Method for removing redeposited veils from etched platinum

Claims

What is claimed is:

1. A method of plasma-etching a workpiece having a multi-layer structure thereon including a substrate, a platinum layer, an insulative layer over the platinum layer, and a patterned resist layer over the insulative layer, the method comprising:

subjecting the workpiece to a plasma comprising a first etching processing gas environment to remove portions of the insulative layer unprotected by the patterned resist to expose portions of the platinum layer beneath the insulative layer;

subjecting the workpiece to a plasma substantially comprising argon to remove portions of the platinum layer exposed by the removal of portions of the insulative layer; and

subjecting the workpiece to a high density plasma substantially comprising a gas selected from the group consisting of oxygen, chlorine, and mixtures thereof to remove deposited veils.

2. A method as in claim 1 in which the high density plasma to remove deposited veils is maintained at an ion density greater than about 10.sup.9 /cm.sup.3.

3. A method as in claim 2 in which the high density plasma to remove deposited veils is maintained using an inductively coupled plasma source.

4. A method as in claim 2 in which the high density plasma to remove deposited veils is maintained using one or more of a helicon resonance and an electron cyclotron resonance source.

5. A method as in claim 1 in which the high density plasma to remove deposited veils is maintained at an ion density greater than about 10.sup.11 /cm.sup.3.

6. A method as in claim 1 in which the plasma substantially comprising argon removes the exposed platinum layer at an etch rate exceeding 1000 Angstroms per minute.

7. A method as in claim 1 in which the resist layer is removed from the insulative layer by subjecting the workpiece to an oxygen-bearing reactive gas environment.

8. A method as in claim 1 in which the first etching processing gas environment comprises a flourine-bearing gas, and the insulative layer comprises silicon oxide or silicon nitride.

9. A method as in claim 1 in which a protective layer is provided between the platinum layer and the insulative layer.

10. A method as in claim 9 in which the protective layer comprises one or more of titanium or titanium nitride, and a second etching processing gas environment is provided to remove said protective layer and said second etching processing gas environment is selected from the group consisting of Cl.sub.2, BCl.sub.3, Ar, and mixtures thereof.

11. A method as in claim 1 wherein said high density plasma comprises from about 50% by volume to about 100% by volume oxygen and from about 0% by volume to about 50% by volume chlorine.

12. A method as in claim 1 wherein said high density plasma comprises from about 75% by volume to about 85% by volume oxygen and from about 15% by volume to about 25% by volume chlorine.

13. A method for removing veils from a platinum electrode formed during etching of the platinum electrode comprising:

providing a platinum electrode having veils formed on the platinum electrode during etching of the platinum electrode; and

etching said platinum electrode in a high density plasma of an etchant gas to remove said veils from said platinum electrode.

14. A method of claim 13 wherein said etchant gas of said high density plasma comprises oxygen.

15. A method of claim 13 wherein said etchant gas of said high density plasma is selected from the group consisting of chlorine, oxygen, argon and mixtures thereof.

16. The method of claim 13 wherein said etchant gas of said high density plasma consists of oxygen ad chlorine.

17. The method of claim 13 wherein said platinum electrode additionally comprises a mask layer disposed on a selected part of said platinum electrode to selectively protect said platinum electrode during said etching of said platinum electrode.

18. The method of claim 17 wherein said platinum electrode additionally comprises a protective layer disposed on said selected part of said platinum electrode between said mask layer and said platinum electrode.

19. The method of claim 18 additionally comprising removing said mask layer during said etching of said platinum electrode.

20. The method of claim 19 additionally comprising removing said protective layer after removing said mask layer.

21. The method of claim 13 wherein said veils having been formed on said platinum electrode by etching of said platinum electrode in a plasma of an etchant gas comprising argon.

22. The method of claim 13 wherein said high density plasma comprises from about 50% by volume to about 100% by volume oxygen and from about 0% by volume to about 50% by volume chlorine.

23. The method of claim 13 wherein said high density plasma comprises from about 75% by volume to about 85% by volume oxygen and from about 15% by volume to about 25% by volume chlorine.

24. A method for producing a capacitance structure including a platinum electrode comprising:

providing a substrate supporting a platinum electrode layer and at least one mask layer disposed on a selected part of said platinum electrode layer;

etching said platinum electrode layer including employing a plasma of an etchant gas to produce said substrate supporting an etched platinum electrode layer with said at least one mask layer disposed on a selected part of said etched platinum electrode layer; and

overetching said etched platinum electrode layer including employing a high density plasma of an etchant gas to produce a capacitance structure.

25. The method of claim 24 wherein said etched platinum electrode layer produced by said etching includes at least one veil formed thereon; and said overetching removes said at least one veil from said etched platinum electrode layer.

26. The method of claim 24 wherein said etched platinum electrode layer produced by said etching includes at least two veils formed thereon with said mask layer disposed on said selected part of said etched platinum electrode layer between said two veils; and said overetching removes said two redeposited veils from said etched platinum electrode layer.

27. The method of claim 26 additionally comprising removing said at least one mask layer after said overetching of said platinum electrode layer.

28. The method of claim 26 additionally comprising removing said at least one mask layer during said overetching of said platinum electrode layer.

29. The method of claim 24 wherein said etchant gas of said high density plasma comprises oxygen.

30. The method of claim 24 wherein said etchant gas of said high density plasma is selected from the group consisting of chlorine, oxygen and mixtures thereof.

31. The method of claim 24 wherein said etchant gas of said high density plasma consists of oxygen and chlorine.

32. The method of claim 24 wherein said high density plasma comprises from about 50% by volume to about 100% by volume oxygen and from about 0% by volume to about 50% by volume chlorine.

33. The method of claim 32 wherein said etching of said platinum electrode layer includes employing said plasma of said etchant gas comprising argon.

34. The method of claim 24 wherein said high density plasma comprises from about 75% by volume to about 85% by volume oxygen and from about 15% by volume to about 25% by volume chlorine.

35. The method of claim 24 wherein said etching of said platinum electrode layer includes employing said plasma of said etchant gas comprising argon.

36. A method of manufacturing a semiconductor device comprising:

forming a resist layer, an insulation layer and a platinum electrode layer on a substrate having circuit elements formed thereon;

etching a portion of said insulation layer including employing a plasma of an etchant gas to break through and to remove said portion of said insulation layer from said platinum electrode layer to produce said substrate supporting said resist layer, a residual insulation layer, and said platinum electrode layer;

removing said resist layer to produce said substrate supporting said residual insulation layer and said platinum electrode layer;

etching said platinum electrode layer including employing a plasma of an etchant gas to produce said substrate supporting said residual insulation layer disposed on an etched platinum electrode layer having at least one veil formed thereon; and

overetching said etched platinum electrode layer including employing a high density plasma of an etchant gas to remove said veil from said etched platinum electrode layer and produce a semiconductor device.

37. The method of claim 36 additionally comprising removing said residual insulation layer after said overetching of said etched platinum electrode layer.

38. The method of claim 36 additionally comprising removing said residual insulation layer after said overetching of said etched platinum electrode layer.

39. The method of claim 36 wherein said forming additionally comprises disposing a protective layer on said platinum electrode layer between said insulation layer and said platinum electrode layer.

40. The method of claim 36 wherein said etched platinum electrode layer produced by said etching of said platinum electrode layer includes a pair of veils opposedly formed thereon with said residual insulation layer disposed on said etched platinum electrode layer between said pair of veils; and said overetching of said etched platinum electrde layer removes said pair of veils from said etched platinum electrode layer.

41. The method of claim 36 wherein said etchant gas of said high density plasma consists of oxygen.

42. The method of claim 36 wherein said etchant gas of said high density plasma comprises chlorine.

43. The method of claim 36 wherein said etchant gas of said high density plasma consists of oxygen and chlorine.

44. The method of claim 36 wherein said high density plasma comprises from about 50% by volume to about 100% by volume oxygen and from about 0% by volume to about 50% by volume chlorine.

45. The method of claim 44 wherein said etching of said platinum electrode layer includes employing said plasma of said etchant gas comprising argon.

46. The method of claim 36 wherein said high density plasma comprises from about 75% by volume to about 85% by volume oxygen and from about 15% by volume to about 25% by volume chlorine.

47. The method of claim 36 wherein said etching of said platinum electrode layer includes employing said plasma of said etchant gas comprising argon.

48. A method for removing redeposited platinum-containing etch material comprising:

providing a multilayered structure including a platinum layer, an etched mask layer disposed on said platinum layer, and redeposited platinum-containing etch material; and,

contacting at least a portion of said redeposited platinum-containing etch material with a high density plasma of an etchant gas, to remove redeposited platinum-containing etch material.

49. The method of claim 48 wherein said etched mask layer comprises at least one etched sidewall which is in contact with said redeposited platinum-containing etch material.

50. The method of claim 49 additionally comprising etching said platinum layer to produce an etched platinum structure having at least one platinum sidewall supporting a redeposited platinum-containing material, prior to removing said redeposited platinum-containing etch material.

51. The method of claim 50 wherein said redeposited platinum-containing material on said sidewall of said etched mask layer and said redeposited platinum-containing material on said platinum sidewall of said platinum layer comprises at least one veil.

52. The method of claim 51 additionally comprising removing a portion of the etched mask layer during said removing of said redeposited platinum-containing material.

53. The method of claim 51 additionally comprising etching said veil in a high density plasma of an etchant gas to remove said veil.

54. The method of claim 53 wherein said etching of said veil includes etching said veil when said wafer has a temperature ranging from 20.degree. C. to 500.degree. C.

55. The method of claim 53 wherein said etching of said veil includes etching said veil when said wafer has a temperature ranging from 100.degree. C. to 300.degree. C.

56. The method of claim 51 wherein said etchant gas of said high density plasma comprises oxygen.

57. The method of claim 51 wherein said etchant gas of said high density plasma is selected from the group consisting of chorine, oxygen, argon, and mixtures thereof.

58. The method of claim 51 wherein said high density plasma comprises from about 50% by volume to about 100% by volume oxygen and from about 0% by volume to about 50% by volume chlorine.

59. The method of claim 51 wherein said etchant gas of said high density plasma comprises chlorine.

60. The method of claim 49 wherein said redeposited platinum-containing material on said mask sidewall comprises a veil.

61. The method of claim 49 additionally comprising removing a portion of the etched mask layer during said removing of said redeposited platinum-containing material.

62. The method of claim 48 additionally comprising etching said platinum layer to produce an etched platinum structure having at least one platinum sidewall supporting a redeposited platinum-containing material, prior to removing said redeposited platinum-containing etch material.

63. The method of claim 62 additionally comprising removing a portion of the etched mask layer during said removing of said redeposited platinum-containing material.

64. The method of claim 62 wherein said removing of said redeposited platinum-containing material includes etching said redeposited platinum-containing material when said wafer has a temperature ranging from 20.degree. C. to 500.degree. C.

65. The method of claim 62 wherein said removing of said redeposited platinum-containing material includes etching said redeposited platinum-containing material when said wafer has a temperature ranging from 100.degree. C. to 300.degree. C.

66. The method of claim 62 wherein said etchant gas of said high density plasma comprises oxygen.

67. The method of claim 62 wherein said etchant gas of said high density plasma is selected from the group consisting of chlorine, oxygen, argon, and mixtures thereof.

68. The method of claim 62 wherein said high density plasma comprises from about 50% by volume to about 100% by volume oxygen and from about 0% by volume to about 50% by volume chlorine.

69. The method of claim 62 wherein said etchant gas of said high density plasma comprises chlorine.

70. The method of claim 48 wherein said removing of said redeposited platinum-containing material includes etching said redeposited platinum-containing material.

71. The method of claim 48 wherein said removing of said redeposited platinum-containing material includes etching said redeposited platinum-containing material when said wafer has a temperature ranging from 20.degree. C. to 500.degree. C.

72. The method of claim 71 wherein said etchant gas of said high density plasma comprises oxygen.

73. The method of claim 71 wherein said etchant gas of said high density plasma is selected from the group consisting of chlorine, oxygen, argon, and mixtures thereof.

74. The method of claim 71 wherein said high density plasma comprises from about 50% by volume to about 100% by volume oxygen and from about 0% by volume to about 50% by volume chlorine.

75. The method of claim 71 wherein said etchant gas of said high density plasma comprises chlorine.

76. The method of claim 48 wherein said removing of said redeposited platinum-containing material including etching said redeposited platinum-containing material when said wafer has a temperature ranging from 100.degree. C. to 300.degree. C.

77. The method of claim 48 wherein said etchant gas of said high density plasma comprises oxygen.

78. The method of claim 48 wherein said etchant gas of said high density plasma is selected from the group consisting of chlorine, oxygen, argon, and mixtures thereof.

79. The method of claim 48 wherein said etchant gas of said high density plasma consists of oxygen and chlorine.

80. The method of claim 48 wherein said etchant gas of said high density plasma consists of oxygen.

81. The method of claim 48 wherein said high density plasma comprises from about 50% by volume to about 100% by volume oxygen and from about 0% by volume to about 50% by volume chlorine.

82. The method of claim 48 wherein said high density plasma comprises from about 75% by volume to about 85% by volume oxygen and from about 15% by volume to about 25% by volume chlorine.

83. The method of claim 48 wherein said etchant gas of said high density plasma comprises chlorine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to plasma etching of platinum. More specifically, this invention provides a method for plasma etching of platinum and for the subsequent removal of redeposited veils formed during the plasma etching of platinum. The plasma etching is conducted for producing semiconductor integrated circuits containing platinum electrodes.

2. Description of the Prior Art

The implemetation of digital information storage and retrieval is a common application of modern digital electronics. Memory size and access time serve as a measure of progress in computer technology. Quite often storage capacitors are employed as memory array elements. As the state of the art has advanced, small-feature-size high density dynamic random access memory (DRAM) devices require storage capacitors of larger capacitance and high dielectric constant materials. The high dielectric constant materials or ferroelectric materials are made primarily of sintered metal oxide and contain a substantial amount of very reactive oxygen. In the formation of capacitors with such ferroelectric materials or films, the electrodes must be composed of materials with least reactivity to prevent oxidation of the electrodes which would decrease the capacitance of storage capacitors. Therefore, precious metals, such as platinum (Pt), palladium (Pd), etc., are preferred metals used in the manufacture of capacitors for high density DRAM.

Among the possible precious metals for capacitor electrodes, platinum has emerged as an attractive candidate because it is inert to oxidation and is known to have a leakage current (<10.sup.-9 amps/cm.sup.2) lower than other electrodes such as Ru0.sub.2 and poly-Si. Platinum also has a high conductivity.

In the prior art, platinum etching has been conducted by means of isotropic etching, such as wet etching with aqua regia, or by anisotropic etching, such as ion milling with Ar gas or by other means. Because of the nature of isotropic etching, using wet etching with aqua regia causes deteriorated processing accuracy. The grade of precision in isotropic etching is not high enough for fine pattern processing. Therefore, it is difficult to perform submicron patterning of platinum electrodes due to its isotropic property. Furthermore, a problem with ion milling (i.e. anisotropic etching) occurs because the etching speed on platinum, which is to form the electrode, is too slow for mass production.

In order to increase processing accuracy in etching platinum, research and development has been quite active, particularly in the area of etching platinum by means of a dry etching process where etchant gases (e.g., Cl.sub.2, HBr, O.sub.2, etc.) are used. The following prior art is representative of the state of art with respect to etching platinum with a plasma of etching gases.

U.S. Pat. No. 5,492,855 to Matsumoto et al discloses a semiconductor device manufacturing method, wherein an insulation layer, a bottom electrode Pt layer, a dielectric film and a top electrode Pt layer are provided on electrode Pt layer, a dielectric film and a top electrode Pt layer are provided on top of a substrate having already-completed circuit elements and wiring, and then, a capacitor is formed by selectively dry etching the bottom electrode Pt layer after selectively dry etching the top electrode Pt layer and the dielectric film. The manufacturing method uses a gas containing an S component as etching gas for Pt etching, or an etching gas containing S component as an additive gas; and also it implants S into the Pt layer before the Pt dry etching process by means of ion implantation to compose a S and Pt compound, and then dry etches the Pt compound thus composed.

U.S. Pat. No. 5,527,729 to Matsumoto et al discloses process steps to form on a substrate in which circuit elements and wirings, etc., are already shaped, an insulation layer, a first metal layer, a dielectric film and a second metal layer. A top electrode and a capacitance film are formed by dry etching the second metal layer and the dielectric film. A bottom electrode is formed by dry etching the first metal layer. The etching gas for dry etching the second metal layer is a mixed gas containing hydrogen hialide (e.g. HBr) and oxygen, having a ratio of oxygen against the total of hydrogen halide and oxygen set at about 10%-35%. The etching gas is also taught as a gas containing hydrocarbon, such as chloroform. Matsumoto et al employs a silicon oxide layer as the insulation layer on the substrate, and a platinum layer or palladium layer as the first and second metal layers. Dry etching of the second metal layer and dielectric film is conducted in a low pressure region not higher than about 5 Pa, where the etching speed is high. Matsumoto et al further teaches that where a mixed gas of hydrogen halide and oxygen is used as the etching gas, the etching speed on the silicon oxide layer can be made sufficiently low relative to that on the second metal layer made of a platinum layer or a palladium layer; in this way, the excessive etching of the silicon oxide layer underlying the first metal layer is avoided, and damage to the circuit elements and wiring, etc. underneath the silicon oxide layer can be prevented. Furthermore according to Matsumoto et al, the ratio of etching speed of the platinum and dielectric material to the resist can be increased by lowering the etching speed on the resist. Therefore, etching of the platinum and dielectric material may be conducted by using a mask of normal lay-thickness resist (generally speaking, about 1.2 .mu.m to about 2.0 .mu.m thick), instead of using a conventional thick-layer resist (about 3 .mu.m and thicker).

Chou et al in an article entitled "Platinum Metal Etching in a Microwave Oxygen Plasma", J. Appl. Phys. 68 (5), Sep. 1, 1990, pages 2415-2423, discloses a study to understand the etching of metals in both plasma and chemical systems. The study found that the etching of platinum foils in an oxygen plasma generated in a flow-type microwave system and that very rapid etching (.about.6 .ANG./s) took place even at low power inputs (200 W). The principal plasma parameters, including oxygen atom concentration, ion concentration, and electron temperature, were measured by Chou et al as a function of distance below the microwave coupler. These were correlated to the rate of foil etching, which decreased with increasing distance from the coupler. On the basis of these correlations Chou et al formulated a simple mechanistic model. The study by Chou et al further found that the etching of platinum in an oxygen plasma jet results from the concomitant action of oxygen atoms and high energy electrons.

Nishikawa et al in an article entitled "Platinum Etching and Plasma Characteristics in RF Magnetron and Electron Cyclotron Resonance Plasmas", Jpn. J. Appl. Phys., Vol. 34 (1995), pages 767-770, discloses a study wherein the properties of platinum etching were investigated using both rf magnetron and electron cyclotron resonance (ECR) plasmas, together with measurement of the plasma parameters (neutral concentration, plasma density, etc.). Nishikawa et al performed experiments in Cl.sub.2 plasmas over a pressure ranging from 0.4 to 50 mTorr. In rf magnetron plasmas, the etch rate of Pt was constant at the substrate temperature of from 20 to 160.degree. C. The etch rate and the plasma electron density increased with gas pressure decreasing from 50 to 5 mTorr. In ECR plasmas for rf power of 300 W, Nishikawa et al found that the etch rate of Pt was almost constant (.about.100 nm/min) with gas pressure decreasing from 5 to 0.4 mTorr, while the plasma electron density gradually increased with decreasing gas pressure. The study by Nishikawa et al discusses these experimental results with respect to the relationship between the etch yield and the ratio of neutral Cl.sub.2 flux and ion flux incident on the substrate.

Yokoyama et al in an article entitled "High-Temperature Etching of PZT/Pt/TiN Structure by High-Density ECR Plasma", Jpn. J. Appl. Phys., Vol. 34 (1995), pages 767-770, discloses a study wherein submicron patterning technologies for the PZT/Pt/TiN/Ti structure with a-spin on glass (SOG) mask are demonstrated using a high-density electron cyclotron resonance (ECR) plasma and a high substrate temperature above 300.degree. C. A 30%-Cl.sub.2 /Ar gas was used to etch a lead zirconate titanate (PZT) film. No deposits remained, which resulted in an etched profile of more than 80.degree.. A 40%-O.sub.2 /Cl.sub.2 gas was used to etch a Pt film. The etching was completely stopped at the Ti layer. 30-nm-thick deposits remained on the sidewall. They were removed by Yokoyama et al after dipping in hydrochloric acid. The etched profile of a Pt film was more than 80.degree.. The Ti/TiN/Ti layer was etched with pure Cl.sub.2 gas. The size shift from the SOG mask was less than 0.1 .mu.m. Yokoyama et al did not detect any interdiffusion between SOG and PZT by transmission electron microscopy and energy dispersive x-ray spectroscopy (TEM-EDX) analysis.

Yoo et al in an article entitled "Control of Etch Slope During Etching of Pt in Ar/Cl.sub.2 /O.sub.2 Plasmas", Jpn. J. Appl. Phys., Vol. 35 (1996), pages 2501-2504, teaches etching of Pt patterns of the 0.25 .mu.m design rule at 20.degree. C. using a magnetically enhanced reactive ion etcher (MERIE). Yoo et al found that a major problem of etching with a MERIE was the redeposition of the etch products onto the pattern sidewall, making it difficult to reduce the pattern size. In both cases separately using a photoresist mask and an oxide mask, the redeposits of the etch products onto the sidewall were reduced by the addition of Cl.sub.2 to Ar, although the etched slope was lowered to 45.degree.. The redeposits were removed by an HCl cleaning process.

Kotecki in an article entitled "High-K Dielectric Materials for DRAM Capacitors", Semiconductor International, November 1996, pages 109-116, the potential advantages of incorporating high-dielectric materials into a storage capacitor of a dynamic random access memory (DRAM) are described and the requirements of the high dielectric layer are reviewed as they relate to use in a simple stack capacitor structure suitable for the gigabit generation. Kotecki teaches that when considering the use of high-dielectric materials in a stack capacitor structure, the following issues need to be addressed: electrode patterning, high-dielectric material/barrier interaction, electrode/high-dielectric material interaction, surface roughness (e.g. hilocking, etc.), step coverage, high-dielectric material uniformity (e.g. thickness, composition, grain size/orientation, etc.), and barrier (e.g. O.sub.2 and Si diffusion, conductivity, contact resistance and interactions, etc.). Various materials and combinations of materials were studied by Kotecki for use with perovskite dielectrics including the noble metals (i.e. Pt, Ir, Pd) and conductive metal oxides (i.e. IrO.sub.2 and RuO.sub.2). The work function of these materials, their ability to be patterned by dry etching, the stability of the surface with regards to surface roughening and their suitability in a semiconductor fabricator are listed by Kotecki in the following Table I:

TABLE I Comparison of the Properties of Various Electrode Materials Suitable for Use with Perovskite Dielectrics Material Work Dry Surface Deposition Selection Function Etch Stability Method Pt 5.6-5.7 difficult potential sputtering problem Ru 4.7 easy/ potential sputtering dangerous problem RuO.sub.2 /Ru easy/ good reactive dangerous sputtering Ir 5.0-5.8 difficult good sputtering IrO.sub.2 /Ir difficult good reactive sputtering Pd 5.1-5.6 difficult ? sputtering

Kotecki further teaches in the article entitled "High-K Dielectric Materials for DRAM Capacitors" that one of the major problems which needs to be overcome with respect to the manufacturing of DRAM chips using capacitors is the problem of electrode patterning. There are minimal volatile species produced during the dry etching of the noble metal electrodes such as Pt, Ru, Pd and Ir. Since the etch mechanism is primarily by physical sputtering, even during a RIE process, fences are typica