JPH07226397A - Etching treatment method - Google Patents

Abstract

PURPOSE:To avoid the abnormal growth of a side wall protective film by a method wherein a plurality of gases including protective film forming gases which contribute to the formation of the side wall protective film of the etching portion of an etching apparatus are used and the supply flow rates of, at least, the side wall protective film forming gases are alternately changed in repeated pulse forms between the respective gases. CONSTITUTION:An etching apparatus 10 has a process chamber 12 in which a treated object 100 is subjected to dry-etching. One (20A) of the flow paths 20A and 20B of a piping 20 is connected to the supply source of argon gas which is inert gas for sputtering etching and the other path 20B is connected to the supply source of CF system gases such as CF4 and CHF3 which contain C and/or F and are examples of active ion generating gases for forming a side wall protective film. Especially, the flow rate of CF4 which generates active ions for forming the side wall protective film is adjusted by the control of a duty cycle, a pulse width and, further, a frequency to suppress the unnecessary growth of the side wall protective film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching method, and more particularly to a method for supplying a gas used in dry etching.

[0002]

2. Description of the Related Art As is well known, an etching step is a step of removing a surface layer of a semiconductor wafer or the like.

One of the methods used for such a surface layer etching treatment is reactive ion etching in which a physical sputtering action and a chemical etching action coexist.

For example, in the reactive ion etching used to remove the oxide film (SiO2) formed on the silicon substrate (Si), as shown in FIG. The side wall protective film A is formed on the inner peripheral wall of the portion etched by the adhesion.
Therefore, the side etching for removing the side wall is suppressed and the etching of the bottom portion is promoted, and the anisotropy can be improved.

By the way, in the reactive ion etching, the processing gas used for this processing is also selected because both physical sputtering and chemical etching are performed. As an example, argon gas (Ar), which is an element belonging to Group 0 of the periodic law, is used for sputtering.
And, in order to obtain active ions, C containing C and F
F-based gas may be used in each case.

When such a gas is used, it goes without saying that the side wall protective film is formed by a CF-based gas for obtaining active ions, but at the end of etching, it also forms on the lower layer surface of the etching layer. A film can be formed to improve the selection ratio.

The mixing ratio in the case of using the above gases is, for example, argon gas: CF series gas = 10:
It is about 1.

[0008]

However, in the case of the above reactive ion etching, as shown in FIG. 9, the hole to be etched may be blocked by the growth of the side wall protective film A. Therefore, there is a risk that the reactive gas cannot be exhausted or that the sputtering ions cannot enter, so that the hole having a predetermined shape cannot be formed. In particular, such a phenomenon is remarkable in trench etching having an aspect ratio (etching depth / opening width) of 1 or more.

Regarding the aspect ratio, in recent years, the diameter of the holes has been reduced, and as an example, it is necessary to form extremely deep and deep holes having a diameter of 0.5 μm or less and an aspect ratio of 2 or more. Is increasing.

Therefore, the thickness of the side wall protective film formed during etching tends to reach a state of closing the hole in a short time in many cases.

Therefore, when such etching becomes impossible, it is conceivable to stop the generation of plasma. However, such a treatment is required to start up the apparatus when the plasma is generated again. It takes time and the throughput deteriorates.

Therefore, in view of the above-mentioned problems in the conventional etching processing method, an object of the present invention is to provide a processing method capable of preventing the abnormal formation of the sidewall protection film and performing proper etching.

[0013]

In order to solve the above-mentioned problems, the invention according to claim 1 is a method of introducing a plurality of kinds of gases to etch an object to be processed, wherein the plurality of gases are etching. A protective film forming gas that contributes to the formation of a side wall protective film at a portion is included, and at least a supply step of repeatedly changing the supply flow rate of the side wall protective film forming gas in a pulsed manner among a plurality of types of gas is characterized. I am trying.

According to a second aspect of the present invention, in the first aspect, the gas for forming the sidewall protective film is a CF-based gas containing at least C and F, and the other gas is 0 in the periodic law.
It is an elemental gas belonging to the group, and is characterized in that the flow rate of the elemental gas of the group 0 is constant.

The invention according to claim 3 is the invention according to claim 1 or 2.
In the above, the pulse width corresponding to the flow rate level is the target, and the pulse width is supplied by pulse modulation which is made different during the etching period.

The invention according to claim 4 is the invention according to claim 1 or 2.
In the above, the side wall protective film forming gas is supplied by pulse modulation in which the pulse amplitude corresponding to the flow rate level is changed during the etching period.

The invention according to claim 5 is the invention according to claim 1 or 2.
In the above, the side wall protective film forming gas is characterized in that it is supplied by pulse modulation for varying the frequency corresponding to the flow rate level during the etching period.

According to a sixth aspect of the present invention, in a method of introducing a plurality of kinds of gases to etch an object to be processed, a valve provided in the middle of a supply path of a gas for forming a sidewall protective film and opening / closing of the valve. By using a piezo element for driving and a means for supplying a pulse-modulated voltage to the piezo element, the piezo element is driven by the pulse-modulated voltage to etch the flow rate of the sidewall protective film forming gas. It is characterized by controlling within the period.

[0019]

According to the present invention, the supply of the gas containing the active ions which forms the side wall protective film can be suppressed within the etching period. Thereby, the growth of the sidewall protective film can be suppressed or stopped. Therefore, the incidence of ions for etching and the exhaust of reaction products are not hindered.

Moreover, unlike the conventional one, since the etching process itself is not stopped, waste of time required for etching can be eliminated.

[0021]

Embodiments of the present invention will be described in detail below with reference to the embodiments shown in the drawings.

FIG. 1 is a schematic diagram showing an etched portion obtained by the etching method according to the present invention.

In FIG. 1, for example, a silicon substrate G1
The oxide film (SiO2) G2 formed above is processed into the hole P by reactive ion etching. This hole P
A side wall protective film G3 is formed on the inner peripheral wall by active ions, and a protective film G3 is slightly formed on the bottom part. The protective film G3 formed on the bottom part forms a base layer by incident sputtering ions. The scraping of G1 is prevented, which contributes to increasing the so-called selection ratio. Then, in the hole P, the sidewall protective film G3 grows as the etching process is performed, but the growth of the protective film G3 is suppressed or stopped by a method described later. In the figure, reference numeral G4 indicates a photoresist.

FIG. 2 shows the structure of an apparatus used for the above etching process.

That is, the etching apparatus 10 is provided with a process chamber 12 used for dry etching of an object to be processed 100 such as a semiconductor wafer and a liquid crystal display substrate.

The process chamber 12 has a parallel plate electrode structure in which the inside is set under a reduced pressure atmosphere and a counter electrode is arranged in the inside. In this embodiment, an upper electrode 14 and a lower electrode 16 facing the upper electrode 14 are provided as parallel plate electrodes.

Among these electrodes, the lower electrode 16 constitutes a mounting electrode for mounting and fixing the object to be processed, and the upper electrode 14 constitutes a counter electrode facing the mounting electrode.

In order to construct a reactive ion etching apparatus for the electrode having such a structure, the upper electrode 14 described above is used.
Is grounded, and the lower electrode 16 has an Rf power supply (not shown)
Are connected.

The upper electrode 14 is located on the wall surface of the cavity 12A formed on the upper wall surface of the process chamber 12 and facing the mounting electrode. And this cavity 1
A large number of gas ejection openings are formed on the surface forming the upper electrode 14 of 2A. A baffle plate 18 for gas rectification is arranged inside the cavity 12A. The cavity portion 12A communicates with the pipe 20 connected to the ceiling surface of the process chamber 12. As a result, the cavity 12A
The reactive ion etching gas introduced therein is set in an evenly dispersed state by the baffle plate 18, and then supplied into the process chamber 12 through the discharge opening.

Further, in FIG. 1, the susceptor forming the lower electrode 16 is provided so as to be able to move up and down between positions shown by a solid line and a two-dot chain line in the figure. Therefore, the object 100 to be processed can be loaded and unloaded when the object 100 is lowered, and the object 100 can be arranged at the processing position when the object 100 is raised.

The object to be processed 100 arranged at the processing position is
A gap that can set a plasma generation space is set between the upper electrode 14 and the upper electrode 14. The lower electrode 16 that can be moved to the carry-in / out position and the processing position of the object 100 by moving up and down in this way is inserted into the opening 12B formed in the lower wall of the process chamber 12.

Therefore, the opening 12B is blocked by the bellows 28 provided between the opening 12B and the lower electrode 16 to prevent dust and the like from entering from the outside. The process chamber 12 is provided with an exhaust unit 12C so that reaction products and processing gas can be exhausted.

On the other hand, the above-mentioned pipe 20 is branched midway, and one flow passage 20A serves as a supply source of argon gas (Ar) which is an inert gas for sputter etching, and the other flow passage 20B serves. A CF-based gas containing C or F, which is an example of a gas for generating an active ion for forming a side wall protective film (hereinafter, a gas for forming a side wall protective film is referred to as an active ion generating gas), for example, CF4, It is connected to a gas supply source such as CHF3.

Flow rate setting means 22 is arranged in the flow path of the gas for generating active ions.

The flow rate setting means 22 is a flow rate adjusting means including a stop of the supply of the gas for generating active ions. For example, the flow rate setting means 22 is controlled by the operating state of the flow path opening adjusting member 24 using a piezo element (not shown). A valve that opens and closes the passage is used. The initial state of the piezo element is a state in which no voltage is applied and the piezoelectric element is not deformed, whereby the flow rate setting means 22 is set to a state in which the flow path of the active ion generating gas is completely closed. ing.

The flow path opening adjusting member 24 described above is used.
Is equipped with a mechanism for amplifying the deformation amount of the piezo element, and amplifies the deformation amount of the piezo element when the drive voltage is output from the control unit 26 shown in FIG. It is designed to communicate. The piezo element is used not only as a single element but also as a laminate to increase the amount of deformation, if necessary.

The adjustment of the flow path opening degree in this case means that at least one or both of the flow path opening / closing time and the opening / closing amount are set.

Therefore, the control unit 26 starts the control from the time when the plasma is generated and the etching process is started. Specifically, the driving voltage of the piezo element is set to a high / low binary output signal. Pulse control is performed. In the pulse control, pulse width control (PWM) or amplitude control (PAM) is targeted for pulse modulation.

The flow rate setting means 22 can set the flow path to an open state when a high level voltage is output from the control unit 26, and can set the flow path to a closed state when a low level voltage is output. You can do it. When setting the closed state, the control unit 26 can select whether the drive voltage is not output or a slight voltage is output.

In this embodiment, when the drive voltage is not output, the piezo element is not deformed and the flow path is completely closed. When the drive voltage is output, the piezo element is slightly closed. It is designed to cause deformation. In the latter case, the minimum amount of gas for active ion generation required to maintain plasma generation is supplied.

FIG. 4 is a timing chart when controlling the duty cycle for the pulse width.
In this case, a constant amount of argon gas, which is an inert gas, is constantly supplied, and CH, which is an example of a gas for generating active ions, is used.
The case where the flow rates of F3 and CF4 are adjusted is shown.
In this case, when the high level voltage is output, the flow rate adjusting means 22 is opened via the flow path opening adjusting member 24, and when the low level is output, the flow rate adjusting means 22 is opened. Is displaced toward the side that closes the gas flow path. In the case shown in FIG. 4, a minute voltage is constantly applied to the piezo element even when a low level signal is output. As a result, the flow rate adjusting means 22 is not in the fully closed state, and at least gas capable of generating plasma can be supplied.

On the other hand, FIG. 5 is a timing chart when controlling the pulse amplitude, and the opening / closing amount of the flow rate adjusting means 22 is determined according to the amplitude.

FIG. 6 is a timing chart in which the cases shown in FIGS. 4 and 5 are combined. In this case as well, even when a low-level signal is output, the gas flow path is not fully closed. At this point, a sufficient amount of gas is generated to generate plasma.

As described above, by supplying the active ion generating gas to continue the generation of plasma and forming the side wall protective film to some extent on the bottom of the etching site,
It becomes possible to maintain a large selection ratio.

Further, regarding the control of opening and closing of the flow path by the flow rate adjusting means 22, not only the flow rate of the active ion generating gas is controlled on the basis of the above-described etching start time, but also the passage of time from the plasma generation start time, for example. It is also possible to adjust the flow rate by using the correlation between the side wall protective film and the growth state as data. As an example, as shown in FIG. 7, the flow rate adjusting member 22 is kept open within a predetermined time (t). Then, the duty cycle of the output pulse or the amplitude of the output pulse described above can be controlled at the time when a predetermined time has elapsed, in other words, at the time when it can be assumed that the opening is closed by the sidewall protection film.

In FIG. 3, reference numeral 28 is a manual switch, and this switch 28 sets the supply state of the active ion generating gas by observing the growth state of the side wall protective film in section, for example, with a microscope. It is used to Regarding the control in this case, the flow rate of the active ion generating gas is arbitrarily adjusted while observing regardless of the information in the control unit 26.

Further, in the timing charts shown in FIGS. 4 to 6, the flow rates of CHF3 and CF4, which are active ion generating gases, were controlled under the same conditions. Among these gases, in particular, they contribute to the formation of the side wall protective film. It is also possible to extract only the gas to be used and control the flow rate.

FIG. 7 is a timing chart showing this case. In particular, the duty cycle, pulse width, or frequency described above should be adjusted with respect to the flow rate of CF4 which produces active ions for forming the sidewall protection film. The supply amount is adjusted by to suppress the unnecessary growth of the side wall protective film.

In this embodiment, by changing the output cycle of the above-mentioned binary signal, that is, the frequency,
It is also possible to adjust the flow rate of the active ion generating gas by changing the number of times the flow rate setting means 22 is opened and closed. The frequency in this case is selected from the range of 100 Hz to 10 KHz. The frequency in such a range is a desirable value in order to secure the exhaust time as well as the incidence of the sputtering ions.

Since this embodiment has the above-mentioned structure,
A process gas is supplied into the chamber 12. That is,
Argon gas for generating plasma and CHF3 and CF4 as active ion generating gas are supplied from the pipe 20, and plasma is generated by supplying high frequency power to the lower electrode 16.

On the other hand, at the etching site, the flow rate of the active ion generating gas is adjusted after the etching is started. By this adjustment, the growth of the side wall protective film is suppressed at the etching site, so that the etching site is not blocked, thereby allowing the injection of sputter etching ions and the exhaustion of reaction products. The size of the opening is secured.

As described above, according to this embodiment, the supply amount is adjusted by repeatedly supplying the gas for active ion generation in a pulsed manner, so that the pulse rises, for example. At a high level, it is possible to use this time as a time for promoting the exhaust of the etched reaction product.

[0053]

As described above, according to the present invention, it is possible to prevent the etching site from being blocked by the sidewall protection film. That is, it is possible to suppress the growth of the sidewall protective film by adjusting the supply amount of the gas containing the active ions that forms the sidewall protective film from the time when the etching is started.

Further, according to the present invention, when removing the side wall protective film formed at the etched portion, it is sufficient to simply adjust the flow rate of the active ion generating gas, so that the plasma generation is continued. The sidewall protection film can be removed. As a result, the etching process does not have to be interrupted, so that it is possible to prevent deterioration of throughput.

[Brief description of drawings]

FIG. 1 is a schematic view showing a structure of an etching site formed by a processing method according to the present invention.

FIG. 2 is a schematic diagram for explaining an outline of an apparatus used in the processing method according to the present invention.

3 is a block diagram showing a configuration of a control unit used in the apparatus shown in FIG.

FIG. 4 is a timing chart for explaining a state of setting a supply state of a gas for generating active ions, which is set by the control unit shown in FIG.

5 is a timing chart for explaining a state of setting another supply state of the active ion generating gas, which is set by the control unit shown in FIG.

FIG. 6 is a timing chart for explaining a state of setting another supply state of the gas for generating active ions, which is set by the control unit shown in FIG.

7 is a timing chart for explaining a state of setting another supply state of the gas for generating active ions, which is set by the control unit shown in FIG.

FIG. 8 is a schematic view showing a part of a processing process according to an example of an etching method.

FIG. 9 is a schematic diagram for explaining problems in the etching method shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Etching apparatus 12 Process chamber 14 Upper electrode 16 Lower electrode 20 Piping 20A Sputter etching gas path 20B Active ion generating gas path 22 Flow rate adjusting valve 26 Control section

Claims (6)

[Claims] 1. A method of introducing a plurality of kinds of gases to etch an object to be processed, wherein the plurality of gases include a protective film forming gas that contributes to forming a side wall protective film at an etching site, and at least the side wall. An etching treatment method comprising a step of changing a supply flow rate of a protective film forming gas between a plurality of kinds of gases by pulse modulation and supplying the same. 2. The side wall protective film forming gas according to claim 1, wherein at least C and F are used.
Is a CF-based gas containing other elements, the other gas is an element gas belonging to Group 0 of the periodic law, and the flow rate of the element gas of Group 0 is constant. 3. The etching according to claim 1 or 2, wherein the sidewall protective film forming gas is supplied by pulse modulation for varying a pulse width corresponding to a flow rate level thereof during an etching period. Processing method. 4. The etching according to claim 1 or 2, wherein the sidewall protective film forming gas is supplied by pulse modulation for varying a pulse amplitude corresponding to a flow rate level thereof during an etching period. Processing method. 5. The etching process according to claim 1, wherein the sidewall protective film forming gas is supplied by pulse modulation that makes a frequency corresponding to a flow rate level thereof different during an etching period. Method. 6. A method of introducing a plurality of kinds of gases to etch an object to be processed, comprising: a valve provided in a supply path of a gas for forming a sidewall protective film; and a piezo element for opening / closing the valve. Controlling the flow rate of the sidewall protective film forming gas within the etching period by driving the piezo element by the pulse-modulated voltage using a means for supplying a pulse-modulated voltage to the piezo element. An etching method characterized by the above.