JP2009249652A - Electroless plating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroless plating method in which a subcritical fluid or a supercritical fluid is used, and with which a uniform film can be obtained by the electroless plating in a short period of time. <P>SOLUTION: When performing the electroless plating on the surface of a metallic base sample 22, electroless plating liquid contains at least one of carbon dioxide and inert gas, and a surfactant, metal powder having the average particle diameter larger than 100 μm is added by the amount at which no more metal powder is dissolved therein, and dispersed, and the electroless plating is performed in a supercritical or subcritical state. A uniform and thick plating layer can be obtained in a short period of time without causing any induction eutectoid phenomenon. In the electroless plating method, metallic powder having the average particle diameter larger than 100 μm can be used, and the electroless plating method is applicable to a damascene process or a dual damascene process which is a method for forming fine metal wiring within a semiconductor element. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electroless plating method for performing electroless plating on the surface of a metal substrate, and in particular, in the presence of a subcritical fluid or a supercritical fluid, a uniform and homogeneous coating in a short time without causing induction eutectoid phenomenon. The present invention relates to an electroless plating method that can be obtained by electroless plating.

  Conventionally, as a method for forming fine metal wiring in a semiconductor element, after forming, for example, an aluminum thin film on a substrate by sputtering, a photoresist is applied, patterning is performed by exposure / development processing, and predetermined wiring is formed by etching. It was done to form. However, with the high integration and miniaturization of semiconductor circuit elements, the wiring forming method has become difficult with such a method. Therefore, grooves and holes for wiring are formed in advance, chemical vapor deposition CVD, sputtering, A method of forming wiring by embedding aluminum or copper in a groove or hole by a plating method or the like and then polishing the surface by a chemical mechanical polishing (CMP) method, so-called damascene method is performed. It has become. In this damascene method, a connection hole to a lower layer wiring is also formed at the time of forming a groove, and this connection hole and groove are filled with aluminum or copper at the same time to form a wiring, which is called a dual damascene method.

  In recent years, a damascene method to which an electroplating method is applied has become the mainstream as a wiring formation process for semiconductor devices (see Patent Documents 1 and 2 below). Here, a method of forming a wiring of a three-dimensional mounting semiconductor device to which the damascene method disclosed as a conventional example in Patent Document 1 below is described will be described with reference to FIGS. 3A, holes 72 are formed on the surface of a substrate 70 such as a silicon substrate by lithography and etching techniques as shown in FIG. 3A, and then, on the surface of the substrate 70 as shown in FIG. 3B. For example, an insulating film 74 made of SiO 2 is formed by CVD, and the surface of the hole 72 is covered with the insulating film 74, thereby preventing electricity from leaking. Further, as shown in FIG. A seed layer 76 as a power feeding layer for plating is formed by, for example, CVD or sputtering.

  Then, as shown in FIG. 3D, the surface of the substrate 70 is subjected to copper plating by electroplating to fill the hole 72 of the substrate 70 with copper and deposit a copper plating film 78 on the insulating film 74. Thereafter, as shown in FIG. 3E, the copper plating film 78 and the insulating film 74 on the substrate 70 are removed by CMP, and the surface of the copper plating film 78 filled in the holes 72 is replaced with the surface of the substrate 70. The embedded wiring is made so as to be substantially in the same plane.

  The embedded wiring disclosed in the following Patent Document 1 can be applied to a hole 72 having a diameter W of about 5 to 20 μm and a depth D of about 50 to 70 μm. In the invention disclosed in Patent Document 1 below, in the copper plating process by electroplating shown in FIG. 3D, copper overhangs near the entrance of the hole 72 as shown in FIG. In order to prevent the formation of voids, a process of etching a part of the plating film is added during the electroplating process as shown in FIG. 4B, and the desired number of times as shown in FIGS. 4C and 4D. By repeating the electroplating process and the plating film etching process, the groove 72 is filled with the copper plating film 78 as shown in FIG. 4E.

Even if the invention disclosed in Patent Document 1 as described above is applied, it is difficult to bury copper without voids in narrow grooves or holes of about 0.20 μm or less. In the invention disclosed in Document 2, the composition of the plating solution is adjusted to adjust the metal deposition rate on the bottom side and the inlet side of the groove or hole.
JP 2003-96596 A (claims, paragraphs [0003] to [0010], [0011], FIG. 4, FIG. 6, FIG. 8) JP 2005-259959 A (claims, paragraphs [0011], [0013], [0029], FIG. 1 and FIG. 2) JP 10-245683 A (claims, paragraphs [0011] to [0015]) Japanese Patent Laying-Open No. 2006-37188 (Claims 7 to 12, paragraphs [0008] to [0012], FIG. 1)

  The fine metal wiring formation method by the electroplating method as described above is an effective method because it is easy to form a power supply terminal when the seed layer 76 as a power supply layer can be formed large. When the size is small or when it is necessary to plate the groove or hole deeper than the size of the opening, it is difficult to form the power supply terminal, so the electroless plating method is adopted. The

  The electroless plating method is used in a wide range of fields because the resulting plating layer is dense, can be plated even on fine parts, and can also be plated on the surface of an insulator, but because the deposition rate of the plating layer is slow It is difficult to apply to the damascene method or dual damascene method as described above, which requires formation of a thick metal layer.

  On the other hand, Patent Document 3 discloses a method of forming a thick tin alloy film by an electroless plating method using a tin or tin alloy plating bath containing powder that forms an alloy with tin and functions as a solder film. Yes. However, in such an electroless plating method, the properties of the plating film itself are not good and the adhesion to the base is not good, so that the heat treatment is performed as a solder film as in the method disclosed in Patent Document 3 above. Even if it is effective in such a use, it is difficult to adopt it for general purposes.

  In addition, in Patent Document 4, the substrate surface is degreased and etched by bringing a subcritical fluid or supercritical fluid in which a metal complex containing the same metal as the plating metal is dissolved into contact with the substrate, The metal complex is supported on the surface of the base material, and the metal complex supported on the surface of the base material is reduced to precipitate the metal in the metal complex on the surface of the base material to form a metal nucleus on the surface. Immersing the substrate on which the metal nuclei are formed in a plating solution containing the plating metal to form a plating layer by using the metal nuclei as they are as a self-catalyst to cause a continuous precipitation reaction. Including electroless plating methods are disclosed.

  However, the electroless plating method disclosed in Patent Document 4 also requires the formation of a thick metal layer because the deposition rate of the plating layer is slow, as in the case of the conventional electroless plating method. It is difficult to apply to the damascene method or the dual damascene method immediately.

  The inventors have conducted various experiments in order to obtain an electroless plating method in which the deposition rate of the plating layer is high and the adhesion to the base metal substrate is good. At least one of the active gas, the metal substrate, and the same kind of metal as at least one of the metal coating obtained by the electroless plating process, and a large amount of metal powder having an average particle size larger than 100 μm is added, and a subcritical state Alternatively, electroless plating was performed in a supercritical state. At this time, first, metal ions are precipitated from the plating solution to form a plating layer. The metal ions deposited and reduced are replenished by dissolving the metal powder having an average particle size larger than 100 μm in the plating solution.

  At this time, since the plating solution is in a subcritical or supercritical environment, friction does not occur and the viscosity is almost zero, the metal powder is difficult to be taken into the plating layer together with the large particle size of the metal powder. Generation of the inductive eutectoid phenomenon can be prevented, and a thin metal layer having a uniform and uniform thickness can be formed. In addition, the induction eutectoid phenomenon in this specification means the phenomenon in which a part of metal powder is simultaneously taken in into a plating film at the time of plating (refer FIG. 5).

  On the other hand, when the particle size of the metal powder is small, the metal powder is easily taken into the plating layer when adsorbed on the plating layer, causing an induction eutectoid phenomenon and forming a convex portion. From this point of view, by increasing the average particle size of the metal particles added in a large amount in the plating solution in the subcritical state or supercritical state to more than 100 μm, the metal ions can be sufficiently replenished, and the induced eutectoid phenomenon The inventors have found that a thin metal layer having a uniform and uniform film thickness can be formed without generating convex portions due to metal powder particles without generating the metal powder particles, and the present invention has been completed.

  That is, the present invention provides an electroless plating method in which a plating layer has a high deposition rate, has good adhesion to an underlying metal substrate, and can provide a uniform and uniform film thickness in a short time. With the goal.

  In order to achieve the above object, in the electroless plating method of the present invention, the electroless plating solution contains at least one of carbon dioxide and an inert gas and a surfactant, and a metal powder having an average particle size of more than 100 μm is made of metal. The powder is added and dispersed in an amount that does not dissolve the powder, and is characterized by performing electroless plating in a supercritical state or a subcritical state.

  In the electroless plating method, the present invention is characterized in that the metal powder is the same type of metal as at least one of a metal substrate and a metal coating obtained by electroless plating.

  According to the electroless plating method of the present invention, when electroless plating is performed on the surface of a metal substrate, the electroless plating solution contains at least one of carbon dioxide and an inert gas and a surfactant, and has an average particle size of 100 μm. A larger metal powder is added and dispersed in an amount that does not dissolve the metal powder. Electroless plating is performed in the supercritical or subcritical state, so the plating solution is subcritical or supercritical. Because it is a critical environment and friction is not generated and the viscosity is almost zero, the metal powder is difficult to be incorporated into the plating layer together with the large particle size of the metal powder and can prevent the occurrence of induction eutectoid phenomenon, A thin metal layer having a uniform and uniform film thickness can be formed.

  Further, according to the electroless plating method of the present invention, since the same kind of metal as the metal base and the metal coating obtained by the electroless plating treatment is dispersed as a metal powder in the plating solution, the electroless plating is performed. Since the metal ions deposited and reduced by the metal powder are replenished by dissolving the metal powder having an average particle size larger than 100 μm in the plating solution, a uniform and uniform film thickness can be obtained in a short time. .

  In addition, the present invention has the following excellent effects particularly when applied for forming fine wiring of highly integrated and miniaturized semiconductor circuit elements by the damascene method or dual damascene method.

  That is, in order to form a fine wiring of a semiconductor circuit element, a hole to be a wiring is provided on a base of a semiconductor substrate as shown in FIG. 3, a seed layer is formed thereon, and metal plating is performed so as to cover the seed layer. After performing the above, it is a general method to expose the fine wiring by polishing the flat surface. However, if the wiring is made finer, the hole becomes very small, and the hole is blocked by the metal particles, so that a cavity called “su” is generated in the fine wiring. (See FIG. 4C.)

  However, in the present invention, as an electroless plating solution, at least one of carbon dioxide and an inert gas and a surfactant are added, and a metal powder having an average particle size of more than 100 μm is added and dispersed in an amount that does not dissolve the metal powder. Since the electroless plating is performed in the supercritical state or subcritical state using the processed material, the plating solution is in a subcritical or supercritical environment and no friction is generated, and the viscosity is almost zero. In addition to the large particle size of the metal powder, the metal powder is difficult to be taken into the plating layer, and the plating solution can be sufficiently penetrated into the fine holes for forming the fine wiring. Can be formed. Therefore, the present invention can be effectively applied to the formation of fine wiring of highly integrated and miniaturized semiconductor circuit elements, particularly by the damascene method or dual damascene method.

[Electroless plating equipment]
As the electroless plating apparatus 10, as shown in FIG. 1, a pressure-resistant electroless plating tank 11 is used so that electroless plating can be performed using a supercritical fluid or a subcritical fluid. The pressure-resistant electroless plating tank 11 can be supplied with carbon dioxide from a carbon dioxide cylinder 12 to an inlet 16 provided in an upper lid 15 via a high-pressure pump unit 13 and a valve 14 as necessary. The carbon dioxide can be discharged from the outlet 17 provided in the upper lid 15 through the pressure adjustment unit 18 into the surrounding atmosphere.

  The pressure-resistant electroless plating tank 11 can be injected with a predetermined amount of electroless plating solution 19 by removing the lid 15, and a stirrer 20 as a stirring means is inserted into the pressure-resistant electroless plating tank 11. Yes. Further, the pressure-resistant electroless plating tank 11 is configured to maintain the electroless plating solution 19 placed in the oven 21 and inserted therein at a predetermined constant temperature. When measurement is performed under atmospheric pressure, the pressure-resistant electroless plating tank 11 can be opened to atmospheric pressure by operating the carbon dioxide cylinder 12, the high-pressure pump unit 13, the valve 14 and the pressure adjusting unit 18. It has become. In the electroless plating apparatus 10, the metal substrate sample 22 is held from the upper part of the pressure-resistant electroless plating tank 11 and can be immersed in the electroless plating solution 19 from the outside as necessary.

[Metal base]
A commercially available brass is used as the metal substrate used in various experimental examples, and the surface of the metal substrate is immersed in a palladium chloride activator aqueous solution as the above catalyst for 3 minutes at 25 ° C. after the pickling pretreatment. An activated metal substrate sample 22 was used.

[Experimental Examples 1 and 2]
As Experimental Examples 1 and 2, electroless plating was performed in each of a case where nickel powder was added (Experimental Example 1) and a case where nickel powder was not added (Experimental Example 2) in a supercritical state or a subcritical state. First, 30 mL of a predetermined electroless plating solution 19 is injected into the pressure-resistant electroless plating tank 11, and the metal substrate sample 22 is placed on the electroless plating solution 19 in the pressure-resistant electroless plating tank 11. 19 was placed so as not to touch. In this state, the temperature of the electroless plating solution in the pressure-resistant electroless plating tank 11 is heated to 80 ° C., and stirring of the electroless plating solution 19 is started by the stirrer 20 (stirring speed is constant at 300 rpm). The pressure in the pressure-resistant electroless plating tank 11 was increased to 10 MPa by manually operating the high-pressure pump unit 13, the valve 14 and the pressure adjusting unit 18.

  Then, since the critical temperature of carbon dioxide is 31.1 ° C. and the critical pressure is 7.38 MPa, the inside of the pressure-resistant electroless plating tank 11 is substantially supercritical or subcritical under the above temperature and pressure conditions. It is in a state. The electroless plating solution 19 is substantially free of friction and has a viscosity of nearly zero. The electroless plating solution 19 in an environmental state in which the friction is not generated and the viscosity is nearly zero is pressure-resistant electroless plating. The tank 11 is filled and fully in contact with the metal substrate sample 22.

  And pressure reduction of the pressure-resistant electroless plating tank 11 was started 30 minutes after the pressure in the pressure-resistant electroless plating tank 11 became 10 MPa, and the pressure in the pressure-resistant electroless plating tank 11 returned to atmospheric pressure. Occasionally, stirring of the electroless plating solution 19 was stopped, the lid 15 was removed, the metal substrate sample 22 was taken out, and the surface of the metal substrate sample 22 was visually observed after washing and drying. FIG. 2 shows a timing flowchart of the pressure-resistant electroless plating tank 11 of Experimental Examples 1 and 2, and Table 1 shows the measurement results obtained in Experimental Examples 1 and 2.

[Experimental Examples 3 and 4]
As Experimental Examples 3 and 4, electroless plating was performed for each of the case where nickel powder was added under atmospheric pressure (Experimental Example 3) and the case where nickel powder was not added (Experimental Example 4). First, 40 mL of a predetermined electroless plating solution 19 was injected into the pressure-resistant electroless plating tank 11 in an open air state, and the temperature of the electroless plating solution in the pressure-resistant electroless plating tank 11 was heated to 80 ° C. in this state. . Next, stirring of the electroless plating solution 19 was started with the stirrer 20 (stirring speed was constant at 300 rpm), and the metal substrate sample 22 was immersed in the electroless plating solution 19. After maintaining this state for 30 minutes, the metal substrate sample 22 was taken out, washed with water and dried, and the surface of the metal substrate sample 22 was visually observed. The measurement results obtained in Experimental Examples 3 and 4 are shown in Table 1 together with the measurement results of Experimental Examples 1 and 2.

  From the results shown in Table 1, the following can be understood. That is, when electroless plating was performed under atmospheric pressure, in the case of Experimental Example 4 in which nickel powder was not added to the electroless plating solution, the plating film was thin and unevenness was observed on the entire surface. Furthermore, in the case of Experimental Example 3 in which nickel powder was added to the electroless plating solution, a plating film was obtained, but the thickness was thin and unevenness was partially observed. The electroless plating solution used in Experimental Examples 3 and 4 is a conventionally used electroless plating solution, and because the deposition rate is slow, the electroless plating time is insufficient for 30 minutes, It is recognized that unevenness was observed. In addition, since Experimental Example 3 in which nickel powder was added to the electroless plating solution had better results than in Experimental Example 4 in which nickel powder was not added, electroless plating under atmospheric pressure However, the effect of improving the deposition rate of the plating layer by adding nickel powder is recognized for the time being.

  Furthermore, when electroless plating was performed in a supercritical state or a subcritical state, in the case of Experimental Example 2 where no nickel powder was added to the electroless plating solution, a good plating film was obtained, but ion supplementation was performed. It was not done sufficiently and the thickness was thin. On the other hand, in the case of Experimental Example 1 in which nickel powder was added to the electroless plating solution, ions were sufficiently replenished and a good thick plating film was obtained. From this result, in electroless plating in the supercritical state or subcritical state, the effect of improving the deposition rate of the plating layer is recognized without adding nickel powder, but the electroless plating time of 30 minutes is still short. Therefore, it can be seen that unevenness was partially recognized. On the other hand, in the case of Experimental Example 1 in which nickel powder is added to the electroless plating solution, the deposition rate of the plating layer is fast, so that a sufficiently thick plating layer is not uneven even after 30 minutes of electroless plating. Is formed.

  From the above, when performing electroless plating in the supercritical state or subcritical state, if the metal powder to be plated is added to the electroless plating solution in advance, the deposition rate of the plating layer is improved. In addition, it has been clarified that a plating film having a uniform and uniform thickness can be obtained and can be applied to the damascene method or the dual damascene method.

  In the above experimental example, a nickel powder having a particle size of 100 μm was used, but this nickel powder deposited a plating layer from the electroless plating solution and at the same time supplemented with nickel ions in the plating solution. As a result, it is possible to prevent unevenness of the plating layer due to the induction eutectoid phenomenon without being taken into the plating layer as the particle size increases. Also, it is preferable that the particle size of the metal particles is large so that the plating can be carried out densely and at high speed without generating “soot” even in a narrow place. In particular, when particles larger than 100 μm are used, the dispersion state in the electrolytic solution is good, so that the substrate structure having an accuracy of less than 1 μm can be easily electrolessly plated without being taken into the plating layer. Become. Further, when the particle size of the metal particles is up to about 1 mm, a good dispersion state can be obtained, and a dense and uniform film thickness can be obtained.

  In each of the above experimental examples, the case where the metal base is brass and the metal to be electrolessly plated has been described as nickel. However, the electroless plating method of the present invention is the case where the metal base and the metal to be electrolessly plated are the same type. Even if they are different types, the same effect can be obtained. Therefore, the metal substrate and the metal to be electrolessly plated are equally applicable not only to brass and nickel but also to copper, zinc, iron, nickel, cobalt, and the like.

It is the schematic of the electroless-plating apparatus used in each experiment example. It is a timing flowchart of the pressure | voltage resistant electroless-plating tank at the time of performing electroless plating using a supercritical fluid or a subcritical fluid. FIG. 3A to FIG. 3E are diagrams for sequentially explaining the wiring formation process of the conventional three-dimensional mounting semiconductor device. It is a figure explaining the void suppression process employ | adopted conventionally shown in FIG. It is a figure explaining the problem of the induction eutectoid phenomenon in which the metal particle was taken in into the plating layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electroless-plating apparatus 11 Pressure-resistant electroless-plating tank 12 Carbon dioxide cylinder 13 High pressure pump unit 14 Valve 15 Lid 16 Inlet 17 Outlet 18 Pressure adjusting unit 19 Electroless plating solution 20 Stirrer 21 Oven 22 Metal base sample

Claims (2)

  In the method of electroless plating on the surface of a metal substrate, the electroless plating solution contains at least one of carbon dioxide and inert gas and a surfactant, and the metal powder does not dissolve the metal powder having an average particle size of more than 100 μm. An electroless plating method, wherein the electroless plating is carried out in a supercritical state or a subcritical state.   2. The electroless plating method according to claim 1, wherein the metal powder is the same type of metal as at least one of a metal substrate and a metal coating obtained by electroless plating.

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