JP3112395B2 - Dry etching apparatus and dry etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of so-called reactive ion etching (RIE) for a conductive film made of metal or other conductive material formed on a substrate such as glass, synthetic resin and semiconductor substrate. Dry etching apparatus and method for selective removal by using

[0002]

2. Description of the Related Art A typical prior art is shown in FIG. A high-frequency power source 7 is provided between a target electrode 4 on which the workpiece 3 is placed and a counter electrode 6 disposed via a plasma discharge space 5 in a matching circuit 8 for impedance matching. And a reactive ion etching apparatus for performing parallel plate etching in this manner. The workpiece 3 is made of a metal film 10 such as Ta on an electrically insulating substrate 9 made of glass or the like.
Is formed, and the metal film 10 is selectively physically and chemically etched. The etching rate of the metal film 10 and the uniformity of the distribution of the etching rate depend on the state of the plasma discharge. Conventionally, in order to change the state of the plasma discharge, the input power of the high-frequency power source 7,
Gas type, gas pressure, gas flow rate and electrode 4 in the container 2
It can only be controlled by a parameter that is the distance between six.

FIG. 9 is a sectional view showing an etched state of the workpiece 3 according to the prior art shown in FIG. Before the etching, as shown in FIG. 9A, a photoresist layer 11 having an etching selectivity with an etching rate of zero, for example, is formed on the metal film 10 by patterning. During etching, as shown in FIG. 9 (2), ions 12 which are etchants formed in the plasma and radicals which are excited active species act on the workpiece 3 at the same time, resulting in physical and chemical anisotropy. Etching is performed, and the portion 10a of the metal film 10 exposed from the photoresist layer 11 is removed, and the etching proceeds.

In the so-called just etching state shown in FIG. 9 (3), the etching of the portion of the metal film 10 where the photoresist layer 11 is not patterned is completed, and a portion 9a of the electrically insulating substrate 9 is exposed. It is easy to make the side portion 10b of the metal film 10 into a shape having a taper, which is a desired target shape, and to perform just etching in a narrow region.

However, in order to manufacture a large liquid crystal display panel, for example, when a large number of elongated electrodes are formed on the substrate 9 by etching over a large area, all the electrodes are formed as shown in FIG. It is difficult to form by just etching. The reason is that the metal film 1
When 0 is removed and a portion 9a of the electrically insulating substrate 9 is exposed, the exposed portion 9a of the substrate 9 is sharply changed, that is, in accordance with a change in etching rate (loading effect) caused by a sudden change in the etching area. The ions 12 in the plasma are concentrated on the side portions 10c of the metal film 10 as shown in FIG. The etching shape of the side portion 10c changes in a very short time. Thus, the uniformity of the etching distribution is not maintained, and the over-etching state shown in FIG. 9D is obtained, and the taper angle θ1 decreases. Therefore, it becomes difficult to control the etching to obtain a taper having a gentle shape shown in the side portion 10b of FIG. 9C over a wide area. As shown in FIG. 9 (4), when the taper angle θ1 becomes small and the over-etching state progresses excessively, the electrode is further formed on the metal film 10 with the electric insulating layer interposed therebetween. In addition, there is a problem that disconnection of the electrode is apt to occur in the over-etched portion, thereby increasing the number of defective products.

In the prior art, when etching is performed on a metal film 10 in a substrate 9 having a large area, the etching is completed up to a region having a low etching rate due to a problem of etching uniformity. turn into. Further, in order to complete the etching of the entire surface of the substrate 9, over-etching is indispensable so that the metal film does not remain. As a result, in order to complete etching over a wide area, over-etching is indispensable as described above. However, FIG.
It is necessary not to proceed until excessive overetching of (4). Even if etching with very good uniformity can be performed, this over-etching is necessary in consideration of variations in mass production. As described above, conventionally, there is no parameter for controlling the etching rate with a quick response to a rapid change in the etching rate in over-etching, and as a result, it is desired that the side portions 10b and 10c of the metal film 10 It is difficult to supply such a shape, and the allowable time for over-etching is too short, and it is difficult to secure a margin for the allowable time.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to easily control the etching rate of a conductive film such as a metal film formed on an electrically insulating substrate accurately. It is another object of the present invention to provide a dry etching apparatus and a dry etching method capable of stably supplying an etching shape of a side portion of the conductive film to a desired shape.

[0008]

According to the present invention, there is provided a dry etching method in which a high-frequency power source is connected to a target electrode arranged facing a plasma discharge space and a counter electrode facing the target electrode to perform reactive ion etching. The apparatus comprises: a DC power supply unit for applying a positive DC voltage to a counter electrode on a conductive film formed on a surface facing a plasma discharge space of an electrically insulating substrate mounted on a target electrode; The voltage is selected to be a predetermined value exceeding a floating voltage in an equilibrium state when the DC voltage is not applied to the conductive film on the plasma discharge space side of the electrically insulating substrate having a conductive film. It is. Further, according to the present invention, the DC power supply means is a detecting means for detecting the light emission luminance of the plasma discharge space, and in response to the output of the detection means, the light emission luminance,
A light emission luminance level discriminating means for discriminating a level at a discrimination level corresponding to a predetermined removed state of the conductive film, a DC power supply for outputting a DC voltage having the predetermined value between the counter electrode, and a light emission luminance level In response to an output of the discriminating means, a switching means is provided for deriving an output voltage of a DC power supply so as to be applied to the conductive film when the light emission luminance reaches the discrimination level. The present invention also provides a timer for setting the conduction time W2 of the switching means, and a high-frequency power supply from the high-frequency power supply to the target electrode when the timer setting time W2 has elapsed in response to the output of the timer. And control means for shutting off. Further, the present invention is characterized in that the set time W2 of the timer is selected to be about 2 to 30% of the time W1 in which the conductive film is partially removed. Further, according to the present invention, a photoresist is formed on an electrically insulative substrate by forming a photoresist layer having higher etching selectivity than the conductive film on the conductive film. Is placed on a target electrode, and a high-frequency power source is connected between the target electrode and a counter electrode facing the target electrode to perform reactive ion etching on a portion of the conductive film exposed from the photoresist layer, thereby performing conductive ion etching. At the point where the portion of the film exposed from the photoresist layer has been etched and removed to a predetermined state,
A DC voltage having a predetermined value exceeding a floating voltage in an equilibrium state when no DC voltage is externally applied to the conductive film on the plasma discharge space side of the electrically insulating substrate having the conductive film is applied to the conductive film. Dry etching method. Further, in the present invention, the DC voltage application time W2 is selected to be about 2 to 30% of the time W1 until the predetermined portion is removed by etching and removing a portion of the conductive film exposed from the photomask layer. It is characterized by.

[0009]

According to the present invention, physical and chemical etching of a conductive film such as a metal film facing a plasma discharge space on an electrically insulating substrate is performed by a reactive ion etching method in a parallel plate type etching structure. During the etching, the conductive film is separated from the target electrode via the substrate, and a positive DC voltage is applied to the conductive film, for example, with respect to a grounded counter electrode by DC power supply means. The etching rate of the conductive film can be easily controlled.

According to the present invention, a DC voltage applied to the conductive film is applied to an electrically insulating substrate on which a conductive film is formed or not formed, while the substrate is placed on a target electrode. When the incident amounts of ions and electrons in the plasma in a certain equilibrium state, the surface of the substrate on the plasma discharge space side has a constant potential, and has a positive floating voltage with respect to the counter electrode, The value is selected to exceed the floating voltage. When there is a conductive film on the substrate, the conductive film is not connected anywhere.

Therefore, when the conductive film is partially removed by etching and the substrate is exposed to a predetermined etching state, the accelerating electric field of ions serving as an etchant can be reduced, and the etching rate can be reduced. become able to. In addition, electrons in the plasma are drawn into the conductive film, so that the accumulation of electric charge on the substrate is suppressed, and charge-up is reduced and improved. This suppresses the plasma discharge from becoming non-uniform. In this manner, by applying the positive DC voltage to the conductive film on the substrate as the workpiece, the etching rate can be reduced and the charge-up can be improved. Therefore, a desired etching shape on the side of the conductive film near the periphery of the photoresist layer can be easily achieved, and a rapid change in the etching shape in the over-etching state can be suppressed, and a time margin can be easily secured. Thus, a stable supply of a desired processing shape can be made possible.

Although not only ions but also radicals, which are excited active species, simultaneously contribute to etching, these radicals are electrically neutral, so that even if a voltage is applied to the conductive film as described above, The speed of the radicals does not change, and there is no charge transfer on the substrate.
In this manner, independently of the potential of the target electrode on which the workpiece is placed, a potential is applied to the conductive film facing the plasma discharge space on the substrate of the workpiece from the outside, and the potential is clamped to reduce the etching rate as described above. Control and suppress the charge-up of the substrate.

According to the present invention, when the substrate is exposed to the plasma discharge space by etching the conductive film, the emission luminance of the plasma discharge space increases or decreases according to the spectrum according to the etching state. When the light emission luminance reaches a predetermined discrimination level which is a threshold value of the light emission luminance level discriminating means, the just-etched state in which the smooth side portions 10b are formed as shown in FIG. Then, the DC voltage is applied to the conductive film by a DC power supply through a switching unit to reduce the etching rate.

According to the present invention, the conduction time W2 for keeping the switching means conductive after the etching means has been made conductive and almost in the just-etched state is:
For example, the time W1 is set by a timer and is about 2 to 30 of the time W1 until the substrate is exposed after the conductive film is partially removed.
%, Preferably about 5-10%. This time W
2 is less than about 2% of the time W1, it is difficult to perform uniform just etching of all the electrodes on a substrate such as a liquid crystal display panel having a relatively large area, and the electrode width is likely to be non-uniform. In addition, when it exceeds about 30%, FIG.
As shown in (4), the taper angle becomes too small and over-etching proceeds excessively. Therefore, for example, when a new electrode is crossed over the conductive film via an electrical insulating layer, the electrode is disconnected. Tends to occur.

[0015]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention. In the hermetic container 15, a horizontal flat plate-like target electrode 16 is vertically spaced and a horizontal flat plate-like counter electrode 17 facing the target electrode 16 is spaced upward. Electrodes 16,
A plasma discharge space 18 is formed between the two, and thus an etching apparatus for the reactive ion etching method for performing parallel plate etching is constituted.

The target electrode 16 has, for example, 1-2
Matching circuit 20 for performing impedance matching from one output terminal of a high-frequency power supply 19 of kW and 13.56 MHz
, And further via switching means 22. The counter electrode 17 is grounded. High frequency power supply 1
The other output terminal which is not connected to the matching circuit 20 of FIG. 9 is also grounded. Target electrode 1
The workpiece 23 is placed facing the plasma discharge space 18 on the substrate 6, and physical and chemical etching is performed. In the container 15, for example, CF ₄ is used as an etching gas.
And a mixed gas composed of O ₂ and O _2,
Conductive film 33 made of Ta or the like to be etched
Dry etching (see FIG. 2) is performed.

The light emission luminance of the plasma discharge space 18 is detected by a light receiving element 24 as a detecting means, and a signal representing the detected light emission luminance is given to a control circuit 25 realized by a microcomputer or the like. The positive output terminal of the DC power supply 26 is connected to the conductive film 3 of the workpiece 23 from the low-pass filter 27 via the switching means 28.
2 via line 29. The switching means 22 and 28 are controlled by the control circuit 25. The negative output terminal of DC power supply 26 is grounded. The output voltage of the DC power supply 26 may be variable.

FIG. 2 is a sectional view showing an etched state of the workpiece 23. As shown in FIG. The workpiece 23 may be, for example, a substrate of a large liquid crystal display panel, and is formed by forming a conductive film 32 made of Ta or the like on an electrically insulating substrate 31 made of glass or synthetic resin. On this conductive film 32, a photoresist layer 33 is formed selectively on a portion 32 a of the conductive film 32 to be left by a photo-etching method, and a remaining portion 32 b of the conductive film 32 is formed in the plasma discharge space 18. Exposure and face. The photoresist layer 33 has an etching selectivity that is less likely to be etched than the conductive film 32, and desired side portions 32c and 32d of the conductive film 32 are formed as shown in FIG. Until the above, it is necessary to remain on the conductive film 32. That is, the photoresist layer 33 is formed of the conductive film 3 to be etched.
The photoresist layer 33 has an etching selectivity that is sufficiently smaller than the etching rate of 2, for example, zero.

FIG. 3 is a diagram for explaining an electric field distribution of the dry etching apparatus shown in FIG. Space 18
During etching by plasma discharge of the electrode 1
The electric field distribution between 6 and 17 is as shown in FIG.
The structure of the electrodes 16 and 17 is simplified and shown in FIG. In the etching state during the plasma discharge, the target electrode 16 is self-biased to the negative voltage Vs. The ions generated in the plasma are accelerated by the self-bias and move toward the target electrode 16 as shown in FIG.
It moves to the left in (2) by being accelerated and acts on the conductive film 32 of the workpiece 23. The digital, which is an excited active species generated in the plasma, is applied to the conductive film 32 of the workpiece 23.
, And physically and chemically performs etching, thereby performing reactive ion etching. The electrically insulating substrate 31 does not have the same potential as the target electrode 16, and this substrate 31 has a certain equilibrium state in which the amounts of ions and electrons incident on the substrate 31 are constant, and the substrate 31 has a positive constant floating voltage Vp. With respect to the grounded counter electrode 17. The floating voltage Vp is applied to the space 18 during plasma discharge in a state where the conductive film 32 is formed on the entire surface of the substrate 31 facing the plasma discharge space 18 and the conductive film 32 is not connected to any part. It may be a voltage in an equilibrium state. This floating voltage Vp is, for example, about 20 to 30V.

FIG. 4 is a flow chart for explaining the operation of the control circuit 25, and FIG. 5 is a diagram showing the lapse of time of the voltage of the conductive film 32. First, at the start of etching in step a1, the control circuit 25 conducts the switching means 22 to cause the space 18 to perform plasma discharge, and at this time, the switching means 28 is kept off. Before etching, the workpiece 23 is shown in FIG.
Has the following cross-sectional shape.

During the etching, as shown in FIG. 2B, the portion 32b of the conductive film 32 exposed from the photoresist layer 33 is removed by the ions 35 as the etchant. Radicals 36 are also present in the plasma discharge space 18. The plasma emission luminance in the space 18 is detected by the light receiving element 24 in step a2.

When the etching is started, the conductive layer 32 is removed, and as shown in FIG. 2C, the conductive layer 32 is removed, and a portion 31a of the substrate 31 is exposed to the plasma discharge space 18, and the conductive film 32 is removed. When the side portion 32c has a desired taper angle and is almost in a just-etched state having a gentle inclination, in step a3,
Plasma discharge space 18 detected by light receiving element 24
Reaches a discrimination level which is a predetermined value. As a result, the exposed portion 31a of the substrate 31 is charged and charged up, and ions in the plasma concentrate on the side portion 32c of the conductive film 32, whereby the etching rate on the side portion 32c of the conductive film 32 increases rapidly. I will.

In order to solve this problem, according to the concept of the present invention, the switching means 28 is turned on in step a4 of FIG. 4 and the voltage of the DC power supply 26 is measured in the period W2 measured by the timer 37 from time t1 to t2. V1 is applied to the conductive film 32. This voltage V1 is a voltage exceeding the floating voltage Vp that is maintained when the amounts of ions and electrons incident on the substrate 31 reach a certain equilibrium state (V1> Vp). This voltage V1 is, for example, 30 to 1
A value of 00V is chosen. When the voltage V1 exceeds about 100 V, the plasma discharge state in the space 18 becomes unstable.

The timer 37 measures the time from the time t1 when the switching means 28 is turned on in step a4, and when a predetermined time W2 has elapsed, it is determined that the over-etching operation has been completed and the switching means 22 is cut off in step a6. At the same time, the switching means 28 is shut off at step a7. Thus, step a8
Then, a series of operations ends. The control circuit 25 measures the time W1 from the time when the switching means 22 is turned on and the etching operation is started to the time t1, and determines the time W2 according to this time. For example, the time W2 is the time W2.
It is set to a value in the range of about 2 to 30% of 1, for example, 5 to
10 seconds. At time t2, the shape of the side portion 32c of the conductive film 32 in the almost just-etched state shown in FIG.
The etched shape of the side portion 32d has a large taper angle, is very close to the just-etched side portion 32c, and has a gentle slope.

[0025] By a DC voltage V1 to the conductive film 32 is applied at time t1, the acceleration field of the ions 35 is an etchant decreases, the etching rate is reduced, electrons e in the plasma ^- in the conductive film 32 The substrate 31 is thus drawn into the substrate 31, whereby the charge-up of the substrate 31 is reduced and improved. Thus, a sudden change in the etching shape during the over-etching operation after the just-etched shape 32c is suppressed,
High-precision, stable supply of the desired tapered shape becomes possible.

FIG. 6 is a simplified plan view of a plate-like body 41 which is a workpiece of a liquid crystal display panel obtained by the embodiment shown in FIGS. 1 to 5 of the present invention, and FIG. It is sectional drawing seen from the cutting surface line VII-VII. The liquid crystal display panel is of a so-called active matrix type, in which a grid-like gate electrode bus line 43 and an electric insulating layer 44 are provided on a transparent electric insulating substrate 42 having a light-transmitting property such as glass or synthetic resin. The source electrode bus lines 45 intersecting with each other are formed orthogonally.

A thin film transistor (TFT) 46 functioning as a switch is arranged near the intersection of these lines 43 and 45, and a voltage is applied to each pixel electrode 47 via the source electrode bus line 45. The gate electrode 48 of the thin film transistor 46 is connected to the line 43, and the source electrode 49 is connected to the line 45. In the liquid crystal display panel, a common electrode of the other plate-shaped body is arranged to face the picture element electrode 47 via the liquid crystal,
A voltage is selectively applied to the liquid crystal between the pixel electrode 47 and the common electrode.

According to the concept of the present invention, the side portions 43a and 43b of the gate electrode bus line 43 need to be etched by a reactive ion etching method with high precision so as to have a gentle taper angle. Figure 2
The side indicated by reference numeral 32d in (3) is realized. Since the side portions 43a and 43b have a gentle taper angle, the source electrode bus line 45 formed above the side portions 43a and 43b is smooth at portions 45a and 45b immediately above the side portions 43a and 43b. It can be formed continuously with an inclination.

If the taper angle θ1 has a steep angle of less than 90 degrees as shown in FIG. 9 (4) described in connection with the above-mentioned prior art, the source electrode bus line 45 immediately above the taper angle θ1 has a sharp angle. In the portions 45a and 45b, the probability of disconnection becomes extremely high, and failures increase. The present invention solves such a problem. Although the plate-like body 41 of the liquid crystal display panel shown in FIGS. 6 and 7 has a configuration using a so-called inverted star-shaped thin film transistor 46,
As another embodiment, the source electrode bus line 45 is connected to the substrate 4
2, the gate electrode bus line 43 is formed via the electric insulating layer 44, and the lines 43 and 45 are arranged upside down. The present invention can be embodied not only in a liquid crystal display panel but also in other fields in a wide range.

In the present invention, the electrically insulating substrate may be, for example, a semiconductor substrate having a large thickness. Although the counter electrode 17 is grounded in the above-described embodiment, it may be maintained at another potential as another embodiment of the present invention, and the power supply 26 for applying a voltage to the conductive film 32 to apply a positive bias is provided. It is sufficient that the voltage has a positive voltage with respect to the counter electrode 17, and the voltage of the DC power supply 26 is set to a value exceeding the floating voltage Vp as described above.

[0031]

As described above, according to the present invention, by applying a positive DC voltage to the counter electrode to the conductive film facing the plasma discharge space on the electrically insulating substrate of the work piece, The film etching rate is reduced and the charge-up of the substrate is improved, so that after the exposure of the substrate by etching the conductive film, the etching shape of the conductive film, for example, the side portion of the conductive film near the periphery of the photoresist layer is desired. As a result, a stable supply is possible, and the margin of the allowable time for over-etching as the etching progresses becomes easier.

As a result, it is possible to prevent a taper angle of a side portion of an electrode on a substrate such as a liquid crystal display panel having a large area from having a small and steep value, and it is possible to accurately process the taper angle into a gentle one. For example, disconnection of electric wiring such as a new electrode crossing over the conductive film via an electric insulating layer can be prevented. Thus, it becomes possible to make the etching shape of the conductive film uniform over a wide area.

In particular, according to the present invention, the light emission luminance in the plasma discharge space is detected and level discrimination is performed. When the light emission luminance reaches a discrimination level that is a predetermined value, the voltage V1 exceeding the floating voltage Vp is applied to the conductive film. Is applied between the counter electrode and, therefore, the conductive film is efficiently etched relatively quickly until just etching is performed, and when the shape of the conductive film approaches a desired processing shape,
By applying a DC voltage to the conductive film, the etching rate is reduced and the charge-up of the substrate is improved, so that even when the region to be etched covers a large area, the stable supply of the etched shape is automatically performed. Automatically and with high precision.

Further, according to the present invention, the time W2 during which the above-described DC voltage is applied to the conductive film is a time period from the start of etching to the time when partial removal of the conductive film is performed, for example, until almost the just-etched state is achieved. About 2 to 30 of time W1
%, Thereby enabling reliable removal of the conductive film and easily avoiding an over-etching state in which the taper angle is too small.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an entire configuration of an embodiment of the present invention.

FIG. 2 is a sectional view showing a state where a workpiece 23 is etched by the dry etching apparatus shown in FIG. 1;

FIG. 3 is a diagram for explaining a potential distribution between a target electrode 16 and a counter electrode 17;

FIG. 4 is a flowchart illustrating an operation of control circuit 25 shown in FIG. 1;

FIG. 5 is a diagram showing a voltage of a conductive film 32 of a workpiece 23.

FIG. 6 is a simplified plan view of a plate-like body 41 of the active matrix type liquid crystal display panel obtained by the embodiment shown in FIGS.

FIG. 7 is a sectional view taken along section line VII-VII of FIG. 6;

FIG. 8 is a simplified system diagram showing the configuration of the prior art.

9 is a cross-sectional view showing a state when the workpiece 3 is dry-etched according to the prior art shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 15 Airtight container 16 Target electrode 17 Counter electrode 18 Plasma discharge space 20 Matching circuit 22, 28 Switching means 23 Workpiece 24 Light receiving element 25 Control circuit 26 DC power supply 32 Conductive film 33 Photoresist layer

────────────────────────────────────────────────── ─── Continuation of the front page (72) Mikio Katayama 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-5-129242 (JP, A) (58) Investigated Field (Int.Cl. ⁷ , DB name) C23F 4/00 H01L 21/3065-21/308

Claims (6)

(57) [Claims] 1. A dry etching apparatus in which a high-frequency power source is connected to a target electrode arranged facing a plasma discharge space and a counter electrode facing the target electrode to perform reactive ion etching, the dry etching apparatus being mounted on the target electrode. A conductive film formed on the surface facing the plasma discharge space of the electrically insulating substrate to be placed, including DC power supply means for applying a positive DC voltage to a counter electrode, wherein the DC voltage has a conductive film. A dry etching apparatus, wherein the predetermined value exceeds a floating voltage in an equilibrium state when the DC voltage is not applied to the conductive film on the plasma discharge space side of the electrically insulating substrate. 2. A DC power supply means comprising: a detecting means for detecting light emission luminance in a plasma discharge space; and a discrimination level corresponding to a predetermined removed state of the conductive film in response to an output of the detection means. A light emission luminance level discriminating means for discriminating a level with a DC power supply for outputting a DC voltage having the predetermined value between the counter electrode, and a light emission luminance discriminating in response to an output of the light emission luminance level discriminating means. 2. The dry etching apparatus according to claim 1, further comprising switching means for deriving an output voltage of a DC power supply to give the conductive film when the voltage reaches a level. 3. A timer for setting the conduction time W2 of the switching means, and responding to the output of the timer, and when the set time W2 of the timer elapses, shuts off high-frequency power from the high-frequency power supply to the target electrode, 3. The dry etching apparatus according to claim 2, further comprising a control unit for shutting off the pressure. 4. The dry etching apparatus according to claim 2, wherein the set time W2 of the timer is selected to be about 2 to 30% of the time W1 during which the conductive film is partially removed. 5. A workpiece formed by forming a conductive film on an electrically insulating substrate, wherein a photoresist layer having higher etching selectivity than the conductive film is partially formed on the conductive film, Is placed on the target electrode, and a high-frequency power source is connected between the target electrode and the counter electrode facing the target electrode to perform reactive ion etching on a portion of the conductive film exposed from the photoresist layer. When a portion of the film exposed from the photoresist layer is etched and removed to a predetermined state, a DC voltage is applied from outside to the conductive film on the plasma discharge space side of the electrically insulating substrate having the conductive film. Wherein a DC voltage having a predetermined value exceeding a floating voltage in an equilibrium state when no voltage is applied is applied. 6. The application time W2 of the DC voltage is selected to be about 2 to 30% of the time W1 until the predetermined state in which a portion of the conductive film exposed from the photomask layer is removed by etching. 6. The dry etching method according to claim 5, wherein: