JP3198538B2 - 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 and the like, and more particularly, to a method excellent in selectivity with respect to resist and selectivity with respect to silicon underlayer.
In addition, the present invention relates to a method for dry-etching a silicon oxide layer at high speed and with low particle contamination.

[0002]

In recent years the VLSI, with the progress of high integration and performance of semiconductor devices, as seen in ULSI or the like, the dry etching method of the silicon compound layer represented by silicon oxide (SiO ₂₎ Even technical requirements are becoming more stringent. First, while the area of device chips has been enlarged and the wafer diameter has been increased due to the high integration, the pattern to be formed has been miniaturized. The mainstream is shifting from the conventional batch type to the single-wafer type. At this time, in order to maintain the same productivity as that of the related art, it is necessary to greatly improve the etching rate. In addition, under the circumstances where the junction depth of the impurity diffusion region becomes shallower and the thickness of various material layers is reduced in order to increase the speed and miniaturization of the device, the selectivity to the underlayer is superior to that of the prior art and less damage is caused. Etching technology is required. For example, an impurity diffusion region formed in a semiconductor substrate,
For example, when a contact is to be formed in a source / drain region of a PMOS transistor used as a resistance load element of an SRAM, etching of an SiO ₂ interlayer insulating film using a silicon substrate or a polycrystalline silicon layer as a base is an example. It is. Further, improvement of the resist selectivity is also an important issue. This is because, in submicron devices, the occurrence of slight dimensional change due to resist receding is no longer allowed. 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 can satisfy all of them.

Conventionally, to dry-etch a silicon compound layer typified by a SiO ₂ layer while maintaining a high selectivity with respect to a silicon-based material layer, CHF ₃ , CF ₄ / H
_Two- mixed systems, CF ₄ / O ₂ mixed systems, C ₂ F ₆ / CHF ₃ mixed systems, and the like have been typically used as etching gases. Each of these is mainly composed of a fluorocarbon gas having a C / F ratio (ratio of the number of carbon atoms to the number of fluorine atoms in a molecule) of 0.25 or more. These gas systems are used because (a) C contained in the fluorocarbon-based gas forms a bond of CO on the surface of the SiO ₂ layer and cuts or weakens the Si-O bond. Yes, (b) SiO
Oxygen in SiO ₂ is reduced to CO ₂ because it can produce _two layers of main etching species, CF _n ⁺ (particularly n = 3), and (c) creates a relatively carbon-rich state in the plasma.
Alternatively, while being removed in the form of CO ₂ , the carbon-based polymer is deposited on the surface of the silicon-based material layer due to the contribution of C, H, F and the like contained in the gas system, and the etching rate is reduced.
This is based on the reason that a high selectivity with respect to the silicon-based material layer can be obtained. Note that the above-mentioned additive gases such as H ₂ and O ₂ are used for the purpose of controlling the selectivity, and can reduce or increase the amount of F ^* generated, respectively. That is, the apparent C of the etching reaction system
It has the effect of controlling the / F ratio.

On the other hand, the applicant of the present application has previously filed Japanese Patent Application No. Hei.
No. 75828 proposes a dry etching method for a silicon compound layer using a saturated or unsaturated chain-like higher-order fluorocarbon-based gas having 2 or more carbon atoms. These are C ₂ F ₆ , C ₃ F ₈ , C ₄ F ₁₀ , C ₄ F ₈
By using a higher-order fluorocarbon-based gas such as that described above, CF _n ⁺ is efficiently generated and the etching speed is increased. However, the sole use of a higher-order fluorocarbon-based gas alone cannot provide a sufficiently high selectivity to resist and a high selectivity to silicon underlayer. For example, when an 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 to resist is as low as about 1.3, and etching resistance is insufficient. -A dimension conversion difference occurs due to the retreat of the edge. Further, since the selectivity with respect to silicon is about 4.1, there remains a problem in over-etching resistance. Therefore, in order to solve these problems, in the above prior art, a chain high-order fluorocarbon.
Etching with the gas alone is stopped immediately before the underlayer is exposed, and when etching the remainder of the silicon compound layer, a hydrocarbon-based gas is further added to this gas to promote the deposition of the carbon-based polymer. Step etching is performed.

However, under the current situation where the design rule of a semiconductor device is highly miniaturized, a dimensional conversion difference from an etching mask has become almost unacceptable. However, it is necessary to further improve the selectivity in the first-stage etching. Also, with the further miniaturization in the future, the effect of particle contamination by the carbon-based polymer may become serious, so the amount of deposition gas such as hydrocarbon-based gas used in the second stage etching is also reduced. I want to reduce it as much as possible. From this point of view, the present inventor has previously described in Japanese Patent Application No. 2-295225 a chain-like structure having at least one unsaturated bond in the molecule while controlling the temperature of the substrate to be treated at 50 ° C. or lower. A technique for etching a silicon compound layer using an unsaturated fluorocarbon-based gas has been proposed. Since the chain unsaturated fluorocarbon-based gas theoretically generates two or more CF _n ⁺ from one molecule by discharge dissociation, Si
O ₂ can be etched at a high speed. Further, since the compound has an unsaturated bond in the molecule, a highly active radical is easily generated 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 less, the deposition of the carbon-based polymer is promoted. Therefore, selectivity with respect to resist and selectivity with respect to silicon underlayer can be improved. Further, in the same specification, the etching with the chain unsaturated fluorocarbon-based gas alone was stopped halfway in the silicon compound layer, and the remaining etching was performed by adding a hydrocarbon-based gas to the above-described chain-shaped unsaturated fluorocarbon-based gas. A technique using gas is also proposed at the same time. 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, a technique of etching SiO ₂ with a mixed gas of hexafluorobenzene (C ₆ F ₆ ) and tetrafluoromethane (CF ₄ ) is disclosed in Japanese Patent Publication No.
No. 60938 discloses this. This is intended to efficiently generate _CFn ⁺ in the plasma by using a cyclic unsaturated higher-order fluorocarbon-based gas and promote polymerization of the carbon-based polymer. It is based on the same idea as the earlier application.

[0007]

However, in the technology using a chain unsaturated fluorocarbon-based gas or a cyclic unsaturated fluorocarbon-based gas conventionally proposed, as is apparent from the above description, In order to obtain a high selectivity, it was practically necessary to use it in combination with another additive gas. Further, according to the technology using C ₆ F ₆ , as mentioned in the gazette which discloses the technology, it is not possible to form the etching gas by C ₆ F ₆ alone. This is because C ₆ F ₆ alone generates a remarkably large amount of CF _n ^{+ in the} plasma, and excessively promotes the polymerization of the carbon-based polymer, so that the etching reaction does not proceed. Therefore, in order to suppress the generation of CF _n ⁺ , CF ₄ having the lowest C / F ratio among all fluorocarbon-based gases is mixed. However, in consideration of the time required for stabilizing the discharge state, controllability, and the like, it is preferable that the gas substantially involved in the etching has a single composition, and that the etching be performed in a one-step process without changing the conditions in the middle. This is advantageous in improving controllability, reproducibility, and throughput. Therefore, an object of the present invention is to provide a novel dry etching method which is excellent in high anisotropy, high speed, high underlayer selectivity, high resist selectivity, low contamination, and reproducibility.

[0008]

SUMMARY OF THE INVENTION A dry etching method according to the present invention is proposed to achieve the above-mentioned object, and controls the temperature of a substrate to be etched to 50 ° C. or less and uses a general formula C _x F _y H _z (where x, y, and z are natural numbers indicating the number of atoms, and x ≧ 2, y> z ≧ 1, 2x +
2> y + z, y ≧ x + z are all satisfied. The etching of the silicon oxide layer is performed using an etching gas mainly containing an unsaturated chain compound represented by the formula (1).

In the present invention, the chain compound C _x F _y H _{z, which} is a 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 of C atoms x is such that the chain compound can be introduced into the etching reaction system in a vaporized state.
There is no particular limitation. Further, since the number z of H atoms is 1 or more, at least one of the F atoms of the higher order fluorocarbon is replaced with an H atom. The number of F atoms y in one molecule is always greater than the number of H atoms z, and the number of F atoms y is equal to or greater than the sum of the number of C atoms x and the number of H atoms z. The condition that the number of H atoms z in one molecule is set as described above is that as the number of H atoms increases, the number of F atoms decreases by that amount, and the etching species of the silicon compound layer from one molecule increases. This is because the generation amount of a certain CF _n ⁺ decreases. If the number z of H atoms becomes extremely large, the properties of the chain compound become close to those of the deposition gas, and the etching rate is significantly reduced, and particle contamination increases due to excessive deposition of the carbon-based polymer. And the like. Further, from the condition that 2x + 2 ≧ y + z, the chain compound may be any of a saturated and unsaturated compound. In particular, when an unsaturated compound is used, monoradicals or, in some cases, highly active biradicals (two-terminal free radicals) such as carbene are generated in the plasma by discharge dissociation, and these generate π electrons in the unsaturated bond. Attacking the system promotes the polymerization of the carbon-based polymer.

When these conditions are combined, for example, x =
The chain compound that can be used in the case of 2 is represented by C
₂ F ₃ H, C ₂ F ₅ H, C ₂ F ₄ H ₂
When x = 3, C ₃ F ₅ H, C ₃ F ₇ H, C ₃ F ₆ H ₂
And when x = 4, C ₄ F ₅ H and C ₄ F _{7
H, C 4 F 6 H 2} , C 4 F 9 H, C 4 F 8 H 2, C 4 F
The six ₇ H _3. Of course, even in the same composition formula, there are a plurality of structural isomers depending on the substitution position of the H atom and the branch of the carbon skeleton.

Further, in the present invention, the temperature of the substrate to be etched during the etching is controlled to 50 ° C. or less. This temperature control may be performed in a room temperature range or in a temperature range of 0 ° C. or lower as in low-temperature etching which has recently attracted attention in the field of dry etching. Usually, the temperature of the substrate to be etched rises to about 200 ° C. unless cooling is particularly performed in the process of dry etching. However, if the temperature is 50 ° C
With the following control, the carbon-based polymer can be efficiently deposited by lowering the vapor pressure. In particular, if the etching is performed at a low temperature of 0 ° C. or less, the selectivity is further improved. Since the etching of the resist material or the silicon-based material layer proceeds mainly by a chemical reaction due to F ^* (fluorine radical), when the temperature of the reaction system is reduced and the movement of the radical is suppressed, the etching rate is also reduced. On the other hand, since etching of a silicon compound layer such as SiO ₂ physically proceeds mainly by sputtering with ions, the decrease in the etching rate due to cooling is not so remarkable as that of a resist material or a silicon-based material. Therefore, further improvement of the selectivity can be expected in the low temperature range.

[0012]

[Function] From one molecule of the chain compound used in the present invention
Is theoretically at least (x-1) CF_n ⁺Is generated
I do. Therefore, under the same gas pressure, CF_ThreeH, CF_Two
H _TwoCompared to the case using a conventionally known gas such as
CF in plasma_n ⁺Increases the absolute amount of to this
Accordingly, F in the plasma^*Also increases the amount of
But the excess F^*Is formed when the above chain compound is dissociated by discharge.
H^*And removed out of the system in the form of HF. did
Therefore, selectivity to base, selectivity to resist, and anisotropy
There is no decrease in sex. Thus, CF_n ⁺Large amount of
Generation and F^*Of the etching reaction system due to the partial consumption of
The F ratio is optimized so that carbon-based
Polymer deposition is promoted. This carbon-based polymer
On the substrate to be etched whose temperature is controlled below 50 ° C
And silicon-based materials such as monocrystalline silicon and polycrystalline silicon
When deposited on the surface of the coating layer or the surface of the resist pattern,
It is not easily removed by ion bombardment or the like. Only
And SiO_TwoOn the surface of a silicon compound layer such as
Oxygen is sputtered out of the carbon-based polymer
Easily removed to contribute to decomposition. Therefore, charcoal
Increasing the deposition of base polymer increases the selectivity to resist.
And the selectivity to the silicon underlayer is improved. However, the present invention
Now, CF which is the etching species of the silicon compound layer_n ⁺of
Increasing absolute amount promotes carbon-based polymer deposition
Even if it is advanced, the etching rate does not decrease at all.

As described above, according to the present invention, etching of a silicon compound layer can be performed while satisfying all requirements for dry etching, such as high base selectivity, high resist selectivity, high anisotropy, high speed, and low contamination. It is possible to do. In view of the fact that H in the chain compound in the present invention is intended to capture excess F ^* , it seems that H ₂ may be simply added to a conventionally proposed higher-order fluorocarbon-based gas or the like. It is. But first,
The benefits of using a single composition gas are lost. Moreover, H ₂ because molecular radius is less easily penetrate into the crystal lattice of the silicon substrate and the like, which makes it easy to induce substrate damage.
Furthermore, handling is dangerous. Therefore, it is desirable to use the chain compound proposed in the present invention in a single composition.

[0014]

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

Embodiment 1 In this embodiment, the present invention is applied to contact hole processing, and C ₃ F ₇ H (1,1,1,2,3,3,3-heptafluoropropane) is used. This is an example in which an SiO ₂ interlayer insulating film is etched. In this embodiment, the etching
Substrate to be etched (wafer) used as sample
Is, SiO ₂ interlayer insulating film is formed on a single crystal silicon substrate in advance impurity diffusion layer is formed, further the SiO ₂
A resist pattern is formed as an etching mask for the interlayer insulating film. The wafer was set on a wafer mounting electrode of a magnetron RIE (reactive ion etching) apparatus. Here, the wafer mounting electrode has a built-in cooling pipe, and by supplying a coolant to the cooling pipe from a cooling facility such as a chiller connected to the outside of the apparatus and circulating the same, the wafer temperature during etching is reduced by 50%.
It is possible to control the temperature to below ° C. Here, ethanol was used as a coolant, and the wafer temperature during etching was maintained at 0 ° C. In this state, as an example, etching was performed under the conditions of a C ₃ F ₇ H flow rate of 46 SCCM, a gas pressure of 2 Pa, an RF power density of 2.0 W / cm ² , and a magnetic field strength of 150 Gauss.

In the above-mentioned etching process, C ₃ F ₇ H
(C / F ratio = １ ／) is dissociated by discharge and CF _n ⁺ is generated in the plasma, whereby the etching of the SiO ₂ interlayer insulating film proceeds by a mechanism mainly using an ion assist reaction. At this time, the carbon-based polymer was efficiently deposited on the surface of the resist pattern, but the carbon-based polymer was also removed on the surface of the SiO ₂ interlayer insulating film along with its etching removal. As a result, a contact hole having a favorable anisotropic shape was formed at a high speed even though no operation such as addition of a deposition gas or switching of etching conditions was performed. The selectivity to resist in this process was 3.5 and the selectivity to silicon was about 15. By obtaining the above selectivity with respect to resist, the dimensional conversion difference was significantly reduced as compared with the conventional case.
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 value of the above selectivity is C ₃ F
The selectivity was equivalent to the case where an etching gas to which a deposition gas was added, such as an ₈ / C ₂ H ₄ mixed gas, was used. However, in this embodiment, a gas having a single composition was used, and a one-step process was employed. Therefore, controllability, reproducibility, throughput, and the like were remarkably improved as compared with the case of using the mixed gas.

For comparison, C ₃ F ₈ (octafluoropropane) having the same number of carbon atoms as C ₃ F ₇ H is used for comparison.
Was used to etch the SiO ₂ interlayer insulating film under the same conditions as described above. At this time, the resist-to-resist selectivity is 1.
5. The selectivity to silicon was 3.9, which was much worse than that using C ₃ F ₇ H. This is because C ₃ F ₈ has a smaller C / F ratio than C ₃ F ₇ H, and the generation of excessive F ^* which causes a decrease in the selectivity was not sufficiently suppressed.

Embodiment 2 In this embodiment, the present invention is applied to contact hole processing, and SiO ₂ is formed using C ₃ F ₆ H ₂ (1,1,1,3,3,3-hexafluoropropane). _This is an example where _two interlayer insulating films are etched. The wafer used in this example is the same as that used in Example 1. The wafer is set in a magnetron RIE apparatus, and as an example, C ₃ F ₆
Etching was performed under the conditions of an H ₂ flow rate of 46 SCCM, a gas pressure of 2 Pa, an RF power density of 2.0 W / cm ² , a magnetic field strength of 150 Gauss, and a wafer temperature of 20 ° C. The progress of the etching reaction and the deposition mechanism of the carbon-based polymer in the above-described etching process are as described in the first embodiment.
However, since C ₃ F ₆ H ₂ has two H atoms in one molecule and these capture and consume F ^* , substantial C / F
The ratio is 3/4. By using a compound having a higher C / F ratio than that of Example 1, sufficient high selectivity was achieved despite the higher wafer temperature than that of Example 1.

Embodiment 3 In this embodiment, the present invention is applied to contact hole processing, and a C ₂ F ₅ H (1,1,3,3,3-pentafluoropropene) is used to insulate the SiO ₂ interlayer. This is an example of etching a film. The wafer used in the present embodiment is also the same as in the first embodiment.
It is the same as that used in. The above wafer is set in a magnetron RIE apparatus, and as an example, a C ₃ F ₅ H flow rate is 46 SCCM, a gas pressure is 2 Pa, and an RF power density is 2.0 W.
/ Cm ² , magnetic field strength 150 Gauss, wafer temperature 20
Etching was performed under the condition of ° C. The progress of the etching reaction and the deposition mechanism of the carbon-based polymer in the above-described etching process are as described in the first embodiment. C ₃ F ₅
H has one H atom in the molecule, but has one double bond in the main chain. Therefore, the C / F ratio is C ₃ F _{6 of} Example 2.
Like H ₂ , it is ／. Also in this example, a sufficiently high selectivity was achieved by controlling the wafer temperature near room temperature.

Although the present invention has been described based on three types of embodiments, the present invention is not limited to these embodiments. For example, the effects of sputtering, dilution, and cooling are expected. In the sense, H
A rare gas such as e or Ar may be appropriately added. These rare gases do not impair the advantages of the single composition gas of the present invention. Further, the material layer to be etched is not limited to the above-mentioned SiO2, but may be PSG, BSG,
It may be BPSG, AsSG, AsPSG, AsBSG, or the like.

[0021]

As is clear from the above description, the present invention uses a saturated or unsaturated higher-order fluorocarbon chain compound containing at least one H atom in a molecule to thereby improve deposition gas. Without any addition of C
By optimizing the / F ratio, it is possible to perform etching of a silicon compound layer excellent in high speed, low contamination, high anisotropy, controllability and reproducibility. Therefore, 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.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/3065 C23F 4/00

Claims (1)

(57) [Claims] A temperature of a substrate to be etched is controlled to 50 ° C. or less, and a general formula C _x F _y H _z (where x, y, and z are natural numbers indicating the number of atoms, and x ≧ 2, y> z) ≧ 1, 2x +
2> y + z, y ≧ x + z are all satisfied. A) etching a silicon oxide layer using an etching gas mainly containing an unsaturated chain compound represented by the formula (1 ).