JPS6244813B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor device, and particularly to the structure of a conductive film for interconnection of devices in a semiconductor device.

Semiconductor devices are becoming increasingly highly integrated and densely packed, and as a result, impurity diffusion region patterns, opening patterns in insulating films, conductive film patterns, etc. are becoming increasingly finer. The miniaturization of these patterns is generally limited by the processing accuracy of the equipment used. However, the miniaturization of the conductive film pattern is limited not only by the processing accuracy but also by the current value that can be passed through the conductive film.

In particular, as machining accuracy has improved significantly in recent years, restrictions based on current values have become more important. Limits on the current value are generally defined by the current density relative to the cross-sectional area of the conductive film.

If a current exceeding a certain current density is passed through the conductive film, the conductive film itself will melt due to self-heating, but even if this does not occur, the current flowing through the conductive film will cause the conductive film to melt. Disconnection may occur due to the movement of ions.
The latter is called disconnection due to electromigration, and is one of the important causes of deterioration and failure of semiconductor devices during actual use.

The electromigration mechanism when using an aluminum (Al) thin film as a conductor will be briefly described. Generally, when a current is passed through a metal thin film, the metal atoms, in the case of an electron conductor, are simultaneously subjected to forces caused by the electric field and force caused by the flow of electrons, both in opposite directions. However, since metal atoms are usually electrically shielded by the electrons surrounding them, the force of the electric field weakens against the metal atoms, and the force of the electrons becomes dominant. For this reason, metal atoms are swept in the direction of the electron flow and accumulate on the positive pole side, creating hills and whiskers. On the other hand, the vacancies after the metal atoms move are swept in the opposite direction and accumulate on the negative pole side, forming voids.
This will cause the wiring to become disconnected.

Methods to suppress such electromigration include (1) improving the metallographic structure of Al, (2) improving the shape of Al, (3) adding certain metals to the Al film, ( 4) Coating Al wiring with dielectric material, etc.

Specifically, method (1) involves increasing the crystal grain size of the Al film by increasing the temperature of the semiconductor substrate when forming the Al film. This is not preferable because it may impair the machining accuracy. Method (2) imposes undesirable restrictions on pattern design of semiconductor devices. Further, method (4) is not desirable because it requires an extra step of coating with a dielectric material. Therefore, the most desirable electromigration suppression method at present is method (3), that is, Al
This method involves adding certain metals to the film. Magnesium (Mg), nickel (Ni), chromium (Cr), etc. are generally effective as metals to be added. However, it is not only difficult to uniformly add the above metals to the Al film, but also difficult to uniformly etch a thin film containing a mixture of different metals.

An object of the present invention is to solve the above-mentioned conventional problems and provide a structure of a conductive layer in which electromigration is suppressed.

The present invention includes a semiconductor substrate, an insulating film having a plurality of selectively provided openings and covering the semiconductor substrate, and an insulating film that is electrically connected to the semiconductor substrate through the openings, and that is electrically connected to the semiconductor substrate through the openings. In a semiconductor device having a conductive film selectively provided extending over a region, the conductive film is composed of a multilayer film having different metal layers each having a thickness equal to or less than a crystal grain size. It is characterized by the presence of

Next, in order to better understand the present invention, the present invention will be explained using the drawings while comparing it with the prior art.

FIG. 1 is a sectional view showing the structure of the prior art.
A conductor layer (metal wiring layer) is formed on the upper surface of a thermal oxide film 12 that covers a semiconductor substrate 11 including a plurality of circuit elements (not shown) and has selectively provided openings.
13 and 14 are formed. The conductor layer 13 is shown in a mosaic pattern as a collection of fine crystal grains.
When a current is passed from the conductor layer 13 to the conductor layer 14 through the semiconductor substrate, the electron flow is 14 to 13.
flows to. In the case of the structure shown in FIG. 1, there are many grain boundaries, and the atoms constituting the conductor move along the grain boundaries, so atoms are accumulated near the contact hole 15, and atoms are accumulated near the contact hole 16. This causes wire breakage. To prevent this, relatively new conventional technology suppresses electromigration by adding copper (Cu), which has a slow movement speed due to electron flow, into the conductor layer and depositing it at the grain boundaries. However, Cu deposited at grain boundaries forms an alloy with the conductor, making it difficult to form a pattern by etching.

FIG. 2 shows an embodiment of the invention.

a semiconductor substrate 21; an insulating film 22 having a plurality of selectively provided openings and covering the semiconductor substrate; electrically connected to the semiconductor substrate through the openings;
In a semiconductor device having a conductive film extending and selectively provided on the insulating film, the conductive film has a two-layer structure with a dissimilar metal 24 having a crystal grain size of 28 or less and a film thickness of 29. There is. In the embodiments of the present invention, since the conductor layer has crystal grain boundaries extending in the film thickness direction, the electromigration phenomenon of conductor atoms at the grain boundaries can be suppressed to an extremely low level. Furthermore, since the dissimilar metals provided between the conductors are formed in layers, etchants suitable for each can be used in pattern formation by selective etching, so there are no processing problems. When the conductor layer is made of Al, the dissimilar metals provided between the conductor layers are those with an atomic radius of Al, such as Cu, Ni, and Cr.
It is desirable to have something that is significantly different from the above.

The size of crystal grains in a conductor layer varies greatly depending on the underlying temperature of the semiconductor substrate when a conductor film is deposited by a method such as vapor deposition or sputtering. In the case of a normal evaporation device, when an Al film is deposited at a substrate temperature of 200°C, the crystal grains will be approximately 1μ.

Therefore, if the Al film thickness is 1.5μm, the Al thickness is 0.75μm.
At the time when 0.03 μm of Cu is applied, for example,
After that, it is desirable to deposit the remaining Al to a thickness of 0.75 μm.

The present invention has been described above using an example with a simple structure, but the elements in the semiconductor substrate in the example include active elements such as a MOS transistor, a bipolar transistor, a FET transistor, a PN junction diode, and a resistor. It is applicable to all passive elements such as capacitors and combination elements thereof. Therefore, the patent rights of the present invention extend to all semiconductor devices shown in the claims.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the prior art. FIG. 2 is a sectional view showing an embodiment of the present invention. The alphanumeric characters shown in the figure each indicate the following. 11, 21... Semiconductor substrate, 12, 22... Insulating film, 13, 14, 23, 25... Conductor layer, 1
5, 16, 26, 27...Opening part of insulating film, 28
. . . Size of crystal grains in the conductor layer, 29 . . . Thickness of the conductor layer.

Claims (1)

[Claims] 1. A semiconductor substrate, an insulating film having a plurality of selectively provided openings and covering the semiconductor substrate, and an insulating film electrically connected to the semiconductor substrate through the openings and extending over the insulating film. 1. A semiconductor device having a conductive film selectively provided as a conductive film, wherein a different metal layer is provided for each part of the conductive film having a thickness within an average crystal grain size of the conductive film.