JP2010080868A - Method and device for plasma etching - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for plasma etching capable of controlling types or density of radical species and ion species existing in plasma, generating plasma suitable for processes, and switching plasma states by presence/absence of irradiation of light. <P>SOLUTION: An induction coil 2, a coil power supply 7, a bias electrode 4 and a bias power supply 8 excite gas existing in a process chamber 1 by a power supply to generate the plasma. A gas introduction line 5 introduces process gas into the process chamber 1 with fixed flow rate. In addition, the gas introduction line 5 and an exhaust means 6 hold pressure inside the process chamber constant. A light source 10 and a window 9 introduce light for inducing electrons, vibration or rotation excitation of gas molecules existing in the process chamber 1 into the process chamber 1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a plasma etching method and apparatus in semiconductor manufacturing and MEMS (Micro Electro Mechanical Systems) manufacturing.

  The plasma etching method and apparatus are used for forming a fine uneven shape on a substrate. In plasma, which can be generated by exciting gas molecules by applying electric power, atoms, molecules, or neutral molecules in a highly reactive state called radicals are ionized in addition to neutral molecules. Electrons and positive ions.

  By causing a chemical reaction or the like between the radicals or positive ions in the plasma and the substrate surface material, the part that caused the reaction is detached from the substrate surface. Hereinafter, this is referred to as an etching reaction.

  If a part covered with a protective film made of resin or the like on the substrate and a part where the substrate surface is exposed are formed and exposed to plasma containing a substance that causes an etching reaction with the substrate surface material, the protective film is removed. Then, a concavo-convex shape on the substrate can be formed, which is composed of a portion from which a part of the surface material is detached by the etching reaction and a portion protected by the protective film.

  When plasma is generated, an external force is applied to the space maintained at a certain pressure, ionizing neutral molecules in the space, and further accelerating the generated electrons. It is necessary to repeatedly generate ionization.

  At this time, if the external force to be applied is very strong, the energy of the electrons generated by ionization becomes very large. Therefore, the neutral molecules existing in the space are fragmented by repeating the collision with the electrons. Therefore, it is important to control the gas species enclosed in the chamber and the force applied from the outside in consideration of the etching reaction means.

  Further, in etching using plasma, a groove with a height of several hundred microns may be formed. A typical example is a deep etching technique of a silicon substrate used in a MEMS manufacturing process or the like. Silicon is very reactive with fluorine atoms. Therefore, it is known that when SF6, which is a representative fluorine source, is selected as a process gas and plasma etching is performed, etching proceeds at a very high speed.

  However, the etching of silicon by SF6 gas plasma is dominated by the spontaneous progress of the etching reaction, and the etching proceeds isotropically. Therefore, in the process using only SF6 gas, the shape with a high aspect ratio is used. Is difficult to form.

  Therefore, by repeating the etching step with fluorine (hereinafter referred to as the etching step) and the side wall protection of the concave and convex shape with the polymer (hereinafter referred to as the deposition step), the progress of isotropic etching is prevented and very deep. A process for forming grooves has been devised (see Patent Document 1).

  At present, a typical method for anisotropic deep etching of silicon is a method called a Bosch method, which employs SF6 as an etching step and CHF3 or C4F8 as a main process gas in a deposition step.

JP 7-503815 A

  However, in the Bosch method, the etching step and the deposition step must be repeated in a short time, and the process gas must be replaced each time, so that the plasma is unstable for a long time and is difficult to control. There is.

  Regardless of the Bosch method, it is difficult to efficiently generate radical species and ionic species that react with the substrate surface, competing with other radical species and ionic species. There is a problem of end.

  An object of the present invention is to control the kind or density of radical species and ion species present in plasma, to generate plasma suitable for the process, and to switch the plasma state depending on the presence or absence of light irradiation. It is an object of the present invention to provide a plasma etching method and apparatus capable of performing the above.

  The plasma etching method according to the first aspect of the present invention includes a step of introducing a process gas into the process chamber at a constant flow rate, a step of keeping the pressure inside the process chamber constant, and a power supply to the inside of the process chamber. In the plasma etching method, comprising the steps of exciting a gas existing in the substrate to generate plasma and etching a material to be etched with plasma, electron, vibration or rotational excitation of gas molecules existing in the process chamber is performed. The inducing light is introduced into the process chamber from a light source.

  A plasma etching method according to a second aspect of the present invention is the plasma etching method according to the first aspect, wherein the light source emits a laser beam.

  A plasma etching method according to a third aspect of the invention is characterized in that, in the first aspect of the invention, the light source emits light having a variable wavelength.

  According to a fourth aspect of the present invention, there is provided a plasma etching method according to the second aspect of the invention, wherein the light source emits a wavelength-variable laser beam.

  A plasma etching method according to a fifth aspect of the present invention is the plasma etching method according to any one of the second and fourth aspects, wherein the power source for exciting the gas and generating the plasma can be pulse-controlled, and The light source is a pulse laser.

  According to a sixth aspect of the present invention, there is provided a plasma etching apparatus comprising: a gas introduction means for introducing a process gas into a process chamber at a constant flow rate; a pressure holding means for keeping the pressure inside the process chamber constant; Plasma generating means for exciting a gas existing inside the process chamber to generate plasma, etching means for etching a material to be etched by the plasma, and electron, vibration or rotational excitation of gas molecules existing inside the process chamber Light introduction means for introducing light for inducing the light into the process chamber from a light source.

  According to a seventh aspect of the present invention, there is provided a plasma etching apparatus according to the sixth aspect, wherein the light source emits laser light.

  The plasma etching apparatus according to an eighth aspect of the present invention is the plasma etching apparatus according to the sixth aspect, wherein the light source emits light having a variable wavelength.

  A plasma etching apparatus according to a ninth aspect of the invention is characterized in that, in the seventh aspect of the invention, the light source emits a wavelength-variable laser beam.

  The plasma etching apparatus according to a tenth aspect of the present invention is the plasma etching apparatus according to any one of the seventh and ninth aspects, wherein the power source for exciting the gas and generating the plasma can be pulse-controlled, and The light source is a pulse laser.

  According to the present invention, by introducing light that induces electronic, vibrational or rotational excitation of molecules existing inside the process chamber, the quantum state of the molecules and the transition path of excitation caused by electron collision accompanying the molecules are changed. Since the behavior of excited molecules such as dissociation and ionization can be changed, the type or density of radical species and ion species present in the plasma is controlled, and a plasma suitable for the process is generated, and The plasma state can be switched depending on the presence or absence of light irradiation.

  Hereinafter, the best mode of the present invention will be described with reference to the drawings. The best mode of the present invention shown below is an external antenna system, and the present invention is applied to an inductively coupled plasma (ICP) etching apparatus in which an induction coil is installed in the upper part of a process chamber. Is the case. The present invention is applicable to a device in which an induction coil is installed on a side wall and an internal antenna type ICP etching device by blocking the optical axis of light that induces molecular electrons and vibrational excitation. it can. The present invention can also be applied to an etching apparatus having another plasma source by making the structure without blocking the optical axis.

(Embodiment 1)
FIG. 1 is a schematic view showing a plasma etching apparatus according to Embodiment 1 of the present invention. The plasma etching apparatus according to the first embodiment of the present invention is an external antenna type ICP etching apparatus, which includes a dielectric coil 2 disposed at the top of a process chamber 1 and covers the periphery of the dielectric coil 2. 3 is provided. A bias electrode 4 is disposed inside the process chamber 1. On the bias electrode 4, a substrate 100 that is an etching target material to be etched is installed.

  Further, the plasma etching apparatus includes a dielectric coil power source 7 and a bias power source 8 that are disposed outside the process chamber 1. The dielectric coil power supply 7 is connected to the dielectric coil 2 and applies predetermined power to the dielectric coil 2. The bias power supply 8 is connected to the bias electrode 4 and applies a predetermined bias voltage to the bias electrode 4.

  Two windows 9 are formed on the side wall of the process chamber 1 so as to face each other. A light source 10 is disposed outside one window 9. Light emitted from the light source 10 is introduced into the process chamber 1 from one window 9 and led out from the other window 9.

  Further, the plasma etching apparatus includes a gas introduction line 5 and an exhaust means 6. Process gas is introduced into the process chamber 1 from the gas introduction line 5 at a constant flow rate, and the exhaust speed is adjusted by the exhaust means 6 to control the pressure in the process chamber 1. The gas introduced from the gas introduction line 5 may be a gas consisting of a single molecule or a mixed gas, but contains molecules whose quantum levels are excited by light from the light source 10.

  The gas introduction line 5 constitutes gas introduction means for introducing a process gas into the process chamber 1 at a constant flow rate. Further, the gas introduction line 5 and the exhaust means 6 constitute a pressure holding means for keeping the pressure inside the process chamber constant.

  When the pressure inside the process chamber 1 becomes constant, a predetermined power is applied to the induction coil 2 by the induction coil power supply 7 and a predetermined bias voltage is applied to the bias electrode 4 by the bias power supply 8 to generate plasma. Let In plasma, due to collisions between electrons and molecules, the molecules transition to an excited state, causing dissociation and ionization. The transition due to this electron collision is based on a transition selection rule. In addition, the transition strength between certain levels is governed by the overlap of the wave functions of the levels before and after the transition. The wave function is expressed by the internuclear distance, time, quantum number, etc. of the atoms constituting the molecule. The substrate 100 that is the material to be etched is etched by plasma.

  The induction coil 2, the coil power source 7, the bias electrode 4 and the bias power source 8 constitute plasma generating means for generating plasma by exciting the gas existing inside the process chamber by the power source. The induction coil 2, the coil power source 7, the bias electrode 4 and the bias power source 8 constitute an etching means for etching the material to be etched by plasma.

  In this state, light emitted from the light source 10 is introduced into the process chamber 1 from one window 9. The light source 10 and the window 9 constitute light introducing means for introducing light that induces electron, vibration, or rotational excitation of gas molecules existing in the process chamber 1 into the process chamber 1.

  When a molecule that has transitioned from the ground state to the excited state due to absorption of the introduced light collides with an electron before relaxation, the transition selection rule is satisfied, and the wave function overlaps sufficiently to a level. This level is different from the level that is shifted from the ground state by direct electron collision.

  Accordingly, neutral molecules in the process chamber 1 are ionized by application of electric power, etc., and the emitted electrons collide with other neutral molecules, and the neutral molecules are excited in the plasma that repeats dissociation and ionization. If the quantum level of the molecule can be controlled before the electron collision by light irradiation, the transition path in the subsequent electron collision changes, and as a result, the behavior such as ionization and dissociation of the molecule after electron excitation changes. For this reason, it is possible to change radical species and ion species in the plasma depending on the presence or absence of light irradiation.

  Light from the light source 10 is introduced into the process chamber 1 to induce excitation of neutral molecules present in the plasma. If necessary, the light that has passed through the process chamber 1 is blocked by the light blocking means 11 installed outside the opposed window 9.

(Embodiment 2)
Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a schematic view showing a plasma etching apparatus according to Embodiment 2 of the present invention. In the second embodiment of the present invention, the same components as those in the first embodiment of the present invention are designated by the same reference numerals, and the description thereof is omitted.

  As shown in FIG. 2, the plasma etching apparatus according to the second embodiment of the present invention includes a laser light source 12 instead of the light source 10 in the first embodiment of the present invention. Since the laser light source 12 has a high photon density, the excitation efficiency of molecules increases.

  The quantized level is unique to each molecule, and when various molecular species are used, the light source used for exciting the molecule needs to be variable in wavelength. When the laser light source 12 excites only between specific quantum levels of a specific molecule, a laser beam that emits existing specific wavelength light such as a solid-state laser, a semiconductor laser, or a gas laser may be used. The laser light source 12 can increase the photon density within one pulse time by performing pulse control. In addition, the lifetime of the excited state of the molecule varies, and there are levels on the femtosecond scale.

(Embodiment 3)
Next, a third embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a schematic view showing a plasma etching apparatus according to Embodiment 3 of the present invention. In the third embodiment of the present invention, the same components as those in the first embodiment of the present invention are denoted by the same reference numerals, and the description thereof is omitted.

  As shown in FIG. 3, the plasma etching apparatus according to the third embodiment of the present invention includes a pulse laser light source 13 instead of the light source 10 in the first embodiment of the present invention, and induces instead of the induction coil power source 7. A coil pulse power supply 14 is provided.

  The laser light source 13 and the induction coil pulse power supply 14 are connected to the pulse generator 15 and can control the plasma state more efficiently by controlling the delay time of overlapping of each pulse.

  For example, when the dissociation of a specific molecular bond can be promoted by inducing photoexcitation of neutral molecules in the process chamber 1, the plasma control method performed by inducing photoexcitation is applied to a dry etching process or the like. be able to.

  Description will be made using the plasma etching apparatus of FIG. If the dissociation of a specific molecular bond is promoted by excitation by light irradiation and two-stage excitation of electron collision, the radical species generated by this dissociation is desired to act on etching. The laser light oscillated from is introduced into the process chamber 1 through the window 9. On the other hand, when it is not desired to cause the radical species generated by dissociation to act on the etching, the oscillation from the pulse laser light source 13 is stopped or the laser light oscillated between the pulse laser light source 13 and the window 9. Should just be blocked.

  A polyatomic molecule has a plurality of vibration modes, many of which can be excited by light in the infrared region. In each vibration mode, the vibration frequency is different, and if a monochromatic infrared laser is used, only a specific vibration mode can be excited. When a molecule is in the ground state for both electrons and vibration, when a specific vibration mode is excited, the wave function changes as described above.

  Therefore, by enlarging the wave function with the electronic state where vibration excitation occurs in the electronic ground state and specific chemical bonds in the polyatomic molecule are selectively dissociated, specific chemical bonds can be generated by electron collision excitation. Dissociation is selectively promoted, and radical species and ion species existing in the plasma are changed.

For example, a case where the density of iodine atoms in the plasma having an effect of adsorbing fluorine atoms is controlled by irradiation and blocking of the infrared laser by the above method from iodine compounds such as CH ₂ I ₂ , CH ₃ I, and CD ₃ I. explain.

Plasma discharge is performed using any one of the above compounds, SF ₆ , C ₄ F ₈ , and a mixed gas to generate plasma controlled so that the etching step using fluorine proceeds sufficiently.

  In order that excitation to an electronic state in which the C—I bond is dissociated is advantageous, by excitation of a specific vibration mode in the electron ground state by irradiation with an infrared laser, more iodine atoms are dissociated as plasma. As a result, the adsorption of fluorine by iodine atoms proceeds, and the progress of etching is suppressed.

On the other hand, behave in the plasma of C4F _8, polymer formed of a compound such as CF ₂ and the polymerization precursor is dominant, by forming a stable compound, the influence of the fluorine adsorbing by iodine atom Can be ignored.

  If the influence of laser light irradiation on the formation of the polymer composed of C and F is negligible, as a result, the deposition step by the polymer composed of C and F is dominant during the laser light irradiation. Become.

  By using this technique, the etching step that has been performed by switching the gas type introduced into the process chamber 1 and the deep etching of the silicon substrate by repeating the deposition process can be performed without switching the gas type. It is possible by switching by introducing and shutting off.

Example 1
Next, Embodiment 1 of the present invention will be described with reference to the drawings. FIG. 4 is a schematic diagram showing Example 1 of the present invention. In Example 1 of the present invention, the same components as those in Embodiment 3 of the present invention are denoted by the same reference numerals, and description thereof is omitted.

The plasma etching apparatus according to the first embodiment of the present invention includes an inductively coupled plasma generator 20, a process chamber 1, a dielectric coil 2, an insulating layer 3, a gas introduction line 5, an exhaust means 6, an electrode 21, a quartz window 22, Nd. A CO ₂ laser 23, a damper 24, a pulse generator 15, a plasma emission spectroscopic device 25, and an ICP coil power supply 28. The Nd: CO ₂ laser 23 is capable of pulse control.

A case will be described in which SF ₆ , O ₂ , and CD ₃ I are selected as the process gases, and these are introduced into the process chamber 1 and plasma discharged.

The plasma discharge was performed using an external antenna type inductively coupled (ICP) plasma generator 21 capable of pulse control. SF ₆ is set to a flow rate of 35 sccm, O ₂ is set to a flow rate of 5 sccm, CD ₃ I is set to a flow rate of 10 sccm, these mixed gases are introduced into the process chamber 1 from the gas introduction pipe 5, and the exhaust means 6 is adjusted. The internal pressure of the process chamber 1 was set to 10 mTorr.

A 10 MHz signal synchronized with no delay time is sent from the pulse generator 15 to the ICP coil power supply 28 and the Nd: CO ₂ laser 23 of the plasma generator 21. 350 W was applied to the induction coil 2 of the ICP, and plasma was generated.

  When the plasma emission spectrum was observed with the plasma emission spectrometer 25, a peak attributed to fluorine atoms at a wavelength of 704 nm was confirmed from the observed plurality of peaks.

A laser beam having a wavelength of about 10.5 μm corresponding to the vibration frequency of the ν2 vibration mode of CD ₃ I is oscillated at a repetition frequency of 10 MHz from the Nd: CO ₂ laser 23 and introduced into the process chamber 1 from the quartz window 22. It was.

By the irradiation of the laser beam by the Nd: CO ₂ laser 23, the peak intensity due to the fluorine atom having a wavelength of 704 nm is decreased in the plasma emission spectrometer 25 as compared with the case where the laser beam of the Nd: CO ₂ laser 23 is not irradiated. It was confirmed that.

The delay time between the pulse signal for applying power to the induction coil 2 of the ICP and the pulse signal for oscillation of the Nd: CO ₂ laser 23 was adjusted to the time when the peak intensity at the above-mentioned wavelength of 704 nm was most reduced.

  From the above, the density of fluorine atoms present in the plasma was successfully suppressed by the incidence of laser light having a wavelength of about 10.5 μm.

It is the schematic which shows the plasma etching apparatus which concerns on Embodiment 1 of this invention. It is the schematic which shows the plasma etching apparatus which concerns on Embodiment 2 of this invention. It is the schematic which shows the plasma etching apparatus which concerns on Embodiment 3 of this invention. It is the schematic which shows Example 1 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Process chamber 2 Inductive coil 3 Insulating layer 4 Bias electrode 5 Gas introduction line 6 Exhaust means 7 Inductive coil power supply 8 Bias power supply 9 Window 10 Light source 11 Light blocking means 12 Laser light source 13 Pulse laser light source 14 Inductive coil pulse power source 15 Pulse generator 20 Electrode 21 Inductively coupled plasma generator 22 Quartz window 23 Nd: CO ₂ laser 24 Damper 25 Plasma emission spectrometer 28 ICP coil power supply 29 Exhaust means 100 Substrate

Claims (10)

  A step of introducing a process gas into the process chamber at a constant flow rate; a step of maintaining a constant pressure in the process chamber; and a step of generating a plasma by exciting a gas present in the process chamber with a power source And a step of etching the material to be etched with plasma, wherein light that induces electron, vibration, or rotational excitation of gas molecules existing in the process chamber from a light source to the inside of the process chamber. A plasma etching method comprising introducing the plasma etching method.   The plasma etching method according to claim 1, wherein the light source emits laser light.   The plasma etching method according to claim 1, wherein the light source emits light having a variable wavelength.   The plasma etching method according to claim 2, wherein the light source emits a wavelength-variable laser beam.   5. The plasma etching method according to claim 2, wherein the power source for exciting the gas and generating the plasma can be pulse-controlled, and the light source is a pulse laser. A gas introduction means for introducing a process gas into the process chamber at a constant flow rate;
Pressure holding means for keeping the pressure inside the process chamber constant;
Plasma generating means for generating plasma by exciting a gas existing inside the process chamber by a power source;
Etching means for etching the material to be etched by the plasma;
Light introducing means for introducing light, which induces electron, vibration or rotational excitation of gas molecules existing in the process chamber, from the light source into the process chamber;
A plasma etching apparatus comprising:   The plasma etching apparatus according to claim 6, wherein the light source emits laser light.   The plasma etching apparatus according to claim 6, wherein the light source emits light having a variable wavelength.   The plasma etching apparatus according to claim 7, wherein the light source emits a wavelength-variable laser beam.   10. The plasma etching apparatus according to claim 7, wherein the power source that excites the gas and generates the plasma can be pulse-controlled, and the light source is a pulsed laser. 11.

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