JPH11176803A - Equipment and method for dry etching - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide equipment and a method for dry etching by which etching selectivity of a BPSG film or PSG film against a silicon oxide film can be increased without CO gas. SOLUTION: In plasma etching equipment which has two independent high frequency power supplies 2, 7 for selectively dry etching a silicon oxide film and a BPSG film or PSG film formed on a semiconductor substrate located in a chamber 10, a mixed gas composed of carbon and fluorine atoms or gas composed of carbon, fluorine, and hydrogen atoms and a noble gas is used as a reactive gas introduced into the chamber 10. The noble gas enobles adjustment of a deposition quantity of the protective film, and thereby a selective deposition quantity of the protective film against the silicon oxide film can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching apparatus and a dry etching method, and more particularly to a dry etching apparatus and a dry etching method having two independent high-frequency power supplies for performing plasma etching on a silicon oxide film.

[0002]

2. Description of the Related Art As semiconductor devices become more highly integrated, there is a demand for finer contact hole diameters, electrode wirings, and electrode wiring intervals. For this reason, as shown in FIG. 7, after forming an electrode wiring 16 on a silicon substrate 11 via a silicon oxide film 12, a boron-phosphosilicate glass (BPSG) film 18 is formed.
In the case where a resist pattern 19 is formed thereon and a resist pattern 19 is formed thereon, and then a contact hole 27 is formed between the electrode wirings 16, a small misalignment of the contact pattern with respect to the electrode pattern causes the electrode wiring 16 and the contact hole The risk of short circuit with 27 increases.

In order to solve this, it is necessary to form contact holes in a self-aligned manner. As a method for forming a contact hole in a self-aligned manner, a method using an etching stopper has been conventionally known. In this method, as shown in FIG. 8, the upper surface and the side surface of the electrode wiring 16 are previously covered with etching stoppers 28 and 29, respectively, and then the BPSG film 18 which is an interlayer insulating film is selected for the etching stoppers 28 and 29. Etching. Thus, as shown in FIG. 8, even if the contact hole 30 is slightly misaligned between the adjacent electrode wirings 16, no short circuit occurs with the electrode wiring 16.

Conventionally, as described in the literature (Dry Process Symposium Proceedings, 1993, p. 193), the etching stoppers 28 and 29 are made of silicon as an insulating film having a selectivity with respect to an interlayer film. Nitride films have been considered. However, the silicon nitride film may have different film characteristics such as a dielectric constant from the silicon oxide film. When this silicon nitride film is used as the etching stoppers 28 and 29, there is a concern that the influence on the transistor characteristics is large. For this reason, it is considered preferable to use a silicon oxide film currently used for the LDD sidewalls for the etching stoppers 28 and 29.

The silicon oxide film is removed by etching stopper 28
And 29, the silicon oxide film
It is necessary to selectively and anisotropically etch the BPSG film 18 (which may be a phosphor-silicate glass (PSG) film). Conventionally, a mixed gas of CHF ₃ and CF ₄ has been used for dry etching of the contact hole. When this mixed gas is used, the etching rate of the BPSG film with respect to the silicon oxide film is 1.5 to 2 times. It is about twice.

On the other hand, using a mixed gas of CHF ₃ , CF ₄ and CO, the BPSG film and CHF ₃ , C
C generated by the reaction with F ₄ is deposited on the etching side wall of the semiconductor substrate, and O generated by the above reaction is reacted with CO in the above mixed gas to generate CO ₂ to the outside of the reaction chamber. A dry etching method of selectively etching a BPSG film with respect to a silicon oxide film by discharging the gas is also conventionally known (Japanese Unexamined Patent Publication No.
244153).

[0007]

However, the above-mentioned CH
In the conventional method of etching with a mixed gas of F ₃ and CF ₄ , the selectivity of the BPSG film to the silicon oxide film is 1.
The value is as low as 5 to 2 times, and selective etching is impossible. The reason why the selectivity is low is that the ability to form a protective film on the silicon oxide film is low.

When dry etching is performed using a fluorocarbon gas, a polymer containing carbon (C) and fluorine (F) as main components is formed simultaneously with the etching. When etching a film containing oxygen, oxygen atoms released from the film during the etching are combined with this polymer to generate volatile CO, COF, etc., and the polymer is not deposited for discharging, and does not become a protective film. .

On the other hand, when a film containing no oxygen (a silicon film or a silicon nitride film) is etched, the above-mentioned volatile products are hardly formed, so that polymer deposition is promoted and this becomes a protective film. . Since this protective film protects the base from ion bombardment, its etching rate is reduced and selective etching becomes possible. The silicon oxide film is
Since the amount of released oxygen during etching is smaller than that of the BPSG film, the protective film is easily formed, but the deposition rate is low. From these, the selectivity of the BPSG film to the silicon oxide film is a low value of about 1.5 to 2 times, and it is difficult to perform selective etching.

As described above, in order to achieve selective etching, it is necessary to have a high ability to form a protective film and to selectively deposit it.

In order to obtain a high ability to form a protective film, it is necessary to promote the dissociation of gas in plasma and generate a large amount of a precursor for polymer formation. Therefore, it is necessary to supply a large amount of power to the high frequency power supply. In the case of using a parallel plate type etching apparatus of the prior art, if the input power is increased, the decomposition of gas is promoted, but the ion bombardment on the substrate is also increased, and the deposited protective film is removed by sputtering.

Further, the conventional dry etching method for selectively etching a BPSG film using a mixed gas of CHF ₃ and CF ₄ has a problem that the ability to selectively form a protective film is low. That is, CHF ₃ gas is performed to form the protective film with etching, CHF ₃
The formation of the protective film proceeds too much using only the gas, and the protective film is deposited on the BPSG film in the contact hole, and the etching stops. Therefore, etching is advanced by adding a CF ₄ gas having a high etching ability.

However, since the CF ₄ gas hardly generates protective film forming components, the CHF ₃ gas also etches the protective film formed on the silicon oxide film. For this reason, in the above-mentioned conventional method, it is difficult to control the formation of the protective film on the silicon oxide film, and it is difficult to perform selective etching.

Conventionally, the addition of CHF ₃ , CF ₄ and CO gas has resulted in a BPS for silicon oxide films.
A dry etching method that improves the selectivity of the G film to about 15 times has been reported (Spring 1993 40th Applied Physics-related Union Lectures, second volume, p.612, 31).
A-ZE-4 or JP-A-6-244153).

However, this conventional method has a problem that the CO gas used is highly toxic, which is dangerous in handling, and that an exclusion facility for converting the CO gas into CO ₂ or the like is required.

The present invention has been made in view of the above points,
Without using CO gas, B against the silicon oxide film
An object of the present invention is to provide a dry etching apparatus and a dry etching method capable of improving the PSG film or the etching selectivity of the PSG film.

Another object of the present invention is to provide a dry etching apparatus and a dry etching method which can improve the yield of semiconductor devices while improving work safety.

[0018]

To achieve the above object, a dry etching apparatus according to the present invention selectively uses a silicon oxide film and a BPSG film or a PSG film on a semiconductor substrate placed in a chamber. In a plasma etching apparatus having two independent high frequency power supplies for performing dry etching, a gas composed of carbon and fluorine atoms or a gas composed of carbon, fluorine and hydrogen atoms is used as a reaction gas introduced into the chamber. , And a mixed gas with a rare gas.

Further, in order to achieve the above object, the dry etching method of the present invention employs a method for etching a silicon oxide film with a B
In the method for selectively performing anisotropic dry etching of a PSG film or a PSG film, a gas composed of carbon and fluorine atoms, or a gas composed of carbon, fluorine and hydrogen atoms, and a rare gas Is used.

Here, as a gas composed of carbon, fluorine and hydrogen atoms, a mixed gas of CF ₄ and hydrogen or C
Using a single gas of HF ₃ , C ₂ F ₆ , C ₃ F ₈ , C ₄ F ₈ or a mixed gas of two or more of them, at least one of Ar, He, Ne and Xe as a rare gas It is intended to be used.

In the present invention, the formation of a protective film is promoted by independent control of plasma by a high-frequency power supply connected to an electrode opposite to an electrode on which an object to be etched is mounted,
As a reaction gas, a gas composed of carbon and fluorine atoms, or a mixed gas of a gas composed of carbon, fluorine and hydrogen atoms, and a rare gas is used. Since the selective deposition amount of the protective film on the oxide film can be promoted, the etching selectivity of the BPSG film or PSG film to the silicon oxide film can be increased.

[0022]

Next, embodiments of the present invention will be described with reference to the drawings. First, a case in which C ₄ F ₈ gas is selected as an example of a compound gas containing carbon and fluorine, and Ar is selected as an example of a rare gas will be described in detail.

FIG. 1 is a schematic diagram showing an embodiment of a dry etching apparatus according to the present invention. In the figure, a wafer 1 is mounted on a lower electrode 4 connected to a first high-frequency power supply 2 via a blocking capacitor 3. The upper electrode 5 disposed at a position facing the lower electrode 4 in the chamber 10 is connected to a second high frequency power supply 7 via a blocking capacitor 6. Thereby, the generation of plasma and the attraction of ions into the wafer 1 can be controlled independently of each other.

The inside of the chamber 10 is evacuated to 10 ⁻² Torr to 10 ⁻⁴ Torr by the turbo molecular pump 8. C ₄
F ₈ gas and Ar gas are introduced into the chamber 10 through the gas inlet 9 and power is supplied to the high-frequency power sources 2 and 7 to generate plasma in the chamber 10 and at least the BPSG film and the silicon oxide film. The wafer 1 having a laminated structure is etched. During the etching, the cooler 31 controls the wafer temperature to be constant.

Next, effects obtained by using the above-described dry etching apparatus will be described. FIG. 2 shows the relationship between the power supplied to the second high frequency power supply 7 and the etching rate of the BPSG film and the silicon oxide film. As indicated by I in the figure, the etching rate of the BPSG film monotonically increases with an increase in input power. On the other hand, as shown by II in the figure, the etching rate of the silicon oxide film once increases with an increase in the applied power, but decreases when the applied power is further increased.

As described above, when dry etching is performed using a fluorocarbon-based gas, a polymer containing carbon and fluorine as a main component is formed simultaneously with the etching.
This works as a protective film. When the power supplied to the second high-frequency power supply 7 is increased, the decomposition of the gas by the plasma is promoted, and the amount of the precursor for polymer formation can be increased.

When the applied power is small, the formation of the polymer is small, the formation of the protective film is not promoted for both the silicon oxide film and the BPSG film, and the etching rate increases as the applied power increases. On the other hand, when the input power is large, the amount of the polymer formed increases, so that the formation of the protective film is promoted on the silicon oxide film where the generation of oxygen is small, and as shown by II in FIG. It is thought that it decreases as the input power increases. As can be seen from FIG. 2, when the power supplied to the second high frequency power supply 7 is set to 2500 W or more, the etching rate of the BPSG film and the etching rate of the silicon oxide film are different from each other by a predetermined value or more. Selective etching of the film becomes possible.

FIG. 3 shows the relationship between the etching rates of the silicon oxide film and the BPSG film when the pressure is changed using the apparatus of FIG. As shown by IV in FIG.
In a region where the internal pressure is less than 0.03 Torr, the formation rate of the protective film is small, so that the etching rate of the silicon oxide film increases, and it is difficult to perform selective etching. On the other hand, in the region where the pressure is larger than 0.1 Torr, FIG.
As shown by, the etching of the contact hole stops. When the pressure is in the range of 0.03 Torr to 0.1 Torr, the above problem does not occur as shown in FIG. 3. Therefore, when the pressure is in the range of 0.03 Torr to 0.1 Torr, the silicon oxide film and the BPSG film are selectively formed. In addition, etching can be performed in a favorable anisotropic shape.

FIG. 4 shows the relationship between the etching rates of the silicon oxide film and the BPSG film when the mixing ratio of Ar to the total gas flow rate of the mixed gas of C ₄ F ₈ and Ar used in the apparatus of FIG. 1 is changed. Show. The deposition amount of the protective film can be controlled by the dilution effect of the Ar gas. Ar mixing ratio is 40 Vol
%, The formation of the protective film proceeds excessively, and the BPS
Since the protective film is also deposited on the G film, the etching rate of the BPSG film decreases as shown by V in FIG. 4, and the etching of the contact hole does not progress.

On the other hand, when the Ar mixing ratio is larger than 70% by volume, the formation amount of the protective film decreases, and as shown by VI in FIG. 3, the etching rate of the silicon oxide film increases, so that selective etching becomes difficult. . However, when the Ar mixing ratio is in the range of 40 Vol% to 70 Vol%, the above-described problem does not occur, so the Ar mixing ratio is 40 Vol% to 70 V.
The BPSG film can be selectively etched with respect to the silicon oxide film within the range of ol%.

[0031]

Next, an embodiment in which the present invention is applied to contact formation will be described. FIG. 5 is a sectional view of a device for explaining a process of a first embodiment of the dry etching method according to the present invention. First, as shown in FIG.
A silicon oxide film 12, a polysilicon film 13, and a silicon oxide film 14 are sequentially deposited thereon. Next, as shown in FIG. 5B, a resist is applied and then developed to form a gate wiring resist pattern 15. Using this as a mask, the silicon oxide film 14, the polysilicon film 13 and the silicon oxide film 12 are dry-etched to form an electrode wiring 16 of polysilicon.

Next, after the resist pattern 15 is removed by a known method, as shown in FIG. 5C, a silicon oxide film 17 is coated on the entire surface, and as shown in FIG.
The silicon oxide film 1 is formed on the upper and side surfaces of the electrode wiring 16 by etching back by anisotropic dry etching.
4 and 17 are formed. Thereafter, as shown in FIG. 5E, a BPSG film 18 serving as an interlayer insulating film is deposited, and a resist is applied thereon and developed to form a resist pattern 19 of a contact hole.

Next, as shown in FIG. 5F, the BPSG film 18 is anisotropically dry-etched using the silicon oxide films 14 and 17 as an etching stopper and using the resist pattern 19 as a mask, as shown in FIG. Then, a contact hole 20 is opened. For example, the thickness of the BPSG film 18 is 8000 mm, the thickness of the electrode wiring 16 is 2000 mm,
The thickness of the stopper-silicon oxide films 14 and 17 is 1000
When the contact hole 20 is opened with an over-etching amount of 50% in the structure of {circle around (1)}, and the amount of shaving of the stopper-silicon oxide films 14 and 17 is set to 500 ° or less, a selectivity of 14 or more is required.

The second high-period of the dry etching apparatus of FIG.
Input power to the microwave power supply 7 is 2600 W, the first high frequency power supply
900W, pressure 0.04 Torr, C
_FourF₈Using gas 40 sccm and Ar gas 60 sccm,
When etching was performed for 2 minutes, 20
The BPSG film 18 can be etched with a selectivity of about
As a result, a contact hole 20 was formed.
Thus, CO Without using toxic gas like
Etching the BPSG film 18 with a selectivity of about 20
Can be.

Thereafter, as shown in FIG. 5 (g), after removing the contact hole resist pattern 19, an upper wiring 21 is formed. At this time, as shown in FIG. 5G, even when the contact hole 20 is misaligned from the electrode wiring 16, short-circuit between the upper wiring 21 and the electrode wiring 16 can be prevented by the silicon oxide films 14 and 17. it can.

Next, a second embodiment of the present invention will be described. FIG. 6 is a sectional view of a device for explaining a process of a second embodiment of the dry etching method according to the present invention. First, FIG.
As shown in FIG. 1A, a silicon oxide film 12 and a polysilicon film 13 are sequentially deposited on a silicon substrate 11. next,
As shown in FIG. 6B, a resist is applied and then developed to form a gate wiring resist pattern 15. Using this as a mask, the polysilicon film 13 and the silicon oxide film 1 are used.
2 is dry-etched to form an electrode wiring 16 of polysilicon.

Next, after removing the resist pattern 15 by a known method, as shown in FIG. 6C, a BPSG film 18 and a silicon oxide film 23 serving as an interlayer insulating film are sequentially deposited on the entire surface. By applying and developing
A contact hole resist pattern 19 is formed.

Subsequently, as shown in FIG. 6D, the silicon oxide film 23 is etched using the resist pattern 19 as a mask until the bottom BPSG film 18 is exposed, and a hole 24 is opened. Next, as shown in FIG. 6E, after removing the resist pattern 19, the silicon oxide film 25 is removed.
Is deposited on the entire surface, and the hole 2 is anisotropically dry-etched.
4 Etch back until the bottom BPSG film 18 is exposed. Thus, a silicon oxide film 25 is formed on the side wall of the silicon oxide film 23.

Next, as shown in FIG. 6F, the BPSG film 18 is anisotropically dry-etched using the silicon oxide films 23 and 25 as etching stoppers (masks) using the apparatus of the present invention, and the contact holes 26 are formed. Open. For example, in a structure in which the thickness of the BPSG film 18 is 8000 mm and the thickness of the silicon oxide film 23 is 2000 mm, when the contact hole 26 is opened with an over-etching amount of 50%, the second high frequency of the dry etching apparatus of FIG. Etching was performed for 2 minutes using 2600 W of power to the power source 7, 900 W of power to the first high frequency power source 2, 0.04 Torr of pressure, 40 sccm of C ₄ F ₈ gas, and 60 sccm of Ar gas. The mask silicon oxide films 23 and 25 were etched at a shaving amount of 500 ° or less.

In this embodiment, the silicon oxide film 25
Accordingly, the diameter of the contact hole 26 is smaller than that of the resist pattern 19, and the margin between the electrode wiring 16 and the contact hole 26 can be increased. According to the present embodiment, the etch back of the silicon oxide film 25 and the opening of the contact hole 26 are performed in the same chamber 1.
0 means that the process can be performed continuously, and since the silicon oxide films 23 and 25 can be used as an interlayer film as they are, there is an advantage that the number of steps can be reduced as compared with the case where a polysilicon film is used.

The present invention is not limited to the above-described embodiments and examples. The dry etching apparatus used is a parallel plate type having two high-frequency power supplies 2 and 7, but for example, the second high-frequency Inductively coupled plasma generation by power supply and electron cyclotron resonance (ECR)
A mold may be used.

As the compound gas containing carbon, fluorine and hydrogen atoms, a mixed gas of CF ₄ and hydrogen gas, C ₂ F ₆ , C ₃ F ₈ and CHF ₃ may be used in addition to C ₄ F ₈ gas. Good. As a rare gas mixed with the etching reaction gas, H
The same effect as Ar can be obtained by using e, Ne, and Xe.

Further, the BPS as the interlayer insulating film described above
The G film 18 may be a PSG film. Also in this case, it is possible to perform etching with a high selectivity to the silicon oxide film due to the difference in the amount of released oxygen during the etching.

[0044]

As described above, according to the present invention,
Using an etching device with two high frequency power supplies, carbon,
By performing dry etching using a mixed gas of fluorine or a compound gas containing hydrogen and a rare gas, the deposition amount of the protective film is adjusted by the rare gas, and the selective deposition amount of the protective film on the silicon oxide film is performed. BPSG film or PSG film for silicon oxide film
Since the etching selectivity of the film can be increased,
The means for opening a contact hole using a self-aligned contact using a silicon oxide film as an etching stopper can be provided without using a toxic gas, so that the yield of semiconductor devices can be improved while improving work safety.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of the device of the present invention.

FIG. 2 is a diagram showing an upper electrode input power vs. etching rate characteristic of the apparatus of FIG. 1 for a BPSG film and a silicon oxide film.

FIG. 3 is a diagram showing pressure versus etching rate characteristics of the apparatus of FIG. 1 for a BPSG film and a silicon oxide film.

FIG. 4 is a diagram showing an Ar mixing ratio versus etching rate characteristic of the apparatus of FIG. 1 for a BPSG film and a silicon oxide film.

FIG. 5 is a sectional view of an element in a process order for explaining a first embodiment in which a contact hole is formed by using the present invention.

FIG. 6 is a sectional view of an element in a process order for explaining a second embodiment in which a contact hole is formed by using the present invention.

FIG. 7 is a sectional view of an example of an element in which a contact hole is formed by a conventional device.

FIG. 8 is a cross-sectional view of another example of an element in which a contact hole is formed by a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wafer 2 1st high frequency power supply 3, 6 blocking capacitor 4 lower electrode 5 upper electrode 7 2nd high frequency power supply 8 turbo molecular pump 9 gas inlet 10 chamber 11 silicon substrate 12, 23, 25 silicon oxide film 13 polysilicon film 14, 17 Silicon oxide film (etching stopper) 15 Resist pattern 16 Electrode wiring 18 BPSG film 19 Contact hole resist pattern 20, 26 Contact hole 21 Upper wiring 24 Hole 31 Cooler

Claims (8)

[Claims] 1. A plasma etching apparatus having two independent high-frequency power supplies for selectively dry-etching a silicon oxide film and a BPSG film or a PSG film on a semiconductor substrate placed in a chamber, A dry etching apparatus characterized in that a gas composed of carbon and fluorine atoms or a mixed gas of a gas composed of carbon, fluorine and hydrogen atoms and a rare gas is used as a reaction gas introduced into the inside. 2. An electric power supplied to a high-frequency power supply connected to an electrode facing an electrode on which an object to be dry-etched is placed is 2500 W or more among the two high-frequency power supplies. Item 4. A dry etching apparatus according to Item 1. 3. The pressure of the mixed gas is 0.03 Torr.
3. The dry etching apparatus according to claim 1, wherein the dry etching apparatus is selected from r to 0.1 Torr. 4. The dry etching apparatus according to claim 1, wherein a mixing ratio of the rare gas with respect to a total gas flow rate of the mixed gas is selected from 40 Vol% to 70 Vol%. 5. A method for selectively performing anisotropic dry etching of a BPSG film or a PSG film on a silicon oxide film, wherein the reaction gas is a gas composed of carbon or fluorine atoms, or a gas composed of carbon, fluorine, and hydrogen. A dry etching method using a mixed gas of a gas composed of atoms and a rare gas. 6. The mixed gas of CF ₄ and hydrogen or CH 2 as the gas composed of carbon, fluorine and hydrogen atoms.
A single gas of each of F ₃ , C ₂ F ₆ , C ₃ F ₈ , and C ₄ F ₈ or a mixed gas of two or more of these gases is used.
6. The dry etching method according to claim 5, wherein at least one of r, He, Ne and Xe is used. 7. An entire surface of a semiconductor device in which an electrode wiring is formed on a silicon substrate via a first silicon oxide film and a second silicon oxide film is formed on an upper surface and a side surface of the electrode wiring, respectively. A step of depositing a BPSG film or a PSG film; a step of applying and developing a resist on the BPSG film or the PSG film to form a contact hole resist pattern; a mask of the contact hole resist pattern; And using the second silicon oxide film on the side surface as an etching stopper and using a gas composed of carbon and fluorine atoms or a mixed gas of a gas composed of carbon, fluorine and hydrogen atoms and a rare gas as a reaction gas. Opening a contact hole by anisotropically dry-etching the BPSG film or PSG film. Dry etching method. 8. A BP is formed on the entire surface of a semiconductor device having an electrode wiring formed on a silicon substrate via a first silicon oxide film.
A step of sequentially depositing an SG film or a PSG film and a second silicon oxide film; a step of applying and developing a resist on the second silicon oxide film to form a contact hole resist pattern; Using the resist pattern as a mask, etching the second silicon oxide film until the bottom BPSG film or PSG film is exposed to form holes, and after removing the contact hole resist pattern,
Depositing a third silicon oxide film on the entire surface; etching back the third silicon oxide film until the BPSG film or PSG film at the bottom of the hole is exposed; The BPSG film is formed by using a third silicon oxide film as a mask and using a gas composed of carbon and fluorine atoms or a mixed gas of a gas composed of carbon, fluorine and hydrogen atoms and a rare gas as a reaction gas. Or a step of anisotropically dry-etching the PSG film to open a contact hole.