DE4232475C2 - Process for plasma chemical dry etching of Si¶3¶N¶4¶ layers highly selective to SiO¶2¶ layers - Google Patents

Description

The invention relates to a method for plasma chemical mixing Dry etching of silicon nitride layers is highly selective Silicon oxide layers.

With regard to the state of etching technology in semiconductor technology, reference is made to D. Widmann et al, "Technology of Highly Integrated Circuits", Springer-Verlag Berlin 1988 , in particular to sections 5.2.2 and 5.3.1.

In plasma chemical etching, for example in a con conventional barrel reactor, are gaseous as etching agents Ge connections used with the material of the removing layer a gaseous, volatile reaction form product. The resulting in the plasma of the etching reactor neutral reactive particles (radicals) diffuse to the process disks in the reactor and react there spontaneous and exothermic with the surface atoms of the caustic layer. The reaction product diffuses closing away from the pane. With plasma chemical etching Zen etching is isotropic, i. H. uniform in any direction.

As a variant of plasma chemical, isotropic etching Downstream or afterglow reactors ("remote plasma") be became known. The plasma is not directly in the Reactor, but generated in an unloading chamber. These generated reactive species subsequently flow over a Line into the etching chamber in which the to be etched Washers. The big advantage of this procedure lies in the fact that the process disk with the bombardment  high-energy ions, also by the gas ent charges are generated, is shielded. Damage with regard to the crystal lattice as well Contamination from sputtered foreign substances are therefore minimal.

Silicon nitride (Si ₃ N ₄ ) layers are mainly used in semiconductor technology as barrier layers against diffusions of all kinds and for passivation of finished integrated circuits against the penetration of corrosive and contaminating substances. Often, in particular in the so-called LOCOS process, it is necessary to remove the entire area of the silicon nitride layer and very selectively from the silicon oxide (SiO ₂ ) base. Since structuring processes are not involved in these cases, it is advantageous to use isotropic etching processes that protect the wafer surface. Since fluorine is the only halogen species that reacts spontaneously with Si ₃ N ₄ , the choice of etchants in plasma-chemical etching is very limited. Mixtures of CF ₄ as a fluorine supplier and other non-halogen-containing gases (e.g. O ₂ and N ₂ ) are usually used.

In general, it should be noted that the selectivity between the Si ₃ N ₄ layer and the underlying SiO ₂ layer is rather low in all processes which have hitherto been customary and only use fluorine-containing gases (maximum 10: 1). For new chip generations, however, a selectivity of at least 15: 1 must be achieved, especially due to the thinning layer thicknesses. Since this cannot be achieved with conventional etching gas mixtures, it has recently been proposed (N. Hayasaka et al, Solid State Technology / April 1988, pages 127 to 130) that a fluorine supplier, for example NF ₃ and additionally, to increase the selectivity, chlorine be used as the etching gas mixture (Cl ₂ ) to use. In this way, the selectivity can be increased to more than 30: 1, but molecular chlorine is a toxic, aggressive etching gas with highly corrosive properties. For technical and health reasons, the use of chlorine should be avoided as far as possible.

From US 4 , 717 , 447 a method of the type mentioned is also given, in which it is proposed to a fluorine supplier, for example F2 or NF ₃ , the is mixed with a carrier gas and acts as an etching gas, and add brominated or chlorinated fluorocarbons as an additive. The. The use of molecular fluorine is also problematic for reasons of occupational safety.

The object of the invention is therefore a method of Specify the type mentioned above that a selectivity of min at least 15: 1, but without the problematic mo molecular chlorine or fluorine.

This object is achieved in that a fluorocarbon compound or a mixture of different fluorocarbon compounds of the general formula C _x H _i F _y X _z (x, y, z ≧ 1, i ≧ 0), wherein X is chlorine and / or bromine, as the etching gas and / or iodine is used.

Developments of the invention are ge in the dependent claims indicates. In the following the invention is based on a Embodiment explained in more detail.

According to the invention, particularly manageable etching gases are obtained by binding the aggressive fluorine and chlorine atoms to carbon atoms. These so-called halocarbons are generally non-toxic, non-corrosive, and are easy to handle for technical reasons and for health reasons. In the given context, the non-toxicity and inertness of the chlorofluorocarbons are particularly advantageous. Examples are CF ₃ Cl, CF ₂ Cl ₂ , CFCl ₃ , C ₂ F ₅ Cl, C ₂ F ₄ Cl ₂ , C ₂ F ₃ Cl ₃ , etc.

The positive effect of the method according to the invention is not restricted by the fact that in the molecular structure fluorocarbon structure are installed.  

Simple representatives of these compounds are, for example, CHF ₂ Cl and CH ₂ FCl.

Oxygen and / or nitrogen atoms can also be incorporated.

A general formula for these compounds is C _x H _a O _b N _C F _y Cl _z Br _u I _v .

Through further experiments it was found that the positive effect on selectivity also occurs if the chlorine atoms are substituted by bromine and / or iodine or be supplemented by these. When choosing a ge suitable connection, however, it must always be ensured that the etchant with the material to be removed is cursed term connection and that the etchant a sufficient has high vapor pressure.

All tests were carried out on a standard downstream system from Tylan Tokuda. CF ₃ Cl, CF ₂ Cl ₂ , CBrF ₃ and CIF _{3 were} used as etching gases. The following typical main process parameters could be defined:
Process pressure: 1 to 500 Pa
Gas flow (CF ₃ Cl): 3 to 3000 cubic centimeters per minute (sccm)
Microwave power: 50 to 5000 W.
Disc temperature: 0 to 80 ° C

The upper limit of the temperature was on the system Limited to 80 ° C. Higher temperatures increase the etch rate and can therefore be an advantage for other systems.

Machine-specific parameters for other equipment influence the principle of the etching according to the invention not and can each be optimized easily the. With sufficient fine tuning, too good results with main other than the aforementioned parameter settings can be achieved. With newer systems For example, process pressures well below 1 Pa can be achieved, which have a rather positive effect on the process can. In addition to the high selectivity, the op  timing of other properties of the etching process wishes, this is easily done by admixture a non-halogen containing carbon, nitrogen, oxygen or hydrogen-containing compound for etching gas mixture possible. In addition, the etching gas composition tongue a carrier gas, e.g. B. an inert noble gas (He, Ne, Ar, Kr, Xe), or nitrogen, oxygen or Hydrogen can be added.

Claims (5)

1. A method for plasma chemical dry etching of silicon nitride layers highly selective to silicon oxide layers, characterized in that a fluorocarbon compound or a mixture of different fluorocarbon compounds of the general formula C _x H _i F _y X _z (x, y, z ≧ 1, i ≧ 0), where X is chlorine and / or bromine and / or iodine. 2. The method of claim 1, wherein the etching gas mixture additional, non-halogen-containing compounds and / or carriers gases are added. 3. The method according to claim 2, wherein the carrier gas is an inert noble gas (He, Ne, Ar, Kr, Xe) is used. 4. The method according to claim 2, in which as a carrier gas stick substance, oxygen or hydrogen is used. 5. The method according to claim 2, in which a non-halogen-containing compound composed of the elements nitrogen, oxygen and hydrogen, in particular N ₂ O, NO ₂ , NH ₃ or H ₂ O, is used.