JP2001267301A - Method for detecting degree of etching, etching method, method of manufacturing semiconductor, device for detection of etching degree and dry etching device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide etching for preventing damages to a ground layer due to overetching. SOLUTION: At etching a material using a two step etching method, a first etching step is terminated before a ground layer is exposed and a system moves to a second etching step, with the condition that etching speed be slower than the first etching step. The termination time of the first etching step is determined by monitoring the etching progress obtained from impedance changes in an etching chamber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of etching a gate electrode material and an apparatus therefor.

[0002]

2. Description of the Related Art As devices become more highly integrated and operation speeds increase year by year, the etching accuracy required for pattern formation is also increasing.

Conventionally, when dry etching a gate electrode material for patterning of a gate electrode, for example,
In order to prevent device failure due to etching residue,
The so-called "over-etching" is performed over the entire surface of the wafer to perform excessive etching with respect to the thickness of the formed film.

Further, in order to prevent the base film from being excessively etched during over-etching, a two-stage etching method is often used. The two-stage etching method is a method in which a material to be etched is first etched under a condition where the etching rate is relatively high, and the condition is changed to a condition where the etching rate of the base film is lower from the middle, and overetching is performed.

[0005]

Recently, in response to a demand for a higher operating speed of a device, the thickness of a gate oxide film has been reduced.
There is also a need to keep it below 0 °.

FIGS. 7A to 7C are views showing an example of a process of forming a gate electrode pattern on such a thin gate oxide film using a conventional two-step etching method. Usually, the density of the circuit pattern formed on the substrate is
It is not uniform over the entire area of the substrate, and dense and rough portions of the circuit pattern are often mixed. In the figure, region A is a region where a gate electrode pattern is densely formed, and region B is
The region indicates a region where the gate electrode pattern is formed roughly.

As shown in FIG. 7A, before starting the dry etching of the gate electrode material, a silicon substrate 51 is formed.
0, a gate oxide film 520 having a thickness of about 30 °, for example.
Then, on the gate oxide film 520, a-Si 530 having a thickness of about 2000 Å is formed as a gate electrode material. Further, an etching mask pattern of the patterned antireflection film 540 and the resist 550 is formed on the a-Si 530. Note that the antireflection film 540 is a film provided to prevent the exposure accuracy from deteriorating due to reflection when the resist 550 is exposed.

When the etching of the a-Si 530 is started, the etching proceeds faster in the coarse circuit pattern region (region B) than in the dense circuit pattern region (region A). At the time when the Si film remains, the gate oxide film 520 of the underlying layer is exposed in the region B.

In the conventional two-step etching method, an initial etching step (hereinafter, referred to as a "first etching step")
And the next etching stage (hereinafter, "second etching stage")
) Was determined while monitoring the emission intensity of the plasma in the etching chamber. That is, the etching end point of the gate electrode material is detected from a change in emission intensity at a predetermined wavelength (385 nm) that occurs when the gate oxide film, which is the base layer of the gate electrode material, is exposed.
This was when the etching conditions were switched.

FIG. 8 shows 385n with respect to the etching time.
6 is a graph showing a change in the intensity of the emission wavelength of m. As shown in the figure, a point C where the emission intensity changes due to a change in the reaction product when the etching proceeds from the a-Si 530 to the underlying gate oxide film 520 is defined as the time of switching between the first etching step and the second etching step. Was. In this conventional detection method, the condition is that the gate oxide film is exposed in principle.

FIG. 7B shows an etching state at the end point of the first etching stage (etching condition switching point C). In the rough circuit pattern region (region B), the underlying gate oxide film 520 is exposed and slightly etched. In the dense circuit pattern area (A area)
A considerable amount of a-Si 530 to be etched still remains.

The a-Si 530 remaining in the dense circuit pattern region (region A) is also etched during the second etching step. Generally, the etching conditions in the second etching step are the same as those in the first etching step. Since the a-Si etching rate is lower than the etching conditions, it takes 5 to 10 times as long as the etching time in the first etching stage before over-etching.

On the other hand, in the rough circuit pattern region (region B), the surface of the underlying gate oxide film 520 has already been slightly etched and reduced, and the gate oxide film has a very low etching rate in the second etching stage. 52
The etching of 0 also proceeds. Since the gate oxide 520 is very thin, the gate oxide 52
0 itself may be completely etched and the Si substrate 510 may be exposed. Once the Si substrate 510 is exposed, a
Etching of Si substrate 510 proceeds at substantially the same speed as -Si 530.

As a result, as shown in FIG.
At the end of the etching phase, the dense pattern circuit area (A
Region), a-Si 530 is processed into a good shape,
Although the gate oxide film 520 also remains, in a rough pattern circuit region (region B), the gate oxide film is completely etched, and there is a possibility that a large etching penetration into the Si substrate 510 may occur.

Such penetration of the Si substrate by etching may damage a diffusion region or the like to be formed in the Si substrate, making it impossible to operate the transistor itself. It becomes bad.

SUMMARY OF THE INVENTION An object of the present invention is to provide an etching method, an etching apparatus, a method of detecting the degree of etching progress, and the like capable of adjusting the etching process with higher precision in view of the above-mentioned problems.

[0017]

The method of detecting the degree of progress of etching according to the present invention is characterized in that the amount of etching of a material to be etched is determined by monitoring a change in impedance in an etching chamber during dry etching.

According to the above detection method, an impedance change depending on the etching amount of the material to be etched can be obtained, so that the degree of etching of the material to be etched can be continuously detected. Therefore, it is possible to control the remaining film thickness of the material to be etched to an arbitrary film thickness.

Here, the impedance in the etching chamber refers to the impedance mainly determined by the resistance of the plasma in the chamber and the space capacitor formed between the plasma and the substrate on which the material to be etched is formed. .

[0020] The etching method of the present invention is characterized in that the etching condition of the material to be etched is adjusted by monitoring the impedance change in the etching chamber.

According to the above-mentioned etching method, since the change in impedance in the etching chamber depends on the amount of etching of the material to be etched, the etching conditions are adjusted according to the amount of etching of the material to be etched, and more accurate etching is performed. be able to.

According to another etching method of the present invention, there is provided a first etching step in which the etching is completed before the underlayer of the material to be etched is exposed, and after the first etching step, and after the first etching step. , Gas type, pressure,
A second etching step of etching the material to be etched at least until the underlying layer is exposed, under the condition that any one of the high-frequency power and the temperature is different from the first etching step.

According to the another etching method, since the etching rate is switched from the first etching step to the second etching step having a low etching rate while the material to be etched remains, damage to the underlying layer due to excessive over-etching is prevented. Can be suppressed.

In the above etching method, the end of the first etching step may be determined by monitoring a change in impedance in the etching chamber.

In this case, since the change in impedance in the etching chamber depends on the amount of etching of the material to be etched, the remaining film thickness of the material to be etched at the end of the first etching step can be adjusted.

In the method of manufacturing a semiconductor device according to the present invention, the above-described etching method is used in the process of forming a gate electrode.

When the gate electrode material is etched to form the gate electrode, excessive over-etching is applied to the gate insulating film and, consequently, to the substrate layer below the gate insulating film because the thickness of the gate insulating film serving as a base layer is particularly small. Since there is a possibility of causing damage, over-etching of the gate insulating film can be suppressed by using the above-described etching method.

The etching progress detecting apparatus of the present invention comprises means for measuring a high-frequency voltage and current applied between a pair of electrodes provided in an etching chamber, and converting the measured voltage and current into digital signals. A / D
It is characterized by having a converter and means for calculating an impedance change from the digital signal of the current and the voltage and obtaining an etching amount or an etching remaining film amount of the material to be etched from the impedance change.

By providing the above-mentioned etching progress detecting device in an existing etching device or the like, it becomes possible to monitor the etching progress of the material to be etched during the etching by various etching devices.

The dry etching apparatus according to the present invention is characterized in that it comprises means for detecting the progress of the etching of the material to be etched from the change in impedance in the etching chamber during the dry etching. The means for detecting the degree of progress of etching includes means for measuring a high-frequency voltage and current applied between a pair of electrodes installed in the etching chamber, and conversion of the measured voltage and current into digital signals. An A / D converter and means for calculating a change in impedance from the digital signal of the current and the voltage and obtaining an etching amount or an etching remaining film amount of the material to be etched from the impedance change may be provided.

According to the dry etching apparatus, since the progress of the etching of the material to be etched can be grasped based on the impedance change during the etching, the etching conditions can be adjusted with higher accuracy.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, R for processing a gate electrode will be described.
An embodiment of the present invention will be described by taking an etching process by an IE (Reactive Ion Etching) method as an example.

In the method of etching a gate electrode material according to the present embodiment, a method of monitoring a change in impedance in an etching chamber is used instead of a conventional method of monitoring the emission intensity of a predetermined wavelength. Is characterized by detecting the degree of etching progress. By using this detection method, in the case of using the two-stage etching method, it is possible to switch from the first etching stage to the second etching stage before the underlayer is exposed, and to achieve a more accurate two-stage etching process. Can be etched.

Hereinafter, this embodiment will be described with reference to the drawings.

FIGS. 1A to 1C are partial cross-sectional views of the substrate in each step of patterning a gate electrode using the dry etching method of the present embodiment.

First, FIG. 1A is a partial cross-sectional view of a substrate when starting etching of a gate electrode material. Si
On the substrate 110, an SiO ₂ film 120 having a thickness of about 30 ° serving as a gate oxide film and an a-Si film 130 having a thickness of about 2000 ° to 2500 ° serving as a gate electrode material are formed thereon. Has a patterned antireflection film 140 and a resist 150 formed thereon. The anti-reflection film 140 under the resist mask removes the influence of reflection in order to obtain a highly accurate exposure pattern when exposing the resist. The anti-reflection film 140
Prior to the etching of the a-Si film 130, an etching process is performed by another etching apparatus, and when the gate electrode is etched, it is present only in the lower layer of the resist mask pattern.

It is to be noted that the left side in the figure is a region (A region) where the gate electrode pattern is densely formed, and the right side in the figure is
This is a region (region B) where the gate electrode pattern is formed roughly.

FIG. 1B is a partial sectional view of the substrate when the etching conditions are switched from the first etching stage to the second etching stage. That is, the state at the end of the first etching stage is shown.

A-Si film 130 in first etching step
The etching condition is, for example, as an etching gas, H
Using a mixed gas of Br and Cl ₂ , the flow ratios are set to 150 sccm and 30 sccm, respectively. The pressure in the chamber is 0.5 Pa. A-Si at this time
The film etch rate is about 2000 ° / min. In addition,
When the SiO ₂ film is etched under the same conditions, the etching rate is 150 ° / min.

A-Si film 130 in second etching step
The etching condition is, for example, as an etching gas, H
With Br and _{0 2} of the gas mixture, respectively flow ratio,
It is 158 sccm and 1.8 sccm. The pressure in the chamber is 9.3 Pa.

At this time, the etching rate of the a-Si film is about 850 ° / min. In addition, under these conditions, SiO ₂
The etching rate of the film becomes 10 ° / min or less.

As described above, the etching condition in the second etching stage is to set the etching rate of the SiO ₂ film as the base film to 1 minute per minute in order to suppress excessive over-etching.
Adjust to a condition that can be suppressed to about 0 °. Accordingly, the etching rate of a-Si in the second etching step is about 1/3 to 1/2 of that in the first etching step.

The etching gas conditions are not limited to the above conditions, but various conditions can be used. For example, HB
Only r gas may be used.

In the present embodiment, the switching between the first etching step and the second etching step is determined by monitoring the change in impedance in the etching chamber, and thereby the progress of the etching of the gate electrode material (a-Si film 130). Perform according to the degree. Areas with coarse patterns (B
Region), in order to ensure that the SiO ₂ film 120 as the underlying layer is not exposed, for example, a-
When the average thickness of the remaining film of the Si film 130 becomes about 100 °, the first etching step is completed, and the operation is switched to the second etching step.

FIG. 2 schematically shows a state in the etching chamber 10 of the parallel plate type RIE apparatus for etching the a-Si film 130. As shown in the figure, an example of a parallel plate type RIE apparatus including an upper electrode 20A and a lower electrode 20B is shown. A gate oxide film (SiO ₂ ) 120 and a gate electrode material (a-Si) on the lower electrode 20B
The Si substrate 110 on which the surface 130 and the resist 150 are formed is placed. Upper electrode 20A and lower electrode 20B
When a high frequency voltage of 13.56 MHz is applied between the upper electrode 20A and the upper electrode side between the upper electrode 20A and the surface of the Si substrate 110 during etching, ionized or neutral active excited molecules of an etching gas or a material to be etched are applied. A plasma region 30 containing the reaction molecules and reactive molecules is generated.

The impedance in the etching chamber 10 mainly depends on the resistance of the plasma region 30 and the plasma region 3.
It is determined by the capacity of a capacitor formed in the space between 0 and the Si substrate 110.

FIG. 3 shows the monitoring while the etching is in progress.
The change in impedance in the etching chamber
It is a graph shown. After the start of etching (T0), etch
The impedance gradually decreases as the
And suddenly changes a little after TII time from the start
I do. This rapid change is caused by the fact that the etching is performed on the underlying SiO 2 ₂
A change in the type of material to be etched after reaching the film 120
The reaction products in the plasma are changed by the
This is because the resistance value changes rapidly.

However, if attention is paid from the start of etching to the point TI or the point TII in the graph, only the a-Si film 30 is mainly etched during this period,
There is almost no change in the reaction product in the plasma, and the impedance changes due to a change in the capacitor component proportional to the etching amount of the gate electrode material (from T0 to TI
I).

When the gate electrode material on the substrate surface is etched, the distance between the plasma region and the substrate surface changes gradually. This change in distance mainly promotes a change in the capacitance of the space capacitor, and appears as a change in impedance.

Since the change in impedance between T0 and TII is proportional to the etching amount of the gate electrode material, if the impedance at the start of etching is r ₀ , and the impedance when the gate electrode material is arbitrarily cut off is r _e , This can be represented by the following approximation:

R _e = kd + r ₀ k: change rate of impedance with respect to etching amount d: etching amount r ₀ : impedance at the start of etching From the above equation, if k and r ₀ are grasped as initial characteristics, impedance is monitored. This indicates that the amount of etching of the a-Si 130 as the gate electrode material (remaining etching film thickness), that is, the degree of etching progress can be detected.

As described above, in this embodiment, since the etching amount is detected by monitoring the impedance in the etching chamber, the etching of the gate electrode material is performed regardless of whether the gate oxide film as the underlying layer is exposed. The degree of progress can be detected. Therefore, for example, at the point I (TI) in FIG.
A transition can be made to a second etching stage.

For example, as described above, in the region where the pattern circuit is rough (region B), when the etching residual film of the a-Si film 130 becomes about 100 °, the etching conditions are switched and the second etching stage is shifted. In this case, in the first etching step in which the etching rate is relatively high, the lower SiO ₂ film 120 has not been etched yet. In the second etching step, at least SiO 2
_{Since the} etching rate is low under the condition that the a-Si film 130 is selectively etched with respect to the _two films 120, even if the SiO ₂ film 120 is exposed in a region where the circuit pattern is coarse, significant etching does not easily proceed. Therefore, it is possible to avoid such a situation that the etching penetrates into the Si substrate 110 as in the related art, and as shown in FIG. 1C, it becomes possible to etch the a-Si film 130 with little damage to the underlying layer.

In the above-described example, the etching in the case where the a-Si film is used as the gate electrode material has been described, but the gate electrode material is not limited to this. For example, polycrystalline Si film or WSi
A film or the like may be used as the gate electrode material. When the material to be etched of the polycrystalline Si film is used, substantially the same etching conditions can be used as in the case of etching the a-Si film, using an etching gas mainly containing HBr gas.

When a WSi film is used, a-
A gate electrode is formed by lamination with a Si film or a polycrystalline Si film. In this case, in a first etching step of mainly etching an electrode material, a WSi film is etched first, and then an a-Si film is etched. Will be done. For etching the WSi film, for example, Cl ₂ ,
Using a mixed gas consisting of HCl, He and O ₂ , respectively, 20 sccm, 40 sccm, 100 sccm,
The etching conditions with a flow rate ratio of 5 sccm are used, and the subsequent etching of the a-Si film uses the above-described etching conditions mainly containing HBr gas. Thereafter, as a second etching step, O ₂ or N ₂ is added to the HBr gas, and the etching conditions are such that the etching rate of the base film is reduced.

FIG. 4 is an apparatus configuration diagram showing the structure of a dry etching apparatus provided with means for detecting the degree of progress of etching from a change in impedance in the etching chamber. FIG. 5 is a block diagram thereof.

As shown in FIG. 4, the dry etching apparatus includes an etching chamber 10 which is a sealed container for etching a material to be etched, and an etching chamber 1.
It has a high-frequency power supply 60 for generating plasma between the upper electrode 20A and the lower electrode 20B in the inner space 0, and a matching box 40 installed between the high-frequency power supply 60 and the etching chamber 10. Although not shown, the etching chamber 10 is provided with a gas supply unit and a gas exhaust unit, and an etching gas, a pressure atmosphere, and the like in the chamber are adjusted.

In the matching box 40, there is a matching circuit 50 for adjusting the impedance of the high frequency power supply (power supply side) so that the power from the high frequency power supply side (power supply side) is injected into the etching chamber side (load side) without loss. The impedance on the load side is 5 which is the impedance on the power supply side.
Adjusted to match 0Ω.

The impedance detecting device for detecting the progress of the etching comprises a probe 210 inserted in the matching box, and a computer terminal 220 for processing a signal output from the probe 210 and displaying the processed signal on a monitor. Also, in the computer or in FIG.
As shown in (1), an A / D converter 225 is provided outside the computer, and an analog signal monitored by the probe 210 is temporarily converted into a digital signal and input to the computer 220.

FIG. 6 is a diagram showing the configuration of the probe 210. As shown in the figure, the probe 210 is provided with a current sensor 214 and a voltage sensor 212 for measuring the voltage and current of the high-frequency circuit, and the impedance is calculated from the measured values of both. An analog signal output from the probe is converted into a digital signal by the A / D converter 225 and input to the computer 220. The computer 220 calculates the impedance value, performs a process for visualizing the impedance value on a monitor in a graph or the like, and performs a signal process for detecting a change in impedance buried in measurement noise.

As described above, according to the etching progress detecting method according to the present embodiment, the etching amount is calculated from the impedance change in the etching chamber. Can be adjusted. Therefore, in the two-step etching method, the end point of the first etching step can be adjusted to the point in time when the material to be etched remains at a constant film thickness. That is,
By using this method, the etching conditions can be automatically adjusted with high accuracy.

The above-described method of detecting the degree of progress of etching is not limited to the case of two-stage etching, and can be used as a method of adjusting the etching of a material to be etched when performing dry etching widely.

Although the present invention has been described in connection with the preferred embodiments, the present invention is not limited to the above-described preferred embodiments. It is apparent to those skilled in the art that various improvements and modifications are possible.

For example, the material to be etched in the above-described etching progress detection method is not limited to the gate electrode material or the conductive material. Even in the case of a non-conductive material, the etching causes a change in the space capacitor between the substrate surface and the plasma, so that the etching progress can be detected from the impedance change.

Further, in this embodiment described above, the etching using the parallel plate type etching chamber has been described.
Alternatively, the same effect can be obtained in a magnetron type etching chamber equipped with a magnet on the upper surface or both. In this case, the same effect can be obtained by using a permanent magnet or an electromagnet as the magnet provided on the side surface, the upper surface, or both of the etching chamber.

The same effect can be obtained in an inductively coupled etching chamber equipped with a high-frequency coil on the side surface, the upper surface, or both sides of the etching chamber.

In the above-described embodiment, 13.56 MHz is used as the frequency of the high-frequency power supplied to the chamber for plasma excitation. However, the value of the frequency is not limited to this and may take any value. Is possible. Also 2
More than two kinds of frequencies may be used in combination.

Further, in the above-described embodiment, of the parallel plate type electrodes, the cathode couple type in which the substrate is mounted on the electrode to which high frequency is applied is shown, but the substrate is mounted on the other electrode side. A mounted anode couple type device may be used.

[0069]

As described above, if the method for detecting the degree of progress of etching according to the present invention is used by using the apparatus for detecting the degree of progress of etching or the apparatus for detecting the degree of progress of etching according to the present invention, the material to be etched is Since the end point of the etching condition can be automatically detected while monitoring the remaining film thickness, the material to be etched can be sufficiently etched without excessively overetching the underlayer.

In particular, when the etching method of the present invention is used in the etching step of the gate electrode material necessary for the gate electrode processing step, excessive overetching of the gate insulating film can be prevented and the device yield can be increased. it can.

[Brief description of the drawings]

FIG. 1 is a diagram showing an etching step of a gate electrode material using an etching method according to the present embodiment.

FIG. 2 is a schematic diagram showing a state inside an etching chamber in the present embodiment.

FIG. 3 is a graph showing a relationship between an etching time and a change in impedance in an etching chamber in the present embodiment.

FIG. 4 is an apparatus configuration diagram showing a structure of a dry etching apparatus in the present embodiment.

FIG. 5 is a block diagram of a dry etching apparatus according to the present embodiment.

FIG. 6 is a device configuration diagram showing a structure of a probe included in the etching progress detection device in the present embodiment.

FIG. 7 is a view showing an etching step of a gate electrode material using a conventional etching method.

FIG. 8 is a graph showing a relationship between an etching time and a change in light emission intensity, obtained using a conventional light emission intensity monitor.

[Explanation of symbols]

Reference Signs List 10 etching chamber 20A upper electrode 20B lower electrode 30 plasma 40 matching box 50 matching circuit 60 high frequency power supply 110 Si substrate 120 SiO ₂ film 130 a-Si film 140 anti-reflection film 150 resist

Continuation of the front page (72) Inventor Hiroyuki Takada 33 Shinisogocho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture F-term in the Toshiba Production Technology Center (Reference) 4M104 BB01 BB28 CC05 DD67 GG09 HH20 5F004 BA04 BA13 BB11 BB13 CB07 CB15 DA00 DA04 DA26 DA29 DB01 DB03 EA28 EB02 5F040 DA01 DA19 DA30 DB01 DC01 EC07 EC09 FC22 FC23

Claims (9)

[Claims] 1. A method for detecting an etching progress, wherein an etching amount of a material to be etched is determined from a change in impedance in an etching chamber during dry etching. 2. An etching method for monitoring a change in impedance in an etching chamber and adjusting an etching condition of a material to be etched. 3. A first etching step in which the etching is completed before the underlayer of the material to be etched is exposed, and after the first etching step, any one of the conditions of gas type, pressure, high frequency power, and temperature is satisfied. And a second etching step of etching the material to be etched under conditions different from the first etching step until at least the underlayer is exposed. 4. The method according to claim 3, wherein the end of the first etching step is determined by monitoring a change in impedance in the etching chamber. 5. A process for forming a gate electrode, comprising: a first etching step of ending the etching of the gate electrode material before a gate insulating film serving as a base layer of the gate electrode material is exposed; A second etching step of performing etching of the gate electrode material at least until the gate insulating film is exposed, under a condition that the etching rate is lower than that of the first etching step. 6. The method according to claim 5, wherein the end of the first etching step is determined by monitoring a change in impedance in the etching chamber. 7. A means for measuring a high-frequency voltage and current applied between a pair of electrodes installed in an etching chamber, and an A for converting the measured voltage and current into a digital signal.
An etching progress detection device comprising: a / D converter; and means for calculating an impedance from the digital signal and obtaining an etching amount of the material to be etched from a change in the impedance. 8. A dry etching apparatus having means for detecting the progress of etching of a material to be etched from a change in impedance in an etching chamber during dry etching. 9. The means for detecting the degree of progress of etching includes: means for measuring a high-frequency voltage and current applied between a pair of electrodes provided in an etching chamber; and a digital signal indicating the measured voltage and current. A to convert to
The dry etching apparatus according to claim 8, further comprising: a / D converter; and means for calculating an impedance based on the digital signal and obtaining an etching amount of the material to be etched from a change in the impedance.