GB2290907A - A method of manufacturing a semiconductor device with aluminium wiring - Google Patents

Abstract

The invention provides a method of manufacturing a semiconductor device e.g. a DRAM. The method comprises etching and patterning, using a gas containing chlorine, a conductive film 20 which is made of aluminium or aluminium alloy, deposited on the surface of an insulating film formed on a substrate 10. The substrate and the conductive film are exposed to a reaction solution, containing a metal, such as silver or lead e.g. silver nitrate, which is capable of reacting with chlorine and forming a metal chloride having a small solubility product. The reaction of chlorine with the metal prevents it from corroding the aluminium-containing conductive film 20. <IMAGE>

Description

A METHOD OF MANUFACTURING SEMICONDUCTOR DEVICES The present invention relates to a method of manufacturing semiconductor devices, and more particularly to a method of manufacturing semiconductor devices having Al (aluminum or aluminum alloy) wiring layers.

As the materials of wiring layers and electrodes of a semiconductor integrated circuit device, a conductive thin film of aluminum (awl) aluminum - copper alloy (AlCu alloy) , AlCuSi alloy r or the like has been used.

In forming a conductive thin film pattern of aluminum.

aluminum alloy. or the like on the surface of a substrate. a process is performed by which a photoresist mask is patterned and the conductive thin film not covered with the mask is etched.

As reactive gas for dry etching aluminum. aluminum alloy, or the like. a gas or a mixed gas selected from a group of chlorine (Cl2) . boron trichloride (BC13). carbon tetrachloride (C1,), silicon tetrachloride (SiCI4) , and the like has been used because of their specific vapor pressures.

Aluminum (alloy) wiring is excellent in the point that it has a low resistance. Low resistance and long lifetime are necessary for the wiring layers of a semiconductor device. The lifetime of aluminum (alloy) wiring is largely dependent on electromigration and corrosion.

Figs is a schematic diagram showing an aluminum wiring on a semiconductor substrate. The surface of the semiconductor substrate 381 is an Si surface or an insulating layer. An Al layer 382 302 deposited deposited on the surface of such an underlying layer has a large number of grains 33 therein. A grain boundary 34 is formed between adjacent grains.

Electromigration of Al atoms is likely to occur particularly at grain boundaries and is a cause of breaking a wiring. It is known that an effective countermeasure for preventing an occurrence of electromigration is to increase the size of Al grains. In order to increase the size of Al grains, a substrate temperature when an Al layer is deposited by sputtering or the like has been set to about 200 to 350 C.

As the degree of integration of an integrated circuit has become high and the number of wiring layers of the circuit has increased, the thickness of a lower wiring layer has become thin. As the thickness of an Al wiring layer becomes thin, a density of current flowing in the Al wiring layer increases.

Therefore. electromigration of atoms pushed by electrons becomes likely to occur.

Electromigration causes an increased wiring resistance and at the worst breaking of the wiring layer. A conventional method of depositing an Al wiring layer is not sufficient for suppressing electromigration in a thin wiring layer.

After an aluminium film is etched and patterned, a protection film containing a large amount of chlorine atoms is formed on the side wall of the aluminium pattern.

Fig.9B of the accompanying drawings is a schematic diagram in section of an aluminium (alloy) film etched and patterned.

A side wall protection film (not shown) containing a large amount of chlorine (Cl) atoms is formed on the side wall of an aluminum (Al) wiring film 32 formed on an insulating film 381. If a wafer formed with such a protection film is exposed in the air, water contents (H20) in the air react with residual chlorine on the Al wiring film 32 to form hydrochloric acid which corrodes the Al wiring film 2. This phenomenon occurs not only during a manufacturing process but also after a semiconductor device is completed. More specifically, water contents may permeate into a semiconductor device during its operation, for example, from an interface between leads and the package. If the water contents reach an Al wiring film and react with chlorine. hydrochloric acid is generated.Therefore, it is desired to remove residual chlorine as much as possible in order to prevent corrosion of a wiring layer.

Conventional processes of preventing corrosion of aluminum wiring includes a pure water washing process, an acid/alkaline process, a passivation process by fluorine containing gas, and other processes.

As the pure water washing process. there are a process of mounting a plurality of wafers on a carrier and immersing them in pure water and a method of rotating each wafer held by a chuck and dropping pure water on it.

As the acid/alkaline process, there is a process of immersing a wafer in solution or dropping solution on a rotating wafer. The solution is acid solution or alkaline solution. The acid solution may be a mixed solution of isopropyl alcohol (IPA) and nitric acid or phosphoric acid, and the alkaline solution may be ammonium or choline. There is another process of exposing a wafer in sprayed acid/alkaline solution. In either process, a rinsing process is required thereafter so as not to leave chemicals.

As the passivation process using fluorine containing.

gas, there is a process of exposing a wafer in a gas of carbon tetrafluoride (CF < ) or a mixed gas of carbon tetrafluoride (CF < ) and fluoroform (CHF3) and irradiating plasma to the wafer. The reason of an improved corrosion resistance by this process is presumably a replacement of residual chlorine by fluorine or a hydrophobic wafer surface because of a formation of fluorocarbon (CF) polymer by fluorine and therefore a prevention of contact of aluminum with water contents.

However, elimination of residual chlorine (Cl) is insufficient even if such a process of preventing corrosion of an etched and patterned aluminum film is performed. It is necessary to suppress corrosion much greater than conventional.

Alloy such as aluminum - copper in particular is likely to be corroded by the voltaic cell effect. With the voltaic cell effect of metals such as aluminum alloy, the metals are corroded by a potential difference generated by a contact of different metals or by a potential difference generated by composition fluctuation (irregularity) on a metal surface. Corrosion prevention is very important to improve device performances.

According to one aspect of the present invention.

there is provided a method of manufacturing a semiconductor device. The method includes the steps of: placing a substrate on substrate holding means installed in a vacuum chamber, for preparation of forming an Al or an Al alloy wiring layer on the substrate; and first depositing a first wiring sub-layer formed of Al or Al alloy on the substrate without intentionally heating the substrate, and from midst of deposition, depositing a second wiring sub-layer formed of Al or an Al alloy as a main composition on the first wiring sub-layer with the substrate being heated.

Since the Al (or Al alloy) layer is deposited first without heating the substrate, the Al layer having a strong tendency of exhibiting (1 1 1) plane ([1 1 1] orientation) can be formed. An Al (or Al alloy) layer having a strong tendency of exhibiting the (1 1 1) plane has a high resistance to electromigration, although the size of grains of the Al layer deposited without heating the substrate is small. It is known that a small grain size is likely to generate electromigration.

By heating the substrate in the midst of Al layer deposition, it becomes possible to increase the grain size while inheriting the strong tendency of the (1 1 1) plane orientation of the underlying layer. If an Al layer is deposited by heating a substrate over the whole period of the deposition process, a strong tendency of the (1 1 l) plane orientation does not appear. However, if an Al layer is deposited on the surface of an underlying Al layer having a strong tendency of exhibiting the (1 1 1) plane, the final Al layer has a strong tendency of exhibiting the (1 1 1) plane even if the substrate is heated at the later deposition process.

In the manner described above, it is possible to deposit an Al layer having a large grain size and a strong tendency of exhibiting the (1 1 1) plane. Accordingly, generation of electromigration can be sufficiently suppressed even if the thickness of an Al film is small.

Furthermore, the deposition without heating a substrate and the deposition with the substrate being heated can be continuously performed in the same vacuum chamber, thereby maintaining a high throughput without increasing the number of processes.

Generation of electromigration can thus be suppressed effectively even if the thickness of an Al film is small.

According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device. The method includes the steps of: forming a metal film of Al or Al alloy on the surface of an insulating film over a substrate; dry-etching and patterning the metal film by using chlorine-based gas to form a metal wiring pattern; and heating the substrate formed with the metal wiring pattern in vacuum to dissociate or release chlorine attached to the metal wiring pattern. The method may include the step of forming an oxide film on the metal wiring pattern by contacting dehumidified oxygen to the metal wiring pattern, after the heating step.

A metal film containing aluminum is dry-etched and patterned by using chlorine-based gas to form a metal wiring pattern. Thereafter, the substrate with the metal wiring pattern is heated in vacuum without exposing it to the air, to thereby release or desorb chlorine attached to the metal wiring.

pattern. The wafer is further subjected to contact with dehumidified oxygen to form a good oxide film on the surface of the metal wiring pattern. A resistant to corrosion is improved and a wiring layer is prevented from being broken.

According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device which includes the steps of: etching and patterning a conductive film by using chlorine-based gas, the conductive film being made of aluminum or aluminum alloy and deposited on the surface of an insulating film formed over a substrate; and exposing the substrate with the conductive film to a reaction solution containing metal capable of reacting chlorine and forming metal chloride having a small solubility product.

The metal is, for example, silver or lead. The reaction solution is, for example, silver nitrate aqueous solution or lead nitrate aqueous solution.

The method may include the step of exposing the substrate to an dissociation solution capable of dissociating or desorbing silver chloride or lead chloride left on the substrate by changing the silver chloride or lead chloride to silver complex ions or lead complex ions, after the step of exposing the substrate to the reaction solution.

An etched wiring pattern made of aluminum or aluminum alloy is post-processed by the reaction solution containing a metal capable of reacting chlorine and forming metal chloride having a small solubility product constant. The metal is, for example, silver or lead. The reaction solution is, for example, silver nitrate aqueous solution or lead nitrate aqueous solution.

Chlorine ions react with metal ions in the reaction solution to form insoluble precipates. Accordingly, chlorine ions are made inactive to stop corrosion of a wiring pattern made of aluminum or aluminum alloy, thereby improving the reliability of the semiconductor device with such a wiring pattern.

As described above, a wafer with a wiring pattern is post-processed by an-aqueous solution containing a metal which forms metal chloride having a small solubility product.

Therefore, it is possible to remove residual chlorine on the side wall of an aluminum (alloy) wiring pattern by metal ions and to suppress corrosion of the wiring pattern and improve the performance of the device.

It will be seen that certain embodiments in accordance with the present invention can provide: a method of forming an Al wiring layer capable of suppressing electromigration even with a thin Al wiring layer; a method of manufacturing a semiconductor device capable of preventing an Al wiring layer from being broken (open-circuited) by corrosion; and a method of manufacturing a semiconductor device capable of reducing residual chlorine near the side wall of an Al wiring pattern as much as possible.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which: Fig.l is a schematic diagram of a sputtering system used for forming an Al wiring layer according to an embodiment of this invention.

Figs.2A and 2B are graphs showing a change with time in the resistance values of Al wiring layers formed by a conventional method and an embodiment method of this invention.

Fig.3 is a cross sectional view of a DRA~I manufactured by using the method of forming an Al wiring layer according to an embodiment of this invention.

Fig.4 is a schematic diagram showing a system used for dry etching an Al film and forming an oxide film.

Fig.5 is a schematic diagram showing another system used for dry etching an Al film and forming an oxide film.

Fig.6 is a schematic diagram showing still another system used for dry etching an Al film and forming an oxide film.

Figs.7A to 7D are cross sectional views explaining a method of manufacturing a semiconductor device according to an embodiment of this invention.

Fig.8 is a schematic diagram showing a system used for manufacturing a semiconductor device of the embodiment shown in Figs.7A to 7D.

Figs.9A and 9B show the structure of an Al layer of a conventional semiconductor device and a cross sectional view explaining corrosion state.

It is generally known that electromigration becomes hard to occur as a grain size becomes large. The reason is presumably that electromigration occurs mainly at grain boundaries. It is also known that electromigration in Al is hard to occur if there is a strong tendency of exhibiting the (1 1 1) plane of Al crystals. A paper by Vaidya, S. and Sinha, A.K. (Thin Solid Films, 15 (1981) pp 253-259), reports that a mean time to failure (MTF) of an Al wiring layer is given by: (s/a2) log (IClll,/IC200,)3 where s is an average grain size, a2 is a variance of grain sizes, and I111) and Ic200, are X-ray diffraction intensities of the (1 1 1) and (2 8 ) planes, respectively.

In order to prolong MTF of an Al wiring layer, the grain size is therefore increased and the tendency of exhibiting the (1 1 1) plane is made strong.

Fig.l is a schematic diagram of a sputtering system used for forming an Al wiring layer according to an embodiment of the invention. A substrate holder 4 is mounted on a side wall of a vacuum chamber 1. In forming a film, a substrate 3 on which a film is formed, is fixed to a substrate holding surface of the substrate holder 4. A cavity with an inlet port and an outlet port is formed in the substrate holder 4 so as to flow Ar gas through the cavity. For example. the substrate 3 held by the substrate holder 4 can be heated by flowing heated Ar gas through the cavity.

A target holder 5 is mounted on the side wall of the vacuum chamber 1 opposite to the substrate holder 4. In forming a film, a sputtering target 2 is fixed to a target holding plane of the target holder 5. In sputtering an Al wiring layer, an Al disk is used as the target 2. In forming a film, sputtering gas such as Ar gas is introduced via a sputtering gas guide pipe into the vacuum chamber 1 and exhausted via a drain pipe to maintain the inside of the vacuum chamber 1 to have a predetermined pressure. As a DC voltage is applied between the substrate holder 4 and the target holder 5, electric discharge occurs in the vacuum chamber 1. Since a negative potential is applied to the target holder 5, Ar ions collide with the target 2 and Al is sputtered.

Next, a method of forming an Al wiring layer according to an embodiment of the invention will be described.

As the substrate 3 on which an Al wiring layer is formed, a Si substrate with a barrier metal lamination film of a Ti layer and a TiN layer formed on the surface thereof was used.

An Al layer on a TiN layer is generally difficult to have a strong tendency of exhibiting the (1 1 1) plane. First, an Al layer having a thickness of 2 nm was deposited by a sputtering process on the surface of the Ti/TiN lamination layer, without heating the substrate 3. Thereafter, the substrate 3 was heated by flowing Ar gas heated to 350 C through the cavity of the substrate holder 4. The substrate temperature was raised to about 350 C in about 5 seconds. An Al layer was deposited to a thickness of 300 nm while heating the substrate 3. Also, during the temperature rise, sputtering was continued. It is sufficient if the substrate temperature reaches 35 C when the deposition is completed.Although the total width of the Al film is 500 nm, any total thickness width may be selected.

Figs.2A and 2B are graphs showing a change with time in the resistance values of Al wiring layers. The graph of Fig.2A shows a change in the resistance values of 1 wiring patterns having a thickness of 35 nm and formed by a conventional sputtering process while setting the substrate temperature to 358 OC, and the graph of Fig.2B shows a change in the resistance values of Al wiring patterns formed by sputtering Al to a thickness of about 158 nm without heating the substrate and thereafter by sputtering Al to a thickness of about 288 nm after the start of heating the substrate toward 358 OC. The abscissa represents a lapse of time in the unit of hour after the start of measurement, and the ordinate represents a resistance in the unit of fl. The width of each Al wiring pattern was 2 m, the length was 800 tim. and a current density was 2 x lO A/cm2.

As seen from the graph of Fig.2A, the resistance value of each Al wiring pattern sample formed by a conventional sputtering process increased greatly as the time lapsed, although there was a resistance variation between samples.

Assuming that a sample having a resistance increase b 10% or more of the initial resistance value is defective. about 40% of all the samples became defective in 588 hours.

As seen from the graph of Fig.2B. the resistance value of each Al wiring pattern sample formed by an embodiment method scarcely increased as the time lapsed. There was no defective sample even after a lapse of 1288 hours after the measurement start.

The sizes of grains on the surfaces of Al wiring patterns formed by a conventional process and an embodiment process were 2.76 m and 2.7 tim, respectively. Each Al wiring pattern formed by a conventional process had a relatively large grain size because the substrate was heated continuously over the whole period of the process. Each Al wiring pattern formed by an embodiment process might possibly have a small grain size because the substrate was not heated at the initial stage of the process. However, because the substrate was heated from the midst of the process, the grain size became large generally the same as that of the wiring pattern formed by the conventional process.

The (1 1 1) crystal planes of Al wiring patterns formed by the conventional process and the embodiment process were measured by X-ray diffraction. Peaks indicating the (1 1 1) crystal planes were 1518 cps in the case of the conventional process, and 710 cps in the case of the embodiment process. It can be understood that the Al wiring layer formed by the embodiment process has a strong tendency of exhibiting the (1 1 1) plane much greater than by the conventional process.

This phenomenon can be hypothesized as in the following.

If an Al layer is deposited while the substrate is heated, the tendency of orientating the (1 1 1) plane on the surface becomes weak although the grain size becomes large. On the other hand, if an Al layer is deposited without heating the substrate. the Al layer having a strong tendency of orientating the (1 1 1) plane is formed although the grain size becomes small. If the substrate is heated thereafter in the midst of deposition, a large grain size can be obtained while inheriting the strong tendency of orientating the (1 1 1) plane. In this manner, an Al wiring layer having a strong tendency of orientating the (1 1 1) plane and a relatively large grain size can be obtained.

With this embodiment, the deposition without heating a substrate and the deposition with the substrate being heated can be continuously performed in the same vacuum chamber. thereby maintaining a throughput similar to a conventional process without increasing the number of processes.

In the above embodiment, Ar gas for heating a substrate is set to a temperature of 350 OC. The temperature may be 380 OC or higher. and is preferably X OC or lower because 1 melts at a temperature higher than 408 OC.

It is preferable to set a thickness of an Al wiring layer deposited without heating a substrate to 28 to 50%, or more preferably 38 to 50%. of the total thickness of a final Al wiring layer.

In the above embodim2nl, although DC sputtering is used for the sputtering process, other sputtering processes may also be used with similar expected effects. such as DC magnetron sputtering, RF sputtering, and RF magnetron sputtering.

In the above embodiment, an Al wiring layer deposited on a Ti/TiN lamination layer has been described. An Al wiring layer may be deposited on other layers such as a barrier metal layer and an insulating layer, while achieving similar expected effects. The invention is particularly effective for depositing an Al wiring layer on a layer which is hard to give the Al wiring layer a strong tendency of exhibiting the (1 1 1) plane if the substrate is heated over the whole period of the process.

Fig.3 is a partial cross sectional view of a DRAM manufactured by using a method of forming an Al layer according to an embodiment of the invention.

A field oxide film 13 selectively formed on the surface of a p-type silicon substrate 1 surrounded and defines an active region. Over the surface of the active region, a gate electrode 14 is formed with a gate oxide film interposed therebetween. On both the sides of the gate electrode 14, n'- type source and drain regions 11 and 12 are formed.

A bit line 16 is disposed on the source region 11.

The bit line 16 is formed. for example, by a laminated structure of a tungsten silicide layer on a polycrystalline silicon layer.

An electrode 17 of a storage capacitor is connected to the drain region 12. A counter electrode 18 is formed facing the electrode 17, with a thin insulating film interposed therebetween. These electrodes 17 and 18 are made of, for example, polycrystalline silicon. Instead of a single layer fin structure of the capacitor electrodes, a two- or multi-layer fin structure or other capacitor structures may also be used.

Over the surface of the silicon substrate, an interlayer insulating film 15 of SiO2 iS formed burying the bit line 16, gate electrode 15, and storage capacitor. A contact hole (via-hole) is formed in the interlayer insulating film 15 at the position corresponding to the bit line 16. A first layer Al wiring pattern is electrically connected to the bit line 16.

The first layer Al wiring pattern is made of a barrier metal lamination film 19 of a TiN layer on a Ti layer and an Al layer 28. The Ti layer has a thickness of, for example, 28 nm, and the TiN layer has a thickness of, for example, 188 nm. The Al layer 28 is formed by the above-described embodiment process, and has a thickness of, for example, 588 nm. Interlayer insulating films 21 and 22 are formed burying the first layer Al wiring pattern 28. The first layer Al wiring pattern 28 is connected via a contact hole formed in the interlayer insulating films 21 and 22 to a second layer Al wiring pattern 23 having a thickness of, for example, 1 tim.

The first Al wiring pattern 28 is thinner than the second layer Al wiring pattern 23, and therefore has a higher current density. However, the first layer Al wiring pattern formed by the above-described embodiment process can suppress an occurrence of electromigration.

The underlying layer of the second layer Al wiring pattern 23 is the interlayer insulating film or first layer Al wiring pattern, so that a TiN layer as a barrier metal layer is not necessarily required to be formed. It is preferable to form a Ti layer having a thickness of, for example, about 38 nm under the second layer Al wiring pattern. On the Ti layer, an Al layer having a strong tendency of exhibiting the (1 1 1) plane can be formed even if the substrate is heated over the whole period of the deposition process. If a barrier metal lamination layer of a Ti layer and a TiN layer is formed under the second layer Al wiring pattern, a resistance to electromigration is improved.In this case, the second layer Al wiring pattern is preferably formed like the first layer Al wiring, by depositing to 38 to 5004 of the total thickness without heating, and thereafter depositing the remainder while heating the substrate.

In this embodiment, Al is used for wiring layers. A material essentially consisting of Al, i.e. containing Al as its main composition and a small amount of other metal(s) and/or semiconductor material, may be used. For example, a wiring layer may be made of Al with 1% Si, Al with 1% Si and 0.5% Cu, Al with 1% Ti, or Al with 1% Si and 8.5 Ti.

The lifetime of an Al wiring layer is dependent on corrosion as well as electromigration. Corrosion is supposed to be generated mainly by water contents permeating into an Al wiring layer from the outside of the device under operation.

Corrosion is accelerated if chlorine or the like is resident on the surface of an Al wiring layer, because chlorine or the like reacts with water contents to generate HCl or other compounds.

Next, a method of preventing corrosion of an aluminum wiring layer according to an embodiment of the invention will be described.

Fig.4 shows the structure of a system in which an aluminum film etching process and an oxidation process are performed in the same vacuum chamber. In Fig.4, reference numeral 181 represents a vacuum chamber, reference numeral 182 represents an etching gas supply port, reference numeral 183 represents an exhaust port connected to a vacuum pump (not shown), reference numeral 184 represents an oxygen supply port, reference numeral 185 represents a dehumidifier in which silica gel, activated alumina, or the like is loaded, reference numeral 186 represents an electrode for applying an RF power generated by an RF power source 187, and reference numeral 188 represents a chuck for holding a wafer. The chuck 188 is formed with a gas passage so as to heat or cool it.

A wafer is held by the chuck 188 in the vacuum chamber 181. The wafer is prepared by forming an insulating film on a substrate. forming an aluminum film on the insulating film, and forming a resist film pattern corresponding to a wiring pattern by lithography. After the inside of the vacuum chamber 181 is evacuated via the exhaust port 183, chlorine-based gas is introduced into the vacuum chamber 181 via the gas supply port 182. The chlorine-based gas is, for example. a mixed gas of chlorine and boron chloride (BCl3), a mixed gas of chlorine and silicon chloride (SiCl < ), a mixed gas of chlorine and hydrogen bromide (HBr), or a mixed gas of chlorine and boron bromide (BBr).Thereafter, an RF power generated by the RF power source 187 is applied to the electrode 186 to generate plasma of the introduced chlorine-based gas. The aluminum film is etched by plasma of the chlorine-based gas to form an aluminum wiring pattern.

After the etching, the vacuum is maintained, the wafer is pushed up by pins mounted on the chuck 188, and the temperature of the chuck is raised to about 588 OC. Next, the wafer is brought down onto the chuck 188 heated to about 588 OC, and stayed thereon for a short time period of about 1 second to heat it. Chlorine attached to the wafer surface is therefore desorbed and removed therefrom. The wafer is preferably heated at about 188 - 658 OC and for about 5 - 68 seconds. The ambient vacuum may be 188 Pa or less.

Next, the temperature of the chuck 188 is lowered by cooling it by gas. The vacuum pump is stopped, and oxygen gas dehumidified by the dehumidifier 185 is introduced from the oxygen supply port 104 into the vacuum chamber 181 to form an oxide film on the surface of the aluminum wiring pattern.

In the above embodiment, the etching, heating, and oxidizing processes are performed in the same chamber. Two or more chambers may also be used instead.

Fig.5 shows a system in which an etching vacuum chamber and an oxidizing vacuum chamber are provided separately.

In Fig.5, similar elements to those shown in Fig.4 are represented by using similar reference numerals. In Fig.5, reference numeral 111 represents an etching vacuum chamber, reference numeral 112 represents an oxidating vacuum chamber, and reference numeral 113 represents a gate valve.

After the etching in the etching vacuum chamber 111, the gate valve 113 is opened and the wafer is transported to the oxidating vacuum chamber 112 to oxidize the surface of an aluminum wiring pattern. The heating process for removing chlorine attached to the surface of the Al wiring layer may be performed either in the etching vacuum chamber 111 or in the oxidizing vacuum chamber 112.

Fig.6 shows the structure of another system in which the heating process is performed in another chamber. In Fig.6, similar elements to those shown in Figs.4 and 5 are represented by using similar reference numerals.

Another vacuum chamber 116 is installed between an etching vacuum chamber 111 and an oxidizing vacuum chamber 112 similar to those shown in Fig.5. This vacuum chamber 116 has a hot plate 114 equipped with heating means and a cold plate 115 equipped with cooling means. After the etching in the etching vacuum chamber 111, the wafer is transported onto the hot plate 114 to heat it and remove chlorine. Next, the wafer is transported onto the cold plate 115 to coo it, and thereafter the wafer is transported to the oxidating chamber 112 to form an oxide film on the surface of the aluminum wiring pattern.

The above embodiments use an aluminum wiring layer containing Al 100%. Other aluminum wiring layers essentially consisting of Al and including a small amount of other metal and/or semiconductor material are widely used in order to improve a resistance to stressmigration and electromigration.

For example, they are Al with 1% silicon, Al with 1% silicon and 8.5 copper, and Al with 1% titanium. The above embodiments are effective for such aluminum alloy wiring layers. If a metal, particularly copper, is contained in an aluminum alloy to improve a resistance to migration, there is a large difference of ionization tendency between copper and aluminum. so that the voltaic cell effect is generated and corrosion is likely to occur.

As an underlying material of an aluminum wiring layer, refractory metal, refractory metal nitride, and refractory metal oxynitride, such as titanium nitride, are widely used mainly for improving a resistance to migration. Also in such a case, the voltaic cell effect is generated and corrosion is likely to occur. The effects of the embodiments are expected to be more distinct in such a case where an aluminum wiring layer forms the voltaic effect in combination with the underlying or overlying adjacent layer.

The above embodiments may be applied not only to an etching process using chlorine-based gas but also to an etching process using halogen-based gas.

Another embodiment will be described in which residues on a wiring layer or the like left during an etching process are reliably removed.

Figs.7A to 7D are cross sectional views explaining a patterning process of an aluminum film or an aluminum alloy film according to an embodiment of the invention. A pattern made of aluminum or aluminum alloy is used as a wiring pattern or an electrode of a semiconductor device.

In the following description, although only an aluminum alloy film is used, the operation and effect of the embodiment are generally applicable also to an aluminum film.

First, an aluminum alloy film is formed to a thickness of 8.5 to 1.2 tim on the surface of an insulating film on a semiconductor wafer. The aluminum alloy film may be made of Al Cu, Al-Cu-Si, or another alloy. A resist pattern is formed on the aluminum alloy film to dry-etch and remove the aluminum alloy film not covered with the resist pattern.

For this dry etching, a mixed gas of, for example, BCl3, Cl2, and SiC14 is used as etching gas, and anisotropic etching with less side etching such as reactive ion etching (RIE) is performed. The cross section after this etching is shown in Fig.7A.

In Fig.7A, an insulating film 211, an aluminum alloy film 212, and a resist pattern 213 respectively after the etching are shown.

During the etching process of the aluminum alloy film 212, a side wall protection film 214 is attached to the patterned side wall of the aluminum alloy film 212, the side wall protection film 214 containing a large amount of All3, Cl2. and the like generated during the etching process. The side wall protection film 214 functions to prevent side etching during the etching process. The thickness of the side wall protection film 214 is about 28 nm. The thickness changes also with a process temperature, and it increases as the temperature becomes lower.

After the aluminum alloy film 212 is patterned, the resist pattern 213 is ashed, for example. by 2 plasma as shown in Fig.7B. As shown in Fig.8, an etching chamber 228 and an ashing chamber 222 are coupled by a load-lock 224 which can maintain vacuum of the interiors of the chambers 228 and 222.

An etching process of patterning the aluminum alloy film 212 is performed in the etching chamber 228, for example, by RIE.

After this etching, the etching gas in the etching chamber 228 is exhausted, and the wafer is transported via the load-lock 224 to the ashing chamber 222. O2 gas is introduced into the ashing chamber 222 to ash the resist pattern 213. After the resist ashing, the wafer with the insulating film 211 and aluminum alloy film 212 is taken out of the ashing chamber 222.

Next. as shown in Fig.7C, the wafer with the insulating film 211 and aluminum alloy film 212 is immersed in silver nitrate (AgN03) aqueous solution 215. The silver nitrate aqueous solution 215 may also be sprayed over the aluminum alloy film 212.

As the aluminum alloy film 212 is immersed in the silver nitrate aqueous solution 215, a reaction given by the following equation (1) occurs by which chlorine ions (Cl-) in the side wall of the aluminum alloy film 212 are picked up by silver ions (Ag+). The reaction byproduct is precipitated.

Ag + Cl 4 AgCl L ... (1) As shown in Fig.7D, as the aluminum alloy film 12 with residual chlorine is immersed in the silver nitrate aqueous solution 215, silver ions (Ag-) react with chlorine ions (Cl ions) and whitish precipitates of silver chloride (AgCl) are formed. Silver chloride (AgCl) transfered from chlorine and silver ions is inactive. In this manner, by using silver nitrate aqueous solution (AgNO3) 215, as a solution containing silver (Ag), residual chlorine can be made completely inactive.

Use of the silver nitrate aqueous solution (AgNO3) 215 as the solution containing silver (Ag) is also advantageous in the following points.

Specifically, after the etching process of the aluminum alloy film 212, a process using nitric acid (HNO3) is often performed. In such a case, if silver nitrate aqueous solution is used in place of nitric acid, the effects of nitric acid and the effects of corrosion prevention are both obtained and the processes can be simplified.

A process using nitric acid (HNO3) after an etching process is performed in order to float polymer film over the aluminum alloy layer 212 and remove it and in order to prevent corrosion of the aluminum alloy film 212 by a formation of an oxide film. The polymer film constitutes a side wall protection film during anisotropic etching and contains substances of resist.

After the silver nitrate aqueous solution process, a washing process with pure water is performed. Only a small amount of silver chloride (AgCl) dissolves in pure water at a room temperature, say 1.5 x 18-3g per 1 litter, and it is chemically stable. Even if a very small amount of silver chloride is left on the side wall after the pure water washing or rensing process, silver chloride as whitish precipitates is very inactive as compared to residual chlorine (Cl). Such whitish silver chloride precipitates rarely generate corrosion of the aluminum alloy film 212 and no voltaic cell effect is generated.

As described above, in the semiconductor device manufacturing method of this embodiment, the aluminum alloy film 212 after resist ashing is immersed in the silver nitrate aqueous solution 215. It is therefore possible to react residual chlorine (Cl) on the side wall of the aluminum alloy film 212 with silver ions (Ag-). Corrosion of the aluminum alloy film 12 can be suppressed and the device performance can be improved.

In the above description, although the silver nitrate aqueous solution 215 is used as a solution containing silver ions (Ag+), it is obvious that the solution containing silver ions is not limited to the silver nitrate aqueous solution 215.

For example, if alkaline is added to silver nitrate aqueous solution, dark brown silver oxide. is precipated by the reaction given by the following equation (2). Silver oxide dissolves much in water, and the water becomes strong alkalic. Aqueous solution containing silver hydroxide (AgOH) changed from silver oxide may be used instead of silver nitrate aqueous solution.

2 Ag- + 2 OH- # 2 AgOH # Ag2 + H2O ... (2) Further, instead of a solution containing silver ions (Ag-) which has [Ag-][Cl-] solubility product of about 1.1 x 10-10 (18 C), an aqueous solution containing a metal which forms metal chloride having a small solubility product may also be used. It is preferable that the solubility product is less than 1 x l-1, and more preferably is 1 x 10-3 or less. For example, lead nitrate aqueous solution containing lead ions (Pb+) which has [Pb2-][Cl-]2 solubility product of about 2.4 x 1-4 (room temperature), instead of silver ions (Ag-), may be used to crystallize residual chlorine (Cl) into whitish lead chloride (PbCl2) precipates and to prevent corrosion of the aluminum alloy film 212.

Silver chloride or lead chloride may be left on a substrate (wafer). If such materials are not suitable to be left from some reasons, they can be removed by either of the following methods (i) and (ii).

(i) AgCl reacts with ammonium hydroxide solution (NH < OH) by the following equation (3) and is dissolved by forming complex ions. AgCl can therefore be released from a substrate (wafer).

AgCl + 2 NH < OH 4 (Ag(NH3)2)Cl + 2 H20 ... (3) where (Ag(NH3)2)Cl is achromatic.

A wafer is processed by AgNO3 and by ammonium hydroxide solution to progress the reaction given by the equation (3). In this manner, AgCl can be dissolved in ammonium hydroxide solution.

Similarly, lead chloride is dissolved in ammonium hydroxide solution to form complex ions to thereby remove lead chloride from a substrate (wafer).

Na2S203 solution instead of ammonium hydroxide solution may be used for dissolving silver chloride and lead chloride as complex ions. Ammonium hydroxide solution is more effective because it does not contain sodium and the performance of a semiconductor device is not degraded unnecessarily.

(ii) A wafer is processed by 1% gelatin solution just before it is processed by AgNO3, and thereafter the wafer is processed by AgNO3 solution added with 1% gelatin. In this manner, residual silver chloride on the wafer can be removed.

Patterning and post processes for an aluminum alloy film have been described above. Similar operation and effects can be expected also for an aluminum film.

Claims (21)

CLAIMS:

1. A method of manufacturing a semiconductor device comprising: etching and patterning a conductive film by using a gas containing chlorine, said conductive film being made of aluminium or aluminium alloy and deposited on the surface of an insulating film formed on a substrate; and exposing said substrate with said conductive film to a reaction solution containing a metal capable of reacting with chlorine and forming a metal chloride having a small solubility product.

2. A method as claimed in claim 1, wherein said metal is silver or lead.

3. A method as claimed in claim 2, wherein said reaction solution is silver nitrate aqueous solution or lead nitrate aqueous solution.

4. A method as claimed in claim 2 or claim 3, further comprising the step of exposing said substrate to a releasing solution capable of releasing silver chloride or lead chloride left on said substrate by changing said silver chloride or lead chloride to silver complex ions or lead complex ions, after said step of exposing said substrate to said reaction solution.

5. A method as claimed in claim 4, wherein said releasing solution contains ammonium hydroxide or Na2S203.

6. A method of manufacturing a semiconductor device, comprising depositing on a substrate a wiring layer comprising Al, said wiring layer being first deposited without said substrate being heated and subsequently with said substrate being heated.

7. A method of manufacturing a semiconductor device comprising: depositing a first wiring sub-layer containing Al as the main component on a substrate without heating said substrate, and then depositing a second wiring sub-layer containing Al as the main component on said first wiring sub-layer whilst heating said substrate.

8. A method as claimed in claim 7 or claim 8, wherein said substrate is placed on substrate holding means installed in a vacuum chamber.

9. A method as claimed in claim 8, wherein heated gas is fed through a cavity in said substrate holding means after said first wiring sub-layer has been deposited to a first thickness.

10. A method as claimed in claim 9, wherein said heated gas has a temperature of 300 to 400"C.

11. A method as claimed in claim 9 or claim 10, wherein said heated gas is Ar gas.

12. A method as claimed in any preceding claim, wherein said substrate includes a surface TiN layer.

13. A method as claimed in claim 12, wherein a Ti layer is formed between said TiN layer and the surface of said substrate.

14. A method as claimed in any preceding claim, wherein said first and second wiring sub-layers are deposited by sputtering.

15. A method as claimed in any preceding claim, wherein said substrate is heated after said first wiring sub-layer is deposited to a thickness 20 to 50W of the total thickness of said first and second wiring sub-layers.

16. A method as claimed in claim 15, wherein said substrate is heated after said first wiring sublayer is deposited to a thickness 30 to 50k of the total thickness of said first and second wiring sub-layers.

17. A method of manufacturing a semiconductor device comprising: forming a film of Al or Al alloy on the surface of an insulating film on a substrate'.

dry-etching and patterning said Al or Al alloy film by using gas containing chlorine to form a metal wiring pattern; and heating said substrate formed with said metal wiring pattern in vacuum to release chlorine attached to said metal wiring pattern.

18. A method as claimed in claim 17, further comprising the step of forming an oxide film on said metal wiring pattern by contacting said metal wiring pattern with dehumidified oxygen after said heating step.

19. A method as claimed in claim 17 or claim 18, wherein said heating step is performed at a temperature in the range of 180 to 6500C for a time in the range of 5 to 60 seconds.

20. A method of manufacturing a semiconductor device substantially as hereinbefore described with reference to Figures 1-3, 4-6 or 7 and 8 of the accompanying drawings.

21. A semiconductor device manufactured by the method of any one of the preceding claims.