GB2145539A - Optical preparation of molybdenum surfaces - Google Patents

Optical preparation of molybdenum surfaces Download PDF

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Publication number
GB2145539A
GB2145539A GB08416974A GB8416974A GB2145539A GB 2145539 A GB2145539 A GB 2145539A GB 08416974 A GB08416974 A GB 08416974A GB 8416974 A GB8416974 A GB 8416974A GB 2145539 A GB2145539 A GB 2145539A
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GB
United Kingdom
Prior art keywords
layer
molybdenum
nitride
molybdenum nitride
angstroms
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB08416974A
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GB2145539B (en
GB8416974D0 (en
Inventor
Manjin Jerome Kim
Dale Marius Brown
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General Electric Co
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General Electric Co
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Filing date
Publication date
Application filed by General Electric Co filed Critical General Electric Co
Publication of GB8416974D0 publication Critical patent/GB8416974D0/en
Publication of GB2145539A publication Critical patent/GB2145539A/en
Application granted granted Critical
Publication of GB2145539B publication Critical patent/GB2145539B/en
Expired legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/004—Photosensitive materials
    • G03F7/09—Photosensitive materials characterised by structural details, e.g. supports, auxiliary layers
    • G03F7/091—Photosensitive materials characterised by structural details, e.g. supports, auxiliary layers characterised by antireflection means or light filtering or absorbing means, e.g. anti-halation, contrast enhancement
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/027—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34
    • H01L21/0271—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising organic layers
    • H01L21/0273—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising organic layers characterised by the treatment of photoresist layers
    • H01L21/0274—Photolithographic processes
    • H01L21/0276—Photolithographic processes using an anti-reflective coating
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02107—Forming insulating materials on a substrate
    • H01L21/02109—Forming insulating materials on a substrate characterised by the type of layer, e.g. type of material, porous/non-porous, pre-cursors, mixtures or laminates
    • H01L21/02112—Forming insulating materials on a substrate characterised by the type of layer, e.g. type of material, porous/non-porous, pre-cursors, mixtures or laminates characterised by the material of the layer
    • H01L21/02172—Forming insulating materials on a substrate characterised by the type of layer, e.g. type of material, porous/non-porous, pre-cursors, mixtures or laminates characterised by the material of the layer the material containing at least one metal element, e.g. metal oxides, metal nitrides, metal oxynitrides or metal carbides
    • H01L21/02175—Forming insulating materials on a substrate characterised by the type of layer, e.g. type of material, porous/non-porous, pre-cursors, mixtures or laminates characterised by the material of the layer the material containing at least one metal element, e.g. metal oxides, metal nitrides, metal oxynitrides or metal carbides characterised by the metal
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02107—Forming insulating materials on a substrate
    • H01L21/02225—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer
    • H01L21/02227—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a process other than a deposition process
    • H01L21/02247—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a process other than a deposition process formation by nitridation, e.g. nitridation of the substrate

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Architecture (AREA)
  • Structural Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Exposure Of Semiconductors, Excluding Electron Or Ion Beam Exposure (AREA)
  • Photosensitive Polymer And Photoresist Processing (AREA)
  • Internal Circuitry In Semiconductor Integrated Circuit Devices (AREA)

Abstract

A layer of molybdenum nitride is formed on a layer of molybdenum prior to the deposition of a layer of photosensitive material thereon to reduce reflections from the layer of molybdenum into the layer of photosensitive material.

Description

SPECIFICATION Optical preparation of molybdenum surafaces The present invention relates, in general, to the optical preparation of molybdenum surfaces, and in particular to the preparation of integrated circuit wafers which include a molybdenum layer on which photosensitive material is deposited for photolithographic patterning.
Metal layers, such as molybdenum, are generally applied to an integrated circuit near the end of the fabrication process. The surface of the wafer on which the integrated circuit is formed is generally not planar at this point in the process and is often characterised by sharp steps. When patterning of the metal layer is done by optical lithographic techniques, the high reflectivity of the metal layer and the presence of steps in the substrate result in nonuniform exposure of the photoresist and hence result in irregularity of the pattern produced therein. Thus, line widths of the pattern etched in the metal layer using the patterned photoresist would be nonuniform in the vicinity of the steps.Line widths of a pattern in the metal layer overlying planar portions of the substrate would also be nonuniform as reflections produce standing waves of radiation resulting in nonuniform exposure of the photoresist.
In accordance with the present invention there is provided a method of preparing a layer of molybdenum for optical transference of a pattern thereto from a mask imprinted with the pattern, the method comprising: forming a layer of molybdenum nitride on the layer of molybdenum to reduce reflections from the layer of molybdenum; and depositing a layer of photosensitive material on the layer of molybdenum nitride.
The invention accordingly provides a method for obtaining substantially uniform exposure of a photosensitive layer overlying the reflective surface of a layer of molybdenum in an integrated circuit wafer. It achieves this by minimising the adverse effect of the reflective surface in a simple manner compatible with existing processes for the fabrication of integrated circuits.
In one embodiment of the invention the layer of molybdenum is exposed to vapours of ammonia at a temperature and for a time sufficient to form the layer of molybdenum nitride.
In the accompanying drawings, by way of example only:~ Figure 1 shows graphs of the relative reflection from layers of molybdenum nitride of various thicknesses on a layer of molybdenum as compared to the reflection from an aluminum surface as a function of wavelength. The graphs also show the relative reflection from layers of sputtered molybdenum and annealed molybdenum as compared to the reflection from an aluminum surface as a function of wavelength.
Figure 2 is a cross sectional view of a structure useful in describing an embodiment of the present invention.
The graphs of Fig. 1 compare the reflection of light from a molybdenum surface covered with various thicknesses of molybdenum nitride with the reflection from a bare aluminum surface as a function of wavelength. Graph 11 was obtained by taking a wafer of silicon on which had been sputter deposited a layer of molybdenum 3000 Angstroms thick and measuring reflections at each of successive wavelengths in the range from 200 to 400 nanometers obtained from the surface thereof and comparing the reflections at corresponding wavelengths from the surface of a reference aluminum plane.Graph 12 was obtained by taking a wafer of silicon on which had been sputter deposited a layer of molybdenum 3000 Angstroms thick and subsequently annealed at 1000 C for 30 minutes and measuring reflections at each of successive wavelengths in the range from 200 to 400 nanometers obtained from the surface thereof and comparing the reflections at corresponding wavelengths from the surface of a reference aluminum plane. Graph 13 was obtained utilizing a wafer of silicon on which had been sputter deposited a layer of molybdenum on which, in turn, a layer of molybdenum nitride (Mo2N) 400 Angstroms thick had been grown.The layer of molybdenum nitride was grown by placing the substrate with the layer of molybdenum thereon in a horizontal open tube furnace in which a flow stream of ammonia and nitrogen in the ratio of 10% by volume of ammonia and the remainder of nitrogen flowing at a rate of 2 liters per minute was established. The substrate was moved into the zone of the furnace in which a temperature of about 500 C was provided.
The substrate was exposed to the flow of ammonia and nitrogen in the furnace for a period of 10 minutes after which it was removed from the furnace. A layer of molybdenum nitride about 400 Angstroms thick was formed during this time overlying and adherent to the unreacted portion of the layer of molybdenum completely covering the top of the layer of molybdenum. The aforementioned method of forming molybdenum nitride on a layer of molybdenum is described for example, in our U.S. patent application 362,682, filed March 29, 1982. Reflection from the surface of the layer of molybdenum nitride 400 Angstroms thick was compared with reflections from the surface of a reference aluminum plane for each of successive wavelengths.Graphs 14, 15, 16 and 17 show relative reflections for wafers or substrates of molybdenum on which layers of molybdenum nitride 600, 800, 1400 and 2200 Angstroms, respectively, had been grown as compared to reflections from a reference aluminum plane as a function of wavelength. Each of these layers of molybdenum nitride of thickness of 600, 800, 1400 and 2200 Angstroms were grown in 10 minutes on layers of molybdenum by the process described above utilizing furnace temperatures of 550 C, 600 C, 650 C and 700 C, respectively.An examination of graphs 13-17 representing layers of molybdenum nitride (Mo2N) of successively increased thickness on a sputtered molybdenum layer, it is apparent that on average absorption of radiation increases and hence reflection decreases with increasing thickness of molybdenum nitride as compared to reflection from a sputtered molybdenum layer as shown in graph 11, and also as compared to reflections from an annealed layer of molybdenum nitride.
The graphs shown in the figures are for relative reflections from the indicated layers in air. These graphs are approximate for reflections from the indicated layers into a photoresist.
The graphs of Fig. 1 can be readily utilized for obtaining the relative reflection of a particular thickness of molybdenum nitride to be applied or formed on a molybdenum layer to minimize reflections in the patterning thereof.
For example, assume a wavelength of about 250 nanometers is to be used for exposing a photoresist, for example, polymethyl methacrylate which is sensitive to this wavelength, which is to be applied over the layer of molybdenum nitride. From an inspection of the graphs of Fig. 1, it is apparent that graph 16 representing a thickness of molybdenum nitride of 1400 Angstroms on a layer of sputtered molybdenum would reduce reflection to approximately 35% of the reflection from an aluminum surface and accordingly this thickness of molybdenum nitride would be used.
Other graphs such as graphs 13-17 may be experimentally obtained from thicknesses of molybdenum nitride below 400 Angstroms and above 2200 Angstroms and also for values of thickness between the values of the thicknesses shown in the graphs, if desired.
Also, the graphs could be extended to wavelengths below 200 and above 400 nanometers, if desired.
A A particular advantage in using molybdenum nitride, in addition to its desirable property of reducing reflections from a sputtered molybdenum surface to an overlying layer of photoresist, is that it is compatible with subsequent processing of the substrate with the molybdenum pattern thereon. The layer of molybdenum nitride formed on the conductor of molybdenum reduces the passage of implantation and mobile ions therethrough and also reduces the formation of oxides thereon and the erosion of molybdenum by various chemical agents, such as nitric acid and hydrogen peroxide, utilized in the fabrication of integrated circuits utilizing molybdenum conductors. After patterning of the photoresist, a suitable dry etchant is utilized for etching the layers of molybdenum nitride and the layer of molybdenum, such as a mixture of carbon tetrachloride and oxygen.
The layer of molybdenum would be etched by this gaseous mixture at a slightly lower rate than the layer of molybdenum nitride.
If desired, the molybdenum nitride layer may be retained on the layer of molybdenum to provide the protection indicated or it may be removed utilizing a suitable etchant, such as mentioned above, or in the alternative, converted back to molybdenum by exposing the molybdenum nitride to a hydrogen reducing atmosphere at a suitable temperature and for a sufficient period of time as described for example, in our U.S. patent application 489,613, filed April 28 1983.
Reference is now made to Fig. 2 which shows a cross section of a structure 20 useful in describing a specific application of the process of the present invention. A substrate 21 of P-type silicon semiconductor material about 10 mils thick having a resistivity of 10 ohm cms. and having a major surface 22 parallel to the (100) plane of the crystal is provided. The substrate is cleaned and thereafter oxidized at 1000 in dry oxygen to grow a layer 23 of silicon dioxide 1000 Angstroms thick. A layer 24 of molybdenum 3000 Angstroms thick is sputter deposited on the layer of oxide using conventional sputtering apparatus in which a target of molybdenum is provided and inert gas ion bombardment of the target causes molybdenum therefrom to be deposited on the layer 23 of silicon dioxide.
Thereafter, the substrate 21 with the layer 24 of molybdenum thereon is placed in a horizon tal open tube furnace in which a flow stream of ammonia and nitrogen in the ratio of 10% by volume of ammonia and the remainder of nitrogen flowing at a rate of 2 liters per minute is established. The substrate is moved into the zone of the furnace in which the temperature of about 650 is provided. The substrate is exposed to the flow of ammonia and nitrogen in the furnace for a period of 10 minutes after which it is removed from the furnace. A layer 25 of molybdenum nitride about 1400 Angstroms thick is formed during this time overlying and adherent to the unreacted portion of the layer of molybdenum completely covering the top of the layer 24 of molybdenum. The aforementioned method of forming molybdenum nitride on a layer of molybdenum is described in our aforementioned U.S. patent application 362,682. As mentioned above, a layer of molybdenum nitride of this thickness reduces reflection from the molybdenum nitride layer to 35% of the reflection obtained from an aluminum surface at 250 nanometers. Thereafter, a layer 26 of a suitable photoresist is deposited on a layer of molybenum nitride. The photoresist utilized would be a photoresist which is sensitive at a wavelength of 250 nanometers, such as PMMA (polymethyl methacrylate). The substrate 20 with the various layers of materials thereon is then placed in suitable apparatus, such as photolithographic projection or printing apparatus operating at about 250 nanometers to form an image in the photoresist which is then developed.The developed photoresist is utilized for etching a pattern in the layer of molybdenum covered with molybdenum nitride. Etching the pattern is accomplished by utilizing a suitable dry etchant such as a mixture of carbon tetrachloride and oxygen as described above. The photoresist would then be removed. The resultant structure would be subject to further processing depending upon the ultimate structure desired in the integrated circuit.
A particular advantage of utilizing molybdenum nitride on molybdenum as an antireflection layer is that molybdenum nitride could be used to provide protection to the layer of molybdenum as it underwent further processing, as mentioned above. If desired, the molybdenum nitride layer could be removed by reactive ion etching described above. The molybdenum nitride layer could also be reconverted into molybdenum by the reduction of the molybdenum nitride into molybdenum by exposure of the layer of molybdenum nitride to a reducing atmosphere, such as hydrogen, as described in our aforementioned U.S. patent application 489,613.

Claims (7)

1. A method of preparing a layer of molybdenum for optical transference of a pattern thereto from a mask imprinted with the pattern, the method comprising: forming a layer of molybdenum nitride on the layer of molybdenum to reduce reflections from the layer of molybdenum; and depositing a layer of photosensitive material on the layer of molybdenum nitride.
2. The method of Claim 1 in which the layer of molybdenum nitride is formed on the layer of molybdenum by exposing the layer of molybdenum to vapours of ammonia at a temperature and for a time to form the layer of molybdenum nitride.
3. The method of Claim 1 in which the film of molybdenum nitride has the composition of Mo2N.
4. The method of Claim 1 in which the thickness of the layer of molybdenum nitride is in the range from about 400 Angstroms to about 2200 Angstroms.
5. The method of Claim 1 in which the layer of photosensitive material is a layer of a photoresist having a sensitivity to wavelengths of light in the range from about 200 to about 400 Angstroms.
6. A method of preparing a layer of molybdenum substantially as herein described with reference to the accompanying drawings.
7. An integrated circuit wafer having a layer of molybdenum prepared by a method according to any one of the preceding claims.
GB08416974A 1983-08-22 1984-07-04 Optical preparation of molybdenum surfaces Expired GB2145539B (en)

Applications Claiming Priority (1)

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US52509083A 1983-08-22 1983-08-22

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GB2145539A true GB2145539A (en) 1985-03-27
GB2145539B GB2145539B (en) 1986-08-28

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DE (1) DE3428564A1 (en)
GB (1) GB2145539B (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3534600A1 (en) * 1985-09-27 1987-04-02 Siemens Ag Integrated circuit with electric conductor tracks and method for producing it
EP0289174B1 (en) * 1987-04-24 1994-11-09 Advanced Micro Devices, Inc. Antireflection coatings for use in photolithography

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5593225A (en) * 1979-01-10 1980-07-15 Hitachi Ltd Forming method of minute pattern
GB2061615A (en) * 1979-10-25 1981-05-13 Gen Electric Composite conductors for integrated circuits

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GB2145539B (en) 1986-08-28
DE3428564C2 (en) 1987-08-13
DE3428564A1 (en) 1985-03-14
JPS6076736A (en) 1985-05-01
GB8416974D0 (en) 1984-08-08
JPH0367260B2 (en) 1991-10-22

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PCNP Patent ceased through non-payment of renewal fee

Effective date: 19980704