JP6180824B2 - Plasma etching method and plasma etching apparatus - Google Patents

Description

  The present invention relates to a plasma etching method and a plasma etching apparatus.

There has been proposed a technique of etching an etching target film such as a silicon film formed on an object to be processed into a desired mask pattern. For example, in Patent Document 1, a silicon-containing film that functions as a protective film is formed on a exposed surface of a mask from a gas containing silicon tetrafluoride gas SiF ₄ and hydrogen gas H _2, and the mask and the silicon-containing film are interposed through the mask. A method for etching an etching film has been proposed.

JP 2008-60566 A

  When the aspect ratio (AR) increases, it becomes difficult to ensure the perpendicularity of the sidewalls of the holes formed in the silicon-containing film by etching. For example, if the product generated by etching is deposited around the opening of the hole and the opening of the hole becomes narrow, the progress of the etching is inhibited by the deposited product. This makes it difficult to keep the etching shape vertical.

  In view of the above problem, an object of one aspect is to improve the etching performance of a film to be etched including a silicon film.

In order to solve the above-described problem, according to one aspect, in a processing chamber having a first electrode and a second electrode that is disposed to face the first electrode and places an object to be processed. A method for plasma-etching an object to be processed, wherein a first high-frequency power is applied to either the first electrode or the second electrode, and the first high-frequency power is applied to the second electrode . A plasma generated by applying a second high-frequency power having a frequency lower than the frequency, supplying a processing gas containing hydrogen bromide gas HBr, oxygen gas O _2, and fluorine-based gas into the processing chamber. Etching the film to be etched including at least the silicon film formed on the object to be processed into a desired mask pattern, and the etching step includes supplying the first high frequency power and the second high frequency power. Communicating A first etching step that is applied continuously or intermittently, and the first high-frequency power is applied continuously or intermittently after the first etching step, and the second high-frequency power is applied intermittently. And a second etching step . A plasma etching method is provided.

In order to solve the above-described problem, according to another aspect, a first electrode, a second electrode disposed opposite to the first electrode, and on which an object to be processed is placed, and a processing chamber And a control unit that controls a process of plasma etching the object to be processed by the control unit, wherein the control unit applies a first high frequency to either the first electrode or the second electrode. A power is applied, a second high-frequency power having a frequency lower than the frequency of the first high-frequency power is applied to the second electrode, and hydrogen bromide gas HBr, oxygen gas O _2, and fluorine are introduced into the processing chamber. Supplying a processing gas containing a gas, etching a film to be etched including at least a silicon film formed on the object to be processed by plasma generated from the processing gas into a desired mask pattern, further controlling the process, The etch A first etching step of continuously applying the first high-frequency power and the second high-frequency power, and a continuous or intermittent application of the first high-frequency power after the first etching step. And a second etching step in which the second high-frequency power is intermittently applied, and the second etching step is controlled .

  According to one aspect, the etching performance of an etching target film including a silicon film can be improved.

The figure for demonstrating the outline of the etching process which concerns on one Embodiment. The example of a by-product production | generation in the etching process which concerns on one Embodiment. The flowchart which showed the etching process which concerns on one Embodiment. The recipe example in the etching process which concerns on one Embodiment. The figure which showed the definition about intermittent application of the high frequency electric power which concerns on one Embodiment. The experimental result example of top CD, bottom CD, mask remain, and etching depth which concerns on one Embodiment. FIG. 6 is an example of experimental results of top CD, bottom CD, mask remain, and etching depth when the LF power according to an embodiment is variable. FIG. 1 is a longitudinal sectional view of a plasma etching apparatus according to an embodiment. The cross-sectional view which showed the dipole ring magnet which concerns on one Embodiment.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In addition, in this specification and drawing, about the substantially same structure, the duplicate description is abbreviate | omitted by attaching | subjecting the same code | symbol. In addition, about a pressure value, 1 Torr can be converted as 133.322 Pa.

[Outline of etching process]
First, an outline of an etching process according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 shows an outline of an etching process according to an embodiment. FIG. 1 shows a silicon layer (Si) 101 as a film to be etched. A silicon oxide film (SiO ₂ ) 103 is formed on the silicon film 101 with a silicon nitride film (SiN) 102 interposed therebetween. The silicon oxide film 102 is an example of a silicon-containing oxide film (SiOx) mask.

  In the present embodiment, the etching target film is a single layer film of the silicon layer 101. However, the film to be etched according to the present embodiment is not limited to a single layer film of silicon, but may be a film containing at least silicon, such as a laminated film of a silicon film and a silicon-containing layer (for example, a silicon oxide film). That's fine.

  The etching process according to the present embodiment is performed in the order of the pretreatment process of FIG. 1A and the main etching process of FIGS. 1B to 1D. In the following, the main etching process of FIG. 1B is referred to as “main etching process A”, and the main etching process of FIGS. 1C and 1D is referred to as “main etching process B”.

(Pretreatment process)
In the pretreatment step shown in FIG. 1A, the silicon nitride film 102 is etched using the silicon oxide film 103 in which the hole pattern is formed as a mask. The process conditions in the pretreatment step shown in FIG.
<Pretreatment process: Process conditions>
Pressure 50mTorr
First high frequency power (HF: for plasma excitation) 400 W
Second high frequency power (LF: for bias) 1500 W / pulseless gas type Nitrogen trifluoride NF ₃
(Main etching process A)
After the above pretreatment process, the silicon film 101 is etched in the main etching process shown in FIGS. 1 (b) to 1 (d). In the main etching step A shown in FIG. 1B, the silicon film 101 is etched in a tapered shape using the silicon oxide film 103 as a mask. The process conditions in the main etching step A shown in FIG.
<Main etching process A: Process conditions>
Pressure 150mTorr
First high frequency power (HF: for plasma excitation) 350 W to 400 W
Second high-frequency power (LF: for bias) 900 to 1100 W / pulseless gas type Hydrogen bromide HBr, nitrogen trifluoride NF ₃ , oxygen O ₂
In the present embodiment, the second high frequency power is continuously applied in the main etching step A. However, the second high frequency power may be applied in a pulsed manner in the main etching step A. In the main etching step A, the first high frequency power may be applied in pulses in synchronization with the second high frequency power.

(Main etching process B)
Of the main etching process B, FIG. 1C shows an etching state when the aspect ratio is low, and FIG. 1D shows an etching state when the aspect ratio is high. The process conditions in the main etching process B will be described later.

  The aspect ratio is the depth h of the hole with respect to the diameter of the opening of the hole in the silicon layer 101. In the following, as shown in FIG. 1D, the diameter of the opening of the hole in the silicon layer 101 is indicated by top CD (Top CD), the diameter of the bottom of the hole is indicated by bottom CD (Btm CD), The length from the opening of the hole in the layer 101 to the bottom is indicated by a depth h. As shown in FIG. 1D, the higher the aspect ratio, the deeper the etching hole, and it becomes difficult to keep the shape of the side wall of the hole vertical. The reason will be described below.

  Under typical etching process conditions, products generated during etching accumulate at the opening of the etching hole and hinder the progress of the etching. With reference to FIG. 2, the mechanism by which the product accumulates in the opening during etching will be described.

As shown on the right side of FIG. 2, during the etching, the silicon 200 is removed from the silicon film 101 by plasma etching. The shaved silicon 200 moves toward the opening Op. A part of the silicon 200 is discharged out of the hole through the opening Op, but the remaining part reacts with oxygen gas to become silicon oxide (SiO _x ) and adheres in the vicinity of the opening Op. The silicon oxide 300 attached to the opening Op narrows the opening of the etching hole.

  When the speed at which the silicon 200 shaved by etching is discharged from the opening Op is faster than the speed at which the silicon 200 is deposited, the amount of silicon oxide 300 adhering to the vicinity of the opening Op is small. Therefore, as shown in the upper left diagram of FIG. 2, the opening portion Op of the etching hole is not narrowed by the deposit 300. For this reason, the progress of the etching is not hindered, and a vertical etching hole is formed with a high aspect ratio.

  On the other hand, when the speed at which the silicon 200 shaved by etching is discharged from the opening Op is lower than the speed at which the silicon 200 is deposited and deposited, the amount of silicon oxide 300 adhering to the vicinity of the opening Op is large. Therefore, as shown in the lower left diagram of FIG. 2, the opening of the etching hole Op is narrowed by the silicon oxide 300. In this case, the progress of the etching is hindered, the etching performance is lowered, and it is difficult to form a vertical etching hole. Therefore, it is preferable that deposition of the deposit 300 during etching is avoided as much as possible and the opening Op is widened to improve the etching progress and improve the etching performance.

  Here, it can also be assumed that the progress of the etching is hindered because the deposit 300 in the hole opening Op prevents the ions from moving vertically into the hole. Under this assumption, it is assumed that the etching progresses if the power of the second high-frequency power is increased and the ion strike is strengthened. Therefore, the inventor performed etching while increasing the power of the second high frequency power and increasing the ion energy. According to this, a result was obtained that the amount of the deposit 300 increased as the power of the second high-frequency power was increased. Depending on this result, in order to reduce the amount of the deposit 300, it is conceivable to perform the etching process in a state where the power of the second high-frequency power is lowered and the ion energy is weakened. However, in this case, ions that move vertically to the inside of the hole are reduced due to a decrease in ion energy, and etching with a high aspect ratio becomes difficult.

  In one embodiment described below, a plasma etching method is proposed in which it is possible to achieve both reduction in deposits on the opening Op of etched holes and realization of etching with a high aspect ratio.

[Etching method]
Hereinafter, a plasma etching method according to an embodiment will be described with reference to FIG. In the plasma etching method according to the embodiment, a control unit of a plasma etching apparatus (described later in FIG. 8) performs etching according to the process conditions and procedures set in the recipe example of “with pulse application” in FIG. It is realized by executing. However, in the recipe example of FIG. 4, the process conditions and procedure of the main etching step A of FIG. 1B are omitted, and the process conditions and procedure of the main etching step B of FIGS. 1C and 1D are omitted. Show only. Since the process conditions of the main etching step A in FIG. 1B have been described above, description thereof is omitted here. In FIG. 4B, a recipe example (standard) of “no pulse application (continuous wave application)” is shown as a comparative example.

  Before explaining the plasma etching method according to the present embodiment with reference to FIG. 3, words used when intermittently applying high frequency power will be described. In the plasma etching method according to the present embodiment, as shown in FIG. 5, at least the second high-frequency power (LF: for bias) is applied intermittently, that is, pulsed in the main etching process B.

  The plasma etching method according to this embodiment is performed using a capacitively coupled plasma etching apparatus that generates plasma by applying high-frequency power between an upper electrode and a lower electrode. FIG. 5 schematically shows a capacitively coupled plasma etching apparatus 1 according to an embodiment. A more detailed apparatus configuration will be described later with reference to FIG.

  The capacitively coupled plasma etching apparatus 1 is provided with a first high frequency power supply 15 and a second high frequency power supply 26. A mounting table 2 on which a semiconductor wafer (hereinafter referred to as a wafer) is mounted is provided in the chamber C (processing chamber). The mounting table 2 also functions as a lower electrode.

  In the present embodiment, first high frequency power (HF) for plasma generation is applied from the first high frequency power supply 15 to the mounting table 2. The first high-frequency power may be applied to the lower electrode or the upper electrode.

  Further, a second high frequency power (LF) for bias is applied from the second high frequency power supply 26 to the mounting table 2. The second high frequency power is a bias high frequency power.

  In the pretreatment process and the main etching process A, the first high-frequency power and the second high-frequency power are continuously applied to the mounting table 2.

  On the other hand, in the main etching process B, only the first high-frequency power is continuously applied to the mounting table 2, and the second high-frequency power is intermittently applied. That is, in the main etching step B of the present embodiment, the first high frequency power is a continuous wave, and the second high frequency power is a pulse wave. However, in the main etching step B, the first high-frequency power and the second high-frequency power may be applied in a pulsed manner in synchronization.

  As shown in FIG. 5, when high-frequency power is intermittently applied, the time during which high-frequency power is applied to the mounting table 2 is Ton, and the time when the high-frequency power is not applied is Toff. During the time Ton when the high frequency power is applied, pulsed high frequency power having a frequency of 1 / (Ton + Toff) is applied to the mounting table 2.

  The duty ratio is indicated by a ratio of the applied time Ton to the total time of the applied time Ton and the non-applied time Toff, that is, Ton / (Ton + Toff).

  A plasma etching method according to this embodiment will be described. When the plasma etching method shown in FIG. 3 is started, the control unit determines whether a wafer is loaded into the plasma etching apparatus 1 (S10). The control unit repeats the process of S10 until the wafer is carried in. When the wafer is carried in, the control unit proceeds to S12. The loaded wafer is subjected to the pretreatment process of FIG.

  The control unit etches the silicon film 101 in a tapered shape as shown in FIG. 1B under the process conditions of the main etching step A described above (S12).

  Next, the control unit starts the main etching process B (S14). The control unit executes the etching of the main etching process B according to the procedure of the recipe shown in FIG. In the recipe example “with pulse application” in FIG. 4A, the process conditions are determined for each step of Step 1 to Step 5 in the main etching process B. Similarly, in the recipe example of “no pulse application” in FIG. 4B, the process conditions are determined for each of steps 1 to 5 in the main etching process B.

First, the control unit supplies a process gas containing a hydrogen bromide gas HBr and oxygen gas _{O 2} and silicon tetrafluoride gas SiF ₄ and nitrogen trifluoride NF ₃ into the chamber C (S16). Further, the control unit controls the pressure in the chamber C to 200 mTorr (S18). The recipe example “with pulse application” in FIG. 4A and the recipe example “without pulse application” in FIG.

  Next, the control unit applies the first high-frequency power and the second high-frequency power (S20). In the present embodiment, as shown in FIG. 4A, the first high-frequency power is a continuous wave, and the second high-frequency power is a pulse wave. Specifically, the control unit controls the power of the first high-frequency power to 500 W in step 2. In addition, the control unit controls the frequency of the second high-frequency power to 10 kHz, the duty ratio of the second high-frequency power to 30% to 50%, and the power of the second high-frequency power to 1960 W to 2800 W in Step 2.

  In the case of “no pulse application” in FIG. 4B, the first and second high-frequency powers are continuous waves, and the power of the first high-frequency power is controlled to 500 W in step 2, and the second The power of the high frequency power is controlled to 1400 W in step 2.

  Next, according to the procedure of the recipe shown in FIG. 4A, the control unit sets the power of the second high-frequency power in the order of 2100 W to 3000 W, 2240 W to 3200 W, and 2380 W to 3400 W in steps 3, 4, and 5, respectively. The voltage is intermittently applied while gradually increasing (S22). In addition, the control unit lowers the pressure in the chamber stepwise in the order of 200 mTorr (Steps 1 and 2), 180 mTorr (Steps 3 and 4), and 150 mTorr (Step 5) (S24), and ends this processing after a predetermined time. .

  In the case of “no pulse application” in FIG. 4B, the power of the second high-frequency power is controlled to 1500 W, 1600 W, and 1700 W in steps 3, 4, and 5, respectively. The pressure in the chamber in the case of “without pulse application” in FIG. 4B is the same as that in the case of “with pulse application” in FIG.

The plasma etching method according to this embodiment has been described above. In S22, at least the second high-frequency power may be applied intermittently, and the power of the second high-frequency power may not be increased stepwise. Further, the step of lowering the pressure in the chamber in S24 step by step is not performed, and the pressure in the chamber may be constant.
However, it is preferable to apply the second high-frequency power intermittently while gradually increasing the power of the second high-frequency power in S22. Moreover, it is preferable to lower the pressure in the chamber stepwise in S24.

[Example of effects]
Next, effects of the plasma etching method according to the present embodiment will be described with reference to FIG. In FIG. 6, the case where the second high frequency power is applied in the form of pulses in the plasma etching method is denoted as “LF pulse”. In the plasma etching method, the case where the first high-frequency power is applied in a pulse form together with the second high-frequency power is referred to as “HF + LF pulse”. The case where the second high-frequency power is applied continuously and the first high-frequency power is applied in a pulse form is referred to as “HF pulse”. Finally, as a comparative example, a case where the first and second high frequency powers are continuously applied is denoted as “continuous wave”. The duty ratio of the pulse wave of the high frequency power to be applied was set to 50%.

  FIG. 6A shows the diameter of the top CD (TopCD in FIG. 1D). FIG. 6 (b) shows the diameter of the bottom CD (BtmCD in FIG. 1 (d)). FIG. 6C shows a mask main (the remaining amount of the silicon oxide film 103 in FIG. 1D). FIG. 6D shows the silicon depth (etching depth h of the silicon film 101 in FIG. 1D).

  In the result of the top CD shown in FIG. 6A, the value of the top CD of the LF pulse is the largest, and the value of the top CD becomes smaller in the order of the HF pulse, the (HF + LF) pulse, and the continuous wave. From this result, it can be seen that the value of the top CD is larger when the high frequency power of the pulse wave is applied than the continuous wave.

  Next, in the result of the bottom CD shown in FIG. 6B, the values of the bottom CD of the continuous wave, the (HF + LF) pulse, the HF pulse, and the LF pulse are almost the same.

  Next, from the result of the mask remaining shown in FIG. 6C, when the high frequency power of the (HF + LF) pulse and the LF pulse was applied to the continuous wave, the remaining amount of the mask increased. On the other hand, when the high frequency power of the HF pulse was applied to the continuous wave, the remaining amount of the mask was reduced.

  Next, in the result of the silicon depth shown in FIG. 6D, the silicon depths of the continuous wave, (HF + LF) pulse, HF pulse, and LF pulse were almost the same.

  From the above, in order to obtain high etching performance without depositing deposits at the openings of the etching holes, it was found that applying high-frequency power in a pulsed manner is preferable to continuous application. However, considering the result of mask remaining, when the silicon film 101 is etched with a high aspect ratio, applying high frequency power of (HF + LF) pulse and LF pulse is more than applying high frequency power of continuous wave or HF pulse. Was also found to be preferable.

  As described above, when the silicon scraped by etching reacts with oxygen gas to form silicon oxide and deposits faster than the speed of silicon exiting the hole without reacting, the opening of the etched hole Silicon oxide is deposited on the hole, and the opening of the hole is narrowed by the deposit.

  Here, as the amount of silicon etched per unit time increases, the amount of silicon oxide deposited increases. Therefore, it is effective to reduce the amount of silicon etched per unit time in order to reduce the amount of silicon oxide deposited, maintain a wide opening, and improve the etching performance.

  As an example for reducing the etching amount of silicon per unit time, there is a method of reducing the power of high frequency power for bias. However, if the power of the high frequency power for bias is simply lowered, there is a problem that the verticality of the etched hole sidewall cannot be ensured due to insufficient ion energy.

  On the other hand, when the bias high frequency power is applied in a pulsed manner, sufficient ion energy is obtained when the pulse is on, so that the verticality of the etched hole sidewall can be ensured. . Further, the amount of silicon etched per unit time can be reduced by reducing the ion energy when the pulse is off.

  In order to reduce the etching amount of silicon per unit time, the duty ratio should be lowered. However, considering the etching rate, the duty ratio is preferably 30% or more. In the present embodiment, the frequency of the high-frequency power to be pulsed is preferably 1 kHz to 10 kHz.

[power]
Next, the inventors changed the power of the high-frequency power for bias to make it appropriate for ensuring the verticality of the sidewall of the etched hole and reducing the etching amount of silicon per unit time. An experiment was conducted to investigate the power value. The result is shown in FIG.

  FIG. 7A shows an etching result when the second high-frequency power of continuous wave is applied. As the etching result, values of mask main, top CD, bottom CD, and silicon depth are shown. FIGS. 7B to 7D show the etching results when the pulsed second high-frequency power (LF pulse) is applied using the plasma etching method according to the present embodiment. The power of the second high-frequency power shown in FIG. 7B is 1.5 times the power shown in FIG. The power of each high frequency power in FIG. 7C and FIG. 7D is 1.7 times and 1.9 times the power shown in FIG. FIG. 7E shows a case where the second high-frequency power is a continuous wave, and a case where a high-frequency power having a power 1000 W higher than that in FIG. 7A is continuously applied.

  In all cases, the power of the first high-frequency power is fixed at 500W.

  As a result, it can be seen that the perpendicularity of the etching shape and the depth of the etched silicon when the continuous wave of FIG. 7A and the LF pulse of FIG. 7B are applied are substantially equal. Further, from the etching result in the case of FIGS. 7C and 7D in which the LF pulse having higher power than that in the case of FIG. 7B is applied, the power of the second high-frequency power applied in a pulse shape is obtained. It can be seen that the higher the value, the better the etching result. In particular, in the etching results in FIGS. 7C and 7D, the difference between the top CD and the bottom CD is small, the etching shape is vertical, and the etched silicon is deep, so that It can be seen that the performance is high.

  On the other hand, from the etching result of FIG. 7E in which a continuous wave whose power of the second high frequency power is 1000 W higher than that in FIG. 7A is applied, FIG. 7B to FIG. ), The remaining amount of the mask main body is small, the difference between the top CD and the bottom CD is large, the perpendicularity of the etching shape cannot be obtained, and the etching depth of silicon is shallow. From the above, it was proved that silicon can be etched deeply and vertically when a pulsed second high-frequency power having a power 1.5 times or more of the continuous-wave second high-frequency power is applied. Further, it has been found that in the case of the continuous wave second high frequency power, a good etching result cannot be obtained even if the power is increased.

  From the above results, in the plasma etching method according to the present embodiment, the second high-frequency power for bias or the high-frequency power for plasma generation and bias (first and second high-frequency power) is applied in a pulse shape. To do. Thus, by reducing the amount of silicon etched per unit time, it is possible to avoid the etching opening from becoming narrow due to deposits during etching. As a result, silicon can be etched deeply and vertically without impairing the etching performance.

  In consideration of the fact that the higher the aspect ratio is, the more difficult it is to make the etched hole into a vertical shape. In the plasma etching method according to this embodiment, the higher the aspect ratio, the higher the aspect ratio. The power of the high-frequency power is gradually increased and the pressure in the chamber is gradually decreased. Thereby, the vertical shape of the etching hole can be maintained by increasing the ion energy as the aspect ratio becomes higher.

In the plasma etching method according to the present embodiment, a processing gas containing hydrogen bromide gas HBr, oxygen gas O _2, and fluorine-based gas is supplied into the chamber. Examples of the fluorine-based gas include, but are not limited to, nitrogen trifluoride gas NF ₃ , carbon tetrafluoride CF ₄ , sulfur hexafluoride SF _{6 and the} like.

The processing gas may contain silicon tetrafluoride gas SiF ₄ . According to this, the mask selection ratio can be increased. Thereby, an etching hole with a high aspect ratio can be formed.

[Overall configuration of plasma etching system]
Finally, an example of a plasma etching apparatus for plasma etching the wafer W using the etching method according to each of the above embodiments will be described with reference to FIGS. FIG. 8 is a longitudinal sectional view showing the overall configuration of a capacitively coupled plasma etching apparatus according to an embodiment. FIG. 9 is a cross-sectional view showing a dipole ring magnet according to an embodiment.

  A capacitively coupled plasma etching apparatus 1 according to an embodiment is configured as a magnetron reactive ion etching (RIE) type plasma etching apparatus. The plasma etching apparatus 1 has a chamber C made of a metal such as aluminum or stainless steel.

  In the chamber C, for example, a mounting table 2 for mounting a wafer W is provided. The mounting table 2 is made of, for example, aluminum, and is supported by a support portion 4 made of a conductor via an insulating member 3. A focus ring 5 made of, for example, silicon or quartz is disposed around the upper surface of the mounting table 2. On the upper surface of the mounting table 2, an electrostatic chuck 6 for holding the wafer W by electrostatic attraction is provided. The mounting table 2 and the support unit 4 can be moved up and down by a lifting mechanism including a ball screw 7, and a lifting drive unit (not shown) provided below the support unit 4 is covered with a bellows 8 made of stainless steel. ing. A bellows cover 9 is provided outside the bellows 8. The lower surface of the focus ring 5 is connected to the baffle plate 10, and the focus ring 5 is electrically connected to the chamber C through the baffle plate 10, the support portion 4 and the bellows 8. Chamber C is grounded.

  The chamber C includes an upper chamber 1a and a lower chamber 1b having a diameter larger than that of the upper chamber 1a. An exhaust port 11 is formed in the side wall of the lower chamber 1b. An exhaust device 12 is connected to the exhaust port 11 via an exhaust pipe. By operating the vacuum pump of the exhaust device 12, the processing space in the chamber C is depressurized to a predetermined degree of vacuum. A gate valve 13 for opening and closing the loading / unloading port for the wafer W is attached to the side wall of the lower chamber 1b.

  A first high-frequency power source 15 for plasma generation and reactive ion etching (RIE) is electrically connected to the mounting table 2 via a matching unit 14. The first high frequency power supply 15 supplies high frequency power having a frequency of, for example, 100 MHz to the mounting table 2 as high frequency power (HF) for plasma generation.

  A second high frequency power supply 26 is also electrically connected to the mounting table 2 via a matching unit 25. The second high frequency power supply 26 supplies high frequency power having a frequency of 13.4 MHz, for example, to the mounting table 2 in a superimposed manner as bias high frequency power (LF).

  On the ceiling portion of the chamber C, a shower head 20 described later is provided as an upper electrode held at the ground potential. Accordingly, high frequency power (HF) from the first high frequency power supply 15 is supplied between the mounting table 2 and the shower head 20.

  The electrostatic chuck 6 is obtained by sandwiching an electrode 6a made of a conductive film between a pair of insulating sheets 6b. A DC voltage source 16 is electrically connected to the electrode 6a. The wafer W is electrostatically attracted to the electrostatic chuck 6 by an electrostatic attractive force caused by a DC voltage from the DC voltage source 16.

  Inside the mounting table 2, for example, a refrigerant chamber 17 extending in the circumferential direction is provided. Refrigerant at a predetermined temperature, such as cooling water, is circulated and supplied to the refrigerant chamber 17 from an external chiller unit (not shown) via pipes 17a and 17b. The wafer W on the mounting table 2 is controlled to a predetermined processing temperature by the temperature of the circulating refrigerant.

  Further, a heat transfer gas from the gas introduction mechanism 18, for example, He gas, is supplied between the upper surface of the electrostatic chuck 6 and the rear surface of the wafer W via the gas supply line 19. The gas introduction mechanism 18 can independently control the gas pressure, that is, the back pressure, at the wafer central portion and the wafer peripheral portion in order to improve the uniformity of the etching process within the wafer surface.

  The shower head 20 on the ceiling has a large number of gas discharge ports 22 on the lower surface facing the upper surface of the mounting table 2 in parallel. A buffer chamber 21 is provided inside the gas discharge surface. A gas supply source 23 is connected to the gas inlet 20a of the buffer chamber 21 via a gas supply pipe 23a. A processing gas is supplied from the gas supply source 23.

  A dipole ring magnet 24 extending annularly or concentrically is disposed around the upper chamber 1a. As shown in the cross-sectional view of FIG. 9, the dipole ring magnet 24 has a plurality of, for example, sixteen anisotropic segment columnar magnets 31 arranged at regular intervals in the circumferential direction in a casing 32 made of a ring-shaped magnetic body. Do it. In FIG. 9, the arrow shown in each anisotropic segment columnar magnet 31 indicates the direction of magnetization, and as shown in the figure, the direction of magnetization of each anisotropic segment columnar magnet 31 is gradually changed along the circumferential direction. By shifting, a uniform horizontal magnetic field B directed in one direction as a whole can be formed.

  Accordingly, in the space between the mounting table 2 and the shower head 20, an RF electric field is formed in the vertical direction by the high frequency power from the first high frequency power supply 15, and a magnetic field is formed in the horizontal direction by the dipole ring magnet 24. Is done. Magnetron discharge using these orthogonal electromagnetic fields generates high-density plasma near the surface of the mounting table 2.

  The plasma etching apparatus having the above configuration is comprehensively controlled by the control unit 40. The control unit 40 includes a CPU 41 (Central Processing Unit), a ROM 42 (Read Only Memory), and a RAM 43 (Random Access Memory). The CPU 41 executes plasma processing according to various recipes (for example, the recipe of FIG. 4) stored in a storage area such as the RAM 43. The recipe includes process time, process chamber temperature (upper electrode temperature, process chamber side wall temperature, electrostatic chuck temperature, etc.), pressure (gas exhaust), high-frequency power and voltage, which are device control information for process conditions, The flow rate of the processing gas, the flow rate of the heat transfer gas, and the like are described.

  In order to perform plasma etching in the plasma etching apparatus 1 configured as described above, first, the wafer W is loaded into the chamber C from the gate valve 13 and placed on the mounting table 2.

  Next, the mounting table 2 on which the wafer W is mounted is raised to the illustrated height position, and the inside of the chamber C is exhausted through the exhaust port 11 by the vacuum pump of the exhaust device 12. Then, the processing gas is introduced into the chamber C from the gas supply source 23 at a predetermined flow rate, and the pressure in the chamber C is set to a set value. Further, predetermined high frequency power (HF, LF) is applied to the mounting table 2 from the first high frequency power supply 15 and the second high frequency power supply 26. Further, a DC voltage is applied from the DC power source 16 to the electrode 6 a of the electrostatic chuck 6 to attract the wafer W to the electrostatic chuck 6. The processing gas introduced from the shower head 20 is ionized or dissociated by magnetron discharge to generate plasma.

In the above embodiment, a processing gas containing hydrogen bromide gas HBr, oxygen gas O _2, and fluorine-based gas is supplied from the gas supply source 23. The silicon film 101 formed on the wafer W is etched into the mask pattern of the silicon oxide film 103 by plasma generated from the processing gas.

  In the capacitively coupled plasma etching apparatus 1 of FIG. 8, high-frequency power for plasma generation (first high-frequency power) is applied to the mounting table 2, but the high-frequency power for plasma generation (first high-frequency power) is applied to the shower. It may be applied to the head 20.

  The shower head 20 functioning as the upper electrode corresponds to the first electrode. The mounting table 2 corresponds to a second electrode on which the object to be processed is mounted. The high frequency power (HF) applied to either the first or second electrode corresponds to the first high frequency power. The high frequency power (LF) lower than the first high frequency power applied to the second electrode corresponds to the second high frequency power.

  The plasma etching method and the plasma etching apparatus have been described above by way of the above embodiments, but the present invention is not limited to the above embodiments, and various modifications and improvements can be made within the scope of the plasma etching method according to the present invention. Is possible.

  For example, an apparatus capable of executing the plasma etching method is not limited to the capacitively coupled plasma etching apparatus 1 shown in FIG. For example, the plasma etching method can be performed using a plasma device using a radial line slot antenna, an inductively coupled plasma device, a helicon wave excitation plasma device, an electron cyclotron resonance plasma device, or the like.

  The object to be processed in the present invention is not limited to the 300 mm wafer W, and can be applied to a 450 mm wafer, a flat panel display, an EL element, or a substrate for a solar cell.

  1: plasma etching apparatus, 2: mounting table (lower electrode), 15: first high frequency power source, 20: shower head (upper electrode), 26: second high frequency power source, 40: control unit, 101: silicon film, 102: Silicon nitride film, 103: Silicon oxide film, C: Chamber

Claims (5)

A method of plasma etching a target object in a processing chamber having a first electrode and a second electrode disposed opposite to the first electrode and mounting the target object,
Applying a first high frequency power to either the first electrode or the second electrode;
Applying a second high frequency power having a frequency lower than the frequency of the first high frequency power to the second electrode;
Supplying a processing gas containing hydrogen bromide gas HBr, oxygen gas O ₂ and fluorine-based gas into the processing chamber;
Etching an etching target film including at least a silicon film formed on a target object by plasma generated from the processing gas into a desired mask pattern;
Has steps,
The etching step includes
A first etching step of continuously applying the first high-frequency power and the second high-frequency power;
A second etching step of applying the first high-frequency power continuously or intermittently after the first etching step and intermittently applying the second high-frequency power ;
A plasma etching method. In the second etching step ,
The duty ratio of the high frequency power applied intermittently is 30% or more.
The plasma etching method according to claim 1. In the second etching step ,
Supplying the processing gas containing silicon tetrafluoride gas SiF ₄ to the processing gas ;
3. The plasma etching method according to claim 1, wherein the plasma etching method is performed. In the second etching step ,
Increasing the power of the second high-frequency power in stages and decreasing the pressure in the processing chamber in stages.
The plasma etching method according to any one of claims 1 to 3, wherein: A first electrode, a second electrode disposed opposite to the first electrode, on which the object to be processed is placed, a control unit for controlling a process of plasma etching the object to be processed in the processing chamber; A plasma etching apparatus comprising:
The controller is
Applying a first high frequency power to either the first electrode or the second electrode;
Applying a second high frequency power having a frequency lower than the frequency of the first high frequency power to the second electrode;
Supplying a processing gas containing hydrogen bromide gas HBr, oxygen gas O ₂ and fluorine-based gas into the processing chamber;
Etching an etching target film including at least a silicon film formed on a target object by plasma generated from the processing gas into a desired mask pattern;
Control the process,
Further, in the etching step, a first etching step in which the first high-frequency power and the second high-frequency power are continuously applied, and the first high-frequency power is continuously applied after the first etching step. Controlling the second etching step in which the second high-frequency power is intermittently applied .
A plasma etching apparatus characterized by that.