DE4310345C2 - Process for dry etching of SiC - Google Patents

Description

The invention is based on a method for dry etching Silicon carbide according to the preamble of claim 1.

Such a procedure is from the German application DE 36 03 725 A1 known. For structuring silicon carbide a substrate is formed by photolithography and plasma etching the silicon carbide on a flat side with a structured silicon layer and then covered the Plasma etching with an oxygen content of at least 40%, in particular made about 70 to 95%. The oxygen will Carbon tetrafluoride added. The Silicon layer with a much lower etching rate removed as the silicon carbide of the substrate.

For the treatment of semiconductor substrates by reactive Ion etching is described in the German patent application DE 39 35 189 A1 proposed a paint mask to cover Doped polycrystalline silicon substrates use that on a preferably made of SiO₂ Pad is attached. As etching gases are chlorine, SiCl₄ and N₂ used. By selecting the process gases, a high Selectivity and high anisotropy in the etching of silicon and silicides reached.

Another method is known from the publication by Barclett, R. W. and Barlow, M .: "Surface Polarity and Etching of Beta-Silicon Carbide" in J. electrochem. Soc .: SOLID STATE SCIENCE, Nov. 1970, pages 1436-1437, known. A gas mixture containing 6% chlorine and 26% Contains oxygen in argon, at 850-900 ° C for etching beta silicon Carbide used. However, this mixture is not intended etch away even layers of SiC, but so-called Etching pits formed, which are an indication of stacking errors, dislocations and should be similar.

A number of processes have been developed for etching pure silicon, but their transfer to SiC is not readily possible. If one starts with dry etching with chlorine, it shows that pure chlorine is relatively ineffective. If BCl _{3 is} added to the chlorine, the etching rate for SiC is too slow. Mixtures of chlorine and oxygen are also unsuitable because the reaction vessel is very difficult to clean from the residues. It is also clear to the person skilled in the art that an etchant for producing etching pits is not absolutely suitable for etching material layers at a sufficient speed.

The invention is suitable for mask technology in connection with SiC and thus for the production of integrated components on the basis of this semiconductor material. The previously used method used fluorine as halogen for the dry etching process and in particular had the disadvantage that one had to use metal masks for this technique.  

In particular, masks made of aluminum are unfavorable to handle because Aluminum is converted very easily to aluminum oxide, which is only is difficult to eradicate. The oxygen comes from the usual Sputtering process, which uses a certain amount to oxidize the carbon Need oxygen content in the etching gas.

The invention is based on the object of designing a method according to the preamble of claim 1 in such a way that in a conventional mask made of SiO _2, surface areas of SiC which have been recessed are progressively removed in the depth of the substrate. Temperature pressure and similar parameters should be set so that the greatest possible etching speed and a relatively steep wall near the 90 ° slope angle of the trench thus formed are achieved.

This problem is solved with the in the characterizing part of the claim 1 specified characteristics.

The subject matter of claim 1 has the advantages that the mask technology known from silicon with SiO ₂ can be used, which has already proven itself there excellently.

Advantageous embodiments of the subject matter of claim 1 are in the Subclaims specified.

The advantages of the embodiments of the invention according to the subclaims can be seen in the fact that technically usable etching speeds can be achieved with the chlorine process with a corresponding choice of the additional gases (CCl ₄ and Ar or N ₂ ).

The invention will now be described using an exemplary embodiment Using the drawing explained.

It shows

Fig. 1 is a SiC crystal, which is thermally oxidized;

FIG. 2 shows the deposition of CVD oxide;

Fig. 3, the patterning of the oxide;

Fig. 4 the etching in the structured gaps and

Fig. 5 shows the wet chemical removal of the oxide.

In the following exemplary embodiment of the invention, the production of trenches for the lateral edge insulation of SiC components is described. First, the SiC substrate is cleaned and thermally oxidized. The thermal oxide layer is about 0.3 µm thick. Next, chemically deposited oxide is produced on this layer (CVD process). These two steps are shown in Figs. 1 and 2. Next, the oxide is structured in the form required for the circuit by means of etching by reactive ions (RIE) ( FIG. 3). The etching of the SiC by means of an etching process going deep into the substrate takes place according to the Cl process according to the invention. The deep trenches, which are shown in FIG. 4, are produced by this etching by means of reactive ions. The last process step, the wet-chemical removal of the oxide FIG. 5 shows.

The following examples relate to the process step which is shown in FIG. 4 and deal with various recipes for the RIE process.

Comparative Example 1

SiC is chosen as the substrate. Fumed oxide, which was applied at 1250 ° C. for four hours, is used as the thermal oxide. The thickness of the oxide is 0.3 µm. The CVD oxide is produced at 0.5 mbar and 6 W high frequency power. The gases are composed of 70 standard cm³ N ₂ O, 7 sccm SiH ₄ . The thickness of the oxide layer is set at about 1 µm. The high-frequency plasma heats the substrate to about 300 ° C in this procedure. The next step in structuring the oxide is carried out using a mixture of CF ₄ with 14 standard cm 3, CH ₃ SF with 50 standard cm 3 at 200 W, a pressure of 0.16 mbar and room temperature. The subsequent and decisive Cl process consists of a RIE process at 0.25 mbar and 300 W output, the gas mixture consisting of 40 standard cm³ Cl ₂ , 10 standard cm³ N ₂ and SiCl ₄ with a proportion of 20 standard -cm³ is carried out. The etching rate is 127-135 nm / min. The selectivity with respect to the removal of the oxide is 2.2.

Comparative Example 2

Another process step is alternatively used for the Cl process suggested. The high-frequency plasma, which at a frequency of 13.56 mHz is generated, is under a pressure of 0.25 mbar and works at a power of 300 W.  

The substrate, ie the cathode, is cooled so that the temperature cannot rise above 50 ° C. The etching gas is composed of 40 standard cm³ Cl ₂ , 10 standard cm³ N ₂ and 20 standard cm³ SiCl ₄ . The etching rate is 127-135 nm / min. The selectivity with regard to the SiO ₂ mask is 2.2.

Example 3

The etching process according to the invention can be successfully carried out with a combination in which some oxygen is added. The gas composition is as follows: 40 standard cm³ Cl ₂ , 20 standard cm³ SiCl ₄ , 10 standard cm³ N ₂ and 2 standard cm³ O ₂ . The etching rate for the other same parameters for the high-frequency plasma is approximately 129 nm / min.

Example 4

Another advantageous embodiment of the invention provides an etching gas with 40 standard cm³ Cl ₂ , 20 standard cm³ SiCl ₄ , 10 standard cm³ Ar and 2 standard cm³ O ₂ . Pressure, temperature and power are chosen as in the previous examples. The etching rate is about 154 nm / min and the selectivity is about 3.4.

Example 5

In this example, a higher proportion of oxygen was used with 40 standard cm³ Cl ₂ , 20 standard cm³ SiCl ₄ , 10 standard cm³ N ₂ and 20 standard cm³ O ₂ .

The examples apply to 6-H SiC and β-SiC.

The components manufactured using these methods are used in all applications where a substrate material with a wide range is needed. Such applications are in space technology, the Automotive industry and seen in all applications where sensors or electronic components exposed to high temperatures are.

Claims (6)

1. A method for dry etching of SiC in a plasma reactor with a chlorine-containing gas, which is used for a reactive ion etching, characterized in that the removal of SiC is done with the aid of SiO ₂ mask technology and that the gas is an inert gas in addition to Cl ₂ and SiCl₄ (N₂, Ar) and up to 30 vol .-% oxygen (O₂) contains. 2. The method according to claim 1, characterized in that the gas contains about 10 standard cm³ nitrogen (N ₂ ) and / or argon as inert gas. 3. The method according to claim 1 or 2, characterized, that the substrate is kept at a temperature of T <50 ° C. 4. The method according to any one of claims 1 to 3, characterized, that the plasma process with a frequency of 5-50 MHz, a Pressure of 0.1-0.5 mbar, an energy of 200-500 W performed becomes. 5. The method according to any one of claims 1 to 4, characterized in that the larger number of chlorine atoms is provided by Cl ₂ . 6. The method according to any one of claims 1 to 5, characterized in that the predominant number of chlorine atoms for the reaction is provided by SiCl ₄ .