JPS5815938B2 - Aluminum high quality aluminum alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a protective film to prevent corrosion of aluminum wiring in a semiconductor device.

As is well known, corrosion of aluminum wiring in semiconductor devices has become a serious problem in practice.

Aluminum is generally considered to be a material with good corrosion resistance due to its strong oxide film, but this often causes problems.

Simply immersing it in water can sometimes speed up corrosion, and trace amounts of chlorine and silicon in water are known to accelerate the dissolution of aluminum.

Furthermore, when aluminum is connected to metals that are more sensitive than aluminum, when an electric field is applied to it, and when it is immersed in water or various solutions, corrosion often becomes severe.

In semiconductor devices, current is passed through aluminum,
Since gold wire, which is more dangerous than aluminum, is sometimes connected to aluminum wiring, impurities that promote corrosion may come out from the silicon oxide film and various resins used for protection, and moisture in the air can reach the aluminum wiring. Once this is reached, conditions conducive to corrosion are present, and corrosion occurs and progresses.

In order to prevent this situation from occurring, conventional methods have been used to prevent water from reaching the aluminum wiring.

The aluminum is covered with a protective film to isolate it from the outside air.

Usually, most of the wiring is covered with a protective film such as silicon oxide and then covered with resin, or the wiring is hermetically sealed without using resin.

Since hermetic sealing is expensive, it is generally not used much anymore, and instead there is a tendency to use resins that are less likely to allow water to penetrate.

However, since there are few resins that can completely protect aluminum wiring in semiconductor devices, it has also been proposed to create a strong film on the aluminum wiring itself by anodic oxidation or the like.

However, forming a strong film through anodic oxidation requires the application of an electric field, which is technically quite difficult and difficult to put into practical use.

Another method proposed is to deposit aluminum as a wiring material over the entire surface of a silicon substrate, cover the parts that will become the wiring with a photoresist, and then anodize the other parts.

If this method works, it would be very convenient, but in reality, there are often areas that cannot be anodized, and as expected,
Practical use is difficult.

Furthermore, once the aluminum wiring has been formed in advance, the aluminum wiring is not all connected on the silicon wafer, and since the aluminum is in contact with the semiconductor element, even if an electric field is applied to the silicon, the electric field will not be applied to the aluminum. Therefore, it is difficult to anodize the entire surface of the aluminum wiring.

Furthermore, after anodic oxidation, the oxide film on the aluminum surface makes it difficult to join the conductor, so it is necessary to remove the oxide film on the electrode portion.

Another possibility is to bond a gold wire, which is often used as a conductor, to the electrode and then anodize the aluminum, but in this case the gold would dissolve, making it impractical.

The present invention was made to solve the above-mentioned conventional problems, and provides a method for forming a corrosion-resistant film after bonding a conductive wire to the surface of an aluminum wiring of a semiconductor device, which requires the application of an electric field. This makes it possible to improve the corrosion resistance of aluminum wiring through simple surface chemical treatment.

The feature of the present invention is that a corrosion-resistant film is formed on the wiring surface without corroding the wiring conductor wire by applying chemical treatment after the conductor wires are joined. Detailed explanation of.

The normal semiconductor device assembly process includes the well-known aluminum vapor deposition, formation of aluminum wiring by photoetching, formation of silicon oxide protective film, formation of electrode holes by photoetching, bullet attachment, and thermocompression bonding of gold wire to aluminum. The semi-finished product formed through the process was immersed in a phosphoric acid-chromic acid solution.

The following composition can be used for this phosphoric acid-chromic acid solution.

38 to 12 g of CrO 3 to 5 g of H3P04 (concentrated) 2 to 7 g of C2H, OH 70 to 90 g of H2O After immersing the semi-finished semiconductor device with all the conductive wires bonded in the above assembly process for at least 10 minutes in solution K consisting of these components, 70 to 5 g of H3P04 (concentrated) Dry at 90°C for 10-20 minutes.

Finally, wash in running pure water (at least 50 ml/sec) for at least 10 minutes.

This treatment allows the aluminum wiring to be removed.

A strong film with extremely high corrosion resistance is formed.

Next, the results of a corrosion test on the aluminum wiring formed with a film according to the present invention will be explained.

Corrosion tests were conducted using three factors: resin for protecting semiconductor devices, water, and gold-aluminum contact.

That is, an epoxy resin extract containing 1 g of epoxy resin, 2 ml of acetone, and 2 ml of pure water was prepared and used as a solution for corrosion testing.

A bonded aluminum wire and a gold wire are treated according to the present invention to form a film, and a portion of this aluminum wire is immersed in the above extraction liquid to serve as one electrode, and the other gold wire is used as the other electrode. It was immersed in the above extract.

Corrosion resistance was determined by connecting both the electrodes via an ammeter outside the extract and comparing the flowing currents.

In addition to those treated according to the present invention, for comparison, Table 1 shows those treated with no treatment, those treated with phosphoric acid, treated with chromic acid, and treated with anodic oxidation.

From Table 1, it can be seen that the current flowing between gold and aluminum for the anodic oxidation and phosphoric acid-chromic acid treated items is the same as that for other treatments, even when immersed in the above resin extract. It can be seen that it is very small in comparison.

The current that flows when connected to an ammeter.

This indicates that the phosphoric acid-chromic acid treatment formed a film on the surface of the aluminum wiring having corrosion resistance comparable to that of anodizing.

In fact, in the manufacturing process of a certain type of product, after aluminum wiring is formed, when gold wires are bonded and immersed in the above resin extract, aluminum wiring with a width of approximately 10 μm is formed in several places within about 5 minutes on untreated products. In contrast, wires that had been anodized or treated with phosphoric acid-chromic acid did not show any disconnection even after being immersed for more than 30 minutes while being observed under a microscope.

Further, in the case of aluminum alone, chromic acid treatment is effective, but as shown in Table 1, good results were not obtained even when chromic acid treatment was applied to aluminum bonded with gold wire.

As is clear from the above description, according to the present invention, aluminum bonded to gold can be bonded to gold without applying an electric field unlike anodizing, and by performing a simple chemical treatment after bonding gold wires. Corrosion resistance can be improved to the same extent as anodizing.

Claims (1)

[Claims] 1 After joining the conductive wire to the aluminum wiring of the semiconductor device, the semiconductor device was heated with 38 to 12 g of CrO and concentrated H3.
P0.3-5g, C2H5OH2-7g and H2O7
A method for forming a protective film for aluminum wiring in a semiconductor device, comprising forming a passive film on the surface of the aluminum wiring by immersing it in a phosphoric acid-chromic acid solution having a composition of 0 to 90 g.