JPH04346427A - Dry-etching method - Google Patents

Abstract

PURPOSE:To attain to the rapidity, high selectivity, high anisotropy, high damage registance and low polluting property by using single composition gas in the dry-etching method of silicon compound layer. CONSTITUTION:In the dry-etching method, saturated or unsaturated high dimensional chain fluorocarbon base compound containing at least one H atom in molecules such as C3F7H, C3F6H2, C3F5H at the temperature of a substrate to be etched at exceeding 50 deg.C is used as an etching gas. At this time, these compounds producing two each or more CFn<+> from one molecule contribute to the rapid anisotropical etching step of an inter SiO2 layer insulating film. Furthremore, since H in the molecules can catch any surplus F*, C/F ratio can be optimized without adding any depositing gas thereto so that the resist selectively and silicon selectivity may be enhanced by the deposition of carbon base polymer. Through these procedures, the dry-etching method as a one stage process using single composition gas can display such characteristics as the excellent controllability, reproducibility and throughput.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a dry etching method applied in the field of manufacturing semiconductor devices, etc., and particularly has excellent resist selectivity and silicon underlayer selectivity.
Furthermore, the present invention relates to a method for dry etching a silicon compound layer at high speed and with less particle contamination.

0002

[Prior Art] As semiconductor devices become more highly integrated and have higher performance, as seen in VLSI, ULSI, etc. in recent years, dry etching methods for silicon compound layers such as silicon oxide (SiO2) have also been developed. Technical requirements are becoming increasingly strict. First, as devices and chips become more highly integrated, the areas of devices and chips are expanding and wafers are becoming larger in diameter, while the patterns to be formed are also becoming finer. The mainstream is shifting from the conventional batch process to the single-wafer process. At this time, in order to maintain the same productivity as before, it is essential to significantly improve the etching rate. In addition, in order to increase the speed and miniaturization of devices, the junction depth of the impurity diffusion region is becoming shallower, and various material layers are becoming thinner. Etching technology is required. For example, when trying to form a contact to an impurity diffusion region formed in a semiconductor substrate or a source/drain region of a PMOS transistor used as a resistive load element of an SRAM, etc., a silicon substrate or polycrystalline silicon layer is used as a base layer. An example of this is etching of a SiO2 interlayer insulating film. Furthermore, improving the selectivity to resist is also an important issue. This is because, in submicron devices, even the slightest difference in dimensional conversion due to resist recession is no longer acceptable. However, characteristics such as high speed, high selectivity, and low damage are mutually selected, and it is extremely difficult to establish an etching process that satisfies all of them.

Conventionally, in order to dry-etch a silicon compound layer typified by a SiO2 layer while maintaining a high selectivity with respect to a silicon-based material layer, CHF3, CF4
/H2 mixed system, CF4 /O2 mixed system, C2 F
6/CHF3 mixed systems have typically been used as etching gases. These are all C/F ratios (
The main component is a fluorocarbon gas with a ratio of the number of carbon atoms to the number of fluorine atoms in the molecule of 0.25 or more. These gas systems are used because (a) C contained in the fluorocarbon gas creates C-O bonds on the surface of the SiO2 layer, and has the effect of cutting or weakening the Si-O bonds. , (b) C which is the main etching species of the SiO2 layer
Fn + (especially n=3) can be generated, and (c
) Since a relatively carbon-rich state is created in the plasma, oxygen in SiO2 is removed in the form of CO or CO2, while the silicon-based material layer is removed due to the contribution of C, H, F, etc. contained in the gas system. This is based on the following reasons: a carbon-based polymer is deposited on the surface of the silicon-based material layer, which reduces the etching rate and provides a high selectivity with respect to the silicon-based material layer. Note that the above-mentioned additive gases such as H2 and O2 are used for the purpose of controlling the selectivity;
* The amount generated can be reduced or increased. That is, it has the effect of controlling the apparent C/F ratio of the etching reaction system.

[0004] On the other hand, the applicant of the present application previously filed a patent application No. 2-
No. 75828 proposes a dry etching method for a silicon compound layer using a saturated or unsaturated chain higher-order fluorocarbon gas having two or more carbon atoms. This is C2 F6 , C3 F8 , C4 F1
By using a higher-order fluorocarbon gas such as 0, C4 F8, etc., CFn + is efficiently generated and etching speed is increased. However, by using only a higher-order fluorocarbon gas alone, it is not possible to obtain a sufficiently large selectivity to the resist and selectivity to the silicon base. For example, when etching a SiO2 layer on a silicon substrate using C3F8 as an etching gas, high speed is achieved, but the selectivity to resist is low at about 1.3, etching resistance is insufficient, and pattern edges are A dimensional conversion difference occurs due to the retreat. Furthermore, since the selectivity to silicon is about 4.1, there remains a problem in over-etching resistance. Therefore, in order to solve these problems, in the prior art described above, etching using only chain-like higher-order fluorocarbon gas is stopped just before the underlying layer is exposed, and when etching the remaining part of the silicon compound layer, etching is performed using a carbon-based polymer. A two-step etch is performed in which a hydrocarbon-based gas is further added to this gas to promote the deposition of .

However, in the current situation where the design rules of semiconductor devices are becoming highly miniaturized, it is already becoming difficult to tolerate the difference in dimensional conversion between the etching mask and the two-step etching described above. Also, it is necessary to further improve the selectivity in the first stage etching. In addition, as further miniaturization progresses in the future, the effects of particle contamination from carbon-based polymers may become more serious, so the amount of deposition gas such as hydrocarbon-based gas used in the second stage etching may also be reduced. We would like to reduce this as much as possible. From this point of view, the present inventor previously proposed in Japanese Patent Application No. 2-295225 that a chain-shaped substrate having at least one unsaturated bond in the molecule was prepared while the temperature of the substrate to be processed was controlled to 50°C or less. We are proposing a technique for etching silicon compound layers using unsaturated fluorocarbon gas. The above-mentioned chain unsaturated fluorocarbon gas theoretically generates two or more CFn + from one molecule by discharge dissociation.
SiO2 can be etched at high speed. In addition, since it has an unsaturated bond in its molecule, highly active radicals are easily generated by dissociation, and the polymerization of the carbon-based polymer is promoted. Moreover, by controlling the temperature of the substrate to be processed to 50° C. or lower, the deposition of the carbon-based polymer is promoted. Therefore, resist selectivity and silicon underlayer selectivity can be improved. Also,
The specification states that etching using a chain unsaturated fluorocarbon gas alone is stopped halfway through the silicon compound layer, and the remaining etching is carried out using a gas obtained by adding a hydrocarbon gas to the chain unsaturated fluorocarbon gas. At the same time, we are also proposing technologies that can be used. This is because a deposition gas is used in the middle of etching in order to further improve the selectivity to the underlying silicon.

Alternatively, hexafluorobenzene (
Japanese Patent Publication No. 1-60938 discloses a technique for etching SiO2 with a mixed gas of C6F6) and tetrafluoromethane (CF4). This is intended to efficiently generate CFn + in plasma by using a cyclic unsaturated higher-order fluorocarbon gas and to promote the polymerization of carbon-based polymers.
After all, it is based on the same idea as the applicant's earlier application.

[0007]

[Problems to be Solved by the Invention] By the way, in the conventionally proposed techniques using chain unsaturated fluorocarbon gases or cyclic unsaturated fluorocarbon gases, as is clear from the above explanation, In practice, it was necessary to use it in combination with other additive gases in order to obtain a high selectivity. Furthermore, according to the technology using C6 F6, as mentioned in the publication disclosing this, C6 F6 alone cannot constitute the etching gas. This is because when C6 F6 alone is used, a significantly large amount of CFn + is generated in the plasma, and the polymerization of the carbon-based polymer is excessively promoted, so that the etching reaction does not proceed. Therefore, in order to suppress the generation of CFn + , CF4, which has the lowest C/F ratio among all fluorocarbon gases, is mixed. However, considering the time required for stabilizing the discharge state and controllability, it is better to use a single composition of gases that are substantially involved in etching and to perform etching in a one-step process without changing conditions midway. This is advantageous in improving controllability, reproducibility, and throughput. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a novel dry etching method that is excellent in high anisotropy, high speed, high base selectivity, high resist selectivity, low contamination, reproducibility, etc.

[0008]

[Means for Solving the Problems] A dry etching method according to the present invention is proposed in order to achieve the above-mentioned object, in which the temperature of the substrate to be etched is controlled to 50°C or less, and the dry etching method according to the general formula Cx Fy is Hz (However, x, y,
z is a natural number indicating the number of atoms, x≧2, y>z≧1,
All the conditions of 2x+2≧y+z and y≧x+z are satisfied. ) is characterized in that the silicon compound layer is etched using an etching gas mainly consisting of a chain compound represented by:

In the present invention, the chain compound CxFy Hz, which is the main component of the etching gas, is a so-called higher-order fluorocarbon derivative because the number of C atoms x is 2 or more. The upper limit of the number x of C atoms is not particularly limited as long as the chain compound can be introduced into the etching reaction system in a vaporized state. Also, the number of H atoms z is 1
Because of the above, at least one of the F atoms in the higher-order fluorocarbon is substituted with an H atom. The number y of F atoms in one molecule is always greater than the number z of H atoms, and
The number y of atoms is equal to or greater than the sum of the number x of C atoms and the number z of H atoms. The reason why the number z of H atoms in one molecule is subject to this condition is that as the number of H atoms increases, the F
This is because the number of atoms decreases, and the amount of CFn + produced from one molecule, which is an etching species for the silicon compound layer, decreases. Furthermore, if the number of H atoms z becomes extremely large, the properties of the chain compound become similar to those of a deposition gas, resulting in a significant decrease in the etching rate and an increase in particle contamination due to excessive carbon-based polymer deposition. Other problems also arise. Furthermore, from the condition 2x+2≧y+z,
The above-mentioned chain compound may be either a saturated or an unsaturated compound. In particular, when using unsaturated compounds, monoradicals or, in some cases, highly active biradicals (bi-radicals) such as carbenes are generated in the plasma due to discharge dissociation, and these π-electrons in unsaturated bonds are generated. Attacking the system promotes polymerization of carbon-based polymers.

[0010] When these conditions are combined, for example, x=
The chain compound that can be used in case 2 is represented by the composition formula C
There are three types: 2 F3 H, C2 F5 H, C2 F4 H2, and in the case of x=3, C3 F5 H, C3
There are three types: F7 H, C3 F6 H2, and x = 4
In the case of C4 F5 H, C4 F7 H, C4 F6
H2, C4 F9 H, C4 F8 H2, C4
There are 6 types: F7 H3. Of course, even with the same compositional formula, multiple structural isomers exist depending on the substitution position of the H atom and the branching of the carbon skeleton.

Further, in the present invention, the temperature of the substrate to be etched during etching is controlled to 50° C. or lower. This temperature control may be performed at room temperature or at a temperature below 0° C. as in low-temperature etching, which has recently attracted attention in the field of dry etching. Normally, in the process of dry etching, the temperature of the substrate to be etched rises to about 200° C. unless cooling is performed. However, the temperature is 50℃
If controlled as follows, the carbon-based polymer can be deposited efficiently due to the reduction in vapor pressure. In particular, if low-temperature etching is performed by cooling to 0° C. or lower, the selectivity will be further improved. Etching of a resist material or a silicon-based material layer proceeds mainly through a chemical reaction caused by F* (fluorine radicals), so when the temperature of the reaction system decreases and the movement of radicals is suppressed, the etching rate also decreases. On the other hand, since the etching of a silicon compound layer such as SiO2 proceeds physically mainly through sputtering using ions, the reduction in the etching rate due to cooling is not as pronounced as with resist materials or silicon-based materials. Therefore, further improvement of the selectivity can be expected in the low temperature range.

0012

[Operation] One molecule of the chain compound used in the present invention theoretically produces at least (x-1) CFn + ions. Therefore, under the same gas pressure, CF3H,C
The absolute amount of CFn + in the plasma is increased compared to when a conventionally known gas such as F2 H2 is used. Along with this, the amount of F* generated in the plasma also increases, but the excess F* is captured by H* generated by discharge dissociation of the chain compounds and removed from the system in the form of HF. . Therefore, the selectivity to the base, the selectivity to the resist, and the anisotropy do not deteriorate. In this way, the C/F ratio of the etching reaction system is optimized by generating a large amount of CFn + and partially consuming F*, and the deposition of carbon-based polymer is promoted without adding a deposition gas. When this carbon-based polymer is deposited on the surface of a silicon-based material layer such as single-crystal silicon or polycrystalline silicon or on the surface of a resist pattern on a substrate to be etched whose temperature is controlled at 50°C or less, it can be damaged by ion bombardment, etc. Not easily removed. However, on the surface of a silicon compound layer such as SiO2, oxygen contained in the layer is sputtered out and contributes to the decomposition of the carbon-based polymer, so it is easily removed. Therefore, increased deposition of carbon-based polymer improves resist selectivity and silicon underlayer selectivity. However, in the present invention, the absolute amount of CFn +, which is an etching species for the silicon compound layer, is increased.
Even if the deposition of carbon-based polymer is promoted, the etching rate is not reduced in any way.

As described above, according to the present invention, high base selectivity, high resist selectivity, high anisotropy, high speed, low contamination, etc.
It becomes possible to perform etching of a silicon compound layer while satisfying all requirements for dry etching. In addition, F* in which H in the chain compound in the present invention is excessive
Considering that the purpose is to capture H2, it seems possible to simply add H2 to the conventionally proposed higher-order fluorocarbon gases. However, first of all,
The benefits of using a single composition gas are lost. Furthermore, since H2 has a small molecular radius, it easily penetrates into the crystal lattice of a silicon substrate, etc., and tends to cause damage to the substrate. Furthermore, it is also dangerous to handle. Therefore, it is still desirable to use the chain compound proposed in the present invention in a single composition.

[0014]

[Examples] Specific examples of the present invention will be described below.

Example 1 In this example, the present invention is applied to contact hole processing, and C3 F7 H (1,1,1,2,3,3,3-heptafluoropropane) is used to form a SiO2 interlayer. This is an example of etching an insulating film. The substrate to be etched (wafer) used as an etching sample in this example was a single crystal silicon substrate on which an impurity diffusion layer was formed in advance, an SiO2 interlayer insulating film was formed on the silicon substrate, and an SiO2 interlayer insulating film was further formed on the silicon substrate.
A resist pattern is formed as an etching mask for the O2 interlayer insulating film. The wafer was set on a wafer mounting electrode of a magnetron RIE (reactive ion etching) device. Here, the wafer-mounted electrode has a built-in cooling pipe, and by supplying and circulating a coolant to the cooling pipe from cooling equipment such as a chiller connected outside the apparatus, the wafer temperature during etching can be kept at 50°C. It is possible to control the temperature below ℃. Here, ethanol was used as a coolant to maintain the wafer temperature at 0° C. during etching. In this state, as an example, the C3 F7H flow rate is 46SCC.
M, gas pressure 2Pa, RF power density 2.0W/cm2
, the etching was performed under the conditions of a magnetic field strength of 150 Gauss.

In the above etching process, C3 F7
Etching of the SiO2 interlayer insulating film proceeds by a mechanism mainly based on an ion-assisted reaction due to CFn + generated in the plasma by discharge dissociation of H (C/F ratio=1/2). At this time, carbon-based polymer was efficiently deposited on the surface of the resist pattern, but SiO2
The carbon-based polymer was also removed from the surface of the interlayer insulating film as it was etched away. As a result, contact holes with good anisotropic shapes were formed at high speed even though no operations such as adding a deposition gas or changing etching conditions were performed. In this process, the resist selectivity was 3.5 and the silicon selectivity was about 15. By obtaining the above-mentioned resist selectivity, the dimensional conversion difference was significantly reduced compared to the conventional method. Further, since a high selectivity to silicon was obtained as described above, the single crystal silicon substrate and the impurity diffusion layer were not significantly damaged even when overetching was performed by as much as 50%. The above selection ratio value is C3
The selectivity was equivalent to that obtained when using an etching gas to which a deposition gas was added, such as a F8 /C2 H4 mixed gas. However, in this example, since a gas of a single composition was used and a one-step process was adopted, controllability, reproducibility, throughput, etc. were significantly improved compared to when the above-mentioned mixed gas was used.

Here, for comparison, the above C3 F7 H
The SiO2 interlayer insulating film was etched under the same conditions as described above using C3F8 (octafluoropropane) having the same number of carbon atoms. At this time, the resist selectivity ratio was 1.5, the silicon selectivity ratio was 3.9, and C3
It was significantly inferior to the case using F7H. this is,
This is because C3 F8 has a smaller C/F ratio than C3 F7 H, and the generation of excessive F*, which causes a decrease in selectivity, was not sufficiently suppressed.

Example 2 In this example, the present invention is applied to contact hole processing, and a SiO2 interlayer insulating film is formed using C3 F6 H2 (1,1,1,3,3,3-hexafluoropropane). This is an example of etching. The wafer used in this example was the same as that used in Example 1. The above wafer is set in a magnetron RIE device, and as an example, C
3 F6 H2 Flow rate 46SCCM, gas pressure 2Pa, R
F power density 2.0W/cm2, magnetic field strength 150Ga
Etching was performed at a wafer temperature of 20°C. The progress of the etching reaction and the deposition mechanism of the carbon-based polymer in the above-mentioned etching process are as described above in Example 1. However, C3 F6 H2 has two H atoms in one molecule, which trap and consume F*, so the effective C/F ratio is 3/4. In this way, C
By using a compound with a high /F ratio, Example 1
Sufficiently high selectivity was achieved despite the higher wafer temperature.

Example 3 In this example, the present invention was applied to contact hole processing, and a SiO2 interlayer insulating film was etched using C3F5H (1,1,3,3,3-pentafluoropropene). This is an example. The wafer used in this example was also the same as that used in Example 1. The above wafer is set in a magnetron RIE device, and as an example, a C3 F5
Etching was performed under the conditions of H flow rate of 46 SCCM, gas pressure of 2 Pa, RF power density of 2.0 W/cm2, magnetic field strength of 150 Gauss, and wafer temperature of 20°C. The progress of the etching reaction and the deposition mechanism of the carbon-based polymer in the above-mentioned etching process are as described above in Example 1. Although C3 F5 H has one H atom in the molecule, it has one double bond in the main chain, so the C/F ratio is 3/4, similar to C3 F6 H2 in Example 2. be. In this example as well, sufficiently high selectivity was achieved by controlling the wafer temperature near room temperature.

Although the present invention has been described above based on three types of embodiments, the present invention is not limited to these embodiments in any way. In the above gas system, He,
A rare gas such as Ar may be added as appropriate. These rare gases do not impair the advantages of the single composition gas of the present invention. Furthermore, the material layer to be etched is the above-mentioned SiO
2, but not limited to PSG, BSG, BPS
G, AsSG, AsPSG, AsBSG, SiN, etc. may be used.

[0021]

Effects of the Invention As is clear from the above explanation, in the present invention, by using a saturated or unsaturated higher-order fluorocarbon chain compound containing at least one H atom in the molecule, deposition gas can be reduced. C without any addition of
By optimizing the /F ratio, silicon compound layers can be etched at high speed, with low contamination, with high anisotropy, and with excellent controllability and reproducibility. Therefore, the present invention is extremely suitable for manufacturing semiconductor devices designed based on fine design rules and having high integration and high performance.

Claims (1)

[Claims] Claim 1: The temperature of the substrate to be etched is controlled to 50°C or less, and the general formula CxFy Hz (where x, y,
z is a natural number indicating the number of atoms, x≧2, y>z≧1,
All the conditions of 2x+2≧y+z and y≧x+z are satisfied. ) A dry etching method characterized by etching a silicon compound layer using an etching gas mainly composed of a chain compound represented by