JPH0467635A - Formation of wiring - Google Patents

Abstract

PURPOSE:To lengthen the wiring life by a method wherein a conductive thin film containing crystal grains mainly comprising Al is formed on a substrate and then a layer comprising crystal grains of different kind of conductive element is formed on the parts whereon a part of the crystal grains is selectively removed. CONSTITUTION:A thermal oxide film 2 is deposited on a p type single crystal Si substrate 1 and after depositing an AlSi alloy film 3 by ordinary high speed sputtering process, a part of the Al alloy film 3 is selectively removed from the grain boundary by processing in ammonia fluoride solution. Next, Cu films 4 are formed and after the heat treatment in nitrogen atmosphere, the Cu films 4 are polished until the surface of the Al alloy film 3 is exposed by coating with resist and using Ar sputtering process. The crystal grains comprising this conductive element restrain the movement of the component atoms in the crystal grains mainly comprising Al due to the electrical stress so that the electromigration may hardly occur. Accordingly, the wiring having high electromigration resistance can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Industrial Application Field) The present invention relates to a method of manufacturing a semiconductor device, and particularly relates to a method of forming wiring.

(Prior Art) High integration of semiconductor devices is brought about by miniaturization of constituent elements. For example, IMDRAM, 256KSR
Very large scale integrated circuits such as AM are manufactured with a design standard of 1.0 to 1.2 μm, and very large scale integrated circuits with a submicron design standard are being created for the purpose of higher integration. With the miniaturization of semiconductor devices, the width of interconnects is becoming smaller and smaller, and the length of interconnects is significantly increasing due to higher integration and integration ratios, making it particularly important to maintain the reliability of interconnects.

An alloy film containing aluminum (All) as a main component is usually used for wiring in VLSIs. As mentioned above, although the wiring shape becomes thinner, the applied voltage remains the same as 5 V DC, so the current stress applied to the unit cross-sectional area of the Al1 alloy wiring increases relatively. A with large current stress applied
With g-alloy wiring, various phenomena that have not occurred in the past become noticeable. For example, due to the flow of electrons, Aj7 atoms are transported in the direction of the electron flow, causing the Ag alloy wiring to become partially thin and eventually break (electromigration), and the phenomenon of the insulating film formed on the Ag alloy wiring. This is a phenomenon (stress migration) in which Ag alloy wiring breaks due to stress if left unattended. When these phenomena occur, the A1 alloy film is disconnected, and the reliability of the wiring is significantly reduced.

These disconnections mainly occur at the grain boundaries of the Aj7 alloy film, and when an Ag alloy film is used, it is necessary to strengthen the grain boundaries.

(Problems to be Solved by the Invention) As described above, there is a problem in that the wiring for VLSI is easily disconnected when energized. The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for forming a wire that is highly resistant to electromigration and the like.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a process of forming a conductive thin film containing crystal grains mainly composed of aluminum on a substrate, and the method comprises the steps of: selectively removing a part of the crystal grains of the conductive thin film; and forming a layer consisting of crystal grains of a conductive element different from the conductive thin film in the removed portion. A method for forming wiring is provided.

(Function) According to the wiring forming method according to the present invention, crystal grains made of a conductive element different from the crystal grains are formed at the grain boundaries of crystal grains whose main component is aluminum.

The crystal grains made of the conductive element suppress the movement of constituent atoms within the crystal grains mainly composed of aluminum caused by electrical stress, so that electromigration is less likely to occur. Therefore, it is possible to form a wiring having high electro-φ migration resistance.

(Example) Hereinafter, the details of the present invention will be explained in detail using examples.

First Embodiment FIG. 1 is a process sectional view for explaining an embodiment of the method for forming wiring according to the present invention.

A thermal oxide film 2 with a thickness of 0.2 μm is deposited on a p-type single crystal St substrate 1, and an Ar1.1% S film is further deposited using a normal high-speed sputtering method.
An i-alloy film 3 was deposited to a thickness of 0.8 μm (FIG. 1(a)). Thereafter, it was treated with an ammonia fluoride solution to selectively remove some of the grains of the Afi alloy film from the grain boundaries (FIG. 1(b)). Furthermore, by appropriately selecting the concentration of the ammonium fluoride solution and the treatment time, the shape of the A1 alloy film 3 is controlled to a desired shape as shown in FIG. 1(C). Next, a Cu film 4 with a thickness of 0.2 μm was formed, and this laminated thin film was
Heat treatment was performed in a nitrogen atmosphere at 0° C. for 30 minutes (FIG. 1(d)).

After that, a resist was applied and the surface was scraped by Ar sputtering until the surface of the Al1 alloy film 3 was exposed (first
Figure (e)). When the surface of this sample is observed from above using a scanning electron microscope (SEM), as shown in the top view of Figure 2, the way each crystal grain shines differs as a unit, with crystal grains 6 made of Ag alloy and crystals made of Cu. It was found that grains 5 were formed respectively. For confirmation, the surface of this thin film was subjected to micro-AES (electronic probe irradiation area is approximately 1 μm).
Therefore, surface analysis can be performed on a grain-by-crystal grain basis. ), AD SS according to the scanning electron probe
There were crystal grains in which i was mainly detected and crystal grains in which Cu was mainly detected. From this, it can be seen that A
It was confirmed that crystal grains 6 made of g alloy and crystal grains 5 made of Cu were formed on thermal oxide film 2, respectively.

Furthermore, due to the heat treatment, Ar1. Si,C
It was confirmed that u were interdiffused.

This alloy film was buttered and subjected to a current conduction test. For comparison, a current test was also conducted on a normal Ag-8i alloy film. Wiring width 0.5 to 2.0 μm, space 1 μm 1 wire length 12
Ic) Form wiring and apply current stress 1.0X10
An accelerated test was conducted at A/Cl11 and a temperature of 150°C.

The life of the A47 alloy film mixed with Cu crystal grains was about 20 to 30 times longer than that of the normal A1 alloy film. Also, Cu
The length was about 3 to 10 times longer than that of an A11St-Cu alloy film formed by doping or sputter deposition and then sintering.

Second Embodiment In the first embodiment, after selectively etching a portion of the AFi alloy film, a Cu film is deposited and heat treated, and the upper Cu film is removed until the surface of the lower Ag alloy film is exposed. Etched. In the second example, this Cu film was also left and used for wiring. Next, a detailed explanation will be given using the drawings. FIG. 3 is a process sectional view for explaining another embodiment of the wiring forming method according to the present invention. A thermal oxide film 8 was deposited to a thickness of 0.2 μm on a p-type single crystal Si substrate 7, and a 1.1% Si alloy film 9 was further deposited to a thickness of 0.8 μm using a conventional high-speed sputtering method (FIG. 3(a)). Thereafter, it was treated with an ammonia fluoride solution to selectively remove part of the grains of the Aj) alloy film from the grain boundaries (FIG. 3(b)). A by appropriately selecting the concentration of ammonium fluoride solution and treatment time.
The first thing is that the shape of I alloy M9 can be controlled to a desired shape.
This is as shown in the example. Next, the Cu film 10 was
A thickness of 15 μm was formed, and the laminated thin film was heat-treated at 450° C. in a nitrogen atmosphere for 30 minutes (FIG. 2(C)).

After that, a resist is applied and patterned using a normal light exposure method, and the Cu films 10 and A11 are etched by reactive ion etching (RIE) using a chlorine-based etching gas.
The alloy film 9 was etched to form a desired wiring pattern. At this time, the processing accuracy of Cu etching is generally not good, but the film thickness of about 0.15 μm could be processed satisfactorily.

No particular analysis was attempted for this sample, but the first
By analogy with the example described above, it is considered that Cu crystal grains are stacked on top of the island-shaped AN alloy crystal grains, and that the grain boundaries of the upper layer of the Cu crystal grains are in contact with each other. Also, A
It is considered that Ag, Si, and Cu are interdiffused at the grain boundaries where the i1 alloy film and the Cu crystal grains are in contact with each other.

This alloy film was buttered and subjected to a current conduction test. For comparison, a normal A11-Si alloy film was also subjected to an electrical conduction test.

Wiring width 0.5-2.0μm 1 space 1μm, wire length 1
Two cranes of Al wiring are formed and the current stress is 1.0xlOA.
/csn, and an accelerated test was conducted at a temperature of 150°C. The life of this sample, in which Cu crystal grains and A1 alloy crystal grains were mixed and connected by a Cu film in the upper layer, was more than 50 times longer than that of a normal single alloy film. Also, after doping or sputter depositing Cu, Al-5i-
It was about 5 to 20 times longer than the Cu alloy film.

Incidentally, in the examples so far, the case of Cu was shown as an example of the second conductive element, but tungsten.

When we tested titanium, tantalum, and magnesium, the change in sheet resistance of the wiring layer varied depending on the second conductive element used, but when we formed a wiring pattern and measured the electrical life, in all cases it was found that 8Ω/Si alloy This is an order of magnitude improvement over the previous case.

Further, in the above embodiment, selective removal of a portion of the grains of Aj7 was performed using an ammonia fluoride solution, but it may also be performed using chemical dry etching using a chlorine gas.

Furthermore, it goes without saying that the type of Si substrate used, the type of oxide film, etc. can be modified as appropriate without departing from the gist of the present invention.

[Effects of the Invention] According to the method for forming a wiring according to the present invention, it is possible to form a wiring that suppresses movement of constituent atoms within crystal grains mainly composed of aluminum caused by electrical stress.

Therefore, the life of the wiring is longer than that of the conventional wiring, and wiring with high electrical reliability can be formed.

[Brief explanation of the drawing]

1 to 3 are process sectional views for explaining the present invention in detail. 1...Si substrate, 2...thermal oxide film, 3...Al1
・1% Si alloy film, 4... Cu film, 5... Crystal grains made of Cu, 6... Crystal grains made of AfI alloy, 7.
...Si substrate, 8...thermal oxide film, 9...All ・
1% Si alloy film, 10...Cu film.

Claims (4)

[Claims] (1) A step of forming a conductive thin film containing crystal grains mainly composed of aluminum on a substrate, a step of selectively removing a part of the crystal grains of the conductive thin film, and a step of forming a 1. A method for forming wiring, comprising the step of forming a layer made of crystal grains of a different type of conductive element than the conductive thin film. (2) The method for forming a wiring according to claim 1, wherein the crystal grains containing aluminum as a main component contain silicon. (3) A claim characterized in that, after the step of forming a layer made of crystal grains of a conductive element different from the conductive thin film in the removed portion, heat treatment is performed to alloy the grain boundary portion. The method for forming the wiring according to item (1). (4) The method for forming a wiring according to claim (1), wherein the different type of conductive element is a substance containing at least one of copper, tungsten, titanium, tantalum, and magnesium.