JP2008028022A - Plasma etching method and computer readable storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma etching method capable of coping with both of excellent etching selectivity and shaping property upon etching a hole, having fine and high aspect ratio, on an oxide film. <P>SOLUTION: The plasma etching method includes a step of carrying a substrate with an oxide film for the object of etching, a hard mask layer and a patternized photo resist which are formed sequentially thereon into a processing vessel 10 to dispose the same on a lower electrode; a step of supplying processing gas containing C<SB>x</SB>F<SB>y</SB>(x is an integer not higher than 3, y is an integer not higher than 8), C<SB>4</SB>F<SB>8</SB>, rear gas and O<SB>2</SB>into a processing vessel 10; a step of producing the plasma of the processing gas by impressing high-frequency power on an upper electrode 34 from a first high-frequency impressing means 48; a step of applying a high-frequency power for bias on a lower electrode 16 from a second high-frequency electric power application means 90; and a step of applying a DC voltage on the upper electrode 34 from a DC voltage application means 50. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a plasma etching method for performing plasma etching on an oxide film formed on a substrate via a mask layer, and a computer-readable storage medium storing a control program for executing such a plasma etching method.

  In a semiconductor device manufacturing process, a photoresist pattern is formed on a semiconductor wafer, which is a substrate to be processed, by a photolithography process, and etching is performed using this as a mask.

  Recently, miniaturization of semiconductor devices has progressed, and fine processing is also required for etching. In response to such miniaturization, the thickness of the photoresist used as a mask is reduced and used. As for the photoresist, an ArF photoresist (that is, ArF gas is emitted) that can form a pattern opening of about 0.13 μm or less from a KrF photoresist (that is, a photoresist that is exposed with laser light using KrF gas as a light source). Photoresist exposed with a shorter wavelength laser beam as a source).

  However, since the ArF photoresist has low plasma resistance, there is a problem that the surface becomes rough during the etching, which is hardly generated in the KrF resist. For this reason, problems such as vertical streaks entering the inner wall surface of the opening or spreading of the opening (expansion of CD) occur, which is favorable in combination with the thin film thickness of the photoresist. There is a disadvantage that the etching holes cannot be formed with the etching selectivity.

  In order to solve such a problem, in Patent Document 1, an amorphous carbon film is formed as a sacrificial hard mask on a layer to be etched, a patterned photoresist film is formed thereon, and an amorphous film is formed using the photoresist pattern as a mask. A technique has been proposed in which a carbon film is etched, and at least an amorphous carbon film is used as an etching mask to etch an etching target layer with a CF gas that is usually used. With this technique, the problems of etching selectivity and shape can be solved to some extent.

However, for example, in etching of a capacitor of a DRAM, it is required to form an extremely high aspect ratio hole having a frontage of 80 nm and a depth of 2 μm in an oxide film. Further, the next generation is 68 nm, and the next generation is 58 nm. A narrower gap is required, and with the technique of Patent Document 1, it is difficult to form holes of such a size with sufficient etching selectivity and good shape without bowing.
JP 2006-41486 A

The present invention has been made in view of such circumstances, and provides a plasma etching method capable of achieving both good etching selectivity and shape when etching fine and high aspect ratio holes in an oxide film. The purpose is to do.
It is another object of the present invention to provide a computer-readable storage medium storing a program for executing such a plasma etching method.

In order to solve the above problems, according to a first aspect of the present invention, a lower electrode that functions as a substrate mounting table and an upper electrode that is formed so as to face the lower electrode are disposed in a processing vessel that can be evacuated. And applying a relatively high frequency high frequency power for plasma generation to the upper electrode or the lower electrode, applying a relatively low frequency high frequency power for bias to the lower electrode, Plasma etching for plasma-etching an oxide film formed on a substrate through a hard mask layer using a plasma etching apparatus that applies a direct-current voltage and converts the processing gas supplied into the processing vessel into plasma to perform plasma etching A method, wherein an oxide film to be etched, a hard mask layer, and a patterned photoresist are sequentially formed in the processing container Loading and includes a step of placing the lower electrode, _C x _F y in the processing container (x 3 an integer, y is 8 or less an _integer), C 4 _{F 8,} a rare gas, the _{O 2} Supplying a processing gas; applying high frequency power to the upper electrode or the lower electrode to generate plasma of the processing gas; applying bias high frequency power to the lower electrode; And a step of applying a DC voltage to the electrode.

In a second aspect of the present invention, a lower electrode that functions as a substrate mounting table and an upper electrode that is formed so as to face the lower electrode are provided in a processing chamber that can be evacuated inside, and the lower electrode is provided. Using a plasma etching apparatus that applies high-frequency power that also serves as a plasma generator and a bias to the electrode, applies a DC voltage to the upper electrode, converts the processing gas supplied into the processing vessel into plasma, and performs plasma etching, Loading a substrate on which an oxide film to be etched, a hard mask layer, and a patterned photoresist are sequentially formed in the processing container and placing the substrate on the lower electrode; and C _x F _y in the processing container (x is 3 or less an integer, y is 8 or less an integer), C 4 _{F 8,} and supplying a rare gas, the process gas containing O _2, and for generating a plasma in the lower electrode via A plasma etching method comprising: a step of generating a plasma of the processing gas by applying a high-frequency power that also serves as an application, and a step of applying a bias; and a step of applying a DC voltage to the upper electrode. .

In the first or second aspect, an amorphous carbon film can be suitably used as the hard mask layer. The C _x F _y is preferably C ₃ F ₈ or CF ₄ , and when C ₃ F ₈ is used as the C _x F _y , the flow rate is equal to or higher than the flow rate of the C ₄ F _8. Preferably there is. Furthermore, the absolute value of the DC voltage is preferably 800 to 1200V. Furthermore, Ar or Xe can be suitably used as the rare gas.

  The plasma etching method of the present invention is particularly effective when a hole having a frontage of 70 to 90 nm and an aspect ratio of 1:15 to 1:25 is formed.

  In a third aspect of the present invention, a lower electrode functioning as a substrate mounting table and an upper electrode formed so as to face the lower electrode are provided in a processing vessel capable of evacuating the inside, and the upper electrode is provided. Alternatively, a relatively high frequency high frequency power for plasma generation is applied to the lower electrode and a relatively low frequency high frequency power for bias is applied to the lower electrode, or a plasma generation is applied to the lower electrode. And a computer for controlling a plasma etching apparatus that applies high-frequency power that also serves as a bias, applies a DC voltage to the upper electrode, and converts the processing gas supplied into the processing vessel into plasma to perform plasma etching A computer-readable storage medium storing a control program that operates above, wherein the control program is executed when the first or second control program is executed. It provides a computer readable storage medium, characterized in that to control the plasma etching apparatus to the computer as the method of the second aspect is performed.

According to the present invention, for a substrate on which an oxide film to be etched, a hard mask layer, and a patterned photoresist are sequentially formed, C _x F _y (x is an integer of 3 or less, y is an integer of 8 or less) , C ₄ F ₈ , a rare gas, and a process gas containing O ₂ are used to perform plasma etching, so even a high aspect ratio hole with a narrow frontage has a practical etching rate and good shape without bowing. Can be etched. Further, in such a gas system, a sufficient etching selectivity cannot be obtained in a normal process, and the mask layer may disappear before the etching is completed. In the present invention, either the upper electrode or the lower electrode is used. When plasma is generated by applying high-frequency power for plasma generation, a DC voltage is applied to the upper electrode, so polymer is supplied from the upper electrode to the hard mask layer, and the plasma resistance of the hard mask layer is increased to perform etching. The selectivity can be increased, and good etching can be performed without erasing the hard mask layer even in the gas system.

Embodiments of the present invention will be specifically described below with reference to the accompanying drawings.
FIG. 1 is a schematic cross-sectional view showing an example of a plasma etching apparatus used for carrying out the present invention.

  This plasma etching apparatus is configured as a capacitively coupled parallel plate plasma etching apparatus, and has a substantially cylindrical chamber (processing vessel) 10 made of aluminum whose surface is anodized, for example. The chamber 10 is grounded for safety.

  A cylindrical susceptor support 14 is disposed at the bottom of the chamber 10 via an insulating plate 12 made of ceramics or the like, and a susceptor 16 made of, for example, aluminum is provided on the susceptor support 14. The susceptor 16 constitutes a lower electrode, on which a semiconductor wafer W as a substrate to be processed is placed.

  On the upper surface of the susceptor 16, an electrostatic chuck 18 that holds the semiconductor wafer W by electrostatic force is provided. The electrostatic chuck 18 has a structure in which an electrode 20 made of a conductive film is sandwiched between a pair of insulating layers or insulating sheets, and a DC power source 22 is electrically connected to the electrode 20. The semiconductor wafer W is attracted and held on the electrostatic chuck 18 by an electrostatic force such as a Coulomb force generated by a DC voltage from the DC power supply 22.

  A conductive focus ring (correction ring) 24 made of, for example, silicon is disposed on the upper surface of the susceptor 16 around the electrostatic chuck 18 (semiconductor wafer W) to improve etching uniformity. A cylindrical inner wall member 26 made of, for example, quartz is provided on the side surfaces of the susceptor 16 and the susceptor support 14.

  Inside the susceptor support 14, for example, a coolant chamber 28 is provided on the circumference. A coolant having a predetermined temperature, for example, cooling water, is circulated and supplied to the coolant chamber from a chiller unit (not shown) provided outside through the pipes 30a and 30b, and the processing temperature of the semiconductor wafer W on the susceptor is controlled by the coolant temperature. Can be controlled.

  Further, a heat transfer gas, for example, He gas, from a heat transfer gas supply mechanism (not shown) is supplied between the upper surface of the electrostatic chuck 18 and the back surface of the semiconductor wafer W via the gas supply line 32.

  Above the susceptor 16 that is the lower electrode, an upper electrode 34 is provided in parallel so as to face the susceptor 16. A space between the upper and lower electrodes 34 and 16 becomes a plasma generation space. The upper electrode 34 faces the semiconductor wafer W on the susceptor 16 that is the lower electrode, and forms a surface that is in contact with the plasma generation space, that is, a facing surface.

  The upper electrode 34 is supported on the upper portion of the chamber 10 via an insulating shielding member 42, and forms an opposing surface to the susceptor 16 and has a number of discharge holes 37, and the electrode plate 36 is detachably supported, and is constituted by a water-cooled electrode support 38 made of a conductive material, for example, aluminum whose surface is anodized. The electrode plate 36 is preferably a low-resistance conductor or semiconductor with low Joule heat, and a silicon-containing material is preferable from the viewpoint of strengthening the resist as will be described later. From such a viewpoint, the electrode plate 36 is preferably made of silicon or SiC. A gas diffusion chamber 40 is provided inside the electrode support 38, and a number of gas flow holes 41 communicating with the gas discharge holes 37 extend downward from the gas diffusion chamber 40.

The electrode support 38 is formed with a gas inlet 62 for introducing a processing gas to the gas diffusion chamber 40, and a gas supply pipe 64 is connected to the gas inlet 62, and a processing gas supply source is connected to the gas supply pipe 64. 66 is connected. The gas supply pipe 64 is provided with a mass flow controller (MFC) 68 and an opening / closing valve 70 in order from the upstream side (FCS may be used instead of MFC). Then, a process gas containing C _x F _y (x is an integer of 3 or less, y is an integer of 8 or less), C ₄ F ₈ , a rare gas, and O ₂ from the process gas supply source 66 as a process gas for etching. The gas reaches the gas diffusion chamber 40 from the gas supply pipe 64 and is discharged into the plasma generation space in the form of a shower through the gas flow hole 41 and the gas discharge hole 37. That is, the upper electrode 34 functions as a shower head for supplying the processing gas.

  A first high frequency power supply 48 is electrically connected to the upper electrode 34 via a matching unit 46 and a power feed rod 44. The first high frequency power supply 48 outputs a high frequency power of 10 MHz or higher, for example, 60 MHz. The matching unit 46 matches the load impedance to the internal (or output) impedance of the first high-frequency power supply 48, and the output impedance and load impedance of the first high-frequency power supply 48 when plasma is generated in the chamber 10. Functions to match. The output terminal of the matching unit 46 is connected to the upper end of the feed rod 44.

  On the other hand, a variable DC power supply 50 is electrically connected to the upper electrode 34 in addition to a first high frequency power supply 48. The variable DC power supply 50 may be a bipolar power supply. Specifically, the variable DC power supply 50 is connected to the upper electrode 34 via the matching unit 46 and the power supply rod 44, and power supply can be turned on / off by an on / off switch 52. The polarity and current / voltage of the variable DC power supply 50 and on / off of the on / off switch 52 are controlled by the controller 51.

  As shown in FIG. 2, the matching unit 46 is provided on the downstream side of the first variable capacitor 54 branched from the power supply line 49 of the first high frequency power supply 48 and the branch point of the power supply line 49. In addition, the second variable capacitor 56 is provided, and these functions are exhibited. The matching unit 46 also has a high frequency (for example, 60 MHz) from the first high frequency power supply 48 and a second to be described later so that a DC voltage current (hereinafter simply referred to as a DC voltage) can be effectively supplied to the upper electrode 34. A filter 58 that traps a high frequency (for example, 2 MHz) from a high frequency power source is provided. That is, a direct current from the variable direct current power supply 50 is connected to the power supply line 49 through the filter 58. The filter 58 includes a coil 59 and a capacitor 60, and traps a high frequency from the first high frequency power supply 48 and a high frequency from a second high frequency power supply described later.

  A cylindrical ground conductor 10a is provided so as to extend above the height position of the upper electrode 34 from the side wall of the chamber 10, and the top wall portion of the cylindrical ground conductor 10a is upper by a cylindrical insulating member 44a. It is electrically insulated from the power feed rod 44.

  A second high frequency power supply 90 is electrically connected to the susceptor 16, which is the lower electrode, via a matching unit 88. By supplying high frequency power from the second high frequency power supply 90 to the lower electrode susceptor 16, ions are drawn into the semiconductor wafer W side. The second high frequency power supply 90 outputs a high frequency power of a frequency within a range of 300 kHz to 13.56 MHz, for example, 2 MHz. The matching unit 88 is for matching the load impedance with the internal (or output) impedance of the second high-frequency power source 90, and when the plasma is generated in the chamber 10, the internal impedance of the second high-frequency power source 90 and the load Functions so that the impedances seem to match.

  The upper electrode 34 is electrically connected with a low pass filter (LPF) 92 for passing a high frequency (for example, 2 MHz) from the second high frequency power supply 90 to the ground without passing a high frequency (for example, 60 MHz) from the first high frequency power supply 48. Connected. The low-pass filter (LPF) 92 is preferably composed of an LR filter or an LC filter, but provides a sufficiently large reactance with respect to the high frequency (60 MHz) from the first high-frequency power supply 48 even with only one conductor. You can do that. On the other hand, the susceptor 16 as the lower electrode is electrically connected to a high pass filter (HPF) 94 for passing a high frequency (60 MHz) from the first high frequency power supply 48 to the ground.

An exhaust port 80 is provided at the bottom of the chamber 10, and an exhaust device 84 is connected to the exhaust port 80 via an exhaust pipe 82. The exhaust device 84 includes a vacuum pump such as a turbo molecular pump, and can reduce the pressure in the chamber 10 to a desired degree of vacuum. Further, a loading / unloading port 85 for the semiconductor wafer W is provided on the side wall of the chamber 10, and the loading / unloading port 85 can be opened and closed by a gate valve 86. A deposition shield 11 is detachably provided along the inner wall of the chamber 10 for preventing the etching byproduct (depot) from adhering to the chamber 10. That is, the deposition shield 11 forms a chamber wall. The deposition shield 11 is also provided on the outer periphery of the inner wall member 26. An exhaust plate 83 is provided between the deposition shield 11 on the chamber wall side at the bottom of the chamber 10 and the deposition shield 11 on the inner wall member 26 side. As the deposition shield 11 and the exhaust plate 83, an aluminum material coated with ceramics such as Y ₂ O ₃ can be suitably used.

  A conductive member (GND block) 91 connected to the ground in a DC manner is provided at a portion almost the same height as the wafer W that constitutes the chamber inner wall of the deposition shield 11, thereby preventing abnormal discharge. Demonstrate.

  Each component of the plasma processing apparatus is connected to and controlled by a control unit (overall control device) 95. In addition, the control unit 95 includes a user interface 96 including a keyboard for a process manager to input commands to manage the plasma processing apparatus, a display for visualizing and displaying the operating status of the plasma processing apparatus, and the like. It is connected.

  Further, the control unit 95 causes the respective components of the plasma processing apparatus to execute processes according to a control program for realizing various processes executed by the plasma processing apparatus under the control of the control unit 95 and processing conditions. A storage unit 97 that stores a program for storing the recipe, that is, a recipe, is connected. The recipe may be stored in a hard disk or semiconductor memory, or set at a predetermined position in the storage unit 97 while being stored in a portable computer-readable storage medium such as a CDROM or DVD. Also good.

  Then, if necessary, an arbitrary recipe is called from the storage unit 97 by an instruction from the user interface 96 and is executed by the control unit 95, so that a desired process in the plasma processing apparatus can be performed under the control of the control unit 95. Processing is performed.

Next, a plasma etching method according to an embodiment of the present invention, which is performed by the plasma etching apparatus configured as described above, will be described.
Here, as shown in FIG. 3, the semiconductor wafer W as an object to be processed is formed on an Si stop 101, an oxide film 103 to be etched, a hard mask layer 104, an antireflection film (BARC) on a Si substrate 101. ) 105 and the photoresist film 106 are sequentially formed, and then the photoresist film 106 having a predetermined pattern is used. First, the hard mask layer 104 is etched using the photoresist film 106 as a mask, and then the oxidation target is etched. The film 103 is etched.

  As the oxide film 103 to be etched in this embodiment, for example, a film formed using tetraethoxysilane (TEOS) as a raw material, a glass film (BPSG or PSG), or the like can be used. The thickness of the oxide film 103 is appropriately set, but is about 1.5 to 3.0 μm when used as a capacitor of a DRAM.

  As the hard mask layer 104, an amorphous carbon film can be suitably used. The amorphous carbon film exhibits plasma resistance equivalent to that of SiN or SiC usually used as a hard mask layer, and is inexpensive. However, a commonly used material such as TiN or SiN can also be used. The thickness of the hard mask layer 104 is about 500 to 900 nm.

  The etching stop film 102 is made of a SiC-based material such as SiCN and has a thickness of about 20 to 100 nm. As the antireflection film (BARC) 105, a SiON film or an organic film can be used, and its thickness is about 20 to 100 nm. The photoresist film 106 is typically an ArF resist and has a thickness of about 100 to 400 nm.

  In the etching process, first, the gate valve 86 is opened, and the semiconductor wafer W having the above structure is loaded into the chamber 10 via the loading / unloading port 85 and placed on the susceptor 16. Then, a processing gas for etching is supplied from the processing gas supply source 66 to the gas diffusion chamber 40 at a predetermined flow rate, and is supplied into the chamber 10 through the gas flow holes 41 and the gas discharge holes 37, while being exhausted. The chamber 10 is evacuated by 84, and the pressure therein is set to a set value within a range of 20 to 30 Pa, for example. The susceptor temperature is about 20-50 ° C.

Here, as a processing gas for etching the oxide film 103, a gas containing C _x F _y (x is an integer of 3 or less, y is an integer of 8 or less), C ₄ F ₈ , a rare gas, and O ₂ is used. Use. Other gases may be included, but it is preferable to use a gas consisting of only four kinds of C _x F _y , C ₄ F ₈ , a rare gas, and O ₂ . C ₄ F ₈ plays a role of making the mask shape vertical, and is an important gas for improving the etching shape. However, if only C ₄ F ₈ is supplied at a flow rate at which a sufficient etching rate is obtained, deposits are generated at the frontage, and shape defects such as bowing are likely to occur in the subsequent etching. Accordingly, such a depot is reduced by using C _x F _y where x is an integer of 3 or less and y is an integer of 8 or less and having a smaller amount of C per molecule than C ₄ F ₈ . In order to reduce the opening deposit effectively, it is preferable to further raise the temperature of the susceptor 16 as the lower electrode to about 50 ° C.

As C _x F _y , C ₃ F ₈ or CF ₄ can be preferably used. _C 3 _{F 8} Among these are preferred. C ₃ F ₈ has an action of increasing the etching rate. When C ₃ F ₈ is used, the flow rate is preferably equal to or higher than the flow rate of C ₄ F ₈ . Thereby, the opening deposit can be effectively eliminated. More preferably, the flow rate of C ₃ F ₈ : the flow rate of C ₄ F ₈ is preferably about 1: 1 to 1.5: 1. Specifically, the flow rate of C ₃ F ₈ is 20 to 60 mL / min (flow rate converted to a standard state (sccm)), and the flow rate of C ₄ F ₈ is 20 to 40 mL / min (sccm). preferable.

O ₂ gas is added in order to secure the escape characteristics of the etching hole, to widen the bottom CD (Critical Dimension) of the etching hole, and to balance the processing gas. It is preferable to add 2.5 to 3.5%. A specific flow rate is preferably 20 to 30 mL / min (sccm).

  The rare gas is added to secure etching hole detachability, to dilute the CF-based gas to balance the processing gas, and to control the deposit and F. It is preferable to add ~ 90%. A specific flow rate is preferably 600 to 900 mL / min (sccm). However, the flow rate of the rare gas varies depending on the material of the hard mask layer 104, and is preferably 800 mL / min (sccm) or more when the hard mask layer 104 is amorphous carbon. However, when a PolyMask material is used, it is preferably set to 300 mL / min (sccm) or less.

  Ar and Xe can be suitably used as the rare gas. In particular, by using Xe as a rare gas, the function as a carrier of C can be enhanced, the etching linearity can be improved, and the etching shape of the hard mask layer 104 and the etching shape of the oxide film 103 can be improved. it can.

In the etching of the hard mask layer 104 performed prior to the oxide film 103, the etching is performed under normal conditions. For example, when the hard mask layer 104 is amorphous carbon, for example, C ₄ F ₆ + rare gas (Ar) + O ₂ is exemplified.

  In this manner, with the processing gas for etching being introduced into the chamber 10, high-frequency power for plasma generation is applied from the first high-frequency power supply 48 to the upper electrode 34 with a predetermined power, and the second high-frequency power supply From 90, a high frequency for ion attraction is applied to the susceptor 16 as the lower electrode with a predetermined power. Then, a predetermined DC voltage is applied to the upper electrode 34 from the variable DC power supply 50. Further, a DC voltage is applied from the DC power source 22 for the electrostatic chuck 18 to the electrode 20 of the electrostatic chuck 18 to fix the semiconductor wafer W to the susceptor 16.

  The processing gas discharged from the gas discharge hole 37 formed in the electrode plate 36 of the upper electrode 34 is turned into plasma in the glow discharge between the upper electrode 34 and the lower electrode susceptor 16 generated by the high frequency power. First, as shown in FIG. 4A, the hard mask layer 104 is etched using the photoresist film 106 as a mask to transfer the resist pattern by the generated radicals and ions, and then the resist pattern is transferred to FIG. As shown, the hole 107 is formed by etching the oxide film 103 using the hard mask layer 104 as a mask.

  Since high frequency power in a high frequency region (for example, 10 MHz or more) is supplied to the upper electrode 34, the plasma can be densified in a preferable state, and high density plasma can be formed even under lower pressure conditions. .

  However, when only the high frequency power is applied and the oxide film is etched using the processing gas, the etching shape can be ensured, but the etching selectivity with respect to the hard mask layer 104 is low, As shown in FIG. 5, the hard mask layer 104 disappears before the etching of the oxide film 103 is completed.

  Therefore, in the present embodiment, a DC voltage having a predetermined polarity and magnitude is applied from the variable DC power source 50 to the upper electrode 34 when plasma is formed in this way. By appropriately adjusting the applied voltage at this time, the selection ratio with respect to the hard mask layer 104 can be improved, and as shown in FIG. 6, the oxide film 103 is shaped with the hard mask layer 104 remaining. It can be etched well. The absolute value of the DC voltage at this time is preferably 800 to 1200V.

This will be described more specifically.
The polymer is attached to the upper electrode 34 by a conventional etching process, in particular, an etching process in which high-frequency power to the upper electrode 34 is small. When an appropriate DC voltage is applied to the upper electrode 34 during the etching process, as shown in FIG. 7, the self-bias voltage V _dc of the upper electrode is increased, that is, V _{dc on} the surface of the upper electrode 34 is increased. The absolute value can be increased. For this reason, the polymer adhering to the upper electrode 34 is sputtered by the applied DC voltage and supplied to the semiconductor wafer W and adheres onto the hard mask layer 104. As a result, the hard mask layer 104 is hardly etched, and the oxide film 103 can be etched with a high selectivity.

  Further, when a DC voltage is applied to the upper electrode 34 in this way when etching the oxide film 103, electrons generated in the vicinity of the upper electrode 34 when plasma is formed are accelerated in the vertical direction of the processing space, By appropriately controlling the DC voltage or the like at that time, electrons can reach the inside of the via, and the shading effect is suppressed and the hole shape becomes better.

  Further, if a DC voltage is applied to the upper electrode 34 when plasma is formed, the plasma density in the central portion can be increased due to plasma diffusion, but the pressure in the chamber 10 is relatively high and When a negative gas such as a CF-based gas is used as the processing gas, the plasma density in the central portion in the chamber 10 tends to be low, and the plasma density in the central portion is increased by applying a DC voltage to make it uniform. Plasma density can be obtained.

  In addition, by applying a DC voltage, it is possible to select a more depolicing condition and ensure a selection ratio only with a photoresist film without using a hard mask layer, but in that case a depot is attached to the frontage. Boeing, taper, etc. will occur. Therefore, it is essential to use the hard mask layer 104.

Next, the experimental results for actually confirming the effect of the method of the present invention will be described.
[Experiment 1]
Here, a SiN film having a thickness of 50 nm is formed as an etching stop film 102 on a Si substrate, and a BPSG film (lower layer) and a TEOS film (upper layer) having a thickness of 1500 nm are formed thereon as an oxide film 103 to be etched. A 500 nm amorphous carbon film as a hard mask layer 104 is formed thereon, and a 60 nm SiON film as an antireflection film (BARC) 105 is formed thereon, and further thereon. A 200 nm ArF resist is formed as a photoresist film 106 to prepare a sample having the structure shown in FIG. 3, and the hard mask layer 104 is etched by the apparatus shown in FIG. The oxide film 103 was etched under various conditions using the mask layer 104 as an etching mask. Here, a circular hole having a diameter of 90 nm was etched. During oxide etching, the pressure in the chamber is 2.7 Pa, the upper high-frequency power is 1200 W, the lower high-frequency power is 3800 W, the DC voltage is -1000 V, the temperatures are the upper electrode: 95 ° C., the lower electrode: 10 ° C., and the processing gas is C Etching was performed using ₃ F ₈ , C ₄ F ₈ , Ar, and O ₂ and changing these flow rates.

First, etching was performed by changing the C ₄ F ₈ / C ₃ F ₈ while fixing the Ar flow rate to 800 mL / min (sccm) and the O ₂ flow rate to 25 mL / min (sccm). The etching shape at that time is shown in FIG. 8A shows C ₄ F ₈ : 35 mL / min (sccm) and C ₃ F ₈ : 30 mL / min (sccm), and B shows C ₄ F ₈ : 30 mL / min (sccm) and C ₃ F _8. : 35 mL / min (sccm), C is C ₄ F ₈ : 25 mL / min (sccm) and C ₃ F ₈ : 40 mL / min (sccm), and D is C ₄ F ₈ : 20 mL / min (sccm) ) And C ₃ F ₈ : 45 mL / min (sccm). As shown in this figure, C had the best shape of the shoulder portion of the opening.

Next, C ₄ F ₈ / C ₃ F ₈ was fixed to the composition of C, and the flow rates of Ar and O ₂ were changed. Etching was performed in the same manner as in the above test under other conditions. The etching shape at that time is shown in FIG. E in FIG. 9 is Ar: 500 mL / min (sccm) and O ₂ : 34 mL / min (sccm), F is Ar: 700 mL / min (sccm) and O ₂ : 32 mL / min (sccm), G Was Ar: 900 mL / min (sccm) and O ₂ : 30 mL / min (sccm), and H was Ar: 1100 mL / min (sccm) and O ₂ : 28 mL / min (sccm). Among these, G improved the shape of the shoulder portion of the opening, and the shape was the best. Furthermore, when process tuning was performed by changing the gas ratio to center rich, a good shape without bowing as shown in FIG. 10 was obtained. At this time, the top CD, the intermediate CD where the bowing occurred, and the bottom CD are 89 nm, 89 nm and 74 nm at the wafer center, respectively 91 nm, 93 nm and 75 nm at the middle, and 85 nm, 87 nm and 73 nm at the edge, respectively. And showed good values.

From the above, it has been confirmed that the etching shape is good under the predetermined conditions with a large amount of C ₃ F _{8 and a} large amount of Ar.

[Experiment 2]
Here, a sample having the same structure as in Experiment 1 is prepared, and after etching the hard mask layer 104 using the apparatus shown in FIG. 1, the oxide film 103 is etched using the remaining portion of the photoresist film 106 and the hard mask layer 104 as an etching mask. Etching was performed. Here, the pressure is 2.7 Pa, the temperature is the upper electrode: 95 ° C., the lower electrode is 10 ° C., and the condition I is upper high frequency power: 1200 W, lower high frequency power: 3800 W, DC voltage: −1000 V, C ₄ F ₈ : 40 mL / min (sccm), C ₃ F ₈ : 25 mL / min (sccm), Ar: 900 mL / min (sccm), O ₂ : 30 mL / min (sccm). 1200 W, lower high-frequency power: 3800 W, DC voltage: −1000 V, C ₄ F ₈ : 25 mL / min (sccm), C ₃ F ₈ : 40 mL / min (sccm), Ar: 1000 mL / min (sccm), O ₂ : 28 mL / min (sccm) and under condition K, upper high frequency power: 1500 W, lower high frequency power 4500 W, the DC _{voltage: -1100V, C 4 F 8:} 25mL / min (sccm), C 3 F 8: 40mL / min (sccm), Ar: 1000mL / min (sccm), O 2: 25mL / min (sccm) Etching was performed. The result is shown in FIG. As shown in this figure, as shown in the condition I → condition J, the etching shape becomes better when the amount of C ₃ F ₈ with respect to C ₄ F ₈ increases, and as shown in the condition J → condition K, the upper high frequency By increasing the power and lower high-frequency power, increasing the DC voltage, and reducing O ₂ , the CD was further shrunk and a better etching shape was obtained.

[Experiment 3]
Here, a SiN film having a thickness of 40 nm is formed on the Si substrate 101 as the etching stop film 102, and a PSG having a thickness of 2.0 μm is formed thereon as the oxide film 103 to be etched, on which Then, a 400 nm amorphous carbon film is formed as the hard mask layer 104, a 60 nm SiON film is formed as the antireflection film (BARC) 105, and a 200 nm ArF resist is formed as the photoresist film 106 thereon. A sample having the structure shown in FIG. 3 is prepared, and the hard mask layer 104 is etched using the apparatus shown in FIG. Etching was performed under the following conditions. Here, etching was performed on an oval having a major axis of 160 nm and a minor axis of 80 nm and an aspect ratio of 25. During the oxide etching, the pressure in the chamber is 3.3 Pa, the upper radio frequency power is 1000 W, the lower radio frequency power is 4500 W, the DC voltage is −500 V, the temperatures are the upper electrode: 95 ° C., the lower electrode: 50 ° C., and the process gas is C _{Using 3} F ₈ , C ₄ F ₈ , Xe, and O ₂ , the flow rate of Xe was fixed at 400 mL / min (sccm), and the others were changed. In Condition L, C ₄ F ₈ : 20 mL / min (sccm), C ₃ F ₈ : 20 mL / min (sccm), and O ₂ : 12.5 mL / min (sccm) (C ₃ F ₈ / C ₄ F ₈ = 1), under condition M, C ₄ F ₈ : 10 mL / min (sccm), C ₃ F ₈ : 30 mL / min (sccm), O ₂ : 10 mL / min (sccm) (C ₃ F ₈ / C ₄ F ₈ = 3), and under condition N, C ₄ F ₈ : 6.7 mL / min (sccm), C ₃ F ₈ : 33.3 mL / min (sccm), O ₂ : 7.5 mL / min (sccm) ( Etching was performed with C ₃ F ₈ / C ₄ F ₈ = 5). The result is shown in FIG. From this figure, when C ₃ F ₈ / C ₄ F ₈ is 1 to 3, the bowing on the edge side is remarkably improved, and when C ₃ F ₈ / C ₄ F ₈ = 5, the bowing on the edge side is almost eliminated. There was a tendency for the spread of In addition, it was confirmed that the etching selectivity was lowered by increasing the ratio of C ₃ F ₈ . Thus, as the ratio of C ₃ F ₈ increases, it changes as Boeing → Boeingless → Opening of frontage. It was confirmed that C ₃ F ₈ / C ₄ F ₈ = 3 is an optimum value in consideration of the shape difference between the center and the edge and the selection ratio. However, it is considered that the C ₃ F ₈ / C ₄ F ₈ ratio for improving the bowing varies depending on the thickness / hardness of the hard mask layer and the short axis / major axis ratio of the hole hardness of the oxide film.

[Experiment 4]
Here, the etching uniformity by DC application was confirmed.
On the Si substrate 101, a SiN film having a thickness of 60 nm is formed as an etching stop film 102, a BPSG having a thickness of 2000 nm is formed as an oxide film 103 to be etched, and an antireflection film (BARC) is formed thereon. ) A 60 nm SiON film is formed as 105, and further a 650 nm ArF resist is formed thereon as the photoresist film 106 to prepare a sample having a structure in which the hard mask layer 104 is removed from FIG. The oxide film 103 was etched under various conditions using the photoresist film 106 as an etching mask. C ₄ F ₆ , CF ₄ , Ar, O ₂ is used as a processing gas, C ₄ F ₆ : 40 mL / min (sccm), CF ₄ : 60 mL / min (sccm), Ar: 350 mL / min (sccm), O ₂ : 45 mL / min (sccm), pressure: 2.67 Pa (20 mTorr), the upper high-frequency power and the direct-current voltage were changed to obtain the etching rate and the selection ratio. As a result, it became as shown in FIG. From this figure, it can be seen that increasing the DC voltage increases the hole etching rate at the center, and increasing the upper high frequency power increases the hole etching rate at the edge. From this, it was confirmed that the in-plane etching rate can be controlled by the DC voltage applied to the upper electrode or the upper high-frequency power. In addition, the center / edge etching rate can be easily reversed.

  The present invention can be variously modified without being limited to the above embodiment. For example, although the case where amorphous carbon is used as the hard mask layer has been described in the above embodiment, other conventionally used hard mask materials can be used as described above. In addition, the oxide film formed using TEOS as a raw material, BPSG, and PSG are exemplified, but the present invention is not limited thereto.

  Further, the apparatus to which the present invention is applied is not limited to that shown in FIG. 1, and various apparatuses shown below can be used. For example, a type in which the upper electrode is divided into two at the center and the periphery and the applied power of the high frequency can be adjusted respectively. Further, as shown in FIG. 14, for example, a high frequency power of 40 MHz for plasma generation is applied from the first high frequency power supply 48 'to the susceptor 16, which is the lower electrode, and an ion is attracted from the second high frequency power supply 90'. For example, a lower two-frequency application type plasma etching apparatus that applies high-frequency power of 2 MHz can be applied. By connecting a variable DC power source 166 to the upper electrode 234 and applying a predetermined DC voltage as shown in the figure, the same effect as in the above embodiment can be obtained.

  Further, as shown in FIG. 15, a high frequency power supply 170 is connected in place of the first high frequency power supply 48 'and the second high frequency power supply 90' connected to the susceptor 16 as the lower electrode in FIG. For example, a plasma etching apparatus of a type that applies high-frequency power of 40 MHz, for example, that serves both for plasma formation and bias formation from the power supply 170 can be applied. In this case as well, as in the case of FIG. By connecting the variable DC power source 166 and applying a predetermined DC voltage, it is possible to obtain the same effect as the above embodiment.

The schematic sectional drawing which shows an example of the plasma etching apparatus used for implementation of this invention. The figure which shows the structure of the matching device connected to the 1st high frequency power supply in the plasma etching apparatus of FIG. Sectional drawing which shows the structure of the semiconductor wafer W used for implementation of one Embodiment of this invention. The schematic diagram for demonstrating the state by which the structure of FIG. 3 is etched. The schematic diagram which shows the state which the hard mask layer lose | disappeared during the etching of the oxide film. The schematic diagram which shows the state at the time of etching an oxide film by this embodiment. The plasma processing apparatus of FIG. 1 WHEREIN: The figure which compares and shows a plasma state with the case where a DC voltage is applied to an upper electrode, and the case where it does not apply. The figure which shows the result of Experiment 1. The figure which shows the result of the experiment 1. FIG. The figure which shows the result of the experiment 1. FIG. The figure which shows the result of the experiment 2. FIG. The figure which shows the result of the experiment 3. The figure which shows the result of the experiment 4. FIG. Schematic which shows the example of the plasma etching apparatus of the other type which can be applied to implementation of this invention. Schematic which shows the example of the further another type of plasma etching apparatus applicable to implementation of this invention.

Explanation of symbols

10 ... Chamber (processing container)
16 ... susceptor (lower electrode)
34 ... Upper electrode 44 ... Feeding rods 46, 88 ... Matching device 48 ... First high frequency power supply 50 ... Variable DC power supply 51 ... Controller 52 ... On / off switch 66 ... Processing gas supply source 84 ... Exhaust device 90 ... Second High-frequency power supply 91 ... GND block 101 ... Si substrate 102 ... Etching stop film 103 ... Oxide film 104 ... Hard mask layer 105 ... Antireflection film (BARC)
106: Photoresist film W: Semiconductor wafer (substrate to be processed)

Claims (9)

In a processing chamber that can be evacuated, a lower electrode that functions as a substrate mounting table and an upper electrode that is formed to face the lower electrode are provided. A high-frequency high-frequency power is applied, a relatively low-frequency high-frequency power for bias is applied to the lower electrode, a DC voltage is applied to the upper electrode, and the processing gas supplied into the processing vessel A plasma etching method of plasma-etching an oxide film formed on a substrate through a hard mask layer using a plasma etching apparatus that performs plasma etching by converting the plasma into a plasma,
A step of carrying a substrate in which an oxide film to be etched, a hard mask layer, and a patterned photoresist are sequentially formed in the processing container, and placing the substrate on the lower electrode;
Supplying a processing gas containing C _x F _y (x is an integer of 3 or less, y is an integer of 8 or less), C ₄ F ₈ , a rare gas, and O ₂ into the processing container;
Applying high frequency power to the upper electrode or the lower electrode to generate plasma of the processing gas;
Applying bias high frequency power to the lower electrode;
And a step of applying a direct current voltage to the upper electrode. In a processing chamber that can be evacuated, a lower electrode that functions as a substrate mounting table and an upper electrode that is formed so as to face the lower electrode are provided, and the lower electrode serves as both a plasma generator and a bias. Using a plasma etching apparatus that applies a high frequency power, applies a DC voltage to the upper electrode, converts the processing gas supplied into the processing vessel into plasma and performs plasma etching,
A step of carrying a substrate in which an oxide film to be etched, a hard mask layer, and a patterned photoresist are sequentially formed in the processing container, and placing the substrate on the lower electrode;
Supplying a processing gas containing C _x F _y (x is an integer of 3 or less, y is an integer of 8 or less), C ₄ F ₈ , a rare gas, and O ₂ into the processing container;
Applying a bias while generating a plasma of the processing gas by applying high-frequency power that serves both as a plasma generator and a bias to the lower electrode;
And a step of applying a direct current voltage to the upper electrode.   The plasma etching method according to claim 1, wherein the hard mask layer is an amorphous carbon film. Wherein _C x _{F y} plasma etching method according to any one of claims 1 to 3, characterized in that the _C 3 _{F 8} or CF _4. 4. The plasma etching method according to claim 1, wherein the C _x F _y is C ₃ F ₈ , and the flow rate thereof is equal to or higher than the flow rate of the C ₄ F ₈ .   6. The plasma etching method according to claim 1, wherein an absolute value of the DC voltage is 800 to 1200V.   The plasma etching method according to claim 1, wherein the rare gas is Ar or Xe.   The plasma etching method according to any one of claims 1 to 7, wherein a hole having a frontage of 70 to 90 nm and an aspect ratio of 1:15 to 1:25 is formed by the plasma etching. . In a processing chamber that can be evacuated, a lower electrode that functions as a substrate mounting table and an upper electrode that is formed to face the lower electrode are provided. A high frequency power having a high frequency is applied, and a high frequency power having a relatively low frequency for bias is applied to the lower electrode, or a high frequency power that serves both as a plasma generator and a bias is applied to the lower electrode. A control program that operates on a computer is stored for controlling a plasma etching apparatus that applies plasma, applies a DC voltage to the upper electrode, converts the processing gas supplied into the processing vessel into plasma, and performs plasma etching. A computer-readable storage medium,
A computer-readable storage medium characterized in that, when executed, the control program causes a computer to control the plasma etching apparatus so that the method of any one of claims 1 to 8 is performed.

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