JP2687787B2 - Dry etching method - Google Patents

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 to any one of resist selectivity, silicon underlayer selectivity, high speed, low damage and low contamination. Also relates to a dry etching method for a silicon oxide-based material layer, which is excellent in

[0002]

2. Description of the Related Art As semiconductor devices have become more highly integrated and have higher performance as seen in VLSI, ULSI and the like in recent years, there is a technical requirement for a dry etching method for a silicon oxide (SiO ₂ ) based material layer. It is getting more and more severe. 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. From the background that high-mix low-volume production is required as described above,
The mainstream of dry etching equipment is shifting from the conventional batch type to the single wafer type. 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, in a situation where the junction depth of the impurity diffusion region is shallow and various material layers are thin in order to increase the speed and miniaturization of the device, the selectivity to the underlayer is more excellent than before. Etching technology with less damage is required. For example, a PM used as an impurity diffusion region formed in a semiconductor substrate or a resistance load element of SRAM.
An example is etching of a SiO ₂ interlayer insulating film, which is performed using a silicon substrate or a polycrystalline silicon layer as a base when a contact is to be formed in the source / drain region of an OS transistor.

Further, improvement of the resist selection ratio is also an important issue. This is because submicron devices have become unacceptable for producing slight dimensional conversion differences due to resist receding. Conventionally, etching of a silicon oxide-based material layer has been performed in a mode with enhanced ionicity in order to break a strong Si—O bond.
Typical etching gas is CHF ₃ , CF _4, etc., and CF _x ⁺ generated from them is the main etching species. However, since high ion energy is required to perform high-speed etching, and the etching reaction is close to a physical sputtering reaction, there has been a problem that high-speed property and selectivity are always contradictory.

Therefore, usually, H ₂ or a depositing hydrocarbon gas is added to the etching gas to obtain an apparent C / F ratio (ratio of the number of carbon atoms and the number of fluorine atoms) of the etching reaction system. High selectivity is achieved by increasing and promoting the deposition of carbon-based polymer that occurs in competition with the etching reaction. In place of these conventional etching gases, the applicant of the present application has previously disclosed in JP-A-3-276626 that dry etching of a silicon compound layer using a saturated or unsaturated high-order chain fluorocarbon-based gas having 2 or more carbon atoms. Proposing a method. This is C ₂ F ₆ , C
CF _x ⁺ is efficiently generated by using a fluorocarbon-based gas such as ₃ F ₈ , C ₄ F ₁₀ or C ₄ F ₈ ,
This is intended to speed up the etching. However, if only the high-order chain fluorocarbon-based gas is used alone, the amount of F ^* produced increases, and the selectivity ratio to resist and the selection ratio to silicon underlayer cannot be made sufficiently large.
For example, when the SiO ₂ layer on a silicon substrate is etched using C ₃ F ₈ as an etching gas, high speed is achieved, but the selectivity ratio to resist is as low as 1.3.
In addition to insufficient etching resistance, the pattern conversion recedes, resulting in a dimensional conversion difference. Further, since the selection ratio to silicon is about 4.1, there remains a problem in overetching resistance.

Therefore, in order to solve these problems, in the above-mentioned prior art, the etching using only the higher-order chain fluorocarbon-based gas is stopped immediately before the underlying layer is exposed, and when etching the remaining portion of the silicon compound layer, Two-step etching is performed in which a hydrocarbon-based gas such as ethylene (C ₂ H ₄ ) is added to the above compound in order to promote the deposition of the carbon-based polymer. This is to supply C atoms into the etching reaction system and consume excess F ^* by H ^* generated in plasma to change it to HF.
The purpose is to increase the apparent C / F ratio.

However, under the present circumstances where the design rules of semiconductor devices are highly miniaturized, the dimensional conversion difference from the etching mask has almost become unacceptable, and the two-step etching as described above is performed. Also, it is necessary to further improve the selection ratio in the first etching. Further, as further miniaturization progresses in the future, the influence of particle contamination by the carbon-based polymer may become more serious, so the amount of deposition gas such as hydrocarbon-based gas used in the second-stage etching may be increased. I would like to reduce it as much as possible.

From this point of view, the inventor of the present invention has previously disclosed Japanese Patent Laid-Open No.
No. 170026, the temperature of the substrate to be processed is 5
A technique for etching a silicon compound layer using a chain unsaturated fluorocarbon-based gas having at least one unsaturated bond in the molecule while controlling the temperature to 0 ° C. or lower is proposed. The chain unsaturated fluorocarbon-based gas is, for example, octafluorobutene (C ₄ F ₈ ) or hexafluoropropene (C ₃ F ₆ ). These gases are theoretically one molecule to two or more carbon atoms due to discharge dissociation.
Since F _x ⁺ is generated, SiO ₂ can be etched at high speed. Further, since it has an unsaturated bond in the molecule, it is easy to generate a highly active radical by dissociation, and the polymerization of the carbon-based polymer is promoted. Moreover, since the temperature of the substrate to be processed is controlled to 50 ° C. or lower, the deposition of the carbon-based polymer is promoted.

By this technique, the selectivity with respect to resist and the selectivity with respect to silicon underlayer can be greatly improved without using a deposition gas, and particle contamination can also be reduced.

[0010]

As described above, the dry etching method using the chain unsaturated fluorocarbon-based gas previously proposed by the applicant of the present application provides an extremely great advantage as compared with the conventional technique. there were. However, this merit is mainly due to the improvement in selectivity, and there is still room for improvement in particle contamination. In other words, this technique is no different from the conventional one in that the mechanism of securing the selection ratio is achieved by the deposition of carbon-based polymer that progresses competitively with the etching reaction. The polymer is accumulated and the particle level deteriorates. Therefore, even if the particle contamination can be reduced, the current situation is that the maintenance frequency for cleaning the etching chamber is reduced.

Therefore, an object of the present invention is to provide a dry etching method for a SiO ₂ -based material layer, which is particularly excellent in high speed, high selectivity and low damage, and in which low contamination is thoroughly achieved.

[0012]

The dry etching method of the present invention is proposed in order to achieve the above-mentioned object, and has the general formula C _m F _n (where m and n are natural numbers indicating the number of atoms). And satisfies the condition of m ≧ 2, n ≦ 2m + 2), and Si—O.
The SiO ₂ -based material layer is etched by using an etching gas containing an additive compound having an atom capable of forming a chemical bond having a higher interatomic bond energy than the bond with the O atom in the molecule.

Here, the fluorocarbon compound C _m
F _n is a so-called higher order fluorocarbon compound because the number of C atoms m is 2 or more. The number of F atoms n is (2
Since m + 2) or less, whether saturated or unsaturated,
The carbon skeleton structure does not matter whether it is linear, branched or cyclic. Alternatively, the etching is performed in two steps, and first, in the first step, the SiO ₂ -based material layer is etched to a depth that does not substantially exceed the layer thickness as described above. Etching of the remaining portion of the SiO ₂ based compound layer and overetching may be performed by using an etching gas in which the content ratio of the added compound is higher than that in the first step.

Further alternatively, in the first step, the SiO ₂ -based material layer is etched substantially by the thickness of the SiO ₂ -based material layer using an etching gas containing the fluorocarbon compound and the additive compound, and then in the second step. S ₂ F ₂ , S
It is also possible to perform overetching using an etching gas containing at least one sulfur fluoride selected from F ₂ , SF ₄ , and S ₂ F ₁₀ and the above-mentioned additive compound.

These sulfur fluorides are compounds that the applicant of the present invention has previously proposed as a gas for etching the SiO ₂ type material layer. The main etching species in this case is SF _x ⁺
It is. In addition, the above sulfur fluoride is sulfur hexafluoride (S
The S / F ratio (ratio between the number of S atoms and the number of F atoms in one molecule) is larger than that of F ₆ ) and free S can be released into plasma under discharge dissociation conditions. This S is removed in the form of SO _x by the supply of oxygen atoms on the surface of the SiO ₂ -based material layer, but remains on the surface of the resist material or Si-based material, or on the pattern side wall within a certain temperature range. It can be deposited and contributes to the achievement of high selectivity and high anisotropy.

By the way, it is particularly preferable to carry out the above-mentioned etching and over-etching by controlling the temperature of the substrate to be etched below room temperature. this is,
This is because it is advantageous for the deposition of the carbon-based polymer, which is a by-product of the etching reaction, or sulfur (S) particularly when sulfur fluoride is used. Further, the additive compound used in the present invention is for accelerating the etching by breaking the Si—O bond constituting the SiO ₂ -based material layer to extract the O atom, and therefore the addition of the Si—O bond Interatomic bond energy [465 kJ / mol; provided that Si
Value calculated from standard enthalpy of formation of O ₂ crystal], it is sufficient to include an atom capable of forming a chemical bond having an interatomic bond energy larger than that of the O atom. Carbon monoxide (CO) can be mentioned as the simplest low-molecular compound satisfying this condition. The interatomic bond energy of the C—O bond was 1076 kJ / mol, and Si—
It is much larger than that of O bond and exerts a strong reducing property on the SiO ₂ -based material layer to accelerate its etching.

[0017]

In the conventional etching of the SiO ₂ -based material layer, the low contamination has not been achieved at a satisfactory level because the mechanism for obtaining high selectivity depends entirely on the deposition of the carbon-based polymer. This is because a relative decrease in the etching rate of the material and the underlying Si-based material was expected. In contrast, the present invention takes the reverse approach of achieving high selectivity by increasing the etching rate of the SiO ₂ based material layer. That is, it becomes possible to break the Si—O bond while utilizing the chemical action in addition to the conventional physical ion-sputtering action.

From one molecule of the higher order fluorocarbon compound used in the present invention, theoretically two or more CF _x ⁺ can be produced. Therefore, under the same gas pressure, CF ₃ H,
The absolute amount of CF _x ⁺ in the plasma becomes large as compared with the case of using a conventionally known gas such as CF ₂ H ₂ .
High speed etching becomes possible. As described above, an additive compound having an atom in the molecule capable of forming a chemical bond with an O atom having a higher interatomic bond energy than the Si—O bond is added to a higher order fluorocarbon compound which is originally excellent in high speed. Therefore, higher speed etching can be performed.

Particularly, when CO is used as the above-mentioned additional compound, a large amount of CF _x ⁺ causes ion sputtering action and CO.
Due to the synergistic effect with the oxygen abstraction effect of ^*, it is possible to etch the SiO ₂ -based material layer at an extremely high speed without increasing the incident ion energy as compared with the conventional case. Moreover, CO has no effect on the resist material and the underlying Si-based material, and the etching rate of these materials is kept low.

Further, when a carbonyl group (> C = O) is introduced into the carbon-based polymer derived from CO, the ion-sputtering resistance of the carbon-based polymer is improved. The deposition amount of carbon-based polymer required to achieve high selectivity is very small. Therefore, more thorough pollution reduction can be achieved as compared with the conventional technique.

The above is the basic idea of the present invention. In addition, if etching is further performed in two stages, a greater merit can be obtained. That is, SiO ₂
The etching of the system material layer is divided into two stages, that is, the stage until immediately before the underlying material layer is exposed and the stage thereafter, and if the CO content ratio in the composition of the etching gas is increased in the latter half stage, the SiO ₂ system material layer is formed. Of these, the etching near the interface with the base proceeds by a mechanism mainly composed of oxygen abstraction reaction. This makes it possible to further reduce damage.

Alternatively, the etching of the SiO ₂ -based material layer is divided into two steps, that is, just-etching and over-etching, and a fluorocarbon compound is not used during over-etching when high speed is not required. Instead, sulfur fluoride and CO are used. Further reduction of pollution can be achieved by switching to a mixed system of and to completely eliminate the deposition of carbon-based polymer. In this case, the etching of the SiO ₂ -based material layer partially remaining on the wafer proceeds by the ion-sputtering action of SF _x ⁺ and the oxygen abstraction of CO ^* . Alternatively, depending on the conditions, the contribution of SF _x ⁺ decreases, and oxygen abstraction becomes the main component. When the underlying Si-based material layer is exposed, S is deposited on its surface and F
^* Erosion of the Si-based material layer due to (fluorine radicals) can be prevented. Moreover, the deposited S easily decomposes or sublimes if the wafer is heated to around 100 ° C. after the etching is completed, so that no particle contamination remains on the wafer. Therefore, etching excellent in high speed, high selectivity, low contamination, and low damage is realized.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described. Example 1 This example, the present invention is applied to the contact hole processing, and octafluorocyclobutane _{(c-C 4 F 8)} C
This is an example in which the SiO ₂ interlayer insulating film is etched using a mixed gas with O. The process of this embodiment will be described with reference to FIG.

The substrate to be etched (wafer) used as a sample in this embodiment is, as shown in FIG. 1A, a SiO ₂ interlayer insulating film formed on a single crystal silicon substrate 1 on which an impurity diffusion region 2 is formed in advance. The film 3 is formed, and the resist pattern 4 is further formed as an etching mask for the SiO ₂ interlayer insulating film 3. The resist pattern 4 is provided with an opening 4a.

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 room temperature or lower. Here, ethanol is used as a coolant, and the wafer temperature during etching is -3.
It was maintained at 0 ° C. As an example, the SiO ₂ interlayer insulating film 3 was etched under the following conditions.

C-C ₄ F ₈ flow rate 35 SCCM CO flow rate 15 SCCM gas pressure 2.0 Pa RF power density 2.0 W / cm ² (13.56 MHz) magnetic field strength 150 Gauss In this etching process, Si exposed in the opening 4 a
On the surface of the O ₂ interlayer insulating film 3, since the oxygen abstraction reaction by CO ^* promotes the etching of SiO ₂ by CF _x ⁺ , it is 950 nm / min even though it is not a condition to give an excessive incident ion energy. Etching proceeded at high speed. As a result, as shown in FIG. 1B, the contact hole 5 excellent in anisotropic shape was quickly formed.

In this embodiment, a carbon-based polymer (not shown) is formed on the surface of the resist pattern 4 and the impurity diffusion region 2.
Although There was deposited, since the relative content of c-C ₄ F ₈ by addition of CO to the etching gas is reduced, the amount of deposition was less crab than the conventional process. However, despite this, high selectivity is achieved, and the film thickness of the resist pattern 4 is reduced and the pattern edge recedes.
Neither destruction of the shallow junction due to overetching was observed. The selection ratio to resist was about 5, and the selection ratio to silicon was about 30. This high selectivity is because the incident ion energy is reduced, and the radical reaction by F ^* is suppressed by the low temperature cooling of the wafer.
This is the result of comprehensively showing the effects that the carbon-based polymer was strengthened by the introduction of the carbonyl group and exhibited high etching resistance even in a small amount.

Further, since the amount of carbon-based polymer deposited is reduced, the frequency of maintenance required for cleaning the etching chamber can be reduced, and the throughput is also improved. Example 2 In this example, using c-C ₄ F ₈ / CO gas mixture S
The etching of the iO ₂ interlayer insulating film was divided into two stages, that is, a stage until immediately before the underlying layer was exposed and a stage thereafter, and in the latter half stage, the CO content ratio was relatively increased to further improve the selectivity. The process of this example is illustrated in FIG. 2 and in FIG.
This will be described with reference to FIG.

The wafer used in this example is shown in FIG.
Is the same as that shown in. This wafer was set in a magnetron RIE apparatus, and as an example, SiO was prepared under the following conditions.
_{2 The} interlayer insulating film 3 was etched until just before the impurity diffusion region 2 was exposed. c-C ₄ F ₈ flow rate 35 SCCM CO flow rate 15 SCCM (content ratio in etching gas 30%) Gas pressure 2.0 Pa RF power density 2.0 W / cm ² (13.56 MHz) Magnetic field strength 150 Gauss Wafer temperature 0 ° C. 1 In the etching of the stage, high-speed etching mainly consisting of a physical sputter reaction by c-C ₄ F ₈ is performed, and the emission spectrum intensity of CO ^* at 483.5 nm or the emission spectrum intensity of SiF ^* at 777 nm is increased. The starting point was used to determine the end point.
As a result, as shown in FIG. 2, the state of the wafer is such that the contact hole 5 is formed up to the midway portion and the S
The remaining portion 3a of the iO ₂ interlayer insulating film 3 was left.

Next, the etching conditions were switched to the following conditions as an example, and the remaining portion 3a was etched and over-etched. c-C ₄ F ₈ flow rate 20 SCCM CO flow rate 30 SCCM (content ratio in etching gas 60%) Gas pressure 2.0 Pa RF power density 1.2 W / cm ² (13.56 MHz) Magnetic field strength 150 Gauss Wafer temperature 0 ° C. 2 In the etching at the stage, the RF power density was reduced to reduce the incident ion energy, and etching was performed mainly by the chemical oxygen abstraction reaction by CO. In addition, c near the interface with the impurity diffusion region 2
Since the content ratio of —C ₄ F ₈ was lowered, the amount of carbon-based polymer deposited on the surface of the impurity diffusion region 2 could be reduced.

As a result, even though the wafer temperature was higher than that in Example 1, excellent high selectivity, low damage,
Low pollution was achieved. Example 3 In this example, c-C ₄ F was used until just etching.
₈ / CO mixed gas, S ₂ F ₂ / in overetching
A CO mixed gas was used to achieve thorough pollution reduction.

First, the wafer in the state shown in FIG. 1A is set in a magnetron RIE (reactive ion etching) apparatus, and as an example, the etching of the SiO ₂ interlayer insulating film 3 is performed by just etching. I went to the state. c-C ₄ F ₈ flow rate 35 SCCM CO flow rate 15 SCCM gas pressure 2.0 Pa RF power density 2.0 W / cm ² (13.56 MHz) magnetic field strength 150 Gauss wafer temperature 0 ° C. By this first stage etching, FIG. The contact hole 5 is almost completed as shown in FIG. However, due to the temperature distribution of the wafer, the plasma density distribution, etc., the remaining portion 3a of the SiO ₂ interlayer insulating film 3 is left on the bottom of the contact hole 5 on the wafer as shown in FIG. Also exists.

Therefore, overetching for removing the residual portion 3a was performed under the following conditions as an example. S ₂ F ₂ 15 SCCM CO flow rate 35 SCCM Gas pressure 2.0 Pa RF power density 1.0 W / cm ² (13.56 MHz) Magnetic field intensity 150 Gauss Wafer temperature 0 ° C. In this over-etching, incident ion energy is reduced and oxygen by CO is generated. The etching reaction was allowed to proceed based on the extraction reaction, and S generated by dissociation from S ₂ F ₂ was deposited on the surface of the resist pattern 4 and the impurity diffusion region 2. As a result, high selectivity could be achieved without using any carbon-based polymer near the interface with the impurity diffusion region 2.

The deposited S can be easily removed by heating the wafer to about 90 ° C. after completion of etching or by sublimation or decomposition when ashing the resist pattern 4. S deposited in the etching chamber can be removed as well. Therefore, in this example, the reduction of pollution was further thorough. As a result, the device yield was improved and the throughput was also improved.

The present invention has been described above based on three embodiments, but the present invention is not limited to these embodiments. For example, the etching gas is O ₂ or the like for the purpose of controlling the etching rate. Or a rare gas such as He or Ar may be appropriately added in the sense of expecting a sputtering effect, a dilution effect, a cooling effect, or the like. Further, the material layer to be etched is not limited to the above-mentioned SiO ₂ , but PSG, BSG, BPSG, AsSG,
It may be AsPSG, AsBSG, or the like.

[0036]

As is apparent from the above description, in the present invention, by using an etching gas in which an additive compound, especially CO is added to a higher order fluorocarbon compound, a carbon-based material for etching a SiO ₂ -based material layer is used. It is possible to achieve high selectivity even if the amount of polymer deposited is reduced. As a result, the device yield can be improved, the maintenance frequency of the etching apparatus can be reduced, and the throughput can be improved. Of course, the high-speed property, which is a feature of higher order fluorocarbon compounds, is utilized as before, and since this is combined with the oxygen abstraction reaction by CO, incident ion energy can be reduced,
It can also reduce damage. Therefore, it is possible to dry-etch the SiO ₂ -based material layer which is excellent in high speed, high selectivity, low damage and low contamination.

The present invention is extremely suitable for manufacturing a semiconductor device which is designed based on a fine design rule and has a high degree of integration and high performance.

[Brief description of the 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 pattern is formed on a SiO ₂ interlayer insulating film, (b) ) Indicates the state where the contact holes are opened.

FIG. 2 is a schematic cross-sectional view showing a state in which a contact hole is formed halfway in another process example in which the present invention is applied to processing a contact hole.

[Explanation of symbols]

1 Single Crystal Silicon Substrate 2 Impurity Diffusion Region 3 SiO ₂ Interlayer Insulating Film 3a Remaining Part (of SiO ₂ Interlayer Insulating Film) 4 Resist Pattern 4a Opening 5 Contact Hole

Claims (6)

(57) [Claims] 1. A fluorocarbon compound represented by the general formula C _m F _n (where m and n are natural numbers indicating the number of atoms and satisfying the condition of m ≧ 2, n ≦ 2m + 2) and Si.
Etching the silicon oxide based material layer using an etching gas containing an additive compound having an atom capable of forming a chemical bond having a higher interatomic bond energy than the -O bond with the O atom in the molecule. Characteristic dry etching method. 2. The dry etching method according to claim 1, wherein the etching is performed while controlling the temperature of the substrate to be etched to be room temperature or lower. 3. A fluorocarbon compound represented by the general formula C _m F _n (where m and n are natural numbers indicating the number of atoms and satisfying the condition of m ≧ 2, n ≦ 2m + 2) and Si.
An etching gas containing an additive compound having an atom capable of forming a chemical bond having a higher interatomic bond energy than that of an —O bond with an O atom in the molecule is used, and the silicon compound layer is substantially formed into a layer thickness thereof. A first step of etching the silicon oxide based compound layer to a depth that does not exceed the first step, and an etching gas having a content ratio of the additive compound to the fluorocarbon compound higher than that in the first step is used to etch the remaining portion of the silicon oxide based compound layer. And a second step of performing over-etching. 4. A fluorocarbon compound represented by the general formula C _m F _n (where m and n are natural numbers indicating the number of atoms and satisfying the condition of m ≧ 2, n ≦ 2m + 2) and Si.
An etching gas containing an additive compound having an atom capable of forming a chemical bond with an O atom having a higher interatomic bond energy than the —O bond in the molecule is used, and the silicon oxide based material layer is substantially Using a first step of etching the layer thickness and an etching gas containing at least one sulfur fluoride selected from S ₂ F ₂ , SF ₂ , SF ₄ , and S ₂ F ₁₀ and the additive compound. Second over-etching
A dry etching method comprising: 5. The dry etching method according to claim 3, wherein the etching and the over-etching are performed while controlling the temperature of the substrate to be etched at room temperature or lower. 6. The dry etching method according to claim 1, wherein carbon monoxide is used as the additive compound.