JP5736945B2 - Partial plating method - Google Patents

Description

  The present invention relates to a method of partially plating only one aluminum electrode layer in a semiconductor substrate composed of an insulating layer and two aluminum electrode layers sandwiching the insulating layer.

  When forming an electroless plating film only on one aluminum electrode layer of a semiconductor substrate composed of an insulating layer and two aluminum electrode layers sandwiching the insulating layer, the other aluminum electrode that does not want to form an electroless plating film It is necessary to take measures to prevent plating metal deposition on the surface of the layer.

  Therefore, in the conventional plating method, the plating process is performed after a masking material such as glass, a resin film, or a semiconductor resist is attached to the surface of the other aluminum electrode layer. In this method, the materials that can be used as the masking material are limited because of the fact that elution into the plating solution and the generation of foreign matter are not possible and the removal after the plating treatment is possible. Furthermore, in order to prevent the plating solution from penetrating between the surface of the aluminum electrode layer where the plating film is not desired to be formed and the masking material, the masking material needs to be adhered to the surface of the aluminum electrode layer with high accuracy and high adhesion. Yes, this pasting process takes a long time.

  For these reasons, there is a problem that the manufacturing time is long and the manufacturing cost is high due to the masking material attaching step and the peeling step after the plating treatment. Furthermore, since the thickness of the semiconductor wafer is generally as thin as about 1 mm or less, a residual stress is generated in the semiconductor substrate by applying a masking material, which may cause warping of the semiconductor substrate, or masking from the semiconductor substrate after the plating process. Cracks may occur in the semiconductor substrate due to the peeling load acting when the material is peeled off, and there is a problem from the viewpoint of manufacturing yield.

  Here, turning to the conventional published technique, in Patent Document 1, a plate-like metal in which another metal plate (II) is arranged on at least one side of the main surface of the metal plate (I) via an insulating layer is disclosed. On the other hand, a partial plating method is disclosed in which an electroless plating is partially applied to the metal plate (II) by supplying a current having a polarity opposite to that of the plating solution.

  According to this technique, since it is not necessary to apply the masking material to one surface of the semiconductor substrate, there is a problem that the manufacturing time is long, and the semiconductor substrate is warped by applying or peeling the masking material. Problems such as cracks and cracks can be solved.

  However, in this method, as described in paragraph 0011, the current load portion may be oxidized depending on the current value to cause surface roughness. In addition, in a semiconductor substrate composed of an insulating layer and two aluminum electrode layers sandwiching the insulating layer, aluminum has a strong passive film (oxide film) on its surface, so a current having a reverse polarity is simply passed. By the way, accurate partial plating cannot be performed, and it is difficult to form a plating film on the surface of the aluminum electrode layer where it is desired to form a plating film.

JP 2003-183842 A

  The present invention has been made in view of the above-described problems, and relates to a method of partially plating only one aluminum electrode layer on a semiconductor substrate composed of an insulating layer and two aluminum electrode layers sandwiching the insulating layer. Issues that may occur when masking material is attached to one side of a semiconductor substrate, such as a problem that the manufacturing time takes a long time, and issues such as warping or cracking of the semiconductor substrate due to attachment or peeling of the masking material occur. An object of the present invention is to provide a partial plating method that can form a plating film on one aluminum electrode layer with high accuracy.

  In order to achieve the above object, a method of partially plating according to the present invention includes a first aluminum layer of a semiconductor substrate comprising an insulating layer and first and second aluminum electrode layers sandwiching the insulating layer. A method in which plating is performed only on the electrode layer, wherein the semiconductor substrate is immersed in a zincate bath, and a potential for preventing zinc deposition is applied to the second aluminum electrode layer by connecting a wiring leading to a power source. In the first step of producing an intermediate in which a zinc-substituted film is formed only on the first aluminum electrode layer by performing a zincate process, an electroless plating process is performed by immersing the intermediate in a nickel plating bath, This comprises a second step of forming an electroless nickel coating on the first aluminum electrode layer.

  The method of partially plating according to the present invention is a semiconductor substrate whose object is an insulating layer and first and second aluminum electrode layers sandwiching the insulating layer, and aluminum (pure aluminum or aluminum alloy). Any electrode layer having a passive film on its surface because of the electrode layer made of any one of them, and therefore, difficult to plate, and thus with partial plating with high precision, that is, one of the two aluminum electrode layers In this method, a plating film can be formed only on the layer.

  This semiconductor substrate is an insulating substrate with an aluminum circuit (DBA: Direct Brazed Aluminum, aluminum nitride) sandwiched between two pure aluminum electrode layers, which is used in inverters for high-power motor power control, etc. Insulating substrate).

  The plating method of the present invention forms an electroless nickel coating only on the first aluminum electrode layer (one aluminum electrode layer) of the first and second aluminum electrode layers constituting the semiconductor substrate. .

  First, as a first step, the semiconductor substrate is immersed in a zincate bath, and a zincate treatment is performed in a state where a potential for preventing zinc deposition is applied by connecting a wiring leading to a power source to the second aluminum electrode layer.

  Here, zincate is zincate and is one of the chemical species of zinc that exists stably in strong alkali. By reacting zincate with aluminum, it dissolves aluminum and zinc on its surface. Is substituted and deposited to form a zinc-substituted film.

  In the method of the present invention, the electroless nickel coating is formed on the surface of the first aluminum electrode layer, and the electroless nickel coating is not formed on the surface of the second aluminum electrode layer. In the step, it is desired to form a zinc replacement film only on the surface of the first aluminum electrode layer during the zincate treatment.

  Therefore, in this zincate treatment, a potential (potential for preventing zinc deposition) based on the difference between the oxidation-reduction potentials of both aluminum and zinc (oxidation-reduction potential difference) required for suppressing zinc deposition is applied to the second aluminum electrode layer. Apply only to.

  In this first step, an intermediate in which a zinc substitution film is formed only on the surface of the first aluminum electrode layer is manufactured.

  Next, as a second step, an electroless plating process is performed by immersing the intermediate in a nickel plating bath.

  In contrast to electro nickel plating, electroless nickel plating has a great advantage in that a nickel coating can be completely formed at a desired site even if the workpiece has a complicated shape.

  Since the passive film is still formed on the second aluminum electrode layer which is one surface of the intermediate body immersed in the nickel plating bath, the nickel film is not formed.

  On the other hand, since the zinc replacement film is formed on the surface of the first aluminum electrode layer, the zinc replacement film is replaced with nickel ions in the initial stage of the nickel plating process. The substitution reaction with the nickel ions is promoted, nickel plating is deposited, and an electroless nickel coating is formed.

  The formed electroless nickel coating and aluminum forming the underlying first aluminum electrode layer are chemically bonded firmly.

  In this way, a semiconductor substrate is produced in which an electroless nickel coating is formed only on the surface of the first aluminum electrode layer.

  According to the verification by the present inventors, when an electroless nickel coating having a thickness of 10 μm is formed, a current having a reverse polarity as disclosed in Patent Document 1 is applied in a nickel plating bath for 60 minutes. A certain amount of continuous energization is required. On the other hand, since the energization time in the zincate process requiring energization as in the method of the present invention may be about 30 seconds, the required power consumption is remarkably reduced.

  The nickel plating bath is preferably one containing nickel sulfate as a main agent and sodium hypophosphite as a reducing agent, and more specifically, in addition to these, an organic acid salt as a complexing agent or It is preferable that sodium hydroxide and ammonia as pH adjusting agents, zinc-based inorganic compounds as stabilizers and sulfur-based compounds as additives are contained.

  According to the present inventors, by using a nickel plating bath in which sodium hypophosphite as a reducing agent is contained in nickel sulfate as a main agent, an electroless nickel coating is completely formed on the surface of the second aluminum electrode layer. Has not been formed.

  As can be understood from the above description, according to the method of partial plating of the present invention, a part of only one aluminum electrode layer is formed with respect to a semiconductor substrate composed of an insulating layer and two aluminum electrode layers sandwiching the insulating layer. In the method of performing electroless plating after forming a zinc-substituted film by zincate treatment on an aluminum electrode layer on which an electroless nickel coating is to be formed, the electroless nickel coating is performed during zincate treatment. By applying a potential for preventing zinc precipitation to an aluminum electrode layer that is not desired to be formed, an electroless nickel coating can be accurately formed only on the surface of one aluminum electrode layer. Moreover, according to this method, since the power consumption required for the zincate process may be extremely small, the processing cost required for the plating process is also low.

It is a schematic diagram explaining the 1st step of the method of performing plating partially of the present invention. It is a schematic diagram explaining the intermediate body manufactured at the 1st step. It is a schematic diagram explaining a 2nd step following FIG. It is a schematic diagram explaining the semiconductor substrate by which the electroless plating process was carried out at the 2nd step. It is a photograph figure which shows the experiment result which imaged the organization of the aluminum electrode layer after electroless plating processing, (a) is a photograph figure of the original aluminum electrode layer surface, and (b) is an electroless nickel coat formation It is a photograph figure of the 2nd aluminum electrode layer surface which is not carried out, (c) is a photograph figure of the electroless nickel coat on the 1st aluminum electrode layer surface. It is the photograph figure which shows the experimental result which verified the presence or absence of formation of the electroless nickel film by the presence or absence of a zincate process, (a) is a photograph figure of the original aluminum electrode layer surface, (b) does not perform a zincate process 2 is a photograph of the surface of the first aluminum electrode layer (without formation of electroless nickel coating), and (c) is a photograph of the electroless nickel coating on the surface of the first aluminum electrode layer when zincate treatment is performed. It is.

  Hereinafter, an embodiment of a method of performing plating partially according to the present invention will be described with reference to the drawings. 1 to 4 are sequential flowcharts of the method of partially plating the present invention. Specifically, FIG. 1 is a schematic diagram for explaining the first step, and FIG. FIG. 3 is a schematic diagram for explaining the second step, and FIG. 4 is a schematic diagram for explaining the electroless plating-treated semiconductor substrate.

  As shown in FIG. 1, first, in the first step, in the zincate bath accommodated in the container Y1, the insulating layer 1 and the first and second aluminum electrode layers 2, 3 sandwiching the insulating layer 1 are arranged. A semiconductor substrate 4 made of (a semiconductor substrate before electroless plating treatment) is immersed.

  Examples of the semiconductor substrate 4 include an insulating substrate (DBA) with an aluminum circuit, and the insulating layer in this case is AIN (aluminum nitride).

  An insoluble electrode F is also immersed in the zincate bath, and a wiring leading to the positive electrode of the power source B is connected to the second aluminum electrode layer 3 constituting the semiconductor substrate 4, and the insoluble electrode F is also connected to the negative electrode of the power source B. It is connected to the wiring that leads to completion of preparation for zincate processing.

  Next, a zincate process is performed. In this zincate treatment, a potential (potential for preventing zinc deposition) based on the difference between the oxidation-reduction potentials of both aluminum and zinc (oxidation-reduction potential difference) required for suppressing zinc deposition is applied to the second aluminum electrode layer 3. To do.

  For example, the zincate treatment is completed by applying a potential of about 5 V having a polarity opposite to that of the zincate bath for about 30 seconds.

  In the zincate treatment, the current application time is less than 1 minute, for example, about 30 seconds, and the zincate reacts with the aluminum only on the surface of the first aluminum electrode layer 2 where no potential is applied, and the aluminum is dissolved. Then, zinc is substituted and deposited on the surface, and a zinc-substituted film 5 is formed as shown in FIG. 2a.

  Note that the surface of the second aluminum electrode layer 3 to which the potential for preventing zinc precipitation was applied is similar to the state before the zincate treatment, as shown in FIG. 2b in which the portion b in FIG. 2a is enlarged. The oxide film 3b which is a passive film remains on the surface of 3a.

  By the first step, the intermediate body 6 in which the zinc substitution film 5 is formed only on the surface of the first aluminum electrode layer 2 is manufactured.

  Next, as a second step, the electroless plating process is performed by immersing the intermediate 6 produced in the first step in a nickel plating bath accommodated in the container Y2.

  In this electroless plating treatment, an electroless nickel coating is not formed on the second aluminum electrode layer 3 where the oxide coating 3b remains on the surface.

  On the other hand, the zinc substitution film 5 on the surface of the first aluminum electrode layer 2 is replaced with nickel ions in the initial stage of the nickel plating process, and further, substitution reaction with the nickel ions is performed by autocatalysis. Is promoted to deposit nickel plating, and an electroless nickel coating 7 is formed as shown in FIG.

  The formed electroless nickel coating 7 and the aluminum forming the underlying first aluminum electrode layer 2 are chemically bonded firmly and only partially on the surface of the first aluminum electrode layer 2. The semiconductor substrate 10 on which plating has been performed is manufactured.

  According to the method comprising the series of flows shown in the figure, in the method of performing electroless plating after forming the zinc-substituted film 5 on the first aluminum electrode layer 2 on which the electroless nickel coating 7 is to be formed by zincate treatment. By applying a potential for preventing zinc precipitation to the second aluminum electrode layer 3 where it is not desired to form the electroless nickel coating 7 during the zincate treatment, the first aluminum electrode layer is finally formed. The electroless nickel coating 7 can be accurately formed only on the surface 2. In addition, according to this method, the time required for the zincate treatment is less than 1 minute, and the power consumption may be significantly less than in the case of a method in which a current having a reverse polarity is continuously energized by the electroless plating treatment. Therefore, the processing cost required for the plating process is also low.

[Results of observation of the structure of the aluminum electrode layer after electroless plating]
The present inventors performed an alkali etching treatment, and formed an electroless nickel coating only on the surface of the first aluminum electrode layer by the method of the present invention described above for the semiconductor substrate subjected to the acid cleaning treatment, The structures of the surface of the electroless nickel coating, the surface of the second aluminum electrode layer on which the electroless nickel coating was not formed, and the surface of the aluminum electrode layer before the electroless plating treatment were observed and imaged.

  In this experiment, Uemura Kogyo Epitus NPR-18 was used as the nickel plating bath used in the electroless plating process. Fig. 5a shows a photograph of the original aluminum electrode layer surface, Fig. 5b shows a second aluminum electrode layer surface on which an electroless nickel coating is not formed, and Fig. 5c shows the first aluminum electrode layer surface. The photograph figure of the electroless nickel coating of each is shown.

  As apparent from these photographic drawings, by applying the method of the present invention and using the plating bath of the above components as the nickel plating bath, the surface of the second aluminum electrode layer is the original aluminum electrode. As with the surface of the layer, no electroless nickel coating is formed, and it has been demonstrated that the surface of the first aluminum electrode layer is completely covered with the electroless nickel coating.

[Results of experiments to verify the presence or absence of electroless nickel coating with and without zincate treatment]
The inventors of the present invention performed both the method of performing electroless plating without performing a zincate treatment and the method of performing the zincate treatment which is the method of the present invention and then performing the electroless plating treatment. An experiment was conducted to verify the presence or absence of film formation.

  In this experiment, the same nickel plating bath as in the experiment described above is used. FIG. 6a shows a photograph of the original aluminum electrode layer surface, FIG. 6b shows a photograph of the first aluminum electrode layer surface when the zincate treatment is not performed, and FIG. 6c shows a first photograph when the zincate treatment is performed. The photograph figure of the aluminum electrode layer surface of each is shown.

  As can be seen from these photographs, when the zincate treatment is not performed, no electroless nickel coating is formed on the surface of the first aluminum electrode layer (also formed on the surface of the second aluminum electrode layer). The same is not done).

  On the other hand, it has been demonstrated that the surface of the first aluminum electrode layer is completely covered with the electroless nickel coating when the zincate treatment is performed and then the electroless plating treatment is performed.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Insulating layer, 2 ... 1st aluminum electrode layer, 3 ... 2nd aluminum electrode layer, 4 ... Semiconductor substrate before electroless-plating process, 5 ... Zinc substituted film, 6 ... Intermediate, 7 ... Electroless nickel Coating, 10 ... Semiconductor substrate after electroless plating treatment

Claims (2)

An insulating layer, a first sandwiching the insulating layer, and a second aluminum electrode layer, of the semiconductor substrate made of a method of performing fit Kki only the first aluminum electrode layer,
Only the first aluminum electrode layer is obtained by immersing the semiconductor substrate in a zincate bath, connecting the wiring leading to the power source to the second aluminum electrode layer and applying a zinc deposition preventing potential to the zincate treatment. a first step of fabricating the intermediate of zincate film is formed,
Immersing the intermediate nickel plating bath performed electroless plating, and a second step of forming an electroless nickel film on the first aluminum electrode layer, a method of performing partial plating. The nickel plating bath is one in which sodium hypophosphite as a reducing agent to nickel sulfate is the main agent is contained, a method for partial plating of claim 1.

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