JP7253729B2 - Gas generation method and etching apparatus - Google Patents

Description

The present embodiment relates to a gas generation method and an etching apparatus.

Ultra-large-scale integration (ULSI) has improved its performance by promoting miniaturization and high integration based on the scaling law. ULSI manufacturing processes include photolithography, film deposition, chemical mechanical polishing, and etching. Etching processes in particular require extremely high-precision shape control, and plasma RIE (reactive ion etching) is required. ) plays an important role. In order to achieve high integration in recent years, in addition to miniaturization (reduction in the planar direction of the wafer), three-dimensionalization (increase in the thickness direction) is progressing.As a result, the aspect ratio of the etched shape, that is, There is a need to cope with the increase in aspect ratio. In an etching apparatus, it is necessary to mix various kinds of etching gases in a desired ratio and introduce them in order to obtain an optimum etching gas for the etching process. In the 1980s, _{a CF 4 /} CHF ₃ mixed gas was _used as _an etching gas _. There is an increasing tendency to develop and use gases with large C/F ratios. However, some of these effective etching gases are expensive or difficult to obtain.

Patent No. 0502817

K. Fujita et al, Journal of Vacuum Science and Technology B, 17 (1999) 957.

A gas generation method and an etching apparatus capable of easily forming a pattern with a high aspect ratio at low cost are provided.

A gas generation method according to this embodiment is a gas generation method in an etching apparatus having a first chamber for generating an etching gas and a second chamber for performing an etching process using the etching gas. A first gas containing carbon (C) and fluorine (F) is supplied to the first chamber, and the pressure inside the first chamber is made higher than the pressure inside the second chamber during the etching process. A second gas containing carbon (C) and fluorine (F) is generated from the first gas by applying high frequency power to the first gas in the first chamber. A second gas is supplied to the second chamber as an etching gas.

1 is a schematic cross-sectional view showing a configuration example of an etching apparatus according to a first embodiment; FIG. FIG. 4 is a flowchart showing an example of a gas generation method according to the first embodiment; 4 is a graph showing composition ratios of gas components of source gas CmFn and etching gas CxFy; 4 is a graph showing the relationship between high-frequency power density and source gas utilization efficiency;

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. This embodiment does not limit the present invention. The drawings are schematic or conceptual, and the ratio of each part is not necessarily the same as the actual one. In the specification and drawings, the same reference numerals are given to the same elements as those described above with respect to the previous drawings, and detailed description thereof will be omitted as appropriate.

(First embodiment)
FIG. 1 is a schematic cross-sectional view showing a configuration example of an etching apparatus 1 according to the first embodiment. The etching apparatus 1 includes a gas generation chamber 10 , an etching chamber 20 and a refiner 30 .

A gas generation chamber 10 as a first chamber comprises a ground electrode 11 as a first electrode and a carbon electrode 12 as a second electrode. The ground electrode 11 is provided as a stage on which the substrate W0 can be mounted. The substrate W0 is, for example, a semiconductor substrate containing silicon or the like, but is not particularly limited.

The carbon electrode 12 is connected to a high frequency power supply 50 via an impedance matching circuit (not shown), and applies an electric field by high frequency power between the carbon electrode 12 and the ground electrode 11 . The carbon electrode 12 is made of high-purity carbon that withstands a temperature rise due to high applied power and does not emit by-products such as metal compounds that may cause undesirable contamination of semiconductor devices even if reacted with gas. The facing surface of the carbon electrode 12 facing the ground electrode 11 is, for example, substantially circular, and has a diameter of, for example, about 10 mm. The gap between the ground electrode 11 and the carbon electrode 12 is about 5 mm or less, preferably about 1 mm or less.

A source gas supply unit 40 is pipe-connected to the gas generation chamber 10 via a pipe P1. After the gas generation chamber 10 is evacuated by a vacuum exhaust system (not shown), the source gas is introduced from the source gas supply section 40 and maintained at a desired pressure. The source gas supply unit 40 is a cylinder that mainly stores the source gas CmFn (m and n are positive integers) to be introduced into the gas generation chamber 10 . In the first embodiment, the source gas (first gas) is CmFn containing carbon (C) and fluorine (F), which is a low-order PFC gas with a relatively low m value and m/n ratio. The source gas CmFn is mainly _CF4 , for example.

The high frequency power supply 50 applies high frequency power of, for example, about 200 W or more to the carbon electrode 12 at about 13.56 MHz to 300 MHz. Also, by setting the pressure in the chamber 10 to 1 Torr or more, preferably 10 Torr or more to shorten the mean free path of the particles, localized plasma is generated near the tip of the electrode 12 . Thereby, the high-frequency power density between the ground electrode 11 and the carbon electrode 12 can be made about 0.5 kW/cm ³ or more, preferably about 3 kW/cm ³ or more. The output (electric power) of the high-frequency power source 50 is changed according to the facing area of the ground electrode 11 and the carbon electrode 12 and the distance between them, and the high-frequency power density is set to about 0.5 kW/cm ³ or more. and preferably about 3 kW/cm ³ or more.

A discharge state is maintained between the high pressure ground electrode 11 and the carbon electrode 12 to ionize the gas between them. That is, the gas generation chamber 10 ionizes the gas therein by applying high frequency power to bring it into a plasma state. Thereby, the gas generation chamber 10 generates an etching gas.

Here, the gas generation chamber 10 ionizes the source gas CmFn into a plasma state D under a pressure higher than the pressure inside the etching chamber 20 during the etching process. For example, if the pressure in the etching chamber 20 during the etching process is 10-100 mTorr, the pressure of the source gas CmFn in the gas generation chamber 10 is 20-400 Torr. That is, the pressure in gas generation chamber 10 is orders of magnitude higher than the pressure in etching chamber 20 . Further, the high frequency power source 50 has a high frequency power density of about 0.5 kW/cm ³ or more between the ground electrode 11 and the carbon electrode 12 . Under such high pressures and high power densities, the ionization of low order PFC gases such as _CF4 results in not only dissociation reactions but also synthesis reactions.

For example, when PFC gas is ionized using inductively coupled plasma (ICP) or capacitively coupled plasma (CCP) under relatively low pressure, CF ₄ → CF ₃ A dissociation reaction such as +F→CF ₂ +2F→CF+3F→C+4F mainly occurs.

On the other hand, when a low-order PFC gas is ionized under relatively high pressure and high power density as in the present embodiment, the collision frequency between radicals generated at high density is high, resulting in CF ₂ + _CF2 → _C2F4 , _CF2 + _{CF2 → C2F2} +2F, _{CF2 + CF3} → _{C2F4 + F} , _{CF3 + CF3} → _C2F6 , _C2F2 + _CF3 → _{C3F 5} , C ₂ F ₄ +C ₂ F ₄ →C ₄ F ₆ +2F, C ₂ F ₄ +C ₂ F ₄ →C ₄ F ₈ and the like also occur with high probability. That is, ionizing _{low order PFC} gases such as _CF4 under relatively high pressure and high power density yields _{C2F2 , C2F4} , _C2F6 , _C3F5 , _C3 A high-order PFC gas (second gas) mainly containing at least one of F ₆ , C ₄ F ₆ , C ₄ F ₈ and the like can be generated.

Generally speaking, the etching apparatus 1 according to the present embodiment ionizes a source gas mainly containing CmFn (m and n are positive integers) under a relatively high pressure and a high power density to produce CxFy (x, y is a positive integer) is generated. Then at least x>m and/or x/y>m/n. That is, the etching gas as the second gas is a PFC gas of higher order than the source gas as the first gas. Higher order here means a PFC gas having a carbon-rich composition with x>m and/or x/y>m/n.

Higher-order gases are needed to form patterns with high aspect ratios, but they are scarce and expensive. For example, the unit price of _C4F8 gas is several times higher than that _{of CF4} gas. _The unit price of _C4F6 gas is higher than _that of _C4F8 gas.

However, according to the present embodiment, it is possible to generate an etching gas that mainly contains an expensive high-order gas using a source gas that mainly contains an inexpensive low-order gas. As a result, a high-order gas can be used as an etching gas while suppressing an increase in the manufacturing cost of the semiconductor device. As a result, a pattern with a high aspect ratio can be formed at low cost.

The description of the configuration of the etching apparatus 1 will be continued with reference to FIG. 1 again. In the gas generation chamber 10, the ionized plasma gas is in an active state, and thus reacts with the gas when an electric field is applied between the carbon electrode 12 and the ground electrode 11 by high-frequency power. It is necessary to select a material that does not have a negative effect on For example, the substrate W<b>0 is placed on the ground electrode 11 to protect the ground electrode 11 . In this case, the substrate W0 is scraped by the gas in the active state, and a gas containing semiconductor components is generated. That is, when silicon is used for the substrate W0 and _CF4 gas is ionized, _SiF4 is generated. SiF ₄ may be utilized in the etching process without adverse effects such as contamination, but can be removed in refiner 30 if not needed. As another embodiment, a substrate W0 of Al ₂ O ₃ or C may be placed on the ground electrode 11 when SiF ₄ is unnecessary. As a result, consumption of the substrate and generation of SiF ₄ due to discharge can be suppressed.

Purifier 30 includes a filter 31 made of an agent, such as zeolite, selected to selectively adsorb particular gases contained in the etching gas obtained from gas generation chamber 10 . The refiner 30 is piped to the gas generation chamber 10 via a pipe P2, and is piped to the etching chamber 20 via pipes P3 and P4. The filter 31 separates and refines the etching gas and allows only the desired etching gas to pass through. For example, the filter 31 selectively adsorbs and removes SiF ₄ gas, which has a relatively large molecular weight, contained in the etching gas. That is, an etching gas having a molecular weight smaller than that of SiF ₄ is allowed to pass through.

The etching chamber 20 can accommodate the semiconductor substrate W1 to be etched, and uses the etching gas obtained from the gas generation chamber 10 through the refiner 30 to etch the semiconductor substrate W1. The etching process is not particularly limited, and for example, a general RIE (Reactive Ion Etching) method may be used. The etching gas used for the etching process is, as described above, _{a high gas} such _{as C2F2 , C2F4} , _{C2F6 , C3F5} , _C3F6 , _C4F6 , _{C4F8 .} It mainly contains at least one of the following gases. As a result, a high-order gas can be used as an etching gas while suppressing an increase in the manufacturing cost of the semiconductor device.

The etching gas used for the etching process is exhausted to the outside of the etching chamber 20 through the pipe P5.

Valve V1 is provided between pipes P2 and P3 and is connected in parallel with filter 31 and valve V2 in refiner 30 . The valve V2 is connected in series with the filter 31 between the pipes P2 and P3. The valve V3 is provided between the pipes P3, P4 and the pipe P6. A valve V4 is connected between the pipe P4 and the etching chamber 20 .

The valves V1 and V3 are provided for exhausting the gas in the gas generation chamber 10 from the pipe P6. Valves V 2 and V 4 are provided to purify the PFC gas from gas generation chamber 10 with filter 31 and supply the purified PFC gas to etching chamber 20 . Thus, when valves V1 and V3 are open to evacuate gas generation chamber 10, valves V2 and V4 are closed. On the other hand, when the PFC gas from the gas generation chamber 10 is purified and supplied to the etching chamber 20 with the valves V2 and V4 open, the valves V1 and V3 are closed.

Next, a gas generation method according to this embodiment will be described.

FIG. 2 is a flow chart showing an example of the gas generation method according to the first embodiment. First, the valves V1 and V3 are opened, the pressure in the gas generation chamber 10 is reduced, and the source gas CmFn is supplied from the source gas supply unit 40 to the gas generation chamber 10 (S10). At this time, the source gas supply unit 40 introduces the source gas CmFn at approximately 150 sccm, for example. The source gas CmFn is a low-order PFC gas containing carbon (C) and fluorine (F), for example, a gas mainly containing _CF4 .

Here, the pressure inside the gas generation chamber 10 is made higher than the pressure inside the etching chamber 20 during the etching process. For example, the pressure of the source gas CmFn in the gas generation chamber 10 is 20 Torr to 400 Torr while the pressure in the etching chamber 20 is 10 mTorr to 100 mTorr during the etching process. For example, the pressure within gas generation chamber 10 is adjusted to approximately 80 Torr.

Next, the valves V1 and V3 are closed, and an electric field is applied between the ground electrode 11 and the carbon electrode 12 in the gas generation chamber 10 to ionize the source gas CmFn (S20). At this time, the high frequency power supply 50 sets the high frequency power density between the ground electrode 11 and the carbon electrode 12 to approximately 0.5 kW/cm ³ or more. Under such high pressure and high power _density , when _the source gas CmFn is ionized into a plasma state, a synthesis _reaction occurs _to produce _C2F2 , _C2F4 , _C2F6 , _C3F5 , Higher order PFC gases such _{as C3F6} , _C4F6 and _C4F8 can be generated as _the etching gas _CxFy . Then at least x>m and/or x/y>m/n.

FIG. 3 is a graph showing composition ratios of the gas components of the source gas CmFn and the etching gas CxFy. In this experiment, FT-IR (Fourier Transform Infrared Spectroscopy) was used to analyze the gas components before and after plasma discharge in the gas generation chamber 10 . The source gas CmFn before plasma discharge contains about 100% _CF4 . On the other hand, the etching gas CxFy after plasma discharge was a mixed gas containing approximately 42% CF ₄ , approximately 30% C ₂ F ₄ , approximately 9% C ₂ F ₆ and approximately 19% SiF ₄ . It was also found that approximately 42% of the original source gas _CF4 had been synthesized into higher order PFC gases.

Refer to FIG. 2 again. The valves V2 and V4 are opened, and the refiner 30 refines the etching gas CxFy (S30). In the gas generation chamber 10, a semiconductor substrate W0 is arranged between the ground electrode 11 and the carbon electrode 12. As shown in FIG. Therefore, when the etching gas CxFy is generated, the etching gas CxFy contains unfavorable gases such as SiF ₄ as impurities. In this embodiment, the purification device 30 selectively and reversibly adsorbs a necessary gas, for example, C ₂ F ₄ gas, by a filter 31, and after passing and discarding other unnecessary gases, C ₂ F ₄ is Concentrate and purify by re-desorption by a method such as temperature elevation. Also in this case, zeolite or the like selected according to the purpose may be used for the filter 31 . In this manner, necessary gases are adsorbed and desorbed to purify the etching gas C ₂ F ₄ . Thereby, PFC gas with high purity is obtained.

Next, the PFC gas from the refiner 30 is supplied to the etching chamber 20 as the etching gas CxFy. The etching chamber 20 etches the semiconductor substrate W1 using a PFC gas higher than _CF4 as an etching gas. (S40). The etching gas CxFy contains high _- order gases such as _C2F4 and _{C2F6 .} Thereby, a pattern with a high aspect ratio can be formed at low cost. Further, in the etching chamber 20, other gases such as O ₂ and Ar may be mixed and etched through a gas introduction pipe (not shown) in addition to the gas introduction pipe for synthetic gas. Properties can be optimally controlled. Furthermore, in this embodiment, the source gas CmFn uses inexpensive CF ₄ gas. Therefore, it is possible to suppress an increase in the manufacturing cost of the semiconductor device.

(Second embodiment)
The etching apparatus 1 according to the second embodiment may have the same configuration as shown in FIG. However, according to the second embodiment, the source gas supply section 40 supplies a higher order gas (eg, C ₄ F ₈ ) to the gas generation chamber 10 as the source gas. Other configurations of the second embodiment may be the same as corresponding configurations of the first embodiment. Also, the operation of the second embodiment may be the same. Accordingly, the gas generation chamber 10 ionizes higher order PFC gases such as _C4F8 under high pressure and _high power density.

In _this case, for _example , when the _source gas is a high-order _PFC gas mainly _{containing C4F8 , C4F8} → _2C2F4 , _C4F8 → _C2F2 + _C2F6 , _C4 Dissociation reactions such as F ₈ →CF ₃ +C ₃ F ₅ and C ₄ F ₈ →C ₄ F ₆ +F ₂ occur. Of course, the PFC gas decomposed by the dissociation reaction may be further synthesized. Thereby, the _etching gas becomes a PFC gas mainly containing at _least one _{of C2F2 , C2F4} , _C2F6 , _{C3F5 , C3F6} , _{and C4F6} . Although this etching gas has a lower order than the source gas C ₄ F ₈ , it is a PFC gas with a higher order than CF ₄ , having the same C/F ratio in many cases. It is known that introduction of C ₂ F ₄ as an etching gas exhibits higher selectivity to a mask than C ₄ F ₈ and is effective for etching. However, C ₂ F ₄ gas is difficult to handle safely and is difficult to obtain as a semiconductor process gas. Therefore, even if a high-order gas is used as the source gas as in the second embodiment, a gas mainly containing a high-order gas effective for etching can be generated on the spot and supplied as in the first embodiment. can be done.

Generally speaking, the etching apparatus according to the second embodiment ionizes a source gas mainly containing CmFn (where m and n are positive integers) under relatively high pressure and high power density to produce CxFy (x, y is a positive integer) is generated. Then at least x≦m and/or x/y≧m/n. That is, the etching gas as the second gas is a PFC gas of a lower order than the source gas as the first gas. On the other hand, the etching gas is preferably higher order than _CF4 . Therefore, it is preferable that x≧2.

Next, a gas generation method according to the second embodiment will be described.

First, the valves V1 and V3 are opened, the pressure in the gas generation chamber 10 is reduced, and the source gas CmFn is supplied from the source gas supply unit 40 to the gas generation chamber 10 (S10). At this time, the source gas supply unit 40 introduces the source gas CmFn at about 200 sccm, for example. The source gas CmFn is a high-order PFC gas containing carbon (C) and fluorine (F), _for example, a gas mainly containing _C4F8 .

Here, the pressure inside the gas generation chamber 10 is made higher than the pressure inside the etching chamber 20 during the etching process. For example, the pressure of the source gas CmFn in gas generation chamber 10 is between 20 Torr and 400 Torr. For example, the pressure within gas generation chamber 10 is adjusted to approximately 50 Torr.

Next, the valves V1 and V3 are closed, and an electric field is applied between the ground electrode 11 and the carbon electrode 12 in the gas generation chamber 10 to ionize the source gas CmFn (S20). At this time, the high frequency power supply 50 sets the high frequency power density between the ground electrode 11 and the carbon electrode 12 to approximately 0.5 kW/cm ³ or more. When the source gas CmFn is ionized into a plasma state under such high pressure and high power density, _{a decomposition reaction} occurs to _{produce C2F2} , _C2F4 , _C2F6 , _C3F5 , A PFC gas having a higher order than CF ₄ such as C ₃ F ₆ and C ₄ F ₆ is generated as the etching gas CxFy.

In the second embodiment, high-frequency power was applied to the gap of 0.5 mm between the ground electrode 11 and the carbon electrode 12 having a diameter of 6.35 mm to ionize the source gas C ₄ F ₈ gas. At that time, the surface temperature of the substrate W0 was maintained at about 500° C. or less by ON/OFF controlling the plasma exposure time at a frequency of 1 Hz.

FIG. 4 shows the relationship between the high-frequency power density and the decomposition efficiency of the C ₄ F ₈ source gas. As shown in the graph of FIG. 4, in this embodiment, by setting the high-frequency power density to about 5 kW/cm ³ or more, the source gas C ₄ F ₈ gas can be decomposed and reformed with high efficiency close to 100%. was made. As a _{result, an etching gas containing 86% C 2 F 4} and 14% C ₂ F ₆ was generated from the source gas C 4 F ₈ gas.

Thereafter, by executing step S30 and subsequent steps in FIG. 2, in the etching chamber 20, although the source gas _C4F8 gas is supplied, the PFC gas having a higher order than _CF4 is used as the etching gas to etch the semiconductor _. Substrate W1 may be etched. In other words, C ₂ F ₄ can be introduced as an etching gas, whereby the second embodiment can obtain the same effect as the first embodiment.

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and equivalents thereof.

1 Etching Device 10 Gas Generation Chamber 11 Grounding Electrode 12 Carbon Electrode 20 Etching Chamber 30 Refining Device 31 Filter 40 Source Gas Supply Unit 50 High Frequency Power Supply W0, W1 Semiconductor Substrate V1 to V4 Valve P1 ~P6 Piping

Claims (9)

A gas generation method in an etching apparatus comprising a first chamber for generating an etching gas and a second chamber for performing an etching process using the etching gas, comprising:
supplying a first gas containing carbon (C) and fluorine (F) to the first chamber, making the pressure in the first chamber higher than the pressure in the second chamber during etching, and generating a second gas containing carbon (C) and fluorine (F) from the first gas by applying high-frequency power to the first gas in the chamber;
supplying the second gas to the second chamber as an etching gas;
The first gas mainly contains CmFn (m and n are positive integers),
The second gas mainly contains CxFy (x, y are positive integers),
A method of gas generation, wherein at least x>m. A gas generation method in an etching apparatus comprising a first chamber for generating an etching gas and a second chamber for performing an etching process using the etching gas, comprising:
supplying a first gas containing carbon (C) and fluorine (F) to the first chamber, making the pressure in the first chamber higher than the pressure in the second chamber during etching, and generating a second gas containing carbon (C) and fluorine (F) from the first gas by applying high-frequency power to the first gas in the chamber;
supplying the second gas to the second chamber as an etching gas;
The first gas mainly contains CmFn (m and n are positive integers),
The second gas mainly contains CxFy (x, y are positive integers),
A method of gas generation, wherein x/y>m/n. A gas generation method in an etching apparatus comprising a first chamber for generating an etching gas and a second chamber for performing an etching process using the etching gas, comprising:
supplying a first gas containing carbon (C) and fluorine (F) to the first chamber, making the pressure in the first chamber higher than the pressure in the second chamber during etching, and generating a second gas containing carbon (C) and fluorine (F) from the first gas by applying high-frequency power to the first gas in the chamber;
supplying the second gas to the second chamber as an etching gas;
The first gas mainly contains _CF4 ,
_The second gas is _{a gas} mainly containing at _least one of _C2F2 , _C2F4 , _C2F6 , _{C3F5 , C3F6 , C4F6} , and _{C4F8 .} generation method. The first chamber comprises a first electrode on which a substrate can be mounted and a second electrode for applying an electric field to the first gas,
4. The method of claim 1, wherein a radio frequency electrode density of about 0.5 kW/cm ^<3> or greater can be set between the first electrode and the second electrode. A gas generation method in an etching apparatus comprising a first chamber for generating an etching gas and a second chamber for performing an etching process using the etching gas, comprising:
supplying a first gas containing carbon (C) and fluorine (F) to the first chamber, making the pressure in the first chamber higher than the pressure in the second chamber during etching, and generating a second gas containing carbon (C) and fluorine (F) from the first gas by applying high-frequency power to the first gas in the chamber;
supplying the second gas to the second chamber as an etching gas;
the first chamber comprises first and second electrodes that apply an electric field to the first gas;
In generating the second gas, generating the second gas by ionizing the first gas between the first electrode and the second electrode;
The first gas mainly contains CmFn (m and n are positive integers),
The second gas mainly contains CxFy (x, y are positive integers),
A method of gas generation, wherein at least x≦m. 6. The gas generation method of claim 5, wherein a radio frequency electrode density of about 5 kW/cm3 or ^greater can be set between the first electrode and the second electrode. a first chamber for applying high frequency power to a first gas containing carbon (C) and fluorine (F) to generate a second gas containing carbon (C) and fluorine (F) from the first gas;
a second chamber for performing an etching process using the second gas as an etching gas;
The pressure in the first chamber during generation of the second gas is higher than the pressure in the second chamber during etching,
Provided between the first chamber and the second chamber, removing unnecessary gases from the second gas, or adsorbing/desorbing and extracting necessary gas groups from the second gas including unnecessary gases An etching apparatus further comprising a refining unit. 8. The etching apparatus according to claim 7, wherein said first chamber comprises a first electrode on which a substrate can be mounted, and a second electrode for applying an electric field to said first gas. The facing surface of the second electrode facing the first electrode is substantially circular,
the diameter of the facing surface of the second electrode is about 10 mm;
9. The etching apparatus of claim 8, wherein the distance between said first electrode and said second electrode is about 5 mm or less.

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