JPH0927472A - Plasma etching method for low-dielectric constant silicon oxide insulation film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma etching method whereby a high selection ratio of low-dielectric constant Si oxide insulation films such as SiOF, practical etching rate and low particle level can be attained. SOLUTION: Using a mixed gas of fluorocarbon gas contg. H2 O and H2 O2 , contact holes 5 are opened through a low-dielectric constant Si oxide insulation film 3 on a semiconductor substrate 1. The flow rate ratio of the mixed gas may be changed to etch at two steps and deposition of S may be used together. Film of fluorocarbon polymer is reinforced to improve the selectivity to a resist mask 5 or semiconductor substrate 1. Since the amount of the polymer to be deposited can be reduced, the particle level also lowers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma etching method for a low dielectric constant silicon oxide insulating film applied in the field of manufacturing highly integrated semiconductor devices and the like. The present invention relates to a plasma etching method for a low dielectric constant silicon oxide insulating film, which is useful when patterning a silicon insulating film with high accuracy.

[0002]

2. Description of the Related Art With the progress of higher integration and higher performance of semiconductor devices such as LSI, the design rule thereof is being reduced from half micron to subquarter micron. Along with this, technical requirements for a plasma etching method for forming a connection hole and the like by performing fine processing on a silicon oxide-based insulating film have become more and more sophisticated.

For example, in order to speed up signal processing of a semiconductor device and miniaturize the semiconductor element itself, for example, MO
In the S transistor, the junction depth of the impurity diffusion layer is shallow and the other wiring material layers are also thin.
In the manufacturing process of such a highly integrated semiconductor device, there is a demand for a plasma etching method which is more excellent in selectivity with respect to the underlying material layer than before and has less damage to the underlying material layer.

Further, improving the selection ratio of resist masks is also an important issue. This is because, in order to stably manufacture a semiconductor device having a fine design rule, it is becoming difficult to allow the dimensional conversion difference due to the receding of the resist mask during plasma etching, even if the difference is extremely small.

In plasma etching of a silicon oxide material film, it is necessary to break a strong Si--O bond.
An ionic etching mode with a strong sputtering effect is used. Common etching gas is CF
_It is mainly composed of CF type gas such as ₄ and C ₂ F ₆ , and has a sputtering action by incident ion energy of CF _x ⁺ generated by dissociation from the CF type gas and Si by reducing property of carbon as a constituent element. It utilizes the breaking action of —O bond and the generation and removal of SiF _x , which is a reaction product having a large vapor pressure. However, as a characteristic of ion-mode plasma etching, the etching rate is not generally large. Therefore, when the incident ion energy is increased by directing high-speed etching, the etching reaction mainly consists of physical sputtering, and the selectivity is lowered.
That is, the plasma etching of the silicon oxide based material layer with the CF based gas is difficult to achieve both high speed and selectivity.

Further, in order to obtain a high selection ratio by the conventional technique, it is necessary to thickly deposit a fluorocarbon-based polymer mainly containing a reaction product of a CF-based gas, and such a gas chemistry is used in the same etching chamber. If the plasma etching is repeated at 1, the etching rate is lowered and the particle level is deteriorated. The lower the etching rate is, the more pronounced the finer the pattern becomes, and the defective contact hole is caused by the so-called microloading effect.

In order to improve the selection ratio in the plasma etching of the silicon oxide type insulating film, there is a conventional technique in which H ₂ is added to CF type gas or CHF type gas such as CHF ₃ containing H in the molecule is adopted. This is due to excess H ^* in the plasma due to H radicals (H ^* ) generated in the plasma ^.
Captured and removed in the form of HF outside the etching chamber,
It is based on the idea of increasing the substantial C / F ratio (ratio of C atoms and F atoms) of the etching reaction system. Increasing the C / F ratio has the effect of reducing the content of F atoms in the fluorocarbon-based polymer that is deposited in competition with etching, and strengthening the film quality such as the resistance to ion incidence, and therefore, it can be used as a base such as Si. Has the effect of improving the selectivity of. Fluorocarbon-based polymers are
On the silicon oxide-based material layer, it reacts with O atoms sputtered out from the surface of the silicon oxide-based material layer and is oxidized and removed.
However, a fluorocarbon polymer is a Si that does not have an oxidizing effect.
Etc. are exclusively deposited on the lower ground and function as a substantial etching stopper to protect the underlying layer from ion incidence, which improves the selection ratio. For the concept of these C / F ratios and the mechanism by which high selectivity is achieved, see J.
Vac. Science. Tech, 16 (2), 39
1 (1979).

Recently, there is a trend to reconsider the film quality of fluorocarbon polymers from a standpoint different from the physical viewpoint of ion incidence resistance. That is, when a fluorocarbon-based polymer rich in F atoms is deposited on an exposed surface such as Si which is the base material layer, the F atoms in the fluorocarbon-based polymer and the base Si atoms are simply adsorbed or attached. Not only the above, but also the process of desorption of chemical reaction and reaction products is assisted by the incidence of ions. This series of processes is an etching reaction, and causes a reduction in the selection ratio of the base material layer. From such a viewpoint, CO is added to a fluorocarbon gas to remove excess F ^* in the plasma from C
The fourth attempt is to capture it in the form of OF _x and increase the C / F ratio.
0th Joint Lecture on Applied Physics (Spring Annual Meeting 1993)
Reported in Lecture Proceedings p614, Lecture No. 31a-ZE-10. From the same point of view, there is a proposal of adding CO to an inorganic fluorine-based etching gas such as NF ₃ to capture surplus F ^* and improving the selection ratio, for example, US Pat.
No. 807,016.

However, in the method of adding H ₂ or CO to the fluorocarbon gas to improve the selectivity with respect to the underlying material layer, sufficient consideration must be given to the flammability and safety of these added gases. . Especially, there is a lot of room for consideration in handling in a closed space such as a clean room. In addition, for practical use, it is necessary to newly install exhaust gas treatment equipment.

On the other hand, in order to prevent the delay of signal propagation in the semiconductor device, an attempt to reduce the dielectric constant of the insulating film between the wirings to reduce the capacitance between the wirings has been earnestly made in a semiconductor device such as a logic LSI which requires high speed. Is being considered. As a low dielectric constant material, SiO _x F _z obtained by adding F to SiO ₂ which is a general interlayer insulating film material is representative, and it is noted that it is continuous with the conventional technique in the film forming process.
As an example, a plasma CVD method using a TEOS / O ₂ / CF ₄ type raw material gas is 1993 Dry Procedures.
s Symposium Proceedings p163, Lecture No. V
-2. The SiO ₂ According to this method 6
at. The relative permittivity is reduced from 4.1 to 3.2 by including about F of F.

However, in plasma etching of the SiOF interlayer insulating film, F etching is performed sequentially during the etching.
^* (F radical) is released, increasing the F ^* concentration in the plasma. Since F ^* can serve as an etchant for silicon as a base material layer or a resist mask, it is more difficult to secure an etching selection ratio as compared with general silicon oxide-based insulating films such as SiO ₂ , PSG, BSG, and BPSG. It will be

[0012]

The present invention is based on the above-mentioned F
It is an object to solve various problems related to plasma etching of a low dielectric constant silicon oxide-based insulating film containing Si. That is, an object of the present invention is to pattern a low dielectric constant silicon oxide insulating film formed on a base material layer, which has an excellent selection ratio of the base material layer and the resist mask, and has a small microloading effect and particle contamination. It is to provide a plasma etching method with less power consumption.

Another object of the present invention is to eliminate from the etching gas system gases such as H ₂ and CO, which should be considered for their flammability and safety in use, and to newly invest in equipment such as an exhaust gas treatment facility. It is an object of the present invention to provide a plasma etching method for a low dielectric constant silicon oxide based insulating film that does not require.

Still another object of the present invention is to provide a plasma etching method for a low dielectric constant silicon oxide insulating film capable of stably manufacturing a highly integrated semiconductor device having a reduced wiring capacitance and an improved signal propagation speed. That is.

[0015]

A plasma etching method for a low dielectric constant silicon oxide type insulating film of the present application is proposed to achieve the above-mentioned problems, and a first invention thereof is to provide H and O. Gas as a constituent element and C and F
The low dielectric constant silicon oxide-based insulating film on the base material layer is patterned by using a mixed gas containing a gas having a constituent element of. C adopted in the present invention
C _n and gas to constituent element F is that or the general formula C _n F _m a portion of the F atoms in these compounds has been substituted with H
It is a compound represented by H ₁ F _ml (n, m and l are natural numbers), and may be a saturated compound or an unsaturated compound. It is desirable to use a high-order fluorocarbon-based gas in which n is 2 or more in view of the generation efficiency of CF _x ⁺ which is the main etchant generated by discharge dissociation.

In the second aspect of the invention, a mixed gas containing a gas containing H and O as constituent elements and a gas containing C and F as constituent elements is used, and a low dielectric constant silicon oxide based insulating material on the underlying material layer is used. A step of patterning the film until just before the underlying material layer is exposed, and increasing the mixing ratio of the gas containing H and O as constituent elements in the mixed gas to form a low dielectric constant silicon oxide insulating film layer of the underlying material layer. The step of patterning the remaining portion in the thickness direction is performed in this order. In the step of patterning until just before the underlying material layer is exposed, the underlying material layer may inevitably be slightly exposed on a part of the substrate to be etched due to slight non-uniformity of the etching rate. The case shall be included.

Further, in the third invention, H and O
On the underlying material layer while controlling the temperature of the substrate to be etched to room temperature or lower while using a mixed gas containing a gas containing the element as a constituent element and a sulfur-based compound gas capable of releasing free sulfur into plasma under discharge dissociation conditions. The low dielectric constant silicon oxide insulating film is patterned. The sulfur-based compound gas capable of releasing free sulfur into plasma under the discharge dissociation conditions used in the present invention is specifically S ₂ F ₂ , SF ₂ , SF ₄ , S ₂ F ₁₀ , S ₂ Cl ₂ ,
S ₃ Cl ₂ , SCl ₂ , S ₂ Br ₂ , S ₃ Br ₂ , S ₂
Halogenated sulfur-based gas such as Br and H ₂ S are exemplified, and these can be used alone or in combination. A compound that is liquid at room temperature may be heated and vaporized by a known method before use. SF ₆ commonly used as halogenated sulfur gas
Excludes free sulfur in the plasma under discharge dissociation conditions, so it is excluded. The room temperature is the room temperature of a clean room used in a normal semiconductor device manufacturing process, and is usually 20 to 25 ° C.

In any of the inventions, in a preferred embodiment thereof, the gas containing H and O as constituent elements is any one of H ₂ O and H ₂ O ₂ (bp = 152 ° C.). Is preferred. Commercially available hydrogen peroxide solution (30% or 2.5-3.0%) as a mixture
May be used. Since all of these are liquid sources, they are introduced into the etching chamber by heating evaporation, bubbling with a carrier gas such as He, ultrasonic vaporization, or the like.

The low dielectric constant silicon oxide type insulating film of the present invention is mainly composed of SiO _x F _z and SiO _x N _y.
Any one of F _z (hereinafter abbreviated as SiOF and SiONF). A low-dielectric-constant silicon oxide insulating film containing impurities such as P, B, and As in these SiOF and SiONF may be used.

[0020]

In the first invention, H in the etching gas is
Dissociation of ₂ O or H ₂ O ₂ supplies H atoms into the plasma. On the other hand, F ^* generated by dissociation from a CF-based or CHF-based gas, and F ^* sequentially released as the low dielectric constant silicon oxide insulating film is etched ^.
These H atoms are captured and removed from the etching chamber in the form of HF or HOF to prevent the F ^* concentration in the etching reaction system from rising and control the C / F ratio.

As a result, it is possible to prevent a decrease in etching selectivity with respect to the resist mask and the underlying material layer due to excessive F ^* . Furthermore, the F atoms in the fluorocarbon polymer deposited on the substrate to be etched are reduced, forming a film that is carbon-rich and has high ion incidence resistance, and is mainly deposited on the exposed underlying material layer of Si or the like or the resist mask and etched. It improves the selection ratio. Since this carbon-rich fluorocarbon polymer has a small amount of fluorine component, it does not proceed with the chemical reaction and the desorption process of the reaction product with the underlying material layer in a form assisted by the ion injection. The etching selectivity with respect to the material layer and the resist mask is improved.

The fluorocarbon-based polymer is also formed on the low dielectric constant silicon oxide-based insulating film, which is the layer to be etched, but is immediately oxidized by O atoms released by etching to form CO and CO _2. As it is removed, the etching proceeds at a high speed. However, in fine contact hole etching, the proportion of the area to be etched is very small, so the amount of O atoms emitted is small. Further, at the bottom of the contact hole having a large aspect ratio, the incident amount of ions decreases, so that the fluorocarbon polymer remains excessively. For this reason, a microloading effect occurs in which the etching rate decreases in the fine contact hole. In this regard, in the present invention, the shortage of the amount of released O atoms from the layer to be etched is replenished by the decomposition products of H ₂ O or H ₂ O ₂ in the etching gas, and the fluorocarbon-based material is formed in the fine contact holes. The polymer is not overly deposited and the occurrence of microloading effects and size conversion differences is avoided. In addition, since the formation of excess fluorocarbon polymer is suppressed even in the entire etching chamber,
Even if the number of lots is increased by continuous processing, the etching rate does not decrease and the particle level does not increase.

The present invention is based on the above technical idea, but proposes a method in which plasma etching is performed in two stages in order to further improve the etching rate and achieve a high selection ratio. That is, in the second invention of the present application, the mixing ratio of the mixed gas is changed at the time of patterning until just before the underlying material layer corresponding to the just etching step is exposed, and H is set in the over etching step.
And increase the mixing ratio of the gas containing O as a constituent element. By this two-step etching, a practical high-speed etching rate can be secured in the just etching process. Further, in the over-etching step, F ^* is further reduced, and a fluorocarbon-based polymer having a small F content is more effectively generated, so that high selective ratio etching can be performed even under the condition that the incident ion energy is reduced. . Naturally, the ion irradiation damage of the base material layer is also reduced.

In the third invention of the present application, there is further provided a method of adding a halogenated sulfur-based gas capable of releasing free sulfur into plasma under discharge dissociation conditions while controlling the temperature of the substrate to be etched below room temperature. Also suggest. The radical reaction is suppressed by controlling the temperature of the substrate to be etched at a low temperature, and the addition of these sulfur halide gases prevents sulfur from being deposited in addition to the fluorocarbon polymer on the substrate to be etched. Due to the synergistic effect,
The selection ratio of the material such as Si to the base material and the selection ratio of the resist mask are further improved. On the other hand, on the surface of the silicon oxide material layer,
O or SO released by sputtering causes SO or SO
_Since it becomes ₂ and is removed promptly, there is virtually no reduction in the etching rate. Therefore, high selectivity etching can be performed while maintaining the etching rate.

After the patterning of the silicon oxide type material layer, if the substrate to be etched is heated to 90 ° C. to 100 ° C., the deposited sulfur can be quickly sublimated and removed, and contamination or particle contamination of the substrate to be etched may remain. There is no. Sulfur can also be oxidized and removed simultaneously with the resist during resist ashing. In addition to these halogenated sulfur-based gases, N ₂ and N
_When N-based gas such as ₂ H ₄ and NF ₃ is added, polythiazyl which is a sulfur nitride polymer is deposited on the substrate to be etched. Polythiazyl has a higher ion incidence resistance than sulfur, and has a high selection ratio improvement and damage prevention effect. Polythiazil can also be removed by sublimation after plasma etching, and the sublimation temperature is about 150 ° C. or higher under reduced pressure. As is clear from the sublimation temperatures of sulfur and polythiazyl, sulfur or polythiazyl can be deposited if the substrate temperature to be etched is lower than these sublimation temperatures. However, from the viewpoint of the stability of the deposited film, it is desirable to control the temperature of the substrate to be etched to room temperature or lower, for example, 20 to 25 ° C. or lower.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments in which the present invention is applied to the processing of contact holes and via holes will be described below with reference to the accompanying drawings.

Example 1 This example applies the first invention, and a mixed gas containing C ₄ F ₈ which is a fluorocarbon gas and H ₂ O is used to form a low dielectric constant of SiOF on a silicon substrate. This is an example in which a silicon oxide insulating film is plasma-etched to form a contact hole, which will be described with reference to FIGS.

First, as shown in FIG. 1A, S is formed on a semiconductor substrate 1 of Si or the like on which an impurity diffusion layer 2 and the like are formed in advance.
A low dielectric constant silicon oxide insulating film 3 made of iOF is formed. This low dielectric constant silicon oxide type insulating film is formed by plasma CVD using a TEOS / C ₂ F ₆ / H ₂ O / O ₂ type source gas as an example. Regarding the plasma CVD method, the applicant of the present invention previously filed Japanese Patent Application No. 6-976.
It was filed as No. 31, and there is little residual hydroxyl group or organic matter, and SiOF excellent in step coverage can be obtained. Next, a chemically amplified resist and KrF excimer laser lithography are used to pattern a resist mask 4 having an opening diameter of 0.25 μm at the connection hole opening position. The thickness of the low dielectric constant silicon oxide insulating film 3 is 500 nm as an example. The sample shown in FIG. 1A formed so far is used as a substrate to be etched.

Next, this substrate to be etched is placed on the substrate stage of a magnetron RIE apparatus that also uses a magnetic field, and the exposed portion of the silicon oxide based material layer 3 is plasma etched under the following conditions. The substrate stage can control the temperature to 0 ° C. or lower by incorporating a cooling pipe in which an alcohol-based refrigerant circulates. C ₄ F ₈ 50 sccm H ₂ O 10 sccm Gas pressure 2.0 Pa RF power source power density 2.0 W / cm ² (13.56 MHz) Magnetic field strength 1.5 × 10 ^-2 T Etched substrate temperature 5 ° C. The etching substrate temperature was maintained at 5 ° C. during the etching process. In this plasma etching process, the anisotropic reaction of the low dielectric constant silicon oxide insulating film 3 proceeded in such a manner that the radical reaction by F ^* was mainly assisted by the ion injection of CF _x ⁺ . Etching rate is 85
It was 0 nm / min.

In the plasma, H ^* and OH ^* produced by dissociation of H ₂ O or these ions are C ₄ F 2.
_It captures the dissociation of ₈ and the excess F ^* released from the layer to be etched. As a result, the fluorocarbon polymer (not shown) deposited on the substrate to be etched had a low content of the F component and had a high resistance to ion incidence. The fluorocarbon polymer is mainly deposited on a semiconductor substrate such as silicon which is a base material layer exposed by plasma etching, to be precise, on the impurity diffusion layer 2 and the resist mask 4, and as a result, a high selection ratio is obtained. That is, when the semiconductor substrate 1, which is the base material layer, is exposed, the fluorocarbon-based polymer is deposited on the surface of the semiconductor substrate 1, so that the etching rate is significantly reduced, and as a result, a high selection ratio is achieved. The selection ratio was about 40 for the base material layer and about 7 for the resist mask. FIG. 1B shows a state after the plasma etching is completed in which the contact hole 5 is opened in the substrate to be etched.

According to the present embodiment, the low dielectric constant silicon oxide based insulating film is plasma-etched by using a mixed gas containing C ₄ F ₈ and water vapor, so that a contact hole opening satisfying both a high selection ratio and uniformity can be obtained. The process was achieved.

Example 2 In this example, the first invention is also applied, and C ₄ F ₈ and
This is an example in which a via hole is opened by plasma-etching a low-dielectric-constant silicon oxide-based insulating film on a lower wiring with a mixed gas containing H ₂ O _2. This will be described with reference to FIGS. explain.

The substrate to be etched shown in FIG. 2A adopted in this embodiment has a lower layer wiring 7 made of polycrystalline silicon containing impurities and a low dielectric constant silicon oxide type insulating film 3 on the lower layer interlayer insulating film 6. Is formed, and the resist mask 4 having an opening of, for example, 0.25 μm, which faces the lower layer wiring 7, is formed. The thickness of the low dielectric constant silicon oxide insulating film 3 is 500 nm as an example.

This substrate to be etched is placed on the substrate stage of the same magnetron RIE apparatus as in the previous embodiment, and the exposed portion of the low dielectric constant silicon oxide type insulating film 3 is plasma-etched under the following conditions. C ₄ F ₈ 50 sccm H ₂ O ₂ 10 sccm Gas pressure 2.0 Pa RF power source power density 2.0 W / cm ² (13.56 MHz) Magnetic field strength 1.5 × 10 ^-2 T Etched substrate temperature 5 ° C. The substrate temperature to be etched was maintained at 5 ° C. during the etching process. In this plasma etching process, the anisotropic reaction of the low dielectric constant silicon oxide insulating film 3 proceeded in such a manner that the radical reaction by F ^* was mainly assisted by the ion injection of CF _x ⁺ . Etching rate is 95
It was 0 nm / min.

In the plasma, H ^* and OH ^* produced by dissociation of H ₂ O ₂ or these ions are converted into C ₄
Dissociation of F ₈ and excess F ^* released from the layer to be etched
Is captured, the same effect as in the first embodiment can be obtained. That is, the etching selection ratio was about 40 for the lower wiring 7 made of polycrystalline silicon as the base material layer, and about 6 for the resist mask 4. Beer hole 8
Fig. 2 shows the state after plasma etching with the opening
(B). According to this embodiment, by plasma etching the low dielectric constant silicon oxide based insulating film using a mixed gas containing C ₄ F ₈ and hydrogen peroxide, a via hole opening process that satisfies both high selectivity and uniformity can be performed. I was able to achieve it.

Example 3 This example applies the second invention, and Si on a silicon substrate is used.
A low dielectric constant silicon oxide insulating film made of OF is subjected to two-step plasma etching with a mixed gas containing C ₃ F ₈ which is a fluorocarbon gas and H ₂ O at different mixing ratios to form contact holes. This is an example of the formation, and this is shown in FIG.
This will be described with reference to (a) to (c).

The substrate to be etched shown in FIG. 3A is the same as the substrate to be etched shown in FIG. The substrate to be etched is placed on the substrate stage of a magnetron RIE apparatus, and the exposed portion of the silicon oxide based material layer 3 is plasma-etched until just before the underlying material layer is exposed under the following conditions. C ₃ F ₈ 50 sccm H ₂ O 10 sccm Gas pressure 2.0 Pa RF power source power density 2.2 W / cm ² (13.56 MHz) Magnetic field strength 1.5 × 10 ⁻² T Etching substrate temperature 15 ° C. Etching The end point of was determined by previously controlling the etching rate of the low dielectric constant silicon oxide insulating film 3 under the same etching conditions. The state after completion of the first-stage plasma etching is shown in FIG. On the bottom surface of the concave portion where the contact hole is to be opened, the residual portion 3a of the low dielectric constant silicon oxide insulating film is seen. In this etching step, the etching proceeds basically based on the same principle as in the first embodiment, but the etching rate was 1200 nm / min because the conditions in which the RF power source power density and the substrate temperature to be etched were increased. .

Next, the following plasma etching conditions in which the mixing ratio of H ₂ O is increased are switched to remove the remaining portion 3a of the low dielectric constant silicon oxide type insulating film. C ₃ F ₈ 40 sccm H ₂ O 20 sccm Gas pressure 2.0 Pa RF power source power density 1.2 W / cm ² (13.56 MHz) Magnetic field strength 1.5 × 10 ⁻² T Etched substrate temperature 15 ° C. main In the over-etching process, F ^* is effectively captured by increasing the mixing ratio of H ₂ O, and the RF power source power density is reduced. 60, the resist mask was about 9. Low dielectric constant silicon oxide insulating film 3
FIG. 3C shows a state after completion of plasma etching in which the contact hole 5 is opened.

According to the present embodiment, by adopting the two-step etching condition for changing the mixture ratio of H ₂ O, a high selection ratio,
This enables plasma etching of a low dielectric constant silicon oxide-based insulating film that satisfies both uniformity and high throughput.

Example 4 In this example, the third invention of the present application is applied, and CF ₄ / H ₂ O is used.
This is an example in which a low dielectric constant silicon oxide based insulating film on a lower wiring is plasma-etched with a / S ₂ F ₂ mixed gas to open a via hole. This will be described again with reference to FIGS. 2 (a) and 2 (b). To do.

The substrate to be etched shown in FIG. 2 (a) used in this embodiment is the same as that described in the second embodiment, and the duplicated description will be omitted. This substrate to be etched is used as a substrate bias application type ICP (Inductive).
The exposed portion of the low dielectric constant silicon oxide insulating film 3 is plasma-etched under the following conditions by placing it on a substrate stage of a Ly Coupled Plasma etching apparatus. The substrate stage of this etching apparatus has a mechanism capable of cooling the substrate to be etched to −several tens of degrees Celsius by circulating an alcohol-based coolant cooled by a chiller. CF ₄ 20 sccm H ₂ O ₂ 20 sccm S ₂ F ₂ 20 sccm Gas pressure 0.8 Pa ICP power supply 1000 W (2.0 MHz) Substrate bias voltage 300 V Etched substrate temperature −30 ° C. Etched substrate temperature is etching. The temperature was maintained at -30 ° C during the process. In this plasma etching process, C
F generated in plasma due to dissociation of F ₄ and S ₂ F ₂
Anisotropic etching of the low dielectric constant silicon oxide insulating film 3 proceeded in such a manner that the radical reaction by ^* was mainly assisted by CF _x ⁺ ion incidence. The etching rate was 950 nm / min.

In the plasma, H ^* and OH ^* produced by dissociation of H ₂ O ₂ or these ions trap excess F ^* , and the activity of F ^* itself is suppressed by cooling at low temperature. In addition, due to the effect that sulfur deposition can be used in addition to the strong fluorocarbon-based polymer having a small F content, the etching selection ratio was higher than that in Example 3. . In addition, it is possible to reduce the amount of fluorocarbon polymer deposited by the amount of sulfur deposited, and as a result, the microloading effect was effectively reduced. Figure 2 shows the state after plasma etching
(B).

According to this embodiment, S ₂ F ₂ is further added to the mixed gas of CF ₄ and H ₂ O, and the low dielectric constant silicon oxide type insulating film is patterned while controlling the substrate to be etched at room temperature or below. By doing so, it is possible to achieve both a high selection ratio and low damage to the underlying material layer. Particularly, in this embodiment, after the plasma etching is completed, the substrate stage is heated to 90 ° C. to 100 ° C., so that the sulfur deposited on the substrate to be etched or in the vicinity of the substrate stage can be easily sublimated and removed, resulting in particle contamination and contamination. It does not cause nation. Further, it is possible to reduce the deposition of the fluorocarbon polymer, and even if the number of substrates to be etched is repeatedly processed continuously, the atmosphere in the chamber in which the fluorocarbon polymer is excessive is not formed, and the etching rate is reduced. No microloading effect occurs. Further, the particle level in the chamber does not increase.

The present invention has been described above with reference to four embodiments, but the present invention is not limited to these embodiments.

For example, as a fluorocarbon gas, C ₄ F ₈
Although C ₃ F ₈ and CF ₄ are exemplified, other CF-based gases can be used alone or in combination regardless of whether they are saturated or unsaturated. A CHF-based gas in which some of the F atoms are replaced with H may be used. Similarly, some of the F atoms are Cl or B.
It may be a compound substituted with another halogen atom such as r.

As a halogenated sulfur-based gas capable of releasing free sulfur into plasma under discharge dissociation conditions, S ₂ F
₂ was taken as a representative, but in addition to this, SF ₂ , SF
₄ , S ₂ F ₁₀ , S ₂ Cl ₂ , S ₃ Cl ₂ , SCl ₂ , S
₂ Br ₂ , S ₃ Br ₂ , and S ₂ Br ₁₀ are exemplified,
These can be used alone or in combination. Since H ₂ S does not have an etching action by itself, it is necessary to use it in combination with a CF-based gas or another halogen-based gas.

Si as a low dielectric constant silicon oxide insulating film
Although OF has been exemplified, it may be SiONF containing nitrogen. These may further contain impurities such as P, B and As. Or SiO ₂ , PSG, BP
It may be a laminated structure film with a general dielectric material such as SG or Si ₃ N ₄ . Application to self-aligned contact without using a resist mask is also possible. Further, it is applicable not only to the processing of contact holes and via holes but also to various types of plasma etching, such as LDD sidewall spacer processing, which requires a high selection ratio with the underlying material layer.

In addition, the structure of the substrate to be etched, the plasma etching apparatus, the plasma etching conditions, etc. can be appropriately selected and applied within the scope of the technical idea of the present invention.

[0049]

As is apparent from the above description, according to the first invention of the present application, control of F ^* in plasma and F in fluorocarbon polymer deposited on the substrate to be etched are performed.
By controlling the content, it is possible to etch the low dielectric constant silicon oxide insulating film with a high selectivity.

According to the second invention, by adopting the two-step etching in which the composition ratio of the mixed gas is changed, the above effect can be thoroughly achieved in addition to the high throughput processing.

According to the third aspect of the present invention, by using the deposition of sulfur or polythiazyl in combination, in addition to further improvement of the selection ratio and low damage, the effect of reducing the microloading effect and low contamination can be obtained.

With the above effects, according to the present invention, a highly integrated semiconductor device using a low dielectric constant silicon oxide insulating film can be manufactured stably and safely.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view illustrating Example 1 to which a plasma etching method of the present invention is applied in the order of steps,
(A) is a state where a resist mask for opening a contact hole is formed on a low dielectric constant silicon oxide insulating film, (b)
Is a state in which the contact hole is completed by patterning the low dielectric constant silicon oxide insulating film.

2A and 2B are schematic cross-sectional views for explaining Examples 2 and 4 to which the plasma etching method of the present invention is applied, in the order of steps, in which (a) is a resist for opening via holes on a low dielectric constant silicon oxide insulating film. Mask formed, (b)
Is a state in which the via hole is completed by patterning the low dielectric constant silicon oxide insulating film.

FIG. 3 is a schematic cross-sectional view for explaining the third embodiment to which the plasma etching method of the present invention is applied, in the order of steps thereof,
(A) is a state where a resist mask for opening a contact hole is formed on a low dielectric constant silicon oxide insulating film, (b)
Is a state where the low dielectric constant silicon oxide insulating film is patterned until just before the underlying material layer is exposed, and (c) is a state where the remaining portion of the low dielectric constant silicon oxide insulating film in the layer thickness direction is patterned to complete a contact hole. Is.

[Explanation of symbols]

 1 Semiconductor Substrate 2 Impurity Diffusion Layer 3 Low Dielectric Silicon Oxide Insulation Film 3a Remaining Low Dielectric Silicon Oxide Insulation Film 4 Resist Mask 5 Contact Hole 6 Lower Interlayer Insulation Film 7 Lower Wiring 8 Via Hole

Claims (5)

[Claims] 1. A low dielectric constant silicon oxide insulating film on a base material layer is patterned using a mixed gas containing a gas containing H and O as constituent elements and a gas containing C and F as constituent elements. A plasma etching method for a low dielectric constant silicon oxide insulating film, comprising: 2. A low dielectric constant silicon oxide-based insulating film on a base material layer is formed by using a mixed gas containing a gas containing H and O as constituent elements and a gas containing C and F as constituent elements. Patterning until just before the material layer is exposed, and increasing the mixing ratio of the gas containing H and O as constituent elements in the mixed gas, in the layer thickness direction of the low dielectric constant silicon oxide insulating film of the underlying material layer. And a step of patterning the remaining part of the above step in this order. A plasma etching method for a low dielectric constant silicon oxide insulating film. 3. A mixed gas containing a gas containing H and O as constituent elements and a sulfur-based compound gas capable of releasing free sulfur into plasma under discharge dissociation conditions is used, and the substrate to be etched is kept at room temperature or below. A plasma etching method for a low dielectric constant silicon oxide based insulating film, which comprises patterning a low dielectric constant silicon oxide based insulating film on a base material layer while controlling. 4. The gas containing H and O as constituent elements is any one of H ₂ O and H ₂ O ₂ , and the gas according to any one of claims 1 to 3. Method for plasma etching low dielectric constant silicon oxide insulating film. 5. The low dielectric constant silicon oxide-based insulating film is any one of SiO _x F _z and SiO _x N _y F _z. A plasma etching method for a low dielectric constant silicon oxide-based insulating film according to claim 1.