JP2009043940A - Semiconductor manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor manufacturing method such that no outgas sticks on a package surface. <P>SOLUTION: The semiconductor manufacturing method includes a process (201) of holding the inside of a furnace at ordinary pressure using dry nitrogen, a process (203) of producing a vacuum in the furnace, a process (205) of curing an adhesive between a semiconductor and a package by raising the temperature in the furnace to 150°C and fixing the semiconductor to the package, a process (207) of lowering the temperature in the furnace down to 70°C, and a process (208) of holding the inside of the furnace at the ordinary pressure using dry nitrogen. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The technical field to which the present invention belongs is a technical field related to a manufacturing process of semiconductor manufacturing in which an element is fixed in a package using an organic adhesive.

  In the case of manufacturing a semiconductor element, the element is generally fixed, wired and sealed in the package. An adhesive is used to fix the element to the package, but a conductive adhesive such as silver paste is often used for the adhesive when the back surface of the element is conductive. On the other hand, when the back surface of the element is insulative, the element is often fixed using an organic adhesive. Many of the organic adhesives are thermosetting and harden by heating the adhesive to cure the element.

  In many cases, organic adhesives maintain viscosity by using an organic solvent as the solvent, and organic solvents are often outgassed in the process of curing the adhesive. The organic solvents contained in the adhesive vary widely, from those having high volatility, that is, those having a low molecular structure to those having low volatility, that is, those having a high molecular structure. Highly volatile organic solvents tend to diffuse after being released, so they are less likely to adhere to the package or element, but polymer organic solvents have low diffusivity and stay on the surface of the package or element. Happens. When the temperature is raised in this state and the curing process is performed, a phenomenon occurs in which the outgas itself attached to the surface is solidified and an organic thin film is formed on the attached surface.

  Since the organic adhesive has a low curing temperature, it can be cured even with a simple thermostatic layer. A continuous furnace is generally used for curing the adhesive. This is advantageous from a flow work point of view. The continuous furnace is structured to always flow an inert gas and a reducing gas, so it is excellent to keep the inside of the furnace always in the same state.

As the adhesive, an insulating semiconductor resin paste containing a thermosetting resin composition and organic resin particles is used, and this paste is cured by applying a temperature (see Patent Document 1).
JP 2003-347322 A

  When the adhesive is cured, if the outgas is low molecular and highly volatile, there is no problem with contamination of the package surface due to outgas, but if the outgas is polymer and stays on the package surface, the outgas will adhere to the package surface. It is necessary not to do it.

  The problem to be finally solved by the present invention is to increase the yield of wire bonds and improve the final product yield, but firstly, it is a problem to prevent the outgas from adhering to the package surface. Become.

  The semiconductor manufacturing method of the present invention includes a step of bringing the inside of a furnace to normal pressure using dry nitrogen, a step of putting the furnace in a vacuum state, and bonding between a semiconductor and a package with the inside temperature of the furnace kept constant. Curing the agent to fix the semiconductor to the package, lowering the furnace internal temperature until the furnace internal temperature is lower than the constant temperature, and using the dry nitrogen And bringing the inside of the furnace to the normal pressure.

After the adhesive is cured, the semiconductor surface is positively cleaned by plasma cleaning.
The plasma cleaning may have a ratio of argon to oxygen of 4: 1. The furnace may be a vacuum-compatible batch furnace. The package may be made of alumina ceramic having four layers of wiring.

  Although the effect expected by the present invention is ultimately an improvement in assembly yield, it prevents the decrease in wire bond yield due to the influence of the insulating thin film formed on the wiring on the package generated as a result of outgas adsorption. It is. It has the effect of increasing wire adhesion strength and reducing defects in electrical property inspection.

  The fact that the outgas from the adhesive does not adhere to the package has two meanings. First, the generated outgas is pulled away from the package surface. The other is to peel out the outgas that has already adhered to the surface of the package from the surface of the package. To do this, lower the pressure at which the package is placed. When the atmospheric pressure is lowered, the momentum of the gas increases, and even if outgas molecules collide with the package surface, they are not adsorbed from the height of the momentum and are separated from the package surface. Similarly, reducing the atmospheric pressure means evacuation, and the outgas is drawn out of the curing furnace by the vacuum pump, so it does not remain in the furnace.

  The process of curing the adhesive curing is generally called a curing process, but there are batch furnaces or continuous furnaces for the curing furnace used in the curing process, but in the continuous furnace, the inlet and outlet of the furnace are always open. Therefore, it is impossible to raise the degree of vacuum even if the inside of the furnace is evacuated. Therefore, in the present invention, a batch furnace that can be evacuated is used.

  In order to carry out the present invention, a semiconductor post-process from the die attach process to the electrical property inspection is required. However, since the equipment related to the present invention is limited to the curing furnace, the best mode will be described focusing on the curing furnace. .

  The curing furnace used in the present invention was a batch furnace. FIG. 1 is a schematic view of a batch furnace used in the present invention. The batch furnace 10 is a vacuum-compatible batch furnace having a maximum temperature increased to 200 degrees Celsius and using a diffusion pump 20. The degree of vacuum used reached 0.1 Torr. After evacuation, dry nitrogen 30 was used as the gas used to return to normal pressure. Dry nitrogen 30 is stored at room temperature and supplied by a method of filtering using a dry filter before use. The dry nitrogen 30 is supplied into the batch furnace 10 when the leak valve 40 is opened, and a vacuum can be drawn by closing the leak valve 40 and operating the diffusion pump 20.

  The object to be subjected to the curing process was one in which six parts were mounted on an individual package using an organic adhesive. The individual package was made of alumina ceramic having four layers of wiring. This package was put in a carrier tape of 40 pieces made of metal, and 10 lots of this carrier tape were put in a stocker to make one lot.

  The adhesive used in the present invention had a specification that the recommended curing temperature was 150 degrees Celsius and the time required for curing was about 10 minutes according to the conditions specified by the manufacturer. However, when this adhesive is actually used, a sufficient cured state cannot be obtained under the conditions specified by the manufacturer. In the examples of the present invention, the curing temperature was 150 degrees Celsius and the curing time was 1 hour.

  As a mounting process, after the adhesive is cured, plasma cleaning is performed to clean the surface, and then wiring is performed using a wire bonder. Plasma cleaning is performed on a line for 90 seconds with an argon to oxygen ratio of 4: 1. For the wiring, an annealed aluminum wire was used, and a wire bonder of a type in which ultrasonic vibration was applied to the element was used.

  In this embodiment, the process from the result of performing the adhesive curing process without any ventilation to the final condition will be described.

  First, the product for one lot shown in the best mode for carrying out the invention is placed in the curing furnace 10 shown in FIG. The curing conditions were a curing temperature of 150 degrees Celsius and a curing time of 1 hour. During the curing process, the curing process was continued without exhausting. After the curing process was completed, plasma cleaning was performed under the above conditions. Furthermore, after wiring with a wire bond, the adhesion state of the wire was inspected using a 20 × microscope. In order to play even those with a somewhat weak adhesion strength, an inspection was performed while blowing dry nitrogen 30 onto the wire. In the inspection, a product with all wires attached was regarded as a non-defective product, and a product with even one wire floating was regarded as a defective product.

  2 and 3 are diagrams showing the peeling rate of the wire, that is, the defective product rate while changing the adhesive curing method. The first to fourth times are defective rates related to wire adhesion when the adhesive curing process is continuously performed without exhausting the air in the batch furnace. The defect rate increases from 17.5% for the first time to 50% for the fourth time. In a vacuum furnace, the air in the batch furnace cannot be replaced unless it is evacuated with a vacuum pump, so it is assumed that the outgas emitted from the adhesive changed at high temperatures to form an organic thin film on the device pattern. ing. It is not clear what kind of film was deposited because elemental analysis was not performed. Although the initial failure rate is 17.5%, the failure rate is too high to be adopted as a mass production method. However, the failure rate increases with each iteration and reaches 50% in the fourth round. It was. This is presumed that after the adhesive outgas was adsorbed on the wall or the like inside the batch furnace, it was reattached on the element when the adhesive was newly cured.

  In order to improve the wire yield, the outgas adsorbed in the batch furnace 10 may be removed before the work of curing the adhesive. First, the workpiece is put in the batch furnace 10 and then the vacuum is drawn to obtain the maximum degree of vacuum. 10 minutes after reaching the temperature, after that, the dry nitrogen 30 was purged into the batch furnace 10 until the normal pressure was reached, and then the adhesive curing operation was performed. The conditions for curing the adhesive were a curing temperature of 150 degrees Celsius and a curing time of 1 hour. The results are the fifth and sixth times in FIGS. The defect rate started to decrease at the fifth time and decreased to 12% at the sixth time, but continued to show a high value at 10%. The cause is due to the outgas released from the curing adhesive.

  From the fifth and sixth results, a method of moving away from the package surface before the adhesive outgas adheres to the package surface will be described in this embodiment.

  In order to instantly diffuse the heavy outgas from the adhesive, it is necessary to evacuate the batch furnace 10. Moreover, since the air can flow in a certain direction by drawing with a vacuum pump, the derived outgas can be removed in the direction of the vacuum pump.

  In the present embodiment, a method of continuously evacuating during the adhesive curing process is employed. That is, after the dry nitrogen 30 is purged into the batch furnace 10 to bring the inside of the furnace to normal pressure (step 201), the work is put into the batch furnace 10 (step 202). Vacuum drawing is started and vacuum is drawn up to the maximum degree of vacuum (step 203). After reaching the maximum degree of vacuum, evacuation is continued without raising the temperature for 10 minutes (step 204). Thereafter, the temperature is increased to a curing temperature, for example, 150 degrees Celsius (step 205). After the furnace temperature reaches 150 degrees, a curing time, for example, 1 hour is waited (step 206). Thereafter, the process waits until the furnace temperature drops to 70 degrees Celsius due to a natural temperature drop (Step 207). The inside of the furnace is purged with dry nitrogen 30, and the inside of the furnace is returned to normal pressure (step 208). Finally, the workpiece is removed from the batch furnace 10 using gloves (step 209).

  The wire defect rate of the workpiece that has been cured with the adhesive using this method is shown in the seventh, eighth and ninth times in FIG. Although there was a slight difference in the defect rate, all fell below 10% and dropped to the highest defect rate of 6.6%. This value becomes almost a common value when this method is repeated, and it is determined that the defect is caused by other than the adhesive outgas.

  The present invention improves the manufacturing yield in a semiconductor mounting / assembling process having a process of detaching using an organic adhesive whose mass of outgas is heavier than air and a system of wire bonding using gold or aluminum wire. Used for

External view of vacuum type batch type curing furnace Transition of wire peeling rate Wire peeling rate graph Flow chart showing adhesive curing method

Explanation of symbols

10 Batch furnace 20 Diffusion pump 30 Dry nitrogen 40 Leak valve

Claims (5)

A step of bringing the inside of the furnace to normal pressure using dry nitrogen;
Placing the furnace in a vacuum state;
Curing the adhesive between the semiconductor and the package at a constant temperature inside the furnace, and fixing the semiconductor to the package;
Lowering the internal temperature of the furnace until the internal temperature of the furnace is lower than the constant temperature;
Using the dry nitrogen to bring the inside of the furnace to the normal pressure;
A semiconductor manufacturing method comprising: The semiconductor manufacturing method according to claim 1, further comprising: cleaning the surface of the semiconductor by plasma cleaning after the adhesive is cured. The semiconductor manufacturing method according to claim 2, wherein the plasma cleaning has a ratio of argon to oxygen of 4: 1. The semiconductor manufacturing method according to claim 1, wherein the furnace is a vacuum-compatible batch furnace. 5. The semiconductor manufacturing method according to claim 1, wherein the package is made of alumina ceramic having four layers of wiring.

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