Method for making a planar suspended microstructure, using a sacrificial layer of polymer material and resulting component

Abstract

Production process of a flat suspended micro-structure using a sacrificial layer of polymer material and component obtained thereby The process successively comprises deposition of a sacrificial layer (2) of polymer material, deposition, on at least a part of the substrate (1) and of the front face of the sacrificial layer (2), of an embedding layer (6), the thickness whereof is larger than that of the sacrificial layer (2), and planarization so that the front faces of the sacrificial layer (2) and of the embedding layer (6) form a common flat surface. A formation layer (3) of a suspended structure (5) is deposited on the front face of the common flat surface. Planarization can comprise chemical mechanical polishing and etching of the embedding layer (6). Etching of the sacrificial layer (2) can be performed by means of a mask formed on the front face of a layer of polymer material eliminated during the planarization step.

Description

BACKGROUND OF THE INVENTION [0001] The invention relates to a production process of an integrated micro-system type component, comprising a flat suspended micro-structure, using a sacrificial layer of polymer material deposited on a substrate and having side walls confining the flat suspended structure, process successively comprising a planarization step, a deposition step of a formation layer of the suspended structure, an etching step of at least one opening of the formation layer up to the level of the front face of the sacrificial layer and a dry etching step of the sacrificial layer. STATE OF THE ART [0002] Many integrated micro electro-mechanical systems (MEMS) comprise flat suspended micro-structures. This is for example the case of suspended volume actuators, sensors, switches, variable capacitors, inductors or acoustic wave resonators. In micro-technology or microelectronics, suspended micro-structures are achieved by the use of a sacrificial layer. The conventional steps ...

AI Technical Summary

Benefits of technology

The invention provides a method for creating flat suspended structures using a planarized polymer sacrificial layer. The process includes depositing an embedding layer on the sacrificial layer and substrate, followed by planarization of the embedding layer. The front faces of the sacrificial layer and embedding layer form a common flat surface, which is ideal for depositing the formation layer of the suspended structure. The side walls of the sacrificial layer are confined by etching a mask, and the process includes deposition of a base layer on salient elements on the substrate and planarization of the base layer to ensure a common flat surface. The invention achieves a flat surface for the formation layer of the suspended structure.

Problems solved by technology

The use of a sacrificial layer that is removed by wet etching, for example SiO2 in a hydrofluoric acid (HF) based bath, gives rise to sticking problems of the structures in the removal step.

This problem is generally associated with capillarity effects and surface forces.

However the exact profile of the suspended structure has repercussions on checking of the system.

Ondulations of the micro-structure, caused by the shape of the sacrificial layer, in fact make the stiffness of the final device and its deformation according to the excitation conditions difficult to know.

Not knowing the exact profile leads to a large discrepancy between simulations and experimental measurements of the device and to risks of stress concentrations at the embeddings and on the mobile structure.

Especially, this makes the devices extremely sensitive to process variations.

However, polymers are materials which are very difficult to planarize.

Chemical mechanical polishing (CMP) tests show very mediocre results, for example tear-off of the resin when polishing, irregularity of planarization or incrustation of colloidal silica (contained in the CMP planarization product) in the polymer, then occurring when the sacrificial layer is removed.

Other dry planarization tests (planarization on abrasive film) also gave mediocre results.

A good rectification of the polymer was obtained, but at the price of a very large number of scratches on the plane of the chip and tear-offs on the polymer pads, as well as incrustation of the abrasive material in the polymer.

However, these processes do not provide a simple solution.

Moreover, these processes are not suitable for all types of polymer (photosensitive resin, polyimide, etc .

These thermal treatments may lead to the polymer being denatured and make it almost impossible to planarize.

In a general manner, and in particular when they are annealed at high temperature, polymers are very sensitive to tearing and tend to trap the abrasive compounds contained in the planarization products which are deposited under the mobile structure when the removal step is performed.

Images