KR100680997B1 - Method of flip chip bonding and its application for optical module - Google Patents

Abstract

A method for bonding a flip chip and an optical module using the same are provided to obtain string cohesion between a solder and a stud bump by melting a solder layer. A metal layer is formed on a substrate(20) and a semiconductor chip(20'). A solder layer is formed on the metal layer. A stud bump(22) is formed on an upper surface of the solder layer. A coining process for the stud bump is performed. The substrate including the coined stud bump or the stud bump of the semiconductor chip comes in contact with the semiconductor chip on which the stud bump is not formed or the solder layer of the substrate. The substrate and the semiconductor chip are fixed by applying the heat and the pressure thereto.

Description

Flip chip bonding method and optical module using the same {METHOD OF FLIP CHIP BONDING AND ITS APPLICATION FOR OPTICAL MODULE}

1A to 1E are diagrams illustrating a flip chip bonding process using a conventional stud bump.

2A and 2B illustrate an optical module manufactured by a flip chip bonding method according to an exemplary embodiment of the present invention.

3A to 3E are views illustrating a process of manufacturing an optical module by fixing a semiconductor chip to a substrate according to a flip chip bonding method according to an embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flip chip bonding technique for semiconductor packaging and optical module packaging, and more particularly, by forming a solder layer on a semiconductor chip and a substrate, forming a stud bump thereon, and bonding the same by thermocompression bonding. The present invention relates to a flip chip bonding method using a stud bump that can secure a height and have a high bonding strength, and an optical module manufactured using the method.

In general, bonding refers to a technique for bonding a semiconductor chip to a substrate, and such bonding includes die bonding and flip chip bonding. Here, flip chip bonding is a method of forming a solder, a bump, or a stud bump on a connection pad of a chip to face down the operation portion of the chip and joining the substrate. There are various methods of flip chip bonding, such as using solder layers, solder bumps, solder balls, stud bumps, etc., depending on the shape of the solder. In particular, when the number of electrical connections (I / O) is small, stud bumps are compared with other methods. It can be economically advantageous to use. Stud bumps may include gold stud bumps, silver stud bumps, aluminum stud bumps, copper stud bumps, and the like, depending on the material.

In the flip chip bonding method using a conventional gold stud bump, since the melting point of gold is high, bonding is performed by applying heat and pressure while applying ultrasonic waves to obtain bonding strength between the semiconductor chip and the substrate. Therefore, the damage of the semiconductor chip due to the ultrasonic wave and the decrease of the height of the stud bump due to the high temperature and high pressure are large, and in order to obtain the desired bonding height, the bump size is large or the stud bump is formed by bonding both the substrate and the semiconductor chip. have. In such a method, when the semiconductor chip is small or in the case of an electrode having a fine pitch, the distance between the bonding pads is shortened, and thus the distance between adjacent stud bumps is narrowed, so that there is a risk of electrical connection (short). In addition, when the substrate to which the chip is bonded is weak, such as a film or the bonding pad may be a problem that the electrical adhesion is reduced.

In particular, optical devices used in optical communication components are very small in size, and the number of stud bumps is small, and the distance between the stud bumps is very small. When bonding optical devices on optical fibers, it is required to secure an appropriate height to align the optical axes. There is a case.

1A to 1E are diagrams illustrating a flip chip bonding process using a stud bump according to the related art. Hereinafter, a flip chip bonding method using a stud bump according to the related art will be described with reference to FIG. 1.

FIG. 1A shows that a metal multilayer film is formed on a substrate 10 and a semiconductor chip 10 'for use as a bonding pad 11. For example, in order to form the bonding pad 11, a nickel layer 11-1 and a gold layer 11-2 on the upper surface of each of the substrate 10 and the semiconductor chip 10 ′. Can be laminated.

FIG. 1B illustrates that the stud bump 12 is formed on the upper surface of the bonding pad 11 of the substrate 10 and the semiconductor chip 10 ′. The stud bump 12 may be formed using a wire bonder.

FIG. 1C illustrates after the stud bumps 12 formed on the substrate 10 or the semiconductor chip 10 'are coined to an appropriate height. The stud bump coining can be made in a wire bonder using a coining capillary.

FIG. 1D illustrates that the substrate 10 or the semiconductor chip 10 'on which the stud bumps 12 are formed is aligned using a flip chip bonder. In this case, a marker may be used to increase the alignment precision.

In FIG. 1E, the optical semiconductor chip 10 ′ and the substrate 10 are adhered to each other by oscillating ultrasonic waves in a state where the optical semiconductor chip 10 ′ and the substrate 10 are aligned and applying high temperature and high pressure. The height (70 μm) according to the distance between the substrate 10 and the semiconductor chip 10 'bonded by the conventional flip chip bonding method is the height of the stud bumps 12 and 12' shown in FIG. It is much lower than 150μm), so it is difficult to secure an appropriate height. In addition, in the case where the size of the semiconductor chip 10 'is small and in the case of flip chip bonding having a fine pitch, the adjacent stud bumps 12 and 12-1 may be narrowed and the semiconductor chip 10' may be damaged by electrical contact. There is a problem that can be.

An object of the present invention for solving the above problems is to minimize the height reduction of the stud bump during flip chip bonding using the stud bump to secure the desired height of the stud bump of a small diameter, to improve the bonding strength of the stud bump In addition, the present invention provides a flip chip bonding method that can reduce the cost of bonding equipment as well as prevent damage to the semiconductor chip by eliminating the need for ultrasonic oscillation during bonding.

In addition, another object of the present invention is a flip chip bonding method which can secure an appropriate height when aligning an optical axis of an optical fiber and an optical device (LD chip, PD chip, mPD chip, etc.) on a silicon substrate and improve the bonding strength and this method It is to provide an optical module manufactured using.

According to the present invention for achieving the above object, a flip chip bonding method of bonding a semiconductor chip to a substrate using a stud bump, the first step of forming a metal layer on the substrate and the semiconductor chip; Forming a solder layer on an upper surface of the metal layer; Forming a stud bump on an upper surface of a solder layer formed on the substrate or the semiconductor chip; A fourth step of coining the stud bumps formed on the upper surface of the substrate or the semiconductor chip; A fifth step of precisely aligning the stud bumps of the coined stud bump or the semiconductor chip with the solder layer of the semiconductor chip or substrate without the stud bump; And a sixth step of applying the pressure while heating to a predetermined temperature at which the solder layer can be melted in the precisely aligned state to fix the substrate and the semiconductor chip.

In addition, the optical module according to the present invention for achieving the above object is characterized in that formed using the flip chip bonding method according to the present invention.

DETAILED DESCRIPTION A detailed description of preferred embodiments of the present invention will now be described with reference to the accompanying drawings. It should be noted that the same reference numerals and the same elements among the drawings are denoted by the same reference numerals and symbols as much as possible even though they are shown in different drawings. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

2 is a view showing an optical module manufactured by a flip chip bonding method according to an embodiment of the present invention. FIG. 2A is a perspective view of an optical module manufactured by the flip chip bonding method according to the present invention, and FIG. 2B is a longitudinal cross-sectional view of the optical module of FIG. 2A taken along line A-A.

2A and 2B, in the optical module according to the present invention, an optical fiber 24 is arranged on a substrate 20 made of silicon (Si), and a semiconductor chip 20 ′ is formed on the substrate 20. This is formed by flip chip bonding. The substrate 20 is formed with a V groove 23 etched in a V shape, and the optical fiber 24 is arranged on the V groove 23 to input and output an optical signal with the semiconductor chip 20 '. FIG. 2A illustrates a case in which a slanted single mode fiber (SMF) is used as the optical fiber 24, but is not limited thereto. The semiconductor chip 20 'may use various types of optical devices, such as an LD chip, a PD chip, and an mPD chip. 2A illustrates a case where a flip chip bonding photo diode (PD) chip and a vertical cavity surface emitting laser (VCSEL) chip are used as the semiconductor chip 20 ′. In this case, light scattered by the Bragg grating 25 formed in the optical fiber 24 may be provided to the photodiode PD. Reference numeral 27 denotes a position at which an optical signal is input from the optical fiber 24 on the photodiode PD. In addition, the VSCEL chip may be used as a light source for converting an electrical signal into an optical signal.

3A to 3E are process diagrams illustrating a process of manufacturing an optical module by fixing a semiconductor chip to a substrate according to a flip chip bonding method according to an embodiment of the present invention.

First, FIG. 3A illustrates a process of forming the metal layers 21-1 and the solder layers 21-2 and 21-3 on the substrate 20 and the semiconductor chip 20 ′. Referring to FIG. 3A, when the flip chip bonding is performed on the substrate 20 or the semiconductor chip 20 ', titanium (Ti) may be protected to protect the semiconductor chip 20' and increase adhesiveness with the solder. , At least one of metals such as nickel (Ni), platinum (Pt), and tungsten (W) is used to form a single layer or a plurality of metal layers 21-1 formed by combining the single layers. The metal layer 21-1 serves as a lower bump metal layer (UBM) that suppresses chemical reaction between the solder and the substrate 20 or the semiconductor chip 20 ′.

After forming the metal layer 21-1, tin (Sn), indium (In), and germanium (Ge) are first formed to form the solder layers 21-2 and 21-3 on the metal layer 21-1. , The lower solder layer 21-2 is first formed using silicon (Si), and then the upper solder layer 21-3 is formed using gold (Au) to prevent surface oxidation and to function as a solder layer. To form. For example, the thickness of the Sn layer 21-2 may be 1.5 μm and the thickness of the Au layer 21-3 may be 3 μm. In addition, the lower solder layer 21-2 may be formed of an element such as Ge, In, or Si. Accordingly, the solder layers 21-2 and 21-3 may be alloy solders composed of elements such as Sn-Au, Ge-Au, In-Au, and Si-Au.

The metal layer 21-1 and the solder layers 21-2 and 21-3 may be formed using any one of a sputtering method, a deposition method, an electrodeposition method, a plating method, and a stencil print method. In particular, the metal layer 21-1 is preferably formed using an electron beam (e-beam) or a sputter.

3B illustrates that the stud bumps 22 are formed on the upper surface of the substrate 20 or the semiconductor chip 20 'on which the metal layer and the solder layer are formed. The stud bump 22 may be made of gold, aluminum, copper, silver, or the like, and may be formed using a wire bonder. And the size of the stud bump 22 can be changed by adjusting the power, the application time, the load of the ultrasonic wave.

FIG. 3C illustrates a process of coining the formed stud bumps 22 to a suitable height using a coining capillary in a wire bonder. By the coining process it is possible to adjust the height of the stud bump 22 and the bonding area with the solder.

FIG. 3D illustrates a state in which the coin 20 is precisely aligned and flip chip bonded using the flip chip bonder to the substrate 20 or the semiconductor chip 20 ′ on which the stud bumps 22 are completed.

In the present invention, the stud bump 22 is formed on only one of the substrate 20 and the semiconductor chip 20 ', and a coining process is performed. The stud bump 22 of the substrate 20 or the semiconductor chip 20 'on which the coined stud bumps 22 are formed, and the semiconductor chip 20' or the substrate 20 on which the stud bumps 22 are not formed. ) And the solder layers 21-2 and 21-3 are precisely aligned to contact each other. In this case, a marker may be used for precise alignment.

Subsequently, the substrate 20 and the semiconductor chip 20 ′ where the precision alignment is completed are suitable temperatures at which the solder layers 21-2 and 21-3 are melted to serve as solders. After heating to a temperature of 280 ° C. or higher (280 to 350 ° C.), which is the melting point of the Sn 20 solder, flip chip bonding is performed by applying a suitable pressure, for example, 0.5 to 2 N. The heating temperature may vary depending on the type of solder and the working conditions. In addition, the applied pressure may vary depending on the size of the semiconductor chip 20 'or the number, size, and material of the stud bumps 22.

As described above, the flip chip bonder used in the flip chip bonding, unlike the prior art, does not require an ultrasonic wave oscillator, so the equipment price can be low, and also the ultrasonic wave is not used during the flip chip bonding operation. The risk of damaging the chip 20 'and the substrate 20 is reduced.

In the present invention, the 'V' shaped V-groove 23 is formed on the substrate 20 so that the optical fiber 24 can be aligned. The V-groove 23 is prepared in advance before the bonding pads 21 formed of the metal layers 21-1 and the solder layers 21-2 and 21-3, or the bonding pads 21 are formed. It may also be produced later. In addition, the optical fiber 24 is placed in the V-groove 23, and is precisely aligned to input and output optical signals with the semiconductor chip 27. The optical fiber 24 may be aligned with the V groove 23 before or after the substrate 20 and the semiconductor chip 20 'are flip chip bonded.

3E shows the state after the flip chip bonding is completed by lowering the temperature of the stud bump 22 to room temperature after the solder between the substrate 20 and the semiconductor chip 20 'is melted and bonded. As can be seen in FIG. 3e, it is possible to secure a large height (for example, 70 μm) by using only one stud bump 22, and a high bond strength by combining the stud bump 22 and the stud bump 22 by solder. You can get it.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the claims below, but also by those equivalent to the claims.

According to the present invention as described above, since the solder layer is formed on the substrate and the semiconductor chip and then the stud bumps are formed on the upper surface thereof, when the flip chip bonding is heated to a suitable temperature to dissolve the solder layer to bond the solder and stud bumps strong Will be able to. In addition, since the chip can be flipped without using ultrasonic waves, the equipment is inexpensive and the bonding pressure can be significantly lowered. Therefore, after the bonding process, the stud bump obtained by flip chip bonding using the normal stud bump has a height higher than that of the stud bump. There is an advantage to secure the stud bump height.

In addition, according to the present invention, by applying the flip chip bonding method as described above, by bonding a semiconductor chip such as LD chip, PD chip, mPD chip on the optical fiber fixed in the V-groove of the silicon substrate, a highly integrated optical module can be manufactured. .

Claims (6)

In the flip chip bonding method of bonding a semiconductor chip to a substrate using a stud bump, Forming a metal layer on the substrate and the semiconductor chip; Forming a solder layer on an upper surface of the metal layer; Forming a stud bump on an upper surface of a solder layer formed on the substrate or the semiconductor chip; A fourth step of coining the stud bumps formed on the upper surface of the substrate or the semiconductor chip; A fifth step of precisely aligning the stud bumps of the coined stud bump or the semiconductor chip with the solder layer of the semiconductor chip or substrate without the stud bump; And And a sixth step of fixing the substrate and the semiconductor chip by applying pressure while heating to the predetermined temperature at which the solder layer can be melted in the precisely aligned state. The method of claim 1, wherein in the first step, the metal layer is a single layer using at least one of titanium (Ti), nickel (Ni), platinum (Pt) or tungsten (W) on the upper surface of the substrate or the semiconductor chip. Or a flip chip bonding method characterized in that formed of a composite layer. The method of claim 1, wherein the second step is Forming a lower solder layer on the metal layer using at least one of tin (Sn), indium (In), germanium (Ge), or silicon (Si); And Forming an upper solder layer on the upper surface of the lower solder layer by using gold (Au) to provide surface oxidation prevention and solder layer functions. The flip chip bonding method of claim 1, wherein the stud bump is formed using at least one of gold, aluminum, copper, and silver. The flip chip bonding method of claim 1, wherein a V groove etched in a V shape is formed on the substrate, and an optical fiber is arranged on the V groove to input or output the semiconductor chip and an optical signal. An optical module manufactured according to any one of claims 1 to 5.

Images