JPH0660402B2 - Selective growth method for tungsten film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The reaction gas of tungsten hexafluoride and hydrogen is thermally decomposed,
The tungsten film is selectively grown, then the inflow of the reaction gas is stopped, and the generated gas is removed by vacuum suction. By repeating such an operation, a tungsten film having a required film thickness is selectively grown.

[Field of Industrial Application] The present invention relates to a selective growth method of a tungsten film used for manufacturing a semiconductor device.

In a semiconductor device such as an IC, a semiconductor element and other circuit elements are formed on a semiconductor substrate, and a large number of electrode wirings leading from these regions are provided on the upper surface.

Aluminum electrodes or their alloy films have been used for these electrode wirings up to now, but aluminum has a drawback that its melting point is low, which limits the formation of interlayer insulating films when forming multilayer wirings. There are drawbacks. for that reason,
A conductive polycrystalline silicon film is widely used as an alternative wiring material, but this has a problem that the conductivity is not so good, and recently, a refractory metal film having good electrical conductivity or a silicide film thereof has been used as an electrode wiring. The method used for is adopted.

However, in the course of studying various methods of depositing such a refractory metal film, it has been found that the tungsten film selectively grows on the semiconductor substrate without applying the photo process. However, the selective growth method is not yet sufficient, and establishment of a sufficiently satisfactory selective growth method is desired.

[Problems to be Solved by the Related Art and Invention] The selective growth method of the tungsten film is, of course, a growth method by chemical vapor deposition (CVD) method, which is tungsten hexafluoride (WF _6). ) And hydrogen (H ₂ ) are mixed and the reaction gas is thermally decomposed and deposited. The reaction formula is as follows.

WF ₆ + 3H ₂ → W + 6HF As can be seen from this reaction formula, since hydrofluoric acid (HF) gas is generated, the HF gas etches the silicon dioxide (SiO ₂ ) film surface, so that the tungsten film is removed from the silicon substrate It is considered that selective growth is performed only on the SiO ₂ film and not on the SiO ₂ film.

However, when the selectively grown film thickness is about 3000 Å or more, the selectivity is lost, and the tungsten film is deposited on the SiO ₂ film. For example, as shown in the sectional view of FIG. 3, a 1 μm-thick SiO 2 film provided on the silicon substrate 1
_{2 When the} electrode window 3 is formed in the film 2 and the tungsten film 4 is deposited on the electrode window, the electrode window 3 cannot be buried only by selective growth. Therefore, at present, the tungsten film is only selectively grown to a thickness of about 5000Å or less.

In this example, burying the electrode window with a conductor film is important for flattening the wiring layer, and if the deposition amount is small as described above, the electrode window will be covered with another conductor film. Must be buried.

The present invention proposes a growth method for eliminating the above-mentioned selective growth of a tungsten film having a limited growth film thickness and selectively growing a tungsten film of a required film thickness.

[Means for Solving the Problems] The purpose thereof is to perform thermal decomposition of a reaction gas composed of tungsten hexafluoride and hydrogen to selectively grow a tungsten film on a semiconductor substrate. This is achieved by a selective growth method of a tungsten film in which the introduction is intermittently stopped and an operation of increasing the vacuum degree of the reaction chamber is added.

[Operation] That is, according to the present invention, the introduction of the reaction gas is stopped during the process of the selective growth and the excessively generated HF is temporarily sucked and removed so that the underlayer is not roughened by the generated HF. . In this way, if the selective growth is performed intermittently, the tungsten film can be selectively grown with no limit on the film thickness.

[Examples] Hereinafter, examples will be described in detail with reference to the drawings.

FIG. 1 shows a schematic view of a CVD apparatus to which the present invention is applied. 11 is a silicon substrate, 12 is a reaction chamber, 13 is a heating body, 14
Is a vacuum exhaust port, 15 is a WF ₆ gas inlet, and 16 is an H ₂ gas inlet.

The reaction chamber 2 of such a CVD apparatus is heated to a constant temperature of 300 to 325 ° C., and WF is supplied from the gas inlets 15 and 16.
₆ gas and H ₂ gas are caused to flow in, and vacuum suction is performed from the other end to keep the inside of the reaction chamber 12 at a reduced pressure degree of about 0.3 Torr. The gas inflow amount is, for example, about 400 cc / min for H ₂ gas while 30 cc / min for WF ₆ gas. Further, at this time, a method of diluting the WF ₆ gas with nitrogen (N ₂ ) gas and allowing the WF ₆ gas to flow in may be adopted.

Then, the WF ₆ gas is thermally decomposed in the reaction chamber, and the tungsten film grows. At that time, as shown in the sectional view of FIG. 3, the tungsten film is not deposited on the SiO ₂ film 2, but the tungsten film 4 is deposited only on the silicon substrate 1 of the electrode window 3.

In this way, after reacting for 30 minutes to grow a film thickness of about 1000 Å, the inflow of WF ₆ gas and H ₂ gas is stopped. However, since the vacuum suction is continued, the degree of reduced pressure becomes high, and the degree of vacuum in the reaction chamber 2 becomes about 0.1 Torr. Then, the WF ₆ gas and the H ₂ gas are caused to flow in again, and they are similarly reacted for 30 minutes to further grow a tungsten film having a film thickness of about 1000 Å.

Thus, by repeating such an operation and performing selective growth, the electrode window 3 can be buried with the tungsten film 4 as shown in the sectional view of FIG. In this way, the thickness of the selective growth is no longer limited because excessively generated HF is removed by vacuum suction and the SiO ₂ film surface is not roughened by excessive HF. Conceivable.

In the above example, the step of burying the electrode window and flattening the wiring layer has been described. However, the ability to selectively grow the required film thickness has various favorable effects on other manufacturing steps as well. Needless to say.

[Effects of the Invention] As is clear from the above description, according to the present invention, a tungsten film having a required film thickness can be selectively grown, and high performance of IC
This greatly contributes to higher quality and higher density.

[Brief description of drawings]

FIG. 1 is a schematic view of a CVD apparatus to which the present invention is applied, FIG. 2 is a sectional view of an electrode window in which a tungsten film according to the present invention is selectively grown, and FIG. 3 is a conventional electrode window in which a tungsten film is selectively grown. FIG. In the figure, 1 and 11 are a silicon substrate, 2 is a SiO ₂ film, 3 is an electrode window, 4 is a tungsten film, 12 is a reaction furnace, 13 is a heating body, 14 is a vacuum exhaust port, 15 is a WF ₆ gas inlet port, Reference numeral 16 indicates an H ₂ gas inlet.

Claims (1)

[Claims] 1. In a growth step of thermally decomposing a reaction gas composed of tungsten hexafluoride and hydrogen to selectively grow a tungsten film on a semiconductor substrate, an inflow of the reaction gas is intermittently stopped to carry out a reaction. A method for selectively growing a tungsten film, characterized in that an operation for increasing the degree of vacuum in a chamber is added.