JP2007250985A - Plasma etching method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-performance plasma etching method required for working etc. of MEMS devices, semiconductor devices, etc. <P>SOLUTION: The plasma etching method supplies treatment gas 1, containing fluorine gas (F<SB>2</SB>), to plasma generating chamber 2, alternately repeats application of high-frequency electric field and stopping of the application to generate a plasma 5, and irradiates a substrate 9 with the plasma 5 to perform substrate treatment. It is the characteristics of the method that (1) the time for applying high-frequency electric field is 20 to 70 μsec, and the time for stopping the application is 20 to 100 μsec, or that (2) the output of the high-frequency electric field to be applied to the substrate is 60 W or higher. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a plasma etching method for processing a substrate using plasma generated using a high-frequency electric field. More specifically, the present invention relates to a plasma etching method suitable for microfabrication in the manufacture of semiconductor elements and micromachine (MEMS) elements.

In a plasma process used for dry etching in a manufacturing process of a semiconductor device or the like, a fluorocarbon-based or inorganic fluoride-based gas (for example, carbon tetrafluoride gas (CF ₄
), Sulfur hexafluoride gas (SF ₆ ), etc.) are used in large quantities. However, fluorocarbon-based and inorganic fluoride-based gases are greenhouse gases having a high global warming potential (GWP), and are a major factor causing global warming along with carbon dioxide. Therefore, there is an urgent need to develop a new process using an alternative gas such as a fluorocarbon or inorganic fluoride in order to reduce the amount of greenhouse gas released to the environment.

On the other hand, in microfabrication in the manufacturing process of a micromachine (MEMS) device, which has been studied for practical use in recent years, a groove for a mechanical structure with a depth of several tens μm to 100 μm or more is formed in a Si substrate. An etching process for forming the film is required. In addition, in order to realize a space-efficient semiconductor device, development of a three-dimensional mounting device having a three-dimensional structure is in progress. For example, a configuration has been proposed in which a plurality of single crystal Si substrates on which logic is formed, single crystal Si substrates on which memories are formed, and the like are stacked and these substrates are connected by wiring. Such a three-dimensional mounting device requires extremely high-speed etching because it is necessary to form wiring holes of about φ10 to 70 μm in a Si substrate having a thickness of about 100 μm. In such a process, plasma etching technology is applied, but the requirements for etching characteristics are mainly the following three items.
(1) A high-speed etch rate is achieved.
(2) The perpendicularity of the etching profile is obtained.
(3) The etching wall has excellent smoothness.

  However, the two characteristics required in (1) and (2) are essentially in a trade-off relationship. This is because, in order to achieve a high etching rate, it is generally necessary to generate high-concentration F radicals in the plasma, but in an isotropic etching mainly based on radicals, the perpendicularity (anisotropy) of the etching profile. This is because cannot be obtained.

  In order to solve this problem, for example, an isotropic etching step and a side wall protective film forming step as disclosed in US Pat. No. 5,498,312 (Patent Document 1) are used as one cycle. Currently, a method called the Bosch process is repeatedly used. However, in such a process using an isotropic etching process, a stepped shape called a scallop is generated in principle on the etching wall surface, so that the etching wall surface smoothness required in the above (3) is obtained. There is a problem that can not be.

On the other hand, fluorine gas (F ₂ ) is supplied to the plasma generation chamber, plasma is generated by alternately repeating the application of the high frequency electric field (RF) and the stop of the application, and the substrate is irradiated with the plasma to perform the substrate processing. A plasma etching method has been proposed. As disclosed in Japanese Patent Application Laid-Open No. 2006-49817 (Patent Document 2), fluorine gas (F ₂ ) is supplied to the plasma generation chamber, and the application of the high-frequency electric field and the stop of the application are alternately repeated to generate plasma. (= Pulse time-modulated plasma) generates high concentrations of positive and negative ions (F ⁻ and F ⁺ ) in the plasma.
On the contrary, it has been clarified that the radical (F) concentration in the plasma is suppressed. In this method, unlike the Bosch process described above, Si etching that does not require a sidewall protective film forming step can be performed. By this method, the etching characteristics of the three items required in the above (1), (2) and (3) can be achieved simultaneously.

However, in the method disclosed in Japanese Patent Application Laid-Open No. 2006-49817 (Patent Document 2), although it is possible to vertically etch Si at an etch rate of about 1 μm / min, a MEMS device or a three-dimensional mounting device can be used. It has been difficult to achieve an ultra-high Si etch rate of several μm / min or more, which is now required for processing. In addition, it has been extremely difficult to etch silicon compounds such as quartz glass and silicate glass, which are difficult to obtain particularly high etching rates, at high speed. Therefore, there has been a strong demand for the development of an etching process that realizes a higher etching rate and has a small side etching and high practicality.
US Pat. No. 5,498,312 JP 2006-49817 A

  An object of the present invention is to provide a high-performance plasma etching method required for processing MEMS devices and semiconductor devices.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have succeeded in making a high-precision plasma etching method using a non-greenhouse gas possible for the first time.
That is, the present invention relates to the following matters.

(1) A processing gas containing fluorine gas (F ₂ ) is supplied to the plasma generation chamber, and plasma is generated by alternately repeating the application of the high-frequency electric field and the stop of the application, and the substrate is irradiated with the plasma. A plasma etching method for performing processing, wherein the time for applying the high-frequency electric field is 20 to 70 μsec, and the time for stopping the application is 20 to 100 μsec.

(2) A process gas containing fluorine gas (F ₂ ) is supplied to the plasma generation chamber, and plasma is generated by alternately repeating the application of the high-frequency electric field and the stop of the application, and the substrate is irradiated with the plasma. A plasma etching method for performing processing, wherein an output of a high-frequency electric field applied to the substrate is 60 W or more.

(3) A plasma etching method of silicon or a silicon compound using the plasma etching method according to (1) or (2).
(4) The plasma etching method according to (3), wherein the silicon compound is silicon oxide, silicon nitride, or silicate.

(5) A semiconductor device manufactured by the method according to any one of (1) to (4).
(6) A micromachine (MEMS) device manufactured by the method according to any one of (1) to (4).

  If the plasma etching method using a non-greenhouse gas according to the present invention is used, microfabrication in the production of next-generation MEMS devices and semiconductor devices can be realized.

Hereinafter, the plasma etching method according to the present invention will be described in detail.
An example of a pulse time modulation plasma etching apparatus capable of performing the plasma etching method according to the present invention is shown in FIG. The configuration of the pulse time modulation plasma etching apparatus of FIG. 1 will be described below.

  In the pulse time modulation plasma etching apparatus of FIG. 1, an inductively coupled plasma generating antenna 3 is spirally wound on the upper surface of a plasma generating / substrate processing chamber 2 in which a port for supplying a processing gas 1 is installed. The antenna 3 is connected to a high frequency power source 4 for plasma generation that can be pulse time modulated.

  When a high-frequency electric field is applied from the outside of the plasma generation / substrate processing chamber 2 supplied with the processing gas 1, plasma 5 is generated in the plasma generation / substrate processing chamber 2. By continuously applying the high-frequency electric field, continuous plasma can be generated, and by alternately repeating the application of the high-frequency electric field and the stop of the application, pulse time-modulated plasma can be generated. The application of the high frequency electric field and the stop of the application can be performed by applying a high frequency (RF) bias of 13.56 MHz as a discharge frequency to the antenna 3 from the high frequency power source 4 in a pulsed manner, for example. In addition, the time (pulse width) for alternately repeating the application (ON) of the high-frequency electric field and the stop (OFF) of the application can be arbitrarily set.

  The substrate 9 is bonded to the substrate holder 8 by an electrostatic chuck. An ion acceleration electrode 6 is installed under the substrate holding table 8, and a voltage application power source 7 is connected thereto. The substrate holding table 8 can be cooled by a cooling device (not shown), and the height of the substrate 9, that is, the distance between the substrate and the plasma generation unit is changed by an elevating device (not shown). Can do.

  The inside of the plasma generation / substrate processing chamber 2 is exhausted by an exhaust pump (not shown), and the exhaust gas 10 is detoxified by an exhaust gas processing device (not shown) and exhausted outside the system. The

In the first method of the present invention, for example, a processing gas containing fluorine gas (F ₂ ) is supplied to a plasma generation chamber using a pulse time modulation plasma etching apparatus as shown in FIG. A plasma etching method in which plasma is generated by alternately repeating the stop of application and the substrate, and the substrate is processed by irradiating the plasma to the substrate, and the time for applying the high-frequency electric field is 20 to 70 μsec, And the time which stops an application is 20-100 microseconds, It is characterized by the above-mentioned.

In a pulse time-modulated plasma of fluorine gas (F ₂ ) (plasma generated by alternately repeating application of a high-frequency electric field and stopping of application), the time for applying a high-frequency electric field (ON) is 20 to 70 μsec, In addition, under the pulse time modulation condition (pulse width) in which the application is stopped (OFF) time is 20 to 100 μsec, the total amount of ions (F ⁻ and F ⁺ ) generated in the plasma becomes large, and radicals (F ) Is suppressed.

  In the method of generating pulsed time-modulated plasma by turning the processing gas into plasma by alternately applying high-frequency electric field application (ON) and application stop (OFF), the combination of ON time and OFF time is arbitrarily set It is generally possible to repeat ON and OFF in the order of several tens of microseconds.

When a gas containing fluorine gas (F ₂ ) is used as the processing gas as in the present invention, O
It is desirable that the FF time is 20 to 100 μsec, more preferably 20 to 50 μsec. High-density electrons generated during the high-frequency electric field ON time dissociately adhere to fluorine gas (F ₂ ) during the high-frequency electrolysis OFF time, thereby generating a large amount of negative ions (F ⁻ ). When the OFF time is 20 μs or longer, the amount of negative ions (F ⁻ ) generated is almost saturated, so
When the time is shorter than the above range, negative ions are not sufficiently generated. If the OFF time exceeds the above range, the density of electrons in the plasma will decrease, making it difficult to discharge at the time of subsequent ON, and the phenomenon that the electron temperature will rapidly increase at the time of ON will cause the electrons to multiply, The effect of pulse time modulation tends to be hindered.

Further, when a gas containing fluorine gas (F ₂ ) is used as the processing gas as in the present invention, the ON time is preferably 20 to 70 μsec, more preferably 25 to 50 μsec. During the ON time of the high-frequency electric field in the pulse time-modulated plasma, electrons collide with fluorine gas (F ₂ ) to dissociate gas molecules, and a large amount of positive ions (F ⁺ ) are generated. To increase. If the ON time is shorter than the above range, the generation of the plasma itself tends to become unstable. If the ON time exceeds the above range, the amount of radicals in the plasma increases and the effect of pulse time modulation is hindered. There is a tendency.

In the second method of the present invention, for example, a processing gas containing fluorine gas (F ₂ ) is supplied to the plasma generation chamber using a pulse time modulation plasma etching apparatus as shown in FIG. A plasma etching method in which plasma is generated by alternately repeating application stop and irradiation, and the substrate is processed by irradiating the plasma to the substrate, and the output of the high-frequency electric field applied to the substrate is 60 W or more It is characterized by.

As described above, in a pulse-time-modulated plasma of fluorine gas (F ₂ ) (plasma generated by alternately repeating application of a high-frequency electric field and stopping of application), high-density positive and negative ions (F ⁻ and F ⁺ ) Produces. The method of the present invention is a plasma etching method in which substrate processing is performed by irradiating a generated plasma to a substrate. A high frequency electric field is applied to an ion acceleration electrode placed under the substrate and a high frequency electric field is applied to the substrate. As a result, positive and negative ions in the plasma are alternately accelerated perpendicularly to the direction of the substrate to be processed, thereby enabling vertical etching of the substrate to be processed. At this time, by setting the high frequency electric field (RF) applied to the substrate to 60 W or more, preferably 100 W or more, particularly preferably 150 W or more, the kinetic energy of ions irradiated on the substrate is increased, and the vertical workability is remarkably improved. .

In the pulse time-modulated plasma of fluorine gas (F ₂ ), ions (charged particles) generated in the plasma are compared with a gas such as sulfur hexafluoride gas (SF ₆ ) conventionally used as an etching gas for Si. It is considered that the effect of the high frequency electric field applied to the substrate appears remarkably. Under process conditions where the output of the high-frequency electric field applied to the substrate is less than 60 W, the side etching (under) spreads horizontally under the mask with respect to the etching rate of the vertical etching that digs in the vertical direction of the substrate along the mask pattern. The ratio of the etching rate of (cut) is increased, and the vertical processing performance is deteriorated.

  The cause of the progress of side etching is that radicals (F) coexisting in the plasma move randomly without directionality. When the material to be treated is silicon (Si), the reaction by Si and radicals proceeds relatively easily, so that side etching appears relatively remarkably. On the other hand, when the material to be treated is a silicon compound such as quartz glass or silicate glass, side etching hardly proceeds because of its poor reactivity with radicals having small kinetic energy.

In the method of generating pulse time-modulated plasma using a gas containing fluorine gas (F ₂ ) as a processing gas, the content concentration of fluorine gas (F ₂ ) in the processing gas is arbitrary depending on the purpose of the plasma processing method, etc. Can be set to It is preferable to use 100% by volume of fluorine gas (F ₂ ), but mixing with other kinds of gas such as inert gas such as halogen gas (Cl ₂ , Br ₂ ) or rare gas (He, Kr, Xe) Gas may be used.

  The plasma etching method of the present invention as described above can be suitably used as a technique for finely processing various substrate surfaces with low damage and high accuracy (anisotropy, selectivity, high speed). Furthermore, it can be suitably used as a plasma etching technique for silicon and silicon compounds which are important in the manufacturing process of MEMS devices and semiconductor devices. In particular, the method of the present invention using fluorine ions having high energy is extremely useful as a plasma etching technique for silicon compounds such as silicon oxide, silicon nitride, and silicates (for example, glassy sodium silicate) that are difficult to etch with radicals. It is valid.

By utilizing the microfabrication technology of the present invention, an unprecedented ultra-high performance semiconductor device and a novel MEMS device can be manufactured. Furthermore, since it is a non-greenhouse gas and inexpensive fluorine gas (F ₂ ) as the processing gas, it is an environmentally conscious and highly practical process, so its technical value is extremely high. It is.

[Example]
EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not limited to these Examples at all.

[Example 1]
Plasma etching of the substrate was performed with pulse time modulated plasma of fluorine gas (F ₂ ), the etching rates of silicon (Si) and silicon oxide (SiO ₂ ) were measured, and the Si etching shape was observed.

Using the pulse time modulation plasma etching apparatus shown in FIG. 1, fluorine gas (F ₂ ) is introduced as a processing gas 1 into the plasma generation / substrate processing chamber 2 at 30 ml / min. An RF bias of 13.56 MHz was applied as a discharge frequency to generate pulse time modulated plasma 5. The plasma output has a peak value (output during ON time) of 1 kW. The pressure in the plasma generation / substrate processing chamber 2 was 50 mTorr. Regarding the pulse time modulation condition (pulse width), the ON time was fixed to 50 μsec, and the OFF time dependency was investigated by variously changing the OFF time.

  An RF bias of 1 MHz was applied to the ion acceleration electrode 6 from the voltage application power source 7 with an output of 30 W. Thus, by applying an RF bias to the ion acceleration electrode 6, positive and negative ions generated in the plasma 5 are accelerated substantially perpendicularly to the direction of the substrate holder 8 and are irradiated onto the substrate 9.

The substrate holder 8 was placed at a position 50 mm below the plasma generation unit and cooled to −20 ° C. A silicon (Si) substrate or a silicon oxide (SiO ₂ ) surface is provided on the substrate holder 8.
A silicon (Si) substrate on which a thin film was deposited or a silicon (Si) substrate on which a silicon oxide (SiO ₂ ) thin film was deposited as an etching mask on the surface was placed, and plasma etching of the substrate was performed with the plasma 5. .

FIG. 2 shows the Si and SiO ₂ etch rates obtained in the experiment. FIG. 3 shows an SEM (scanning electron microscope) image obtained by observing the etching shape of Si.
[Example 2]
As a pulse time modulation condition (pulse width), the OFF time is fixed to 25 μs, and the ON time dependency is investigated by changing the ON time in various ways. Plasma etching of the substrate was performed by pulse time-modulated plasma of gas (F ₂ ). The etching rate of silicon (Si) and silicon oxide (SiO ₂ ) was measured, and the Si etching shape was observed. FIG. 4 shows the Si and SiO ₂ etch rates obtained in the experiment. Further, an SEM (scanning electron microscope) image obtained by observing the etching shape of Si is shown in FIG.

2 to 5, in the pulse time modulated plasma of fluorine gas (F ₂ ) (plasma generated by alternately repeating the application of the high frequency electric field and the stop of the application), the time for applying the high frequency electric field (ON) is 75 μm. It was found that the etching shape abnormality occurred when the time was increased to 2 seconds. In addition, when the application stop (OFF) time is 25 μsec, the Si etch rate is maximum and the anisotropy of the etching shape is increased (the etch rate in the direction perpendicular to the side direction etch rate = y The ratio, i.e. the value of y / x, is found to be minimal). From these results, by setting the pulse time modulation condition (pulse width) to ON time = 20 to 70 μsec and OFF time = 20 to 100 μsec, the ions (F ⁻ and F ⁺ ) generated in the plasma It became clear that the total amount became large and the generation of radical (F) was suppressed.

Example 3
The pulse time modulation condition (pulse width) is set to 50 μsec for the ON time and 50 μsec for the OFF time, and the output (power) of the 1 MHz RF bias applied to the ion acceleration electrode 6 from the voltage application power source 7 is varied. Thus, plasma etching of the substrate was performed with a pulse time-modulated plasma of fluorine gas (F ₂ ) in the same manner as in Example 1 except that the dependency on the lower RF bias power was investigated. Silicon (Si) and silicon oxide (SiO ₂
) Was measured, and the Si etching shape was observed. The Si and SiO ₂ etch rates obtained in the experiment are shown in FIG. In addition, S observed the etching shape of Si
An EM (scanning electron microscope) image is shown in FIG.

6 and 7, in the pulse time-modulated plasma of fluorine gas (F ₂ ) (plasma generated by alternately repeating the application of the high-frequency electric field and the stop of the application), the RF bias power applied to the substrate to be processed is determined. It was found that the etching rate of Si and SiO ₂ increased almost linearly with increasing, and the anisotropy of the Si etching shape also improved monotonously. In particular, a practical etching process can be expected when the RF bias applied to the substrate is 60 W or more so that the Si etch rate is about 1 μm / min or more.

Example 4
Fluorine gas (F ₂ ) introduction rate is 40 ml / min, pulse time modulation condition (pulse width) is ON time 50 μsec, OFF time is 25 μsec. The pulse time modulation of fluorine gas (F ₂ ) is performed in the same manner as in Example 1 except that the output (power) of 1 MHz RF bias is 100 W and the cooling temperature of the substrate holder 8 is −35 ° C. Plasma etching of the substrate was performed with plasma. An SEM (scanning electron microscope) image obtained by observing the etched shape of Si is shown in FIG. The Si etch rate obtained in the experiment is also shown in FIG.

Example 5
A fluorine gas (F ₂₎ is produced in the same manner as in Example 4 except that the output (power) of 1 MHz RF bias applied to the ion acceleration electrode 6 from the voltage application power source 7 is 150 W.
The substrate was plasma etched by the pulse time modulated plasma of FIG. 9 shows an SEM (scanning electron microscope) image obtained by observing the etching shape of Si. The Si etch rate obtained in the experiment is also shown in FIG.

8 and 9, in the pulse time modulated plasma of fluorine gas (F ₂ ) (plasma generated by alternately repeating the application of the high-frequency electric field and the stop of the application), the RF bias power applied to the substrate to be processed is shown. It was found that as the increase, the anisotropy of the Si etching shape was improved.

[Comparative Example 1]
Plasma etching of the substrate was performed by continuous plasma of fluorine gas (F ₂ ).
Except that the RF bias applied to the antenna 3 from the high-frequency power source 4 is a continuous discharge, continuous plasma is generated, and the pressure in the plasma generation / substrate processing chamber 2 is 40 mTorr, the same method as in Example 1 is used. Plasma etching of the substrate was performed by continuous plasma.

  An SEM (scanning electron microscope) image obtained by observing the etched shape of Si is shown in FIG. The Si etch rate obtained in the experiment is also shown in FIG. As is clear from FIG. 10, it has been confirmed that the continuous plasma that has been studied conventionally has an isotropic etching shape because large side etching (undercut) occurs.

[Comparative Example 2]
Plasma etching of the substrate was performed using pulse time-modulated plasma of sulfur hexafluoride gas (SF ₆ ).

Plasma generation by using processing gas 1 introduced into the plasma generation / substrate processing chamber 2 as sulfur hexafluoride gas (SF ₆ ), pulse time modulation conditions (pulse width), ON time 50 μsec, OFF time 50 μsec The substrate was etched by pulse time-modulated plasma of sulfur hexafluoride gas (SF ₆ ) in the same manner as in Example 1 except that the pressure in the substrate processing chamber 2 was 40 mTorr.

FIG. 11 shows an SEM (scanning electron microscope) image obtained by observing the etching shape of Si. The Si etch rate obtained in the experiment is also shown in FIG. As is apparent from FIG. 11, in the case of sulfur hexafluoride gas (SF ₆ ) that has been conventionally studied as an etching gas for Si,
Although a large Si etch rate can be realized, it has been confirmed that an isotropic etching shape is obtained because a large side etching (undercut) occurs.

It is the schematic which shows an example of the pulse time modulation plasma etching apparatus which can implement the plasma etching method concerning this invention. FIG. 3 shows the etching rates of silicon (Si) and silicon oxide (SiO ₂ ) measured by pulse time modulated plasma of fluorine gas (F ₂ ) measured in Example 1. FIG. Was observed in Example 1, a SEM observation image of the substrate is etched by the pulse time modulation plasma fluorine gas (F _2). FIG. 5 shows the etching rates of silicon (Si) and silicon oxide (SiO ₂ ) measured by pulse time-modulated plasma of fluorine gas (F ₂ ) measured in Example 2. FIG. Was observed in Example 2, a SEM observation image of the substrate is etched by the pulse time modulation plasma fluorine gas (F _2). FIG. 5 shows the etching rates of silicon (Si) and silicon oxide (SiO ₂ ) measured by pulse time modulated plasma of fluorine gas (F ₂ ) measured in Example 3. FIG. Was observed in Example 3, a SEM observation image of the substrate is etched by the pulse time modulation plasma fluorine gas (F _2). Was observed in Example 4, a SEM observation image of the substrate is etched by the pulse time modulation plasma fluorine gas (F _2). Was observed in Example 5, a SEM observation image of the substrate is etched by the pulse time modulation plasma fluorine gas (F _2). Was observed in Comparative Example 1, a SEM observation image of the substrate is etched by continuous plasma of fluorine gas (F _2). Was observed in Comparative Example 2, a SEM observation image of the substrate is etched by the pulse time modulation plasma sulfur hexafluoride gas (SF _6).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Process gas 2 Plasma production / substrate processing chamber 3 Inductively coupled plasma generation antenna 4 High frequency power source for plasma generation capable of pulse modulation 5 Plasma 6 Ion acceleration electrode 7 Voltage application power source 8 Substrate holder 9 Substrate 10 Exhaust gas

Claims (6)

A processing gas containing fluorine gas (F ₂ ) is supplied to the plasma generation chamber, and plasma is generated by alternately repeating the application of the high-frequency electric field and the stop of the application, and the substrate is irradiated with the plasma to perform the substrate processing. A plasma etching method comprising:
A plasma etching method, wherein the time for applying the high-frequency electric field is 20 to 70 μs and the time for stopping the application is 20 to 100 μs. A processing gas containing fluorine gas (F ₂ ) is supplied to the plasma generation chamber, and plasma is generated by alternately repeating the application of the high-frequency electric field and the stop of the application, and the substrate is irradiated with the plasma to perform the substrate processing. A plasma etching method comprising:
A plasma etching method, wherein an output of a high frequency electric field applied to the substrate is 60 W or more.   A plasma etching method for silicon or a silicon compound, wherein the plasma etching method according to claim 1 or 2 is used.   The plasma etching method according to claim 3, wherein the silicon compound is silicon oxide, silicon nitride, or silicate.   A semiconductor device manufactured by the method according to claim 1.   A micromachine (MEMS) device manufactured by the method according to claim 1.