JP3282292B2 - 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 to the processing of semiconductor devices and the like, and more particularly to a method of forming an amorphous carbon (aC: H) thin film, a silicon carbide (SiC) thin film, a diamond thin film and the like. The present invention relates to a method for anisotropically etching a carbon-based inorganic material film by a practical dry process using a resist mask.

[0002]

2. Description of the Related Art In the field of semiconductor device development in recent years, there is a coexistence between the pursuit of the fine processing technology of silicon devices to the physical limit and the pursuit of new devices using materials having different physical properties from silicon. are doing.

One of the techniques for pursuing the fine processing technology to the physical limit is the use of an antireflection film for the purpose of improving the resolution in photolithography. In particular,
High pressure mercury lamp i-line (365 nm) and KrF (249
nm) as an exposure light source and in UV lithography forming a fine resist mask having a line width of 0.4 μm or less, an antireflection film is almost essential. As an antireflection film material exhibiting good light absorption characteristics in the far ultraviolet region, see the 40th Annual Meeting of the Japan Society of Applied Physics (Spring Annual Meeting, 1993), p. 559, Abstract No. 30a-L-
2, aC: H is proposed.

On the other hand, as a new material for a semiconductor device which has a possibility of breaking the operation limit of an existing semiconductor device such as a silicon device or a GaAs device, a p-type or n-type material is used.
Silicon carbide (SiC) containing p-type impurities and diamond containing p-type impurities have been proposed. These have band gaps (β-SiC of 2.2 eV, diamond of 5.5 eV) having a band gap of Si (1.1 eV) and Ga.
As larger than any of As (1.4 eV), 600
It can operate at high temperatures of up to 700 ° C. and has excellent radiation resistance. Therefore, it is expected as a material for realizing a semiconductor device that operates with high reliability even in a severe environment such as the outer space or the vicinity of a nuclear reactor exposed to strong radiation or high temperature.

[0005]

The above-mentioned a-
For C: H, SiC, and diamond, it is necessary to establish an appropriate dry etching method in order to put them into practical use as a material for a semiconductor device.

First, as for aC: H thin film, US Pat. No. 4,975,144 discloses a dry etching method using NF ₃ . Since the etching at this time is based on the chemical mechanism by F ^* , it proceeds isotropically. It has also been shown that the use of H ₂ instead of NF ₃ enables anisotropic etching indispensable for microfabrication. However, for this purpose, it is necessary to increase the self-bias potential on the substrate side. There is a concern that damage may occur.

As for the SiC thin film, a method using a fluorine-based gas has been known so far.
No. 293234 discloses a method using an Ar / CHF ₃ mixed gas. Vac. Sci. Technol. ,
B4 (1) p. 349 to 354 disclose a method using a CF ₄ / O ₂ mixed gas, SF ₆ / He mixed gas or the like.

[0008] Etching methods using these fluorine-based etching species have a common problem that it is difficult to simultaneously achieve a stable etching rate, an excellent anisotropic shape, and high resist selectivity. That is, if the C / F ratio (ratio of the number of carbon atoms to the number of fluorine atoms) of the etching reaction system is too high, CF _x in the etching reaction product
Becomes excessive, and a stable etching rate cannot be obtained. Therefore, if an attempt is made to lower the C / F ratio by increasing the supply amount of F ^* , the etching mechanism becomes isotropic. Alternatively, if an attempt is made to lower the C / F ratio by burning off C by adding O ^* , the selectivity to the resist mask is reduced.

Since a diamond-based thin film is a material composed of only carbon atoms except for a small amount of impurities, it can be easily etched in principle by using O ^* (oxygen radical) as an etching species. . In this case, it is also known that the use of NO ₂ having excellent surface adsorption ability greatly increases the etching rate as compared with the case of using O ₂ , but in any case, the basis of the etching mechanism is O ^* Combustion reaction. Therefore, maintaining high selectivity for the resist mask in such a process is still extremely difficult.

Therefore, the present invention provides a conventional aC: H, Si
It is an object of the present invention to solve the above-mentioned problems in dry etching of C and diamond and to provide a technique capable of anisotropically etching these by a practical process.

[0011]

Means for Solving the Problems The present inventor has made the following solution in the course of intensive studies in order to achieve the above object. First, as a means for overcoming the decrease in selectivity with respect to resist, use of an etching mask made of an inorganic material such as SiO ₂ can be considered, but this requires extra steps for deposition and etching of the inorganic material layer. Therefore, a reduction in throughput and economy is unavoidable. Therefore,
As an etching mask, a resist mask that can be formed by photolithography is used.

Next, in order to improve the selectivity to the resist mask, the use of O ^* should be avoided, and for that purpose, a halogen radical is required as an etching species. In addition, fluorine radicals are necessary in consideration of the magnitude relationship between the interatomic bond energies of the material molecules to be etched and the etching reaction product molecules. Further, in order to achieve an anisotropic shape while maintaining a practical etching rate, it is effective to protect the side wall by using some kind of deposit. However, depositing a large amount of the carbon-based polymer as this deposit is not preferable in preventing particle contamination. From this viewpoint, it is considered effective to use a sulfur-based deposit having sublimability or heat-decomposability, and the present invention has been proposed.

[0013] The dry etching method according to the present invention is proposed based on the above-mentioned concept, and can produce at least fluorine radicals and free sulfur under discharge dissociation conditions, and has an F / S ratio. Is to etch a carbon-based inorganic material film while depositing a sulfur-based deposit on a region to be etched using an etching gas containing a sulfur fluoride compound of less than 6. (However, F represents the number of fluorine atoms and S represents the number of sulfur atoms, respectively.) The sulfur fluoride compound used here is S ₂ F ₂ , SF ₂ , SF
₄ and S ₂ F ₁₀ .

Further, the dry etching method according to the present invention can produce a gas capable of generating at least fluorine radicals under discharge dissociation conditions, a free sulfur, and a X
The carbon-based inorganic material film is etched while depositing a sulfur-based deposit on the region to be etched using an etching gas containing a halogenated sulfur compound having a / S ratio of less than 6.
(Where X represents the number of fluorine atoms and S represents the number of sulfur atoms, respectively.) The halogenated sulfur compound used here is S
_{2 F 2, SF 2, SF} 4, S 2 F 10, S 3 Cl 2, S
₂ Cl ₂ , SCl ₂ , S ₃ Br ₂ , S ₂ Br ₂ , SBr
Any one of the _two .

A gas containing a nitrogen compound may be further used as an etching gas used in the dry etching method according to the present invention, and a sulfur nitride compound may be deposited as the sulfur deposit. N ₂ , NF ₃ , NCl ₃ , NBr _{3 and the} like can be used as the nitrogen-based compound.

Alternatively, H is used as the etching gas.
_2, at least one selected from H ₂ S and silane compounds
The use of a gas containing various types of halogen radical consuming compounds can promote the deposition of sulfur-based deposits.

The present invention is particularly suitable when the carbon-based inorganic material film is at least one of an aC: H thin film, a SiC-based thin film, and a diamond-based thin film. Here, as a constituent material of the SiC-based thin film, in addition to pure SiC, an SiC semiconductor containing N as an n-type impurity, or B, Al, Ga, or the like as a p-type impurity can be used.

Further, as a constituent material of the diamond-based thin film, in addition to pure diamond, B as a p-type impurity is used.
Can be used.

[0019]

The possibility of etching the material layer to be etched is as follows.
This can be inferred to some extent from the magnitude relationship between the interatomic bond energies of the material layer molecules to be etched and the etching reaction product molecules. In the dry etching of the carbon-based inorganic material film of the present invention, F ^* instead of O ^* is used as a main etching species. This can be considered from the following relation of chemical bond energy.

C—O (799 kJ / mol)> C—F (484 kJ / mol)> C—C (354 kJ / mol) where the C—O bond is CO ₂ molecule, the C—F bond is CF ₄ molecule, The -C bond is a calculated value in a diamond crystal. For a-C: H and SiC, F
^* Etching is possible.

In the dry etching method of the present invention, free sulfur (S) coexists with the above-mentioned fluorine radical in the etching reaction system. This S is a sublimable substance, and the temperature of the wafer is lower than the sublimation temperature (about 90 ° C.).
) Is deposited on the region to be etched. In particular, S deposited on the side wall surface of a pattern in which vertical incidence of ions does not occur in principle functions as a side wall protective film. Therefore, both a practical etching rate and shape anisotropy can be achieved. In addition, since S is easily sublimated when the wafer is heated to a temperature equal to or higher than the sublimation temperature, there is no risk of causing particle contamination unlike carbon-based polymers.

Here, S ₂ F ₂ , SF ₂ , SF ₄ , S ₂
F ₁₀ , S ₃ Cl ₂ , S ₂ Cl ₂ , SCl ₂ , S ₃ Br
₂ , S ₂ Br ₂ and SBr ₂ are compounds capable of efficiently releasing free sulfur under discharge dissociation conditions. When a nitrogen-based compound is added to the sulfur halide, free S reacts with a nitrogen-based species dissociated from the nitrogen-based compound to form polythiazyl (SN).
Various sulfur nitride-based compounds including _X are produced.
This sulfur nitride-based compound has a lower sublimation temperature or decomposition temperature than S alone. That is, in the etching reaction system, the vapor pressure is lower and the deposition property is stronger. For this reason, a more excellent side wall protection effect than S alone is exhibited.

[0023] H ₂ as a sulfur halide, or which nitrogen-based compound further halogen radical consuming compound in the etching gas system was _added, H 2 _S, the addition of at least one silane compound, S, or sulfur-based nitride Compound deposition can be promoted. This is due to H ^* and Si ^* generated from halogen radical consuming compounds ^.
Traps the halogen radicals X ^* in the etching reaction system and removes them in the form of volatile substances such as HX (hydrogen halide) and SiX ₄ to form an S / X ratio of the etching reaction system. This is because the ratio of the number of S atoms to the number of halogen (X) atoms increases.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described.

Embodiment 1 In this embodiment, trench etching of a β-SiC film was performed using S ₂ F ₂ gas. This process will be described with reference to FIG.

As shown in FIG. 1A, the wafer used as an etching sample in this embodiment is obtained by heteroepitaxially growing a β-SiC film 2 having a thickness of about 2 μm on a single crystal silicon substrate 1. A resist mask 4 having a predetermined pattern and a thickness of about 1 μm is formed thereon. Here, as the single crystal silicon substrate 1,
A substrate having a crystal plane orientation of (100) or (111) was used.
The β-SiC film 2 is, for example, SiH ₄ / C ₂ H ₄ / H
_The film is formed by a CVD method at a wafer temperature of 1000 to 1300 ° C. using _two mixed gases.

This wafer was set in an RF bias applying type magnetic field microwave plasma etching apparatus, and as an example, the β-SiC film 2 was etched under the following conditions.

S ₂ F ₂ flow rate 30 SCCM Gas pressure 1.33 Pa Microwave power 850 W (2.45 GHz) RF bias power 10 W (2 MHz) Wafer mounting electrode temperature −10 ° C. By this etching, the β-SiC film 2 becomes SiF _x , C
It was removed in the form of F _x. In addition, S free from S ₂ F ₂
Was generated and deposited on the side wall surface of the pattern to form an S deposition layer 6 as shown in FIG. This S deposition layer 6
Exhibits a sidewall protection effect, that the ion sputtering action by SFx ⁺ can be used, and that the S / F of the etching reaction system
The trench 5 having an anisotropic shape could be formed because the ratio was originally large and the radical reactivity was suppressed by cooling the wafer. The trench 5 can be used for forming a buried gate electrode, an element isolation region, a capacitor, and the like.

In the above-described process, O ^* is not involved in the etching reaction system, and the RF bias power necessary for securing anisotropy is reduced by the amount that the side wall protection effect can be expected. There was almost no retreat in the fourth. When O ₂ plasma ashing was performed under normal conditions after the completion of the etching, as shown in FIG. 1C, the S deposition layer 6 was removed together with the resist mask 4, and no particle contamination occurred on the wafer. Did not. Since the ashing was performed under the condition of extremely low incident ion energy, the β-SiC film 2 was not etched.

Embodiment 2 In the present embodiment, the same trench etching of the β-SiC film 2 was performed using an S ₂ F ₂ / H ₂ mixed gas. An example of the etching conditions is shown below.

S ₂ F ₂ flow rate 25 SCCM H ₂ flow rate 5 SCCM Gas pressure 1.33 Pa Microwave power 850 W (2.45 GHz) RF bias power 10 W (2 MHz) Wafer mounting electrode temperature 10 ° C. In this embodiment, H 2 Addition of S in the etching reaction system
Since the / F ratio is increased and the formation of the S deposition layer 6 is promoted and efficient side wall protection is performed, a favorable anisotropic shape is obtained despite the higher wafer temperature as compared with the first embodiment. The trench 5 could be formed.

Embodiment 3 In this embodiment, the same trench etching of the β-SiC film 2 was performed by using an S ₂ F ₂ / N ₂ mixed gas.

An example of the etching conditions is shown below.

S ₂ F ₂ flow rate 25 SCCM N ₂ flow rate 5 SCCM Gas pressure 1.33 Pa Microwave power 850 W (2.45 GHz) RF bias power 10 W (2 MHz) Wafer mounting electrode temperature 30 ° C. In this embodiment, N ₂ Addition of polythiazyl (SN)
_A sulfur nitride-based deposited layer 7 mainly composed of _x was formed. Since the sulfur nitride-based deposited layer 7 has a lower vapor pressure than the above-mentioned S deposited layer 6, excellent anisotropic processing can be performed even though the wafer temperature is further increased compared to the second embodiment. Was.

Example 4 In this example, a diamond film was etched using S ₂ F ₂ gas. As shown in FIG. 1A, a wafer used as an etching sample in this embodiment is a diamond film 3 formed on a single crystal silicon substrate 1 by a low-pressure synthesis method.
Is formed, and a resist mask 4 having a predetermined pattern is formed.

The wafer was set in an RF bias application type magnetic field microwave plasma etching apparatus, and the diamond film 3 was etched under the following conditions as an example.

S ₂ F ₂ flow rate 30 SCCM Gas pressure 1.33 Pa Microwave power 850 W (2.45 GHz) RF bias power 30 W (2 MHz) Wafer mounting electrode temperature 10 ° C. By this etching, as shown in FIG. So that
While the S deposition layer 6 was formed on the pattern side wall surface, the trench 5 having an anisotropic shape could be formed.

In the present embodiment, O ^*
Was not used as an etching seed, so that the selectivity to the resist mask 4 was good. After the etching is completed, O ₂ plasma ashing is performed to form a resist mask 4.
And the S deposition layer 6 were removed. No particle contamination occurred during this process. Further, since the O ₂ gas is hardly adsorbed on the diamond surface, the diamond film 3 was not etched at all during the ashing.

[0039] It should be noted _that, in place of the _{S 2 F 2 S 2 F 2} (25S
When a mixed gas of (CCM) / H ₂ (5SCCM) was used, anisotropic processing could be realized even when the temperature of the electrode on the wafer was 30 ° C. Further, S ₂ F ₂ (25 SCC
M) / N ₂ (5 SCCM) mixed gas,
Since the sulfur nitride-based deposited layer 7 having a lower vapor pressure than the S deposited layer 6 can be formed, the wafer mounting electrode temperature is reduced to 50
It was possible to realize anisotropic processing even at a temperature of ° C.

Embodiment 5 In this embodiment, an aC: H antireflection film on a tungsten polycide (W-polycide) film was etched using S ₂ F ₂ gas. This process will be described with reference to FIG.

As shown in FIG. 2A, the wafer used as an etching sample in this embodiment has a W-polycide film 14 and an aC: H antireflection film 15 on an SiO ₂ interlayer insulating film 11. The resist masks 16 are sequentially laminated, and a resist mask 16 is formed thereon in a predetermined pattern.

[0042] Here, W- polycide film 14, tungsten silicide polysilicon layer 12 and the thickness of about 100nm thickness of about 100nm containing impurities (WSi _x)
The layers 13 are sequentially laminated.

The aC: H antireflection film 15 was etched on the above wafer by RF bias application type magnetic field microwave plasma etching, for example, under the following conditions.

S ₂ F ₂ flow rate 30 SCCM Gas pressure 1.33 Pa Microwave power 850 W (2.45 GHz) RF bias power 30 W (2 MHz) Wafer mounting electrode temperature 10 ° C. By this etching, as shown in FIG. So that
While the S deposition layer 17 was formed on the side wall surface, the aC: H antireflection film pattern 15a was formed. This process can be performed without increasing the self-bias potential as in the conventional process.
It progressed anisotropically. The selectivity to the resist mask 16 was also good.

[0045] It should be noted _that, in place of the _{S 2 F 2 S 2 F 2} (25S
When a mixed gas of (CCM) / H ₂ (5SCCM) was used, anisotropic processing could be realized even when the temperature of the electrode on the wafer was 30 ° C.

Further, S ₂ F ₂ (25 SCCM) / N ₂
(5SCCM) When the mixed gas is used, the S deposition layer 1
Since the sulfur nitride-based deposited layer 18 having a lower vapor pressure than 7 can be formed, anisotropic processing can be realized even when the wafer mounting electrode temperature is set to 50 ° C.

By the way, after etching the aC: H antireflection film 15 using any of the above-mentioned gas systems, the W-polycide film 14 can be continuously etched. For example, an example of the conditions when the W-polycide film 14 is continuously etched using the S ₂ F ₂ gas will be described below.

S ₂ F ₂ flow rate 30 SCCM Gas pressure 1.33 Pa Microwave power 850 W (2.45 GHz) RF bias power 30 W (2 MHz) Wafer mounting electrode temperature −10 ° C. Here, the wafer temperature is lowered. , F ^* , the etching rate of the W-polycide film 14 is higher than that of the aC: H anti-reflection film 15, and
This is to prevent the side etch from entering the horn. By this etching, as shown in FIG. 2C, the W-polycide wiring 14a having an anisotropic shape was formed while the S deposition layer 17 was formed on the pattern side wall surface. In the drawing, each material layer after etching is represented by adding a suffix a to the original code.

If N ₂ is added to the gas system at this time, a sulfur nitride-based deposited layer 18 is formed on the pattern side wall surface. The S deposited layer 17 or the sulfur nitride based deposited layer 18 could be removed together with the resist mask 16 when O ₂ plasma ashing was performed after the etching.

Although the present invention has been described based on the five embodiments, the present invention is not limited to these embodiments. For example, in each of the embodiments described above, trench etching and wiring processing were described on the premise of manufacturing a semiconductor device. However, for SiC, synchrotron radiation light or short-wavelength light was utilized by utilizing its excellent heat resistance and thermal conductivity. There is known a use as a diffraction grating for a laser. The present invention is also effective as a technique for etching such fine grooves of the diffraction grating.

In addition, it goes without saying that the configuration of the sample wafer, the type of etching apparatus to be used, the composition of the etching gas, the etching conditions, and the like can be appropriately changed.

[0052]

As is apparent from the above description, the present invention makes it possible to perform anisotropic etching of a carbon-based inorganic material layer, which has been conventionally difficult, with good controllability using a resist mask. Becomes Therefore, the present invention makes a great contribution in expanding the use of the carbon-based inorganic material layer. In the field of semiconductor devices, in particular, we will not only improve the performance of semiconductor devices formed on silicon substrates and GaAs substrates, but also realize SiC semiconductor devices and diamond semiconductor devices that exceed the performance of these existing semiconductor devices. Also paves the way.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a process example of performing trench etching by applying the present invention in the order of the steps, (a) showing a state in which a resist mask is formed on a β-SiC film or a diamond film, (b) shows a state in which a trench is formed while depositing an S deposition layer or a sulfur nitride-based deposition layer, and (c) shows a state in which the resist mask and the S deposition layer or the sulfur nitride-based deposition layer are removed by ashing.

FIG. 2 is a schematic cross-sectional view showing an example of a process for performing continuous etching of an aC: H antireflection film and a W-polycide film thereunder according to the order of steps by applying the present invention;
(A) shows a state in which a resist mask is formed on an aC: H antireflection film, and (b) shows a state in which an aC: H antireflection film is etched while depositing an S deposition layer or a sulfur nitride-based deposition layer. (C) shows a state in which etching is further continued to form a W-polycide wiring, and (d) shows a state in which the resist mask and the S deposited layer or the sulfur nitride based deposited layer are removed by ashing.

[Explanation of symbols]

1 single-crystal silicon substrate, 2 β-SiC film, 3
Diamond film, 4,16 resist mask, 5
Trench, 6,17S deposited layer, 7,18 sulfur nitride based deposited layer, 11 SiO ₂ interlayer insulating film, 14 W
-Polycide film, 15 aC: H antireflection film

Claims (7)

(57) [Claims] Claims: 1. Discharge dissociation conditions can produce at least fluorine radicals and free sulfur, and have an F / S ratio
A dry etching method characterized by etching a carbon-based inorganic material film while depositing a sulfur-based deposit on a region to be etched using an etching gas containing a sulfur fluoride compound having a value of less than 6 . (However, F represents the number of fluorine atoms, and S represents the number of sulfur atoms, respectively.) 2. The method according to claim 1, wherein the sulfur fluoride compound is S ₂ F ₂ ,
_{SF 2,} SF 4, a dry etching method according to claim 1, characterized in that any one of a S _{2 F 10.} 3. A gas capable of generating at least fluorine radicals in the discharge dissociation conditions, if capable of generating free sulfur
In both cases, a halogenated sulfur compound having an X / S ratio of less than 6 is used.
A dry etching method characterized by etching a carbon-based inorganic material film while depositing a sulfur-based deposit on a region to be etched using an etching gas containing the etching gas. (However, X represents the number of fluorine atoms, and S represents the number of sulfur atoms, respectively.) 4. The method according to claim 1, wherein the sulfur halide compound is S ₂ F
_{2, SF 2, SF 4,} S 2 F 10, S 3 Cl 2, S 2 C
4. The dry etching method according to claim 3, wherein the dry etching method is any one of l ₂ , SCl ₂ , S ₃ Br ₂ , S ₂ Br ₂ , and SBr _{2. 5} . 5. The etching gas according to claim 1, wherein the etching gas contains a nitrogen-based compound, and a sulfur nitride-based compound is deposited as the sulfur-based deposit.
The dry etching method described. 6. The method according to claim 1, wherein the etching gas contains at least one kind of halogen radical consuming compound selected from H ₂ , H ₂ S and a silane-based compound, and promotes the deposition of the sulfur-based deposit. Item 6. The dry etching method according to any one of Items 1 to 5. 7. The dry etching method according to claim 1, wherein the carbon-based inorganic material film is at least one of an amorphous carbon thin film, a silicon carbide-based thin film, and a diamond-based thin film. .