JP4800077B2 - Plasma etching method - Google Patents

Description

The present invention relates to a plasma etching method for plasma etching a CFx film.

Conventionally, in a manufacturing process of a semiconductor device, plasma etching is often used in which etching gas plasma is generated and etching is performed by the action of the plasma. Further, in a semiconductor device, a low dielectric constant film is used as an interlayer insulating film, and the use of a CF _x film as one of such low dielectric constant films is also being studied ( For example, see Patent Document 1.) As a method of plasma etching such a CF _x film, there is a method of using a mixed gas of N ₂ and H ₂ as an etching gas.
JP 2000-232158 A

However, as described above, there is a problem that when a CF _x film is plasma-etched using a mixed gas of N ₂ and H ₂ as an etching gas to form a trench or the like, a micro-trench is generated at the bottom of the trench or the like. .

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a plasma etching method capable of suppressing the generation of micro-trench in plasma etching of a CFx film as compared with the conventional one.

The plasma etching method according to claim 1 uses a capacitively coupled parallel plate etching apparatus having an upper electrode and a lower electrode, and applies a high frequency to the upper electrode and the lower electrode in the processing chamber to generate plasma of an etching gas. Is generated, and the CFx film formed on the substrate to be processed is etched by the plasma. The etching gas is a mixed gas containing CH ₄ gas and O ₂ gas, and the CFx film is used as the plasma. The formation of micro-trench is suppressed when the trench is formed by etching .

The plasma etching method according to claim 2, there is provided a claim 1 Symbol placement of the plasma etching process, the etching gas, which further comprises a hydrogen-containing gas.

The plasma etching method of claim 3, there is provided a plasma etching method according to claim 2, wherein the hydrogen-containing gas, characterized in that it is a CHF ₃ or CH ₂ F _2.

According to the present invention, plasma etching that can suppress the occurrence of micro-trench in the CFx film plasma etching (the bottom of the trench has a mountain shape and the skirt portion is extremely sharpened) compared to the prior art. it is possible to provide a mETHODS.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an enlarged cross-sectional configuration of a semiconductor wafer (semiconductor substrate) W in the plasma etching method according to the present embodiment, and FIG. 2 shows a configuration of the plasma etching apparatus according to the present embodiment. is there. First, the configuration of the plasma etching apparatus will be described with reference to FIG.

  The plasma etching apparatus 1 is configured as a capacitively coupled parallel plate etching apparatus in which electrode plates are opposed in parallel in the vertical direction and a power source for plasma formation is connected.

  The plasma etching apparatus 1 has a processing chamber (processing container) 2 formed of, for example, aluminum whose surface is anodized and formed into a cylindrical shape, and the processing chamber 2 is grounded. A substantially cylindrical susceptor support 4 for placing an object to be processed, for example, a semiconductor wafer W, is provided at the bottom of the processing chamber 2 via an insulating plate 3 such as ceramic. Further, a susceptor 5 constituting a lower electrode is provided on the susceptor support 4. A high pass filter (HPF) 6 is connected to the susceptor 5.

  A refrigerant chamber 7 is provided inside the susceptor support 4, and a refrigerant is introduced into the refrigerant chamber 7 through a refrigerant introduction pipe 8, circulated, and discharged from a refrigerant discharge pipe 9. Then, the cold heat is transferred to the semiconductor wafer W through the susceptor 5, whereby the semiconductor wafer W is controlled to a desired temperature.

  The upper center portion of the susceptor 5 is formed in a convex disk shape, and an electrostatic chuck 11 having substantially the same shape as the semiconductor wafer W is provided thereon. The electrostatic chuck 11 is configured by disposing an electrode 12 between insulating materials. Then, when a DC voltage of, for example, 1.5 kV is applied from the DC power source 13 connected to the electrode 12, the semiconductor wafer W is electrostatically attracted by, for example, Coulomb force.

  The insulating plate 3, the susceptor support 4, the susceptor 5, and the electrostatic chuck 11 are formed with a gas passage 14 for supplying a heat transfer medium (for example, He gas) on the back surface of the semiconductor wafer W. The cold heat of the susceptor 5 is transmitted to the semiconductor wafer W via the heat transfer medium so that the semiconductor wafer W is maintained at a predetermined temperature.

  An annular focus ring 15 is disposed at the upper peripheral edge of the susceptor 5 so as to surround the semiconductor wafer W placed on the electrostatic chuck 11. The focus ring 15 is made of, for example, a conductive material such as silicon, and has an effect of improving etching uniformity.

  An upper electrode 21 is provided above the susceptor 5 so as to face the susceptor 5 in parallel. The upper electrode 21 is supported on the upper portion of the processing chamber 2 via an insulating material 22. The upper electrode 21 includes an electrode plate 24 and an electrode support 25 made of a conductive material that supports the electrode plate 24. The electrode plate 24 is configured, for example, by providing a quartz cover on aluminum whose surface is anodized (anodized) and has a large number of discharge holes 23. The electrode plate 24 forms a surface facing the susceptor 5. The distance between the susceptor 5 and the upper electrode 21 can be changed.

  A gas inlet 26 is provided in the center of the electrode support 25 in the upper electrode 21, and a gas supply pipe 27 is connected to the gas inlet 26. Further, a processing gas supply source 30 is connected to the gas supply pipe 27 via a valve 28 and a mass flow controller 29. An etching gas for plasma etching processing is supplied from the processing gas supply source 30.

  An exhaust pipe 31 is connected to the bottom of the processing chamber 2, and an exhaust device 35 is connected to the exhaust pipe 31. The exhaust device 35 includes a vacuum pump such as a turbo molecular pump, and is configured to be able to evacuate the processing chamber 2 to a predetermined reduced pressure atmosphere, for example, a predetermined pressure of 1 Pa or less. Further, a gate valve 32 is provided on the side wall of the processing chamber 2 so that the semiconductor wafer W is transferred to and from an adjacent load lock chamber (not shown) with the gate valve 32 opened. It has become.

  A first high frequency power supply 40 is connected to the upper electrode 21, and a matching device 41 is inserted in the feeder line. Further, a low pass filter (LPF) 42 is connected to the upper electrode 21. The first high frequency power supply 40 has a frequency in the range of 50 to 150 MHz. By applying such a high frequency, it is possible to form a high-density plasma in a preferable dissociated state in the processing chamber 2.

  A second high-frequency power source 50 is connected to the susceptor 5 serving as a lower electrode, and a matching unit 51 is interposed in the power supply line. The second high-frequency power supply 50 has a lower frequency range than the first high-frequency power supply 40. By applying a frequency in such a range, the semiconductor wafer W that is the object to be processed is damaged. Appropriate ion action can be given without giving. The frequency of the second high frequency power supply 50 is preferably in the range of 1 to 20 MHz.

  The operation of the plasma etching apparatus 1 having the above configuration is controlled by the control unit 60. The control unit 60 includes a process controller 61 that includes a CPU and controls each unit of the plasma etching apparatus 1, a user interface 62, and a storage unit 63.

  The user interface 62 includes a keyboard that allows a process manager to input commands in order to manage the plasma etching apparatus 1, a display that visualizes and displays the operating status of the plasma etching apparatus 1, and the like.

  The storage unit 63 stores a recipe in which a control program (software) for realizing various processes executed by the plasma etching apparatus 1 under the control of the process controller 61 and processing condition data are stored. Then, if necessary, an arbitrary recipe is called from the storage unit 63 by an instruction from the user interface 62 and is executed by the process controller 61, so that a desired one in the plasma etching apparatus 1 is controlled under the control of the process controller 61. Is performed. In addition, recipes such as control programs and processing condition data may be stored in a computer-readable computer storage medium (eg, hard disk, CD, flexible disk, semiconductor memory, etc.), or It is also possible to transmit the data from other devices as needed via a dedicated line and use it online.

  When performing plasma etching of the semiconductor wafer W by the plasma etching apparatus 1 having the above configuration, first, after the gate valve 32 is opened, the semiconductor wafer W is carried into the processing chamber 2 from a load lock chamber (not shown), It is placed on the electrostatic chuck 11. The semiconductor wafer W is electrostatically attracted onto the electrostatic chuck 11 by applying a DC voltage from the DC power source 13. Next, the gate valve 32 is closed, and the processing chamber 2 is evacuated to a predetermined degree of vacuum by the exhaust device 35.

  Thereafter, the valve 28 is opened, and the flow rate of a predetermined etching gas from the processing gas supply source 30 is adjusted by the mass flow controller 29 while passing through the processing gas supply pipe 27 and the gas inlet 26, so that the upper electrode 21 is hollow. Then, the liquid is uniformly discharged onto the semiconductor wafer W through the discharge holes 23 of the electrode plate 24 as shown by the arrows in FIG.

  Then, the pressure in the processing chamber 2 is maintained at a predetermined pressure. Thereafter, high frequency power having a predetermined frequency is applied to the upper electrode 21 from the first high frequency power supply 40. As a result, a high-frequency electric field is generated between the upper electrode 21 and the susceptor 5 as the lower electrode, and the etching gas is dissociated into plasma.

  On the other hand, high frequency power having a frequency lower than that of the first high frequency power supply 40 is applied from the second high frequency power supply 50 to the susceptor 5 serving as the lower electrode. Thereby, ions in the plasma are drawn to the susceptor 5 side, and the anisotropy of etching is enhanced by ion assist.

  Then, when the predetermined plasma etching process is completed, the supply of high-frequency power and the supply of process gas are stopped, and the semiconductor wafer W is unloaded from the process chamber 2 by a procedure reverse to the procedure described above.

Next, the plasma etching method according to this embodiment will be described with reference to FIG. FIG. 1 schematically shows a cross-sectional configuration of a semiconductor wafer W as a substrate to be processed used in examples described later. As shown in FIG. 1 (a), the semiconductor wafer W made of silicon, CF _x film 101 is formed in the upper portion of the CF _x film 101, SiCN film 102, an antireflection film (BARC) 103, A photoresist film 104 is formed in this order from the bottom. In addition, an opening 105 for forming a trench is formed in the photoresist film 104.

The structure of the semiconductor wafer W is a sample for verifying the etching state of the CF _x film. In the actual manufacturing process of the semiconductor device, the SiCN film is formed on the lower layer and the upper layer of the CF _x film 101. Various films such as an insulating film may be formed.

  Then, from the state of FIG. 1A, the antireflection film (BARC) 103 and the SiCN film 102 are plasma etched using the photoresist film 104 as a mask to obtain the state of FIG.

Next, using a mixed gas containing CH ₄ and O ₂ as an etching gas, the CF _x film 101 is plasma-etched to form a trench 106 in the CF _x film 101 as shown in FIG. As an etching gas for plasma etching the CF _x film 101, for example, a mixed gas of CH ₄ and O ₂ or a mixed gas obtained by adding another gas to the mixed gas can be used. As the additive gas, for example, a hydrogen-containing gas (such as CH ₃ F or CH ₂ F ₂ ) can be used. As described above, when the hydrogen-containing gas is added, H radicals increase and the tendency of isotropic etching increases, so that generation of micro-trench can be suppressed. Further, for example, _if the lower layer of the CF _x film is a SiCN-based film or a SiCOH-based film, the lower layer film may be scraped by F radicals generated during the etching of CF _x and the etching shape may be deteriorated. However, this unnecessary F radical can be eliminated by the H radical, and the etching shape can be prevented from deteriorating.

  As an example, the plasma etching apparatus 1 shown in FIG. 2 was used, and plasma etching was performed on the semiconductor wafer W (diameter 20 cm) having the structure shown in FIG. 1 according to a recipe as shown below.

  The processing recipe of the embodiment shown below is read from the storage unit 63 of the control unit 60 and is taken into the process controller 61, and the process controller 61 controls each unit of the plasma etching apparatus 1 based on the control program. By doing so, the plasma etching process according to the read processing recipe is performed.

(Etching of antireflection film (BARC) 103)
Etching gas: CF ₄ = 100 sccm, pressure 6.65 Pa (50 mTorr), power (upper / lower) = 1000/100 W, temperature (lower / upper / side wall) = 20/60/50 ° C., distance between electrodes = 60 mm, Helium pressure for cooling (center / peripheral) = 1330/4655 Pa (10/35 Torr), etching time = 20 seconds.

(Etching of SiCN film 102)
Etching gas: CH ₂ F ₂ / Ar / O ₂ = 20/200/15 sccm, pressure 6.65 Pa (50 mTorr), power (upper / lower) = 2000/100 W, temperature (lower / upper / side wall) = 20 / 60/50 ° C., distance between electrodes = 55 mm, cooling helium pressure (center / peripheral) = 1330/4655 Pa (10/35 Torr), etching time = 25 seconds.

(Etching of CF _x film 101)
Etching gas: CH ₄ / O ₂ = 450/300 sccm, pressure 7.98 Pa (60 mTorr), power (upper / lower) = 2000/200 W, temperature (lower / upper / side wall) = 20/60/50 ° C., electrode Inter-space distance = 45 mm, cooling helium pressure (center / peripheral) = 1330/4655 Pa (10/35 Torr), etching time = 45 seconds.

The etching rate of the CF _x film 101 in the above plasma etching was 288 nm / min at the central portion of the semiconductor wafer and 296 nm / min at the peripheral portion of the semiconductor wafer. When observed with an electron microscope, no micro-trench was found in the trench 106 of the CF _x film 101.

Next, as a comparative example, after the antireflection film (BARC) 103 and the SiCN film 102 were etched in the same process as the above example, the CF _x film was etched as follows.

(Etching of CF _x film 101)
Etching gas: N ₂ / H ₂ = 300/300 sccm, pressure 3.99 Pa (30 mTorr), power (upper / lower) = 1500/200 W, temperature (lower / upper / side wall) = 20/60/50 ° C., electrode Inter-space distance = 45 mm, cooling helium pressure (center / peripheral) = 1330/4655 Pa (10/35 Torr), etching time = 30 seconds.

The etching rate of the CF _x film 101 in the above plasma etching was 257 nm / min at the central portion of the semiconductor wafer and 266 nm / min at the peripheral portion of the semiconductor wafer. Moreover, was observed with an electron microscope, as shown in FIG. 3, bottom 106a of the trench 106 of the CF _x film 101 becomes a mountain shape, the foot 106b was seen micro trench shape shaved extreme.

As described above, according to the present embodiment, generation of micro-trench in plasma etching of the CF _x film can be suppressed as compared with the conventional case. In addition, this invention is not limited to said embodiment, Various deformation | transformation are possible. For example, the plasma etching apparatus is not limited to the parallel plate type upper and lower high frequency application type shown in FIG. 2, and various plasma etching apparatuses can be used.

The figure which shows the cross-sectional structure of the semiconductor wafer which concerns on the plasma etching method of embodiment of this invention. The figure which shows schematic structure of the plasma etching apparatus which concerns on embodiment of this invention. The figure which shows the generation | occurrence | production state of the micro trench in a comparative example.

Explanation of symbols

101 ...... CF _x film, 102 ...... SiCN film, 103 ...... antireflection film (BARC), 104 ...... photoresist film, 105 ...... opening 106 ...... trenches, W ...... semiconductor wafer.

Claims (3)

A capacitively coupled parallel plate etching apparatus having an upper electrode and a lower electrode is used, and a plasma of an etching gas is generated by applying a high frequency to the upper electrode and the lower electrode in the processing chamber. A plasma etching method for etching a CFx film formed in
A plasma etching method, wherein the etching gas is a mixed gas containing CH ₄ gas and O ₂ gas, and the generation of micro-trench is suppressed when the CFx film is etched with the plasma to form a trench. A claim 1 Symbol placement of the plasma etching method,
The plasma etching method, wherein the etching gas further contains a hydrogen-containing gas. The plasma etching method according to claim 2 ,
The plasma etching method, wherein the hydrogen-containing gas is CHF ₃ or CH ₂ F ₂ .

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