JP2006332374A - Semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an economical semiconductor device having a large heat dissipation amount. <P>SOLUTION: This semiconductor device 1 comprises a silicon substrate 2 not packaged, and can be subjected to so-called flip-chip bonding. The silicon substrate 2 has a flat and nearly rectangular parallelepiped shape. The region to a fixed depth from the surface 2a of the silicon substrate 2 is a functional device forming region 3 wherein a functional device is formed. A plurality of bumps 4 connected to the functional device are formed at the predetermined positions on the surface 2a. Many linearly extending nearly parallel and nearly evenly spaced grooves 5 are formed in the underside 2b of the silicon substrate 2. A metal thin film is formed on the underside 2b of the silicon substrate 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor device that mainly dissipates heat from the back surface of a semiconductor chip, and particularly to a flip-chip connected semiconductor device.

  As a semiconductor device mounting technique, there is a so-called flip chip connection in which a semiconductor chip is directly bonded to a wiring board without being packaged. Such a semiconductor chip that generates a large amount of heat is used with a heat sink made of a metal such as aluminum. In this case, the heat generated in the semiconductor chip is well dissipated through the heat sink.

However, if a heat sink is attached, the cost of the semiconductor device increases.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an inexpensive semiconductor device that has a large heat dissipation amount.

  In the invention according to claim 1 for solving the above-mentioned problem, a functional element forming region (3) having a constant thickness is formed on one surface (2a), and this one surface is formed. A semiconductor substrate (2) having a recess (5, 15) formed on the other surface (2b) different from the depth of the other surface (2b) shallower than the depth at which the functional element formation region is formed. A semiconductor device (1, 11) is provided.

Numbers in parentheses indicate corresponding components in the embodiments described later. The same applies hereinafter.
In the semiconductor device according to the present invention, an external connection electrode (for example, a bump-like electrode) electrically connected to a functional element formed in the functional element formation region is formed on one surface of the semiconductor substrate. can do. In this case, the semiconductor device can be mounted on the wiring board by facing one surface of the semiconductor substrate to the wiring board and bonding an electrode for external connection to an electrode pad or the like formed on the wiring board. In this case, the other surface of the semiconductor substrate, that is, the surface on which the recess is formed is directed to the side opposite to the wiring substrate side.

Since the recess is formed, the area of the other surface of the semiconductor substrate is larger than that in the case where the other surface is a flat surface. The other surface is well dissipated. Therefore, this semiconductor device is inexpensive because it can be used without attaching a heat sink.
In particular, when the semiconductor substrate is made of a semiconductor material having high thermal conductivity such as silicon (Si), silicon carbide (SiC), gallium nitride (GaN), etc., heat can be radiated from the other surface of the semiconductor substrate.

The recess can be formed by, for example, dry etching (for example, reactive ion etching) or wet etching using an etching solution.
A groove (5) as the recess may be formed on the other surface of the semiconductor substrate as described in claim 2. In this case, a plurality of the grooves may be formed on the other surface of the semiconductor substrate. The width of the groove is preferably 1 μm to 100 μm. The depth of the groove is preferably 1 μm to 100 μm. Further, when a plurality of the grooves are formed, the interval between two adjacent grooves is preferably 1 μm to 200 μm.

Thereby, the area of the other surface of the semiconductor substrate can be remarkably increased as compared with the case where the other surface is flattened, and the amount of heat released from the other surface can be increased.
The interval between two adjacent grooves is preferably 2 μm to 200 μm. Thereby, in the semiconductor substrate, the strength of the portion between the two adjacent grooves (hereinafter referred to as “rib”) can be increased, and the rib can be hardly broken.

  Further, a hole (15) as the recess may be formed on the other surface of the semiconductor substrate as described in claim 3. In this case, a plurality of the holes may be formed on the other surface of the semiconductor substrate. The width of the hole (for example, the length along one direction in the plane of the semiconductor substrate) is preferably 1 μm to 100 μm. The depth of the hole is preferably 1 μm to 100 μm. Furthermore, when a plurality of the holes are formed, the interval between two adjacent holes is preferably 1 μm to 100 μm.

Also in this case, the area of the other surface of the semiconductor substrate can be remarkably increased as compared with the case where the other surface is flattened, and the amount of heat released from the other surface can be increased.
The area of the other surface of the semiconductor substrate is preferably at least twice the area of the other surface when the semiconductor substrate is viewed vertically. That is, the area of the other surface is preferably set to be twice or more compared to the case where the other surface is made flat by forming the recess.

The invention according to claim 4 is characterized in that a thin film (7) having a higher thermal conductivity than the semiconductor substrate is formed on the other surface of the semiconductor substrate. Device.
According to the present invention, the heat generated in the semiconductor substrate can be favorably dissipated through the thin film having a higher thermal conductivity than the semiconductor substrate, so that the heat radiation from the other surface of the semiconductor substrate can be further increased.

The thin film may be made of metal (for example, silver (Ag), copper (Cu), or gold (Au)), diamond, ceramic having high thermal conductivity (for example, aluminum nitride (AlN)), or the like. it can. Thereby, the thermal conductivity of the thin film can be made higher than the thermal conductivity of the semiconductor substrate.
The thin film is preferably formed along the inner wall surface of the recess inside the recess. In this case, since the area of the other surface of the semiconductor substrate (the surface area of the thin film) can be kept large, the heat radiation from the other surface can be increased.

  Such a thin film can be formed by vapor deposition or sputtering.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic perspective view showing the structure of a semiconductor device according to the first embodiment of the present invention. The semiconductor device 1 has a substantially plate-like shape. FIG. 1 (a) is a view facing one surface, and FIG. 1 (b) is a view facing the other surface.
The semiconductor device 1 includes a silicon (Si) substrate 2 that is not packaged, and so-called flip chip connection is possible. The silicon substrate 2 has a flat and substantially rectangular parallelepiped shape.

  A region extending from one surface (hereinafter referred to as “surface”) 2a to a depth of 1 μm to 100 μm (for example, about 10 μm) of the silicon substrate 2 is a functional element formation region 3 in which functional elements are formed. A plurality of bumps (metal electrodes) 4 that are electrically connected to the functional elements are formed at predetermined positions on the functional element forming region 3 as external connection electrodes (see FIG. 1A).

On the other surface (surface opposite to the front surface 2a; hereinafter referred to as “back surface”) 2b of the silicon substrate 2, a plurality of linearly extending grooves 5 are formed substantially in parallel with each other at substantially the same interval. (See FIG. 1 (b)). The groove 5 is formed in a direction parallel to the short side of the silicon substrate 2 in a plan view of the silicon substrate 2 looking down in the thickness direction. A rib 6 protruding from the bottom surface of the groove 5 is formed between two adjacent grooves 5. The width W _{11 of the} groove 5 is 1 μm to 100 μm, the depth D ₁ of the groove 5 is 1 μm to 100 μm, and the interval W ₁₂ between two adjacent grooves 5, that is, the width W _{2 of the} rib 6 is 1 μm to 200 μm. It is.

The thickness of the silicon substrate 2 is, for example, about 400 μm, and the groove 5 has a depth that does not reach the functional element formation region 3. That is, the groove 5 has a depth shallower than the depth in which the functional element formation region 3 is formed. The thickness of the silicon substrate 2 excluding the functional element formation region 3 is, for example, about 100 μm to 400 μm.
With such a structure, the area of the back surface 2b of the silicon substrate 2 is significantly larger than that when the back surface 2b is a flat surface. The width W ₁₂ of the rib 6 is preferably 2 μm to 200 μm, whereby the strength of the rib 6 can be increased and the rib 6 can be hardly broken.

The groove 5 can be formed by dry etching (for example, reactive ion etching; RIE) or wet etching using an etchant on the back surface 2b of the silicon substrate 2 having a flat surface. By reactive ion etching, for example, even when the width W _{11 of the} groove 5 is reduced to about 2 μm, the depth D ₁ of the groove 5 can be increased to about 60 μm.
FIG. 2 is an illustrative sectional view showing the vicinity of the back surface 2b of the silicon substrate 2 in an enlarged manner.

A metal thin film 7 is formed on the back surface 2 b of the silicon substrate 2. The metal thin film 7 is made of, for example, silver (Ag), copper (Cu), or gold (Au). Since the thermal conductivity of silver, copper and gold is higher than that of silicon, the thermal conductivity of the metal thin film 7 is higher than that of the silicon substrate 2.
The metal thin film 7 is formed so as to completely cover the back surface 2 b of the silicon substrate 2 including the inside and the outside of the groove 5. In the groove 5, the metal thin film 7 is formed along the inner wall surface of the groove 5. Thereby, the area of the back surface 2b of the silicon substrate 2 is kept large.

The metal thin film 7 can be formed by, for example, vapor deposition or sputtering.
This semiconductor device 1 can be flip-chip connected by bonding bumps 4 to electrode pads formed on a wiring board by soldering or the like. As a result, the functional element formed in the functional element formation region 3 can be electrically connected to the outside via the bumps 4.
In a state where the silicon substrate 2 is flip-chip connected to the wiring substrate, the back surface 2b of the silicon substrate 2 is directed to the side opposite to the wiring substrate side. Since the back surface 2b has a large area, the heat generated in the silicon substrate 2 is dissipated well from the other surface of the silicon substrate 2. After the semiconductor device 1 is mounted on the wiring substrate, heat can be dissipated directly into the atmosphere from the back surface 2b of the silicon substrate 2 when resin sealing is not performed.

Further, the amount of heat released from the back surface 2b of the silicon substrate 2 is also increased by forming the metal thin film 7 having a higher thermal conductivity than that of the silicon substrate 2 on the back surface 2b of the silicon substrate 2.
From the above, this semiconductor device 1 is inexpensive because it can be used without attaching a heat sink. That is, the semiconductor device 1 has a large heat radiation amount and is inexpensive. Further, the semiconductor device 1 can be reduced in size because it is not necessary to attach a heat sink.

FIG. 3 is a schematic perspective view of a semiconductor device according to the second embodiment of the present invention. Components and the like corresponding to those of the semiconductor device 1 shown in FIG.
The semiconductor device 11 includes a silicon substrate 2 that is not packaged, and so-called flip chip connection is possible. The silicon substrate 2 has a flat and substantially rectangular parallelepiped shape.

  A large number of holes 15 are formed in the back surface 2 b of the silicon substrate 2. The holes 15 are arranged along the long side and the short side of the silicon substrate 2 in a plan view looking down the silicon substrate 2 in the thickness direction. Further, in a plan view when the silicon substrate 2 is looked down in the thickness direction, each hole 15 has a substantially square shape, and the side of the hole 15 is substantially the long side or the short side of the silicon substrate 2. It is parallel.

The width W _{21 of the} hole 15 (the length along the long side direction of the silicon substrate 2) is 1 μm to 100 μm, the depth D ₂ of the hole 15 is 1 μm to 100 μm, and the interval W ₂₂ between two adjacent holes 15. Is 1 μm to 100 μm. The hole 15 has a depth that does not reach the functional element formation region 3. That is, the hole 15 has a depth shallower than the depth in which the functional element formation region 3 is formed.

  With such a structure, the area of the back surface 2b of the silicon substrate 2 is significantly larger than when the back surface 2b is a flat surface, and the heat generated in the silicon substrate 2 can be improved from the back surface 2b. Can be dissipated. Therefore, since this semiconductor device 11 can be used without attaching a heat sink, it is inexpensive and can be miniaturized.

The hole 15 can be formed by dry etching (for example, reactive ion etching) or wet etching using an etchant on the back surface 2b of the silicon substrate 2 having a flat surface. By such a method, the hole 15 having the above size can be formed.
A metal thin film 7 (see FIG. 2) similar to that of the semiconductor device 1 may be formed on the back surface 2b of the silicon substrate 2. Thereby, the heat dissipation from the back surface 2b of the silicon substrate 2 can be further increased.

  Although the embodiments of the present invention have been described above, the present invention can be implemented in other forms. For example, instead of the silicon substrate 2, a semiconductor substrate made of silicon carbide (SiC) or gallium nitride (GaN) may be used. Since silicon carbide and gallium nitride have high thermal conductivity, by forming grooves 5 and holes 15 similar to those of the semiconductor devices 1 and 11 on the back surface of the semiconductor substrate made of such a material, efficiency can be improved from the back surface of the semiconductor substrate. Heat can be released.

Further, a thin film made of a material other than metal and having a higher thermal conductivity than the silicon substrate 2 (semiconductor substrate) may be formed on the back surface 2b of the silicon substrate 2 (semiconductor substrate). Such a thin film can be made of, for example, diamond or ceramic having high thermal conductivity (for example, aluminum nitride (AlN)).
Both the groove 5 and the hole 15 may be formed on the back surface 2 b of the silicon substrate 2. Moreover, it is not necessary that all the grooves 5 and holes 15 have the same width W _11, W ₂₁ and same depth D _1, D _2, the width W ₁₁ for each groove 5 or hole 15, W ₂₁ and deep D ₁ and D ₂ may be different. Similarly, the intervals W ₁₂ and W ₂₂ between two adjacent grooves 5 and holes 15 may be different.

Instead of the linearly extending groove 5, a groove extending in a bent or curved manner may be formed. In a plan view of the semiconductor substrate 2 looking down vertically, the shape of the hole 15 is not limited to a square, and may be a rectangle, a triangle, a circle, an ellipse, or the like.
In addition, various modifications can be made within the scope of the matters described in the claims.

1 is an illustrative perspective view of a semiconductor device according to a first embodiment of the present invention. It is an illustration sectional view expanding and showing the neighborhood of a rib. FIG. 4 is a schematic perspective view of a semiconductor device according to a second embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,11 Semiconductor device 2 Silicon substrate 2a Front surface 2b Back surface 3 Functional element formation area 5 Groove 7 Metal thin film 15 Hole

Claims (4)

  On one surface, a functional element is formed and a functional element forming region having a certain thickness is formed. On the other surface different from the one surface, the depth from the other surface side is the functional element forming region. A semiconductor device comprising a semiconductor substrate in which a recess shallower than a formed depth is formed.   2. The semiconductor device according to claim 1, wherein a groove as the recess is formed on the other surface of the semiconductor substrate.   2. The semiconductor device according to claim 1, wherein a hole as the recess is formed in the other surface of the semiconductor substrate.   4. The semiconductor device according to claim 1, wherein a thin film having a higher thermal conductivity than the semiconductor substrate is formed on the other surface of the semiconductor substrate.

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