Dry etching

The term dry we group in semiconductor technology and microsystem technology together a group of subtractive ( ablative ) microstructure procedure that is not on wet chemical reactions (such as wet chemical etching, chemical mechanical polishing) are based. The removal of material (for example, silicon dioxide on silicon wafers ) is carried out either by accelerated particles (e.g., argon ion ) or using plasma activated gases. There are thus exploited chemical and physical effects depending on the procedure.

Classification

The dry-etching process can be divided into three groups. Firstly, the physical dry etching, they are based on the material by bombardment with particles, on the other chemical dry etching, they are based on a chemical reaction of a most active Bankrupts plasma gas. The third group, the physico-chemical dry etching processes holds together that share both mechanisms of action, and is thus able to minimize the disadvantages of the first two groups.

Physical dry etching

In the physical dry etching, the surface of the substrate is etched by the bombardment of ions, electrons or photons. The bombardment results for sputtering of the substrate material; the processes involved are similar to those at the cathode (sputtering ), which is usually not counted among the dry etching. The methods are named depending on the applied particles. The best known and most frequently used are: electron beam method ( engl. electron beam) or the Laserzerstäubung ( engl. laser vaporization ). Both can be found among others in the photolithography application ( see also electron and Laserstrahlverdampfen ).

The etching is generally carried out in a high vacuum chamber in order to prevent interaction of the particle beam with the residual gas atoms ( scattering, etc. ). For textured samples both methods exist, based on a grouping of the particle, the etch very targeted, as well as large etching process using a mask applied to the surface (see photo lithograph ) which are not to be etched areas protects against particle bombardment.

Considering ion etching process, some important drawbacks to the purely physical dry etching show. They usually have a relatively low etch rate, which also has only a small material selectivity. By the associated etching of the mask rounded result at the edges. Furthermore are necessary for etching high energy so that the ions can penetrate deeper into the material. Therefore, it is etched not only superficial, but also deeper layers are damaged. A further disadvantage is parasitic depositions (English redeposition ) of the etched particles on the substrate and the mask or the mask edges.

Chemical dry etching

In the chemical dry etching ( engl. chemical dry etching, CDE), a chemical reaction between the neutral particles / molecules (usually but radicals) exploited and the surface of the substrate. The prerequisite is that the reaction product is exactly as the starting materials used in gaseous and volatile, for example, silicon tetrafluoride ( SiF4 ) during silicon etching. Substituting a uniform supply of the etching gas ahead of this process are isotropic and, depending on the materials used often highly selective material (similar to the wet chemical etching). The reactions are generally carried out in the previously evacuated reactor chambers. Then the reaction gas is introduced into the chamber for the process, the process pressure is about 100 Pa.

The etching process itself proceeds in principle as follows. The neutral atoms or molecules are passed through a plasma in the reaction chamber and to flow over the substrate (e.g. silicon wafer ). There they react with the atoms located at the surface. They form volatile gaseous reaction products, which are sucked through a vacuum pump.

An application used to be the removal of the photoresist by oxygen plasma.

Physico-chemical dry etching

The physico-chemical dry etching ( engl. physical- chemical dry etching) are combinations of physical and chemical dry etching. They have great importance in the manufacture of modern integrated circuits and micro-mechanical systems, since very fine and deep structures can be made with them. For the etching process, it is again important that the gaseous, volatile reaction products are formed.

The starting materials are usually activated by a plasma or radicalized and then fed for the reaction on the substrate. This can be done either by convection or by electrostatic acceleration of ions via an applied electric field. Due to the various possibilities of the plasma generation and particle acceleration to a variety of sometimes very similar method has formed. The most important are currently (2008) the reactive ion etching ( engl. reactive ion etching, RIE), its development for reactive Ionentiefenätzen (german deep reactive ion etching, DRIE ), reactive ion beam etching the (English reactive ion beam etching ) and the HDP etching (of English. high-density plasma etching).