Conductive bonding material, method for producing conductive bonding material, and bonding member

Abstract

To provide a conductive bonding material consisting of a metal powder molding, the conductive bonding material capable of being enlarged in area and approximated in a film state, and a manufacturing method thereof.SOLUTION: In a conductive bonding material consisting of a molding of a metal powder formed on a substrate and having a predetermined area, the metal powder is a powder consisting of a metal such as gold of which the purity is 99.9 mass% or more and the average grain diameter is 0.005 μm or more and 1.0 μm or less. The conductive bonding material is divided into a first region and a second region, which is a residual region, in a planar view, both a minimum dimension L1 of the first region and a minimum dimension L2 of the second region are 5 μm or more and a ratio of L1 and L2 is 0.25 or more and 4 or less. In the conductive bonding material, a clearance between the first region and the second region in a cross-sectional view is less than 1 μm and the conductive bonding material is in such a mode that it can be approximated in a film state. Examples of concrete shapes of the first region may include a lightning pattern, a waveform pattern, a concentric circle pattern, and a wave crest pattern.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a conductive bonding material that is applicable to bonding processes such as die bonding and flip-chip mounting of semiconductor chips, and a method for manufacturing the same, and a bonding member that includes the conductive bonding material. [Background technology]

[0002] The applicant has previously proposed methods for manufacturing various devices using conductive bonding materials made of compacted metal powders for die bonding, flip-chip mounting, and the like (Patent Documents 1 to 4). This conductive bonding material is a sintered or dried body of metal powder made of high-purity metal within a specific particle size range. To form the conductive bonding material, a metal paste in which the above-mentioned metal powder is dispersed in a solvent is used as a precursor. In the bonding process using the applicant's conductive bonding material, the metal paste is applied to a substrate or base material such as a device, and then dried or fired to form the conductive bonding material. Subsequently, members to be bonded, such as semiconductor elements, are placed on the conductive bonding material, and pressure and heat are applied to sinter the metal powder, completing the bonding.

[0003] The present applicant's conductive joining material made from metal powder compacts offers many advantages. Specifically, the conductive joining material made from metal powder allows for joining temperatures below 300°C. This allows for low-temperature joining compared to traditional brazing filler metals (e.g., gold brazing, silver brazing, etc.), which have long been used as joining materials. Such low-temperature joining properties are useful for reducing thermal damage to substrates, semiconductor devices, etc. Furthermore, joining using metal powder compacts is also effective from the perspective of ensuring the bonding strength of the joint. During the joining process, necking and plastic deformation of the metal particles themselves occur within the heated and pressurized metal powder sintered compact, reducing internal voids and resulting in densification. The densified conductive joining material can firmly bond semiconductor devices, etc., to substrates. Furthermore, the metal paste, which is the precursor to the conductive joining material, exhibits excellent coatability and printability when appropriately configured with solvents, etc., making it easy to form the joining material into the desired shape.

[0004] Due to these advantages, in addition to various semiconductor devices made of Si-based semiconductors (single-crystal Si, SiC, etc.), the scope of application of the conductive bonding material made of a metal powder compact is also being considered for joining processes of power devices, etc. made of compound semiconductors such as Ga-based semiconductors (GaAs, GaN, GaP).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] With the expansion of the application scope as described above, for the conductive bonding material made of a metal powder compact, improvements in characteristics other than the conventionally known low-temperature joining property, etc. are required. For example, for the joining of power devices, etc. expected in the future, since the compound semiconductors to be mounted are relatively brittle, a reduction in the pressure applied during joining is required. The above Patent Document 3 discloses a conductive bonding material that can be joined even with low pressure by applying a metal powder compact in which the deformation resistance having predetermined parameters is adjusted.

[0007] Furthermore, bonding of power devices, etc., where chip size increases with increasing capacity, requires larger-area bonding materials. In this regard, conductive bonding materials using metal paste as a precursor are inherently difficult to fabricate in large areas. Manufacturing conductive bonding materials on substrates typically involves applying a resist to the substrate, then exposing and developing the resist to create through-holes. Metal paste is then applied and filled into these holes, followed by drying and firing to form the desired pattern of conductive bonding material. Because the metal paste contains a solvent in addition to the metal powder, excess metal paste is filled relative to the depth of the through-holes to account for volume loss due to solvent evaporation after drying and firing. The metal powder that protrudes from the through-holes is then scraped off with a squeegee or other tool. However, the shear stress generated during the scraping process can gouge the surface of the conductive bonding material, damaging its flatness. The loss of flatness becomes more pronounced as the scraping distance increases, making it difficult to fabricate conductive bonding materials in large areas.

[0008] The above-mentioned Patent Document 3 also proposes a conductive bonding material that takes into consideration both a large area and flatness. In this prior document, multiple conductive bonding materials are set and placed close to each other with a spacing of 1 μm. In this way, a quasi-integrated film-like bonding material composed of multiple conductive bonding materials can be obtained.

[0009] However, even though the conductive bonding material in Patent Document 3 is approximated to a film, there are still gaps. And even if the gaps are as small as about 1 μm, they can affect the conductivity and heat dissipation at the junction of the device.

[0010] The present invention has been made under the above-mentioned circumstances, and its object is to provide a conductive bonding material and a manufacturing method thereof, which is made by the applicant of the present application and is composed of a molded body of a predetermined metal powder, and which can increase the area in which the metal powder molded body is formed and minimize gaps within the area, thereby forming a conductive bonding material that is closer to a film-like state than conventional conductive bonding materials. [Means for solving the problem]

[0011] The present inventors have considered that, in order to increase the area of ​​a conductive bonding material made of a metal powder compact, it is preferable to carry out the process of applying a metal paste and forming a metal powder compact in two stages. If it is unavoidable to form gaps of 1 μm or more when manufacturing a metal powder compact using a metal paste as a precursor, it is thought that a compact can be manufactured with gaps intentionally in the first stage, and then, in the second stage, the gaps can be filled with metal paste and dried to form an integrated compact.

[0012] However, according to the inventors' investigations, even in such a two-stage manufacturing process, depending on the width of the gap between the molded bodies formed in the first stage, it has been confirmed that the metal powder of the metal paste cannot be sufficiently filled into the gap in the second stage. For example, referring to Patent Document 3, the inventors have confirmed that when a conductive bonding material is formed while leaving a gap of 1 μm or more (4 μm) and then a metal paste is applied to fill the gap, the metal powder remains at the top of the gap (near the opening) and does not fill to the bottom of the gap (near the substrate). This is thought to be because, although the size (particle size) of the metal powder in the metal paste itself is smaller than the gap, it does not reach the bottom of the gap due to the influence of the viscosity and surface tension of the metal paste, etc.

[0013] Therefore, the inventors conducted research to find suitable shape and size conditions based on the two-stage process of forming a metal powder compact, and as a result, came up with the conductive bonding material of the present invention.

[0014] That is, the present invention provides a conductive bonding material comprising a metal powder compact having a predetermined area formed on a substrate, wherein the metal powder constituting the compact is a powder consisting of one or more metals selected from the group consisting of gold, silver, platinum, and palladium with a purity of 99.9% by mass or more and having an average particle size of 0.005 μm or more and 1.0 μm or less, wherein the conductive bonding material is divided into a first region and a second region which is the remaining region in a planar view, wherein the minimum dimension L1 of the first region and the minimum dimension L2 of the second region are both 5 μm or more, and the ratio L1 / L2 of L1 to L2 is 0.25 or more and 4 or less, and further wherein the conductive bonding material has a gap of less than 1 μm between the first region and the second region in a cross-sectional view.

[0015] Here, the minimum dimensions L1 and L2 of the first and second regions are preferably 140 μm or less.

[0016] The first region may have a shape in which two or more unit squares, each having a side length equal to the minimum dimension L1, are formed in a regular pattern.Furthermore, the first region may have a shape in which curves, each having a line width equal to the minimum dimension L1, are formed in a regular pattern.

[0017] The bonding member according to the present invention includes a base material and at least one of the above-described conductive bonding materials.

[0018] The conductive bonding material according to the present invention is formed by applying a predetermined metal paste and performing drying and sintering in two steps. That is, the method for producing a conductive bonding material according to the present invention is a method for producing a conductive bonding material using a metal paste containing metal powder having an average particle size of 0.005 μm or more and 1.0 μm or less, and includes the steps of: coating a substrate surface with a resist; forming first through holes in regions corresponding to first regions of the resist, filling the first through holes with the metal paste, and then forming a compact of the metal powder contained in the metal paste; forming second through holes in regions corresponding to second regions of the resist, filling the second through holes with the metal paste, and then forming a compact of the metal powder contained in the metal paste; and removing the remaining resist. [Effects of the Invention]

[0019] As described above, the conductive bonding material according to the present invention is divided and segmented into a first region and a second region having appropriately defined dimensions. This allows the area of ​​the metal powder molding to be increased while narrowing the gap more than ever before. The conductive bonding material according to the present invention can exhibit more effective heat dissipation and conductivity than ever before. Furthermore, the present invention makes it easy to achieve both a large area and flatness in a conductive bonding material, which has been difficult to achieve until now. [Brief explanation of the drawings]

[0020] [Figure 1] 1A to 1C are diagrams illustrating the planar shape, cross-sectional structure, and minimum dimensions of one embodiment of a conductive bonding material according to the present invention. [Figure 2] 1 is a diagram showing a specific example of a planar shape of a conductive bonding material of the present invention that is formed of a unit square. [Figure 3] 1A and 1B are diagrams showing specific examples of the planar shape of the conductive bonding material of the present invention that is configured with curves. [Figure 4] 1A and 1B are diagrams showing examples of the overall shape of a conductive bonding material of the present invention. [Figure 5a]FIG. 2 is a diagram (first region) illustrating a process for forming a conductive bonding material of the present invention. [Figure 5b] FIG. 2 is a diagram (second region) illustrating the process of forming the conductive bonding material of the present invention. [Figure 6] 1A to 1C are diagrams illustrating a mode of use of a bonding member to which the conductive bonding material of the present invention is applied [Figure 7] Photographs of the manufacturing process of the conductive bonding material of the example. [Figure 8] 3A and 3B are photographs showing the appearance and cross section of the conductive bonding material produced in the examples. [Figure 9] 3A and 3B are photographs of the appearance and cross section of the conductive bonding material produced in the reference example. DETAILED DESCRIPTION OF THE INVENTION

[0021] (A) First and second regions of conductive bonding material The configuration and embodiments of the present invention will be described below using specific examples. Figure 1 shows an example of a specific embodiment of the conductive bonding material according to the present invention. As shown in Figure 1(a), this conductive bonding material has a rectangular shape as a whole in a plan view, and is formed with a first region in which a plurality of zigzag patterns are aligned. The remaining regions, i.e., the gaps between the zigzag patterns, form second regions. In this conductive bonding material, both the first region and the second region are formed from a compact of metal powder of the same metal type and particle size.

[0022] FIG. 1(b) shows the cross-sectional structure of this conductive bonding material. A fine gap exists between the metal powder compact in the first region and the metal powder compact in the second region, dividing the first and second regions. The cause of this gap is due to the two-stage method of forming the metal powder compact, which will be described later. However, even though it is called a gap, the distance between the first and second regions in the present invention is less than 1 μm. Therefore, this is narrower than the gap (1 μm or more) in the prior art (Patent Document 3), and can function as a more continuous film-like conductive bonding material than before. The gap between the first and second regions in the present invention is preferably 0.8 μm or less, and more preferably 0.5 μm or less.

[0023] The minimum dimensions L1 and L2 of the first and second regions are the smallest dimensions measured at any position on the metal powder compact in each region. For example, as shown in Figure 1(c), in the conductive bonding material of this embodiment, the first region has a zigzag pattern formed by straight lines of the same width, and the minimum dimension L1 of the first region is the line width. On the other hand, the minimum dimension L2 of the second region in Figure 1 corresponds to the smallest value of the spacing between the aligned zigzag patterns.

[0024] In the present invention, both the minimum dimension L1 of the first region and the minimum dimension L2 of the second region must be 5 μm or more. In the process of forming a metal powder compact using a metal paste, the minimum dimensions L1 and L2 are the minimum widths of the holes into which the metal powder is filled. According to the inventors' investigations, if the width of the holes is less than 5 μm, it becomes difficult to fill the metal powder all the way to the bottom of the holes. This reduces the contact area of ​​the conductive bonding material with the substrate, resulting in reduced heat dissipation and conductivity.

[0025] It is preferable that the minimum dimensions L1 and L2 are both 10 μm or more. Furthermore, the larger the minimum dimensions L1 and L2, the easier it is to fill the metal powder at each stage. However, if the minimum dimensions are excessively large, the surface of the metal powder may be gouged out significantly when scraping off the excess metal powder, potentially damaging flatness. From this perspective, it is preferable that the minimum dimensions L1 and L2 be 140 μm or less, and more preferably 80 μm or less.

[0026] Furthermore, taking into consideration the relationship between the first region and the remaining second region, the ratio of the minimum dimension L1 of the first region to the minimum dimension L2 of the second region, L1 / L2, is set to 0.25 or more and 4 or less. The smaller this difference in dimensions, the more similar patterns of width are formed, which tends to ensure more reliable filling of the metal powder. L1 / L2 is preferably 0.5 or more and 2 or less, and more preferably 0.8 or more and 1.25 or less.

[0027] In the conductive bonding material according to the present invention, the planar shapes of the divided first and second regions can be determined on the premise that their minimum dimensions L1 and L2 satisfy the above-mentioned relationship. Therefore, the first region may have a shape of an array of simple rectangles, and the remainder may be the second region.

[0028] However, in order to stably form metal powder compacts in both regions, it is preferable that the planar shape of the first region be a patterned shape with bent portions. In the conductive bonding material of the present invention, which is manufactured through the stepwise processes of the first and second processes described below, the metal powder compact in the first region is already formed when the metal powder compact in the second region is formed. Forming the metal powder compact requires a scraping process to remove excess metal powder, which may cause deformation or damage to the metal powder compact in the first region due to shear forces. Therefore, by forming the first region in a bent pattern, the shear strength of the metal powder compact in the first region is ensured in the vertical, horizontal, and diagonal directions. This allows for the stable formation of metal powder compacts with little risk of deformation, etc.

[0029] Specifically, the first region is formed in a regular pattern of two or more consecutive unit squares with a side length of the minimum dimension L1. Two or more consecutive unit squares means that the unit squares are connected in any of the vertical, horizontal, or diagonal directions. The first region may also be formed in a regular pattern of consecutive curves with a line width of the minimum dimension L1. Continuous curves are not limited to cases where the ends of the curves are connected to each other, but also include cases where part of a curve is connected to part of another curve. Continuous curves also include circles and spiral patterns.

[0030] More specific examples of the planar shape of a conductive bonding material consisting of a first region and a second region, which is the remaining region, include the pattern shapes shown in Figures 2 and 3. The specific example shown in Figure 2 is a pattern of continuous unit squares with a side length of L1, such as a checkerboard pattern and a straight wave pattern. The snake pattern in Figure 1 also falls into this category. The snake pattern and wave pattern in Figure 2 are patterns formed by continuous unit squares with a minimum dimension of L1 and lines with a line width of L1. The checkerboard pattern in Figure 2 can also be said to be a pattern of continuous unit squares with a minimum dimension of L1 in a diagonal direction. On the other hand, Figure 3 is a specific example of a first region mainly consisting of curves, such as a concentric circle pattern and a wave pattern.

[0031] The shape and dimensions of the combined first and second regions, i.e., the overall shape and dimensions of the conductive bonding material of the present invention, are not particularly limited. As shown in Fig. 4, the overall shape of the conductive bonding material may be rectangular or circular. The dimensions may also be set arbitrarily, taking into consideration the members to be bonded, such as elements to be bonded.

[0032] (B) Composition of metal powder compact The first and second regions of the conductive bonding material according to the present invention are both metal powders made of one or more metals selected from the group consisting of gold (Au), silver (Ag), platinum (Pt), and palladium (Pd), with a purity of 99.9% by mass or more and an average particle size of 0.005 μm to 1.0 μm.

[0033] The purity of the metal constituting the metal powder is set to a high purity of 99.9% by mass or more in order to impart to the metal powder the plastic deformability required for a joining material. The conductive joining material of the present invention forms a joint by densifying from a compact state to a state close to bulk metal. High purity of the metal powder is an essential condition for causing plastic deformation by pressure in the joining process. When the purity of the metal powder is low, less than 99.9% by mass, the hardness of the metal powder increases, making it difficult for plastic deformation of the metal particles themselves to occur in the joining process, and preventing compressive deformation of the compact. In particular, it becomes difficult to form a suitable joint when the pressure applied during joining is low.

[0034] The average particle size of the metal powder is set to 1.0 μm or less because metal powder with a particle size exceeding 1.0 μm tends to have too large gaps between particles when used as a conductive bonding material. Large voids within the conductive bonding material hinder densification during the bonding process, making it difficult to achieve suitable bonding strength. The lower limit of the average particle size of the metal powder is set to 0.005 μm because particles below this size tend to aggregate when made into a paste. The constituent metal is selected from gold, platinum, silver, and palladium because these metals have good conductivity and good deformability when made into a pure metal. The present invention does not preclude the use of a mixture of powders with different average particle sizes, as long as the average particle size is within the range of 0.005 μm to 1.0 μm.

[0035] The term "metal powder compact" does not necessarily refer to a sintered metal powder compact, but also includes an unsintered state (hereinafter referred to as a "dried body") in which metal powder is layered and dried. A sintered metal powder compact is a compact formed by strong bonding between metal powder particles due to necking or thermal diffusion. A dried metal powder compact is a compact formed by relatively weak bonding between metal powder particles, with the metal powder particles in contact with each other but without necking or thermal diffusion. Therefore, the hardness of each metal powder particle in the dried compact is approximately the same before and after the compact. Note that the weak bonding is not so weak that the compact will collapse during use in a joining process, etc. In the present invention, whether the metal powder compact is formed as a sintered or dried compact is determined by taking into account the pressure required in the subsequent joining process, etc. For example, when low-pressure joining is required, the use of a dried compact is preferable. This is because a compact formed from metal powder particles that is formed by drying and has little thermal change can be densified at low pressure.

[0036] The metal powder compacts in the first and second regions may both be sintered or dried, or one of them may be a sintered body and the other a dried body.

[0037] The metal powder compact constituting the conductive bonding material of the present invention preferably has a relative density of 50% to 95% of the bulk material. The relative density is the value expressed as a percentage (%) obtained by dividing the true density of the metal by the measured density of the conductive bonding material (relative density (%) = [(measured density of the conductive bonding material) / (true density of the metal)] × 100). Sintered bodies tend to have a higher relative density, while dried bodies tend to have a lower relative density than sintered bodies.

[0038] Furthermore, in the conductive bonding material of the present invention, the metal powder compact is divided into a first region and a second region, and the minimum dimensions L1 and L2 of these regions are specified, thereby achieving a large area while maintaining excellent flatness. Regarding flatness, the ratio of the maximum amount of erosion to the average thickness of the metal powder compact is 50% or less. This standard applies to both the first and second regions. The average thickness of the compact is the average value obtained by observing and measuring the thickness at multiple points on an arbitrary cross section. The maximum amount of erosion is the deviation from the average thickness at the point with the smallest thickness. The thickness of the conductive bonding material of the present invention is not particularly limited.

[0039] The conductive bonding material made of the above-described metal powder compact undergoes thermal diffusion between the metal particles when heated after bonding, transforming into a dense sintered body and enabling a strong bond between a semiconductor chip and a substrate. Furthermore, the conductive bonding material according to the present invention is a bonding member that has an appropriate hardness while suppressing deformation resistance when pressure is applied. Positioning of semiconductor chips and the like during bonding can also be performed accurately and with high precision.

[0040] (C) a joining member having a conductive joining material The conductive bonding material according to the present invention is formed on the surface of an appropriate substrate and used as a bonding member. The substrate is a member for supporting the conductive bonding material to facilitate efficient handling of the conductive bonding material. The substrate may be a substrate for a semiconductor device or the like. In this case, the conductive bonding material according to the present invention is formed on the substrate, and then elements or the like are bonded to form a device. The conductive bonding material according to the present invention can also be applied to a transfer substrate (Patent Document 4). In this case, the conductive bonding material is first formed on the transfer substrate, and then transferred to the substrate or the like of the device, where it functions as a bonding material for the elements or the like.

[0041] The substrate may be made of any material capable of supporting the conductive bonding material. Examples include glass, quartz, silicon, and ceramics. The shape and dimensions of the substrate are not particularly limited, and a rectangular, circular, polygonal, or other flat plate may be used. The substrate may consist solely of glass or silicon, or may have a thin film of a metal or an oxide of such a metal formed on its surface. This thin film serves as a base film that improves adhesion between the substrate and the conductive bonding material. The base film may be made of a metal or metal oxide such as Ti, Cr, Cu, or Ni, and may consist of at least one thin film layer. The thickness of the base film is preferably 5 nm to 300 nm.

[0042] The bonding member of the present invention may have only one conductive bonding material formed on the substrate, or may have a plurality of conductive bonding materials formed on the substrate.

[0043] The bonding member according to the present invention may have an intermediate film made of a metal or an oxide of such a metal formed between the conductive bonding material and the substrate. Like the undercoat film described above, the intermediate film can adjust the adhesion between the conductive bonding material and the substrate, thereby ensuring the ease of handling of the conductive bonding material and the bonding quality. That is, the intermediate film prevents the conductive bonding material from falling off during handling of the bonding member, while also suppressing the conductive bonding material from remaining on the substrate when the conductive bonding material is peeled off from the substrate during the bonding process.

[0044] The material of the intermediate film is preferably one or more metals selected from the group consisting of Au, Ag, Pt, and Pd, and more preferably the same metal as the conductive bonding material. The reason for selecting these materials is to increase the affinity between the intermediate film and the metal constituting the conductive bonding material while achieving low resistance. Pure metals and alloys of the above metals can be used as long as they do not interfere with this purpose. The intermediate film can also be composed of at least one thin film layer. Furthermore, the intermediate film may be formed together with the above-mentioned base film between the substrate and the conductive bonding material, or only the intermediate film may be formed.

[0045] The intermediate film can be composed of a single layer or multiple layers. When multiple intermediate films are formed, they may be made of the same metal or different metals. However, it is more preferable that the intermediate film in contact with the conductive bonding material is made of the same metal as the conductive bonding material.

[0046] The thickness of the interlayer film is preferably 5 nm or more and 300 nm or less. If it is less than 5 nm, the above effect is weak, and if it exceeds 300 nm, there is no difference in the effect and it only increases the material cost. When forming multiple interlayer films, it is preferable that the total thickness is within the above range.

[0047] The intermediate film is provided at least between the conductive bonding material and the substrate. The intermediate film may be present only on the bottom surface of the conductive bonding material, or may be formed on the entire surface of the substrate. The intermediate film may also be present in the gap between adjacent conductive bonding materials. Furthermore, the intermediate film may be present at least on the bottom surface of the conductive bonding material, but may also be formed on the side surface of the conductive bonding material.

[0048] (D) Method for manufacturing conductive bonding material Next, an embodiment of a method for producing a conductive bonding material according to the present invention will be described. The conductive bonding material of the present invention is basically produced by applying a metal paste containing a predetermined metal powder to a substrate, followed by drying or sintering to form a molded body. As described above, in the present invention, in order to form a molded body of metal powder having narrowed gaps, the molded body is divided into first and second regions, and the process of forming the molded body of metal powder is carried out twice, step by step, as a first step and a second step, for each region. In the following description of the method for producing a conductive bonding material according to the present invention, the preparatory steps for the substrate (I) a resist coating step and a through-hole forming step, and the steps (II) a filling step of the through-holes by applying a metal paste, which are common to the first and second steps, and (III) a step of forming a molded body from the metal powder will be described, followed by a description of the overall process.

[0049] (I) Resist coating process and through-hole formation process The metal powder compacts of the first and second regions of the conductive bonding material of the present invention are expected to be formed into a pattern, such as that shown in Figure 2. Because these have more complex shapes than compacts with simple shapes such as rectangles, they are preferably formed by patterning using a resist (protective film). Regarding the resist, photoresists used in ordinary device manufacturing are preferred, but there are no limitations on the photosensitive wavelength or type, such as positive or negative. There are also no limitations on the resist application method, and conventional methods can be used. After forming a resist coating film, through-holes are formed, patterned according to the shape of the first region. Through-holes are holes that penetrate the resist film and reach the bottom (substrate surface) from the resist surface. The through-hole formation process involves resist exposure and etching, and these methods are also commonly used.

[0050] (II) Filling the through-holes by applying metal paste After the above preparation process of coating with resist and forming through holes, a metal paste is applied to the substrate. The metal paste is composed of a slurry in which one or more metal powders selected from the group consisting of gold powder, silver powder, platinum powder, and palladium powder, each having a purity of 99.9% by mass or more and an average particle size of 0.005 μm to 1.0 μm, are dispersed in an organic solvent. The organic solvent preferably has a boiling point of 250°C or less. The reason for setting the boiling point of the organic solvent to 250°C or less is that drying requires a high temperature and a long time, which causes necking between the metal particles of the molded body, inhibiting the movement of the metal particles when pressed during bonding and reducing the bonding strength.

[0051] Examples of organic solvents that can be used in the present invention include branched saturated aliphatic dihydric alcohols, monoterpene alcohols, halocarbons, etc. More specifically, examples of branched saturated aliphatic dihydric alcohols that can be used include propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,3-pentanediol, 2,4-pentanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 1,5-hexanediol, 1,6-hexanediol, and 2,4-diethyl-1,5-pentanediol, as well as derivatives thereof. Monoterpene alcohols include citronellol, geraniol, nerol, menthol, terpineol (α, β), carveol, thuyl alcohol, pinocampheol, β-phenthyl alcohol, dimethyloctanol, hydroxycitronellol, 2,4-diethyl-1,5-pentanediol, trimethylpentanediol monoisobutyrate, and their derivatives. Saturated linear hydrocarbons include pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, and their derivatives. Compounds obtained by the condensation reaction of monocarboxylic acids with polyhydric alcohols are also effective, such as triethylene glycol di-2-ethylhexanoate and triethylene glycol di-2-ethylbutanoate. Halocarbon organic solvents include tetrachloroethylene, tetrabromoethylene, tetraiodoethylene, and trichloromethane. The boiling point of an organic solvent tends to depend on its carbon number, so it is preferable that the solvent used has 5 to 20 carbon atoms. From this perspective, aromatic hydrocarbons are also acceptable, and for example, terpineol, menthanol, and alkylbenzenes, which are used as solvents for thick film pastes, also have no functional problems. One type of organic solvent may be used, or a mixture of two or more organic solvents with different boiling points may also be used.By using organic solvents with low and high boiling points, the organic solvent with the low boiling point can be evaporated and removed during the process of adjusting the content of metal particles, making the adjustment easier.

[0052] The method for applying the metal paste to the substrate is not particularly limited, and various methods can be used depending on the size of the substrate, such as spin coating, screen printing, inkjet coating, and blade coating. The metal paste can be applied at room temperature and atmospheric pressure. However, it may also be applied in a reduced pressure atmosphere. In particular, when applying the metal paste to a substrate on which a pattern has been formed using a resist, it is preferable to apply it in a reduced pressure atmosphere in order to sufficiently fill the pores with the metal paste.

[0053] (III) Metal powder compact forming process The metal powder filled into the through holes by applying the metal paste is dried or sintered to form a metal powder compact. Whether to dry or sinter this process is determined based on the required strength of the compact and the required pressure when used as a joining material.

[0054] When forming a dried compact from metal powder, the drying process involves heating the metal paste without pressure, volatilizing and removing the organic solvent in the paste to form a compact. The drying temperature should be less than 100°C. If the drying process is performed at a temperature higher than this, sintering of the metal powder occurs even without pressure, resulting in a sintered compact, either partially or entirely. The drying temperature is preferably 65°C or lower, more preferably 60°C or lower. The lower limit of the drying temperature is sufficient as long as it is above the temperature at which the organic solvent can volatilize. However, to form a dried compact that exhibits favorable deformation when pressure is applied during bonding, a temperature of 20°C or higher is preferred. The drying process can be performed under atmospheric pressure, or in a vacuum atmosphere of 0.01 Pa to 40 kPa. Vacuum drying contributes to lower drying temperatures, and in this case, the temperature is preferably 10°C to 30°C. Under these drying conditions, the drying time is preferably 0.1 hour to 1 hour. These drying processes are carried out under relatively mild thermal conditions, and usually allow the solvent to be removed without disrupting the arrangement of the metal powder in the metal paste.

[0055] When forming a sintered body from a metal powder compact, the sintering conditions are preferably a heating temperature of 80°C or higher and 300°C or lower. At temperatures below 80°C, it is difficult to obtain a sintered state. Furthermore, sintering at temperatures above 300°C causes excessive sintering, which leads to necking between the metal powder particles and results in strong bonding, making it difficult to form a dense joint when subjected to a joining process. Furthermore, the present invention aims to achieve joining at 300°C or lower in order to protect the joining components. The heating time during sintering is preferably 5 minutes or higher and 120 minutes or lower. When forming a sintered body, the above-mentioned drying process may be performed as a preliminary step before sintering.

[0056] The above-described drying or sintering process can produce the conductive bonding material and bonding member according to the present invention. Furthermore, as described above, a bonding member including the conductive bonding material of the present invention may include at least one intermediate film between the conductive bonding material and the substrate. In this case, the intermediate film is preferably formed after the application of the resist and the formation of the through-holes, but before the application of the metal paste. This allows the intermediate film to be selectively formed between the conductive bonding material and the substrate. Furthermore, by forming an intermediate film after the application of the resist and covering the resist with metal, direct contact of the solvent in the metal paste with the resist can be prevented, thereby reducing damage to the resist caused by the solvent. Conventional thin film forming processes such as sputtering, vacuum deposition, and chemical vapor deposition can be used to form the intermediate film.

[0057] A specific embodiment of the method for producing a conductive bonding material of the present invention, which includes the basic steps (I) to (III) described above, is described with reference to Figures 5a and 5b. This specific embodiment is a process that includes forming an intermediate film between the conductive bonding material and the substrate. Figure 5a illustrates the first step of forming a compact of metal powder in the first region, and Figure 5b illustrates the second step of forming a compact of metal powder in the second region, which completes the production of the conductive bonding material of the present invention.

[0058] Referring to FIG. 5a, first, a substrate 1 is prepared and a resist 2 is applied to the substrate 1 (FIG. 5a(i)). A Ti film or the like may be formed on the substrate 1 in advance as an undercoat film. Then, a photomask 3 having a pattern that will become the first region is used to expose and etch the resist in the area that will become the first region, thereby forming a through-hole 4 (FIG. 5a(ii)). Next, an intermediate film 5 made of gold or the like is formed on the bottom surface of the through-hole and on the surface of the resist (FIG. 5a(iii)).

[0059] Next, metal paste 6 is applied onto the resist 2 of the substrate 1, and the through holes 4 in the first region are filled with metal powder (Fig. 5a(iv)). A drying process is then performed to form a metal powder compact (Fig. 5a(v)), and excess metal powder is removed with a squeegee or the like to form a metal powder compact corresponding to the first region (Fig. 5a(vi)).

[0060] After forming the first region in the first step, a metal powder compact is formed in the second region in the second step. In the second step, the resist in the portion corresponding to the second region must be removed by exposure and etching. Here, the intermediate film remaining on the entire resist surface is first etched away, and then a metal film 8 is formed on the resist surface other than the first and second regions using a masking 3 (FIG. 5b(i)). Next, exposure and etching are performed to form a through hole 9 that will become the second region (FIG. 5b(ii)), and an intermediate film 5 is then formed on the bottom of the through hole (FIG. 5b(iii)). In addition to this embodiment, after the intermediate film is etched away from the entire resist surface, only the resist in the second region may be exposed and etched using a photomask.

[0061] After forming the through holes corresponding to the second region, metal paste 6 is applied in the same manner as in the first step to fill the through holes with metal powder, and a drying process is performed to form a metal powder compact for the second region (Figure 5b(iv)). Thereafter, excess metal powder is removed (Figure 5b(v)). Finally, the resist is removed to form a metal powder compact 10 for the second region, and the conductive bonding material 11 of the present invention is produced (Figure 5b(vi)).

[0062] (E) Aspects of the bonding method using conductive bonding materials The conductive joining material made of the metal powder compact according to the present invention is suitable for joining a substrate of a semiconductor device, etc., to a workpiece, such as an element or chip. Three specific examples of joining methods using this conductive joining material are described with reference to Figures 6(a), (b), and (c).

[0063] 6(a), a substrate such as a device is used as the base material of the bonding member of the present invention, and a bonding member is formed by forming a conductive bonding material on the substrate, and then bonding members to the bonding member. In the bonding process, the bonding members are placed on the conductive bonding material, and then pressure and heat are applied to sinter the metal powder of the conductive bonding material, thereby forming a densified bonded joint.

[0064] The pressure applied in the bonding process is set taking into consideration the pressure that the semiconductor chips being bonded can withstand. Semiconductor chips with relatively high strength, such as Si-based semiconductor chips, can be bonded with a pressure of 30 MPa or less. On the other hand, for bonding compound semiconductor chips, which tend to be weak and brittle, the pressure is preferably 10 MPa or less, with 5 MPa or less being particularly preferred. The lower limit of the pressure is preferably 1 MPa or more, regardless of the type of semiconductor chip. If the pressure is less than 1 MPa, the metal powder does not easily deform, and the bonded portion cannot be densified.

[0065] The heating in the joining process is primarily intended to enhance the plastic deformability of the metal powder and assist in densification through pressure application. This heating is also expected to promote sintering of the metal powder in part or all of the conductive joining material. The heating temperature is preferably between 80°C and 300°C. At temperatures below 80°C, the plastic deformability of the metal particles cannot be enhanced, resulting in insufficient bonding. Furthermore, temperatures above 300°C may result in damage to the semiconductor chip and substrate.

[0066] The heating temperature is set taking into consideration the heat resistance temperature of the semiconductor chip and the substrate. For example, in the case of a resin-based organic substrate, if the glass transition temperature (Tg) is exceeded, physical properties such as mechanical strength and dielectric constant may change significantly. The heating temperature for such a substrate with low heat resistance is preferably 230°C or less, and more preferably 200°C or less. The present invention can contribute to reducing the heating temperature as well as the pressure force in the bonding process. The conductive bonding material is heated from either or both the semiconductor chip side and the substrate side. It is preferable that the heating temperature from either side be within the above range.

[0067] The heating time (pressure application time) in the bonding process affects the bond strength between the conductive bonding material and the bonded members and the density of the conductive bonding material, with the bond strength and density increasing with increasing time. Even with a relatively short heating time of 0.5 to 120 seconds, it is possible to compress and deform the conductive bonding material and bond the semiconductor chip to the substrate. Furthermore, a heating time of 10 to 120 minutes can achieve a stronger bond.

[0068] After the bonding step, the conductive bonding material may be heated. By performing such post-heat treatment, the metal powder is sintered (post-sintered), and the voids inside the conductive bonding material are reduced or eliminated, thereby achieving further densification. For example, the heating time in the bonding step may be set to 0.5 seconds or more and 120 seconds or less, and then the heat treatment for post-sintering may be performed after bonding.

[0069] The heating temperature for post-sintering the conductive bonding material is preferably 100°C or higher and 300°C or lower. If the temperature is lower than 100°C, the desired sintering and densification cannot be expected. If the temperature exceeds 300°C, sintering will proceed excessively, leaving only the bonded portion too hard. This heating temperature is also set taking into consideration the heat resistance temperature of the semiconductor chip and substrate. Therefore, the heating temperature for substrates with low heat resistance, such as resin-based organic substrates, is preferably 230°C or lower, and more preferably 200°C or lower.

[0070] The heating time for post-sintering is preferably 10 minutes or more and 120 minutes or less. If it is less than 10 minutes, the desired sintering cannot be completed, and if it is heated for more than 120 minutes, further densification cannot be expected. The heat treatment for sintering may be carried out without pressure, but may also be carried out with pressure. If pressure is applied, it is preferable that the pressure be 10 MPa or less.

[0071] In the bonding step shown in Fig. 6(b), the substrate of the bonding member functions as a support for forming and supporting the conductive bonding material, and the conductive bonding material is bonded to a substrate of a device separate from the substrate together with the bonded member. In this embodiment, the conductive bonding material is mounted (fixed) to the bonded member, such as an element, by applying pressure and heat, and then the bonded member and the conductive bonding material are picked up from the substrate. Then, the picked-up conductive bonding material and bonded member are placed on the substrate of the device or the like and bonded by applying pressure and heat.

[0072] The fixing conditions for mounting the conductive bonding material on the bonded members are preferably a pressure of 1 MPa or more and 5 MPa or less, and a heating temperature of 100°C or more and 200°C or less. After mounting the bonded members, the semiconductor chip is picked up from the substrate to obtain a semiconductor chip with the conductive bonding material fixed thereto.

[0073] The bonded members with the fixed conductive bonding material are then placed on a substrate such as a device, and pressure and heat are applied to bond the bonded members to the substrate. Regarding the pressure, heat, and pressure / heating time in this bonding process, the pressure is preferably 1 MPa to 30 MPa, and the heating temperature is preferably 80°C to 300°C. The details of the preferred conditions are the same as those for the bonding process of the embodiment shown in FIG. 6(a) above.

[0074] In this embodiment of the bonding step, post-sintering may be performed in which the conductive bonding material is heated under the same conditions as in the embodiment of FIG. 6(a) described above.

[0075] There are no restrictions on the material, shape, or dimensions of the substrate of the device or other device to which the bonded member is bonded in this manner. It can be used with resin-based organic substrates, and is also useful for substrates (wafers) made of Si-based materials and ceramic substrates.

[0076] In the bonding step shown in FIG. 6(c), the conductive bonding material on the base material is transferred to a substrate such as a device, and then a bonded member such as an element is bonded to the substrate. This embodiment is the same as the embodiment shown in FIG. 6(b) in that the base material of the bonding member is used as a support for the conductive bonding material. In this embodiment, the substrate such as a device is placed on the bonding material on which the conductive bonding material has been formed, and heated to transfer the conductive bonding material to the substrate, and then the substrate is picked up. Then, a bonded member such as an element is placed on the conductive bonding material transferred to the substrate, and bonded by applying pressure and heat.

[0077] When transferring the conductive bonding material of the bonding member to the substrate, it is preferable to heat the transferred conductive bonding material to 100 to 200°C. This is to make it easier to transfer the conductive bonding material from the substrate of the bonding member to the substrate. This heating may involve heating the conductive bonding material together with the substrate of the bonding member. In addition, it is preferable to apply pressure with a stress equal to or less than the yield strength of the conductive bonding material while heating.

[0078] The pressure, heat, and pressure / heating time in the bonding step of bonding a member to a substrate onto which a conductive bonding material has been transferred are preferably set to a pressure of 1 MPa to 30 MPa and a heating temperature of 80°C to 300°C. Details of the preferred conditions are the same as those for the bonding step of the embodiment shown in Figure 6(a) above. Heating for post-sintering may also be performed in this bonding step.

[0079] In the specific embodiment of the bonding step shown in Figures 6(a) to 6(c) described above, it is preferable to form a metal film on the bonding surface between the substrate of a device or the like and the bonded member of an element or the like. This is to improve adhesion between the substrate and the bonded member. The metal film can be formed on either or both of the bonding surface of the bonded member and the substrate. The metal film is preferably made of one or more metals selected from Au, Ag, Pt, and Pd, and may have a single-layer structure or a multi-layer structure. Furthermore, the surface (layer) that comes into contact with the conductive bonding material is more preferably made of the same metal as the conductive bonding material. [Example]

[0080] A specific example of the present invention will be described. In this example, a metal paste (gold paste) using gold powder as the metal powder was prepared, and a conductive bonding material and a bonding member were manufactured. Then, a bonding test of a semiconductor chip using this bonding member was carried out.

[0081] [Preparation of gold paste] A metal paste (gold paste) was prepared by mixing gold powder (average particle size: 0.3 μm) with a purity of 99.9% by mass, produced by the wet reduction method, with tetrachloroethylene (product name: Asahi Park Roll) as an organic solvent. The gold powder content of the gold paste was 90% by mass. The particle size of the gold powder was measured using a scanning electron microscope (SEM). The observed image (30,000x magnification) was analyzed, and the particle sizes of 100 gold particles were measured to calculate the average particle size.

[0082] [Formation of the first region (first step)] A conductive bonding material consisting of the first and second regions was manufactured using the same process as shown in Figures 5a and 5b. A silicon wafer (150 mm diameter, 0.6 mm thickness) was used as the substrate. A 50 nm thick Ti film was previously formed on the entire surface of the substrate as a base film. First, a 10 μm thick resist was applied to the entire surface of the substrate, and then a Cr metal photomask with a zigzag pattern similar to that shown in Figure 1 was placed over the resist and exposed to light. The resist in the area that would become the first region was then removed with an etching solution to form a through-hole. Next, a 200 nm thick gold film was deposited as a metal film by sputtering.

[0083] Next, the gold paste prepared above was dropped onto the substrate and spread using a blade coating method, filling the through-holes with gold powder. After applying the gold paste, the gold powder in the through-holes was vacuum dried to form a compact. The vacuum drying conditions were an atmosphere of 10 -1 The mixture was heated at room temperature for 1 hour at 100 Pa. The excess gold powder was then scraped off with a squeegee to form the first region of the metal powder compact. Figure 7(a) is a photograph of the first region of the metal powder compact at this stage, taken from above. In this image, the dark areas are the metal powder compact, and the light areas are the resist.

[0084] [Formation of the second region (second process)] After etching away the gold film on the resist surface, the first and second regions were masked and another gold film (200 nm) was deposited. The resist in the second region was removed by exposure and etching under the same conditions as above to form a through-hole that would become the second region. A gold film (200 nm) was then sputtered onto the bottom of this through-hole. Figure 7(b) is a photograph of the metal powder compact in the first region at this stage, taken from above. In this image, the dark-colored area is the metal powder compact, and the light-colored area is the through-hole.

[0085] The gold paste was then applied to the through-holes corresponding to the second region, dried, and the gold powder was then removed. The gold paste application method and drying conditions were the same as those in the first step.

[0086] Finally, the gold film on the surface of the remaining resist was etched away, and the resist was peeled off. This resulted in the production of a conductive bonding material having metal powder compacts in the first and second regions. Figure 8 shows a photograph of the conductive bonding material produced in this example (Figure 8(a)) from above and a cross-sectional photograph near the center of the pattern (Figure 8(b)). The first and second regions are very close to each other, with a gap of approximately 0.5 μm between them. The conductive bonding material is essentially a continuous film. In this example, the minimum dimension L1 of the first region (the zigzag pattern) is the line width of the pattern, which is 20 μm. The second region is the gap between the patterns, and its minimum dimension L2 is 20 μm (L1 / L2 = 1). Regarding the flatness of the conductive bonding material, the average thickness was 11 μm, and the maximum depth of indentation was 3 μm. The ratio of the maximum depth of indentation to the average thickness was 27%, confirming the good flatness of the conductive bonding material of this example.

[0087] [Reference example] As a reference example, metal paste was applied and dried in two stages based on a pattern referring to the prior art (Patent Document 3). In this reference example, as shown in FIG. 9(a), rectangular (20 μm × 20 μm) metal powder compacts were formed at intervals of 4 μm using the same substrate and gold paste as in the example. The same gold paste was then applied to fill the gaps in the formed metal powder compacts and dried. The method for forming the metal powder compacts in this case was basically the same as in the example.

[0088] Figure 9(b) is a cross-sectional photograph of the conductive bonding material of the reference example obtained after the second application and drying of gold paste. As shown in the figure, the gold powder is filled near the surface of the metal powder compact, resulting in a flat conductive bonding material with no gaps on the surface. However, the metal powder does not fill the bottom of the gaps, so gaps at the interface with the substrate remain. The gaps in the conductive bonding material of this reference example are not particularly large at 4 μm, but as the area of ​​the conductive bonding material is increased, the proportion of gaps also increases, raising concerns about reduced heat dissipation. When forming a metal powder compact using metal paste in two stages, it is considered necessary to create an appropriate gap (5 μm or more).

[0089] [Bonding test] A semiconductor chip bonding test was conducted using the bonding member manufactured in the above-described example. Here, based on the embodiment described above with reference to FIG. 6(b), the conductive bonding material of the bonding member was bonded and transferred to a semiconductor chip, which was then bonded to a substrate. First, a Si chip (plate thickness 0.525 mm × 2 mm square) was transferred as a semiconductor chip to the conductive bonding material of the bonding member. Metal films of Ti (thickness 50 nm), Pt (thickness 50 nm), and Au (thickness 200 nm) were previously formed on the bonding surface of the Si chip.

[0090] After placing the Si chip on the conductive bonding material, the conductive bonding material was transferred to the Si chip by pressing and heating. The heating conditions for this transfer process were a substrate temperature of 200°C and a semiconductor chip temperature of 200°C. The pressure was 1.7 MPa and applied for 10 minutes. After heating and pressing, the Si chip and the transferred conductive bonding material were picked up.

[0091] The Si chip was then placed on a substrate and bonded to the base material via the conductive bonding material by pressing and heating. The heating conditions for this bonding process were a substrate temperature of 250°C and a semiconductor chip temperature of 250°C. The pressure was 1.7 MPa and applied for 60 minutes.

[0092] After bonding the semiconductor chips using the above process, the shear strength of the bonded joint was measured. The shear strength was measured using a die shear tester at a shear speed of 100 μm / s and a step-back interval of 100 μm, and the shear load was divided by the area of ​​the semiconductor chip (2 mm square). The shear strength of the bonded joint in this example was approximately 10 MPa, confirming that sufficient bonding strength was obtained. [Industrial Applicability]

[0093] As described above, the conductive bonding material according to the present invention is divided into a first region and a second region formed by applying and molding a metal paste in two stages, but the gap between the first and second regions is extremely narrow, resulting in a substantially continuous film-like conductive bonding material. Furthermore, the conductive bonding material according to the present invention can be made large-area even though it uses a metal paste as a precursor. The present invention exhibits excellent heat dissipation and conductivity as a conductive bonding material applied to die bonding and flip-chip mounting of semiconductor elements to substrates. [Explanation of symbols]

[0094] 1. Base material (substrate) 2. Resist 3 Photomask 4 Through hole (first area) 5 Interlayer 6 Metal Paste 7 Metal powder compact (first area) 8 Metal Film 9 Through hole (second area) 10 Metal powder compact (second area) 11 Conductive bonding materials 12 Joint materials C. Joined material (semiconductor chip) S Device substrate

Claims

1. A conductive bonding material comprising a molded body of a dried or sintered metal powder having a predetermined area formed on a substrate, the metal powder constituting the compact is a powder made of one or more metals selected from the group consisting of gold, silver, platinum, and palladium, each having a purity of 99.9% by mass or more, and having an average particle size of 0.005 μm or more and 1.0 μm or less; the conductive bonding material is divided into a first region and a second region that is a remaining region in a plan view, a minimum dimension L1 of the first region and a minimum dimension L2 of the second region are both 5 μm or more and 140 μm or less, and a ratio L1 / L2 of L1 to L2 is 0.25 or more and 4 or less; Furthermore, the conductive bonding material is characterized in that, in a cross-sectional view, there is a gap between the first region and the second region, and the gap is less than 1 μm.

2. 2. The conductive bonding material according to claim 1, wherein the first region is formed in a regular pattern of two or more consecutive unit squares each having a side length of the minimum dimension L1.

3. 2. The conductive bonding material according to claim 1, wherein the first region is formed in a regular pattern of continuous curves with a line width of a minimum dimension L1.

4. A bonding member comprising a substrate and the conductive bonding material according to claim 1.

5. 5. The joining member according to claim 4, further comprising an undercoat film made of a metal or metal oxide and / or an intermediate film made of a metal or metal oxide between the substrate and the conductive joining material.

6. 2. The method for producing a conductive bonding material according to claim 1, wherein a metal paste containing metal powder made of one or more metals selected from the group consisting of gold, silver, platinum, and palladium having a purity of 99.9% by mass or more and having an average particle size of 0.005 μm or more and 1.0 μm or less is used, Coating a surface of one substrate with a resist; a first step of forming a first through hole in a region corresponding to a first region of the resist, filling the first through hole with the metal paste, and then drying or firing the metal paste to form a molded body of the metal powder; a second step of forming a second through hole in a region corresponding to the second region of the resist after the first step, filling the second through hole with the metal paste, and then drying or firing the metal paste to form a molded body of the metal powder; removing residual resist; A method for manufacturing a conductive bonding material comprising:

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