JPH02301907A - Metal circuit and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a metal circuit with high durability and resistance to environments by nitriding the surface of a circuit of copper or a copper alloy. CONSTITUTION:A substrate 6 bearing a metal thin film on which a mask pattern is formed is set in a vacuum container 3, a reaction gas containing nitrogen element is introduced into the container and excited, and the surface of the metal thin film is nitrided by the nitrogen element-containing reaction gas. A sputtering gas is subsequently introduced into the vacuum container 3 and excited and a circuit is formed by sputter-etching the copper nitride formed by nitridation with the excited sputtering gas. After that, nitridation of the circuit is carried out in a way similar to the previous process to form a metal circuit bearing copper nitride on a part of the surface.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to pattern wiring for printed circuit boards, IC5LS
It relates to copper or copper-containing metal wiring, such as fine wiring used in I, etc. or lead wire used in wire bonding, etc., and its manufacturing method, and in particular, improves durability by nitriding the surface, and further improves durability. The present invention relates to a metal wiring with improved adhesion to an insulating material applied to the surface thereof, and a method for manufacturing the same.

(Prior art) As a method for improving the durability of copper or copper alloy wiring containing copper in the prior art, for example, Japanese Patent Application No. 1982-
As described in No. 154042 and Japanese Patent Application No. 62-99843, the surface of the wiring is oxidized to form copper oxide (1) Cu2.
0, or a method of surface treatment with an a-type corrosion inhibitor has been proposed.

Further, methods for etching copper or copper-containing metal thin films are described in Journal Electrochemical Society, 130(8), (1983) pp. 1777 to 1.
Page 779 (J, EleetrOeheIIl.

Soc, 130(8), (1983) PP177
As discussed in No. 7-17791, a halogen-based gas was used.

(Problems to be Solved by the Invention) In the above-mentioned conventional technology, strength deterioration occurs due to the copper (I) oxide Cu 20 changing to copper oxide (II) CuO over time, and the wiring is coated with an insulating film. No consideration is given to the deterioration of the adhesion between the wiring and the insulating material, especially when using thinner or finer metals.
There was a problem with lack of reliability.

In addition, metal materials containing copper have high conductivity and excellent electromigration resistance, and are therefore increasingly being used for wiring in integrated circuits.

However, the above-described active ion etching methods using halogen gases have poor selectivity between the mask material and the underlying material, and also cannot perform strong anisotropic etching according to the dimensions of the mask, making them difficult to use in highly integrated circuits. It could not be used for etching copper or metal thin films containing copper.

(Means for Solving the Problems) In order to solve the above problems, the present invention takes the following measures.

(1) By nitriding at least a portion of the surface of a wiring made of copper or a copper alloy, the wiring is made into a metal wiring having copper nitride on at least a portion of the surface.

(2) introducing a reactive gas containing at least nitrogen atoms into a vacuum container containing wiring made of copper or copper alloy;
By exciting the nitrogen atoms and nitriding the surface of the wiring, a metal wiring having copper nitride on at least a portion of the surface is formed.

(3) A substrate with a mask pattern formed on the metal thin film on the surface is housed in a vacuum container, and a reaction gas containing at least nitrogen atoms is introduced into the vacuum container and excited to cause a reaction containing nitrogen atoms. Nitriding the surface of the metal thin film with gas, then introducing and exciting a sputtering gas into the vacuum chamber, and sputter etching the copper nitride produced by the nitriding with the excited sputtering gas. By forming a wiring and then subjecting the wiring to nitridation according to (2) above, a metal wiring having copper nitride on at least a portion of the surface was formed.

(4) A substrate with a mask pattern formed on the metal thin film on the surface is housed in a vacuum container, and a reaction gas containing at least nitrogen atoms and a sputtering gas are introduced into the vacuum container and excited. Nitriding the surface of a metal thin film with a reactive gas containing nitrogen atoms and the resulting copper nitride.
Sputter etching using the sputtering gas is performed simultaneously to form a wiring, and then the wiring is nitrided according to (2) above to form a metal wiring having copper nitride on at least a portion of the surface. I did it like that.

(Function) According to the configuration described above, the following effects are achieved.

(1) Copper nitride is stronger than pure copper or copper oxide, and has high adhesion with copper at the interface.Furthermore, unlike copper oxide, nitride steel prevents oxygen from permeating, so it has excellent oxidation resistance. can be improved.

Therefore, it becomes possible to provide metal wiring with excellent durability.

(2) Nitrogen atoms in copper nitride strongly bond with oxygen, silicon, carbon, and hydrogen, which are the main components of silicon oxide, polyimide, and the like used as insulating films.

Therefore, when a metal wiring whose surface is nitrided is covered with an insulating film, no tll separation occurs at the interface between the copper nitride and the insulating film, and high reliability can be obtained when used in ICs, LSIs, etc.

(3) During etching, if copper is nitrided to form copper nitride, and then sputter etching is performed using sputtering gas, copper nitride has a low sublimation temperature, so it can be easily sputtered. .

(4) Furthermore, if nitriding using nitrogen gas and sputter etching using sputtering gas are performed simultaneously, sputtering can be performed in a short time and with less side etching.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view of a plasma processing apparatus suitable for manufacturing metal wiring of the present invention, in which a vacuum vessel 3 and a microwave 1 output from an oscillator (not shown) are introduced into the vacuum vessel 3. A waveguide 2 to carry out the reaction, a reaction gas supply pipe 4, an exhaust port 5, a substrate holder 7 on which the substrate 6 is placed, a high frequency power source 8 for applying a bias voltage to the substrate 5, and an electron cyclotron resonance installed at a suitable place in the vacuum container 3. It is constituted by a magnetic field coil 9 that generates a magnetic field sufficient to cause .

[First Example] In this example, a plasma processing apparatus having the above-mentioned configuration is used, and the substrate 6 is a silicon substrate with a molybdenum film formed on the surface, on which copper is deposited to a thickness of 1 μm by sputtering. did.

[Experiment 1] 8750auss was generated in the vacuum container 3 by the magnetic field coil 9.
By generating the above magnetic field, introducing nitrogen gas at 70 ml/win from the reaction gas supply pipe 4, and adjusting the exhaust volume, the pressure inside the vacuum container 3 was set to 0.2 Pa, and the frequency was set to 2.45 G)lz, Microwaves with an output of 300 W were introduced to turn the nitrogen gas into plasma, thereby nitriding the surface of the copper thin film.

The relationship between the reaction time and the film thickness of the nitrided steel at this time is shown by a solid line in FIG.

The results of this experiment show that the surface of the copper thin film is nitrided by plasma treatment with nitrogen.

[Experiment 2] Next, 50 ml/ll of nitrogen gas was supplied from the reaction gas supply pipe 4.
1 inch of hydrogen gas was introduced at the same time, and the pressure inside the vacuum vessel 3 and the microwave conditions were the same as above to nitridize the surface of the copper thin film.

The relationship between the reaction time and the copper nitride film thickness at this time is shown by the broken line in FIG.

Comparing the results of Experiment 1 and Experiment 2, it can be seen that the copper nitridation rate is faster when hydrogen gas, which is a reducing agent, is simultaneously introduced.

[Experiment 3] Next, the durability of the steel material whose surface was nitrided was investigated under the above conditions.

The samples were Samples A and B whose surfaces were nitrided for 20 minutes under the conditions of Experiment 2, and for comparison, the surface of a metal containing copper containing 10% silver was nitrided for 20 minutes using the method of Experiment 1. Sample C made of untreated copper (same in all figures shown below) was used.

Since the durability of steel depends on the depth and thickness of the copper oxide film formed by surface oxidation treatment, an asher device using oxygen was used for the durability test, and a reaction pressure of 100
Microwaves with a frequency of 13.56 GHz and an output of 200 W were used to generate oxygen plasma to oxidize the surface of the sample, and the results were judged based on the thickness of the copper oxide film formed on the surface.

The relationship between the copper oxide film thickness and the asher time at this time is shown in FIG.

From the figure, it can be seen that the nitrided samples A and BSD have significantly better oxidation resistance than the untreated sample C.

It is also clear that samples containing other metals have better oxidation resistance than pure copper.

[Second Embodiment] FIG. 4 is a sectional view of another substrate processing apparatus suitable for manufacturing the metal wiring of the present invention, and the same reference numerals as in FIG. 1 represent the same or equivalent parts.

This device excites gas using light energy from a low-pressure mercury lamp housed in a lamp house 11.

[Experiment 4] In this example, nitrogen gas (N2), a mixed gas of nitrogen gas and hydrogen gas (reducing gas) (N2 + H2), or ammonia gas containing reducing atoms was used as the reaction gas for nitriding. (NH3), reaction pressure 10
The surface of the steel material was nitrided at 0 Pa. FIG. 5 shows the relationship between the reaction time and the copper nitride film thickness.

The results of this experiment show that the copper surface can also be nitrided by photoexciting a gas containing nitrogen atoms.

Furthermore, it can be seen that the nitriding rate is faster when a mixed gas with a reducing gas or a compound gas containing reducing atoms is used than when nitrogen gas is used alone.

[Experiment 5] Figure 6 shows the relationship between oxidation time by ashing and sheet resistance when a sample nitrided to a depth of 200 nm under the above conditions was oxidized by ashing. The experimental results are shown for Sample E, which was nitrided with a mixed gas of nitrogen gas and hydrogen gas, and Sample G, which was nitrided with ammonia gas.

The experimental results show that the nitrided sample has stronger oxidation resistance and maintains high electrical conductivity than the untreated sample.

Note that even if the reaction gas is excited by heating instead of light, the nitriding rate will be somewhat slower;
It was confirmed that copper nitridation is possible.

In addition to the above, as the reaction gas, a mixed gas of ammonia gas and nitrogen gas, a mixed gas of ammonia gas and hydrogen gas, or a mixed gas of ammonia gas, nitrogen gas, and hydrogen gas, etc. may be used. It was confirmed that copper nitridation is also possible.

[Third Example] As a substrate to be processed, silicon nitride was formed on a silicon substrate, copper was deposited on this by 1 μm, and a resist pattern with a thickness of 1 μm was formed on it. We conducted an experiment.

[Experiment 6] Using the plasma processing apparatus shown in FIG. 1, nitrogen gas was introduced at 70 ml/min from the gas supply pipe (H), nitrogen gas was introduced at 50 ml/min, and argon gas was introduced at 2Q arl/min. When introducing a mixed gas with mIn (1
), nitrogen gas 35 ml/min, and argon gas 35 ml/min
When introducing a mixed gas with m1/min (J) and when introducing argon gas at 70 ml/n+in (K
), the etching speed was compared.

The reaction pressure at this time was Q, 2 Pa, the microwave power was 400 W, and the etching rate was measured by varying the RF power applied to the substrate.

FIG. 7 is a diagram showing the relationship between RF application power and etching rate for each reaction gas.

From the results of this experiment, we found that when only argon gas is used as the scorching and irrigating gas, copper is hardly etched or soothed, but without nitriding with nitrogen gas, by inducing a bias potential on the substrate, It can be seen that when the etching effect is added, the copper is etched.

For example, if copper is halogenated by introducing only halogen gas, copper nitride will not be etched easily due to its high sublimation temperature, but if copper nitride is produced by introducing nitrogen gas, copper nitride will be etched. This is because the sublimation temperature of copper halide is sufficiently lower than that of copper halide, so sublimation is easily carried out.

Furthermore, from the results of this experiment, it can be seen that the etching/etching speed becomes faster when the mixing ratio of argon gas is increased. Better,
This is due to the increased sputtering effect.

Note that the gas used for nitriding is not limited to nitrogen gas, and may be ammonia gas containing nitrogen atoms, or may be used in combination with a reducing gas as described above.

[Experiment 7] In Fig. 8, the RF power was 300W, and the above (H), (
1) is a diagram schematically showing the cross-sectional shape when etched under the conditions of (J), 12 is a resist, and 13 is copper.

In this way, increasing the mixing ratio of argon gas reduces damage to the resist and enables highly accurate etching with less side etching.

This is because when heavy argon atoms are included, the energy that acts perpendicularly to the metal wiring becomes greater than when only nitrogen gas is used.

Once the desired wiring has been formed in this manner, the surface of the wiring is nitrided as in the first and second embodiments, whereby a metal wiring with excellent oxidation resistance can be obtained.

In addition, in this example, the nitriding of the wiring material and the sputtering of the nitrided part were described as being performed simultaneously, but as mentioned above, since the sublimation temperature of copper nitride is sufficiently low, the nitrogen gas is Alternatively, the portion to be etched may be nitrided to copper nitride by introducing only a sputtering gas, and then only a sputtering gas may be introduced to sputter the copper nitride.

Furthermore, this etching/sotting method, which involves sputtering after nitriding or without nitriding, is not only applied to forming wiring by etching thin metal films, but also to etching metal thin films made of copper or copper alloys. It can be applied to etching (processing) all sorts of things.

[Fourth Example 1 [Experiment 8] The copper thin film on the surface of the substrate used in the third example was etched using a mixed gas of nitrogen gas and argon gas to form a wiring with a wiring width of 1 μm and a length of 2 m. After removing the resist, the surface was subjected to Experiment 1 (
L) and Experiment 2 (M) were nitrided.

Next, a 2 μm silicon oxide film was deposited on this wiring by CVD method, and then the wiring resistance in a 600°C annealing test and the disconnection rate in a 20°C-200°C heat cycle test (24 cycles/day) were measured. I looked into it.

FIG. 9 is a diagram showing the relationship between annealing time and wiring resistance, and FIG. 10 is a diagram showing the relationship between the number of days of a heat cycle test and wire breakage rate.

From the results of this experiment, the rate of increase in resistance of nitrided wiring is approximately 1/100 of that of untreated wiring, and the rate of disconnection is approximately 30%.
You can see that it is 1/1.

These experimental results show that in devices such as integrated circuits that require the formation of an insulating film such as a silicon oxide film on metal wiring, using copper wiring with a nitrided surface significantly improves reliability. I understand that.

[Fifth Example] In this example, a copper wiring having a width of 0.1 mm and a thickness of 0.1 μm is formed on a substrate coated with polyimide and cured, and its surface is nitrided. At this time, the portion nitrided by the method of Experiment 1 is referred to as Sample P, and the portion nitrided by the method of Experiment 2 is referred to as Sample Q.

[Experiment 9] Polyimide was applied to the sample surface, and on the cured substrate,
The peeling rate and reliability between each sample and polyimide were investigated.

Figure 11 shows the same temperature as in Experiment 8, 20°C-200°.
12 is a diagram showing the relationship between the number of days of the heat cycle test and the peeling rate of C. FIG. 12 is a diagram showing the relationship between the annealing time and the resistance value similar to that in Experiment 8.

From the results of this experiment, it can be seen that the nitrided sample PSQ has higher adhesion to polyimide than the untreated sample C.

This is because the nitrogen atoms in the nitrided shell strongly bond with carbon, oxygen, hydrogen, etc., which are the main components of polyimide.

Furthermore, since the resistance increase rate is small, it can be seen that it is resistant to corrosion by moisture, oxygen, etc. from polyimide, and is resistant to oxidation.

Therefore, it can be seen that durability is improved when a steel material whose surface is nitrided is used as a wiring material for a printed circuit board or a laminated circuit board.

[Sixth Example] [Experiment 10] After wire-bonding an integrated circuit and a lead frame using copper lead wires, the surface of the lead wires was nitrided and the wires were encapsulated in resin, and the durability was investigated.

The nitriding conditions at this time were the methods of Experiment 1 (R) and Experiment 2 (S) described in the first embodiment.

FIG. 13 is a diagram showing the relationship between the test time and the defective rate when the heat cycle test shown in the fourth embodiment was performed on an IC having such a configuration.

From the results of this experiment, it can be seen that the durability of the lead wire is significantly improved by nitriding the surface.

From the above experimental results, it has been found that nitriding the surface of copper or copper-containing metal wiring improves the durability and environmental resistance of the metal material itself. , fine wiring used in LSIs, or bonding wires, the durability thereof is significantly improved.

Furthermore, since the nitrided portion has stronger adhesion with the insulating material, it is possible to improve the reliability of ICs, LSIs, etc. that use an insulating film on the surface of the wiring. become.

Note that in order to improve durability, it is desirable that the thickness of the copper nitride formed on the surface of the metal wiring be 10 nm or more or 1% or more of the thickness of the wiring.

In addition, in the above-described embodiments, the present invention was explained using an example in which electrically conductive wiring is nitrided, but since nitrided steel has excellent oxidation resistance and adhesion with an insulating film,
The present invention can be used for applications other than metal wiring, and has oxidation resistance,
It is obvious that the present invention can be applied to any copper or copper alloy that requires high adhesion to an insulating film.

(Effects of the Invention) As is clear from the above description, the following effects are achieved according to the present invention.

(1) A steel material whose surface is nitrided has excellent durability and environmental resistance, so if it is used as a wiring material, highly reliable metal wiring can be obtained.

(2) Since copper nitride has strong adhesion to the insulating material, the occurrence of peeling between the wiring material and the insulating material is reduced, and highly reliable metal wiring can be obtained.

(3) Since copper nitride prevents the permeation of oxygen, the oxidation resistance of copper wiring can be improved.

(4) After or without nitriding the wiring material
``Sputtering enables high-definition etching in a short time and with less side etching.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a plasma processing apparatus suitable for manufacturing the metal wiring of the present invention. FIG. 2 is a diagram showing the relationship between nitriding reaction time and copper nitride film thickness. FIG. 3 is a diagram showing the relationship between the copper oxide film thickness and the asher time. FIG. 4 is a sectional view of a substrate processing apparatus suitable for manufacturing the metal wiring of the present invention. FIG. 5 is a diagram showing the relationship between reaction time and copper nitride film thickness. FIG. 6 is a diagram showing the relationship between oxidation curve due to ashing and sheet resistance. FIG. 7 is a diagram showing the relationship between RF applied power and etching rate. FIG. 8 is a diagram schematically showing the cross-sectional shape when etched. FIG. 9 is a diagram showing the relationship between annealing time and wiring resistance. FIG. 10 is a diagram showing the relationship between the number of days of the heat cycle test and the wire breakage rate. FIG. 11 is a diagram showing the relationship between the number of days of the heat cycle test and the peeling rate. FIG. 12 is a diagram showing the relationship between annealing time and resistance value. FIG. 13 is a diagram showing the relationship between the number of heat cycle tests and the defective rate.

Claims (8)

[Claims] (1) A metal wiring for electrical conduction made of copper or a copper alloy, characterized in that copper nitride is formed on at least a portion of its surface. (2) The metal wiring according to claim 1, wherein the metal wiring is a printed wiring formed on an insulating substrate by a printing technique. (3) The metal wiring according to claim 1, wherein the metal wiring is a fine wiring formed on a semiconductor substrate by an etching technique. (4) The metal wiring according to claim 1, wherein the metal wiring is a lead wire that connects a semiconductor device and a lead frame. (5) A method for manufacturing metal wiring having copper nitride on at least a portion of the surface by nitriding the surface of copper or copper alloy wiring for electrical conduction, the copper or copper alloy wiring being housed in a vacuum container. A method for manufacturing a metal wiring, comprising the steps of: introducing a reaction gas containing at least nitrogen atoms into the vacuum container; and exciting the nitrogen gas to nitrid the surface of the wiring. (6) A method of manufacturing a metal wiring by etching a metal thin film made of copper or a copper alloy formed on a substrate, wherein the copper or copper alloy wiring according to claim 5 comprises: a metal thin film After the step of accommodating the substrate on which the mask pattern is formed in a vacuum container, introducing a reaction gas containing at least nitrogen atoms into the vacuum container, and nitriding the surface of the metal thin film with the reaction gas, the vacuum container is manufacturing a metal wiring characterized in that it is formed by a step of introducing a sputtering gas into a sputtering chamber and exciting it; and a step of sputter etching copper nitride produced by nitriding with the excited gas. Method. (7) A method of manufacturing a metal wiring by etching a metal thin film made of copper or a copper alloy formed on a substrate, wherein the copper or copper alloy wiring according to claim 5 comprises: a metal thin film a step of accommodating a substrate on which a mask pattern is formed in a vacuum container, introducing into the vacuum container a reaction gas containing at least nitrogen atoms and a sputtering gas to excite them; Nitriding the surface of the metal thin film with a reactive gas,
A method of manufacturing a metal wiring, characterized in that the metal wiring is formed by a step of simultaneously performing sputter etching of copper nitride produced as a result using the sputtering gas. (8) The reaction gas containing nitrogen atoms is at least one of nitrogen gas, a mixed gas of nitrogen gas and a reducing gas, and a compound gas containing nitrogen atoms and reducing atoms, or the mixed gas and a compound gas. , a combination gas of a compound gas and nitrogen gas, and a combination gas of a compound gas and a reducing gas, according to any one of claims 5 to 7. The method for manufacturing metal wiring described in .