JP2005142223A - Atmospheric plasma etching method for tungsten - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an atmospheric plasma etching method for tungsten by which a tungsten film of a semiconductor substrate can be etched with plasma under an almost atmospheric pressure field. <P>SOLUTION: A process gas supplied from a supply source 2 is ionized into plasma in a plasma discharging space 1a and blown upon the semiconductor substrate 90 coated with the tungsten film to be etched. As the process gas, the mixed gas of a halogen-based gas, such as a fluorine-based gas etc., including CF<SB>4</SB>and oxygen is used. The ratio of the flow rate of the halogen-based gas to the total flow rate of the process gas is adjusted to 30-75 vol%. In addition, the temperature of the substrate 90 is adjusted to 50-120°C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for plasma etching tungsten in a substantially normal pressure field.

  Tungsten is used, for example, as a conductive material that connects wirings of each layer in a multilayer semiconductor substrate.

Patent Document 1 describes using a mixed gas of fluorine gas such as SF ₆ and nitrogen as a process gas for etching tungsten. In the literature 1, for example, the etching process is performed in a low pressure field of 8.7 Pa.

In low-pressure plasma etching, it is known to use a halogen-based gas such as CF ₄ , SF ₆ , NF ₃ , or Cl ₂ as a process gas for tungsten. This type of halogen-based gas is ionized and dissociated by plasma, and is vaporized and removed as tungsten fluoride or tungsten chloride. Since the boiling point of fluoride is 17.1 ° C. and the boiling point of chloride is 347 ° C., the etching rate can be further increased by using a fluorinated gas among halogen-based gases.

JP 7-147271 A

  As described above, tungsten can be etched in a low pressure field. However, the technique of etching in a normal pressure field has not yet been realized.

The inventor diligently conducted experimental research to plasma-etch tungsten in a normal pressure field. As a result, it was found that etching can be performed by mixing oxygen with a halogen-based gas such as a fluorine-based gas.
The present invention has been made on the basis of the above-mentioned knowledge. In a substantially normal pressure field, the process gas is converted into plasma (excited and activated) and sprayed onto the substrate, and tungsten coated on the substrate surface is converted into plasma. An atmospheric pressure plasma etching method for etching, wherein a mixed gas of oxygen and a halogen-based gas (halogen gas or halogen compound gas) is used as the process gas.

In addition, the substantially normal pressure (pressure near atmospheric pressure) in the present invention refers to a range of 1.333 × 10 ^{4 to} 10.664 × 10 ⁴ Pa. In particular, the range of 9.331 × 10 ^{4 to} 10.9797 × 10 ⁴ Pa is preferable because pressure adjustment is easy and the apparatus configuration is simple.

Here, the flow rate ratio of the halogen-based gas is preferably 30 to 75 vol% with respect to the total flow rate of the process gas.
As the halogen gas, fluorine, chlorine, bromine, or the like can be used. In particular, the use of a fluorine-based gas (fluorine or fluorine compound gas) is preferable because it facilitates atmospheric etching. Among the fluorine-based gases, use of CF ₄ or C ₂ F ₆ is more preferable because safety can be improved.

  The substrate is preferably etched at a temperature of 50 to 120 ° C. Thereby, the etching rate can be further reliably increased.

  According to the present invention, tungsten can be plasma etched in a substantially normal pressure field.

Embodiments of the present invention will be described below.
The present invention is applied to plasma etching of tungsten coated on the surface of a semiconductor substrate in a substantially normal pressure field. The method of the present invention is carried out using an atmospheric pressure plasma etching apparatus M illustrated in FIG. The apparatus M includes a processing head 1, a process gas supply source 2 and a power source 3 (electric field applying means) connected to the processing head 1, an exhaust pump 4, and a stage 5 disposed below the processing head 1. ing. A semiconductor substrate 90 to be etched is disposed on the stage 5. The stage 5 is heated by a heater 6 (base material heating means). As a result, the base material 90 is heated. As for the heating temperature of the base material 90, 50-120 degreeC is preferable. The apparatus M and the base material 90 are placed in a substantially normal pressure field.

  A pair of electrodes 11 and 12 are accommodated in the processing head 1. One electrode 11 is connected to the power source 3 to serve as an electric field application electrode, and the other electrode 12 is grounded to serve as a ground electrode. The power supply 3 outputs a voltage having a pulse waveform, for example. It is desirable that the rise time and / or fall time of this pulse is 10 μs or less, the pulse duration is 200 μs or less, the electric field strength is 1-1000 kV / cm, and the frequency is 0.5 kHz or more. Not only the pulse wave but also a continuous wave such as a sine wave may be output.

  A solid dielectric layer is coated on the opposing surface of at least one of the electrodes 11 or 12. A passage 1 a is formed between the electrodes 11 and 12. A process gas supply path 2a extends from the process gas supply source 2, and is connected to the upper end (upstream end) of the interelectrode path 1a. The downstream end of the interelectrode passage 1a is connected to the blowout hole 1b at the lower end of the processing head 1. The blowout hole 1b has a spot shape, for example.

  Further, a suction hole 1 c is formed at the lower end of the processing head 1. The suction hole 1c surrounds the blow hole 1b in the immediate outer periphery of the blow hole 1b. The suction hole 1c is connected to the exhaust pump 4 through the suction path 4a.

The process gas supply source 2 of the atmospheric pressure plasma etching apparatus M stores CF ₄ (halogen-based gas) and oxygen as process gases separately, mixes them in appropriate amounts, and sends them to the process gas supply path 2a. . The process gas component may be stored in a liquid phase and vaporized by a vaporizer. Flow ratio of CF ₄ is relative to the total flow rate of the process gas _(CF 4 + _{O 2)} is set in the range of 30~75vol%.

  This process gas is introduced into the interelectrode passage 1a through the supply passage 2a. On the other hand, an electric field is applied to the interelectrode passage 1a by voltage supply from the power source 3 to the electric field applying electrode 11, and plasma discharge is formed. The discharge form is preferably glow discharge, but may be corona discharge, creeping discharge, or arc discharge. This discharge turns the process gas into plasma (excitation, activation). The plasma-processed process gas is blown out from the blow hole 1b at the lower end of the processing head 1 and blown onto the upper surface (surface) of the substrate 90.

As a result, the tungsten film of the substrate 90 can be etched in a substantially normal pressure field. Since CF ₄ is used as the halogen gas of the process gas component, a high etching rate and safety can be ensured. By heating the substrate 90 with the heater 6, the etching rate can be further increased.

In addition, instead of CF ₄ , other fluorine-based gas such as C ₂ F ₆ may be used as the halogen-based gas of the process gas component. Instead of fluorine-based gas, other halogen-based gas such as chlorine-based or bromine-based gas may be used.

  The treated gas and by-products are sucked into the suction hole 1c and exhausted from the exhaust pump 4 through the suction path 4a.

The present invention is not limited to the above-described embodiment, and various modifications can be made.
For example, the atmospheric pressure plasma etching apparatus M of the present embodiment is a so-called remote apparatus that disposes the base material away from the interelectrode space, but a so-called direct apparatus that disposes the base material inside the interelectrode space. It is also applicable to.

Next, examples of the present invention will be described. Of course, the present invention is not limited to the following examples.
In Example 1, the same apparatus as in FIG. 1 was used to perform atmospheric pressure plasma etching of the tungsten film. The processing conditions are as follows.
Process gas component: CF ₄ + O ₂
Tungsten film thickness: 4000 mm
Stage and substrate temperature: room temperature (about 20 ° C)
Environmental temperature: 22.3 ° C
Environmental humidity: 64.7% RH
Then, the total flow rate of the process gas was set to 100 ccm, the flow rate ratio of CF ₄ was changed in the range of 0 to 100 vol%, and the etching rate was measured.

The results are shown in FIG.
Etching was not possible with O ₂ alone (O ₂ = 100 vol%) or CF ₄ alone (CF ₄ = 100 vol%). If the O ₂ if mixed CF ₄ even a small amount, or, if mixed even O ₂ a small amount to CF _4, it was confirmed tungsten can be etched. And it turned out that a sufficiently practical high etching rate can be obtained in the range of CF ₄ / (CF ₄ + O ₂ ) = 30 to 75 vol%.

The mechanism by which atmospheric pressure plasma etching of tungsten by a mixed gas of CF ₄ and O ₂ is not clear. However, oxides that could be seen as WOF ₄ and WO ₃ were confirmed around the etched portion. From this, tungsten becomes tungsten oxide or tungstic acid fluoride due to the excited species of oxygen and is easily broken, and further, vaporized as tungsten hexafluoride by the excited species of fluorine. It is guessed.

In Example 2, the flow rate ratio of CF ₄ to the total flow rate of process gas of 100 ccm is fixed at 30 vol%, the stage and thus the temperature of the substrate is changed in the range of ambient temperature to 150 ° C., and other conditions are the same as in Example 1. Then, the etching rate was measured.

The results are shown in FIG.
As the substrate temperature was raised from the ambient temperature, the etching rate also increased. It has been confirmed that the etching rate reaches a substantially peak at a substrate temperature = 50 ° C. and maintains a substantially peak up to about 120 ° C. At higher temperatures, the etching rate decreased.

The reason why the etching rate increases when the substrate is made higher than the environmental temperature is considered to be because vaporization of tungsten hexafluoride is promoted. On the other hand, when the temperature exceeds 120 ° C., the etching rate is considered to decrease because the amount of O ₃ generated by the excitation of O ₂ decreases and the oxidizing action of tungsten decreases.

It is a schematic block diagram of the atmospheric pressure plasma etching apparatus which concerns on one Embodiment of this invention. 3 is a graph showing the results of Example 1. 10 is a graph showing the results of Example 2.

Explanation of symbols

M Normal pressure plasma etching equipment 1 Processing head 1a Inter-electrode passage (plasma discharge space)
2 Process gas supply source 6 Heater (base heating means)
90 Semiconductor substrate

Claims (5)

In a substantially normal pressure field, a process gas is converted into plasma and sprayed onto the substrate, and the tungsten coated on the substrate surface is plasma etched using a mixed gas of oxygen and a halogen-based gas as the process gas. A method for atmospheric pressure plasma etching of tungsten. 2. The tungsten atmospheric pressure plasma etching method according to claim 1, wherein a flow rate ratio of the halogen-based gas is 30 to 75 vol% with respect to a total flow rate of the process gas. 3. The atmospheric pressure plasma etching method for tungsten according to claim 1, wherein the halogen-based gas is a fluorine-based gas. Atmospheric plasma etching method of the tungsten according to claim 3, wherein the fluorine-based gas is CF ₄ or C ₂ F _6. 5. The atmospheric pressure plasma etching method for tungsten according to claim 1, wherein the substrate is etched at a temperature of 50 to 120 ° C. 5.

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