可选择性去除氧化铝的湿式蚀刻法

Etching is a class of common processes for the  controlled removal of material. Etching of alumina is found  in various applications including the fabrication of microde  vices, Specifically thin film magnetic structures and more  Specifically magnetic heads. There are various types of  etching processes; however they all generally include the  common actions of transport of reactants to the Surface,  Surface reaction, and transport of products from the Surface.

of etching processes. The etch rate is the decrease  in etch material thickness verSuS time. Faster etch rates are  usually favored, but must be balanced with the ability to  control the total amount of material removed. Uniformity of  etching acroSS a Surface and between Surfaces is desired.  Isotropy of the etching process is also considered. The  characteristics of Selectivity and damage caused by the etch  process often control which type of etch process is used for  a particular application. Selectivity and damage will be  further discussed below.

Frequently the Surface is composed of more than  one type of material, only one of which is desired to be  etched. The material to be etched is referred to as etch  material. Underlayers and Surrounding material refer to the  rest of the structure that is not to be etched. Selectivity is  generally defined as a ratio of the etch rate of the etch  material to the etch rate of the other portions of the structure  that are not to be etched. Damage is often directly related to  selectivity. If perfect selectivity could be achieved, only the  etch material would be removed and no etching would occur  to other materials. If Selectivity is poor, then etching to the  other materials is likely extensive, therefore described as  damage. Damage may also occur by incompatibility, usually  chemical in nature, between components of the etching  proceSS and materials in the Structure resulting, for example,  in corrosion of the Structure.  

Wet etching, as compared to dry etching, is gen  erally simpler, cheaper and faster. The general proceSS is to  drop the items to be etched into a container holding the wet  etchant. The main ingredients of conventional wet etchants  are: an oxidizer, for example hydrogen peroxide or nitric  acid; an acid or base to dissolve the oxidized Surface, for  example Sulfuric acid or ammonium hydroxide; and a dilu  ent media to transport reactants and products, for example  water or acetic acid. When etching is complete, the items are  removed and cleaned. Wet etching can be performed as a  batch process, So is fast for processing larger numbers of  items and reproducible. Control of wet etching is achieved  by adjusting the etching time (e.g. the time in the bath) and  the etching rate, which is related to the temperature and  composition of the bath. Wet etching is preferred over dry  etching for reasons of efficiency, but is limited in its appli cation by poor Selectivity and damage with Some materials.

There are several disadvantages to conventional  wet etching for the etching of alumina. The main problem is  that alumina is typically to be etched on Structures that also  contain transition metals. Conventional wet etchants for  alumina, Such as: EDTA (ethylenedinitrilo)tetraacetic acid,  concentrated acids, and concentrated bases, all have poor Selectivity between alumina and transition metals. Poor  Selectivity results in damage and corrosion to the metal  portions of the structure. Metal underlayers beneath the  alumina etch material are exposed and often Suffer damage  affecting later connections to be made at those metal under  layers. Additionally, the resist materials that are applied to  the Structure to control where etching occurs often fail in  acid etching environments detrimentally affecting the Struc  tures. In addition, purity is a critical concern in all electronic  materials processing. Highly corrosive materials, Such as  acids and other very reactive materials are difficult to purify.

The novel wet etchant demonstrates high selectiv  ity for etching alumina Versus other Sputtered or electro  plated transition metals and alloys typically used in the  manufacturing process for magnetic heads. Selectivity of the  novel wet etchant was measured by comparing the etch rate  of alumina to the etch rate of metal layers. A graph showing  the decrease in layer thickness over time due to etching by  the novel wet etchant is shown in FIG.1. As shown in FIG.  1, the alumina is etched with a substantially uniform rate of  approximately 12 nm/min. The Cu, NiFe and Ru. Samples  show very little change in thickness with etching times of an  hour or more at an approximate loSS less than or equal to 1  nm of material thickness per minute. The selectivity of the  novel wet etchant for alumina to copper is greater than 10:1;  for alumina to NiFe and alumina to NiV is greater than 16:1;  and for alumina to Pt, alumina to Au and alumina to Ru, the  selectivity is greater than 1000:1.

Fig1

Dry etching of alumina has proved challenging.  Solid alumina or aluminum oxide is thermodynamically Stable in comparison to the products produced through  chemical dry etch processes. Consequently, alumina  requires dry etching dominated by physical attack, e.g. a lot  of ion bombardment, to basically knock the atoms apart and  then etch the aluminum Separately. A commonly used tech  nique for dry etching alumina is reactive ion etching, which  is a type of Sputtering. In reactive ion etching, a Voltage is  applied to the plasma and the Substrate Surface. The Voltage difference acts to accelerate particles out of the plasma to  Strike the Surface with an increased energy. A combination of  chemical and physical etching of the Surface takes place. A  variation of reactive ion etching is ion beam etching, where  an ion gun provides the ions used to Strike the Surface.