JPH04234116A - Dry etching method - Google Patents

Abstract

PURPOSE:To enable the etching of a high melting metal layer of W or the like or a high melting metal compound layer of WSix or the like to be improved in shape anisotropy and selectivity to resist and base. CONSTITUTION:Gas of WF6/SF6/N2, WF6/HBr, or WF6/HBr/SF6 type is used as a gas for etching a W layer. All gases contain high melting point metal halide (WF6), and the halide concerned is made to serve as a supply source which feeds etching seeds and to enable products of WN, WBr, and the like to be deposited from a vapor phase. The deposit concerned is made to serve as a side wall protection. As a conventional resist decomposition product is unneeded, ion implantation energy can be lessended and particle contamination can be also decreased. Furthermore, an undercut is prevented from occurring in over-etching.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method of etching a material layer made of a high melting point metal such as tungsten or a high melting point metal compound such as tungsten silicide in the field of manufacturing semiconductor devices, etc. Related to improving resist selectivity and base selectivity.

0002

[Background Art] As semiconductor devices become more highly integrated and have higher performance, as seen in VLSI, ULSI, etc. in recent years, the design rules for wiring will become finer from submicron to quarter-micron levels. It is said that Conventionally, DOPOS (doped polys
The pattern width of gate electrodes formed from ilicon (Ilicon) layers is also being reduced to 0.35 μm or less. However, the increase in resistance value associated with the reduction in pattern width is an obstacle to speeding up devices, so polycide wiring using high-melting point metal silicide, which has a resistance value about one order of magnitude lower than that of DOPOS, or even more Refractory metal interconnects with an order of magnitude lower resistance are attracting attention. In particular, tungsten (W), a typical high-melting point metal, has a higher melting point than aluminum, which has traditionally been most widely used as an electrode wiring material for semiconductor devices, and has the advantage that various heat treatments after wiring formation can be performed without any problems. has.

By the way, methods for anisotropically etching a tungsten layer include: (1) using resist decomposition products to protect the sidewalls, (2) low-temperature etching, and (2) adding a high-melting point metal halide to the etching gas in advance. Several methods have been proposed. The above method of using resist decomposition products for sidewall protection includes, for example, SF6 and Cl2.
In this method, the tungsten layer is etched using a mixed gas using the resist pattern as a mask. According to this method, SFx + , Cl+ , Cl2 +
A carbon-based polymer produced by sputtering of the resist material by ions such as the like is deposited on the sidewalls of the pattern, thereby protecting the sidewalls. The low-temperature etching described in (■) above refers to freezing or suppressing radical reactions on the pattern sidewalls while maintaining the etching rate in the depth direction through ion-assisted reactions by controlling the wafer temperature during etching to below 0°C. This technique attempts to prevent shape defects such as undercuts. Anisotropic etching of the tungsten layer can be achieved by setting the wafer cooling temperature to about -50°C. The method of adding high melting point metal halide mentioned in (■) above is as follows:
For example, as disclosed in Japanese Unexamined Patent Publication No. 2-45927, WF6 is added to an etching gas mainly composed of SF6.
etc. are added in advance. According to this method, instead of the carbon-based polymer described in (1) above, a sidewall protective film is formed which is mainly composed of a low-volatility reaction product containing tungsten.

0004

However, each of the conventional dry etching methods for a tungsten layer has its advantages and disadvantages. First, in the method of using resist decomposition products for sidewall protection, high anisotropy can be achieved relatively easily, but since it requires sufficient ion incident energy to sputter the resist material, it inherently has high anisotropy. Resist selectivity and substrate selectivity cannot be expected. Regarding low-temperature etching, etching with excellent anisotropy and selectivity is possible under conditions where the ion incident energy is relatively low. There are many problems that need to be resolved before practical use, such as dew condensation when taken out, reduced throughput due to the time required for cooling, insufficient cooling stability, and heat accumulation in the etching chamber. Furthermore, the method of adding a high melting point metal halide to the etching gas described above has the advantage that there is less risk of particle contamination than the method of using a carbon-based polymer for sidewall protection. However, WFx (x=
1 to 5) have relatively high vapor pressures, and it is actually difficult to provide effective side wall protection. In order to obtain a sufficient sidewall protection effect, the amount of WF6 added must be increased considerably, which may lead to contamination of the entire etching chamber.

[0005] Therefore, the present invention solves the above-mentioned problems, and
It is an object of the present invention to provide a dry etching method that can achieve high anisotropy and good resist selectivity and base selectivity.

[0006]

Means for Solving the Problems The dry etching method of the present invention is proposed to achieve the above-mentioned objects. That is, the dry etching method according to the first aspect of the present invention etches a material layer made of a high melting point metal or a compound thereof using an etching gas containing a high melting point metal halide gas, a fluorine gas, and a nitrogen gas. It is characterized by etching.

A dry etching method according to a second aspect of the present invention includes etching a material layer made of a high melting point metal or a compound thereof using an etching gas containing a high melting point metal halide gas and a bromine gas. It is characterized by:

Furthermore, the dry etching method according to the third aspect of the present invention uses an etching gas containing a high melting point metal halide gas, a bromine gas, and a fluorine gas to remove a high melting point metal or a compound thereof. This method is characterized by etching a material layer.

[0009]

[Operation] In all of the inventions of the present application, the etching gas contains a high melting point metal halide gas. Since a halogen gas is generally used for etching a material layer made of a high melting point metal or its compound, the high melting point metal halide is an etching reaction product. If a reaction product exists in the gas phase in the etching reaction system, separation of the reaction product from the layer of material to be etched is suppressed by an amount corresponding to the partial pressure. This suppressing effect is more pronounced on the pattern sidewall portions, which hardly receive ion incidence, than on the horizontal planes, which receive ion incidence, so that side etching is suppressed. The above effects are
This is already known from Japanese Patent Application Laid-Open No. 2-45927.

[0010] The present application further aims at improving the side wall protection effect by devising the gas system. In the first aspect of the present invention, the components constituting the sidewall protective film are mainly high melting point metal nitrides. This nitride is formed by the reaction of high-melting point metal-based chemical species and nitrogen-based chemical species generated in the gas phase through discharge decomposition of high-melting point metal halide gas and nitrogen-based gas. The high melting point metal fluoride produced by the reaction between the fluorine-based chemical species produced by discharge decomposition of the system gas and the material layer to be etched is further produced by reacting with the nitrogen-based gas in the gas phase. Refractory metal nitrides generally have a high melting point and a low vapor pressure in the etching reaction system, so they are deposited on the wafer surface. Of these, those deposited on the surface to be etched are removed by the sputtering action of incident ions, and those deposited on the sidewalls of the pattern, where fewer ions are incident, play the role of protecting the sidewalls.

[0011] In the second aspect of the present invention, the components constituting the sidewall protective film are mainly high melting point metal bromides. This bromide is formed by the reaction between high melting point metal species and bromine species generated in the gas phase through discharge decomposition of high melting point metal halide gas and bromine gas.
It is also generated by the reaction between bromine-based chemical species generated by discharge decomposition of bromine-based gas and the material layer to be etched. Since this bromide also has a low vapor pressure, it accumulates on the sidewalls of the pattern and plays a role in protecting the sidewalls. In the case of the second invention, the high melting point metal halide gas also serves as a source for the main etching species of the material layer to be etched.

The side wall protection effect achieved in the third aspect of the present invention is similar to that in the second aspect, but by further adding a fluorine gas to the gas system used in the second aspect, the etching effect is improved. It is possible to increase the speed.

[0013] The common effects of the above three inventions are as follows:
(a) High melting point metal halide gas is also a source of etching species (halogen-based chemical species), so high-speed etching is possible; (b) Sidewall protection does not rely on resist decomposition products, so ion incidence Energy can be reduced and resist selectivity and underlayer selectivity can be improved (
c) Since the constituent components of the sidewall protection film are supplied not only from the etching material layer but also from the etching gas system, sidewall protection can be performed efficiently, even during over-etching after most of the etching layer has disappeared. (d) Since the main component of the sidewall protective film is a compound containing the same metal element as the material layer to be etched, there is no risk of causing particle contamination like carbon-based polymers, etc. For example, there are few

[0014]

[Embodiments] Preferred embodiments of the present invention will be described below.

Example 1 This example is an example in which the first aspect of the present invention is applied and a W layer is etched using a mixed gas containing WF6, SF6, and N2. First, as an example, a W layer is laminated on an interlayer insulating film made of silicon oxide, and then the W layer is stacked on an interlayer insulating film made of silicon oxide.
A wafer was prepared in which a photoresist pattern patterned into a predetermined shape was formed on the layer as an etching mask. This wafer was subjected to parallel plate RIE (
WF6 flow rate 20SCCM, SF6 flow rate 1
0SCCM, N2 flow rate 10SCCM, gas pressure 6.7P
a (50mTorr), RF power density 0.5W/cm
The above W layer was etched under the conditions of 2.2 (13.56 MHz).

In this etching process, WF6 and SF
6 F* (fluorine radicals) supplied in large quantities from both, or WFx + , SFx + , N+ ,
Etching progressed rapidly due to the action of ions such as N2 + . On the other hand, a sidewall protective film was formed on the sidewalls of the pattern, and a good anisotropic shape was achieved by protecting the sidewalls from side attack by F*. This sidewall protective film also contains a small amount of carbon-based polymer derived from the photoresist material, but mostly W2N, WN2, W
Tungsten nitride WN expressed by a composition formula such as 2N3
It consists of x. The above-mentioned WNx is formed from the gas phase by the reaction between W and N generated from WF6 and N2 by discharge decomposition, and also by the reaction of F* etc. generated by discharge decomposition of SF6 with the W layer.
It is also produced when Fx further reacts with N2 in the gas phase.

Note that under the above conditions, since the ion incident energy is relatively small, the underlying interlayer insulating film was not excessively etched away during over-etching. Moreover, even though most of the W layer disappears during over-etching, WNx from the gas phase
Side wall protection continued with the supply of Also, the interior of the etching chamber was not contaminated with excess WFx. Furthermore, in conventional etching reaction systems in which a sidewall protective film is formed using a carbon-based polymer, the amount of carbon-based polymer deposited tends to fluctuate depending on the density of the pattern, but in this example, such fluctuations were significantly reduced. It was suppressed.

Example 2 This example is an example in which the second aspect of the present invention is applied and a W layer is etched using a mixed gas containing WF6 and HBr. The wafer to be etched in this example is:
It is the same as that used in Example 1. Parallel plate type RI
Using E equipment, WF6 flow rate 50SCCM, HBr flow rate 20SCCM, gas pressure 6.7Pa (50mTorr)
, RF power density 0.5W/cm2 (13.56MH
The W layer was etched under the conditions of z).

In this etching process, F* (fluorine radicals) supplied from WF6 or WFx
Etching progressed due to the action of ions such as +, Br+, and Br2+. On the other hand, a sidewall protective film was formed on the sidewalls of the pattern, and a good anisotropic shape was achieved. This sidewall protective film includes WBr2, WBr5, WBr
It is mainly composed of tungsten bromide WBrx, which is represented by the composition formula be.

Embodiment 3 This embodiment applies the third aspect of the present invention and uses WF6,
This is an example in which the W layer was etched using a mixed gas containing HBr and SF6. The wafer to be etched in this example is the same as that used in Example 1. Using magnetic field microwave plasma etching equipment,
WF6 flow rate 50SCCM, HBr flow rate 50SCCM,
SF6 Flow rate 50SCCM, gas pressure 1.3Pa (10m
The W layer was etched under the following conditions: microwave power of 850 W, and RF bias power of 40 W (13.56 MHz).

In this etching process, a large amount of F* (fluorine radicals) supplied from WF6 and SF6, or WFx + , SFx + , Br+ ,
Etching progressed rapidly due to the action of ions such as Br2 + . On the other hand, tungsten bromide WBrx is attached to the pattern side wall part based on the same mechanism as in the above-mentioned embodiment.
A sidewall protective film mainly composed of was formed, and a good anisotropic shape was achieved.

Embodiment 4 This embodiment is an example in which the third aspect of the present invention is applied during over-etching after etching the W layer by approximately the thickness thereof using a conventionally proposed gas system. . The wafer to be etched in this example is the same as that used in Example 1. First, a magnetic field microwave plasma etching system was used for the first etching step, with an SF6 flow rate of 50SCCM and an HBr flow rate of 30SCCM.
, gas pressure 1.3 Pa (10 mTorr), microwave power 850 W, RF bias power 40 W (13.5
The W layer was etched by approximately the thickness of the W layer under the condition of 6 MHz). In this first etching step, SF6
F* (fluorine radical) supplied from
Etching progressed due to the action of ions such as Fx + , Br + , Br2 + , etc. On the other hand, a sidewall protective film mainly composed of tungsten bromide WBrx was formed on the pattern sidewall by the reaction between HBr and the W layer, and a good anisotropic shape was achieved.

Next, as a second etching step, WF6 was added to the above gas system to over-etch the W layer. Gas supply conditions are SF6 flow rate 50SCCM, H
Br flow rate is 50SCCM, WF6 flow rate is 50SCCM, and RF bias power is 10 in consideration of substrate selectivity.
It was reduced to W. Here, if over-etching was performed under the gas supply conditions in the first etching step, there would be a small amount of W layer remaining on the wafer, so the supply of W would be insufficient and WBrx would not be sufficiently formed, resulting in shape anisotropy. There is a risk that the quality may deteriorate. However, in this example, as a result of providing the second etching step as described above, W was supplied from the gas phase even during over-etching, and a good anisotropic shape was maintained.

By the way, the present invention is not limited to the above-mentioned embodiments; for example, the fluorine-based gas may include F2, ClF3, CF4 in addition to the above-mentioned SF6.
, NF3, etc. can be used. As the bromine-based gas, in addition to the above-mentioned HBr, a gas obtained by vaporizing Br2 by bubbling or the like using an inert gas, BBr3, etc. can be used. The high melting point metal halide gas is not limited to the above-mentioned WF6, but can include Ti, Mo, etc. as long as it can be introduced into the etching reaction system in gaseous form.
A compound formed by appropriately combining a high melting point metal such as Ta and a halogen atom such as Cl or F may also be used. The etching gas used in the present invention includes O2 and N2 for the purpose of controlling the etching rate and enhancing the side wall protection effect.
A gas containing oxygen as a constituent element, such as O, N2 O3, NO2, etc., may be added as appropriate. However, in this case, since excessive oxygen deteriorates the selectivity to resist, the conditions etc. need to be optimized. or,
From the viewpoint of expecting a sputtering effect, a dilution effect, a cooling effect, etc., a rare gas such as He or Ar may be added as appropriate. In each of the above-mentioned embodiments, the W layer is exemplified as the material layer to be etched, but other high melting point metals such as Ti, Mo, and Ta, or silicides of these high melting point metals may also be used. Furthermore, if the present invention is further combined with low-temperature etching, it becomes possible to effectively protect the sidewalls even if the amount of high-melting point metal halide gas added is reduced.

[0025]

As is clear from the above explanation, according to the present invention, by adding high melting point metal halide gas to the etching gas, deposits that are less likely to cause particle contamination can be removed from the gas phase. can be generated. Since there is no particular need to supply resist decomposition products, resist selectivity and base selectivity can be improved, and there is no need to perform low-temperature etching, so existing etching equipment can be used. Therefore, the present invention
This will greatly advance the practical application of high-melting point metal interconnects to replace conventional DOPOS interconnects, and will have extremely high industrial value.

Claims (3)

[Claims] 1. A dry etching method comprising etching a material layer made of a high melting point metal or a compound thereof using an etching gas containing a high melting point metal halide gas, a fluorine gas, and a nitrogen gas. 2. A dry etching method comprising etching a material layer made of a high melting point metal or a compound thereof using an etching gas containing a high melting point metal halide gas and a bromine gas. 3. A dry etching method comprising etching a material layer made of a high melting point metal or a compound thereof using an etching gas containing a high melting point metal halide gas, a bromine gas, and a fluorine gas.