WO1999019102A1

WO1999019102A1 - Sputter targets and methods of making same

Info

Publication number: WO1999019102A1
Application number: PCT/US1998/021852
Authority: WO
Inventors: Eugene Y. Ivanov
Original assignee: Tosoh Smd, Inc.
Priority date: 1997-10-14
Filing date: 1998-10-14
Publication date: 1999-04-22

Abstract

Refractory metal/Si sputter targets and methods of preparing such targets are disclosed. The targets are made via atomization techniques wherein an inert gas stream impinges upon the requisite molten metals to form powder particles. The particles are pressure consolidated into the near net shape desired for a given target configuration. Ti/Si targets are preferred and are characterized by having low oxygen content on the order of about 50-1,000 ppm with an oxygen content of about 100-1,000 ppm being more preferred. These targets also have a grain size distribution wherein substantially all of the grains are less than 20 νm in size. Sputtering of such targets minimizes the amount of harmful particulates formed on the sputter coated substrates.

Description

SPUTTER TARGETS AND METHODS OF MAKING SAME

1. Field of the Invention The present application pertains to methods for forming refractory metal/Si sputter targets and to targets made by such methods.

Background of the Invention Refractory metal suicide materials are useful in formation of electrodes, semiconductor wiring and semiconductor barrier layers. Typically, these materials are sputter coated onto the requisite substrate.

In many cases however, unsatisfactory high oxygen level contents of the refractory metal sputter target result in high particulate sputter processing. In the same light, too little oxygen in the target can result in excessive target brittleness with its own attendant problems.

In order to avoid these problems, it is desirable to control the oxygen content of such targets to acceptable levels. For example, refractory metal suicide sputter targets having oxygen level contents of about 50 - about 1,000 ppm, most preferably about 100 - about 1,000 ppm, are thought desirable from the dual viewpoint of target ductility and lowered particulate emission during sputtering. As used herein, the phrase "refractory metals" shall include those members of the Groups IVB, VB, VIB, and VIII of the periodic table that have high melting points (as defined to be = 1400°C and greater). These are more specifically chosen as follows:

Group VIB W, Mo, Cr

Group IVB Ti, Zr, Hf

Group VB Ta

Group VIII Co, Ni

Specific problems have been encountered when Ti/Si containing targets have been sputtered to provide barrier layer films and the like. As aforementioned, excessively high oxygen content in these targets leads to undesirable particulate emission during sputtering. On the other hand, if the oxygen content of these targets is too low (i.e., less than about 100 ppm), then the target is too brittle and is difficult to machine, handle and insert in the sputtering apparatus. Typically, Ti/Si targets are manufactured from powder blends. The Ti and Si powders are blended at high temperature under vacuum conditions, crushed, milled and then screened. These steps are followed by a hot compaction step to form the target shape.

Such powder formation steps can be used for synthesis of titanium/silicide with the compositions being limited to known brittle intermetallic compounds: Ti₂Si, Ti₅Si₃, TiSi₂ or their combination.

The task of conducting such reactions or processes has not been without problem. The titanium suicides prepared by these powder blending methods contain up to 2000 ppm of oxygen, as a result of the oxidation of solid powder with developed specific surface area. An especially high oxygen concentration can be present in fine (=10 microns) powders.

For most PVD (Physical Vapor Deposition) applications, a fine microstructure (or small grain size of the solid material in the sputter target) is required. Titanium silicides prepared in accordance with conventional powder metallurgy methods as referred to above may have the required microstructure but are subject to the above noted problems associated with high oxygen content. Accordingly, there is a need in the art for a method of forming refractory metal-silicide targets of controlled oxygen content. There is an even more specific need for methods for forming such targets wherein the microstructure or grain size of the solid material in the target is small.

The invention will be further explained in the following description and in the appended drawings.

IN THE DRAWINGS Figure 1 is a graph showing the grain size distribution of a target made in accordance with the invention; and Figure 2 is a graph showing the grain size distribution of a target made in accordance with prior art PM techniques in solid bar form with the Figure 1 grain size distribution superimposed on the graph and shown in open bar form.

DESCRIPTION OF THE INVENTION

Generally, the methods comprise melting the requisite refractory metal and silicon to form a molten liquid blend of the requisite metals. Then the molten metal blend is atomized to form a powder blend. The powder blend is then hot pressure consolidated such as under hot press or HIP conditions to form the desired target shape. After the pressure consolidation step, the target is subjected to a light machining step to impart the desired finished shape to the target.

In some cases, it may be desirable to add oxygen to the powder blend so that the target content in terms of ppm falls between about 50 or 100, preferably 200 - about 1 ,000 ppm oxygen. This may be accomplished, for example by adding requisite amounts of SiO₂ into the molten metal prior to the atomization step.

In order to atomize the refractory metal/Si blend, high purity bars or blocks of the metals are melted in a crucible or the like via arc melting or induction melting. Preferably this melting step is performed under an inert or reducing atmosphere to minimize oxidation of the molten bars. In accordance with conventional techniques, a free falling stream of the molten metals is formed by passing it through a nozzle means. The nozzle forms a free-falling stream of the molten metal which is struck with an inert gas jet, solidifying the molten stream, thereby forming particles of the refractory metal and silicon. The particles are cooled as by falling through a cooling chamber or the like which is also preferably maintained under an inert or reducing atmosphere. The cooled, solidified particles are collected at the exit end of the atomization chamber.

Techniques for atomizing the requisite metals are disclosed for example in U.S. patents, 4,544,404 (Yolton et al.) and 5,213,610 (Yolton et al.). The disclosures of these patents are incorporated by reference herein. Additionally, the metals may be atomized from rods or bars by the use of a plasma gas jet which simultaneously melts and atomizes the metals. One patent directed toward plasma arc atomization, U.S. patent 4,374,075 (Yolton et al. ) is incorporated by reference herein.

The refractory metal/silicide can be blended in a wide range of proportions from about Si trace - 80 wt%/refractory metal 99.99 -20 wt%. The method has demonstrated promise when used to blend Ti/Si in varying proportions. Exemplary proportions include Si-60-40 wt%, Ti 40-60 wt%.

More specifically, targets composed of 50-50 wt% Ti/Si are especially desirable and have shown promise. A Ti Si 2.4 target (42 wt% Ti 58 wt% Si) is presently preferred. After the powdered blend is obtained via atomization, it is hot compacted by hot pressing, hot rolling or HIP technique. Preferably, the blend is

HIPed at a time of from about 15 min - 3 hours at a pressure of about 15 -30k and at a temperature maintained below the eutectic temperature.

Promising results have been shown by HIPing Ti-50 Si blends in an evacuated HIP canister at about 1000- 1300°C, most preferably 1180°C, for a period of about 90 minutes.

The invention will be further described in conjunction with the following example that is included for purposes of illustration and should not in any sense be deemed as limitations on the invention.

EXAMPLE 1

Ti blocks of about 1 cubic inch and Si (3-10 mm.) in about a 1 :1 weight ratio were placed in a copper crucible and were melted in an induction furnace. The liquid melt was sprayed (atomized) in an inert atmosphere (Ar) to form Ti-Si powder. This powder was analyzed by atomic emission spectroscopy and was found to have an oxygen content of 97 ppm.

The powder is then HIPed at a temperature of 1380°C at 250 kg/cm² for a period of about 2 hours to form the desired sputter target shape. The thus

HIPed Ti-Si target is machined into the desired final shape and is used as a sputter target in cathodic sputter coating methods. The target is expected to result in effective magnetron sputtering while resulting in reduced particulate emissions. EXAMPLE 2 Ti Si₂₄ (atomized)

Ti blocks and Si blocks in a wt ratio of 41.54% Ti and 58.46% Si were melted in a copper crucible at 1500°C. Ti used was produced by the iodide process and was available from Wah Chang. The Si was purchased from Serac, Milwaukee, Wisconsin. Melting of the blocks resulted in a molten liquid stream that was fed thru a nozzle into a collection box containing an Ar Jet that impinged upon the stream. The droplets from the molten liquid stream crystallized as powder and were collected.

The powder was placed in a HIP canister and HIPPED at 15,000 psi for 3 hours at 1180 °C. The resulting blank was machined into a circular target having a 3" diameter and a thickness of Vβ".

Sputtering Tests

The target made in accordance with Example 2 was compared to a Ti Si₂₄ target that had been prepared by conventional PM techniques, that is, the Ti and Si powders were crushed, milled, and screened to obtain a -100 mesh Ti Si₂₄ powder. HIPing of the powders into the target blank was conducted under the same conditions as those reported above for the atomized target made in Example 2. The microstructures of the targets were measured with the grain sizes of the respective targets shown in Figures 1 and 2 respectively. Figure 2 also includes the Figure 1 graph superimposed thereon. Here, in Figure 2, the Figure 1 , atomized method, grain size distribution is shown in open bar form with the solid bars used to show the PM formation grain size distribution.

Sputtering of the atomized Ti Si 2.4 (Example 2) target and the PM Ti Si₂₄ target was conducted at a power of 0.160 KW and with a 4μ Argon back fill. Sputter coated wafers were placed on a "Tencor" apparatus to measure particulates. Total particulate counts were found as follows:

Example 2 Comparative

Ti Si₂₄ Ti Si₂₄ atomized PM sample 1 262 1136 sample 2 301 1325 From the above it can be seen that the Example 2 atomized Ti Si₂₄ target results in substantially fewer particulates upon sputtering than the comparative Ti Si target made by conventional PM methods.

In accordance with the disclosed atomization techniques, targets comprising RM/Si are provided wherein RM is a refractory metal as previously defined. RM is present in an amount by weight of about 99.99 - about 20 wt% with the Si present in an amount of about 0.01 - about 80 wt%. The targets have a grain size distribution as shown in Figure 1. That is, substantially all of the grains are less than 20 μm, with most of the grains (i.e. ~ 52%) ranging from about 6.25 - 13.8 μm in size. The average grain size is about 10 μm.

Additionally, the targets in accordance with the invention are further characterized as having a lower oxygen content of less than about 1 ,000 ppm oxygen, with a range of about 50-1,000 ppm being more preferred with the range of about 100-1,000 ppm even more preferred and the range of about 100-500 ppm most preferred.

Upon sputtering of the targets, the formation of undesirable particulates is minimized when compared with the sputter performance of Ti/Si targets made via conventional powder metallurgy techniques.

While the methods described herein and sputter targets made by such methods have been described above in conjunction with certain specific forms and modifications thereof, it will be appreciated that a wide variety of other modifications can be made without departing from the spirit and scope of the invention as defined in the appended claims. Also as used herein, reference to a metal element shall also be construed to include alloyed forms of that particular element.

Claims

-CLAIMS-

1. Method of making a refractory metal/Si sputter target comprising: a) melting a refractory metal and Si to form molten refractory metal and molten Si; b) atomizing said molten refractory metal and said molten Si to form powder; c) pressure consolidating said powder into a desired shape.

2. Method as recited in claim 1 further comprising d) forming said desired shape into a final shape useful as a sputter target.

3. Method as recited in claim 2 wherein said forming d) comprises machining.

4. Method as recited in claim 1 wherein said refractory metal is an element selected from Groups IVB, VB, VIB, and VII of the periodic table having a melting point of about 1400┬░C and greater.

5. Method as recited in claim 4 wherein said refractory metal is W, Mo, Cr, Ti, Zr, Hf, Ta, Co or Ni.

6. Method as recited in claim 4 wherein said refractory metal is present in said step a) in an amount by weight of 99.99 - 20 wt% and said Si is present in an amount by weight of about 00.01 - 80 wt%.

7. Method as recited in claim 6 wherein said atomizing comprises impinging said molten refractory metal and said molten Si with a stream of an inert gas.

8. Method as recited in claim 7 wherein said inert gas is Ar.

9. Method as recited in claim 7 wherein said atomizing further includes cooling said molten refractory metal and said molten Si.

10. Method as recited in claim 6 wherein said step c) comprises hot pressing.

11. Method as recited in claim 6 wherein said step c) comprises hot isostatic pressing.

12. Method as recited in claim 11 wherein said hot isostatic pressing comprises pressing said powders at a pressure of 15-30 K psi at a temperature of about 1000-1300 ┬░C for a period of about 15 min. - 3 hours.

13. Method of forming a Ti/Si sputter target comprising : a) providing Ti and Si in a weight amount of about 99.99 - 20 wt% Ti and about 0.01 - 80 wt% Si, with the foregoing percentage equaling about 100 wt%; b) melting said Ti and Si to form a molten liquid stream; c) atomizing said molten liquid stream to form powdered particles; and d) pressure consolidating said powdered particles to form a desired shape.

14. Method as recited in claim 13 wherein said Ti and Si are provided in a weight % of about 50 wt% Ti and 50 wt% Si.

15. Method as recited in claim 13 wherein said Ti is provided in an amount of about 42 wt% and said Si is provided in an amount of about 58 wt%.

16. Method as recited in claim 13 wherein said step c) comprises HIPing said powdered particles at a pressure of about 15,000-30,000 psi at a temperature of about 1000-1300┬░C for a period of about 15 min. to about 3 hours.

17. Method as recited in claim 16 wherein said HIPing occurs at about 1180┬░C.

18. Method as recited in claim 13 wherein said atomizing comprises impinging said molten liquid stream with a stream of an inert gas.

19. Method as recited in claim 13 wherein said inert gas comprises Ar.

20. Method as recited in claim 19 wherein said atomizing further includes cooling said molten liquid stream.

21. Sputter target made by the process of any of the claims 1 -20.

22. Sputter target comprising a refractory metal and Si, said refractory metal present in an amount of about 99.99 wt% - about 20 wt%, said Si present in an amount of about 0.01 wt% - about 80 wt%, with the foregoing weight percentages adding up to about 100 wt%, said target having a low oxygen content of about 100- 1,000 ppm oxygen.

23. Sputter target as recited in claim 22 wherein said refractory metal is an element selected from Groups IVB, VB, VIB, and VII of the periodic table and has a melting point of about 1400┬░C.

24. Sputter target as recited in claim 22 wherein said refractory metal is selected from the group consisting of W, Mo, Cr, Ti, Zr, Hf, Ta, Co, or Ni.

25. Sputter target as recited in claim 23 wherein said refractory metal is Ti.

26. Sputter target as recited in claim 25 wherein said oxygen content is from about 200-1,000 ppm.

27. Sputter target as recited in claim 25 wherein said oxygen content is about 100-500 ppm.

28. Sputter target comprising a refractory metal and Si, said refractory metal present in an amount of about 99.99 wt% - about 20 wt%, said Si present in an amount of about 0.01 wt% - about 80 wt%, with the foregoing weight percentages adding up to about 100 wt%, said target having a low oxygen content of about 50- 1,000 ppm.

29. Sputter target comprising a refractory metal and Si, said refractory metal present in an amount of about 99.99 wt% - about 20 wt%, said Si present in an amount of about 0.01 wt% - about 80 wt%, with the foregoing weight percentages adding up to about 100 wt%, said target having a low oxygen content of less than about 1 ,000 ppm oxygen.

30. Sputter target as recited in claim 29 wherein said refractory metal is an element selected from Groups IVB, VB, VIB, and VII of the periodic table and has a melting point of about 1400┬░C.

31. Sputter target as recited in claim 29 wherein said refractory metal is selected from the group consisting of W, Mo, Cr, Ti, Zr, Hf, Ta, Co, or Ni.

32. Sputter target as recited in claim 30 wherein said refractory metal is Ti.

33. Sputter target comprising Ti and Si present in an amount of about 50 wt% Ti and about 50 wt% Si, said target having an oxygen content of about 100- 1,000 ppm.

34. Sputter target comprising Ti Si₂₄, said target having an oxygen content of about 100-1,000 ppm.

35. Sputter target comprising TI Si₂₄, said target having an oxygen content of about 50 - 1,000 ppm.

36. Sputter target comprising Ti and Si present in an amount by weight of about 40-60 wt % Ti and 60-40 wt% Si, said target having an oxygen content of about 100-1,000 ppm.

37. Sputter target comprising Ti and Si present in an amount by weight of about 40-60 wt% Si, said target having an oxygen content of about 50-1,000 ppm.

38. Sputter target comprising a refractory metal and Si, said refractory metal present in an amount of about 99.99 wt% - about 20 wt%, said Si present in an amount of about 0.01 - 80 wt%, with the foregoing weight percentages adding up to about 100 wt%, said target having a grain size distribution substantially as shown in Figure 1.

39. Sputter target as recited in claim 38 having an oxygen content of about 100-1,000 ppm.

40. Sputter target comprising a refractory metal and Si, said refractory metal present in an amount of about 99.99 wt% - 20 wt%, said Si present in an amount of about 0.01 - 80 wt%, with the foregoing weight percentages adding up to about 100 wt%, said target having a grain size distribution wherein substantially all of said grains are less than about 20 ╬╝m.

41. Sputter target as recited in claim 40 wherein most of said grains range from about 6.25 - 13.8 ╬╝m in size.

42. Sputter target as recited in claim 40 wherein the average grain size is about 10 ╬╝m.

43. Sputter target as recited in claims 40, 41, or 42 having an oxygen content of about 100-1,000 ppm.

44. Sputter target as recited in claims 40, 41, or 42 having an oxygen content of about 50-1,000 ppm.

45. Sputter target comprising Ti and Si wherein said Ti is present in an amount of about 99.99 wt% - 20 wt%, and said Si is present in an amount of about 00.01 wt% - about 80 wt%, said target having a grain size distribution substantially as shown in Figure 1.

46. Sputter target as recited in claim 45 having the empirical formula Ti Si₂₄.

47. Sputter target as recited in claims 45 or 46 having an oxygen content of about 100- 1,000 ppm.

48. Sputter target as recited in claims 45 or 46 having an oxygen content of about 50-1,000 ppm.

49. Sputter target comprising Ti and Si wherein said Ti is present in an amount of about 99.99 wt% - 20 wt% and said Si is present in an amount of about 0.01 - 80 wt%, said target having a grain size distribution wherein substantially all of the grains are less than about 20 ╬╝m.

50. Sputter target as recited in claim 49 wherein most of the grains range from about 6.25 - 13.8 ╬╝m in size.

51. Sputter target as recited in claim 49 wherein the average grain size is about 10 ╬╝m.

52. Sputter target as recited in claim 49, 50, or 51 wherein said Ti is present in an amount of about 40-60 wt% and said Si is present in an amount of about 60-40 wt%.

53. Sputter target as recited in claim 49, 50, 51, or 52 wherein said Ti is present in an amount of about 50 wt%.

54. Sputter target as recited in claim 49, 50, 51 , 52 or 53 having an empirical formula Ti Si₂₄.

55. Sputter target as recited in claims 49, 50, 51 , 52, 53, or 54 having an oxygen content of about 100-1,000 ppm.

56. Sputter target as recited in claims 49, 50, 51 , 52, 53, or 54 having an oxygen content of about 50-1,000 ppm.