JPH06163476A - Dry etching method - Google Patents

Abstract

PURPOSE:To enable a high speed, high selective yet low pollution and low damage dry etching step to be performed while suppressing the mirco-loading effect in the fine hole formation step, etc., by using an etching gas containing a fluorocarbon base compound exceeding two carbon number having carbonyl radical and fluorine stoms. CONSTITUTION:A silicon compound layer is to be etched away using an etching gas containing fluorocarbon base compound exceeding two carbon number having a carbonyl radical and fluorine atoms in molecules. For example, an SiO2 interlayer insulating film 3 is formed on a single crystalline Si substrate 1 whereon an impurity diffused region 2 as a lower layer wiring is formed and then a wafer whereon a resist mask 4 patterned in a specific shape is formed is to be set up on a wafer loading electrode of a magnetron RIE device. Finally, CF3COCF3 (hexafluoroacetone) is used as an etching gas to etch away the SiO2 interlayer insulating film 3 for the formation of a contact hole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method applied in the field of manufacturing semiconductor devices, etc., and particularly realizes high speed / high selective etching while suppressing the microloading effect in the processing of fine connection holes. On how to do.

[0002]

2. Description of the Related Art As semiconductor devices have become more highly integrated and have higher performance as seen in VLSI in recent years, there are technical requirements for dry etching of silicon compound layers typified by silicon oxide (SiO ₂ ). The severity is increasing. First of all, the area of device / chip is increasing due to high integration, the diameter of the wafer is increasing, the pattern to be formed is highly miniaturized, and uniform processing within the wafer surface is required. As described above, the mainstream of the dry etching apparatus is shifting from the conventional batch type to the single-wafer type because of the demand for high-mix low-volume production. At this time, in order to maintain the same productivity as the conventional one, it is necessary to greatly improve the etching rate per wafer.

Further, under the condition that the junction depth of the impurity diffusion region is shallow and the various material layers are thin in order to increase the speed and miniaturization of the device, the underlayer selectivity is superior to that in the prior art and damage is prevented. Etching technology with less energy consumption is required. For example, in order to open a connection hole (hole processing) to face an impurity diffusion region formed in a semiconductor substrate and a source / drain region of a PMOS transistor used as a resistance load element of SRAM, a silicon substrate or a polycrystalline silicon layer is formed. An example is when the SiO ₂ interlayer insulating film is etched above.

Conventionally, the etching of the SiO ₂ type material layer is performed in a mode in which the ionicity is enhanced in order to break the strong Si—O bond. Typical etching gases are CHF ₃ , CF _4, etc., which use the incident ion energy of CF _x ⁺ produced from them. However, in order to perform high-speed etching, this incident ion
Since it is necessary to increase the energy, and the etching reaction is close to the physical sputtering reaction, the requirement for high speed and the requirement for high selectivity and low damage have always been in conflict.

Therefore, it is usual to add H ₂ or a depositing hydrocarbon gas to the etching gas to increase the apparent C / F ratio (ratio of the number of carbon atoms and the number of fluorine atoms) of the etching reaction system. In addition, high selectivity is achieved by promoting the deposition of the carbon-based polymer that competes with the etching reaction.

Instead of these conventional etching gases,
The applicant of the present application has previously proposed in JP-A-3-276626 a method for dry etching a silicon compound layer using a saturated or unsaturated high-order chain fluorocarbon-based gas having 2 or more carbon atoms. This is C ₂ F ₆ , C
By using a fluorocarbon-based gas such as ₃ F ₈ or C ₄ F _{8, a} large amount of CF _x ⁺ is efficiently generated from one molecule, and the etching speed is increased.

However, if a high-order chain fluorocarbon-based gas is used alone, the amount of F ^* produced also increases, and it is difficult to achieve a sufficiently high resist selectivity and silicon underlayer selectivity. Therefore, in the above publication, the etching using only the higher-order chain fluorocarbon-based gas is stopped immediately before the underlying layer is exposed, and a hydrocarbon-based gas such as ethylene (C ₂ H ₄ ) is used when the remaining portion of the silicon compound layer is etched. We also propose a two-step etching in which is added. This is to increase the C / F ratio of the etching reaction system to promote the deposition of the carbon-based polymer.

On the other hand, from the viewpoint of reducing particle contamination, it is desirable that the amount of carbon-based polymer produced is as small as possible. In order to realize high selective etching while suppressing the amount of carbon-based polymer deposited, the present inventor has previously described in Japanese Patent Laid-Open No.
In Japanese Patent Publication No. 170026, octafluorobutene (C ₄ F ₈ ) and hexafluoropropene (C ₃ F ₆ )
Et al. Disclose a method of using a chain unsaturated fluorocarbon compound having an unsaturated bond in the molecule. These gases easily generate highly active radicals due to discharge dissociation and accelerate the polymerization of the carbon-based polymer. Since this highly polymerized carbon-based polymer exhibits excellent etching resistance,
The amount of deposition required to secure selectivity was small, and it was not necessary to use a deposition gas together.

Further, the inventor of the present invention previously disclosed in Japanese Patent Laid-Open No. 4-258.
Japanese Patent No. 177 proposes a technique using an etching gas containing a saturated or unsaturated fluorocarbon compound having a ring portion in at least a part of its molecular structure.
Since the cyclic fluorocarbon compound has at least 3 or more carbon atoms and has a higher C / F ratio than a chain fluorocarbon compound having the same carbon number, high-speed etching with a large amount of CF _x ⁺ and high selection due to efficient polymer formation. Etching is now possible.

[0010]

As described above, the number of carbon atoms is 2
By using the above high-order fluorocarbon compound and selecting the structure of this compound, it has become possible to perform high-speed and high-selective etching of the silicon compound layer basically with an etching gas having a single composition. However, under the recent fine design rules, it has become clear that the microloading effect is likely to be actualized when the above-mentioned technique is applied to hole processing.

In a semiconductor device having a degree of integration of 16 MDRAM class, the area to be etched during hole processing is less than 5% of the wafer area. Generally SiO ₂
In the etching of the system material layer, the O atom sputtered out to the incident ions burns and removes a part of the carbon system polymer, so that the deposition amount of the carbon system polymer required to secure the selectivity is a practical etching rate. It is maintained moderately so as not to damage it. However, as described above, when the area to be etched becomes small, the number of O atoms sputtered out becomes extremely small. Moreover, at the bottom of the hole with a large aspect ratio, the probability of ion incidence also decreases. For these reasons, the carbon-based polymer is excessively deposited inside the hole, and the etching rate is significantly reduced. This is the microloading effect, and in the future field of semiconductor device manufacturing, in which single-wafer etching becomes the mainstream, it becomes a factor that directly affects the decrease in productivity.

Therefore, the present invention provides a high-speed operation while suppressing the microloading effect even in the processing of fine holes.
It is an object of the present invention to provide a dry etching method which enables high selection, low pollution, and low damage etching.

[0013]

The dry etching method for a silicon compound layer of the present invention is proposed to achieve the above-mentioned object, and has 2 carbon atoms having a carbonyl group and a fluorine atom in the molecule. An etching gas containing the above fluorocarbon compound is used.

According to the present invention, the etching gas contains carbon monoxide.

The present invention further includes the etching gas containing a sulfur-based compound which releases free sulfur under discharge dissociation conditions.

[0016]

In the present invention, a fluorocarbon compound having 2 or more carbon atoms having a carbonyl group and a fluorine atom in the molecule is used as a constituent of the etching gas. This fluorocarbon-based compound can supply (a) F ^* and CF _x ⁺ , and (b) can supply a carbonyl group to strengthen carbon-based polymers derived from its decomposition products and the decomposition products of a resist mask. (C) The speed of etching can be increased by supplying CO ^* , (d) O ^*
The effect of suppressing excessive carbon-based polymer deposition can be achieved by basically supplying a single composition. These effects will be sequentially described.

First, the constituent elements of the fluorocarbon compound are C, F and O. Therefore, the above (a)
As described in the above section, this compound is
Can emit ^* . Needless to say, F ^* and CF _x ⁺ contribute as the main etching species of the silicon compound layer typified by the SiO ₂ -based material layer.

The carbon-based polymer described in the item (b) can be strengthened from both aspects of increasing the degree of polymerization and strengthening the chemical bond. The fluorocarbon compound is
Although it has a carbonyl group in the molecule, the polarization structure of this carbonyl group promotes the polymerization reaction of the carbon-based polymer and functions to increase the resistance to ion injection and radical attack. Further, when a C—O bond or a carbonyl group is introduced into a carbon-based polymer, it is more chemically and physically than a conventional carbon-based polymer having a repeating structure of —CX ₂ — (X represents a halogen atom). Recent studies have also revealed increased stability. When comparing the binding energies between two atoms, this is the C—O bond (1077 kJ /
It is also intuitively understood that (mol) is much larger than the C—C bond (607 kJ / mol). Furthermore, the introduction of a carbonyl group increases the polarity of the carbon-based polymer,
The surface protection effect of the carbon-based polymer is also improved by increasing the electrostatic adsorption force with respect to the wafer being etched that is negatively charged.

As described above, the enhancement of the film quality of the carbon-based polymer itself means that the deposition amount of the carbon-based polymer necessary for securing the selectivity can be reduced, and as a result, the reduction of process pollution can be achieved. Can be realized.

Further, the fluorocarbon compound is
CO ^* can be produced under discharge dissociation conditions. This radical has a strong reducing action, and O in SiO ₂
Can pull out atoms. That is, in the present invention, Si-
The breaking of the O bond can be performed by utilizing not only the physical ion sputtering action of CF _x ⁺ but also the chemical action. As a result, the etching speed can be increased as described in the item (c). This is
The interatomic bond energy of the C—O bond is Si—O bond (4
It can also be understood from the fact that it is larger than 65 kJ / mol).
The Si atoms after the O atoms are extracted are combined with F ^* existing in the etching reaction system, and are quickly removed in the form of SiF _x .

By thus speeding up the etching, incident ion energy required to obtain a practical etching rate can be reduced, and excellent high selectivity and low damage can be achieved. . In addition, as a method for improving the underlayer selectivity, etching
Although the process is often divided into just etching and over etching, the present invention basically achieves sufficiently high selectivity even in one-step etching.

Furthermore, the fluorocarbon compound can also generate O ^* under discharge dissociation conditions. This O ^* is a chemical species that contributes to the combustion of the carbon-based polymer. As described above, under the recent miniaturized design rule, the O ^* sputtered out from the SiO ₂ -based material layer is extremely reduced, but in the present invention, this O ^* can be supplemented from the gas phase. Therefore, excessive deposition of the carbon-based polymer is prevented as described in the section (d), and as a result,
The microloading effect can be suppressed and the etching speed can be increased.

The above is the basic idea of the present invention.
In addition to this, the present invention also proposes a technique for precisely controlling high speed, high selectivity, low damage and low contamination. One is to add carbon monoxide to the etching gas. This is intended to accelerate the etching rate by increasing the amount of CO ^* produced in the gas phase to accelerate the abstraction reaction of O atoms in SiO ₂ . Thereby, the selectivity and the low damage property are further improved.

Another is to replace a part of the carbon-based polymer which contributes to the surface protection of the wafer with another substance which is not likely to become a particle contamination source. Specifically, a sulfur-based compound that releases free sulfur (S) under discharge dissociation conditions is added to the etching gas. The generated S is adsorbed to the wafer maintained at a temperature lower than the sublimation temperature, and exerts a surface protection effect on the surface of the resist mask, the exposed surface of the underlying silicon-based material layer, and the like. this is,
This is because the S deposition process and the sputter removal process compete on these surfaces. However, S does not significantly slow down the etching of SiO ₂ . This is SiO
_This is because S is immediately burned and removed by O atoms sputtered out from the surface ₂ to be etched. Moreover, S
Can be burned and removed at the same time by performing ordinary O ₂ plasma ashing for the purpose of removing the resist mask after the etching. Alternatively, sublimation can be removed by simply heating the wafer to approximately 90 ° C. or higher. In any case, there is no possibility that S will become a particle contamination source.

Further, by utilizing the deposition of S, it is possible to relatively reduce the deposition amount of the carbon-based polymer required to secure the selectivity, so that it is possible to suppress the particle contamination extremely effectively. Becomes

[0026]

EXAMPLES Specific examples of the present invention will be described below.

Example 1 In this example, the present invention is applied to the processing of contact holes, and the SiO ₂ interlayer insulating film is etched using CF ₃ COCF ₃ (hexafluoroacetone; boiling point-27.4 ° C.). Is. This process will be described with reference to FIG. As shown in FIG. 1A, the wafer used as a sample in this example is a single crystal Si substrate 1 in which an impurity diffusion region 2 as a lower layer wiring is formed in advance.
An SiO ₂ interlayer insulating film 3 is formed on top of this, and a resist mask 4 patterned into a predetermined shape is formed on top of this. The resist mask 4 has an opening 4a having an opening diameter of about 0.35 μm.

The above wafer was set on the wafer mounting electrode of a magnetron RIE (reactive ion etching) apparatus. Here, the wafer mounting electrode has a built-in cooling pipe, by supplying a refrigerant to the cooling pipe from a cooling equipment such as a chiller connected to the outside of the apparatus to circulate the cooling pipe,
It is possible to control the wafer temperature during etching to be room temperature or lower. As an example, SiO under the following conditions
_{2 The} interlayer insulating film 3 was etched.

CF ₃ COCF ₃ flow rate 50 SCCM gas pressure 2.0 Pa RF power density 2.0 W / cm ² (1
3.56 MHz) Magnetic field strength 1.50 × 10 ^-2 T (= 150
G) Wafer temperature -30 ° C (using alcohol refrigerant)

In this etching process, CF₃COCF
₃To F^*, CF_x ⁺, CO^*, O ^*Chemical species such as
To do. F^*Is SiO₂Extraction of Si atoms from the interlayer insulating film 3
Perforated, CO^*Are also related to the extraction of O atoms.
Give CF_x ⁺Reacts these radical reactions to their incident ions.
Assisted by giving energy. the above
High selectivity is achieved in the etching process, which is
A strong carbon-based poly that incorporates a carbonyl group and CO bond
Generated by the mer, which causes the surface of the resist mask 4 and
The exposed surface of the impurity diffusion region 2 is protected, and
The resist mask 4 and
As in the single crystal Si substrate 1, mainly by radical reaction
The etching rate of the material layer being etched is relatively low
This is due to reasons such as what was done.

However, the amount of the carbon-based polymer produced is not so large. This is because the incident ion energy required for high-speed etching is small due to the contribution of CO ^* , so that the RF power density is set low and the sputtering of the resist mask 4 is suppressed, and the gas is supplied from the gas phase. This is because a part of the carbon-based polymer is burned and removed by the O ^* . Therefore, the microloading effect could be suppressed. In addition, the reduction of such carbon-based polymer reduces particle
In addition to the level being greatly improved compared to the past, etching
The frequency of maintenance required for cleaning the chamber can be reduced, and productivity is significantly improved.

In this process, the etching rate of the SiO ₂ interlayer insulating film 3 was about 850 nm / min, the selection ratio to resist was about 7, and the selection ratio to Si was about 25. Further, even after the over-etching, the receding of the resist mask 4 and the destruction of the shallow junction were not observed.

Embodiment 2 In this embodiment, the same contact hole processing is performed with CF ₃ C.
It was performed using an OCF ₃ / CO mixed gas. That is, the wafer shown in FIG. 1A is set in a magnetron RIE apparatus, and as an example, the SiO ₂ interlayer insulating film 3 is formed under the following conditions.
Was etched.

CF ₃ COCF ₃ flow rate 35 SCCM CO flow rate 35 SCCM gas pressure 2.0 Pa RF power density 1.5 W / cm ² (1
3.56 MHz) Magnetic field strength 1.50 × 10 ^-2 T (= 150
G) Wafer temperature 0 ° C (using alcohol refrigerant)

The etching mechanism in this embodiment is almost the same as that described in the first embodiment. However, in this example, since the amount of CO ^* produced was increased, the reaction of extracting O atoms from the SiO ₂ interlayer insulating film 3 was promoted, and the RF power density was lowered as compared with Example 1. Nevertheless, almost the same high speed etching proceeded. In addition, since the incident ion energy is reduced in this way, the resist mask 4 and the single crystal Si substrate 1 (more precisely, the impurity diffusion region) are formed even though the wafer is not cooled at a low temperature as in the first embodiment. It was possible to secure sufficient selectivity for 2).

Embodiment 3 In this embodiment, the same contact hole processing is performed with CF ₃ C.
It was performed using an OCF ₃ / S ₂ F ₂ mixed gas. That is, the wafer shown in FIG. 1A was set in a magnetron RIE apparatus, and the SiO ₂ interlayer insulating film 3 was etched under the following conditions as an example.

CF ₃ COCF ₃ flow rate 35 SCCM S ₂ F ₂ flow rate 15 SCCM gas pressure 2.0 Pa RF power density 1.5 W / cm ² (1
3.56 MHz) Magnetic field strength 1.50 × 10 ^-2 T (= 150
G) Wafer temperature 0 ° C (using alcohol refrigerant)

Here, the above S ₂ F ₂ is one of four types of sulfur fluoride that the applicant of the present application has previously proposed for etching a SiO ₂ based material layer in Japanese Patent Laid-Open No. 4-84427. is there. The main etching species generated from S ₂ F ₂ are SF _x ⁺ and F ^* . Further, the sulfur fluoride has a large S / F ratio (ratio of the number of S atoms and the number of F atoms in one molecule) compared to SF ₆ which has been practically used as an etching gas, and it is under discharge dissociation conditions. It is possible to emit free S into the plasma.

In the above etching process, S₂F₂Raw
F to make^*And SF_x ⁺Can be used as an etching species
Others, also S₂F₂S efficiently generated from
It has a big feature that it can be deposited on the surface and used for surface protection.
It That is, CF₃COCF ₃And resist mask 4
In addition to the derived carbon-based polymer, S₂F₂From S
It can be supplied to enhance the surface protection effect. to this
Therefore, the incident ion energy is lower than that of the first embodiment.
In addition, even though the wafer temperature is high,
Good high speed and high selective etching could be performed.

Note that S deposited on the wafer was burned and removed together with the resist mask 4 and the deposited carbon-based polymer when normal O ₂ plasma ashing was performed after the etching was completed, and no particles were formed on the wafer. No pollution was left.

The present invention has been described above based on the three embodiments, but the present invention is not limited to these embodiments. For example, as the number 2 or more fluorocarbon compounds carbon having a carbonyl group and a fluorine atom in the molecule, although in the above embodiment using _{CF 3 COCF 3, CF 3 CF} 2 COF ( hydrofluoric is this structural isomer Almost the same result could be obtained when etching was performed under the same conditions using pentafluoropropionyl chloride (boiling point -27 ° C.). Furthermore, CF ₃ COF (trifluoroacetyl fluoride; boiling point −59 ° C.), (CF ₃ C
O) ₂ O (trifluoroacetic anhydride; boiling point 40 ° C), FO
C (CF ₂ ) ₃ COF (hexafluoroglutaryl fluoride; boiling point 46 ° C.) and the like can be used as well. Of these, for compounds that are liquid at room temperature, He gas
It may be introduced into the etching chamber after being vaporized by means such as bubbling.

Ions that release free S under discharge dissociation conditions
As the c-based compound, the above S₂F ₂And SF₂, S
F_Four, S₂F_TenEtc. can be used. Can release S
If you pay attention only to the point₂Cl₂, S₂Br₂, H₂
There are other applicable compounds such as S, but especially SiO.
₂Etching is assumed when etching the material layer
F as a seed^*Compounds capable of producing are preferred.

The silicon compound layer is formed of PSG, BSG, BPSG, AsSG, A in addition to the above-mentioned SiO ₂ interlayer insulating film.
It may be made of SiO ₂ silicon-based material such as sPSG or AsBSG, or SiN _x . The structure of the wafer used as the etching sample is not limited to the above structure. For example, the base of the SiO ₂ interlayer insulating film may be a polycrystalline silicon layer, a polycide film, or Al-1% other than the single crystal Si substrate. It may be a metal material layer such as a Si layer.

A rare gas such as He or Ar may be appropriately added to the etching gas for the purpose of obtaining a sputtering effect, a dilution effect, a cooling effect and the like. Needless to say, the etching apparatus used, the etching conditions, and the like can be changed as appropriate.

[0045]

As is clear from the above description, in the present invention, a fluorocarbon compound having 2 or more carbon atoms having a carbonyl group and a fluorine atom in the molecule is used as a constituent of the etching gas for the silicon compound layer. Therefore, basically, an etching gas of a single composition is used,
High-speed, high-selection, low pollution, and low damage / etching can be realized by the one-step process. Furthermore, CO
It is also possible to satisfy these requirements at a higher level by adding a sulfur-based compound to the etching gas.

The present invention contributes to a great improvement in yield and productivity in the manufacture of semiconductor devices which are designed based on fine design rules and which are required to have high integration, high performance and high reliability.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a process in which the present invention is applied to processing a contact hole in the order of steps, (a) showing a state where a resist mask is formed on a SiO ₂ interlayer insulating film, (b) ) Represents the state where the contact holes are formed.

[Explanation of symbols]

1 ... monocrystalline Si substrate 2 ... impurity diffusion regions 3 ... SiO ₂ interlayer insulating film 4 ... resist mask 4a ... opening 5 ... contact hole

Claims (3)

[Claims] 1. A dry etching method comprising etching a silicon compound layer using an etching gas containing a fluorocarbon compound having a carbonyl group and a fluorine atom in the molecule and having 2 or more carbon atoms. 2. The dry etching method according to claim 1, wherein the etching gas contains carbon monoxide. 3. The dry etching method according to claim 1, wherein the etching gas contains a sulfur-based compound that releases free sulfur under discharge dissociation conditions.