Method for Inspecting Defects of Thin Material Film

This invention relates to a method for inspecting the qualities of a thin material film for use in a semiconductor device.

In semiconductor integrated circuit (IC) devices, thin films of a metal, a semiconductor, or an insulator are commonly used to form conductor layers, gate electrodes, gate indulating layers, or the like. In general, these films are formed by spattering, vapor-deposition, or chemical-vapor deposition (CVD) processes. In case such process conditions for making a thin material film are introduced into IC device manufacturing lines, it is important to carefully inspect and ascertain the quality of the thin film for the purpose of improving the yield of semiconductor IC devices. Ideally, it is desirable that such thin material films have no pinholes therein to obtain a good yield of IC devices. A thin material film having a large pinhole density will degrade the reliability of IC devices.

There are a number of ways for inspecting the quality of a thin material film. For example, pinhole inspection of an aluminum film over a semiconductor substrate has been carried out by directly counting the pinholes therein under a microscope. However, since this method counts pinholes in an aluminum film in a narrow limited scope of microscope, it has been difficult to determine the pinhole density in a short time. In addition, there is the copper decoration method which is applicable to thin insulating material film. Mary L. Long describes this method in his paper entitled "Quantitative Evaluation of Photoresist", on page 228, in the paper on Microminiaturization issued by Kodak Seminar in 1970. The method comprises the steps of applying a photoresist film having a predetermined thickness on the surface of a silicon substrate, baking the photoresist film at 150.degree. C. for about 30 minutes, immersing the structure obtained by the above steps into an electrolyte with the substrate being connected to a positive electrode of a battery and an electrode in the electrolyte being connected to a negative electrode of the battery, and then counting the copper deposited portions in the pinholes therein under microscope. However, it is difficult to accurately count the pinholes, since copper material sometimes deposits on the surface of a thin film in addition to the inside of the pinholes therein. Furthermore, this method has required a long time to deposit a copper film, and it is not suitable to inspect the defects of thin metal film.

It is therefore an object of the present invention to provide a method of accurately inspecting the pinhole defects of a thin material film.

It is another object of the present invention to provide a method of being capable of counting the pinholes in a thin material film in a short time with the naked eye.

The present invention provides an improved method of inspecting pinhole defects of a thin material film for use in the manufacture of a semiconductor device. The method according to the present invention comprises the steps of forming on the surface of a semiconductor substrate a reactive material film which can gasify through a chemical reaction with a reactive solution; forming on the surface of the reactive material film a thin material film to be tested which can chemically resist the reactive solution; and immersing the structure obtained by the above steps into the reactive solution.

The above and other objects, features and advantages of the invention will be more apparent from the ensuring detailed description taken in conjunction with the accompanying drawings.

In the accompanying drawings:

FIGS. 1 through 3 are sectional views showing the steps for finding pinhole defects in an aluminum film according to this invention.

One embodiment according to this invention will be described with reference to FIGS. 1 to 3.

First, a semiconductor substrate, e.g., a silicon substrate, and a reactive solution which can produce a reactive gas by a chemical reaction with a heat-resistant organic molecular resin material are prepared. For example, a polyimide resin material is used as an organic molecular resin or reactive material, having the following molecular structure. ##STR1## The polyimide resin material has a weight reduction starting temperature of about 500.degree. C.

As shown in FIG. 1, the polyimide resin film 2 is applied on the entire surface of a silicon wafer 1 by using a spinner. Then, the polyimide resin film 2 is baked at temperatures of 100.degree.-300.degree. C. for about 30 minutes to cure and has a thickness of 1-2 .mu.m.

Next, as shown in FIG. 2, an aluminum layer 3 to be inspected as a thin material film in respect to its film properties is formed on the entire surface of the silicon substrate 1 by a vapor-deposition or spattering process. The thin material film to be inspected may be 0.1-1 .mu.m in thickness and is desirable to be formed at a temperature less than the heat-resistant temperature of the reactive material.

Thereafter, the structure obtained by the above steps is immersed into a 98% concentrated nitric acid for 5 to 10 minutes a room temperature, and the rinsed in clean water.

If the aluminum film 3 has a pinhole 4, the polyimide resin film 2 in the pinhole 4 reacts with the concentrated nitric acid to produce a reactive gas. The gas causes the lift of aluminum film 3 around the pinhole 4 so as to make a pimple 6 on the surface thereof, a hollowed portion 6 is formed. In case the pinhole in the aluminum film 3 is about 1 .mu.m in diameter, the lifted portion or aluminum pimple 5 having a diameter of several millimeters will be formed, whereby the presence of pinholes can be easily observed as white spots with the naked eyes. Then, the pinhole density is measured by directly counting the aluminum pimples per unit area. This method according to this invention is repeated by changing the thickness of aluminum film to evaluate the property thereof.

In the first embodiment, as the material film to be tested can be used an Al-Si-Cu material, tungsten, and molybdenum. In case insulating materials, such as chemical vapor deposition (CVD) polycrystalline silicon, CVD silicon nitride, CVD silicon oxide are tested, there is selected as the reactive solution, a mixed solution of hydrochloric acid and hydrogen peroxide, or of sulfuric acid and hydrogen peroxide (see Table I).

In the second embodiment according to this invention, an epoxy resin material can be used as an organic molecular resin, for example, having the following molecular structure. ##STR2##

In this case, first, an epoxy resin film is formed on the surface of a substrate with a spinner, and then baked to cure. Next, for example, an aluminum film to be tested is formed on the surface of the epoxy resin film. Thereafter, the structure obtained by the above steps is immersed into a concentrated nitric acid, and then rinsed in clean water. If the aluminum film has pinholes, the epoxy resin film therein chemically reacts with concentrated nitric acid to gasify the epoxy resin film. This raises the aluminum layer around the pinholes and makes easy for a viewer to inspect the surface condition of the film. In the second embodiment, as the material film to be tested can be applied an Al-Si-Cu material, tungsten, and molybdenum. In case insulating materials such as chemical vapor deposition (CVD) polycrystalline silicon, CVD silicon nitride, CVD silicon oxide are tested, there is used a reactive solution, a mixed solution of hydrochloric acid and hydrogen peroxide, or of sulfuric acid and hydrogen peroxide (see Table II).

As described above, according to this invention, since an observer can measure the pinhole density of a thin material film with naked eyes, the quality evaluation thereof is carried out in a short time. The method according to this invention is particularly effective for a thin material film of 0.01 to several .mu.m in thickness. Therefore, the process condition for a thin material film ascertained by this invention will boost the reliability and quality of IC devices.