JP2014216331A - Plasma etching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma etching method by which a silicon nitride film can be selectively and quickly etched and can be etched to have high anisotropy.SOLUTION: In a plasma etching method, a silicon nitride film 203 arranged on a polysilicon film 204 is plasma etched using a resist 201 as a mask. The plasma etching method includes: a first step of etching the silicon nitride film 203 until the polysilicon film 204 starts to be exposed; and a second step of etching the silicon nitride film 203 after the first step using mixed gas composed of CHF gas and COgas. The ratio of the flow rate of the COgas to the flow rate of the CHF is 1 or less.

Description

  The present invention relates to a plasma etching method.

  Hard mask etching using a silicon nitride film in a semiconductor manufacturing process by plasma etching is a hard mask between a resist patterned by lithography and a polysilicon film or silicon oxide film to be etched. A layer of a silicon nitride film and a layer of an antireflection film (hereinafter referred to as BARC) for improving resolution during photolithography are provided. Then, plasma etching is consistently performed in the order of BARC and silicon nitride film, and the pattern shape of the resist is transferred to the hard mask. Thereafter, plasma etching of the polysilicon film or the silicon oxide film is performed using the hard mask on which the pattern is formed.

  Here, an organic film is often used for the resist and BARC. Therefore, when etching the silicon nitride hard mask, the consumption of resist, BARC, which is an organic film, is suppressed, the selection ratio of the underlying polysilicon film and silicon oxide film is high, and these are made vertical. It is required to be processed.

  As background art of this technical field, there is JP-A-2001-217230 (Patent Document 1). In this publication, in a method of selectively anisotropically etching a silicon nitride film with respect to a silicon oxide film, a polysilicon film, and silicon, the substrate temperature is set to 10 ° C. or less, and a compound gas containing fluorine, carbon, and hydrogen is used. It is described that a mixed gas with carbon oxide (CO) is used as a reaction gas, and the mixing ratio of the CO gas to the total gas flow rate of the reaction gas is 70 to 95% by volume. JP-A-8-59215 (Patent Document 2) discloses that a certain combination of a hydrofluorocarbon gas and an oxygen-containing gas has selectivity for oxides, silicides, and silicon under specific etching conditions. The nitride is etched while being shown.

JP 2001-217230 A JP-A-8-59215

  In the etching having a selection ratio with respect to the silicon oxide film and the polysilicon film as in the above prior art, the BARC disposed on the silicon nitride film is etched in order to set the substrate temperature during processing to 10 ° C. or less. The processing speed during processing is reduced. Further, when the mixing ratio of CO is 70 to 95% by volume, the consumption of the organic film is increased, and etching cannot be performed with good anisotropy.

  An object of the present invention is to provide a technique for enabling a silicon nitride film to be selectively and quickly etched and etched with good anisotropy.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

The plasma etching method according to an embodiment of the present invention includes a first step of selectively etching a silicon nitride film using a resist mask. Further, the silicon gas remaining using the processing gas after switching is switched to a mixed gas of the CO ₂ gas and the CH ₃ F gas, which contains more CH ₃ F gas than CO ₂ gas. A second step of etching the nitride film;

The plasma etching method according to an embodiment of the present invention is a plasma etching method in which a silicon nitride film disposed on a polysilicon film is plasma-etched using a resist as a mask, and the silicon nitridation is performed until the polysilicon film starts to be exposed. A first step of etching the film. And a second step of etching the silicon nitride film after the first step using a mixed gas of CH ₃ F gas and CO ₂ gas. In the second step, the ratio of the CO ₂ gas flow rate to the CH ₃ F gas flow rate is set to 1 or less.

In another embodiment, in a plasma etching method of plasma etching a silicon nitride film disposed on a silicon oxide film using a resist as a mask, the silicon nitride film is etched until the silicon oxide film starts to be exposed. Having a first step. And a second step of etching the silicon nitride film after the first step using a mixed gas of CH ₃ F gas and CO ₂ gas. In the second step, the ratio of the CO ₂ gas flow rate to the CH ₃ F gas flow rate is set to 1 or less.

  Among the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows.

  According to an embodiment of the present invention, a silicon nitride film can be selectively and quickly etched and etched with good anisotropy.

In the plasma etching method in Embodiment 1 of this invention, it is a figure which shows the outline | summary of the structural example of a plasma processing apparatus. In the plasma etching method in Embodiment 1 of this invention, it is a figure which shows the outline | summary of the structural example of the wafer before a plasma etching process is performed. (A)-(d) is a figure for demonstrating the plasma etching process in the plasma etching method in Embodiment 1 of this invention. In the plasma etching method in Embodiment 2 of this invention, it is a figure which shows the outline | summary of the structural example of the wafer before a plasma etching process is performed. (A)-(d) is a figure for demonstrating a plasma etching process in the plasma etching method in Embodiment 2 of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.

[Embodiment 1]
The first embodiment will be described with reference to FIGS.

<Example of overall configuration>
FIG. 1 is a diagram showing an outline of a configuration example of a plasma processing apparatus in a plasma etching method according to Embodiment 1 of the present invention. In FIG. 1, the plasma processing apparatus includes, for example, a cylindrical vacuum vessel 101, a wafer placement electrode 111 provided in a processing chamber 104 in the vacuum vessel 101, and a shower provided above the wafer placement electrode 111. A plate 102, a gas supply device 105 connected to the shower plate 102, and a vacuum exhaust port 106 provided below the processing chamber 104 are provided.

  The shower plate 102 has a disk shape, and a plurality of processing gas inlets are formed near the center position of the disk. Then, the processing gas supplied from the gas supply device 105 is introduced into the processing chamber 104 through these processing gas introduction ports.

  The processing gas introduced into the processing chamber 104 is turned into plasma, and the surface of the wafer 112 mounted on the wafer mounting electrode 111 is processed using the plasma formed in the processing chamber 104.

  The processing chamber 104 is connected to a vacuum exhaust device (not shown) via a vacuum exhaust port 106. The vacuum evacuation apparatus is constituted by, for example, a variable valve, a turbo molecular pump, and a dry pump, and can adjust the pressure of the processing chamber 104 during the plasma etching process.

  The vacuum vessel 101 is provided with an observation window 122 for observing the light emission state of plasma. A spectroscope 124 for observing the emission spectrum of the plasma is connected to the observation window 122 via the optical fiber 123.

  A dielectric window 103 is provided above the shower plate 102, and a waveguide 107 that radiates electromagnetic waves is provided above the dielectric window 103. An electromagnetic wave (for example, 2.4 GHz microwave) is oscillated in the waveguide 107 from an electromagnetic wave generating power source 109.

  A magnetic field generating coil 110 that forms a magnetic field is provided on the outer periphery of the processing chamber 104. The electric power oscillated from the magnetic field generating coil 110 converts the processing gas introduced into the processing chamber 104 into plasma by the formed magnetic field and electron cyclotron resonance.

  The wafer mounting electrode 111 has an electrode surface covered with a thermal spray film (not shown), and is connected to a DC power supply 116 for electrostatic adsorption through a high frequency filter 115. Further, a high frequency power supply 114 is connected to the wafer mounting electrode 111 via a matching circuit 113. Further, the wafer mounting electrode 111 has a refrigerant flow path 117 and is connected to the temperature controller 118, and has a heater 119 and is connected to the heater controller 120. Furthermore, the wafer mounting electrode 111 is provided with a temperature sensor 121, and a signal from the temperature sensor 121 is transmitted to the heater controller 120. Then, the heater controller 120 controls the temperature controller 118 to adjust the temperature output from the heater 119 so that the temperature of the wafer 112 becomes a desired temperature.

  The wafer 112 placed on the wafer placement electrode 111 is attracted to the wafer placement electrode 111 by the electrostatic force of the DC voltage applied from the electrostatic suction DC power supply 116.

  By applying a high frequency bias power from a high frequency power supply 114 connected to the wafer mounting electrode 111, a negative voltage generally called a self-bias is generated on the wafer mounting electrode 111. Then, ions are accelerated by the generated self-bias, ions are attracted from the plasma to the wafer 112, and the wafer 112 is subjected to plasma etching. The output of the high frequency power supply 114 is a time scheduling bias (hereinafter referred to as TM bias) that periodically applies a 440 kHz sine wave or a 400 kHz sine wave high frequency bias power.

<Detailed configuration example>
FIG. 2 is a diagram showing an outline of a configuration example of a wafer before the plasma etching process is performed in the plasma etching method according to the first embodiment of the present invention.

  In FIG. 2, a wafer 112 is composed of a plurality of layers, and is disposed on the polysilicon film 204 between the polysilicon film 204 to be a gate electrode of a transistor and a resist 201 on which a pattern by lithography is previously formed. It has a silicon nitride film 203 which is a hard mask, and a BARC 202 disposed on the silicon nitride film 203 (this BARC 202 is for improving resolution during photolithography).

<Plasma etching process>
FIGS. 3A to 3D are views for explaining the plasma etching process in the plasma etching method according to the first embodiment of the present invention.

  FIG. 3A shows the configuration of the wafer 112 before the plasma etching process is performed.

First, the BARC 202 shown in FIG. 3A is etched using a mixed gas composed of Hbr, O ₂ and N ₂ , and the wafer 112 is etched into the shape shown in FIG. 3B.

  Next, the silicon nitride film 203 of FIG. 3B is etched using the resist 201 and the BARC 202 as a mask, and the wafer 112 is etched into the shape of FIG. In this case, a first process is performed in which the silicon nitride film 203 is etched until the polysilicon film 204 starts to be exposed under the condition that the etching rate is high.

  Here, Table 1 shown below shows the conditions of the first step.

As shown in Table 1, the first step is performed using a mixed gas composed of CHF ₃ and SF ₆ .

  Further, in the first step, it is detected that the exposure of the polysilicon film 204 is started by an end point determination method using a change in emission intensity from plasma measured by the spectroscope 124. Under the conditions shown in Table 1, the etching rate of the silicon nitride film 203 measured using the wafer 112 is 140.6 nm / min, and the silicon nitride film 203 can be quickly etched in the first step.

  Here, when the etching is performed until the polysilicon film 204 starts to be exposed as in the first step, the silicon nitride film 203 in the vicinity of the polysilicon film 204 is not vertical but skirts from the BARC 202 as shown in FIG. Etched into a shape with a minus.

After the first step, in the second step, the processing gas is switched to a mixed gas composed of CH ₃ F and CO _2, and the shape portion with the bottom is etched using the processing gas after switching. Thus, the shape of the silicon nitride film 203 can be made perpendicular to the polysilicon film 204, and the silicon nitride film 203 can be etched with good anisotropy.

  Here, Table 2 shown below shows the conditions of the second step.

In the second step, as shown in Table 2, using a mixed gas composed of CH ₃ F and CO ₂ while supplying time-modulated high frequency power to the sample having the silicon nitride film 203, the silicon nitride film 203 is formed. Etching is performed, whereby the wafer 112 is etched into the shape of FIG.

In order to reduce the amount of etching of the organic film such as the resist 201 and the BARC 202 when the silicon nitride film 203 is etched, the mixed gas is made of CO ₂ gas as shown in Table 2 rather than O ₂ gas. It is desirable to use it. Etching of the organic film proceeds by combining carbon in the organic film and oxygen radicals generated by plasma. When etching with addition of O ₂ gas is performed, oxygen radicals are generated excessively and the etching of the organic film proceeds. Therefore, by using CO ₂ gas, which is carbon-containing O ₂ gas, generation of oxygen radicals can be suppressed, and when the gas itself contains carbon, bonding with carbon in the organic film can be suppressed. .

Furthermore, in the second step, it is desirable that the ratio of the gas flow rate obtained by dividing the flow rate of CH ₃ F from the flow rate of CO ₂ contained in the mixed gas is 1 or less. That is, it is desirable that the mixed gas contains more CH ₃ F gas than CO ₂ gas. If the mixed gas contains more CO ₂ than CH ₃ F gas, oxygen in the plasma will increase, thereby increasing consumption of the resist 201 and BARC 202, deteriorating the shape of the mask, and improving the vertical shape. It can no longer be obtained. In addition, when CH ₃ F gas is used as an etching gas, a reaction product containing carbon adheres to the side wall of the silicon nitride film 203 and serves as a side wall protective film to suppress the progress of etching in the lateral direction. When the CO ₂ flow rate ratio is made larger than 1, carbon in the side wall protective film and oxygen in the CO ₂ gas are combined to have high volatility C _x O _y (x and y are integers of 1 or more) And the sidewall protective film is reduced. As a result, the vertical shape of the silicon nitride film 203 cannot be obtained.

  The high frequency bias current in Table 2 is a TM bias. By using the TM bias, it is possible to control the balance between the deposition of the reaction product by the plasma and the etching, and further reduce the consumption of the resist 201 and the BARC 202. 200 W in Table 2 represents a 400 kHz sine wave power. Further, 200 Hz in Table 2 represents a modulation frequency for periodically repeating ON / OFF of the 400 kHz sine wave. Further, 25% in Table 2 indicates a ratio (duty ratio) in which this modulation frequency is on during one period.

  When the wafer 112 is etched under the conditions shown in Table 2, the etching rate of the silicon nitride film 203 is 17.5 nm / min, whereas the etching rate of the polysilicon film 204 is 1.5 nm / min. A ratio is obtained. By etching using the second step, the shape of the silicon nitride film 203 can be made perpendicular to the polysilicon film 204, and the silicon nitride film 203 can be etched with good anisotropy.

<Effect of Embodiment 1>
As described above, according to the first embodiment, the first step of etching the silicon nitride film 203 until the polysilicon film 204 begins to be exposed and the mixed gas of CH ₃ F gas and CO ₂ gas are used. And a second step of etching the silicon nitride film 203 after the first step, and the second step is to reduce the ratio of the CO ₂ gas flow rate to the CH ₃ F gas flow rate to 1 or less, The nitride film 203 can be etched selectively and quickly and can be etched with good anisotropy.

[Embodiment 2]
A second embodiment of the present invention will be described with reference to FIGS.

<Detailed configuration example>
FIG. 4 is a diagram showing an outline of a configuration example of a wafer before the plasma etching process is performed in the plasma etching method according to the second embodiment of the present invention.

  In FIG. 4, a wafer 306 is composed of a plurality of layers, and is disposed on the polysilicon film 305 between a polysilicon film 305 to be a gate electrode of a transistor and a resist 301 on which a pattern by lithography has been formed in advance. It has a silicon oxide film 304, a silicon nitride film 303 disposed on the silicon oxide film 304, and a BARC 302 disposed on the silicon nitride film 303.

<Plasma etching process>
FIGS. 5A to 5D are diagrams for explaining the plasma etching process in the plasma etching method according to the second embodiment of the present invention.

First, the BARC 302 of FIG. 5A is etched using a mixed gas composed of Hbr, O ₂ and N ₂ , and the wafer 306 is etched into the shape of FIG. 5B.

  Next, the silicon nitride film 303 of FIG. 5B is etched using the resist 301 and the BARC 302 as a mask, and the wafer 306 is etched into the shape of FIG. 5C. In this case, a first step is performed in which the silicon nitride film 303 is etched until the silicon oxide film 304 starts to be exposed under the condition that the etching rate is high.

  Thereafter, in the second step, the silicon nitride film 303 is etched, whereby the wafer 306 is etched into the shape of FIG. In this case, by disposing the silicon oxide film 304 as a stopper layer on the polysilicon film 305, the silicon nitride film 303 can be etched without substantially etching the polysilicon film 305. That is, the selection ratio of the silicon nitride film 303 to the polysilicon film 305 can be obtained as a very large value, and the silicon nitride film 303 can be etched with good anisotropy.

<Effect of Embodiment 2>
As described above, according to the second embodiment, by etching the silicon nitride film 303 until the silicon oxide film 304 disposed on the polysilicon film 305 starts to be exposed, the polysilicon film 305 is substantially The silicon nitride film 303 can be etched without being etched.

  As mentioned above, although the invention made by this invention was concretely demonstrated based on Embodiment 1 and Embodiment 2, this invention is not limited to the said Embodiment 1 and Embodiment 2, and the summary It goes without saying that various changes can be made without departing from the scope of the invention.

For example, in order to adjust the dissociation and dissociation distribution of CH ₃ F, a rare gas such as Ar gas, Kr gas, or Xe gas is attached to the mixed gas, whereby the etching rate of the silicon nitride films 203 and 303 and the wafers 112 and 306 The etching rate distribution may be adjusted.

  In addition to a plasma processing apparatus using a plasma generation method using electron cyclotron resonance, for example, an inductively coupled plasma processing apparatus or a capacitively coupled plasma processing apparatus may be used. There are also certain embodiments.

DESCRIPTION OF SYMBOLS 101 Vacuum container 102 Shower plate 103 Dielectric window 104 Processing chamber 105 Gas supply apparatus 106 Vacuum exhaust port 107 Waveguide 108 Cavity resonator 109 Electromagnetic wave generation power supply 110 Magnetic field generation coil 111 Wafer mounting electrode 112,306 Wafer 113 Matching Circuit 114 High-frequency power source 115 High-frequency filter 116 Electrostatic adsorption DC power source 117 Refrigerant flow path 118 Temperature controller 119 Heater 120 Heater controller 121 Temperature sensor 122 Observation window 123 Optical fiber 124 Spectroscope 201, 301 Resist 202, 302 BARC
203, 303 Silicon nitride film 204, 305 Polysilicon film 304 Silicon oxide film

Claims (5)

In a plasma etching method of plasma etching a silicon nitride film disposed on a polysilicon film using a resist as a mask,
A first step of etching the silicon nitride film until the polysilicon film begins to be exposed;
A second step of etching the silicon nitride film after the first step using a mixed gas of CH ₃ F gas and CO ₂ gas,
The plasma etching method according to the second step, wherein the ratio of the CO ₂ gas flow rate to the CH ₃ F gas flow rate is 1 or less. In a plasma etching method for plasma etching a silicon nitride film disposed on a silicon oxide film using a resist as a mask,
A first step of etching the silicon nitride film until the silicon oxide film begins to be exposed;
A second step of etching the silicon nitride film after the first step using a mixed gas of CH ₃ F gas and CO ₂ gas,
The plasma etching method according to the second step, wherein the ratio of the CO ₂ gas flow rate to the CH ₃ F gas flow rate is 1 or less. In the plasma etching method according to claim 1 or 2,
The plasma etching method according to claim 2, wherein the second step performs etching while supplying time-modulated high frequency power to the sample having the polysilicon film. In the plasma etching method according to claim 1 or 2,
The plasma etching method, wherein the mixed gas of the CH ₃ F gas and the CO ₂ gas further contains a rare gas. The plasma etching method according to claim 3, wherein
In the plasma etching method, the first step is performed by using a mixed gas of the CHF ₃ gas and the SF ₆ gas.

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