JP3359538B2 - Metal thin film forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal thin film forming method for forming a metal thin film made of a copper alloy used for a multilayer wiring structure in a semiconductor device.

[0002]

2. Description of the Related Art In a semiconductor integrated circuit using silicon, a multilayer wiring technique is indispensable for realizing higher density electronic components. In this multilayer wiring, aluminum or an alloy containing aluminum as a main component is widely used as a main material of the wiring metal. However,
In silicon semiconductor integrated circuits using aluminum wiring,
The influence of wiring delay on circuit performance and the decrease in reliability due to wiring electromigration have become serious.

First, as a signal delay due to wiring, there is a signal delay caused by wiring resistance. Also, as the signal delay,
Some are caused by wiring capacitance. This is a delay caused by the wiring capacitance between the wirings integrated at a high density.
In order to reduce the wiring capacitance, it is necessary to miniaturize not only the wiring but also the thickness direction. Therefore, if an attempt is made to suppress the signal delay caused by the wiring capacitance, the current flowing through the wiring increases, and electromigration is likely to occur. In order to solve the above-mentioned problems, copper having low electric resistance and migration resistance is expected to be used as a wiring material instead of aluminum (Japanese Patent Laid-Open No. 2-256238).

As described above, when a wiring layer or the like is formed by using copper or an alloy thereof for wiring, a thin film made of copper or an alloy thereof is formed. And chemical vapor deposition (C
VD method) and a plating method. In addition, since a film-forming material cannot be completely embedded in a fine hole by the sputtering method, a method of newly embedding a metal film in a connection hole by heating under a high pressure after sputtering (Reference 2: AJMa
cgeown, Extended Abstract of Advanced Metallization
in l995, Material Research Society, p. 635) is being studied as a method for filling the connection holes with metal. This combination of the sputtering method and the high-pressure treatment is similar to the extrusion processing in principle, and is a method in which the metal is pushed into the connection hole by high pressure at a temperature at which the metal softens.

[0005]

However, these conventional metal filling methods have the following problems. First, the CVD method has a problem that the raw material cost is high. Further, the plating method has no track record in the LSI process, and costs for waste liquid treatment are high. When copper is used in the combination of the sputtering method and the high-pressure treatment, the temperature of the extrusion processing is 700 ° C. to 800 ° C. (Metal Data Book, edited by The Japan Institute of Metals, p. 322). It is difficult to bury at a temperature (450 ° C. or lower).

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and a metal thin film made of a copper alloy can be formed at low cost at a temperature and pressure within an allowable range in an LSI wiring forming process. The purpose is to be.

[0007]

According to the present invention, there is provided a metal thin film forming method comprising the steps of: forming a metal thin film made of a metal material composed of tin, indium, cadmium, or a copper alloy thereof on a substrate having a recess formed thereon; Is formed, and by pressing the metal thin film while heating the metal thin film to a temperature equal to or lower than its melting point, the concave portion is filled with the metal thin film, and subsequently, a thin film made of copper is formed on the metal thin film, The metal thin film and the thin film made of copper were mutually diffused by heating, and thereafter, the thin film made of copper was removed.
Since the metal thin film is formed as described above, the formed metal thin film is made of a copper alloy. Further, according to the metal thin film forming method of the present invention, any one of tin, indium, and cadmium is
Alternatively, a metal thin film made of a metal material composed of the copper alloy is formed, and the metal thin film is heated to a temperature equal to or lower than its melting point so that the concave portion is filled with the metal thin film. Is formed, and the metal thin film and the copper thin film are heated to cause mutual diffusion, and thereafter, the copper thin film is removed.
Since the metal thin film is formed as described above, the formed metal thin film is made of a copper alloy.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. First, an overview will be given. In the present invention, a low melting point metal having a melting point of 200 ° C. to 300 ° C. or a copper alloy thereof is used as a metal thin film material instead of aluminum or the like as a material.
Then, first, a metal thin film made of a metal material made of such a low melting point metal was formed in a state where the metal material was filled in a concave portion such as a connection hole. Since these low-melting metals soften at a low temperature, if a metal thin film is formed on a substrate having a concave portion, it is possible to push the metal material into the concave portion with a small force. As a way to push it,
As described above, there is a method in which a metal thin film made of a low melting point metal is formed, and the metal material is buried in the concave portion by heating the metal thin film to a temperature equal to or lower than the melting point of the metal material under high pressure.

Further, a metal thin film made of such a low melting point metal is formed on a base material such as a sheet film, and the thin metal film is bonded to a substrate having a concave portion formed thereon, and is pressed while being heated. There is a method of forming a metal thin film made of a low melting point metal in a state where a metal material is embedded. In addition, if a low-melting metal material having good wettability with the underlying material is used, for example, a metal thin film can be formed in a state where the concave portion is filled with the metal material by heating and melting the metal material to about the melting point. At this time, when the low melting point metal is formed into an alloy with copper, the solid solubility in copper is low at 100 ° C. or less,
It is desirable that the solid solubility in copper at about 0 ° C. is several percent or more. Further, when a copper alloy containing about 1% of these low-melting metals in copper is a precipitation hardening type, the electromigration resistance can be enhanced. The above low melting point metals include tin,
Indium and cadmium are raised.

Then, after forming a metal thin film made of a low melting point metal in a state in which the grooves and recesses of the semiconductor substrate are buried,
A copper thin film is formed thereon. At this time, the total amount of copper is set to be about 100 times the total amount of the low melting point metal existing under the copper thin film. Thereafter, the substrate is heated to cause the low melting point metal and copper to interdiffuse. The low melting point metal constituting the metal thin film formed under the copper foil film becomes less than the solid solution limit in copper at a temperature of about 400 ° C. and is uniformly diffused. For this reason, the grooves and recesses originally filled with the low melting point metal are replaced with an alloy containing copper as a main component. Thereafter, assuming that the substrate is cooled to room temperature, the intermetallic compound precipitates at the crystal grain boundaries and hardens. As described above, a metal thin film made of a copper alloy can be formed in a state in which the groove or the concave portion is buried at a temperature or a pressure that is allowed in an LSI wiring forming step. Further, if a wiring layer is formed by finely processing a metal thin film made of such a copper alloy, the wiring layer has higher reliability such as high migration resistance and low resistance.

Embodiment 1 Hereinafter, a first embodiment of the present invention will be described.
FIG. 1 is an explanatory diagram illustrating a method for forming a metal thin film according to the first embodiment of the present invention. First, as shown in FIG. 1A, a heat-resistant sheet film (substrate) such as polyimide is used.
A metal thin film 102 made of, for example, tin is formed on 101. Instead of the sheet film 101, the metal thin film 102 may be formed on a base material having a certain strength and heat resistance, such as a metal plate or a plate made of a metal oxide. The metal thin film 102 is not limited to tin, and may be made of, for example, a metal having a low melting point such as indium or cadmium. Further, those copper alloys may be used.

Next, as shown in FIG. 1B, an inverted pattern having a width of 0.25 μm and a depth of about 0.5 to 1 μm is formed at a wiring formation position on an interlayer insulating film 104 formed on the semiconductor substrate 103. (Recess) 105 is formed. Next, a barrier layer 10 made of titanium nitride and having a thickness of about 100 nm is formed thereon.
6 is deposited and formed by a sputtering method or the like. Then, the sheet film 101 and the semiconductor substrate 103 are bonded together such that the surface of the sheet film 101 on which the metal thin film 102 is formed faces the surface of the semiconductor substrate 103 on which the barrier layer 106 is formed.

Next, as shown in FIG. 1C, pressure is applied from the back surface of the sheet film 101 and the back surface of the semiconductor substrate 103, and heating is performed at the same time. At this time, the heating temperature is 100 ~
The temperature may be 200 ° C. and the pressure may be 10 to 100 kg. This heating softens the metal thin film 102, and fills the inverted pattern 105 with the metal thin film 102 softened by pressing. Then, when the sheet film 101 is peeled off from the metal thin film 102, the metal thin film 102 is formed on the interlayer insulating film 104 so as to fill the concave portion of the inversion pattern 105, and the surface of the metal thin film 102 is formed flat. .

Next, as shown in FIG. 1D, the metal thin film 102 is removed by chemical mechanical polishing so that the metal portion 102a is left only in the concave portion of the inverted pattern 105. Then, as shown in FIG.
By depositing copper by sputtering or the like, the copper thin film 10
7 is formed. Then, by heating them at 400 ° C. for 30 minutes or more, as shown in FIG.
02a and the copper thin film 107 react with each other to cause mutual diffusion.
As a result, the copper alloy wiring 108 is formed by the metal thin film made of the copper alloy.

Then, the copper thin film 10 is formed by chemical mechanical polishing.
By removing 7, a state where copper alloy wiring 108 is formed on interlayer insulating film 104 via barrier layer 106 is obtained. As described above, according to the first embodiment,
A wiring layer made of a copper alloy can be formed at a heating temperature of about 400 ° C. at the maximum. That is, according to the first embodiment, the temperature does not become higher than the temperature (450 ° C. or less) permitted in the LSI wiring forming step,
Further, it is possible to form a wiring layer made of a copper alloy without applying a high pressure of 100 MP. Note that copper may diffuse into silicon oxide to adversely affect a transistor element, or may have poor adhesion to an insulating film. However, as described above, since the barrier layer is disposed on the underlayer, diffusion of copper is prevented, and adhesion to the insulating film is improved. Note that tantalum or tantalum nitride may be used as the barrier layer.

Embodiment 2 Hereinafter, a second embodiment of the present invention will be described.
FIG. 2 is an explanatory diagram showing a method for forming a metal thin film according to Embodiment 2 of the present invention. First, as shown in FIG. 2A, an interlayer insulating film 20 formed on a semiconductor substrate 201 is formed.
A hole 203 having a diameter of 0.2 μm and a depth of about 1 μm is formed at a predetermined position on 2. Next, a barrier layer 204 made of titanium nitride and having a thickness of about 100 nm is formed thereon by sputtering or the like.

Then, a metal thin film 205 made of, for example, tin is formed thereon by, for example, a sputtering method. At this time, when the metal thin film 205 is formed by the sputtering method, a space 205a is formed inside the hole 203 as shown in FIG. This is because the film is formed by the sputtering method, and the space 205a is not formed by the CVD method or the like. The metal thin film 20
5 is not limited to tin, and for example, any low-melting metal such as indium or cadmium may be used. Further, those copper alloys may be used.

Next, as shown in FIG. 2B, while heating the semiconductor substrate 201, the metal thin film 205 is pressed using a flattened pressing plate 206 on the metal thin film 205 so that the metal thin film 205 is Push in. Heating temperature is 100-2
It should be about 00 ° C. This is a temperature at which the metal thin film 205 does not melt. The pressure for pressurization is 20 to 100.
kg. Next, as shown in FIG. 2C, the metal thin film 205 is polished by chemical mechanical polishing, so that a metal portion 205b made of the metal thin film 205 is formed in the hole 203.

Next, as shown in FIG. 2D, copper is deposited thereon by sputtering or the like to form a copper thin film 20.
7 is formed. Then, by heating them at 400 ° C. for 30 minutes or more, as shown in FIG.
05b and the copper thin film 207 are caused to react and diffuse with each other to form a hole filling portion 208 made of a copper alloy. Then, by removing the copper thin film 207 by chemical mechanical polishing, the holes 20 are removed.
3, a hole filling portion 208 made of a copper alloy is formed via the barrier layer 204, and the upper surface thereof is exposed. The hole filling portion 208 can be used, for example, as a plug for connecting upper and lower wiring layers.

As described above, according to the first embodiment, a metal thin film made of a copper alloy can be formed only by applying a heating temperature of about 400 ° C. at the maximum. Plugs and the like can be formed. That is, according to the first embodiment, LS
A metal thin film made of a copper alloy can be formed without a temperature higher than the temperature (450 ° C. or lower) permitted for the I wiring formation step and without applying a high pressure of 100 MPa. Then, for example, a plug can be formed by the metal thin film made of the copper alloy. this,
Migration resistance is required for the plug connecting the wiring layers, but the migration resistance can be further improved by using a copper alloy.

Embodiment 3 Hereinafter, a third embodiment of the present invention will be described.
FIG. 3 is an explanatory diagram illustrating a method for forming a metal thin film according to the third embodiment of the present invention. First, as shown in FIG. 3A, an interlayer insulating film 30 formed on a semiconductor substrate 301 is formed.
A hole 303 having a diameter of about 0.2 μm and a depth of about 1 μm is formed at a predetermined position on 2. Next, a barrier layer 304 made of titanium nitride and having a thickness of about 100 nm is formed thereon by sputtering or the like.

Then, a metal thin film 305 made of, for example, tin is formed thereon by, for example, a sputtering method. At this time, the metal thin film 305 has a thickness of about 100 to 200 nm.
It is formed to a film thickness of about. Here, when the metal thin film 205 is formed by the sputtering method, as shown in FIG. 3A, the inside of the hole 303 is not completely filled with the metal thin film 305. The metal thin film 305 is not limited to tin, and may be made of, for example, a metal having a low melting point such as indium or cadmium. Further, those copper alloys may be used.

Next, by heating the semiconductor substrate 301, the metal thin film 305 is melted or surface-diffused as shown in FIG.
05 is assumed to be filled. Thereafter, in the same manner as in the second embodiment, a state in which the inside of the hole 303 is filled with a hole filling portion made of a copper alloy is obtained by forming a copper thin film and interdiffusing it. As a result, also in the third embodiment,
The same effect as in the second embodiment can be obtained.

Embodiment 4 Hereinafter, a fourth embodiment of the present invention will be described.
FIG. 4 is an explanatory diagram showing a method for forming a metal thin film according to the fourth embodiment of the present invention. First, as shown in FIG. 4A, an interlayer insulating film 40 formed on a semiconductor substrate 401 is formed.
A hole 403 having a diameter of about 0.2 μm and a depth of about 1 μm is formed at a predetermined position on 2. Next, a barrier layer 404 made of titanium nitride and having a thickness of about 100 nm is formed thereon by sputtering or the like.

Then, a metal thin film 405 made of, for example, tin is formed thereon by, for example, a sputtering method. At this time, when the metal thin film 405 is formed by the sputtering method, a space 405a is formed inside the hole 403 as shown in FIG. The metal thin film 405 is not limited to tin, and may be made of, for example, a metal having a low melting point such as indium or cadmium. Further, those copper alloys may be used.

Next, the semiconductor substrate 401 is heated at a high pressure with an inert gas such as argon, so that the semiconductor substrate 401 shown in FIG.
As shown in (b), the metal thin film 405 is in a molten or surface-diffused state, and the inside of the hole 403 is filled with the metal thin film 405. The high pressure of this inert gas is 10
Atmospheric pressure or higher. Thereafter, in the same manner as in Embodiments 2 and 3, a copper thin film is formed and interdiffused to form holes 4.
03 is filled with a hole filling portion made of a copper alloy. As a result, also in the fourth embodiment, the same effects as in the second and third embodiments can be obtained.

[0027]

As described above, according to the present invention, a metal thin film made of a metal material composed of any one of tin, indium, and cadmium or a copper alloy thereof is formed on a substrate having a concave portion. By pressing the metal thin film while heating the metal thin film to a temperature equal to or lower than its melting point, the concave portion is filled with the metal thin film, and subsequently, a thin film made of copper is formed on the metal thin film, and the metal thin film and The thin film made of copper was mutually diffused by heating, and thereafter, the thin film made of copper was removed. Further, the method for forming a metal thin film of the present invention includes the steps of:
A metal thin film made of a metal material composed of tin, indium, cadmium or its copper alloy is formed, and the metal thin film is heated to a temperature lower than its melting point so that the concave portion is filled with the metal thin film. Subsequently, a thin film made of copper was formed on the metal thin film, and the metal thin film and the thin film made of copper were mutually diffused by heating, and thereafter, the thin film made of copper was removed. Since the metal thin film is formed as described above, according to the present invention, there is an effect that a metal thin film made of a copper alloy can be formed at a temperature and a pressure within an allowable range in an LSI wiring forming process without increasing costs. .

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a method for forming a metal thin film according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a method for forming a metal thin film according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram illustrating a method for forming a metal thin film according to a third embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a method for forming a metal thin film according to a fourth embodiment of the present invention.

[Explanation of symbols]

101: sheet film (substrate), 102: metal thin film,
Reference numeral 103 denotes a semiconductor substrate, 104 denotes an interlayer insulating film, 105 denotes an inverted pattern (recess), 106 denotes a barrier layer, 107 denotes a copper thin film, and 108 denotes a copper alloy wiring.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kuragi Billion 3-9-1-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Akihiko Hirata 3-19 Nishishinjuku, Shinjuku-ku, Tokyo No. 2 Within Nippon Telegraph and Telephone Corporation (56) References JP-A-6-326100 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/3205

Claims (4)

(57) [Claims] A first step of forming a metal thin film made of a metal material made of any one of tin, indium, and cadmium or a copper alloy thereof on a substrate having a recess formed therein; A second step of pressing the metal thin film while heating the metal thin film to a temperature equal to or lower than the melting point of the metal material so that the concave portion is filled with the metal thin film; and a thin film made of copper on the metal thin film. A fourth step of heating the metal thin film and the thin film made of copper to interdiffuse each other, and a fifth step of removing the thin film made of copper. Characteristic metal thin film forming method. 2. A first step of forming a metal thin film made of a metal material composed of any one of tin, indium, and cadmium or a copper alloy thereof on a substrate having a recess formed thereon, and the metal thin film A second step of heating the substrate to a temperature equal to or lower than the melting point of the metal material so that the concave portion is filled with the metal thin film; and a third step of forming a thin film made of copper on the metal thin film. A fourth step of mutually diffusing the metal thin film and the thin film made of copper by heating, and a fifth step of removing the thin film made of copper. . 3. The metal thin film forming method according to claim 1, wherein a part of the metal thin film is left before the third step so as to leave a portion of the metal thin film filled inside the groove. A method for forming a metal thin film, comprising: removing the metal thin film. 4. The metal thin film forming method according to claim 1, wherein the substrate on which the metal thin film is formed and the substrate are formed, and the concave portion of the metal thin film and the substrate are formed. A method for forming a metal thin film, wherein the metal thin film is formed on the substrate by bonding together such that the surfaces face each other.