HK1129708A - Method of making sputtering target and target produced - Google Patents

Description

Method of manufacturing a sputtering target and target product manufactured thereby

This application claims benefit and priority from U.S. provisional application No. 60/831,521 filed on 17.7.2006.

Technical Field

The present invention relates to a method of manufacturing a sputtering target, and in particular to a method of casting a metallic sputtering target having an equiaxed, cellular, nondendritic microstructure.

Background

One prior method for manufacturing metallic sputtering targets includes crushing a slab of metallic material, screening and selecting suitable sized crushed particles, hot isostatic pressing (HIP' ing) the sized particles in an evacuated sealed can to form a target body, and then machining the hot isostatically pressed target body to produce the desired target shape.

Another current method for manufacturing large molybdenum sputtering targets is Cold Isostatic Pressing (CIP) of Mo powder, sintering the cold isostatic pressed body to reduce the oxygen content, and then hot rolling the sintered body into flat plates or discs of the desired length/width/thickness. The plate or disc is then machined to final tolerances.

To manufacture sputtering targets, these methods involve many processing steps and considerable cost.

Disclosure of Invention

The present invention provides a method of making a fine-grained, cast sputtering target. The present invention provides in one embodiment a method of making a sputtering target by melting a metallic target material, controlling the temperature of the melted target material in such a way that the melted target material is less overheated, introducing the melted target material into a mold having internal walls that form a mold cavity in the shape of the desired target, and solidifying the melted target material by withdrawing heat from the mold at a rate to solidify the target material to form a metallic sputtering target having a substantially equiaxed, cellular nondendritic microstructure uniformly throughout the target. Optionally, the mold may be heated to a high enough mold temperature that prevents the formation of a large number of columnar grains directly adjacent the inner mold wall.

In another embodiment the invention also provides a metallic sputtering target having a substantially equiaxed, cellular nondendritic microstructure uniformly throughout the target. The sputter target can be used in casting conditions that do not require additional post-casting processing other than finishing or hot isostatic pressing of the as-cast target to compact the as-cast target.

It is an advantage of the present invention to provide a cast sputtering target that does not require many of the processing steps used in the prior art and to provide a sputtering target having favorable microstructural properties for sputtering.

The present invention also provides a method of controlling the grain size of a target that reduces the lead time from material selection to target manufacture and increases the flexibility of material selection, such as more alloying options.

Other advantages, features and embodiments of the invention will become apparent from the following description.

Drawings

FIG. 1 is a schematic perspective view of a molten target material in a crucible ready for pouring into a steel or ceramic mold.

Detailed Description

The present invention provides a method of manufacturing a sputter target comprising a metallic target material. The metallic target material may comprise a metal or an alloy of two or more metals. For illustrative purposes and without limitation, the target material may comprise molybdenum, tungsten, and other metals and high temperature melting alloys, such as nickel-based, chromium-based, cobalt-based, iron-based, tantalum-based, molybdenum-based, tungsten-based, and other alloy materials. For illustrative purposes and without limitation, the target alloy may comprise a cobalt-based alloy including an alloying element selected from the group consisting of boron, chromium, platinum, tantalum, ruthenium, niobium, copper, vanadium, silicon, silver, gold, iron, aluminum, zirconium, and nickel. For example, the target may comprise a cobalt-based alloy including, but not limited to, Co-Ta-Zr alloys, Co-Ta-B alloys, Co-Cr-Pt-B-Cu alloys, and other alloys. These target metals or alloys are commercially available from raw material suppliers with suitable purity for a particular sputtering target application. The target metal or alloy is supplied in the form of a mass, powder, bulk, etc. (as indicated by "input: alloy control" in fig. 1).

Referring to fig. 1, one embodiment of the present invention includes melting a selected metal (metal or alloy) target material TM in a crucible C or other suitable melting vessel using a suitable melting method, such as Vacuum Induction Melting (VIM) or Electron Beam (EB) melting. The crucible or melting vessel may be selected according to the particular metal or alloy to be melted. Where the particular metal or alloy to be melted requires, the melting may be conducted under an inert atmosphere or vacuum (as indicated by "furnace ambient vacuum"). When an inert atmosphere or vacuum is required for the metal or alloy during melting, conventional vacuum induction melting equipment (as shown in "VIM melting system") may be used.

The particular conventional vacuum induction melting furnace used in the examples uses a melting crucible that is poured directly into the underlying mold M. However, the present invention contemplates the use of a pouring vessel, such as a pouring crucible, optionally as an intermediate vessel between the melting vessel and the mold to be cast.

Preferably, the melted target material in the melting vessel or pouring vessel is maintained in a substantially quiescent state so that all low density non-metallic inclusions float to the surface so that they can be removed from the melt. For example, when using a vacuum induction melting process to melt a charge of target material, a susceptor, such as graphite, can be placed between the induction coil IC and the melting vessel such that the susceptor is heated and in turn heats the charge, and such that the melted target material is not agitated. Alternatively, very high frequency or resistance heating may be used to achieve the same result.

In addition, the use of a bottom pour crucible allows the introduction of the melted target material into the mold without the need to carry away non-metallic inclusions floating on the melt surface. Alternatively, a teapot-shaped crucible can be used to prevent non-metallic inclusions floating on the melt surface from entering the mold. Other techniques for minimizing the amount of non-metallic inclusions entering a mold are described in U.S. patent 4832112, which is incorporated herein by reference in its entirety.

The invention further includes controlling the temperature of the melted target material TM in the melting or pouring vessel in a manner such that the melted target material is barely superheated prior to being introduced into the mold. The temperature of the melted target material is reduced to remove substantially all of the superheat of the melted target material. The reduced temperature should be substantially uniform throughout the melted target material and, for most target materials, controlled to be within 0-20 ° f above the measured melting point of the particular metal or alloy target material, although the range can be adjusted depending on the particular target metal or alloy. The measured melting point may be determined as described in us patent 4832112.

The temperature of the melted target material in the melting vessel can be reduced by gradually reducing the power or energy supplied to the melting furnace in which the melting vessel is located. For example, when a feed of target material is melted by vacuum induction melting as described in the examples below, the power supply to the induction coil IC may be gradually reduced to lower the temperature of the melted target material so that substantially all of the superheat is removed prior to introducing the melted target material into the mold. The temperature of the molten material may be measured using an infrared pyrometer as shown or other temperature measuring device (as indicated by "temperature measurement").

The mold M may comprise a metal mold or a ceramic mold that includes interior walls defining a mold cavity having the desired sputtering target shape. Typical sputtering target shapes that can be manufactured include, but are not limited to, rectangular, square or other polygonal plates, and circular discs.

In addition to when investment casting sputter targets, the present invention contemplates optionally creating turbulence in the melted target material after introduction into the mold. For most target materials, it is sufficient to pour the melted target material directly into the mold. Alternatively, the turbulent flow is imparted to the molten target material in the mold by electromagnetic stirring, mechanical stirring, and crushing of the melt as it is poured into the mold, such as by splitting the melt into multiple streams or droplets as it enters the mold as described in U.S. patent 4832112.

According to the present invention, the molten target material in the mold is solidified by withdrawing heat from the mold at a rate to achieve a substantially equiaxed, cellular, nondendritic grain structure throughout the sputtering target. The thus solidified (as-cast) sputter target preferably has an equiaxed, cellular, 3 or less ASTM grain size throughout the sputter target. To achieve this equiaxed, cellular grain structure, the rate of heat extraction is controlled. In some cases, the initial temperature gradient between the melted target material and the relatively cold mold is sufficient to produce dendritic columnar grains at the interface. The present invention contemplates optionally heating the mold to a sufficiently high mold temperature (as shown by "controlled preheating process" and "preheating mold") that will prevent substantial formation of columnar grains directly adjacent the inner mold wall. The cured target has the final or near final shape of the desired target, requiring only minimal machining prior to use as a target.

As the aspect ratio of the mold increases, it is more important to extract heat more quickly from the solidified target material in order to maintain the fine grain size and associated cellular microstructure and to minimize the tendency for the pores to increase and possible segregation. The improved heat extraction can be facilitated by the aforementioned disclosure of pulverizing the melted target material as it is poured into the mold.

In the case of a solidified as-cast sputter target having pores, the pores may be removed by various techniques, including hot isostatic pressing of the as-cast sputter target using a conventional hot isostatic gas pressing process whose gas pressure, temperature and time parameters will depend on the particular target metal and alloy used. Control and removal of as-cast pores of such sputter targets is described in U.S. patent 4832112.

For purposes of further illustrating the invention, but not limiting in any way, rectangular sputtering targets having dimensions of 27 inches long by 4.25 inches wide by 0.2 inches thick can be cast in a conventional preheated ceramic investment mold located in the lower cavity of a conventional vacuum induction furnace. The preheated investment mold will include a mold cavity that closely replicates the desired shape of the sputtering target. A target metal or alloy comprising a cobalt-based alloy, such as of the type described above, may be heated in the upper chamber of the crucible to a temperature about 20-50 ° f above its melting point under a vacuum of less than 10 microns of mercury to melt it in the zirconia crucible. The power of the induction coil in the furnace can be gradually reduced until the melted target material is within 0-20 DEG F of its melting point. The melted target material may then be poured into a mold that may include a constriction at the top of the mold that will promote rapid local solidification at the centerline of the mold cavity. This can prevent interconnected pore formation at the centerline and allow compaction of the as-cast sputter target by hot isostatic pressing the target for 1 hour at 2100 ° f, 29KSI, if necessary. The hot isostatically pressed sputter target exhibits a fine-grained, equiaxed cellular grain structure.

Although certain embodiments of the present invention have been described above, it will be appreciated by those skilled in the art that the present invention is not limited to these embodiments, and that modifications and variations can be made to the embodiments without departing from the spirit and scope of the invention.

Claims (13)

1. A method of manufacturing a sputter target comprising the steps of: melting a metallic target material, controlling the temperature of the melted target material in such a way that the melted target material is hardly overheated, introducing the melted target material into a mold having inner walls forming a mold cavity in the shape of the desired target, and solidifying the melted target material by extracting heat from the mold at a rate to solidify the target material to form a sputtering target having a honeycomb-like nondendritic microstructure uniformly throughout the target.

2. The method of claim 1, comprising: prior to introducing the melted target material, the mold is heated to a high enough mold temperature to prevent formation of a large number of columnar grains directly adjacent the inner walls of the mold.

3. The method of claim 1, wherein the temperature of the melted target material is controlled to within 0 to 20 ° f of the melting point of the target material.

4. The method of claim, further comprising: hot isostatic pressing the solidified sputter target.

5. The method of claim 1, wherein heat is extracted at a rate to produce an as-cast sputtering target having an ASTM grain size of 3 or less.

6. The method of claim 1, wherein the mold comprises a ceramic mold, a graphite mold, or a metal mold.

7. The method of claim 1, wherein the temperature of the melted target material is controlled by reducing the power supplied to the induction coil.

8. The method of claim 1, comprising: the target material is solidified into a target shape requiring minimal machining.

9. The method of claim 1, wherein the target material comprises a cobalt-based alloy comprising an alloying element selected from the group consisting of boron, chromium, platinum, tantalum, ruthenium, niobium, copper, vanadium, silicon, silver, gold, iron, aluminum, zirconium, and nickel.

10. A sputtering target comprising a metallic target material having a substantially equiaxed, cellular nondendritic microstructure uniformly throughout the target.

11. The target of claim 8 having an ASTM grain size of 3 or less.

12. The target of claim 8, which is densified by hot isostatic pressing.

13. The target of claim 10, comprising a cobalt-based alloy comprising an alloying element selected from the group consisting of boron, chromium, platinum, tantalum, ruthenium, niobium, copper, vanadium, silicon, silver, gold, iron, aluminum, zirconium, and nickel.