JP2541508B2 - Bump bonding method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bump bonding method, and more particularly to a bump bonding process performed in a heated state.

[0002]

2. Description of the Related Art There is a bump bonding method as a bonding method of elements for electrically and mechanically bonding two chips or substrates such as LSI mounting and a hybrid type two-dimensional array image sensor. This method is a method in which bumps are provided in advance on two chips or a substrate, the bumps on both sides are brought into contact with each other in a state of being heated to the extent that metal atoms forming the bumps are activated, and further pressure is applied to join them. At this time, as a method for aligning the two chips, a method of inserting an optical probe between the sample tables and observing with visible light is widely used because of its versatility and obtaining a clear monitor image. Here, as an example of bump bonding, a method of bonding two chips using this optical probe will be described with reference to FIG.

FIG. 2 (a) is a diagram showing an alignment process. This step is performed at room temperature for the reason described below. The chips 3 and 4 are vacuum-sucked to the sample tables 1 and 2 so that the bumps provided on the surfaces face each other. Insert the optical probe 5 between the chips 3 and 4 and move the sample tables 1 and 2 while monitoring the alignment marks provided on the chips 3 and 4 so that the bump positions on the chips 3 and 4 match each other. Adjust to

There are two reasons for carrying out the aligning step at room temperature even though the bumps are brought into contact with each other in a heated state in the pressure-bonding step to be described later. First, when the alignment is performed in a heated state, the optical probe located extremely close to the chip causes thermal expansion due to the heat radiated from the chip and the sample table, which causes an optical deviation. Such an optical deviation in the heated state is generally a problem in the optical alignment method. Secondly, in many cases, the metal forming the bumps forms an oxide film on the bump surface as the temperature rises and reduces the bonding strength of the bump bonding, so it is possible to increase the temperature of the bumps to prevent oxide film formation. This is because it needs to be as short as possible. These problems are solved by performing alignment at room temperature.

FIG. 2B is a diagram showing the temperature raising step. The inserted optical probe 5 is pulled out, and the sample tables 1 and 2 and the chips 3 and 4 are heated to a predetermined temperature while leaving a gap between the chips 3 and 4.

FIG. 2C is a diagram showing a pressure bonding step. While maintaining the temperature, the sample tables 1 and 2 are vertically moved to bring the bumps on the chips 3 and 4 into contact with each other and apply a predetermined pressure. After applying pressure for a predetermined time, the vacuum suction of the sample table 1 is released, the sample tables 1 and 2 are separated,
The sample tables 1 and 2 and the joined chips 3 and 4 are cooled, and the chips 3 and 4 are removed.

Instead of such a pressure-bonding step, another pressure-bonding step in which bumps are brought into contact with each other at room temperature and the temperature is raised while applying pressure is also used.

[0008]

As described above, in the conventional joining method, the aligning step is performed at room temperature, and the crimping step is performed by raising the temperature of the chip and the sample table. At this time, the upper and lower sample tables are thermally expanded separately as the temperature rises, which causes a problem that the bumps are bonded in a state in which the positions of the two chips aligned at room temperature are displaced from each other. When the method of inserting the optical probe between the two chips and performing the alignment is used, this deviation is ± 5 μm or more. As an example, using this method, a chip in which photodiodes of 1 cm square are formed in a 256 × 256 array and a signal reading electrode are formed in a 256 × 256 array are formed.
Consider a case where an IC chip is formed with In bumps each having a diameter of 16 μm on the photodiode and the signal readout electrode and bonded. At this time, a deviation of ± 5 μm or more corresponds to a 40% or more reduction in the contact area between the bumps, which causes a significant decrease in the bonding strength. Further, the bump on the opposite side directly applies pressure to the photodiode, which causes deterioration of diode characteristics.

Further, in the method described in the last paragraph, in which the two chips are brought into contact with each other at room temperature and the temperature is raised while applying pressure, the bump contact is already completed when the sample table is thermally expanded, and misalignment is avoided. Although it is possible, the two chips are displaced with respect to each other while the bumps are still in contact with each other, so that the bumps are tilted.

As described above, in the conventional bonding method, the bumps are misaligned or tilted due to the thermal expansion of the sample table, and the mechanical bonding strength of the bump bonding between the two chips becomes unsatisfactory after the bonding process is completed. There was a problem of being sufficient.

An object of the present invention is to provide a bump bonding method which does not cause misalignment or inclination of bumps due to thermal expansion of a sample table in a bump bonding process performed in a heated state.

[0012]

The bump bonding method of the present invention comprises the steps of adsorbing two chips for bump bonding on two upper and lower sample tables, respectively, and aligning the two chips at room temperature, A first crimping step of moving a sample table and applying a low pressure at room temperature, releasing the adsorption of the upper sample table of the sample table, separating the upper chip and the upper sample table while the chips are joined, It is characterized by including a step of raising the temperature of the chip and the sample table to a predetermined value, and a second pressure bonding step of moving the sample table again while maintaining the temperature and applying a high pressure to the chip. , A bump bonding method.

[0013]

According to the joining method of the present invention, after the alignment is performed at room temperature, the joining is performed in two steps, that is, the first crimping step at room temperature and the second crimping step in the heated state, and the temperature is raised during the joining. The process is performed with the tip separated from the sample table on one side. Therefore, it is possible to realize bump bonding with sufficient strength because the alignment accuracy is maintained at the room temperature level and the bonding is performed in a heated state without being affected by the thermal expansion of the sample table.

[0014]

Embodiments of the present invention will be described in detail with reference to FIG. Here, a case will be described in which a 256 × 256 array of In bumps with a diameter of 16 μm provided on two 1 cm square substrates is bonded using a method of inserting an optical probe between two chips and performing alignment.

FIG. 1A is a diagram showing a step of aligning two chips. This step is performed at room temperature. Chips 3, 4
Are vacuum-sucked to the sample tables 1 and 2 so that the In bump arrays provided on the surfaces face each other.
Insert the optical probe 5 between the chips 3 and 4,
The sample tables 1 and 2 are moved while monitoring the alignment marks provided on the chip 4, and the positions of the In bump arrays on the chips 3 and 4 are adjusted so as to match each other.

FIG. 1B is a diagram showing the first pressure bonding step. This step is performed at room temperature. Optical probe 5 inserted
Is pulled out, the sample tables 1 and 2 are moved in the vertical direction to bring the In bump arrays on the chips 3 and 4 into contact with each other, and 1 ×
A small pressure of 10 ⁶ N / m ² is applied for 10 seconds. At this time, the two chips are bonded to each other to such an extent that they will not be displaced from each other due to the vibration even if the sample tables 1 and 2 are moved in the temperature raising step described below.

FIG. 1C is a diagram showing a temperature raising step. The vacuum suction of the sample table 1 is released and the sample tables 1 and 2 are released.
Is moved in the vertical direction to separate the chip 3 from the sample table 1. After purging oxygen in the space around the sample tables 1 and 2 and the chips 3 and 4 with an inert gas such as nitrogen, the sample tables 1 and 2 are heated to 80 to 100 ° C. At this time, the chips 3 and 4 reach the same temperature as the sample table 2 due to heat conduction.

FIG. 1D is a diagram showing the second pressure bonding step. While maintaining the temperatures of the sample tables 1 and 2 and the chips 3 and 4, the sample tables 1 and 2 are moved in the vertical direction, and 1 × 1
A pressure of 0 ⁷ N / m ² is applied for 5 minutes. At this time, the vacuum suction of the sample table 1 is still released. After the bonding is completed, the sample tables 1 and 2 are moved in the vertical direction to lower the temperatures of the sample tables 1 and 2 and the chips 3 and 4 of the substrate, the vacuum suction of the sample table 2 is released, and the bonded chips 3 and 4 are released.
Remove.

In the joining method according to the present invention, since the alignment and the application of pressure through the sample table are not affected by the thermal expansion of the sample table, the deviation between the bumps is within the range of mechanical error. It is reproducible within 2 μm and the bump does not tilt when pressure is applied.

Although the bonding of the In bump array has been described in detail in the present invention, similar effects can be obtained even when bonding with other bumps by appropriately setting the bonding temperature, bonding pressure and bonding time. Needless to say.

[0021]

As described in detail above, when the bump bonding method of the present invention is used, misalignment or bump inclination due to thermal expansion of the sample table can be avoided.
High alignment accuracy can be realized, and the yield of the bonding process and the reliability of bump bonding can be greatly improved.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a bump bonding method according to the present invention.

FIG. 2 is a schematic diagram showing a conventional bump bonding method.

[Explanation of symbols]

 1 sample table 2 sample table 3 tip 4 tip 5 optical probe

Claims (1)

(57) [Claims] 1. A step of adsorbing two chips for bump bonding to upper and lower two sample tables and aligning the two chips at room temperature, and moving the sample table to apply a low pressure at room temperature. The first press-bonding step, the adsorption of the upper sample table of the sample table is released, the upper chip and the upper sample table are separated while the chips are bonded, and the temperature of the chip and the sample table is set to a predetermined value. And a second pressure bonding step of moving the sample table again while applying temperature and applying a high pressure to the chip while maintaining the temperature.