JP5545234B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a semiconductor device formed by sealing a semiconductor element with a resin and a manufacturing method thereof.

  In a semiconductor device (hereinafter referred to as a power semiconductor device), a semiconductor element (hereinafter referred to as a power semiconductor element) that controls and supplies power (power) is sealed with resin to ensure electrical insulation. Conventionally, as this type of power semiconductor device, a metal body and a mounting body in which an electronic element such as a power semiconductor element is electrically connected to the metal body is sealed with a mold resin (for example, , See Patent Document 1). In this power semiconductor device, a copper alloy having excellent workability and conductivity is used as the metal body, and after the power semiconductor element is soldered (die-bonded) to the copper alloy as the metal member, the power semiconductor element and the copper alloy Some are connected by wire bonding. However, the copper alloy is likely to be oxidized by the thermal history of the member manufacturing / storage process and the power semiconductor device manufacturing process. For this reason, the bonding property, wire bonding property, and adhesion to the sealing resin are remarkably lowered by the oxide film formed on the surface of the copper alloy. Therefore, a BTA (benzotriazole) rust preventive film is generally formed on the surface of the copper alloy as a rust preventive agent.

  On the other hand, the BTA rust preventive film used as a general copper alloy rust preventive film forms a reaction layer with copper on the surface of the copper alloy by oxidation. The reaction layer on the surface of the copper alloy also has bondability and wire bonding. And adhesiveness with the sealing resin are reduced. Therefore, as a countermeasure against oxidation of the copper alloy surface, a method of plating a metal body with a metal that is less oxidized than copper is conceivable. However, metals that are harder to oxidize than copper, such as nickel, palladium, silver, and gold, are very expensive, resulting in high manufacturing costs and low adhesion to the sealing resin. Since it is necessary to do so, the manufacturing process becomes complicated. Therefore, a non-BTA rust inhibitor that has a lower thermal decomposition temperature than the BTA rust preventive agent and can be decomposed and removed at the process temperature is applied to the copper alloy surface, and the power semiconductor is below the thermal decomposition temperature of the non-BTA rust inhibitor. There is a method in which the element is die-bonded and wire-bonded at a temperature at which the non-BTA rust preventive decomposes (see, for example, Patent Document 2). Moreover, when using a BTA type rust preventive film, there is a method for suppressing a decrease in adhesion to the sealing resin by managing the oxide film and the rust preventive film on the surface of the copper alloy before mounting the copper alloy ( For example, see Patent Documents 3 to 5).

Japanese Patent Laid-Open No. 9-129822 (page 6-7, FIG. 1) Japanese Patent Laid-Open No. 2003-197827 (page 4, FIG. 2) JP 2001-160610 A (page 3-4, FIG. 1) JP 2000-307051 (Page 5, Table 1) JP 7-48641 A (page 4-5, Table 1)

  In conventional power semiconductor devices, when a BTA rust preventive film is used, an oxide film and a rust preventive film on the surface of the copper alloy before the mounting process as described in Patent Documents 3 to 5 are used to suppress a decrease in adhesion with the sealing resin. Although a method for managing the adhesive film has been proposed, special equipment is required for the management, the surface condition of the actual copper alloy varies widely, and the evaluation area is the surface area of the power semiconductor device. The evaluation value is extremely small compared to the power semiconductor device, so it is difficult to apply it to the actual process as a method for managing the oxide film and rust preventive film on the copper alloy surface. There was a problem.

  The present invention has been made to solve the above-described problems, and copper that is a metal member can be obtained without special equipment and processes for managing an oxide film and a rust preventive film on the surface of a copper alloy. It is possible to prevent a rust preventive film from interfering with these adhesions at the interface between the alloy and the sealing resin, and to obtain a highly reliable semiconductor device having excellent adhesion between the metal member and the sealing resin. .

A semiconductor device according to the present invention is a semiconductor device formed by sealing a mounting body in which a semiconductor element is mounted on a copper alloy metal member with a sealing resin, and at the interface between the metal member and the sealing resin, A rust-preventing film that is formed in a gas atmosphere having a film thickness of 100 nm or less and having an acidic and reducing property, and an oxide film having an oxygen and copper component concentration of 50 at% or more intervenes to rust the metal member. Is not intervening.

The present invention provides an oxide film having a film thickness of 100 nm or less, an acidic and reducing gas atmosphere at the interface between a metal member and a sealing resin, and an oxygen and copper component concentration of 50 at% or more. Since a rust preventive film for preventing rust of the metal member is not interposed, a highly reliable semiconductor device having excellent adhesion between the metal member and the sealing resin can be obtained.

It is a cross-sectional schematic diagram of the power semiconductor device in Embodiment 1 of this invention. It is a flowchart which shows the manufacturing process of the power semiconductor device in Embodiment 1 of this invention. It is another flowchart which shows the manufacturing process of the power semiconductor device in Embodiment 1 of this invention. It is a measurement result of the film thickness of the rust preventive film on the copper alloy frame surface in Embodiment 1 of this invention, and the film thickness of an oxide film. It is a measurement result of the interface peeling rate of sealing resin in Embodiment 1 of the present invention. It is a flowchart which shows the manufacturing process of the power semiconductor device in Embodiment 2 of this invention. It is a measurement result of the film thickness of the oxide film of the copper alloy frame surface in Embodiment 2 of this invention, and the interface peeling rate of sealing resin.

Embodiment 1 FIG.
FIG. 1 is a schematic cross-sectional view of a power semiconductor device according to Embodiment 1 of the present invention. As shown in FIG. 1, the power semiconductor device 7 includes a heat spreader 1, lead frames 2a and 2b, bonding materials 3a and 3b, a power semiconductor element 4, a bonding wire 5, a sealing resin 6, and the like. The heat spreader 1 and the lead frames 2a and 2b are formed of a copper alloy that is a metal member.

  The heat spreader 1 radiates heat generated from the power semiconductor element 4, and the power semiconductor element 4 is provided on one surface thereof. The heat spreader 1 and the power semiconductor element 4 are bonded by a bonding material 3a. One end of the lead frame 2 a is electrically connected to the power semiconductor element 4 through a bonding wire 5. One end of the lead frame 2 b is joined to the power semiconductor element 4 by a joining material 3 b and is electrically connected to the power semiconductor element 4. The other ends of the lead frames 2a and 2b protrude outside the power semiconductor device 7 and can be connected to external wiring. A mounting body is configured by the heat spreader 1, the lead frames 2 a and 2 b, and the power semiconductor element 4. Then, the power semiconductor device 7 is formed by sealing the mounting body with the sealing resin 6.

  Thus, since the power semiconductor device 7 is sealed with the sealing resin 6, the adhesion between the heat spreader 1 and the lead frames 2a, 2b and the sealing resin 6 greatly affects the reliability of the power semiconductor device 7. To do. The heat spreader 1 and the lead frames 2a and 2b use a copper alloy having excellent electrical and thermal conductivity, and usually a rust preventive agent for preventing discoloration is applied to the surface. However, the rust preventive agent may inhibit the adhesion between the heat spreader 1 and the lead frames 2 a and 2 b and the sealing resin 6.

  We consider that the factor that affects the adhesion between the copper alloy and the sealing resin 6 is the heating at the time of joining the power semiconductor element 4 and the lead frames 2a and 2b. We investigated the relationship with the adhesion of the. As a result, the influence of the presence or absence of a rust inhibitor on the surface of the copper alloy is greatly affected by the adhesion of the sealing resin, and the growth process of the oxide film differs depending on the presence or absence of the rust prevention treatment on the copper alloy surface. When applied, it was found that the adhesiveness of the sealing resin was significantly lowered as the heating temperature increased. Furthermore, as a result of investigating the thermal characteristics of the rust preventive agent, the rust preventive film on the copper alloy surface undergoes multi-stage thermal decomposition in the general temperature range (180 to 400 degrees) at the time of joining, and the reaction causes the oxide film It has been found that the adhesive strength of the sealing resin is reduced by changing the form. Therefore, it was decided to prevent the adhesion strength of the sealing resin from being lowered by the following method.

  FIG. 2 is a flowchart showing manufacturing steps of the power semiconductor device according to the first embodiment of the present invention. In the metal member forming step, the metal members of the heat spreader 1 and the lead frames 2a and 2b are formed by pressing a copper alloy or etching a copper alloy. After the cleaning process, in the rust preventive coating process, a rust preventive film mainly composed of BTA is formed on the surface of the copper alloy, and the rust preventive film is stored. The BTA rust preventive film is composed of BTA and a reaction layer of BTA and a copper alloy. For example, after immersing a copper alloy in a diluted solution of BTA, the copper alloy is dried to obtain a BTA rust preventive film having a thickness of 1 nm to 300 nm.

  Next, in the element mounting step, the power semiconductor element 4 is mounted through a bonding material 3a at a predetermined position of the heat spreader 1 having a rust preventive film formed on the surface. Then, the heat spreader 1 and the power semiconductor element 4 are exposed to an atmosphere of an acidic / reducing gas (for example, nitrogen gas containing 3% by weight of formic acid), and the heat spreader 1 and the power semiconductor element 4 are combined in one heating step. The power semiconductor element 4 is die-bonded to the heat spreader 1 by heating and bonding. If the heating conditions are an atmospheric temperature of 180 ° C. or more and a heating time of 5 minutes or more, the heating conditions can be selected depending on the bonding material to be used. In addition, when using joining materials with melting, such as solder, it is desirable that the gas atmosphere is in a negative pressure state. As the bonding materials 3a and 3b, a solder mainly composed of tin is used. However, various solders such as zinc and bismuth, a metal sintered type for sintering a conductive inorganic filler at a low temperature, and an inorganic filler with a binder resin. It may be a conductive adhesive to be fixed. Moreover, the supply form of the bonding materials 3a and 3b may be a paste or powder in addition to pellets. The acidic / reducing gas preferably has a carboxyl group in the molecule such as formic acid and acetic acid (carboxylic acid), and a single or mixed gas containing polyvalent carboxylic acid such as oxalic acid or malic acid is acidic / reduced. It can be used as a sex gas.

  Next, in the frame mounting process, the lead frame 2b having a rust preventive film formed on the surface thereof is bonded to the heat spreader 1 and the main surface of the power semiconductor element 4 opposite to the surface where the heat spreader 1 is bonded. Install through. Heat spreader 1 and power semiconductor element 4 and lead frame 2b are exposed to the same acidic / reducing gas atmosphere as described above, and the main surface of heat spreader 1 and power semiconductor element 4 and lead frame 2b are heated in two heating steps. And join. In the present embodiment, the process of heating the heat spreader 1 and the power semiconductor element 4 and the process of heating the heat spreader 1, the power semiconductor element 4 and the lead frame 2b are separated, but simultaneously as shown in FIG. You may heat. The heating process in an acidic / reducing gas atmosphere decomposes and removes the BTA anticorrosive film and / or the reaction layer of the anticorrosive and copper on the surfaces of the heat spreader 1 and the lead frame 2b, which are copper alloys. The oxide film is reduced to a thickness of 5 nm or less.

  Next, the process proceeds to a wire bonding process (wiring process), and the power semiconductor element 4 and the lead frame 2 a are connected by the bonding wire 5. As a method for connecting the bonding wires 5, known wire bonding processes such as gold or copper ball bonding can be used in addition to aluminum stitch bonding. In this way, the heat spreader 1, the lead frames 2a and 2b, and the power semiconductor element 4 are joined to obtain a mounting body.

Thereafter, the process proceeds to a sealing process, and the mounting body is covered with a sealing resin 6 while leaving a part of the lead frames 2a and 2b by a molding method such as transfer molding or liquid casting, and the sealing resin 6 is applied in a curing process. Curing is performed to obtain the power semiconductor device 7. For the sealing resin 6, a general resin sealing material is used in addition to an epoxy resin composition mainly composed of an epoxy resin, a curing agent, and an inorganic filler. Here, the surface of the copper alloy of the heat spreader 1 and the lead frames 2a and 2b is thinner than 100 nm (more preferably 60 nm or less) by the wire bonding process and the sealing process, and the oxygen component and the copper component An oxide film having a total of 50 at% or more is formed, and no rust preventive film is interposed at the interface between the copper alloy and the sealing resin 6. The copper alloy and the sealing resin 6 are firmly bonded through this oxide film, and are difficult to peel off. If the oxide film component contains a large amount of nitrogen, carbon, and other alloys other than oxygen and copper, the film quality of the oxide film deteriorates. However, if the total of the oxygen component and the copper component is 50 at% or more, The original characteristics of the oxide film can be obtained, and the adhesion between the copper alloy and the sealing resin 6 can be improved. In addition, the oxide film is mainly composed of CuO and Cu ₂ O. However, if the thickness of the oxide film is greater than 100 nm, the film quality of Cu ₂ O, which is brittle in film quality, is increased. However, if the thickness of the oxide film is 100 nm or less, the adhesion between the copper alloy and the sealing resin 6 is also good.

  Hereinafter, the measurement results of the surface state of the copper alloy frame (corresponding to the heat spreader 1 and the lead frames 2a and 2b) when heated in an acidic / reducing gas atmosphere, and the interface peeling between the copper alloy frame and the sealing resin The measurement result of the rate will be explained, and the effect of improving the adhesion between the copper alloy frame and the sealing resin will be clarified. In FIG. 4, the measurement result of the film thickness of the rust preventive film and oxide film of the copper alloy frame surface measured according to heat processing conditions is shown. In FIG. 4, the horizontal axis represents heat treatment conditions, and the vertical axis represents the rust preventive film thickness (unit: nm) or oxide film thickness (unit: nm). The copper alloy frame used in the experiment has a rust preventive film formed mainly of BTA in advance.

  Heat treatment conditions are as follows: a copper alloy frame coated with a BTA rust inhibitor is heated in an acidic / reducing gas (nitrogen gas containing 3% by weight formic acid) atmosphere for 3 minutes, 5 minutes, 15 minutes, or 30 minutes. For comparison, there are five conditions for heat treatment in a nitrogen gas atmosphere for 3 minutes for comparison. For reference, an untreated case corresponding to the heat treatment is also shown. FIG. 4A, FIG. 4B, and FIG. 4C show the results when the heating temperatures are 150 ° C., 180 ° C., and 250 ° C., respectively. The film thickness was measured in depth profile mode by X-ray photoelectron spectroscopy (XPS) on 20 copper alloy frames with different production lots. The film thickness of the anticorrosive film was calculated using the photoelectron intensity ratio between nitrogen and copper, and the film thickness of the oxide film was calculated using the photoelectron intensity ratio between oxygen and copper. In FIG. 4 and FIG. 5 to be described later, the error bar shown for each condition indicates the maximum / minimum of the measurement results of 20 copper alloy frames, and symbols such as “Δ” and “◇” indicate the respective conditions. Average values are shown.

  In FIG. 5, the interface peeling rate of the sealing resin according to heat processing conditions is shown. 5 (a), 5 (b), and 5 (c) show the results when the heating temperatures are 150 ° C., 180 ° C., and 250 ° C., respectively. The interfacial peeling rate is a value indicating the ratio of the area where the sealing resin is peeled per unit area. The adhesion between the copper alloy frame and the sealing resin can be understood from the interface peeling rate. As the sealing resin, CEL-4650 manufactured by Hitachi Chemical Co., Ltd. was used. Using a push-pull tester (RX-20 manufactured by Aiko Engineering Co., Ltd.), a lateral load is applied at a constant speed of 1 mm / sec. Comparison was made by the area ratio of interfacial debonding at the fracture surface when shear fracture occurred. If the interfacial peel rate is 30% or less, there is no problem in practical use, and the interfacial peel rate of 30% is the adhesion standard. In order to satisfy the interface peeling rate of 30%, the film thickness of the rust preventive film needs to be approximately 0 nm, and the film thickness of the oxide film needs to be 100 nm or less.

  4 (a) and 5 (a), when the heating conditions in the acidic / reducing gas atmosphere are 150 ° C. or higher, the rust preventive film on the copper member surface has an average of 150 nm regardless of the heating time, and the interface peeling It can be seen that the rate is almost 100%, which is a condition in which the copper alloy frame and the sealing resin are hardly adhered to each other. On the other hand, from FIG. 4 (b) and FIG. 5 (b), in the case of heating conditions in an acidic / reducing gas atmosphere at 180 ° C. for 5 minutes or more, the rust preventive film on the surface of the copper member is 0 nm, The oxide film on the surface of the copper member is 100 nm or less, and the interface peeling rate is 30% or less, which satisfies the adhesion standard. Moreover, from FIG.4 (c) and FIG.5 (c), when the heating conditions in acidic / reducing gas atmosphere are 250 degreeC or more and 3 minutes or more, the rust preventive film on the surface of a copper member is 0 nm, The oxide film on the surface is 100 nm or less, and the interface peeling rate is 30% or less, which satisfies the adhesion standard. That is, when the heating conditions in an acidic / reducing gas atmosphere are 180 ° C. or more and 5 minutes or more, or 250 ° C. or more and 3 minutes or more, the rust preventive film on the surface of the copper member is 0 nm, The oxide film has a thickness of 100 nm or less, an interface peeling rate of 30% or less, and satisfies the adhesion standard between the copper alloy frame and the sealing resin. On the other hand, when heated in a nitrogen gas atmosphere, the rust preventive film remains and the interfacial peeling rate is almost 100% regardless of the heating temperature (150 ° C., 180 ° C., 250 ° C.). It can be seen that the sealing resin and the sealing resin are difficult to adhere to each other.

  As described above, the copper alloy constituting the mounting body is formed by heating the mounting body for 5 minutes or more at a temperature of 180 ° C. or higher in an acidic and reducing gas atmosphere to seal the mounting body and the sealing resin. In the interface between the sealing resin and the sealing resin, only copper oxide having a film thickness of 100 nm or less and oxygen and copper components of 50 at% or more may be interposed, and a rust preventive film for preventing rust of the copper alloy may not be interposed. it can. In addition, a BTA-based anticorrosive film and / or a reaction layer of copper and an antirust agent is formed on the surfaces of the heat spreader 1 and the lead frames 2a and 2b, which are copper alloys in the mounting body, by a heating process in an acidic / reducing gas atmosphere. Is decomposed and removed, and the oxide film is reduced to 5 nm or less. By such a manufacturing method, there is no rust preventive agent that inhibits adhesion at the interface between the copper alloy and the sealing resin, the reaction layer of the rust preventive agent and the copper alloy, and the oxide film that has grown into a fragile structure. A highly reliable semiconductor device having excellent adhesion between the alloy and the sealing resin can be obtained. In addition, a special equipment or process for managing the oxide film and the rust preventive film on the surface of the copper alloy is not required, and a mounting body in a surface state with excellent adhesion to the sealing resin can be obtained.

Embodiment 2. FIG.
FIG. 6 is a flowchart showing manufacturing steps of the power semiconductor device according to the first embodiment of the present invention. The first embodiment is different from the first embodiment in that it includes a step of exposing the mounting body to a dry gas containing oxygen immediately after heating the lead frame which is a copper alloy. As shown in FIG. 6, immediately after the step of heating the heat spreader 1 and the power semiconductor element 4 and the lead frame 2b in an acid / reducing gas atmosphere and bonding them via the bonding material 3b, the oxygen-containing water content is 500 ppm. A process of exposing to the following oxygen gas (dry gas) has been added.

  FIG. 7 shows the thickness of the oxide film formed on the surface of the copper alloy frame, which is a metal member, the components in the oxide film (oxygen and copper component concentrations), with respect to the heat treatment conditions and the presence or absence of the oxygen gas exposure step. The result of having measured the interface peeling rate showing the adhesiveness of a copper alloy frame and sealing resin is shown. The component concentration of oxygen and copper indicates the component concentration of oxygen and copper contained in the oxide film, and the unit is at%. As a copper alloy frame, oxygen-free copper coated with a BTA-based rust preventive agent and Cu-0.5 wt% Sn alloy were prepared, and at 150 ° C. or 180 ° C. in nitrogen gas containing 3% by weight of formic acid, respectively. After heating for 15 minutes, it was immediately replaced with a dry gas of 50 at% oxygen and 50 at% nitrogen having a water content of 500 ppm or less, and then stored in the atmosphere.

  The film thickness was measured in the depth profile mode by X-ray photoelectron spectroscopy (XPS) on 20 copper alloy frames with different production lots as in the first embodiment. In addition, the component ratio of each detection component (C, N and alloy component) was measured in the wide scan mode. From FIG. 7, the one exposed to a dry gas containing oxygen after heating at 180 ° C. has better adhesion between the copper alloy frame and the sealing resin than the one exposed to the air immediately after heating, and the oxide film at this time Satisfies the condition that the concentration of oxygen and copper components is 50 at% or more (the concentration of other components other than oxygen and copper is 50 at% or less). On the other hand, the Cu-0.5 wt% Sn alloy containing Sn has a high interface peeling rate (average value) of about 30% even when heated at 180 ° C. for 15 minutes. It can be seen that the adhesion with the stop resin is not good.

  As described above, immediately after heating a metal member in an acid / reducing gas at 180 ° C. or more and for 5 minutes or more, a step of exposing to a dry gas containing oxygen and a water content of 500 ppm or less is added to form a copper alloy as a metal member By sealing the sealing resin with the sealing resin, it is possible to form an oxide film on the surface of the copper alloy by contacting with oxygen before exposure to the atmosphere. An excellent and highly reliable semiconductor device can be obtained.

  In the first and second embodiments, the case where solder is used as the bonding material 3 has been described, but silver nanopaste may be used as the bonding material 3. Using silver nanopaste, after heating at 180 ° C. for 15 minutes in nitrogen gas containing 3% by weight of formic acid, it was replaced with 50 at% oxygen and 50 at% nitrogen mixed gas with a water content of 500 ppm or less and baked at 300 ° C. for 15 minutes. In this case, the adhesion strength between the silver nanopaste and the sealing resin is 1.5 times that when fired in the air, and it is known that the adhesion standard with the sealing resin is satisfied.

  DESCRIPTION OF SYMBOLS 1 Heat spreader, 2a, 2b Lead frame, 3a, 3b Bonding material, 4 Power semiconductor element, 5 Bonding wire, 6 Sealing resin, 7 Power semiconductor device.

Claims (4)

A semiconductor device formed by sealing a mounting body in which a semiconductor element is mounted on a copper alloy metal member with a sealing resin,
At the interface between the metal member and the sealing resin, an oxide film having a film thickness of 100 nm or less, an acidic and reducing gas atmosphere, and an oxygen and copper component concentration of 50 at% or more is interposed. And a rust preventive film for preventing the metal member from being rusted. A manufacturing method of a semiconductor device formed by sealing a mounting body in which a semiconductor element is mounted on a copper alloy metal member with a sealing resin,
A sealing step of sealing the mounting body with the sealing resin;
A method of manufacturing a semiconductor device comprising: a heating step of heating the mounting body for 5 minutes or more at a temperature of 180 ° C. or higher in an acidic and reducing gas atmosphere before the sealing step.   3. The method of manufacturing a semiconductor device according to claim 2, further comprising a step of exposing the mounting body in an oxygen-containing gas atmosphere having a moisture concentration of 500 ppm or less following the heating step before the sealing step. . Wherein the heating step, the method of manufacturing a semiconductor device according to claim 2 or claim 3, characterized in that a film thickness Gaze Hollow rust preventing film formed on the surface of the metal member.

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