.

      To add strength, adding more dummy pillars (trenches/vias) is one conventional solution. Alternatively, low-pressure CMP processes are performed. Another solution is the massive redesigning of the circuit.

      Typically, an air gap is created after completing one process layer. For example, after a CMP process step, the ILD can be thermally decomposed (if the ILD is thermally decomposable) through a hard mask. The trench profile is slightly tapered (see Figure 1). However, it does not provide sufficient mechanical support. As a result, the hard mask hanging at the edge of the adjacent two-trench corner may fall during the mechanically harsh CMP process (see Figure 2).

General description

      The disclosed method is the integration of air gap with an etch process to improve the structural strength and integrity of the hard mask.

              The key elements of the method include:

•             Creating slightly bowed (undercut) trench-etch profile

•             Use conventional barrier/seed and Cu plating

Advantages

              The disclosed method provides advantages, including:

•             Improved performance due to improving the s...