JPH10313005A - Metal film reflow method - Google Patents

Abstract

(57) [Problem] To enable reliable reflow of a metal film even when the surface of the metal film is oxidized. A wafer having an oxidized surface of a metal film (4) is transferred to a chamber holding a reduced-pressure hydrogen (H ₂ ) reducing atmosphere (20), and the metal film (4) is laser-reflowed in the reduced-pressure hydrogen reducing atmosphere. While scanning the surface of the substrate, a laser beam including a xenon chloride (XeCl) laser beam 21 or the like is irradiated to cause reflow. Since the atmosphere for the reflow is the hydrogen reducing atmosphere 20, the oxide film 10 formed on the surface of the metal film 4 is efficiently reduced. Since the surface of the metal film 4 becomes a clean surface without the oxide film 10 due to this reduction reaction, the surface diffusion of the metal film 4 is promoted at the time of reflow, the surface migration is assisted, and the metal film 4 can be satisfactorily reflowed. it can.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a metal film reflow method for flattening a metal film having a step.

[0002]

2. Description of the Related Art Due to the high integration and high speed of LSI (Large Scale Integration), miniaturization and multi-layering of internal wiring are progressing, and accordingly, flattening technology at the time of wiring formation and processing of fine wiring. And ensuring reliability are important issues. As one of the means to solve these problems,
An embedded wiring technique using copper (Cu) or the like has been studied.

Here, the buried wiring is a groove of a wiring pattern on the interlayer insulating film (hereinafter, simply referred to as “wiring groove”).
And a connection hole for electrical connection between layers are formed, a wiring material such as copper is buried in the wiring groove or the like, and an excess portion is etched back or CMP (Chemical and Mechanical Polishing).
g; chemical mechanical polishing) to remove the wiring material such as copper only in the groove. According to this method, since the wiring portion has a shape embedded in the interlayer insulating film, there is an advantage that the interlayer flattening in the subsequent steps is facilitated.

In the buried wiring technique, copper or the like is buried in a wiring groove or a connection hole. As the burying method, a CVD (Chemical Vapor Deposition) method or a sputtering (hereinafter simply referred to as “sputtering”) method is used. After forming a film of copper or the like by a method, there is a method in which the formed copper or the like is heated and reflowed. In the case of such a method, the CVD method is superior in embedding characteristics, but there is a problem in the film quality related to the reliability of wiring,
Currently, studies for practical use are underway.

On the other hand, in the case of a method in which copper or the like is formed by a sputtering method and the formed copper or the like is heated and reflowed, there is no problem in the copper film itself, and low resistance and high reliability are obtained. Wiring is obtained. In addition, aluminum alloy (Al) alloy-based wiring can be reflowed at a lower temperature compared to the case of forming the wiring, and even if the wafer is once taken out to the atmosphere after film formation of copper or the like, reflow can be performed. On the other hand, it has many advantages, and has recently been particularly noted. However, since the filling characteristics are inferior to those of the CVD method, various methods for improving the filling characteristics by the reflow method have been studied.

FIG. 4 is a process diagram of a wiring process for explaining a conventional embedded wiring technology using a reflow method.

In the case of embedded wiring, first, elements are formed on a wafer by a normal LSI manufacturing process, and then,
An interlayer insulating film 101 is formed, and a wiring groove 102 and a connection hole (not shown) are formed in the interlayer insulating film 101 (FIG. 4).
(A)). Next, after a barrier metal (TiN / Ti) film 103 made of titanium nitride (TiN) and titanium (Ti) is formed as a base on the interlayer insulating film 101 by sputtering, a metal such as copper as a wiring material is formed. The metal film 104 is formed by film formation (FIG. 4B). In the steps so far, since the metal such as copper serving as the wiring material is not completely filled in the wiring groove 102, the metal film 104 is heated and flattened by the reflow method to obtain the metal such as copper. Is embedded in the wiring groove 102 (FIG. 4).
(C)). Finally, the barrier metal film 103 and the metal film 104 in the region other than the wiring groove 102 are removed (FIG. 4).
(D)). Thereby, the wiring groove 10 of the interlayer insulating film 101 is formed.
2 is buried in the metal film 104 only.

[0008]

However, when the reflow method is used for the embedded wiring technique as described above, for example, at the stage before the reflow (FIG. 4B), the wafer is once taken out into the atmosphere. And metal such as copper is easily oxidized, so that the surface of the formed metal film 104 is oxidized,
There is a problem that the surface diffusion of the metal film 104 is suppressed, and the reflow characteristics are significantly deteriorated.

FIG. 5 is a cross-sectional view of the wafer for explaining the state of the oxidized metal film 104. As shown in this figure,
When the surface of the metal film 104 is oxidized,
Oxide film 110 of a metal oxide is formed on the surface of.
As described above, when the oxide film 110 is formed on the surface of the metal film 104, a problem occurs that the metal film 104 cannot be reflowed well unless the oxide film 110 is removed from the surface.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a metal film reflow method capable of reliably reflowing a metal film even when the surface of the metal film is oxidized. Is to do.

[0011]

The method of reflowing a metal film according to the present invention is to flatten a metal film while reducing a metal oxide generated on the surface of the metal film. At this time, for example, the metal oxide may be reduced by irradiating the surface of the metal film with a thermal energy beam in a reducing atmosphere, or by blowing heated hydrogen on the surface of the metal film, The metal oxide may be reduced.

In such a metal film reflow method, the flattening of the metal film is performed together with the reduction of the metal oxide generated on the surface of the metal film. This makes it possible to satisfactorily embed a wiring material such as copper in a wiring groove in a buried wiring technique using a reflow method, for example.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the following description, an example in which the metal film reflow method of the present invention is applied to a metal embedded wiring technique will be described.

First, a first embodiment of the present invention will be described. FIGS. 1 and 2 are process diagrams for explaining a metal embedded wiring process according to the first embodiment of the present invention.

In the buried wiring, first, as shown in FIG. 1A, after an element is formed on a wafer such as a silicon substrate by a normal LSI manufacturing process, an interlayer insulating film 1 is formed. A wiring groove 2 and a connection hole (not shown) are formed in the interlayer insulating film 1. Here, as a method of forming the wiring groove 2, for example, normal lithography or RIE
(Reactive Ion Etching) method is applied. The wiring groove 2 formed here is
For example, the groove has a width of 0.4 μm and a depth of 0.5 μm.

Next, as shown in FIG. 1B, a barrier metal (TiN / TiN / TiN) and titanium (Ti) are formed on the interlayer insulating film 1 by magnetron sputtering in a high vacuum. Ti) film 3 is formed as a base. After the barrier metal film 3 is formed as a base, the metal film 4 is continuously formed on the barrier metal film 3 by a magnetron sputtering method or the like in a high vacuum. In this step, the metal film 4 is not completely filled inside the wiring groove 2.

Here, the conditions for forming the titanium film include, for example, a DC power of 5 kW, a process gas of 100 sccm of argon (Ar), a pressure of 0.4 Pa,
The film is formed under the conditions that the substrate temperature is 150 ° C. and the film thickness is 20 nm. The conditions for forming the titanium nitride are, for example, D
C power is 5 kW, and argon (A
r) is introduced at 30 sccm, nitrogen (N ₂ ) is introduced at 80 sccm, the film is formed under the conditions of a pressure of 0.4 Pa, a substrate temperature of 150 ° C., and a film thickness of 50 nm.

The metal film 4 is formed using, for example, pure copper or a copper alloy. In general, when performing reflow, the metal is placed in the wiring groove 2 (or the connection hole).
It is preferable to avoid a structure in which the voids are formed inside the groove by connecting the openings at the upper portion of the groove. For this reason, as a method for forming the metal film 4, it is desirable to use a long-distance sputtering method with good coverage, which takes the distance between the target and the wafer (distance between TS). In addition, it is desirable to prevent the metal from migrating and prevent the metal film 4 from having a continuous shape at the opening by not heating the substrate as in the case of aluminum (Al) film formation. Here, for example, when copper is used as the metal film 4, the film forming conditions are as follows: DC power is 15 kW, and argon (Ar) is introduced as a process gas at 100 sccm.
The film is formed under the conditions that the pressure is 0.4 Pa, the substrate temperature is 150 ° C., the distance between TS is 250 mm, and the film thickness is 1000 nm.

The formation of the metal film 4 of copper or the like is not limited to a long-distance sputtering method, but may be another sputtering method having good coverage.
For example, it may be performed using collimated sputtering, ionization sputtering, or the like.

After the barrier metal film 3 and the metal film 4 are formed as shown in FIG. 1B, the wafer is once removed in a state where the metal film 4 is not completely filled in the wiring groove 2. Remove to atmosphere. Once the wafer is taken out into the atmosphere as described above, as shown in FIG.
Is oxidized to form an oxide film 10 made of a metal oxide. When the oxide film 10 is formed on the surface of the metal film 4 as described above, the metal film 4 cannot be sufficiently reflowed by the ordinary reflow method.

Therefore, as shown in FIG. 2A, the wafer with the surface of the metal film 4 oxidized is decompressed with hydrogen (H
₂ ) The substrate is transferred to a chamber holding a reducing atmosphere 20 and xenon chloride (XeC) is scanned while scanning the surface of the metal film 4 with a laser reflow apparatus in this reduced-pressure hydrogen reducing atmosphere.
1) Irradiate a laser beam composed of the laser beam 21 or the like to cause reflow. As a result, the portion of the oxide film 10 that has been irradiated with the laser is reduced, so that the metal that is not completely filled in the wiring groove 2 and whose surface is oxidized as shown in FIG. The film 4 is satisfactorily heated and flattened by the reflow method, and is completely embedded in the wiring groove 102. The laser reflow conditions include, for example, introducing hydrogen (H ₂ ) as a process gas at 500 scc,
The pressure was 67 Pa, the substrate temperature was 400 ° C., the laser wavelength was 308 nm (XeCl), and the laser output was 667 mJ.
And The laser light here corresponds to the thermal energy beam in the present invention.

As described above, the metal film 4 is formed by the reflow method.
Is flattened so as to be buried inside the wiring groove 2, finally, as shown in FIG. 2B, the metal film 4 and the barrier metal existing in portions other than the wiring groove 2 (and the connection hole) are formed. The film 3 is removed by a CMP method or the like. This allows
Metal film 4 is formed only in wiring groove 2 (and connection hole) of interlayer insulating film 1. Here, the conditions of the CMP method include, for example, a polishing pressure of 100 g / cm ² , and a rotation speed of the platen 30.
rpm, polishing head 30 rpm, polishing pad is SUBA
IV, slurry is H202 base (containing alumina slurry), flow rate is 100 cc / min, temperature is 25-30 ° C
It is.

As described above, according to the buried wiring technique according to the first embodiment of the present invention, when the metal film 4 is reflowed by the laser beam, the atmosphere is the hydrogen reducing atmosphere 23. The oxide film 10 formed on the surface of the metal film 4 is efficiently reduced. Since the surface of the metal film 4 becomes a clean surface without the oxide film 10 due to this reduction reaction, the surface diffusion of the metal film 4 is promoted at the time of reflow, the surface migration is assisted, and the metal film 4 can be satisfactorily reflowed. it can. As a result, the embedding characteristics are improved, the metal film 4 can be reliably embedded in the wiring groove 2, a low-resistance wiring can be obtained, and reliability in forming the wiring can be secured.

Next, a second embodiment of the present invention will be described. In the present embodiment, the steps up to the step shown in FIG. 1 are the same as those in the first embodiment, so that the description thereof will be omitted below, and only the subsequent reflow processing step will be described.

FIG. 3 is a process diagram for explaining a metal buried wiring process according to a second embodiment of the present invention.

In the first embodiment, an example is shown in which the wafer in which the surface of the metal film 4 is oxidized (FIG. 1C) is reflowed by a laser reflow apparatus in a hydrogen reducing atmosphere. FIG. 2 (a)) and FIG.
As shown in (a), the wafer with the surface of the metal film 4 oxidized is transferred onto a heater heated to about 400 ° C., and heated hydrogen 30 is sprayed while scanning the surface of the metal film 4. And reflow. As a result, the portion of the oxide film 10 to which the heated hydrogen has been blown is reduced, so that the metal film 4 that is not completely filled in the wiring groove 2 and whose surface is oxidized can be satisfactorily reflowed. It is heated and flattened by the method, and is completely embedded in the wiring groove 102. The conditions for the reflow treatment here are, for example, a substrate temperature of 400 ° C., hydrogen introduced as a process gas, a hydrogen blowing pressure of 1 kg / cm ² , and a hydrogen heating temperature of 400 ° C.

As described above, the metal film 4 is formed by the reflow method.
Is flattened to be embedded in the wiring groove 2 and finally, the metal film 4 existing in a portion other than the wiring groove 2 (and the connection hole) as in the first embodiment.
And the barrier metal film 3 are removed by a CMP method or the like (FIG. 3B). Thereby, the metal film 4 is formed only in the wiring groove 2 (and the connection hole) of the interlayer insulating film 1. Note that parts other than those described above are the same as in the first embodiment.

As described above, according to the embedded wiring technique according to the second embodiment of the present invention, the heating hydrogen 30 is directly blown onto the surface of the metal film 4 in the reflow process. Oxide film 10 generated on the surface of metal film 4 is efficiently reduced. Since the surface of the metal film 4 becomes a clean surface without the oxide film 10 due to this reduction reaction, the surface diffusion of the metal film 4 is promoted at the time of reflow, the surface migration is assisted, and the metal film 4 can be satisfactorily reflowed. it can. As a result, the embedding characteristics are improved, the metal film 4 can be reliably embedded in the wiring groove 2, a low-resistance wiring can be obtained, and reliability in forming the wiring can be secured.

The present invention can be variously modified regardless of the first and second embodiments. For example, in the above-described first and second embodiments, an example has been described in which after forming the barrier metal film 3 and the metal film 4, the wafer is once taken out into the atmosphere and reflow processing is performed by laser irradiation or hydrogen spraying. However, the barrier metal film 3 and the metal film 4 can be used without taking out the wafer once into the atmosphere.
It is also possible to consistently perform from the formation of the film to the reflow treatment in a vacuum.

In the above description, an example in which the metal film reflow method of the present invention is applied to a metal embedded wiring technique has been described. However, the present invention may be applied to other techniques utilizing reflow processing.

[0031]

As described above, according to the metal film reflow method according to any one of the first to fourth aspects, the flattening of the metal film is performed together with the reduction of the metal oxide generated on the surface of the metal film. As a result, the reduction of the metal oxide effective for improving the reflow process becomes possible. Thereby, even when the surface of the metal film is oxidized, the metal film can be reliably reflowed. For example, in the embedded wiring technology using the reflow method, the embedding characteristics are improved, and a wiring material such as copper is used. The wiring can be satisfactorily embedded in the wiring groove to obtain a low-resistance wiring, and the reliability in forming the wiring can be secured.

[Brief description of the drawings]

FIG. 1 is a process diagram for explaining a metal embedded wiring process according to a first embodiment of the present invention.

FIG. 2 is a process chart for explaining a process following FIG. 1;

FIG. 3 is a process chart for explaining a metal embedded wiring process according to a second embodiment of the present invention.

FIG. 4 is a process chart for explaining a conventional embedded wiring technique.

FIG. 5 is a cross-sectional view of a wafer illustrating a state of a conventional oxidized metal film.

[Explanation of symbols]

1, 101: interlayer insulating film, 2, 102: wiring groove, 3, 1
03: barrier metal film, 4,104: metal film, 10, 1
10. Oxide film

Claims (4)

[Claims] 1. A metal film reflow method for flattening a metal film, wherein the metal oxide formed on the surface of the metal film is reduced,
A method for reflowing a metal film, comprising flattening the metal film. 2. The method according to claim 1, wherein the surface of the metal film is irradiated with a thermal energy beam in a reducing atmosphere to reduce the metal oxide and planarize the metal film. A reflow method for a metal film according to the above. 3. While reducing the metal oxide by spraying heated hydrogen on the surface of the metal film,
The method according to claim 1, wherein the metal film is flattened. 4. The metal film reflow method according to claim 1, wherein the flattening of the metal film is performed so as to bury the metal film in a wiring groove formed of an insulating film.