JP3712548B2 - Electroless copper plating apparatus and electroless copper plating method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electroless copper plating apparatus and an electroless copper plating method , and more particularly, to an electroless copper plating apparatus and an electroless copper plating method for uses such as filling a wiring groove formed in a semiconductor substrate with copper. .
[0002]
[Prior art]
Conventionally, in order to form a wiring circuit on a semiconductor substrate, after forming a conductor film on the substrate surface by sputtering or the like, an unnecessary portion of the film is further formed by chemical dry etching using a pattern mask such as a resist. Had been removed.
[0003]
Generally, aluminum (Al) or an aluminum alloy has been widely used as a metal material for forming a wiring circuit. However, as the degree of integration of semiconductors increases, the wiring width becomes narrower, the current density increases, causing thermal stress and temperature rise, and stress migration and electromigration eventually cause disconnection or short circuit. This tendency tends to become more prominent as the aluminum wiring becomes thinner.
[0004]
Therefore, in order to avoid resistance loss due to energization, it is required to adopt a material such as copper having higher conductivity for wiring formation. However, copper or an alloy thereof is difficult to dry-etch, and it is difficult to adopt the above method of forming a pattern after forming a film on the entire surface of the substrate. Therefore, a process of forming a wiring groove having a predetermined pattern in advance and filling copper or an alloy thereof therein may be considered. According to this, the process of removing the film by etching is unnecessary, and the copper wiring layer can be formed by performing the polishing process for removing the surface step. Further, there is an advantage that a portion called a plug that connects the upper and lower layers of the multilayer wiring circuit can be formed at the same time.
[0005]
However, the shape of such a wiring groove or plug has a considerably high aspect ratio (ratio of depth to diameter or width) as the wiring width becomes finer, and uniform metal filling is difficult in sputtering film formation. It was. Also, chemical vapor deposition (CVD) is used as a film forming means for various materials. However, it is difficult to prepare an appropriate gas source for copper or an alloy thereof, and an organic source is used. In this case, there is a problem that carbon (C) is mixed into the deposited film and migration is improved. Therefore, a method for performing electroless copper plating by immersing the substrate in a plating solution has been proposed. In film formation by such plating, high aspect ratio wiring grooves can be uniformly filled with copper.
[0006]
Here, the plating solution used for electroless copper plating contains a reducing agent such as formalin (HCHO) and glyoxylic acid (CHOCOOH). In addition, when the plating deposition rate and the quality (elongation) of the coating are increased by electroless copper plating, the appropriate temperature of the plating solution is about 50 to 80 ° C. Therefore, the plating solution is generally a thermostatic bath equipped with a heating device ( In the plating solution circulation tank), it is stored at a constant temperature (around 60 ° C.), and is configured to circulate between the plating treatment tank for performing the plating treatment.
[0007]
[Problems to be solved by the invention]
Since the plating solution used for electroless copper plating contains a reducing agent, the following reaction occurs in the Cannizzaro reaction which is a side reaction of the reducing agent, that is, formalin or glyoxylic acid.
2HCHO + OH ⁻ → CH ₃ OH + HCOO ⁻
2CHOCOOH + 2OH ⁻ → C ₂ O ₄ ²⁻ + HOCH ₂ COOH + H ₂ O
[0008]
And since it is impossible to suppress this reaction completely, the by-product produced | generated by this reaction will reduce the purity of a plating solution and the amount of dissolved oxygen, and will affect the plating growth rate. For this reason, electroless copper plating has been a current plating method that is difficult to manage. In order to prevent the deterioration of the plating solution due to the Cannizzaro reaction, methanol is added to the plating solution, but this method does not suppress the Cannizzaro reaction itself, and its effect is constant. There was a limit.
[0009]
The present invention has been made in view of the above circumstances, and an electroless copper plating apparatus and an electroless copper plating method that can suppress the Canizzaro reaction itself as much as possible to extend the life of the plating solution and facilitate the management of the plating solution. The purpose is to provide.
[0010]
[Means for Solving the Problems]
The electroless copper plating apparatus of the present invention is a plating bath that holds a substrate and performs electroless copper plating on the substrate, and a plating solution circulation that stores a plating solution inside and circulates the plating solution between the plating bath. A plating solution in the plating treatment tank, and a plating solution in the plating treatment tank, the plating solution entering the plating treatment bath on the heating side and the plating solution returning to the plating solution circulation bath on the cooling side. The temperature is higher than the temperature of the plating solution in the plating solution circulation tank.
[0011]
According to the present invention, the Cannizzaro reaction is considered to be promoted in the thermal activation process, and this reaction can be suppressed by lowering the temperature of the plating solution. Therefore, by setting the temperature of the plating solution in the plating bath to the appropriate temperature for the plating bath of the substrate and the temperature of the plating solution in the plating solution circulation bath to a temperature lower than the appropriate temperature of the plating bath for the substrate, it is usually most of the time. The Canizzaro reaction itself in the plating solution circulation tank in which the plating solution is held can be suppressed. In addition, the amount of heat of the plating solution can be effectively used for heating and cooling of the plating solution, and energy consumption can be minimized.
[0015]
In addition, a heating device is provided in a path connecting the opposed heat exchanger and the plating treatment tank, and a cooling device is provided in the path connecting the opposed heat exchanger and the plating solution circulation tank. To do. Thereby, the shortage of the amount of heat by the opposed heat exchanger can be compensated by the heating device and the cooling device.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an electroless copper plating apparatus according to an embodiment of the present invention will be described with reference to the drawings. This electroless copper plating apparatus is used to form a wiring layer made of a copper layer by performing copper plating on a groove on the surface of a semiconductor substrate, and this process will be described with reference to FIG.
[0017]
That is, the semiconductor the substrate W, as shown in FIG. 1 (a), an insulating film 2 made of SiO ₂ is deposited on a conductive layer 1a on a semiconductor substrate 1 on which semiconductor devices are formed, lithography etching technology Thus, a contact hole 3 and a wiring groove 4 are formed, and a barrier layer 5 made of TiN or the like is formed thereon.
[0018]
Then, as shown in FIG. 1B, the surface of the semiconductor substrate W is plated with copper so that the contact holes 3 and the grooves 4 of the semiconductor substrate 1 are filled with copper, and the copper is formed on the insulating film 2. Layer 6 is deposited. Thereafter, the copper layer 6 on the insulating film 2 is removed by chemical mechanical polishing (CMP), and the surface of the copper layer 6 filled in the contact hole 3 and the wiring groove 4 and the surface of the insulating film 2 Are polished to substantially the same plane. As a result, a wiring made of the copper layer 6 is formed as shown in FIG.
[0019]
FIG. 2 shows an outline of the electroless copper plating apparatus according to the first embodiment of the present invention. As shown in FIG. 2, the plating apparatus holds a semiconductor substrate W and contains a plating solution 10. A plating treatment tank 11 for introducing electroless copper plating onto the semiconductor substrate W and a plating solution circulation tank 12 for storing the plating solution 10 and circulating the plating solution 10 between the plating treatment vessel 11 are provided. It has been. The plating solution 10 contains, for example, 0.1 mol / liter formalin as a reducing agent.
[0020]
The plating solution circulation tank 12 and the plating treatment tank 11 are connected by a forward path 13 and a return path 14 that constitute a circulation path. A circulation pump 15 and a heating device 16 are provided in the forward path 13, and a cooling device 17 is provided in the return path 14. Are provided. Further, a heat exchanger 18 for keeping the temperature of the plating solution 10 stored therein is disposed inside the plating solution circulation tank 12.
[0021]
Accordingly, the plating solution 10 is sequentially sent into the plating treatment tank 11 as the circulation pump 15 is driven, and is returned to the plating solution circulation tank 12 after the plating bath of the substrate is completed. At this time, the temperature T ₁ of the plating solution 10 in the plating bath 11 is appropriate temperature of the plating bath of the substrate, it is heated by the heating device 16 as for example a 60 ° C. before and after. On the other hand, the plating solution circulating tank 12 the plating solution 10 that has been accumulated in, the temperature T ₂ is a temperature lower than an appropriate temperature of the plating bath of the substrate is cooled in the cooling device 17, as for example of the order of 30 to 50 ° C. Then, it is returned to the plating solution circulation tank 12 and is configured to be maintained at a constant temperature (for example, 30 to 50 ° C.) by the heat exchanger 18.
[0022]
For example, the cannizzaro reaction, which is a side reaction of a reducing agent such as formalin, is promoted in the thermal activation process. Conceivable. Therefore, plating solution temperature T ₂ of the plating solution 10 in the circulation tank 12 from around 60 ° C. is appropriate temperature of the plating bath of the substrate, than this by about cold 30 to 50 ° C., the plating solution circulating tank 12 The cannizzaro reaction itself occurring inside can be suppressed. Moreover, the plating solution 10 is completely returned to the plating solution circulation tank 12 while the semiconductor substrate W is put in and out of the plating treatment tank 11, and is present in the plating solution circulation tank 12 for most of the time. In addition, since the substrate is heated to the appropriate temperature of the plating bath only when necessary, the cannizzaro reaction can be greatly suppressed as compared with the case where the temperature is always kept at about 60 ° C., which is the appropriate temperature for plating.
[0023]
In the electroless copper plating apparatus of this embodiment, the plating solution 10 held at, for example, 30 to 50 ° C. is stored in the plating solution circulation tank 12, and the semiconductor substrate W is held in the plating treatment tank 11. After that, the plating solution 10 is circulated in the plating treatment tank 11 and the semiconductor substrate W is plated. At this time, plating is performed at an appropriate temperature of about 60 ° C., and except when plating is performed, the plating solution 10 is maintained at, for example, 30 to 50 ° C., and the Cannizzaro reaction is suppressed.
[0024]
FIG. 3 shows an electroless copper plating apparatus according to a second embodiment of the present invention. This plating apparatus includes an opposed heat exchanger 20, and a heating side 21 of the opposed heat exchanger 20 is provided. The plating solution 10 entering the plating tank 11 flows into the heating side 21 and disposed in the forward path 13, and the cooling side 22 is disposed in the return path 14 to the plating solution circulation tank 12 in the cooling side 22. Each of the returning plating solutions 10 flows, and a heating device 23 is connected in the forward path 13 connecting the opposing heat exchanger 20 and the plating treatment tank 11, and the opposing heat exchanger 20 and the plating solution circulation tank 12 are connected. A cooling device 24 is provided in each return path 14.
[0025]
According to the electroless copper plating apparatus of this embodiment, the amount of heat of the plating solution 10 is effectively used for heating and cooling the plating solution 10 via the opposed heat exchanger 20, and the opposed heat exchanger is used. By supplementing the shortage of the heat quantity due to 20 with the heating device 23 and the cooling device 24, energy consumption can be minimized.
[0026]
【The invention's effect】
As described above, according to the present invention, the temperature of the plating solution in the plating bath is set to an appropriate temperature for the plating bath of the substrate, and the temperature of the plating solution in the plating solution circulation bath is set to a temperature lower than the appropriate temperature of the plating bath for the substrate. By doing so, the cannizzaro reaction itself in the plating solution circulation tank in which the plating solution is usually held for most of the time can be suppressed. Thereby, while extending the lifetime of a plating solution, management, such as a composition maintenance of this plating solution, can be performed easily.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of a step of performing plating by an electroless copper plating apparatus of the present invention.
FIG. 2 is a diagram showing an outline of the electroless copper plating apparatus according to the first embodiment of the present invention.
FIG. 3 is a diagram showing an outline of an electroless copper plating apparatus according to a second embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Plating solution 11 Plating treatment tank 12 Plating solution circulation tank 13 Outward path 14 Return path 16, 23 Heating device 17, 24 Cooling device 20 Opposite heat exchanger W Semiconductor substrate

Claims (4)

A plating tank for holding the substrate and applying electroless copper plating to the substrate;
A plating solution circulation tank for storing a plating solution inside and circulating the plating solution with the plating treatment tank;
A plating solution that enters the plating treatment tank on the heating side is provided with an opposing heat exchanger that allows the plating solution that returns to the plating solution circulation tank to flow on the cooling side.
An electroless copper plating apparatus characterized in that the temperature of the plating solution in the plating treatment tank is higher than the temperature of the plating solution in the plating solution circulation tank.   A heating device is provided in a path connecting the opposed heat exchanger and the plating tank, and a cooling device is provided in a path connecting the opposed heat exchanger and the plating solution circulation tank. The electroless copper plating apparatus according to claim 1.   A plating solution that enters the plating treatment tank on the heating side of the opposed heat exchanger between a plating treatment tank that holds the substrate and performs electroless copper plating on the substrate and a plating solution circulation tank that stores the plating solution therein. However, the plating solution is circulated so that the plating solution returning to the plating solution circulation tank flows on the cooling side, and the temperature of the plating solution in the plating treatment tank is higher than the temperature of the plating solution in the plating solution circulation tank. An electroless copper plating method characterized by being made high.   The plating solution flowing into the plating tank from the opposed heat exchanger is heated by a heating device, and the plating solution returning from the opposed heat exchanger to the plating solution circulation tank is cooled by a cooling device. The electroless copper plating method according to claim 3.

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