JPH05114573A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To form connecting holes with high precision without etching away an underneath Al film at all in the case of making the connecting holes on an Al wiring by a method wherein an insulating film is etched away at an etching rate in a range lower than that of the Al at the pressure not exceeding a specific value. CONSTITUTION:A W film 103 is formed on an Al thin film 102. Next, the W film 103 and the Al film 102 are successively etched away using resist patterns 104, furthermore, after removing the resist patterns 104, a silicon oxide film 105 is formed. Next, the silicon oxide film 105 is etched away at the pressure not exceeding 100mTorr using the resist patterns 106 on the silicon oxide film 105 and CHF3 or mixed gas of CHF3 and CO so as to form connecting holes 107. At this time, the etching step is stopped at the W film 103 so as not to etch away the Al film 102 at all. Through these procedures, the connecting holes 107 can be formed while sustaining the high precision.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of forming a contact hole in an insulating film on aluminum (Al) wiring.

[0002]

2. Description of the Related Art Conventionally, in a semiconductor integrated circuit, after opening an insulating film formed on a source / drain region of a silicon substrate, a gate electrode of polysilicon, etc., an insulating film is formed so as to fill the opening. An Al wiring is formed on the above to make contact with the above region and electrode. However, as the degree of integration has increased, multilayer wiring technology has come to be used,
It has become necessary to open a connection hole in the insulating film on the Al wiring.

In the process of forming a contact hole in a silicon oxide film used as an insulating film, RIE (Reactive Ion Ecthi) is used.
ng) method is used. In the step of opening the connection hole, a high selection ratio is required not only for the silicon substrate but also for polysilicon and Al.

Usually, in RIE of an oxide film, CF ₄ , CHF ₃ or the like is used as an etching gas. CF4 and C
HF3 is decomposed in plasma and CF _x radicals (x = 0
~ 3) are generated. CF _x radicals generated by decomposition in plasma are adsorbed on the surface and are decomposed by ion collision to generate F.

When the surface on which CF _x radicals are adsorbed is a silicon surface, Si and F react with each other to be released as SiF _x having a high vapor pressure. As a result, CF _x is drawn out of F and the ratio of C / F is increased to form a polymerized film, so that a polymerized film of CF _x is deposited on the silicon surface. In contrast oxide film, because oxygen Si and F is free in addition to leaving become SiF _x reacts reacts with C leaves become high CO vapor pressure, the polymerization film of CF _x is Not formed. Therefore, although the etching of the oxide film proceeds, the etching of silicon is suppressed by the CF _x polymerized film, and as a result, selective etching of the oxide film and silicon becomes possible. It is also reported that the addition reaction of hydrogen gas or carbon monoxide CO to the etching gas promoted the deposition reaction of the fluorocarbon polymer film, and that a selection ratio with silicon of 30 or more could be obtained.

On the other hand, the R of the via hole whose base is Al
Also in IE, Al did not contain oxygen that reacts with C like Si, and it was thought that the fluorocarbon polymer film was deposited on Al as well, and that it was possible to perform high-selectivity etching of the oxide film and Al. .. However, no attempt has been made yet to perform via hole RIE on the low-pressure side by magnetron RIE or the like, and it was not known whether the via hole could be opened with a sufficient selection ratio to Al.

[0007]

Conventionally, in RIE in which a contact hole is formed in an insulating film, a fluorocarbon polymer film is deposited on silicon when the base is silicon, and selective etching is possible because etching is suppressed. Yes, but the base is A
In the case of 1, it was not known whether or not the via hole could be opened while maintaining a sufficient selection ratio to Al, especially on the low pressure side.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method capable of obtaining a sufficient selection ratio even when a connection hole on an Al wiring is opened.

[0009]

Therefore, according to the present invention, a film made of a material having a high vapor pressure of fluoride is formed on an Al thin film, an insulating film is deposited on the film, and a gas containing carbon and fluorine is added. Using the pressure of 100 mTorr or less, the connection hole is opened by selectively etching the insulating film in a range in which the etching rate of the material is smaller than the etching rate of Al.

Desirably, any one of W, Si, Mo and C is used as the thin film made of a material having a high vapor pressure as a fluoride.

Preferably, the etching gas is C
HF ₃ gas or a mixed gas of CHF ₃ and CO is used.

[0012]

First, the principle of the present invention will be described.

A reactive gas containing at least C and F,
For example, when Si is exposed to CHF ₃ gas plasma, Si reacts with F to become SiF ₄ having a high vapor pressure, which is separated from the surface and etching proceeds. However, C remains on the surface and remains C
Combining with each other to form a fluorocarbon polymer film, S
Suppress i etching. On the other hand, S in CHF ₃ plasma
When exposed to iO ₂ , Si reacts with F to produce SiF _{4 and} is released. The remaining C reacts with O contained in SiO ₂ to become CO, which is vaporized and released. Therefore, it is known that a fluorocarbon polymer film is not formed on SiO ₂ and etching proceeds.

On the other hand, when Al containing no O was exposed to CHF ₃ plasma, it was considered that a fluorocarbon polymer film was formed on Al and was not etched. However, as a result of various experiments, it was found that a fluorocarbon film was not formed on Al. This causes Al to react with F to form stable aluminum fluoride. However, since the vapor pressure of aluminum fluoride AlF ₃ is extremely low, the Al surface is covered with stable aluminum fluoride, and C
This is also because the reaction of pulling F out of F _x stops. As described above, the etching rate of Al by CHF ₃ plasma depends on the pressure as shown in FIG. 3, and sharply increases as the pressure decreases. It is considered that this is because the fluorocarbon polymer film is not formed on the Al surface, and aluminum fluoride is sputter-etched due to the increase in ion energy accompanying the pressure decrease.

Next, when W, Mo, C, B, Se, N, Nb, Ta, and MoSi, which are fluorides having a high vapor pressure, are exposed to CHF ₃ plasma, a fluorocarbon film is formed on the surface, and the etching reaction occurs. It turned out to be suppressed.

On the other hand, fluorides such as Ti, Ni, Co, Cd, K, Au, Ag, Cu and T, which are compounds having a low vapor pressure, are obtained.
When e, Pd, Pt, and Fe are exposed to CHF ₃ plasma, a fluorocarbon polymer film is not formed on the surface, a fluoride layer is formed on the surface, and the etching rate rapidly increases as the pressure decreases.

The present invention has been made in view of this point. Since the conductive thin film having a high fluoride vapor pressure is formed on the Al thin film, the insulating film is formed on the upper layer of the conductive thin film. For example, when the connection hole is opened by CHF ₃ plasma etching, the Al thin film surface can be opened with good selectivity without etching. Further, when the underlayer is Al, it is apt to be redeposited on the side wall of the connection hole due to ion collision during overetching, but a fluorocarbon polymer film is formed on the material with high vapor pressure of fluoride formed on Al. Therefore, nothing is sputtered and redeposited on the side wall. The etching gas is CHF ₃
Other than these, CF ₄ , C ₂ H ₆ , CH ₂ F ₂ , C ₃ H _{8 and the} like may be used. When using a gas containing C, H, and F among these, CO gas may be added. In any case, the etching rate of Al is almost 0 in the range larger than 100 mTorr, but increases sharply at a pressure of 100 mTorr or less. On the other hand, the etching rate of W, Si, etc. increases with a decrease in pressure, but the rate of increase is small, and the etching rate decreases when CO gas is added (see FIGS. 3 and 5). Therefore, according to the present invention, the pressure of 100 mT can be obtained by adding CO gas.
Even in the region of orr or less, the Al surface can be better protected.

Further, in the etching for forming a contact hole in the insulating film on the Al thin film by using CHF ₃ plasma, the etching is performed under a pressure condition (80 to 300 mTorr) such that the generated aluminum fluoride is not sputter-etched. As a result, it is possible to suppress the etching of the Al thin film and etch it with good selectivity.

[0019]

Embodiments of the present invention will now be described in detail with reference to the drawings.

First, the etching apparatus used in the present invention will be described.

FIG. 1 shows this, and the magnetron R
IE device. This apparatus uses magnetron discharge, and includes a grounded vacuum container 10 forming a reaction chamber 11, and a sample support table equipped with a temperature control mechanism such as a cooling pipe 23 installed in the vacuum container 10. The lower electrode 20 which also serves as the lower electrode 20, the upper electrode 30 formed facing the lower electrode 20, and the exhaust system 13 for evacuating the inside of the vacuum container 10
And a gas introduction system 12 for etching the substrate 31 placed on the lower electrode 20.

The lower electrode 20 has a matching circuit 21.
Is connected to the power source 22 via the, and high frequency power of 13, 56 MHz is applied. Also the lower electrode 2
A copper plate 25 sandwiched by a polyimide thin film 24 is stuck on the surface of 0. By applying a voltage of 4 KV from a power supply 26 to the copper plate 25, the gas to be treated 31 is electrostatically adsorbed on the lower electrode. It is like this. Further, a magnetic field generator including a plurality of permanent magnets 14 and a drive mechanism 15 for the permanent magnets is installed above the upper electrode 30 to apply a magnetic field to the space between the lower electrode 20 and the upper electrode 30. Reference numeral 27 in the drawing denotes a gas introduction pipe for introducing gas into the back surface of the substrate 30 to be processed so as to conduct heat and control the substrate temperature.

As a first embodiment of the present invention, a process of forming a connection hole on an Al wiring using this apparatus will be described.

Here, the upper layer of the Al thin film is covered with a W film, patterned, a silicon oxide film is formed thereon, and a contact hole is formed by reactive ion etching using CHF _3. And a fluorocarbon polymer film is formed on the surface of the W film, and etching does not proceed,
Only the silicon oxide film is selectively etched.

First, as shown in FIG. 2A, an Al thin film 102 is formed on the silicon oxide film 101 covering the surface of the silicon substrate 100 by a sputtering method.

After this, as shown in FIG. 2 (b), this Al
A W film 103 is formed on the thin film 102 by 10 nm sputtering. Here, the W film has a thickness of 5 to 30 nm.

Next, as shown in FIG. 2C, a resist pattern 1 is formed on the W film 103 by photolithography.
To form 04.

Then, as shown in FIG. 2D, the W film 103 is etched by RIE using a mixed gas of CF ₄ and O ₂ with the resist pattern 104 as a mask, and then Al by RIE of Cl ₂ gas. The thin film 102 is etched.

Further, this resist pattern 104 is changed to O ₂
After removing by plasma etching, a silicon oxide film 105 is formed by plasma CVD using TEOS (Tetra Ethyl Ortho Silane) and O ₂ , as shown in FIG. 2 (e).

Subsequently, a resist pattern is formed on the silicon oxide film 105 (FIG. 2 (f)), and with this as a mask, CHF ₃ / C is used as a reactive gas using the apparatus shown in FIG.
The silicon oxide film 105 is etched at O = 45 SCCM / 133 SCCM, pressure of 40 mTorr and RF power of 800 W to form a connection hole 107. Here, the silicon oxide film 105 and W
The etching selection ratio of the thin film 103 is about 40, and the etching of the silicon oxide film 105 stops at the W thin film 103.
Al is not etched.

In this way, the connection hole can be formed while maintaining high pattern accuracy without etching the underlying Al.

Next, in order to investigate the relationship between the pressure and the etching rate, etching was performed while changing the pressure. Here, a mixed gas of CHF ₃ and CO is used as the reactive gas, and the gas flow rate is CHF ₃ / CO = 45/155 SCCM, R
F power was 800 W. The result is shown in FIG.

The etching rate of Al is 100 mTorr at a pressure.
Almost 0 in the larger range, but 100mTorr
It increases sharply in the pressure range below. At a pressure of 40 mTorr as shown in the above embodiment, Al will be etched. However, as shown by the dotted line in the figure, W increases the etching rate due to the decrease in pressure as in silicon, but the increase rate is small. From this also, it is understood that the Al etching is prevented by coating the Al surface with W.

The pressure dependence of the etching rates of silicon and carbon is also shown in the same figure, but the rate of increase is small although the etching rate increases with the decrease in pressure.

In the above embodiment, the surface of the Al film is covered with W, but the same effect can be obtained by using Si, C, Mo, MoSi films or the like.

In addition to these metal films, a C film, a polysilicon film or the like may be used. Further, in the above embodiment, the W thin film was formed on the Al thin film and then patterned, but the W thin film may be formed on the surface of the Al thin film by the selective CVD method after patterning the Al thin film.

Next, as a second embodiment of the present invention, Al
An example in which a C thin film 203 is used instead of W103 as a film covering the surface will be described.

First, as shown in FIG. 4A, an Al thin film 102 is formed by a sputtering method on a silicon oxide film 101 covering the surface of a silicon substrate 100, as in the above embodiment.

After this, as shown in FIG.
A C film 203 is formed on the thin film 102 by sputtering to have a thickness of 10 nm.

Next, as shown in FIG. 4C, a resist pattern 1 is formed on the W film 203 by photolithography.
To form 04.

Then, as shown in FIG. 4D, R using O ₂ gas is used with this resist pattern 104 as a mask.
After etching the C film 203 by IE, the Al thin film 102 is etched by RIE of Cl ₂ gas.

Further, the resist pattern 104 is CF
The resist is ashed by downflow using 4 and O ₂ . At this time, the C film is not etched at all (FIG. 4 (e)).

After this, as shown in FIG. 4 (f), TEOS
A silicon oxide film 105 is formed by plasma CVD using (TetraEthyl Ortho Silane) and O ₂ .

Subsequently, a resist pattern is formed on the silicon oxide film 105 (FIG. 4 (g)), and using this as a mask, the silicon oxide film is formed under the same conditions as in the above embodiment using the apparatus shown in FIG. 105 is etched to form a connection hole 107
Are formed (FIG. 4 (h)). Here, the silicon oxide film 10
5 and the C thin film 203 have an etching selection ratio of 40, the etching of the silicon oxide film 105 stops at the W thin film 203, and Al is not etched.

After that, the resist and the C film in the opening are removed by O ₂ plasma ashing, and the Al thin film 102 is removed.
Conduct electrical connection with (Fig. 4 (i)).

In this way, the connection hole can be formed while maintaining high pattern accuracy without etching the underlying Al.

Thus, according to the above embodiment, Al
Thin film of a material with high vapor pressure of fluoride on the thin film (W, C)
And forming a connection hole in the oxide film formed on the thin film by RIE using a mixed gas of CHF ₃ and CO gas in a pressure range of 1 to 100 mTorr without etching Al. it can.

In this example, as shown in FIG. 4 (i),
The resist and the C film in the opening were removed by O ₂ plasma ashing so as to establish electrical connection with the Al thin film, but they may be left if the reduction in contact resistance does not pose a problem.

Next, FIG. 5 shows the results of measuring the pressure dependence of the etching rate of Al when CHF ₃ gas was used. The etching rate of Al showed the same behavior as when a mixed gas of CHF ₃ and CO was used. Si and W, C
The etching rate was about twice as fast as when a mixed gas of CHF ₃ and CO was used, but the pressure dependence was low in all cases. The method of Example 1 and 2, but in which a mixed gas of CHF ₃ and CO using a CHF ₃ gas S
The same effect can be obtained by performing RIE of iO ₂ .

Although the etching rate of Al does not change by adding CO to CHF ₃ , the etching rates of Si, W, C, and Mo have a pressure dependency more than that in the case of using CHF ₃ gas. growing. Therefore S
If the pressure region where the etching rates of i, W, and C are low is used, the film thickness of Si, W, and C formed on the Al surface can be reduced.

Next, in order to confirm the function of the present invention, the surface condition after etching was measured.

First, a contact hole was formed by reactive ion etching using CHF ₃ and the surface condition after this etching was measured. First, the Si surface state is shown in FIGS.
FIG. 6 shows XPS (x-ra after etching at a pressure of 40 mTorr).
It is the C _1S signal of y photospectoro-scopy). CF, C
There are peaks indicating the signals of F2 and CF3. AE in FIG.
The depth direction analysis of S (Auge electron spectroscopy) is shown. It shows that there is a 5 nm C layer on Si. S
A fluorocarbon polymer film is deposited on the i surface, which suppresses etching.

Next, the pressure at which Al is etched is 40 mT.
FIGS. 8 to 12 show the Al surface state under the condition of orr and the pressure of 100 mTorr where Al is hardly etched. FIG. 8 shows XPS C _1S signals on the Al surface after etching at a pressure of 40 mTorr. C on Al surface
Has no bond with F. Fig. 9 shows A at this time.
It is a depth direction analysis of ES. The C layer on the Al surface is extremely thin, about 1 nm.

On the other hand, FIG. 10 shows an XPSC _1S signal on the Al surface after etching at a pressure of 100 mTorr. C is not bound to F. FIG. 11 shows the depth direction analysis of AES at this time. C is less than 1 nm. As a result, A
It can be seen that even in the case of a pressure of 100 mTorr where l is hardly etched, in the case of Si, a fluorocarbon polymer film, which is formed to a thickness of about 5 nm and suppresses etching, is not formed. FIG. 12 shows the XPSC _1S signal of the W surface etched at a pressure of 40 mTorr. It shows that the fluorocarbon polymer film is also deposited on the W surface.

Thus, in addition to W, Mo, C, MoS
It can be seen that a fluorocarbon polymer film is deposited on a material having a high vapor pressure of fluoride such as i. The etching rate of the material on which the fluorocarbon polymer film is deposited has little pressure dependency like Si, and the etching rate at a pressure of 100 mTorr or less is 20 nm / min or less.

As described above, according to the method of the present invention, it was confirmed that Al etching can be prevented by coating the Al surface with a material having a high vapor pressure of fluoride.

Next, as another example, in the etching for forming a contact hole in the insulating film on the Al thin film by using CHF ₃ plasma, the sputter etching rate of aluminum fluoride produced is zero or negligible. Bottom (80 ~
By performing etching at 300 mTorr), it is possible to perform etching with good selectivity while suppressing the etching of the Al thin film.

This method will be described with reference to FIG.

According to this method, a thin film of a material having a high vapor pressure of fluoride is not formed on the Al thin film to prevent the etching of Al, but under a high pressure such that the fluoride on the Al thin film is not sputter-etched. It is characterized in that the insulator is etched.

First, as shown in FIG. 13A, an Al thin film 102 is formed on the silicon oxide film 101 covering the surface of the silicon substrate 100 by a sputtering method.

After this, as shown in FIG.
A resist pattern 104 is formed on the thin film 102 by photolithography.

Next, as shown in FIG. 13C, using this resist pattern 104 as a mask, RI of Cl ₂ gas is used.
The Al thin film 102 is etched with E.

Further, the resist pattern 104 is changed to O ₂
After removing by plasma etching, TEOS (Tetra Ethyl Ortho Silane) and O ₂ are removed as shown in FIG.
Silicon oxide film 105 formed by plasma CVD using
To form.

Subsequently, a resist pattern is formed on the silicon oxide film 105 (FIG. 13 (e)). Using this as a mask, CHF3 gas is used as the reactive gas and the pressure is 100 mTorr using the apparatus shown in FIG. The silicon oxide film is etched (FIG. 13 (f)). At this time, the Al thin film 102 is not etched.

The present invention is not limited to the above embodiments. For example, a conductive thin film having a high vapor pressure of fluoride has a similar effect even when the above-mentioned W, Mo, B, Si or the like is ion-implanted on the Al surface. The reactive gas used for RIE of the oxide film may be a gas containing C and F, and CH ₂ F ₂ or CF ₄ + H ₂ gas can be used to obtain the same effect.

[0066]

As described above, according to the method of the present invention, when the connection hole is formed on the Al wiring, the underlayer A is formed.
It is possible to form a highly accurate connection hole without etching l.

[Brief description of drawings]

FIG. 1 is a view showing an etching apparatus used in a connection hole forming step according to an embodiment of the present invention.

FIG. 2 is a diagram showing a connection hole forming step according to the first embodiment of the present invention.

FIG. 3 is a characteristic diagram showing the relationship between pressure and etching rate.

FIG. 4 is a diagram showing a connection hole forming step according to the second embodiment of the present invention.

FIG. 5 is a characteristic diagram showing the relationship between pressure and etching rate.

FIG. 6 is a characteristic diagram showing a surface state after etching.

FIG. 7 is a characteristic diagram showing a surface state after etching.

FIG. 8 is a characteristic diagram showing a surface state after etching.

FIG. 9 is a characteristic diagram showing a surface state after etching.

FIG. 10 is a characteristic diagram showing a surface state after etching.

FIG. 11 is a characteristic diagram showing a surface state after etching.

FIG. 12 is a characteristic diagram showing a surface state after etching.

FIG. 13 is a diagram showing a connection hole forming step of another example.

[Explanation of symbols]

 100 Silicon Substrate 101 Silicon Oxide Film 102 Al Thin Film 103 W Thin Film 104 Resist Pattern 105 Silicon Oxide Film 106 Resist Pattern 107 Contact Hole

Claims (3)

[Claims] 1. A thin film forming step of forming a film made of a material having a high vapor pressure of fluoride on the surface of a film containing aluminum as a main component, an insulating film depositing step of depositing an insulating film on the upper layer, and a carbon And a gas containing fluorine, and a step of opening a connection hole by selectively etching the insulating film in a range where the etching rate of the material is lower than the etching rate of aluminum at a pressure of 100 mTorr or less. A method of manufacturing a semiconductor device, comprising: 2. The manufacturing of a semiconductor device according to claim 1, wherein the film made of a material having a high vapor pressure of fluoride contains at least one of tungsten, silicon, molybdenum, and carbon. Method. 3. The gas containing carbon and fluorine is CHF.
_The method of manufacturing a semiconductor device according to claim 1, wherein the gas is ₃ gas or a mixed gas of CHF ₃ and CO.