Method for precisely controlled masked anodization

Abstract

The present invention is related to a method for masked anodization of an anodizable layer on a substrate, for example an aluminum layer present on a sacrificial layer, wherein the sacrificial layer needs to be removed from a cavity comprising a Micro or Nano Electromechanical System (MEMS or NEMS). Anodization of an Al layer leads to the formation of elongate pores, through which the sacrificial layer can be removed. According to the method of the invention, the anodization of the Al layer is done with the help of a first mask which defines the area to be anodized, and a second mask which defines a second area to be anodized, said second area surrounding the first area. Anodization of the areas defined by the first and second mask leads to the formation of an anodized structure in the form of a closed ring around the first area, which forms a barrier against unwanted lateral anodization in the first area.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 61 / 418,194, filed Nov. 30, 2010, the disclosure of which is hereby expressly incorporated by reference in its entirety and is hereby expressly made a portion of this application.FIELD OF THE INVENTION[0002]Methods for precisely controlling a masked anodization process are provided. The preferred embodiments are further related to manufacturing semiconductor devices, especially to methods of encapsulation and to such devices. More specifically they may relate to zero-Level or wafer level packaging of semiconductor devices. More particularly, the preferred embodiments relate to Nano- and / or Micro-Electro-Mechanical Systems (NEMS and / or MEMS) and to processes of encapsulating (or packaging) said systems.BACKGROUND OF THE INVENTION[0003]Creating patterns of a dielectric or porous material within a conductive thin film by means of masked anodization ...

AI Technical Summary

Benefits of technology

[0012]It is an object to provide an improved method for creating precise patterns of anodized material within an anodizable layer by means of masked anodization. More specifically it is an object to create precise patterns of a dielectric or porous material within a conductive thin film using masked anodization. It is thereby in particular an object to provide an improved and cost-efficient masked anodization process for application in manufacturing of semiconductor devices on (full) wafer scale to make the anodization process applicable in large scale production of semiconductor devices.

[0013]It is further an object of preferred embodiments to provide a reliable and controllable method for performing wet anodization processes which locally transform an anodizable layer e.g. a conductive (metal) layer into an anodized layer e.g. a dielectric or porous layer. It is the goal of the preferred embodiments to perform said anodization uniformly on a (full) wafer scale.

[0015]The above objectives are accomplished by a method and device according to the preferred embodiments. The preferred embodiments solve the problem of achieving a uniform and controllable anodization by surrounding a group (plurality) of mask structures with an additional surrounding mask structure. In other words the problem is solved by using an additional surrounding photoresist or other mask structure with high precision which defines small areas on the surface to be exposed selectively to the anodization process without causing over-anodization leading towards delamination or undercut of the mask layer during the anodization. The presence of said additional surrounding mask structure results in self-limitation of the anodization process as the anodized border becomes anodized (oxidized) simultaneously with the anodized areas within said border, so that said border prevents further anodization current from reaching the anodized region of the mask structures to avoid unwanted further anodization. Since the electrical current needed for the anodization process is supplied at the edge (perimeter) of the substrate, surrounding every group of structures on the anodization mask with an additional surrounding mask structure (defining a borderline of anodized material) results in self-limitation of the anodization process as the anodized border becomes simultaneously anodized (oxidized) and prevents further anodization current from reaching the anodized region. The additional surrounding mask structure (defining the borderline or protection ring) may be applied at different scales during the mask design for the anodization process (i.e. the borderline can surround a small group or a large group of structures, or possibly surround the whole substrate (wafer). The width of the additional surrounding mask structure and the surrounded area can be chosen (or adjusted) to guarantee a full vertical anodization of the enclosed structures, and at the same time protect these structures from large lateral extensions of the anodization process.

[0016]By applying the masked anodization process according to the preferred embodiments in a packaging process for NEMS / MEMS devices, an additional surrounding mask structure is surrounding a group of individual NEMS / MEMS devices and will result in self-limitation of the anodization process as the anodized border becomes simultaneously anodized (oxidized) and prevents further anodization current from reaching the anodized region of the mask structures to avoid unwanted further anodization.

[0017]It is an advantage of preferred embodiments that providing the additional surrounding mask structure does not need extra processing steps as said additional mask structure may be provided simultaneously with the provision of the first mask structure(s).

Problems solved by technology

Since the electrical current needed for the anodization process is supplied at the edge (perimeter) of the substrate, surrounding every group of structures on the anodization mask with an additional surrounding mask structure (defining a borderline of anodized material) results in self-limitation of the anodization process as the anodized border becomes simultaneously anodized (oxidized) and prevents further anodization current from reaching the anodized region.

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