WO2022114172A1

WO2022114172A1 - Heat transfer structure for lsi element and method for manufacturing lsi element having such heat transfer structure

Info

Publication number: WO2022114172A1
Application number: PCT/JP2021/043578
Authority: WO
Inventors: 光治加藤; 兆嶋田; 孝幸古澤; 幹土砂入
Original assignee: 有限会社Mtec; アスカコーポレーション株式会社
Priority date: 2020-11-30
Filing date: 2021-11-29
Publication date: 2022-06-02
Also published as: JP2022086775A

Abstract

The present invention provides a heat transfer structure for an LSI element that transfers heat generated in an LSI to the outside thereof by means of a metal substrate joined to a thin Si layer, and a method for manufacturing an LSI element having such heat transfer structure. A method for manufacturing an LSI element having a heat transfer structure is characterized by comprising: a first joining step for joining a provisional substrate 5 to a main surface 11 side of a Si substrate 100 having an LSI 1 formed in an upper layer portion thereof; a Si film-thinning step for forming a Si thin film 10 by removing a back surface side of the Si substrate while leaving a thickness corresponding to the depth of the upper layer portion; a second joining step for joining, at a temperature not exceeding an upper limit of an LSI operation temperature, the back surface of the Si thin film to a second substrate 25 of which at least an upper layer comprises a metal substrate 20; and a peeling step for removing the provisional substrate 5.

Description

A heat transfer structure of an LSI element and a method for manufacturing an LSI element having the heat transfer structure.

The present invention relates to a heat transfer structure of an LSI element and a method of manufacturing an LSI element having the heat transfer structure. More specifically, the present invention relates to a heat transfer structure of an LSI element that transfers heat generated by an LSI by a metal substrate bonded to a Si thin film to the outside, and a method of manufacturing an LSI element having the heat transfer structure.

With the progress of semiconductor miniaturization technology, the performance of LSI has improved remarkably. In recent years, high-performance LSIs that generate more than 20 watts of heat have been put into practical use in LSIs for AI applications and the like. The operating temperature range of the LSI element using Si is approximately 150 ° C. or less at the PN junction temperature of the element. Therefore, how to transmit the heat generated in the LSI formed on the surface layer portion of Si to the outside is important.

FIG. 9A shows a mounting example of a conventional typical high-performance LSI. A chip-sized LSI element 300 in which the LSI 100 is formed on the surface layer portion on the main surface (lower surface in the drawing) side of the silicon (Si) substrate 310 is mounted on the printed circuit board 200 by a face-down technique. The heat generated by the LSI 100 is dissipated from the main surface of the face-down mounted LSI element 300 to the printed circuit board 200 via the face-down bonding terminal 120. A first heat spreader 410 or the like having a heat distribution function is provided on the back surface side of the printed circuit board 200, and heat is radiated to the outside. On the other hand, heat is radiated to the outside from the back surface (upper surface in the drawing) of the LSI element 300 by the second heat spreader 430 provided via the heat transfer material 420 such as the heat transfer sheet and the heat transfer gel. .. Since the printed circuit board 200 connected to the main surface side of the LSI element 300 is generally made of resin, the thermal conductivity is not good. By providing a metal hole (thermal via) for heat transfer penetrating the printed circuit board 200, heat conduction is improved, but the effect is limited. As the heat generated by the LSI 100 increases, it becomes important to transfer heat from the back surface side of the LSI element 300 to the second heat spreader 430 via the heat transfer material 420. Normally, the second heat spreader 430 also serves as the control system terminal of the LSI 100 and the housing of the case, and has a structure that easily radiates the heat generated by the LSI to the outside.
FIG. 9B shows an example of face-down mounting of a high-performance LSI having a fan-out structure. The heat generated by the LSI 100 is transferred to the printed circuit board 200 via the fan-out substrate 320, which is joined to the main surface side of the LSI element 300 to form fan-out wiring, and the face-down bonding terminal provided on the lower surface thereof. Then, it is radiated to the outside by the first heat spreader 410 or the like. On the other hand, heat is radiated from the back surface of the LSI element 300 to the outside from the second heat spreader 430 via the heat transfer material 420. Since the printed circuit board 200 is generally made of resin, its thermal conductivity is not good. Normally, the second heat spreader 430 also serves as the control system terminal of the LSI 100 and the housing of the case, and has a structure that easily radiates the heat generated by the LSI to the outside. As the heat generated by the LSI 100 increases, it becomes important to transfer heat from the back surface side of the LSI element 300 to the second heat spreader 430 via the heat transfer material 420.

FIG. 10 shows the case where a heat dissipation fan is used. The LSI element 300 is face-down mounted on the printed circuit board 200. The heat generated by the LSI 100 is transferred to the printed circuit board 200 via the face-down bonding terminal and radiated to the outside from the first heat spreader 410 or the like. On the other hand, the heat generated in the LSI 100 is radiated from the back surface side of the LSI element 300 to the outside air by using the heat dissipation fan 440. Since the thermal conductivity of the printed circuit board 200 is generally not good, it is important to transfer heat from the back surface side of the LSI element 300 to the heat dissipation fan 440 as the heat generation of the LSI 100 increases.

As described above, heat dissipation of a high-performance LSI has become an issue, and in particular, from the LSI formed on the surface layer portion on the main surface side of the LSI element, the back surface of the LSI element via the Si substrate which is the substrate portion thereof. It is important to improve the heat conduction to the heat spreader and heat dissipation fan installed on the side.
In order to improve thermal conductivity, there is a method of bonding a metal substrate to a Si substrate. For example, a method of using a metal for the substrate portion of a Si semiconductor element is known (see Patent Document 1). In Patent Document 1, molybdenum having a high melting point is bonded to a metal at a high temperature of 1000 ° C., and bonding is performed by mutual diffusion of molybdenum and Si at the interface. In addition, a method of metallizing the bonded surface of the Si substrate using high melting point solder and bonding it to the copper substrate at about 400 ° C is conceivable, but face-down bonding is performed by soldering at about 220 ° C. Soldering the Si substrate and the copper substrate requires soldering using high melting point solder, which has a higher temperature. However, regardless of whether the molybdenum substrate and the Si substrate are bonded at 1000 ° C or the copper substrate and the Si substrate are bonded at 400 ° C, the practical temperature of the face-down mounted element is generally-. Since the temperature is about 40 ° C. to + 85 ° C., stress is generated due to the difference between the temperature at the time of joining and the temperature in the practical state, and warpage occurs. Further, due to the stress generated at the bonding interface, it is not preferable for the connection life and the element life of the connection interface.

Japanese Unexamined Patent Publication No. 4-49271

As described above, heat dissipation of high-performance LSI elements has become an issue. In particular, when the LSI element is face-down mounted, a heat spreader or a heat dissipation fan provided on the back surface side of the LSI element from the surface layer portion of the main surface of the Si substrate on which the LSI element is formed via the Si substrate which is the substrate portion. It is necessary to improve the heat conduction leading to. Further, in that case, it is preferable that the thickness of the Si substrate is thin.
However, in the conventional technique of joining the molybdenum substrate and the Si substrate at 1000 ° C. or the copper substrate and the Si substrate at 400 ° C., the operating temperature of the LSI element is generally about -40 ° C to + 85 ° C. Therefore, stress is generated at the joining interface due to the difference between the temperature at the time of joining and the temperature in the practical state, and warpage occurs. Further, due to the stress generated at the bonding interface, it is not preferable for the connection life and the element life of the connection interface. In particular, the thinner the Si layer, the greater the effect on the element on the Si surface due to the internal stress generated at the bonding interface.

An object of the present invention is to provide a heat transfer structure of an LSI element that transfers heat generated in an LSI by a metal substrate bonded to a Si thin film to the outside, and a method of manufacturing an LSI element having the heat transfer structure.

The point of view for solving the above problems is to set the bonding temperature between the Si substrate and the metal substrate to a temperature within the operating temperature range of the LSI element in order to reduce the stress at the bonding interface. By this joining near room temperature, the stress generated at the joining interface is small when the LSI element is used, and a good effect can be obtained on the device life and the interface joining life.
Further, in order to minimize the thickness of the Si layer on which the LSI is formed, a temporary substrate is attached to the main surface side of the Si substrate after the LSI is formed, and the Si layer is formed to the limit where the LSI function can be created. Is to be thinly polished and then joined to a metal substrate.

Further, since the LSI exists in a region of several μm on the surface layer of the Si substrate and the remaining several hundred microns only serve as a substrate, the substrate portion should be made of a metal (copper) material having good thermal conductivity. It is in. As a result, the heat generated by the LSI is quickly transmitted to the copper substrate portion, and the heat can be transferred from the copper substrate portion to the external heat spreader.

The present invention is as follows.
1. 1. The first joining step of joining the main surface side of the Si substrate on which the LSI is formed on the surface layer and the temporary substrate, and
A Si thin film step of forming a Si thin film by removing the back surface side of the Si substrate while leaving a thickness corresponding to the depth of the surface layer portion.
A second joining step of joining the back surface of the Si thin film and the metal surface of the second substrate whose surface layer is at least a metal substrate at a temperature not exceeding the upper limit of the operating temperature of the LSI.
The peeling step for removing the temporary substrate and
A method for manufacturing an LSI element having a heat transfer structure, which comprises.
2. 2. A fan-out mounting step of mounting a fan-out board in which fan-out wiring is formed on the main surface side of the Si board is included.
In the first joining step, the Si substrate and the temporary substrate are joined via the fan-out substrate. A method for manufacturing an LSI element having the heat transfer structure described above.
3. 3. After performing the Si thin film forming step, a barrier metal layer forming step of forming a barrier metal layer made of a barrier metal on the back surface of the Si thin film is included.
In the second joining step, the Si thin film and the second substrate are joined via the barrier metal layer. Or 2. A method for manufacturing an LSI element having a heat transfer structure according to the above.
4. The thickness of the Si thin film is 100 μm or less. To 3. A method for manufacturing an LSI element having a heat transfer structure according to any one of the above.
5. The metal substrate is a copper substrate. To 4. A method for manufacturing an LSI element having a heat transfer structure according to any one of the above.
6. An LSI is formed on the surface layer portion of the main surface thereof, and a Si thin film having a thickness corresponding to the depth of the surface layer portion is formed.
A second substrate whose surface layer is at least a metal substrate bonded to the back surface of the Si thin film is provided.
A heat transfer structure of an LSI element, characterized in that heat generated by an LSI is transferred to the outside through the metal substrate.
7. 6. A fan-out wiring is formed, and the fan-out substrate is provided on the main surface side of the Si thin film. The heat transfer structure of the LSI element described.
8. The thickness of the Si thin film is 100 μm or less. Or 7. The heat transfer structure of the LSI element described in 1.
9. The metal substrate is a copper substrate. ~ 8. The heat transfer structure of the LSI element according to any one of.

According to the method for manufacturing an LSI element having a heat transfer structure of the present invention, a first joining step of joining a temporary substrate and a main surface side of a Si substrate in which an LSI is formed on a surface layer portion and a depth of the surface layer portion. A Si thinning step of forming a Si thin film by removing the back surface side of the Si substrate while leaving a thickness corresponding to the thickness, and at least the back surface of the Si thin film at a temperature not exceeding the upper limit of the operating temperature of the LSI. Since the surface layer includes a second joining step of joining the metal surface of the second substrate made of a metal substrate and a peeling step of removing the temporary substrate, the surface layer on the main surface side of the Si substrate on which the LSI is formed is included. A thin Si thin film is formed according to the depth of the portion, and the Si thin film and the metal substrate are joined in a normal temperature range. As a result, the stress generated at the bonding interface is extremely small, and the difference between the temperature at the time of bonding and the temperature at the time of using the element is small, so that peeling of the bonding interface is prevented and deterioration of the LSI element due to stress is minimized. be able to.

Further, according to the heat transfer structure of the LSI element of the present invention, an LSI is formed on the surface layer portion of the main surface thereof, and a Si thin film having a thickness corresponding to the depth of the surface layer portion is formed. A second substrate having at least a surface layer made of a metal substrate bonded to the back surface of the Si thin film is provided, and heat generated by the LSI is transferred through the metal substrate, so that the heat generated by the LSI is rapidly made of the metal substrate. It is transmitted to the substrate portion, and heat can be transferred from the metal substrate portion to an external heat spreader or the like. By providing the function of the heat pipe to the external heat spreader or the like, the heat from the metal substrate can be transferred to the outside more efficiently. As the metal substrate, a copper substrate having excellent thermal conductivity can be used. Further, since the metal substrate serves as a substrate, an LSI element suitable for face-down mounting can be configured. The generation of warpage is suppressed by the metal substrate, and further, by joining the metal substrate and the Si thin film on which the LSI is formed at a temperature below the upper limit of the temperature at which the element is used, the Si thin film and the metal when using the LSI element are used. Deterioration due to stress generated at the bonding interface with the substrate can be suppressed.

The present invention will be further described in the following detailed description with reference to the plurality of references mentioned with reference to non-limiting examples of typical embodiments according to the invention, although similar reference numerals are in the drawings. Similar parts are shown through several figures.
It is a schematic cross-sectional view which shows the heat transfer structure of the LSI element which concerns on embodiment. It is a schematic sectional drawing for demonstrating each process in the manufacturing method of the LSI element provided with a heat transfer structure. It is a schematic cross-sectional view which shows the heat transfer structure of the LSI element which has a fan-out structure. It is a schematic cross-sectional view for demonstrating each process in the manufacturing method of the LSI element which has a heat transfer structure in the case of having a fan-out structure. It is a schematic diagram for demonstrating the joining method using a FAB gun. It is a TEM image of the joint portion of a Si thin film and a metal substrate. It is a schematic cross-sectional view for demonstrating the face-down mounting of an LSI element provided with a heat transfer structure. It is a figure which shows the temperature of each part in the face-down mounting of the LSI element which has a heat transfer structure. It is a schematic cross-sectional view for demonstrating the face-down mounting of the conventional LSI element. It is a schematic diagram for demonstrating the example which uses the heat dissipation fan for the conventional LSI element which was face-down mounted.

The matters shown here are for illustrative purposes and embodiments of the present invention, and are the most effective and effortless explanations for understanding the principles and conceptual features of the present invention. It is stated for the purpose of providing what seems to be. In this regard, it is not intended to show structural details of the invention beyond a certain degree necessary for a fundamental understanding of the invention, and some embodiments of the invention are provided by description in conjunction with the drawings. It is intended to clarify to those skilled in the art how it is actually realized.

In the heat transfer structure (50) of the LSI element according to the present embodiment, the LSI (1) is formed on the surface layer portion of the main surface (11), and the thickness is formed thin corresponding to the depth of the surface layer portion. A second substrate (25) having a formed Si thin film (10) and a second substrate (25) having at least a surface layer bonded to the back surface (12) of the Si thin film (10) made of a metal substrate (20) is provided, and the metal substrate (20) is provided. It is characterized in that the heat generated in the LSI (1) is transferred to the outside through the LSI (1) (see FIG. 1). The type of LSI is not particularly limited.
Further, in the heat transfer structure (51) of another LSI element, a fan-out wiring is formed, and a fan-out substrate (9) bonded to the main surface (11) side of the Si thin film (10) is further formed. It can be provided (see FIG. 3 (b)).

The thickness of the Si thin film (10) corresponds to the depth of the surface layer portion and is made as thin as possible to create an LSI function, and the metal substrate (20) serves as a substrate for the LSI element. The depth of the surface layer portion is set according to the impurity concentration, withstand voltage, and the like of the impurity layer constituting the LSI. Usually, the depth of the impurity layer is several μm. Therefore, in the present embodiment, the thickness of the Si thin film (10) can be 100 μm or less (5 to 100 μm). Further, the thickness of the metal substrate (20) may be appropriately set according to the strength of the material and the thickness of the Si thin film (10). For example, when a copper substrate is used, it can be about 50 to 300 μm. ..
Even when LSI is mounted on the ceramic package, it is effective to use a metal (copper) substrate for the base portion of the Si element as described above in order to improve the heat conduction from the Si element to the ceramic package. ..

The method for manufacturing an LSI element (50) having a heat transfer structure according to the present embodiment is a method of manufacturing a Si substrate (100) having an LSI (1) formed on a surface layer portion on the main surface (11) side and a temporary substrate (5). A first joining step of joining and a Si thinning step of forming a Si thin film (10) by removing the back surface side of the Si substrate (100) while leaving a thickness corresponding to the depth of the surface layer portion. , The back surface (12) of the Si thin film (10) and the metal substrate (20) of the second substrate (25) whose surface layer is at least the metal substrate (20) at a temperature not exceeding the upper limit of the operating temperature of the LSI (1). It is characterized by including a second joining step of joining and a peeling step of removing the temporary substrate (5) (see FIG. 2).
Further, another method of manufacturing the heat transfer structure (51) of the LSI element is to mount a fan-out board (9) in which fan-out wiring is formed on the main surface (11) side of the Si board (100). The first joining step, which includes an out-mounting step, joins the Si substrate (100) and the temporary substrate (5) via the fan-out substrate (9) (see FIG. 4).

Since the bonding between the metal substrate (20) on the surface layer of the second substrate (25) and the Si thin film (10) is performed at a temperature (normal temperature) that does not exceed the upper limit of the operating temperature of the LSI element, the metal substrate 20 and the Si thin film are bonded. The stress generated at the bonding interface with 10 can be reduced, the warp of the substrate can be significantly reduced, and the stress generated at the bonding interface due to the temperature cycle or the like generated in a practical state can be reduced. It is possible to increase the reliability of joining.

FIG. 1A shows a structural example of an LSI element 50 having a heat transfer structure according to the present embodiment. A multi-layer element structure in which a Si thin film 10 having a required thickness on which LSI 1 is formed and a second substrate (25) having a thickness required for mounting and having at least a surface layer made of a metal substrate (20) are joined. be. The surface layer of the second substrate (25) refers to a portion having a constant plate thickness constituting the joint surface with the Si thin film 10. In this example, the entire second substrate (25) is composed of one metal substrate (20). As the metal substrate (20), it is preferable to use a copper substrate having excellent thermal conductivity.
Conventionally, heat generated by an LSI formed on the surface layer of an LSI element is conducted to the outside from a Si substrate of the same material via a heat spreader. On the other hand, the LSI element 50 of this example uses a metal (copper) substrate instead of a Si substrate in order to more efficiently conduct heat conduction in the substrate portion made of Si. With this structure, the heat generated by the LSI 1 can be efficiently conducted to the heat spreader provided outside via the metal substrate 20 made of copper.
This heat transfer structure can also be applied to a multi-terminal structure of an LSI called a fan-out structure, and a fan-out structure element 51 having a copper substrate can be configured (see FIG. 3 (b)).

As shown in FIG. 1 (b), the second substrate 25 having at least the surface layer made of a metal substrate may be configured by laminating the metal substrate 20 to be the surface layer and the adhesive tape 26. The adhesive tape 26 is effective when the thickness of the metal substrate 20 is kept thin, and in addition, the adhesive tape 26 can also serve as a base adhesive tape when the LSI element is divided into chips.
Further, as shown in FIG. 1 (c), the second substrate 25 may be formed by a metal substrate 20 as a surface layer and a solder layer 27. The solder layer 27 can be used as a connecting means when the LSI element is mounted on the ceramic package.
Further, as shown in FIG. 1D, the second substrate 25 may be formed of a metal substrate 20 as a surface layer and an insulating sheet 28. The insulating sheet 28 can serve as an insulating layer when the metal substrate potential of the LSI element is different from the potential of the heat spreader.
In addition, various materials can be selected as the base layer of the metal substrate 20 as the surface layer. Hereinafter, an example will be described in which the base layer constituting the second substrate 25 is omitted, and the entire second substrate 25 is composed of one metal substrate 20.

With reference to FIG. 2, each step in the method of manufacturing an LSI element having a heat transfer structure according to the present embodiment will be described. Each manufacturing process performs processing in a wafer (for example, 8-inch size wafer) state, and each figure shows a cross section of a portion corresponding to an LSI element in one chip size package.
FIG. (A) shows a state in which the LSI 1 is formed on the surface layer portion on the main surface 11 side of the Si substrate 100. The substrate is the same Si substrate as the LSI. A bonding terminal 30 for face-down mounting is formed on the main surface 11 of the Si substrate 100. The standard thickness of the Si substrate (100) is, for example, 725 μm in the case of an 8-inch wafer.

(First joining process)
FIG. 2B shows a state in which the main surface 11 side of the Si substrate 100 on which the LSI 1 is formed on the surface layer portion and the temporary substrate 5 are joined by the first joining step.
As the temporary substrate 5, for example, a transparent glass substrate can be used. The main surface 11 side of the Si substrate 100 and the temporary substrate 5 can be bonded by applying a UV release resin that is peeled off by ultraviolet light as a bonding material to the bonding surface. In a later step, the flatness of the bonding is required in order to polish the Si substrate 100 thinly, but the flatness can be ensured by applying the UV release resin and then pressurizing it while keeping it parallel.
It is also possible to use an adhesive resin tape as the temporary substrate 5. Due to the rigidity of the resin tape, the Si substrate 100 can be thinly polished in the subsequent Si thinning step.

(Si thin film process)
The Si thin film thinning step is a step of forming the Si thin film 10 by removing the back surface side of the Si substrate 100 while leaving a thickness corresponding to the depth of the surface layer portion.
FIG. 2C shows a state in which the Si thin film 10 using the Si substrate 100 as a base material is formed by removing the back surface side of the Si substrate 100 bonded to the temporary substrate 5 by the Si thin film step. ing. The method of removing the back surface side of the Si substrate 100 is not particularly limited, and for example, the thickness can be reduced to about 5 μm by grinding and polishing the back surface side of the Si substrate 100 with the temporary substrate 5 as a support. As described above, the thickness corresponding to the depth of the surface layer portion depends on the withstand voltage required for the element, and is about 5 μm for the low withstand voltage element. Therefore, the thickness of the Si thin film 10 may be 5 μm or more. can. Actually, it is selected based on the balance between the ease of thin film processing and the improvement of thermal conductivity, and the thickness of the Si thin film 10 may be 10 μm or more from the viewpoint of thin film processing technology. Therefore, for example, in the case of an 8-inch wafer, the surface layer portion having a thickness of 10 to 100 μm on the main surface side of the standard Si substrate 100 having a thickness of 725 μm is left as a Si thin film (10).
The portion having a certain thickness on the main surface 11 side of the Si substrate 100 left in this way becomes the Si thin film 10. The back surface 12 of the Si thin film 10 is polished to a surface roughness Ra of about 0.5 nm for later bonding with the metal substrate 20.

(Barrier metal layer forming process)
The barrier metal layer forming step is a step of forming a barrier metal layer made of a barrier metal on the back surface of the Si thin film after performing the Si thinning step (not shown).
When a copper substrate is used as the metal substrate 20 to be bonded to the Si thin film 10, the barrier metal layer 8 may be formed on the back surface 12 of the Si thin film 10 in order to prevent the copper from diffusing into the Si layer after bonding. preferable. Ni, Ta, or the like can be used as the barrier metal, and the barrier metal layer 8 having a thickness of about 10 nm can be formed on the back surface 12 of the Si thin film 10 by sputtering.

(Second joining process)
The second joining step is a step of joining the back surface of the Si thin film and the metal substrate of the second substrate at a temperature not exceeding the upper limit of the operating temperature of the target LSI element.
FIG. 2D shows a state in which the back surface 12 of the Si thin film 10 and the second substrate 25 whose surface layer is at least the metal substrate 20 are bonded in the second bonding step. The second substrate 25 is a substrate whose surface layer is at least a metal substrate 20, but the illustration is omitted except for the metal substrate 20.
Generally, the operating temperature of the semiconductor element is about −20 ° C. to + 85 ° C. Therefore, the Si thin film 10 and the metal substrate 20 are joined at 85 ° C. or lower, which is the upper limit of the operating temperature range. In practice, the joining can be performed at room temperature. The material of the metal substrate 20 is not particularly limited, but for example, a copper substrate that is inexpensive and has excellent thermal conductivity can be used. When the barrier metal layer 8 is formed on the back surface of the Si thin film, the Si thin film 10 and the metal substrate 20 are joined via the barrier metal layer 8.
In order to bond the metal substrate 20 and the Si thin film 10, it is preferable to polish each joint surface so that the surface roughness is about 0.5 nm, but it is easy with recent polishing techniques.

The method of joining at room temperature is not particularly limited, but for example, a method of activating both sides to be joined by an argon beam using a FAB (fast atomic beam) gun can be applied. As shown in FIG. 5, the Si thin film 10 and the metal substrate (copper substrate) 20 can be joined by using a FAB gun. In recent years, the joining method using a FAB gun has become widespread in room temperature joining of semiconductor substrates. As shown in the figure, both sides to be joined are activated by irradiating an argon beam obtained from an argon beam source 200, and then pressurized at room temperature for joining. The feature of this joining method is that if the joining surface has a flatness of 0.5 nm level, it can be directly joined at room temperature. The figure is a schematic diagram of the main part of the bonding device. Two substrates to be bonded in a vacuum chamber are arranged so as to face each other at regular intervals, and the FAB gun 200 is placed on both surfaces from the side thereof. The argon beam (201, 202) is scanned and irradiated. The degree of vacuum in the vacuum chamber is about 1 × 10 ^-4 to 1 × 10 ^-6 Pa. By this irradiation, the surface layers (20b, 10b) of both substrates are activated and can be bonded at room temperature. It is also possible to activate and bond with an ion gun regardless of the FAB gun.
FIG. 6 shows a TEM (transmission electron microscope) image of the bonding interface between the Si thin film 10 and the copper substrate 20. It can be seen that the Si thin film 10 and the copper substrate 20 are bonded at the atomic level.

In addition, a method of forming a thin gold thin film with a thickness of about 10 nm on the surface for joining has also been developed. The Si thin film 10 and the metal substrate 20 can also be joined via such a thin gold thin film.

(Peeling process)
FIG. 2 (e) shows a state in which the temporary substrate is removed by the peeling step. When the barrier metal layer 8 is formed on the back surface 12 of the Si thin film 10, the Si thin film 10 is bonded to the metal substrate 20 via the barrier metal layer 8 (not shown).
When the temporary substrate 5 made of transparent glass and the main surface 11 of the Si thin film 10 are bonded with a UV release resin, the bonding interface can be separated by irradiating ultraviolet rays from the glass substrate side. As a result, the LSI element has a multi-layer element structure composed of a thin Si layer on which the LSI is formed and a metal substrate as a support substrate thereof. The transparent glass substrate can be reused.
Further, when a resin tape having adhesiveness is used as the temporary substrate 5, it can be peeled off from the end face of the resin tape, and the resin tape can be disposable.

(LSI element with fan-out structure)
The LSI element can have a fan-out structure. Fan-out mounting is a mounting method that has been put into practical use as the terminal pitch has become finer due to the increase in the number of pins of LSI. FIG. 3A shows how the conventional LSI element 300 is mounted on the fan-out substrate (Si substrate) 320 and the terminal pitch is widened. Terminals are formed on the LSI element 300 side of the fan-out board 320 at the same pitch as the LSI element 300, mutual wiring is made in the inner layer of the fan-out board, and terminals having a wide pitch on the external mounting surface terminal 13 of the fan-out board. Is formed. The external mounting surface terminal 13 is a terminal having a wide pitch so that it can be face-down mounted on a printed circuit board. In this example, the LSI element 300 is face-down mounted on the fan-out substrate 320 in the wafer state, then the resin 14 is filled, and the resin is molded in the wafer state. The Si substrate of the element is exposed on the back surface side of the LSI element 300. As the fan-out substrate 320, a resin substrate may be used in addition to the Si substrate.

FIG. 3B shows the LSI element 51 in which the fan-out substrate 9 having the fan-out wiring formed is bonded to the main surface 11 side of the Si thin film 10 in the method of manufacturing the LSI element of the present embodiment. ing. A metal substrate 20 is bonded to the back surface of the Si thin film 10, and the metal substrate 20 is exposed on the back surface side of the LSI element 51. The thickness of the Si thin film 10 is the minimum thickness necessary for the configuration and operation of the LSI, and the thickness of the metal substrate 20 which is the base portion thereof is necessary for face-down mounting of an element having a fan-out structure. It is said to be thick. According to this configuration, the heat generated by the LSI can be quickly conducted to the substrate portion having high thermal conductivity, and efficiently conducted and radiated to the outside via the heat spreader connected to the substrate portion.

In the present embodiment, the fan-out mounting step of mounting the fan-out board (9) in which the fan-out wiring is formed on the main surface (11) side of the Si board (100) is included, and the first joining step includes a fan-out mounting step. It can be configured to join the Si substrate (100) and the temporary substrate (5) via the fan-out substrate (9).
With reference to FIG. 4, each step in the manufacturing method of the LSI element which can be fan-out mounted will be described. Each manufacturing process is performed in an 8-inch wafer state, and each figure shows a cross section of a portion corresponding to an LSI element in one chip size package.

FIG. (A) shows a state in which the LSI 1 is formed on the surface layer portion on the main surface 11 side of the Si substrate 100. The substrate is the same Si substrate as the LSI. A bonding terminal 30 is formed on the main surface 11 of the Si substrate 100, and a fan-out substrate 9 made of Si is bonded to the main surface side of the bonding terminal 30. Mutual wiring is made in the inner layer of the fan-out board 9, and bonding terminals 13 having a wide pitch are formed on the external mounting surface of the fan-out.
FIG. 4B shows a state in which the temporary substrate 5 is bonded to the upper surface of the fan-out substrate 9 by the first bonding step.
FIG. 3C shows a state in which the back surface side of the Si substrate 100 is removed by polishing or the like by the Si thin film step, and the Si thin film 10 remains. Since the temporary substrate 5 serves as a support, the thickness of the Si thin film 10 can be reduced to about 5 to 10 μm.
FIG. 3D shows a state in which the metal substrate 20 is bonded to the back surface 12 of the Si thin film 10 by the second bonding step. A room temperature joining technique such as using a FAB gun can be applied to this joining. It can also be bonded via a gold thin film having a thickness of about 10 nm.
FIG. 3E shows a state in which the temporary substrate 5 is peeled off by the peeling step.
As described above, the fan-out structure element 51 having an element structure made of a metal (copper) substrate is completed. The specific contents of each step are the same as those of each step described with reference to FIG.

The LSI element 50 manufactured as described above and the LSI element 51 having a fan-out structure can be mounted on a printed circuit board by face-down and used.
FIG. 7A shows an example in which the LSI element 50 of the chip size package is face-down mounted on the printed circuit board 200. FIG. 3B shows an example in which an LSI element 51 having a fan-out structure is face-down mounted on a printed circuit board 200. In this example, a copper substrate is used as the metal substrate 20, and the thickness thereof is 300 μm. The thickness of the Si thin film 10 on which the LSI is formed is 10 μm. The thin Si thin film 10 and the metal substrate 20 can efficiently transfer the heat generated by the LSI. Further, since the Si thin film 10 is bonded to the metal substrate 20, there is no warp, and stable soldering is possible even in face-down mounting.
In the examples shown in FIGS. 7A and 7B, the heat generated on the surface of the LSI is dissipated mainly by conduction from the copper substrate 20 which is a substrate to the heat spreader 430 which is a housing.

FIG. 8 describes a simulation of heat dissipation by heat conduction from the LSI element 50 mounted as described above to the housing. The thickness of the Si thin film 10 constituting the LSI element 50 is 10 μm, and the thickness of the copper substrate as a substrate is 300 μm.
In the element structure of the copper substrate according to the present embodiment, when heat generation of 20 watts and an ambient temperature of 25 ° C., the heat spreader portion D that also serves as a housing has a temperature of 30 ° C., and the heat spreader portion C has a temperature of 53 ° C. The temperature is 76 ° C. in the heat conductive resin portion B and 90 ° C. in the LSI portion A. Therefore, even under the condition that the ambient temperature is 85 ° C., the LSI unit A can be set to 150 ° C. When the heat spreader is provided with the function of a heat pipe, the heat conduction from the heat spreader portion D to the outside is further increased, and the temperatures in the heat conductive resin portion B and the LSI portion A are further lowered.
On the other hand, in the element structure of a general Si substrate (see FIG. 9A), when the heat generation is 20 watts and the ambient temperature is 25 ° C. The temperature is 75 ° C. at the point corresponding to the heat spreader portion C, 98 ° C. at the point corresponding to the heat conductive resin portion B, and 135 ° C. at the point corresponding to the LSI portion A.
The above temperature difference in the LSI unit A can be said to be an effect of the element structure according to the present embodiment, and by using the element as a copper substrate, the temperature can be lowered by 45 ° C. as compared with the case of the Si substrate. Conversely, it can be used up to a temperature range of 45 ° C. higher. If the operating temperature is the same, it means that a device with high heat generation of 20 watts or more can be used. This also applies to the LSI element 51 provided with the fan-out substrate.

Further, in the element structure of the metal substrate according to the present embodiment, the metal substrate and the Si layer (Si thin film) on which the LSI is formed are bonded at the bonding interface by performing the bonding at a temperature equal to or lower than the upper limit of the temperature at which the device is used. The stress generated can be minimized. That is, the LSI element in which the Si layer is bonded to the metal substrate at room temperature significantly suppresses the influence of stress generated at the bonding interface when the LSI element is used, as compared with the case where the Si layer is bonded to the metal substrate at high temperature. be able to.
For example, assuming that the thickness of the metal substrate made of copper is 300 μm, the thickness of the Si thin film is 10 μm, and the operating temperature of the LSI element is 85 ° C., the effect of normal temperature bonding is calculated. The coefficient of linear expansion is 16.8 × ^10-6 for copper and 2.4 × ^10-6 for Si, and the difference is 14.4.
Conventionally, when copper is used as the substrate of an element, the Si layer and the copper substrate are bonded at a high temperature. Assuming that the Si layer and the copper substrate are bonded at 400 ° C., a temperature difference of 315 ° C. occurs between the temperature at the time of bonding and the temperature at 85 ° C. when the semiconductor element is used. Then, although the Si layer does not warp due to the thick copper substrate, the difference in the coefficient of linear expansion between the time of joining and the time of use is 315 × 14.4 × 10 ^-6 = 4.5 × 10 ^-3 , and this coefficient of linear expansion becomes Interfacial stress between copper and Si is generated due to the difference between the two, and the influence of stress is generated on the Si layer, which is not preferable in terms of element characteristics.
On the other hand, when the Si layer (Si thin film) and the copper substrate are bonded at room temperature (25 ° C.), the temperature difference from the temperature of 85 ° C. when the LSI element is used is only 60 ° C. Then, the thick copper substrate does not warp the Si thin film, and the difference in the coefficient of linear expansion between the time of joining and the time of use is 60 × 14.4 × 10 ^-6 = 0.86 × 10 ^-3 . Therefore, the difference in the coefficient of linear expansion is much smaller than when the temperature at the time of joining is 400 ° C., the stress generated at the interface between copper and Si during use is small, and the effect of the stress generated on the Si thin film side is It will be minor.
In this way, it is possible to construct an LSI element having excellent thermal conductivity by using a copper material which is inexpensive and has extremely high thermal conductivity (401 W / (m · K)) among metals, and is a bonding interface. It is possible to reduce the stress generated in.

The present invention is not limited to the embodiment detailed above, and various modifications or changes can be made within the scope shown in the claims of the present invention. Not only when the resin package is used, but also when the LSI is mounted on the ceramic package, in order to improve the heat conduction from the LSI part to the ceramic package, the base part of the LSI element may be a metal (copper) substrate. effective.

With the progress of semiconductor miniaturization technology, LSIs have become more sophisticated and generate high heat. The multi-layered element structure of the present invention makes it possible to apply it to applications with a higher environmental temperature by effectively conducting heat with high heat generation, and it is also possible to mount a larger heat generating element.

1; LSI, 5; temporary substrate, 8; barrier metal layer, 9; fan-out substrate,
10; Si thin film, 100; Si substrate, 20; metal substrate (copper substrate), 25; second substrate,
50-54; LSI element, 200; printed circuit board.

Claims

The first joining step of joining the main surface side of the Si substrate on which the LSI is formed on the surface layer and the temporary substrate, and
A Si thin film step of forming a Si thin film by removing the back surface side of the Si substrate while leaving a thickness corresponding to the depth of the surface layer portion.
A second joining step of joining the back surface of the Si thin film and the metal surface of the second substrate whose surface layer is at least a metal substrate at a temperature not exceeding the upper limit of the operating temperature of the LSI.
The peeling step for removing the temporary substrate and
A method for manufacturing an LSI element having a heat transfer structure, which comprises.
A fan-out mounting step of mounting a fan-out board in which fan-out wiring is formed on the main surface side of the Si board is included.
The first joining step is the method for manufacturing an LSI element having a heat transfer structure according to claim 1, wherein the Si substrate and the temporary substrate are joined via the fan-out substrate.
After performing the Si thin film forming step, a barrier metal layer forming step of forming a barrier metal layer made of a barrier metal on the back surface of the Si thin film is included.
The method for manufacturing an LSI element having a heat transfer structure according to claim 1 or 2, wherein the second joining step joins the Si thin film and the second substrate via the barrier metal layer.
The method for manufacturing an LSI element having a heat transfer structure according to any one of claims 1 to 3, wherein the thickness of the Si thin film is 100 μm or less.
The method for manufacturing an LSI element having a heat transfer structure according to any one of claims 1 to 4, wherein the metal substrate is a copper substrate.
An LSI is formed on the surface layer portion of the main surface thereof, and a Si thin film having a thickness corresponding to the depth of the surface layer portion is formed.
A second substrate whose surface layer is at least a metal substrate bonded to the back surface of the Si thin film is provided.
A heat transfer structure of an LSI element, characterized in that heat generated by an LSI is transferred to the outside through the metal substrate.
The heat transfer structure of the LSI element according to claim 6, wherein the fan-out wiring is formed and the fan-out substrate is joined to the main surface side of the Si thin film.
The heat transfer structure of the LSI element according to claim 6 or 7, wherein the thickness of the Si thin film is 100 μm or less.
The heat transfer structure of the LSI element according to any one of claims 6 to 8, wherein the metal substrate is a copper substrate.