Copper film containing tungsten carbide for improving electrical conductivity, thermal stability and hardness properties and a manufacturing method for the copper film
A copper film containing tungsten carbide is adapted to be formed on a substrate and contains a copper layer having tungsten carbide in atomic ratios of 0.4 to 12.2% in tungsten and of 0.7 to 7.4% in carbon. To achieve the copper film, a manufacturing method has the acts of: adjusting a non-overlapping area between a copper target and a tungsten carbide target; co-sputtering the copper target and the tungsten carbide target to form the copper film containing tungsten carbide; and optionally annealing the copper film containing tungsten carbide to change the microstructure of the copper film. By sputtering the tungsten carbide with copper, the achieved copper film has excellent electrical conductivity, thermal stability at high temperatures and hardness properties.
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1. Field of the Invention
The present invention relates to a copper film, and more particularly to a copper film that contains tungsten carbide to improve electrical conductivity, thermal stability and hardness properties. A manufacturing method for the copper film is also disclosed in the present invention.
2. Description of Related Art
Because cupric materials such as copper and cupric alloy have excellent electrical conductivity, thermal conductivity, and mechanical properties at room temperature, these cupric materials are commonly used in the semiconductor field. However, these cupric materials have poor mechanical properties at high temperatures and thus are used at low operational temperatures, whereby the cupric materials can not be used efficiently and temperature limitation restricts further applications of these cupric materials.
Additionally, the cupric materials substitute aluminum to construct conductive layers in semiconducting elements because of their excellent electrical conductivity, high resistance for electromigration, long durability and good stability. Therefore, the cupric materials have more utilization such as forming copper films in semiconducting elements. However, the copper films still have some drawbacks such as forming oxidation membrane that reduces electrical conductivity or having poor attachment to the semiconducting elements, which make the copper film incomplete in use. If the copper film is added with other metal elements, electrical conductivity of the copper film is reduced and hardness of the copper film is increased.
Therefore, some references disclose adding insoluble elements (such as carbon) or pure metals into the copper film instead of the metal elements and this may overcome the drawbacks. These references are:
J. P. Chu, C. H. Chung, P. Y. Lee, J. M. Rigsbee, and J. Y. Wang, “Microstructure and Properties of Cu—C Pseudoalloy Films Prepared by Sputter Deposition”, Metallurgical and Materials Transactions A, 29A, pp. 647-658, (1998);
J. P. Chu and T. N. Lin, “Deposition, Microstructure and Properties of Sputtered Copper Film Containing Insoluble Molybdenum” in Journal of Applied Physics, 85,6462-6469(1999);
C. H. Lin, J. P. Chu, T. Mahalingam, T. N. Lin and S. F. Wang, 2003/06, “Thermal Stability of Sputtered Copper Films Containing Dilute Insoluble Tungsten: A Thermal Annealing Study” in Journal of Materials Research, Vol 18, o. 6, P. 1429-1434;
Zhang S L, Harper J M E and D'Heurle F M, “High Conductivity Copper-boron Alloys Obtained by Low Temperature Annealing”, in Journal of Electronic Materials, 30, L1, (2001); and
Invention Patent application No 88113088 (certification No. 152100), “Forming Copper Film Containing Tantalum by Sputter Method to Increase Hardness and Electrical Conductivity of the Copper Film”.
However, the copper films with an additional layer made of the insoluble elements in the foregoing references have rough crystallites because boundaries between crystallites are empty. Moreover the diffusion rates of copper atoms are high.
The present invention has arisen to mitigate or obviate the disadvantages of the conventional copper films and conventional manufacturing methods for forming the copper films.
SUMMARY OF THE INVENTIONA first main objective of the present invention is to provide a copper film that contains tungsten carbide whereby the copper film has fine crystallites, excellent electrical conductivity, high hardness, and good stability at high temperature.
A second main objective of the present invention is to provide a manufacturing method that particularly forms the copper film containing tungsten carbide.
To achieve the foregoing first main objective, the copper film contains tungsten carbide adapted to be formed on a substrate and comprises:
a copper layer containing tungsten carbide in atomic ratios of 0.4 to 12.2% in tungsten and of 0.7 to 7.4% in carbon, the atomic rations are on a basis of total atoms in the copper film.
To achieve the foregoing second main objective, the copper film having the tungsten carbide layer is made by the method having acts of:
adjusting a non-overlapping area between a copper target and a tungsten carbide target; and
co-sputtering the copper target and the tungsten carbide target to form the copper film containing tungsten carbide, wherein sputtering power is 100W and sputtering pressure is 1×10−2 to 10×10−3;
by adjusting the non-overlapping area between the copper target and the tungsten carbide target, ratios of tungsten carbide in the copper film are regularized.
In this present invention, adding the tungsten carbide that is insoluble to copper makes the copper film have excellent electrical conductivity, thermal stability and hardness properties at high temperature. Moreover, by adjusting the non-overlapping area of the copper target and the tungsten carbide target, tungsten carbide is conveniently adjusted in different ratios to achieve various embodiments of the copper films.
Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 6(a) to 6(d) are SEM photos in cross-sectional views of four copper films having different contents of tungsten carbide, wherein the four copper films respectively represent (a) pure copper film, (b) Cu(W1.0C1.5), (c) Cu(W2.1C2.1) and (d) Cu(W12.2C7.4);
FIGS. 7(a) to 7(b) are SEM photos in planar views of two copper films having different contents of tungsten carbide, wherein the two copper films are respectively represented as (a) pure copper film and (b) Cu(W12.2C7.4);
FIGS. 8(a) to 8(b) are two SEM photos in cross-sectional views of a pure copper film and a copper film of Cu(W12.2C7.4) both are annealed at different temperatures for a one-hour duration, wherein (a) represents the copper films annealed at 200° C. and (b) represents the copper films annealed at 400° C.;
FIGS. 9(a) to 9(b) are two SEM photos in planar views of a pure copper film and a copper film of Cu(W12.2C7.4) both are annealed at different temperatures for a one-hour duration, wherein (a) represents the copper films annealed at 530° C. and (b) represents the copper films annealed at 650° C.;
FIGS. 13(a) to (c) are cross-sectional FIB micrographs taken from copper films on Si substrates after annealing for 1 hour: (a) pure Cu, at 400° C. (b) Cu(W0.4C0.7) at 400° C., and (c) Cu(W0.4C0.7) at 530° C., wherein arrows in (c) indicate formations of Cu4Si at interfaces of the copper film and the Si substrate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTA copper film containing tungsten carbide in accordance with the present invention is adapted to be formed on a substrate and comprises a copper layer in the form of a supersaturated solid solution and tungsten carbide present inside the copper layer that is in structure of nano-crystallite. In the copper film, tungsten carbide is represented in atomic ratios of 0.4 to 12.2% in tungsten and of 0.7 to 7.4% in carbon.
In the copper film, carbon atoms of the tungsten carbide fill in boundaries between metallic materials to make the crystallites minimized. Moreover, tungsten carbide has a high melting point to efficiently reduce lattice diffusion of copper atoms. Therefore, the tungsten carbide is better than the conventional insoluble elements (such as carbon) or pure metal elements.
To achieve the copper film containing a certain ratio of tungsten carbide, a manufacturing method for the copper film is developed and comprises the acts of: adjusting a non-overlapping area between a copper target and a tungsten carbide target; co-sputtering the copper target and the tungsten carbide target to form the copper film containing tungsten carbide, wherein sputtering power is 100W and sputtering pressure is 1×10−2 to 10×10−3; and optionally annealing the copper film containing tungsten carbide to change the microstructure of the copper film.
In this manufacturing method, the non-overlapping area is adjusted to reveal parts of the tungsten carbide target. With reference to
The RF magnetron sputter deposition system enables the making of insoluble elements or compounds to synthesize in atom-by-atom growth to form supersaturated solid solution. Therefore, synthesized materials in this system are not limited by phase-equilibrium and particularly have non-equilibrium property and nano-scale microstructure to increase thermal stability and mechanical strength.
Moreover, the copper film is further annealed at different annealing temperatures to change the microstructure of the copper to improve hardness and thermal stability of the copper film. Preferably, the copper film containing tungsten carbide is annealed at an annealing pressure of 1×10−6 to 1×10−7 torr, with a heating speed of 4 to 6° C. per min, at an annealing temperature ranging from 200 to 650° C. for a one-hour duration.
<Qualitative and Quantity Analyses of Tungsten and Carbon in the Copper Layer>
The quantities of tungsten and carbon were detected by an electron probe micro-analyser (EPMA) and respectively shown in FIGS. 3(a) and 3(b) that correspond to Table 1. With reference to
<Mechanical Properties Test for the Copper Film Containing Tungsten Carbide>
Thermal stability at high temperature and the hardness of the copper film are the major subjects in this test. With reference to
Thermal stability of the copper films containing different ratios of tungsten carbide is evaluated in use of depositing copper films deposited on Si substrates and results are shown in XRD patterns in
With regard to ultra-microhardness of the copper film, as shown in
The invention has been described in detail with particular reference to certain preferred embodiments. However, variations and modifications can be effected within the spirit and scope of the invention.
Although the invention has been explained in relation to its preferred embodiment, many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.
Claims
1. A copper film containing tungsten carbide for improving electrical conductivity, thermal stability and hardness properties, the copper film comprising:
- a copper layer in a form of a supersaturated solid solution; and
- tungsten carbide present inside the copper layer in nano-crystallite.
2. The copper film as claimed in claim 1, wherein tungsten carbide is represented as atomic ratios of 0.4 to 12.2% in tungsten and of 0.7 to 7.4% in carbon, the atomic rations are on a basis of total atoms in the copper film.
3. A manufacturing method for forming a copper film containing tungsten carbide as claimed in claim 1, wherein the manufacturing method comprising acts of:
- adjusting a non-overlapping area between a copper target and a tungsten carbide target; and
- co-sputtering the copper target and the tungsten carbide target to form the copper film containing tungsten carbide, wherein sputtering power is 100W and sputtering pressure is 1×10−2 to 10×10−3 torr;
- by adjusting the non-overlapping area of the tungsten carbide target, ratios of tungsten carbide in the copper film are regularized.
4. The method as claimed in claim 3, wherein the sputtering temperature in the sputtering act has a range from 25° C. to 100° C.
5. The method as claimed in claim 3, wherein ratios of the non-overlapping area of the tungsten carbide target to the copper target are selectively preferable 4.0%, 21.3%, 29.3% and 49.9 to obtain the copper film containing tungsten carbide in different ratios.
6. The method as claimed in claim 3, wherein the method further comprising an annealing act after the sputtering act and the annealing acts is of:
- annealing the copper film containing tungsten carbide at an annealing pressure of 1×10−6 to 1×10−7 torr, a heating speed of 4 to 6° C. per min, at an annealing temperature ranging from 200 to 650° C. for one hour duration.
7. The method as claimed in claim 2, wherein an ultra-microhardness of the copper film containing tungsten carbide increases with increment of the tungsten carbide and maximally is 4 times greater than an ultra-microhardness of a pure copper film.
8. The method as claimed in claim 6, wherein an ultra-microhardness of the copper film containing tungsten carbide after annealing is 3 times greater than an ultra-microhardness of a pure copper film.
9. The method as claimed in claim 4, wherein an ultra-microhardness of the copper film containing tungsten carbide after annealing at 650° C. for one-hour duration is 4 times greater than an ultra-microhardness of a pure copper film.
Type: Application
Filed: Oct 20, 2004
Publication Date: Apr 28, 2005
Applicant: (Keelung)
Inventors: Jinn Chu (Keelung), Yung-Yen Hsieh (Miaoli City)
Application Number: 10/969,482