Processes for producing a sputtering target from a silicon-based alloy, a sputtering target

Abstract

A process for producing a sputtering target from a silicon-based alloy with an aluminum content of 5-50 wt. %. The target material is produced by a casting technique in which the material is melted and vacuum-cast, such that the casting is carried out in a hollow cylindrical casting mold.

Description

BACKGROUND OF THE INVENTION

The invention concerns processes for producing a sputtering target from a silicon-based alloy with an aluminum content of 5-50 wt. %, a sputtering target and its use.

Silicon-based alloys with an Al content of a few wt. % have long been known for use as sputtering targets in coating technology, for example, see U.S. Pat. No. 5,094,288 A, and DE 198 10 246 A1. In addition to the planar targets that were originally used, rotating targets are also frequently used to produce reactively sputtered Si₃N₄ or SiO₂ (EP 00 70 899). These rotating targets are usually produced by plasma spraying techniques (U.S. Pat. No. 5,853,816 A), in which either mixtures of Si and Al elemental powders or alloy powder (DE 101 40 589) are sprayed onto a support tube. The SiAl tubular sputtering targets obtained in this way can be produced only up to a thickness of about 6-8 mm Si(Al) wall thickness, since the walls break at greater thicknesses due to the high thermal stress to which they are subjected during plasma spraying. Furthermore, DE 100 63 383 C1 describes a process for casting metal tubular targets, in which the outer target coating consists of a metal with a melting point of at most 800° C., and the casting material runs into the mold from below.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a process for producing a tubular sputtering target and a sputtering target that can be produced as inexpensively as possible. A further object of the invention is to specify a use for the target.

In accordance with the invention, this object is achieved by a process in which a sputtering target is produced from a silicon-based alloy with an Al content of 5-50 wt. %.

The target material is produced by a casting technique in which the material is melted and vacuum-cast, such that the casting is carried out in a hollow cylindrical casting mold. Preferably, the casting is carried out in a thin-walled casting mold. It is advantageous for the tubular sections produced by casting to be soldered or cemented on a support tube and for the tubular sections possibly to be machined before they are soldered or cemented on the support tube. Surprisingly, it was found to be advantageous for the tubular sections to be cast by top-casting. The process makes it possible, especially as a result of the addition of aluminum, to produce excellent tubular sputtering targets, which can be used in a tubular cathode.

The casting mold comprises an outer wall and a core, and the target material is filled between the outer wall and the core. The outer wall and the core may be advantageously arranged symmetrically around the same axis. Furthermore, the cross-section of the core and the outer wall may be circular.

The wall thickness of the hollow cylindrical mold is only slightly greater than the desired target wall thickness. The hollow cylindrical mold is filled by top-casting. Surprisingly, despite the extraordinarily broad melting range of 577° C. to a maximum of 1,380° C., one obtains a macroscopically homogeneous casting with only slight porosity and, above all, after removal of the casting mold, a crack-free tubular section.

The head of the tubular casting is separated. The casting is machined to the necessary target dimensions on both the outside and inside diameter.

The entire tubular target is then constructed in such a way that the tubular sections described above are centrically positioned around the support tube and integrated into a complete target by soldering or cementing on the support tube.

The invention is explained below with reference to an embodiment of the invention shown in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the casting process schematically.

FIG. 2 shows a cross section of a tubular sputtering target.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A hollow cylindrical graphite mold is produced. It consists of a graphite core 1 with a diameter of 131 mm and an outer wall 2 with an inside diameter of 158 mm, an outside diameter of 170 mm, and a height of 600 mm. An alloy of 90 wt. % silicon and 10 wt. % aluminum is melted 3 in a vacuum. After complete melting of the alloy components, the temperature of the melt is stabilized at 1,430° C. The graphite mold is preheated to 300° C. and brought into the vacuum melting chamber, and the molten alloy is poured into the mold cavity 7 by a mold funnel or hopper 4. After solidification of the melt and cooling of the casting to below 300° C., the mold can be removed from the furnace. Both the inner core of the mold and the outer wall of the mold can be removed from the casting by a hydraulic press. The top of the cylindrical casting is sawed off to a length of 100 mm. The inside diameter of the casting is hollowed out to 134 mm by turning, and the outside diameter is turned to 154 mm. The inner surface of the turned casting is metallized by electrochemical deposition with nickel strike and copper. The metallized Si—Al tubular sections 5 are wetted with indium solder and slid onto the likewise metallized and prewetted support tube 8. The entire target, which consists of seven SiAl tubular segments and the support tube, is heated to the soldering temperature of 180° C., and the space between the outside diameter of the inner tube and the inside diameter of the SiAl castings is filled with molten indium 6. The entire tube is slowly cooled, subsequently freed of excess solder, and ground to the final target dimension (d=152 mm) on an outside diameter grinding machine. The finished target can be installed in a commercial tubular cathode and used to produce oxidic or nitridic silicon coatings.

The invention is not limited by the embodiments described above which are presented as examples only but can be modified in various ways within the scope of protection defined by the appended patent claims.

Claims

1. A process for producing a sputtering target from a silicon-based alloy with an Al content of 5-50 wt. %, comprising the steps of: melting the alloy; and vacuum-casting the alloy in a hollow cylindrical casting mold to produce tubular sections.

2. A process in accordance with claim 1, including casting the alloy in a thin-walled casting mold.

3. A process in accordance with claim 1, further including the step of soldering or cementing the tubular sections on a support tube.

4. A process in accordance with claim 3, further including the step of machining the tubular sections, the tubular sections being soldered or cemented on the support tube after machining.

5. A process in accordance with claim 1, wherein the tubular sections are cast by top-casting.