JP6087425B2 - Joining method - Google Patents

Description

  The present invention relates to a bonding method for performing a bonding process on an object to be processed, and more particularly to a technique for performing a bonding process by sintering fine particles of metal or metal oxide.

  Solder using lead by increasing the maximum allowable junction temperature of semiconductors (maximum temperature when heating semiconductors in use) and complying with restrictions on the use of certain hazardous substances such as lead (RoHS: Restriction of Hazardous Substances) The use of bonding technology has been limited. Lead-free solder has also been developed, but there is a problem that cracking occurs when used as a joining application. Therefore, a joining technique using a conductive paste is being promoted as an alternative technique for solder. Solder is made of gold, silver or copper fine particles of several tens of microns, and conductive paste is made of gold, silver, copper or oxide fine particles of nano size to 1 micron or less. Development is underway.

  The bonding process by heating and pressurization is also called “solid phase diffusion bonding”, and utilizes the diffusion of atoms generated between the bonding surfaces by pressing the base material (here, conductive paste) in close contact. And join. In solid phase diffusion bonding, the bonding surfaces on which diffusion bonding is performed are bonded in a solid state. Thus, pressure bonding is essential in solid phase diffusion bonding.

  Here, due to technological development of a power semiconductor (semiconductor used in power electronics) that uses a large current and has a high withstand voltage, such as a switching technique, a large area of a semiconductor chip is required. In the case of pressure bonding when bonding large-area semiconductor chips, uniform pressure is required, and if too much load is applied or if the pressure is locally different only in some places, damage (damage) Receive. Further, when bonding a silicon carbide (SiC) chip that has been attracting attention as a high-current application, it is difficult to apply a load because SiC is brittle. Thus, when bonding a chip for a power semiconductor, particularly a SiC chip, damage caused by pressure bonding is regarded as a problem, and the demand for pressureless bonding or self-pressure bonding is increasing.

  Therefore, heat treatment is performed on the object to be processed with the conductive paste made of silver or silver oxide fine particles interposed therebetween, and the silver or silver oxide fine particles are sintered to perform pressureless bonding or self-weight pressure bonding. There is a technique for performing a bonding process on an object to be processed (see, for example, Patent Documents 1 and 2). By using silver or silver oxide, it is possible to perform a bonding process on the object to be processed by pressureless bonding or self-pressure bonding, and the object to be processed is a semiconductor such as silicon (Si) or the above-described SiC. Even if there is, damage can be prevented. In addition, there is an effect that the joining ability (adhesion ability) is high.

  By the way, as a technique for sintering metal fine particles, combined heating in which heat treatment and vacuum treatment are combined, and combined heating in which heat treatment and plasma treatment are combined have been proposed by the present applicant (for example, Patent Documents). 3). In these combined heating, the heating time is reduced to a low temperature, and the fine particles can be efficiently sintered at a low temperature while preventing thermal deformation and damage due to heat.

JP 2010-257880 A JP 2011-175871 A JP 2012-142551 A

  However, there are the following problems when performing the bonding process on the workpieces by the above-described pressureless bonding or self-weight pressure bonding. That is, when heated using a conductive paste other than silver, it has been found that the bonding ability (adhesion ability) is low in pressureless bonding or self-pressure bonding.

  Further, even when silver or silver oxide is used as the conductive paste, the use of a conductive paste containing silver or the like causes the temperature to be higher than that of solder. Therefore, when a frame material (for example, a lead frame) made of an easily oxidizable metal such as copper (Cu) is used to join a workpiece, a reducing atmosphere or an oxygen-free atmosphere is used to prevent the frame material from being oxidized. Need to be fired. In that case, the conductive paste itself is difficult to be fired in a reducing atmosphere or an oxygen-free atmosphere, and problems such as being unable to be bonded occur.

  Furthermore, even if it can be joined, it will oxidize if exposed immediately to the atmosphere, so it must be cooled for a long time in an oxygen-free atmosphere. In this way, shortening of processing time is also desired.

  This invention is made | formed in view of such a situation, Comprising: It aims at providing the joining method with high joining capability.

  As a result of earnest research to solve the above problems, the inventors have obtained the following knowledge.

  That is, the conductive paste contains a solvent for dissolving fine particles of gold, silver, copper, and oxides thereof, and a dispersant for dispersing fine particles of gold, silver, copper, and oxides thereof. When heated to sinter the fine particles of gold, silver, copper, and oxides thereof, the dispersant vaporizes and voids are generated in the conductive paste. It was found that the bonding ability was low without the voids being removed at the pressure of. Therefore, paying attention to the above-mentioned Patent Document 3, in the case of combined heating in which heat treatment and vacuum treatment are combined, voids disappear due to the vacuum, and the joining ability increases even in pressureless joining or self-pressure joining. I came up with an idea.

  On the other hand, when focusing attention on the bonding state of the metal, it was found that even when the fine particles of gold, silver, copper, and oxides thereof were sintered by heating, the bonding between the metals was weak and the bonding ability was low. Accordingly, paying attention to the above-mentioned Patent Document 3 as well, in the case of the combined heating in which the heat treatment and the plasma treatment are combined, the metal treatment can be achieved by strengthening the bond between the metals by the plasma treatment. The inventors have come up with the idea that bonding capability is increased even in bonding or self-pressure bonding.

  For the above reasons, it is conceivable that the bonding capability can be enhanced by applying a combination of heat treatment, vacuum treatment, and plasma treatment to the bonding. These fine particles have a size of nano size to 1 micron or less in the case of the conductive paste as described above. On the other hand, the maximum thickness of the junction is about several hundreds of micrometers. Therefore, when fine particles having a size of nano size to 1 micron or less are arranged with each other, it is considered that the gap between the fine particles adjacent to each other in the lateral direction becomes small as shown in the schematic diagram of FIG.

  On the other hand, when flake shapes are stacked, as shown in the schematic diagram of FIG. 3B, the contact area between the flakes increases and the stress remaining in the metal (hereinafter referred to as “residual stress”) (FIG. 3 (b) (see arrow in FIG. 3) plays a role of a spring, and it is considered that the joining ability is higher than that in FIG. 3 (a) in the vertical direction.

  In addition, about the gap of flake shape, since the bonding occurs at the atomic level by performing the plasma treatment, the knowledge that solid-phase sintering joining between particles (here between the flakes) combined with the plasma treatment can be realized. Got.

The present invention based on such knowledge has the following configuration.
That is, the joining method according to the present invention is a joining method in which fine particles of metal or metal oxide are sintered and a joining process is performed on the objects to be processed. Among them, at least one is a semiconductor, and the relative amount of radicals with respect to ions in the plasma is controlled to be increased , and flakes shaped from the fine particles by mechanical stress are used to interpose the flakes. By providing a plasma treatment process for performing plasma treatment on the workpiece, the flakes are sintered and the joining treatment is performed on the workpiece.

  According to the bonding method of the present invention, using the flakes shaped from the fine particles of metal or metal oxide by mechanical stress, the plasma treatment process performs the plasma treatment on the object to be treated with the flakes interposed. Do. Increase the contact area between the flakes and apply residual stress inside the flakes. Furthermore, since the diffusion of the metal is promoted by the plasma treatment, the bonding ability is increased. Further, the processing time can be shortened as compared with the conventional heat bonding process (without performing plasma processing), and the processing efficiency is improved and the effect of greatly contributing to the productivity is also achieved.

In the present invention described above, the plasma treatment is performed while controlling the relative amount of radicals to ions in the plasma to be increased . Since the workpiece may be damaged by the ions, the ions can be damaged by blocking the ions or radicalizing the ions so that the amount of radicals relative to the ions increases. It is possible to perform the bonding process without imparting the above. In particular, when at least one of a plurality of objects to be bonded is a semiconductor, semiconductor damage due to ions increases, so by controlling so that the relative amount of radicals to ions increases, Bonding can be performed without damaging the semiconductor by the ions.

  In the present invention described above, at least one of the plurality of objects to be bonded is a semiconductor. Even when a large-sized semiconductor is bonded using flakes formed from metal or metal oxide fine particles, pressureless bonding or self-pressure bonding is performed in a state where the bonding capability is high due to a vacuum state. It is also possible to increase the metal selectivity without damaging the semiconductor. Therefore, not only precious metals such as gold and silver but also base metals such as copper, tin, zinc and aluminum or alloys thereof can be selected. Therefore, it is possible to obtain a bonding material that is cheaper and has equivalent electric / thermal conduction / bonding characteristics.

  In the present invention described above, it is preferable to cool the processing portion containing the object to be processed with a cooling gas containing noble gas, nitrogen or hydrogen without oxygen after the plasma processing process. After the plasma treatment process, the treatment part is cooled by a cooling gas containing noble gas, nitrogen or hydrogen without oxygen, thereby forcibly cooling to the stage temperature as well as preventing oxidation while having a reducing effect. Therefore, it is not necessary to cool for a long time in an oxygen-free atmosphere, and the treatment time can be shortened while preventing oxidation while having a reducing effect. In particular, even when joining a workpiece using a frame material made of an easily oxidizable metal such as copper, or when selecting an easily oxidizable material such as a base metal having a higher ionization tendency than hydrogen as the joining material. In the plasma treatment process, the adhesive itself containing flakes shaped from fine particles of metal or metal oxide can be baked, and can be joined at the stage of the plasma treatment process. Furthermore, the frame material and the bonding material can be immediately cooled after the plasma processing process, and the processing time can be shortened while preventing the frame material and the bonding material from being oxidized. Note that flakes shaped from metal oxide fine particles can be used for bonding due to the reduction effect.

  An example of the cooling gas is a gas containing a rare gas, and a plasma treatment is performed using the gas containing the rare gas described above in the plasma treatment process, and a treatment using the same gas as the plasma treatment is performed after the plasma treatment process. Cooling the part. In this case, since it is possible to perform processing using a gas containing the same noble gas in the plasma processing step and the subsequent cooling, the processing time is further shortened while performing reduction processing from the stage of the plasma processing step. be able to. In addition, gas consumption can be reduced.

  Moreover, you may perform a plasma process using a hydrogen simple substance regardless of the presence or absence of the cooling after a plasma processing process. Since hydrogen has a reducing effect, the reduction treatment can be performed at the stage of the plasma treatment process. In view of improving safety, it is more preferable to perform plasma treatment using helium alone or a mixed gas of helium and hydrogen. Further, since hydrogen and helium penetrate into the inside as compared with an element having a small atomic number and a large molecular size, there is also an effect that it is easily diffused in the reduction treatment while alleviating damage to the surface of the object to be treated.

According to the bonding method of the present invention, using the flakes shaped from the fine particles of metal or metal oxide by mechanical stress, the plasma treatment process performs the plasma treatment on the object to be treated with the flakes interposed. By doing so, the bonding ability is increased. Further, the processing time can be shortened as compared with the conventional heat bonding process (without performing plasma processing), and the processing efficiency is improved and the effect of greatly contributing to the productivity is also achieved.
Further, at least one of the plurality of objects to be bonded is a semiconductor, and plasma processing is performed by controlling the relative amount of radicals to ions in plasma to be increased. Since damage to the semiconductor due to ions increases, the bonding process can be performed without damaging the semiconductor due to ions by controlling the relative amount of radicals relative to ions to be increased.

It is the schematic of the joining apparatus which concerns on an Example. It is a flowchart which shows a series of flows of the joining method which concerns on an Example. (A) is a schematic diagram of the joining state of microparticles, (b) is a schematic diagram of the joining state of flakes.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of a joining apparatus according to an embodiment. In the present embodiment, description will be made by taking an example of die bonding in which a diced semiconductor chip is bonded and mounted (mounted) on a frame including a mounting substrate and a lead frame. Therefore, in the present embodiment, a semiconductor chip and a frame will be described as an example of objects to be bonded.

  In this embodiment, as shown in FIG. 1, the bonding apparatus includes a chamber 1 and an electric heater 2 in the chamber 1. A vacuum pump 3 is provided in order to reduce the pressure inside the chamber 1 to make a vacuum. In this embodiment, the chamber 1 corresponds to the processing unit in the present invention.

  In addition, the bonding apparatus includes a stage 4 on which the semiconductor chip C and the frame F with the conductive paste P interposed are placed. The electric heater 2 described above is provided in the stage 4. In the frame F, the mounting substrate is plated or wired, and the semiconductor chip C is provided with back metal or electrodes, but these are not shown. For the semiconductor chip C, a semiconductor such as silicon (Si), silicon carbide (SiC), or gallium nitride (GaN) is used. As the mounting substrate, a metal substrate for heat dissipation and an insulating substrate such as a glass epoxy substrate or a ceramic substrate are used between the wirings. For the conductive paste P, a paste containing flakes shaped from metal or metal oxide fine particles by mechanical stress is used. The semiconductor chip C and the frame F correspond to objects to be processed in the present invention.

  In the case where bonding is performed using the conductive paste P in a vacuum state by the vacuum pump 3 as in this embodiment, pressureless bonding or self-weight pressure bonding can be performed in a state where the bonding capability is high due to the vacuum state. Therefore, metal selectivity is widened, and metals other than noble metals such as gold and silver can be used. In particular, base metals such as copper, tin, zinc, and aluminum, or alloys thereof can be used.

  In this embodiment, reduction is performed in addition to the plasma treatment. Therefore, as the conductive paste P, a paste containing flakes shaped from metal fine particles may be used, or a paste containing flakes shaped from metal oxide fine particles may be used due to the reduction effect. Also good.

  In addition, the metal can be selected according to the material and temperature characteristics of the base material (here, the frame F) and the chip (here, the semiconductor chip P). There is also an effect that damage to the chip due to temperature can be reduced. Furthermore, for example, a chip provided with an aluminum pad (aluminum pad) due to the difference in the rate of temperature rise due to metal can also selectively raise the temperature of the metal at the connection without raising the temperature of aluminum. . Even if a brittle material such as SiC is used for the semiconductor chip, it is not damaged in the case of pressureless bonding.

  As for the conductive paste P, as described above, a noble metal such as gold or silver may be used, or a base metal such as copper, tin, zinc or aluminum or an alloy thereof may be used. The conductive paste P is not a conventional metal fine particle having a nano size of 1 micron or less, but a paste containing flakes shaped from fine particles by mechanical stress. Here, the flakes are shaped into a flake shape by physical treatment such as hitting spherical particles. “Mechanical stress” also refers to the physical treatment described above. The size of the flakes may be a micrometer size, and the major axis is 1 μm to 100 μm, preferably 1 μm to several tens of μm.

  By using this size, it is possible to reduce or eliminate the amount of the dispersant required for the nano paste (conductive paste containing fine particles of nano size to 1 micron or less). Further, by reducing the amount of the dispersant in the conductive paste, there is an effect that the amount of shrinkage after application can be reduced.

  In FIG. 1, the electric heater 2 is provided in the stage 4, but the electric heater 2 is not necessarily provided in the stage 4, and the electric heater is provided in the vicinity of the semiconductor chip C and the frame F with the conductive paste P interposed. 2 may be provided. Further, the electric heater 2 is not necessarily required. As illustrated in a microwave heater or a lamp heater made of SiC, a heating unit that is normally used for heat treatment is provided in the chamber 1. The heating unit is not particularly limited.

In addition, the bonding apparatus has a supply flow path 5 for supplying a gas for plasma (indicated by “Gas” in FIG. 1) and a large number of holes 6a to block ions in the plasma and only radicals. And a punching metal 6 that passes through the hole 6a. Although two supply flow paths 5 are illustrated in FIG. 1, the number may be single or three or more. As a gas (process gas) for plasma, a rare gas such as argon (Ar) or helium (He) is used in addition to hydrogen (H ₂ ), oxygen, or nitrogen.

  In particular, in the case of the present embodiment, after the plasma treatment process, the chamber 1 is cooled by a cooling gas containing noble gas, nitrogen or hydrogen without oxygen. When the chamber 1 is cooled using the same gas as that used in the plasma treatment, a gas containing a rare gas is used as a plasma gas (process gas). In particular, when the chamber 1 is cooled using the same gas as in the plasma treatment, a gas containing helium is optimal.

Since helium penetrates into the interior as compared with an element having a large molecular size, damage to the surface of an object to be processed such as the semiconductor chip C or the frame F is further alleviated. As long as the gas contains helium, it may be a mixed gas of helium and another element, or helium alone. In particular, when the gas containing helium is a mixed gas of helium and hydrogen (H ₂ ), it can be cooled while having a reduction effect by hydrogen. Further, like helium, hydrogen penetrates into the inside as compared with an element having a large molecular size, so that the damage to the surface of an object to be processed such as the semiconductor chip C or the frame F is further reduced. .

  Further, when the chamber 1 is cooled using a gas different from the plasma treatment, the cooling gas may not necessarily include a rare gas. For example, the cooling gas may be a gas containing nitrogen. However, in the chamber 1, it is not necessary to replace the gas for plasma (process gas) with a gas containing nitrogen, and the gas containing nitrogen in the chamber 1 through the supply flow path 5 to an amount that can be cooled. May be supplied for cooling. Cooling can be performed with nitrogen.

  Plasma is generated in the chamber 1 by supplying a gas into the chamber 1 through the supply channel 5 and adding energy such as microwaves (indicated as “Power” in FIG. 1) to the process gas. Then, plasma processing is performed on the semiconductor chip C and the frame F placed on the stage 4. In addition to adding energy such as microwaves to the process gas, power may be applied to electrodes (not shown) to generate plasma in the chamber 1 by plasma discharge.

  The punching metal 6 is not particularly limited as long as it is a metal that blocks ions and allows radicals to pass. The punching metal 6 may be grounded or simply installed in the chamber 1.

  Next, the bonding method according to the present embodiment will be described with reference to FIG. FIG. 2 is a flowchart showing a series of flows of the joining method according to the embodiment. Since the electric heater 2 is used, FIG. 2 will be described assuming that step S1 is first performed in order to uniformly distribute heat under atmospheric pressure.

(Step S1) Heating under atmospheric pressure First, the electric heater 2 is operated under atmospheric pressure to heat the chamber 1 under atmospheric pressure. By heating under atmospheric pressure, heat is evenly distributed under atmospheric pressure.

(Step S2) Placement of Semiconductor Chip and Frame Semiconductor Chip C with Conductive Paste P Containing Flakes Shaped from Fine Particles by Mechanical Stress with Electric Heater 2 Continued to Operate at Atmospheric Pressure The frame F is placed on the stage 4.

(Step S3) Heat Treatment When the semiconductor chip C and the frame F with the conductive paste P interposed are placed on the stage 4 in a state where the electric heater 2 is kept operating at atmospheric pressure, it is provided in the stage 4. When the electric heater 2 heats the semiconductor chip C and the frame F, the semiconductor chip C and the frame F are heated at atmospheric pressure.

(Step S4) Vacuuming / Vacuum Processing Inside the chamber 1 with the semiconductor chip C and the frame F placed on the stage 4 and accommodated in the chamber 1 after the heat treatment with the electric heater 2 kept operating. The vacuum pump 3 is evacuated by reducing the pressure using a vacuum pump 3. Due to this evacuation, the inside of the chamber 1 is evacuated, so that the semiconductor chip C and the frame F are processed in a vacuum. Then, by continuing to operate the electric heater 2 in a vacuum state, the heat treatment is continuously performed in a vacuum state.

(Step S5) Plasma generation After the heat treatment in steps S3 and S4, and further after the vacuum treatment in step S4, the semiconductor chip C and the frame F are placed on the stage 4 and accommodated in the chamber 1 and supplied. Gas is supplied through the passage 5 into the chamber 1 until a predetermined pressure (for example, about 20 Pascals) is reached. Then, plasma energy is generated in the chamber 1 by adding energy such as microwaves (indicated as “Power” in FIG. 1) to the process gas. In the case where the semiconductor chip C and the frame F are accommodated in the chamber 1 and any of the semiconductor chip C, the frame F, or the plasma generation is disturbed, the semiconductor chip C is necessary as necessary until the next step S6. The frame F may be once lifted from the chamber 1.

(Step S6) Plasma Processing With the semiconductor chip C and the frame F placed on the stage 4 and accommodated in the chamber 1, the semiconductor chip C and the frame F are subjected to plasma processing. Since the semiconductor chip C and the frame F may be damaged by the ions, in order to prevent the damage, the ions are blocked by the punching metal 6 and controlled so that the relative amount of radicals to the ions is increased. This step S6 corresponds to the plasma processing process in the present invention.

(Step S7) Chamber Cooling After the plasma treatment process in step S6, the chamber 1 is cooled by a cooling gas containing noble gas, nitrogen or hydrogen without oxygen. When the chamber 1 is cooled using the same gas as the plasma treatment, only energy such as microwaves needs to be stopped. If the amount of gas that can be cooled is not sufficient, the gas is appropriately supplied into the chamber 1 through the supply channel 5. Further, when the chamber 1 is cooled using a gas different from the plasma treatment, the gas is supplied into the chamber 1 through the supply flow path 5 and cooled to an amount that can be cooled as described above.

(Step S8) Are there semiconductor chips and frames?
After the plasma processing in step S6, the semiconductor chip C and the frame F after cooling in step S7 are lifted from the chamber 1. Until there are no semiconductor chips C and frames F to be subjected to the single wafer process, the process gas filling state is returned to the atmospheric pressure, and the process returns to step S1 to repeat steps S1 to S8. That is, the single wafer processing is performed by repeatedly placing the next semiconductor chip C and the frame F on the stage 4 after performing the processing in steps S1 to S8. When the semiconductor chip C and the frame F to be subjected to the single wafer processing are eliminated, a series of joining processes is finished.

  When the next semiconductor chip C and the frame F are placed on the stage 4, it is not always necessary to return from the process gas filling state to the atmospheric pressure and return to step S1 as long as the heat uniformity is not affected. Returning to step S2 from step S8, steps S2 to S8 may be repeated. In other words, if heating at atmospheric pressure in step S1 can be substituted with process gas or cooling gas, the gas may be returned to atmospheric pressure without degassing.

  According to the bonding method according to the present embodiment, using the flakes shaped from the fine particles of metal or metal oxide by mechanical stress, the plasma processing process in step S6 includes the semiconductor chip C and the flakes interposed therebetween. Plasma processing is performed on the frame F. Increase the contact area between the flakes and apply residual stress inside the flakes. Furthermore, since the diffusion of the metal is promoted by the plasma treatment, the bonding ability is increased. Further, the processing time can be shortened as compared with the conventional heat bonding process (without performing plasma processing), and the processing efficiency is improved and the effect of greatly contributing to the productivity is also achieved.

  In this embodiment, it is preferable to perform the plasma treatment by controlling the relative amount of radicals to ions in the plasma to be increased. In the present embodiment, the punching metal 6 is used to block ions, and control is performed so that the relative amount of radicals to ions increases. Since the semiconductor chip C and the frame F may be damaged by the ions, the semiconductor chip C and the frame F are damaged by the ions by controlling the ions so that the relative amount of radicals with respect to the ions increases. It is possible to perform the bonding process without imparting the above. In particular, as in this example, when at least one of a plurality of objects to be bonded (two in this example) is a semiconductor (semiconductor chip C, for example, a semiconductor such as SiC), Since damage to the semiconductor due to ions increases, the bonding process can be performed without damaging the semiconductor due to ions by controlling the relative amount of radicals relative to ions to be increased.

  Note that the method for controlling the relative amount of radicals to ions to be increased is not limited to the punching metal 6. For example, the ion may be radicalized by a laser or the like, and control may be performed so that the relative amount of the radical with respect to the ion increases.

  In the present embodiment, at least one of a plurality (two in this embodiment) of objects to be bonded is a semiconductor. In this embodiment, one of the two objects to be processed is a semiconductor chip C made of a semiconductor such as SiC. Even when a large-sized semiconductor (here, semiconductor chip C) is bonded using flakes shaped from fine particles of metal or metal oxide, pressureless bonding is performed in a state where the bonding capability is high due to the vacuum state. Or self-weight pressurization joining can be performed and there also exists an effect that the selectivity of a metal spreads, without giving a damage to a semiconductor. Therefore, not only precious metals such as gold and silver but also base metals such as copper, tin, zinc and aluminum or alloys thereof can be selected. Therefore, it is possible to obtain a bonding material that is cheaper and has equivalent electric / thermal conduction / bonding characteristics.

  Further, in this embodiment, after the plasma processing process in step S6, a processing unit (in this embodiment) that accommodates the semiconductor chip C and the frame F with an oxygen-free cooling gas containing noble gas, nitrogen, or hydrogen. The chamber 1) is preferably cooled. After the plasma treatment process, the treatment part (chamber 1) is cooled with a cooling gas containing noble gas, nitrogen or hydrogen without oxygen, thereby preventing oxidation and reducing the temperature to the stage 4 temperature. Force cooling. Therefore, it is not necessary to cool for a long time in an oxygen-free atmosphere, and the treatment time can be shortened while preventing oxidation while having a reducing effect. In particular, when using a frame material made of an easily oxidizable metal such as copper or the like to join an object to be processed (in this case, the semiconductor chip C), or as a bonding material, an easily oxidized material such as a base metal having a higher ionization tendency than hydrogen Even in the case of selection, in the plasma treatment process, the adhesive (conducting paste P in this embodiment) containing flakes shaped from metal or metal oxide fine particles can be baked, and the plasma treatment process Can be joined in stages. Furthermore, the frame material and the bonding material can be immediately cooled after the plasma processing process, and the processing time can be shortened while preventing the frame material and the bonding material from being oxidized. Note that flakes shaped from metal oxide fine particles can be used for bonding due to the reduction effect.

  An example of the cooling gas is a gas containing a rare gas (for example, helium). Plasma treatment is performed using the gas containing the rare gas described above in the plasma treatment process, and the same gas as the plasma treatment after the plasma treatment process. Is used to cool the processing unit (chamber 1). In this case, since the processing can be performed using the gas containing the same rare gas in the plasma processing process and the subsequent cooling (step S7), the processing time can be further increased while performing the reduction process from the stage of the plasma processing process. It can be further shortened. In addition, gas consumption can be reduced.

  The present invention is not limited to the above embodiment, and can be modified as follows.

  (1) In the above-described embodiment, the bonding using the conductive paste has been described. However, if bonding is performed using flakes shaped from metal or metal oxide fine particles by mechanical stress, bonding using solder is performed. You may apply to.

  (2) In the above-described embodiment, the semiconductor chip and the frame by die bonding are taken as an example of the object to be processed. However, it is applied to the wire bonding after die bonding, or the wiring substrate on which the electrodes are wired. As exemplified in application to electrode bonding for bonding semiconductor chips, there is no particular limitation as long as it can be a bonding target.

  (3) In the embodiment described above, among a plurality (two in the embodiment) of objects to be joined, one is a semiconductor chip, for example, and the other is a mounting substrate made of a metal substrate or an insulating substrate, for example. As described above, either one is a semiconductor, but both may be semiconductors. Of course, the semiconductor is not limited to a semiconductor as long as it can be a bonding target. Further, the number of junctions is not limited to two and may be three or more.

  (4) In the above-described embodiment, after the plasma processing process, the processing portion (chamber 1 in the embodiment) is cooled by a cooling gas containing oxygen and a rare gas, nitrogen, or hydrogen. When there is no reduction or when it is not necessary to perform reduction, it is not always necessary to perform reduction and cooling. In addition, with or without cooling after the plasma treatment process, only reduction is performed during the plasma treatment process, only reduction is performed after the plasma treatment process, or only reduction is performed continuously from the plasma treatment process to the plasma treatment process. Also good. For example, plasma treatment may be performed using hydrogen alone. Since hydrogen has a reducing effect, the reduction treatment can be performed at the stage of the plasma treatment process. In view of improving safety, it is more preferable to perform plasma treatment using helium alone or a mixed gas of helium and hydrogen. Further, since hydrogen and helium penetrate into the inside as compared with an element having a small atomic number and a large molecular size, there is also an effect that it is easily diffused in the reduction treatment while alleviating damage to the surface of the object to be treated.

  (5) In the embodiment described above, the punching metal 6 (see FIG. 1) is controlled so that the relative amount of radicals to ions is increased. However, when there is no damage to the semiconductor, or other than the semiconductor is the target of bonding. In this case, it is not always necessary to control the amount of radicals relative to ions to be increased.

  (6) In the above-described embodiment, the vacuum processing is performed before the plasma processing. However, the vacuum processing is not necessarily performed as long as the workpieces to be bonded can withstand pressurization.

  (7) In the above-described embodiment, the heat treatment is performed before the plasma treatment, but the heat treatment is not necessarily performed.

DESCRIPTION OF SYMBOLS 1 ... Chamber C ... Semiconductor chip F ... Frame P ... Conductive paste

Claims (4)

A joining method in which fine particles of metal or metal oxide are sintered to perform a joining process on an object to be processed,
Among the plurality of objects to be joined, at least one is a semiconductor,
Control the plasma so that the amount of radicals relative to ions in the plasma increases, and use the flakes shaped from the fine particles by mechanical stress to perform the plasma treatment on the object to be processed with the flakes interposed A joining method comprising: performing a joining process on the object to be processed by sintering the flakes by providing a plasma treatment process. The bonding method according to claim 1 ,
After the plasma treatment step, the bonding method is characterized in that the treatment portion containing the object to be treated is cooled with a cooling gas containing oxygen and a rare gas, nitrogen, or hydrogen. The joining method according to claim 2 ,
The cooling gas is a gas containing a rare gas,
Performing the plasma treatment using a gas containing the rare gas in the plasma treatment process;
A bonding method characterized in that after the plasma treatment process, the treatment portion is cooled using the same gas as in the plasma treatment. In the joining method in any one of Claims 1-3 ,
A bonding method, wherein the plasma treatment is performed using hydrogen alone, helium alone, or a mixed gas of helium and hydrogen.

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