JP6533998B2 - Dry etching method - Google Patents

Description

  The present invention relates to a dry etching method. Specifically, the present invention relates to a dry etching method capable of realizing an excellent etching rate and capable of processing at a high aspect ratio.

  The use of a stacked integrated circuit (3D-IC) formed by stacking a plurality of chips has attracted attention. In stacked integrated circuits, chips are connected via through silicon vias (TSVs: Through Silicon Vias), and high integration can be achieved without depending on the rules of miniaturization thus far, so a conventional integrated circuit can be used. Also, miniaturization, speeding up, multifunctionalization and power saving can be realized.

  The TSV is formed by forming a through hole for TSV in a silicon wafer, forming a seed layer in the through hole, and filling with copper or the like to be an electrode by electroplating. By forming the seed layer, the through holes are easily filled with copper or the like to be an electrode.

  Here, an etching method generally called a Bosch process is considered to be advantageous for the processing of through holes for TSV. The Bosch process is a dry etching method in which etching of silicon and deposition of a polymer for sidewall protection are alternately repeated, and etching with a high aspect ratio is enabled.

  In the Bosch process, it is possible to form a through hole having a high aspect ratio by repeating the replacement of different gases, repeating the bottom etching process of the hole and the protective film forming process for protecting the side wall of the etching hole every few seconds. However, when the time of gas replacement takes a long time, the side wall of the through-hole has an unevenness called scallop. In the scallop region, a shadowed portion occurs when the through hole is viewed from the normal direction of the wafer surface, where the seed layer formed in the process such as sputtering is not formed on the side wall of the through hole and adhesion of the electrode material Failure may occur. As a result, a void may be generated in the electrode at the time of plating formation, which may lead to deterioration of the quality of the TSV.

  There are also methods for reducing the time interval of gas replacement and reducing scallop, but when forming a hole with a high aspect ratio, it takes a long time for the net etching step. Therefore, the production efficiency of the TSV is lowered and it is difficult to adopt it industrially.

  Further, in the dry etching method which does not perform gas replacement instead of the Bosch process, it is considered difficult to obtain etching holes having a high aspect ratio when obtaining a high etching rate.

  Under such circumstances, there is an etching apparatus that attempts to achieve both a high etching rate and formation of holes with a high aspect ratio. For example, an etching apparatus described in Patent Document 1 has been proposed.

  Here, the etching apparatus described in Patent Document 1 includes an insulating first chamber provided with a helicon wave type plasma generation unit, and a conductive second chamber. The first chamber and the second chamber are in communication via the opening.

  An inert gas is introduced into the first chamber, and the inert gas is turned into a plasma by the action of the helicon wave type plasma generation unit. In the second chamber, a reactive gas is introduced, and plasma electrons in the first chamber excite the reactive gas to generate active species.

  Active species in the second chamber are drawn to the side of the mounting table which is at a negative potential due to the self bias effect, and are adsorbed on the oxide film of the wafer. Furthermore, ion irradiation of the inert gas is performed along the direction of the electric field directed to the mounting table side, the active species react with the oxide film by ion assist, and chemical etching is promoted in a low pressure atmosphere.

Unexamined-Japanese-Patent No. 6-89880

D. L. Flamm et al .: J. Appl. Phys 52, 3633 (1981)

  However, the etching apparatus described in Patent Document 1 is not capable of obtaining an etching rate that can realize the production efficiency necessary for industrially manufacturing TSV.

  Further, it is considered that there is room for improvement in forming a through hole having a high aspect ratio and excellent anisotropy.

  The present invention has been made in view of the above points, and it is an object of the present invention to provide a dry etching method capable of realizing an excellent etching rate and capable of processing at a high aspect ratio.

  The estimation of the total amount of radicals, the specification of the plasma source for obtaining the plasma density, the design guideline of the vacuum system for obtaining the total amount of radicals, and the optimum shape of the through hole, which are the premise of the configuration of the present invention to achieve the above object Will be described below.

  Here, a control principle of a plasma process for realizing a silicon etching rate of 50 μm / min using a dry etching method to which the present invention is applied will be described.

(1) Estimation of Total Amount of Radicals As through holes for TSVs necessary for mass production of stacked integrated circuits, it is assumed that through holes having a diameter of 20 μm and a depth of 50 μm can be formed in one minute. The processing speed for dry etching of silicon wafers by conventional fluorine radicals is at most 5.0 μm / min in the Bosch process, and in order to improve this to 50 μm / min, supply of radicals which is reaction-limited in dry etching It will be necessary to increase the amount.

The etching rate ER _si of silicon by fluorine radicals is calculated by the following [Equation 1] from the description of Non-Patent Document 1.

When processing a through hole having a diameter of 20 μm and a depth of 50 μm in one minute, it is expressed as ER _si = 50 μm / min. Further, assuming that the room temperature is 25 ° C. (-300 K) and the ion assist effect is 10, the necessary fluorine radical density is represented by the following [Equation 2]. In addition, the description of the nonpatent literature 1 was referred to about the ion assist effect.

  Assuming that the radical generation efficiency is 65%, considering that the radical generation efficiency from gas is several tens%, the gas density required for 1 minute to obtain the above-mentioned [Equation 2] fluorine radical density is , It is represented by the following [Equation 3].

Here, as described in [Equation 3], 10 ¹⁷ cm ^-3 is a gas represented by pressure (p), molecular number density (n), absolute temperature (T), and Boltzmann constant (k) of the gas. When calculated from the state equation, p = 1 kPa. Here, T to 300K. That is, it is understood that the supply of 10 ¹⁷ cm ^-3 gas particles per minute is necessary as the gas supply amount necessary to realize ER _si = 50 μm / min. Also, based on the possibility that the radical generation efficiency does not reach 65%, it is assumed that 10 times the amount of 10 ¹⁸ cm ^-3 radicals equivalent is supplied per minute as a gas supply with allowance. That is, 10 ¹⁸ cm ¹³ per minute was defined as the required gas particle supply amount as a guide for device design capable of achieving ER _si = 50 μm / min.

Since the general ionization degree of capacitively coupled plasma (CCP) method, which is a typical plasma source, is 10 ^-3 %, the aforementioned gas particle supply rate is 10 ¹⁸ cm ^-3 per minute. Considering the case, the plasma density required to obtain the fluorine radical density is the value of the following [Equation 4].

  However, in order to obtain the plasma density shown in [Equation 4] by the general CCP method, high power of 10 kW or more is required, and power supply facilities and the like become expensive, and plasma is generated efficiently. Is difficult. Further, even if plasma can be generated, the steady-state gas pressure becomes high, the ion scattering phenomenon occurs due to the collision between the ions and the neutral particles, and the probability that the ions are incident on the side wall of the through hole becomes high. Similarly, when the steady-state gas pressure increases, the probability that radicals enter the side wall of the through hole also increases. That is, it becomes difficult to enhance the anisotropy of the through hole processed by etching.

(2) Specification of plasma source for obtaining high plasma density From the above point, it is possible to generate plasma with high density even with power of several kW, and a plasma generation source capable of keeping steady gas pressure low is required. It becomes. More specifically, it satisfies a steady gas pressure of 0.1 to 1.0 Pa, which can secure both the plasma generation method capable of achieving a plasma density of 10 ¹⁸ (m ^-3 ) and the anisotropy of the through holes formed. It is necessary to use a suitable plasma source. The steady gas pressure in the range of 0.1 to 1.0 Pa is difficult to cause ion and radical scattering and has a diameter of 20 μm and a diameter of 50 μm at which the shape of the through hole can be processed. It is a range.

  In addition, when the steady gas pressure is increased to increase the gas supply amount, the mean free path of ions and radicals becomes short, and a scattering phenomenon that causes the etching of the side wall of the through hole is likely to occur. It becomes difficult to form. Therefore, it is required to lower the steady gas pressure.

  From the type of plasma source, as a plasma source satisfying the above conditions, a Helicon wave excited plasma (HWP: Helicon Wave Plasma) method or an electron cyclotron resonance plasma (ECR: Electron Cyclotron Resonance) method can be mentioned. These plasma sources are capable of densifying plasma in the range where the steady gas pressure is low.

(3) Design Guideline of Vacuum System for Obtaining Total Radical Amount Subsequently, about the vacuum system for supplying 10 ¹⁸ cm ^-3 per minute, which is the gas particle supply amount necessary for 1 minute described above, into the vacuum vessel explain. First, there is a gas residence time (τ) as a quantity representing the ease of gas flow in the vacuum vessel. Assuming that the gas particle supply rate of 10 ¹⁸ cm ^-3 (corresponding to filling -167 Pa per minute) necessary for 1 minute can be obtained at a steady gas pressure of 0.1 Pa, the condition is that 167 Pa / 0 It can be seen that it is necessary to carry out 1670 gas purges in the vacuum vessel at 1 Pa per second at 1 Pa. That is, the gas residence time τ (sec) is calculated to be 1/1670 to 0.5 msec. Here, the gas residence time was calculated by setting the gas particle supply rate to 10 ¹⁸ cm ⁻³ per minute and the steady gas pressure to 0.1 Pa, but the gas supply rate was calculated to obtain a desired etching rate. It can also be set as a gas equivalent (eg 10 ¹⁷ cm ^-3 per minute). Also, the steady gas pressure can be set similarly (when obtaining 50 μm / min, it will be 1.0 Pa or more). The gas particles per 10 ¹⁷ cm ^-3 1 minute was charged, the constant gas pressure as 1.0 Pa, calculating the gas residence time tau, the τ (sec) ~60msec.

  Subsequently, given the gas pressure p (Pa) and the volume V (L) of the vacuum vessel, consider the flow rate (Q) of the introduced gas necessary to achieve the etching rate of 50 μm / min. The steady gas pressure p (Pa) with respect to the flow rate of the gas to be introduced is expressed by the following [Equation 5].

  In the above [Equation 5], since q is 1/1000 or less of Q in the usual case and can be almost ignored, it can be approximated as p ̃Q / S. Here, since the residence time τ (sec) is expressed by the equation τ = V / S, the following equation 6 is obtained.

  Here, assuming that the steady gas pressure p is 0.1 Pa and the vacuum vessel volume is V to 0.5 L (cylindrical vacuum vessel having a diameter of about 80 mm and a height of about 100 mm), it is introduced to obtain τ to 0.5 msec. The gas flow rate Q (Pa · L / s) to be obtained is Q to 100 (Pa · L / s) according to the equation [6]. Further, when converted as 1 Pa · L / s = 0.592 sccm, Q is 60 sccm. The gas flow rate Q is an amount determined when assuming the vacuum vessel volume, and the amount of supplied gas per unit time required to obtain an etching rate of 50 μm / min, and etching of 50 μm / min. The gas flow rate is not limited as long as it satisfies the use of a plasma source to obtain a radical generation rate required to obtain a rate.

  The value 60 sccm of the flow rate Q of the gas introduced above is generally below the value of Q = 100 sccm, which is a standard of the amount of gas used in the etching process, and it is an industrially applicable gas. It is used.

Moreover, in the present invention, a vacuum system capable of satisfying a gas particle supply rate of 10 ¹⁸ cm ^-3 (or 10 ¹⁷ cm ^-3 per minute) required for one minute and a steady gas pressure of 0.1 to 1.0 Pa is provided. It is important to be realized, and as mentioned above, the volume of the vacuum vessel of V to 0.5 L is not limited to a small one. For example, even if the volume is a large vacuum vessel, an etching rate of 50 μm / min can be realized by using a vacuum system having an effective pumping speed such that the gas supply amount and the steady gas pressure can be satisfied. is there.

  As an advantage of using a small vacuum vessel with a small volume, even when the steady gas pressure is set to 0.1 to 1.0 Pa, it can be introduced into the vessel per minute without using a vacuum pump with a large displacement. The point is that the total amount of gas can be increased. Since the total amount of gas that can be introduced into the container per minute can be easily obtained without using a pump having a large displacement, the total amount of radicals necessary to obtain a high etching rate can be easily obtained.

(4) Optimization of Through Hole Shape According to the contents described above, it is possible to obtain a high etching rate, but in the present invention, it is also important to form a through hole having a high aspect ratio. In order to efficiently form a small diameter and deep through hole, it is necessary to reduce the frequency of elastic scattering of ions due to collision of ions and gas neutral particles and to guide the ions to the bottom of the through hole at a straight incident angle There is.

  Specifically, by making the gas pressure in the vacuum vessel as low as possible, the collision frequency of the ions with the neutral particles of the gas is reduced to make elastic scattering of the ions less likely to occur. The lower the pressure, the better, and within the range of a steady gas pressure of 0.1 to 1.0 Pa, elastic scattering of ions hardly occurs. However, a steady gas pressure of about 0.1 Pa is required to obtain a high density by a Helicon Wave Excited Plasma (HWP) method or an Electron Cyclotron Resonance Plasma (ECR) method.

  Further, by forming a linear magnetic field in the vacuum chamber and causing ions to be incident substantially perpendicularly to the wafer surface, it is possible to control the ion trajectory that enhances the ion assist effect, and to efficiently guide the ions to the bottom of the through hole. Can. As a result, high-speed etching of highly anisotropic through holes becomes possible.

Based on the above points, in order to achieve the above object, the dry etching method of the present invention is characterized in that the mean free path of the ions generated by the plasma generating portion generating the electromagnetic field excited plasma in the vacuum chamber is the surface of the material to be treated So that the steady gas pressure is in the range of 0.1 to 1.0 Pa, and the total amount of gas supplied per minute is 1.0 × 10 ¹⁷ cm ⁻³ or more. A gas supply step of supplying a gas into the vacuum chamber; an ion induction step of guiding ions generated by the plasma generation unit to a material to be treated located on a sample support placed in the vacuum chamber; And an etching process step of radicalizing the gas and etching the surface to be treated of the material to be treated, by setting the plasma density in the vicinity of the material to 10 ¹⁸ m ⁻³ or more.

Here, it is necessary for high etching rate processing by the gas supply process in which the mean free path of ions generated by the plasma generation unit for generating the electromagnetic field excitation plasma in the vacuum chamber is longer than the sheath thickness generated on the surface of the workpiece It is possible to obtain an ion density that can realize a high ion assist effect. More specifically, a radical density for achieving an etching rate of ER _si = 50 μm / min, which is a value of an etching rate for 1 minute when processing a silicon wafer with fluorine radicals, can be obtained.
The mean free path of ions is the average value of the distance that ions generated in the plasma can travel without being disturbed by the collision with the scattering source. The sheath thickness is the thickness of a space in the vicinity of a wafer to be treated, in which a sheath electric field acts. If the mean free path of ions is longer than the sheath thickness generated on the surface of the material to be treated, ion scattering does not occur in the sheath and sufficient etching reaction can be efficiently obtained near the bottom of the through hole Become.

  Plasma density required for desired amount of radical formation by helicon wave excitation plasma method or electron cyclotron resonance plasma method by gas supply process of supplying gas into vacuum chamber with steady gas pressure in the range of 0.1 to 1.0 Pa The anisotropy of the through holes that are formed and formed can be enhanced. In general, when using an etching apparatus having a small vacuum vessel with a small volume, the plasma collides with the wall of the apparatus and disappears, and the plasma density is said to decrease. If plasma can be generated at high density in the steady gas pressure range by the above-described method, it is possible to secure a plasma generation component that compensates for the loss of plasma. Therefore, by using the above-described method, the generation amount of plasma can be sufficiently secured even in a small device, and the plasma can be densified. In addition, since the pressure of the gas becomes low and ion scattering due to the collision of the gas and the ions does not easily occur, the formed through holes can be highly anisotropic.

  Here, when the steady gas pressure is less than 0.1 Pa, in the helicon wave excitation plasma system or the electron cyclotron resonance plasma system, the ionization frequency of electrons and gas decreases, and the amount of plasma generation becomes insufficient. On the other hand, when the steady-state gas pressure exceeds 1.0 Pa, scattering of ions and radicals is likely to occur even if the plasma generation amount is sufficient, and the anisotropy of the formed through holes is insufficient.

Also, the radical density necessary to obtain a higher etching rate by the gas supply process of supplying the gas into the vacuum chamber so that the total amount of gas supplied per minute is 1.0 × 10 ¹⁷ cm ^-3 or more You can get More specifically, a radical density for achieving an etching rate of ER _si = 50 μm / min or more can be obtained.

  In addition, the ion induction step of guiding the ions generated by the plasma generation unit to the material to be treated located on the sample support placed in the vacuum chamber causes the ions to be made to strike the treatment surface of the material to be treated straight. The anisotropy of the through holes formed can be enhanced. In addition, when the steady gas pressure is in a low range, the efficiency of ion incidence on the bottom of the through hole can be enhanced, and the etching rate can be improved.

In addition, the plasma density in the vicinity of the target material located on the sample support is 10 ¹⁸ m ^-3 or more, and the gas is radicalized by the etching processing step of etching the target surface of the target material with high efficiency. It is possible to radicalize and perform an etching process. That is, it is possible to obtain a radical density necessary for processing at a high etching rate. More specifically, a radical density for achieving an etching rate of ER _si = 50 μm / min or more can be obtained.

Here, when the plasma density in the vicinity of the material to be treated located on the sample support is less than 10 ¹⁸ m ⁻³ , a sufficient amount of radicals is not generated to realize an etching rate of ER _si = 50 μm / min. The etching process with a high etching rate can not be performed.

Also, assuming that the vacuum vessel volume is V to 0.5 L (cylindrical vacuum vessel with a diameter of about 80 mm and a height of about 100 mm) as in the above example, and the residence time of the gas in the gas supply step is 0.5 msec. In the following cases, it is possible to obtain more radical density than required for high etching rate processing. More specifically, it becomes possible to sufficiently supply the total amount of gas required for 1 minute, which is required to realize the etching rate of ER _si = 50 μm / min.

  In addition, if a vacuum system capable of high-speed evacuation is provided and the flow rate of gas introduced in the gas supply step is 100 sccm or less, the amount of gas used decreases, and the manufacturing cost required for processing can be reduced. Become.

When the plasma generation unit generates plasma using the helicon wave excitation plasma method or the electron cyclotron resonance plasma method, the steady gas pressure is in the range of 0.1 to 1.0 Pa with an output of 1 kW to several kW. In addition, plasma with a plasma density of 10 ¹⁸ m ⁻³ or more can be generated. The helicon wave excitation plasma system referred to here includes one having a plasma source of an inductive coupling plasma system.

  Further, the ion induction step draws the magnetic force lines of the magnetic field generated in the plasma generation unit and the vacuum chamber into the sample support via the magnetic force lead-in portion provided on the sample support, and the ions are substantially perpendicular to the sample support In the case of making the light incident on the surface, it is possible to control the incident direction of the ions and to improve the anisotropy of the formed through holes. More specifically, the plasma density is increased to allow ions to enter the bottom of the etching hole, and the anisotropy and etching rate of the formed through hole are increased.

  In addition, when the ion induction process controls the ions by applying a high frequency electric field to the sample support, if the steady gas pressure is in a low range, the incident velocity of the ions toward the sample support is increased to perform ion sputtering. The etching rate by the effect can be improved.

  The dry etching method according to the present invention is a method capable of realizing an excellent etching rate and capable of processing at a high aspect ratio.

It is the schematic which shows an example of the dry etching apparatus in which the dry etching method to which this invention is applied is possible. It is the schematic which shows a part of structure of a dry etching apparatus. It is the figure which showed the vacuum chamber in cross section. It is the schematic diagram which expanded a part of vacuum chamber. It is an explanatory view of a line of magnetic force when arranging a stage near a magnetic coil. It is explanatory drawing of a magnetic force line when providing a magnetic force line drawing-in member on a stage. It is a figure which shows the position of the various plasma generation sources in the relationship between steady-state gas pressure and plasma density.

Hereinafter, embodiments of the present invention will be described with reference to the drawings to provide an understanding of the present invention.
FIG. 1 is a schematic view showing an example of a dry etching apparatus capable of the dry etching method to which the present invention is applied. The structure shown below is an example of an apparatus for implementing the method to which the present invention is applied, and the contents of the present invention are not limited to this.

  A dry etching apparatus 1 as an example of a dry etching apparatus capable of the dry etching method to which the present invention shown in FIG. 1 is applied includes a vacuum chamber 2, a high frequency coupling antenna 3, a magnetic coil 4 and a stage 5.

  The dry etching apparatus 1 further includes a plasma termination plate 6 and a gas exhaust unit (not shown) connected to a vacuum pump for exhausting the gas in the vacuum chamber 2. In FIG. 1, the direction of the supplied gas is indicated by symbol X, and the direction of the exhausted gas is indicated by symbol Z. Further, a symbol Y indicates the direction of magnetic lines of force formed by the magnetic coil 4.

  In this configuration, a process gas such as an inert gas (Ar, Kr, Xe, etc.) or a fluorine-based gas is introduced into the vacuum chamber 2 through a hollow tube connected to the plasma termination plate 6. Further, the introduced process gas is evacuated through the gas exhaust unit to maintain the inside of the vacuum chamber 2 at a constant steady gas pressure.

  The high frequency coupling antenna 3 is connected to the matching box 7 and the high frequency power supply 8. A high frequency power is supplied from the high frequency power supply 8 to the high frequency coupling antenna 3 and impedance matching is performed by adjusting each element value of the circuit element in the matching box 7 to generate a high frequency electromagnetic field in the vacuum chamber 2 Plasmatize.

  The magnetic coil 4 also generates magnetic lines of force in the vacuum chamber 2. The charged particles in the plasma are transported substantially parallel to the magnetic lines of force toward the sample placed on the stage 5 while being spirally moved so as to wind around the magnetic lines of force, and the sample is etched.

  Further, magnetic lines of force generated by the magnetic coil 4 are substantially orthogonal to the base surface of the stage 5. For this reason, the ions fly along the magnetic lines of force and strike the pedestal 5 of the stage 5 substantially perpendicularly. As a result, the side wall of the smooth etching hole is realized, that is, the anisotropy of the through hole to be formed becomes high, and the etching rate is improved.

  FIG. 2 is a schematic view showing a part of the configuration of the dry etching apparatus. FIG. 2 shows an example of the shape and positional relationship of the high frequency coupling antenna 3, the magnetic coil 4 and the stage 5. FIG. 3 is a cross-sectional view of the vacuum chamber. FIG. 4 is a schematic view enlarging a part of the vacuum chamber.

  As shown in FIG. 2, in the vacuum chamber 2, a plasma generation chamber 10 and a plasma processing chamber 11 are formed between the plasma termination plate 6 and the stage 5. The plasma termination plate 6 is provided at a position near the plasma generation chamber 10. The stage 5 is connected to a stage shaft 9.

  Further, the stage 5 is provided at a position close to the plasma processing chamber 11. With the above configuration, the process gas flows through the plasma generation chamber 10 and the plasma processing chamber 11.

  Further, the vacuum chamber 2 is in the form of a straight cylinder having a diameter of 70 mm and a height of 1000 mm. In addition, the vacuum chamber 2 is formed of an insulating material that transmits an electromagnetic wave. The vacuum chamber 2 is provided with a plasma generation chamber 10 and a plasma processing chamber 11 at different portions along the axial direction of the cylinder. The plasma generation chamber 10 and the plasma processing chamber 11 are formed in the same cylindrical vacuum chamber 10 with the same diameter.

  Furthermore, the vacuum pumping system, including the vacuum suction pump, is operable in a wide pressure range. The amount of radicals supplied per unit time in the plasma generation chamber 10 and the plasma generation chamber are adjusted by adjusting the vacuum suction of such an evacuation system and the process gas supply from the hollow tube connected to the plasma termination plate 6. The refresh rate of the process gas in 10 can be controlled.

  A high frequency coupling antenna 3 is disposed on the outer peripheral surface of the plasma generation chamber 10 coaxially with the central axis of the plasma generation chamber 10. High frequency power of a predetermined frequency is supplied to the high frequency coupling antenna 3 from a high frequency power source via a matching circuit. The high frequency coupling antenna 3 is composed of a double loop antenna.

  The high frequency coupling antenna 3 excites a high frequency electric field in the plasma generation chamber 10 by an electromagnetic induction action to plasmify the process gas flowing in the plasma generation chamber 10. The high frequency coupling antenna 3 applies, for example, an electromagnetic wave of up to several kW in the range of several MHz to several hundreds MHz. It is desirable that the high frequency coupling antenna 3 be cooled by a water cooling method or the like.

  A ring-shaped magnetic coil 4 larger than the vacuum vessel diameter is disposed coaxially with the central axis of the plasma generation chamber 10 outside the plasma generation chamber 10 and on the outer peripheral portion of the high frequency coupling antenna 3. The magnetic coil 4 is composed of a solenoid coil.

  The magnetic coil 4 generates magnetic lines of force in the plasma generated in the plasma generation chamber 10. The magnetic lines of force generated in the plasma, at least a part of which, for example, the magnetic lines of force near the central axis of the cylindrical vacuum vessel, are in a straight line parallel to the central axis of the plasma generation chamber. In the plasma in the plasma generation chamber 10, a helicon wave (Whistler wave), which is a type of electromagnetic wave, is excited inside by the magnetic field applied by the magnetic coil 4.

  Further, in the dry etching apparatus 1, the mean free path of ions generated in the plasma generation chamber 10 is longer than the sheath thickness. Specifically, the vacuum chamber 2 is depressurized into a steady gas pressure range of 0.1 to 1.0 Pa, in which the probability (collision rate) of collision of ions with gas particles before collision with the wafer becomes constant or less. There is.

The pressure and the magnetic field strength in the vacuum chamber 2 are adjusted so that the hole parameter of the ion is sufficiently larger than 1 immediately above the wafer, and the mean free path of the ion is between the high frequency coupling antenna 3 and the stage 5 It is secured over the distance. The Hall parameters of the ions can be adjusted by controlling the pressure and the magnetic field in the vacuum chamber 2. The Hall parameter h is expressed by the following [Equation 7] using the cyclotron frequency ω _c / 2π and the collision frequency イ オ ン of ions and neutral particles mainly.

  Here, the shape of the vacuum chamber 2 is not limited to a cylindrical shape. For example, various shapes such as a square and a tapered cylindrical structure can be adopted.

  Further, the size of the vacuum chamber 2 is not necessarily limited to a cylindrical shape having a diameter of 70 mm and a height of 1000 mm. That is, the volume of the vacuum portion is not limited to a small device having a small volume. However, the use of the small device brings about the following advantages.

  Generally, it has been said that as the device is miniaturized, the plasma density does not increase because the plasma collides with the chamber sidewall and disappears. However, the electromagnetic field excitation plasma generation source employed in the dry etching method to which the present invention is applied has high plasma density by using the electromagnetic field excitation plasma generated by the high frequency excitation antenna which has achieved impedance matching even when the device is miniaturized. It can be kept at the density. In the case of a small-sized apparatus, when the steady gas pressure and the exhaust rate of the vacuum pump are constant, the amount of gas that can be introduced into the container per minute is large. By increasing the gas supply amount that can be introduced into the container per minute, it is possible to obtain the total amount of radicals necessary to obtain a high etching rate. In addition, since the gas refresh rate is short, high-speed processes can be performed with a vacuum pump having a small evacuation speed. Even when a large vacuum vessel is used, the present invention can be implemented as long as the evacuation speed of the vacuum pump used for evacuation is high.

  Moreover, the plasma generation chamber 10 and the plasma processing chamber 11 do not necessarily have to be formed with the same diameter in the same cylindrical vacuum chamber 2. However, in the present invention, since the plasma confinement effect by the magnetic lines of force generated by the magnetic coil can reduce the loss of plasma to the sidewall surface of the vacuum vessel, the plasma generating chamber 10 and the plasma processing chamber 11 have the same cylindrical shape. The same diameter may be formed in the vacuum chamber 2 of FIG.

  The insulator forming the vacuum chamber 2 is not limited, but the higher the volume resistivity, the more preferable. For example, heat-resistant glass with a reduced coefficient of thermal expansion, quartz glass, a ceramic tube, or the like can be used.

  Further, the type of the high frequency coupling antenna 3 is not limited to the double loop antenna, and various types of excitation antennas such as single, helical and Bosewell can be used.

  Further, the magnetic coil 4 does not necessarily have to be constituted of a solenoid coil, and it is sufficient if it can generate magnetic lines of force in the plasma generated in the plasma generation chamber 10. For example, in place of the solenoid coil, a permanent magnet magnetized in the same axial direction as the central axis of the plasma generation chamber 10 can be used.

  Further, if the magnetic coil 4 generates magnetic force lines B near the central axis of the vacuum cylindrical container generated in the plasma generation chamber 10 to transport the plasma, the magnetic flux 4 converges and diverges in the axial direction if it does not intersect the inner side wall of the vacuum chamber 2 The magnetic lines of force B may be generated by magnetic field configuration.

  As shown in FIG. 3, a stage 5 as a sample support is disposed in the plasma processing chamber 11. The pedestal surface of the stage 5 is disposed to intersect perpendicularly with the magnetic field applied by the magnetic coil 4. The wafer 12 to be subjected to the etching process is placed on the upper surface of the stage 5.

  Further, on the opposite side of the mounting surface of the wafer 12 of the stage 5, a bias voltage application electrode 13 and a permanent magnet 14 as a magnetic line lead-in member are disposed. Further, the stage 5 has a temperature control mechanism capable of adjusting the temperature within a predetermined temperature range.

  The bias voltage application electrode 13 is connected to a high frequency power supply via a blocking capacitor outside the vacuum chamber 2 and a matching box, and applies a high frequency power of 13.56 MHz, for example, to apply an RF bias. By adjusting the bias voltage, the incident velocity of ions can be adjusted.

  As shown in FIG. 4, magnetic lines of force B generated by the magnetic coil 4 are configured to be orthogonal to the pedestal surface of the stage 5. In general, the magnetic lines of force B of the magnetic field generated by the ring-shaped magnetic coil 4 diverge as the distance from the magnetic coil 4 increases, so it is difficult to arrange the stage 5 so that all the magnetic lines of force B are orthogonal to the pedestal surface. Here, by providing the permanent magnet 14, it is possible to draw the magnetic force lines B into the stage 5.

  The formation range of the pull-in magnetic field by the permanent magnet 14 is set to include the range in which the wafer 12 is placed on the pedestal surface of the stage 5. By making the magnetic lines of force B orthogonal to the pedestal surface of the stage 5, ions are incident substantially perpendicularly on the pedestal surface of the stage 5. As a result, ions enter the bottom of the etching hole formed in the wafer 12, and it becomes possible to form an etching hole having a smooth side wall shape and a size faithful to the mask. Further, the momentum transport effect between the ion and neutral particles contributes to the improvement of the etching rate.

  Here, the magnetic force lead-in member does not necessarily have to be constituted by the permanent magnet 14, and it is sufficient if it can draw in the magnetic force lines generated by the magnetic coil 4. For example, a solenoid coil disposed concentrically with the stage 5 may be employed.

  Also, the stage 5 does not necessarily have to have a temperature control mechanism. However, the stage 5 has a temperature control mechanism because it can cool the wafer heated by etching and reduce the thermal damage of the wafer and that the etching reaction rate can be controlled by heating the stage 5. Is preferred. Moreover, as a temperature control range, control in the range of -100 degreeC-100 degreeC is considered, for example.

  As a structure for making the magnetic lines of force B orthogonal to the pedestal surface of the stage 5, one as shown in FIG. 5 can also be adopted. In the structure shown in FIG. 5, by disposing the stage 5 near the magnetic coil 4, the ratio of the lines of magnetic force B vertically incident on the pedestal surface of the stage 5 is increased.

  The stage 5 is disposed at a position closer to the magnetic coil 4 than the position P1 at which the magnetic field lines B begin to diverge. As a result, the lines of magnetic force B are incident substantially perpendicularly and uniformly from the center of the wafer 12 to the periphery. In addition, in FIG. 6, the mode of the magnetic force line at the time of arrange | positioning the permanent magnet 14 as a magnetic-force lead-in member mentioned above is shown as a comparison.

  The above-described dry etching apparatus 1 adopts the helicon wave excitation plasma method as a plasma generation source, but in the dry etching method to which the present invention is applied, the electron cyclotron resonance plasma (ECR) method is used as a plasma generation source Is also possible.

  When the ECR system is used as a plasma generation source, a plasma density equivalent to the helicon wave system can be obtained in a steady gas pressure range of 0.1 to 1.0 Pa. In the ECR method, it is common to use a diffusion type chamber to reduce the disappearance of the plasma because of the divergent magnetic field configuration. Further, as in the above-described structure, it is also possible to dispose a permanent magnet as a magnetic field lead-in member on the stage so that magnetic lines of force can be drawn in perpendicularly to the stage.

FIG. 7 shows a diagram in which various plasma generation sources are classified by steady gas pressure and plasma density. In the dry etching method to which the present invention is applied, a helicon wave excitation plasma method indicated by reference numeral 15 as a plasma generation source capable of realizing a plasma density of 10 ¹⁸ m ⁻³ in a steady gas pressure range of 0.1 to 1.0 Pa, or An electron cyclotron resonance plasma (ECR) system indicated by reference numeral 16 is adopted. Reference numeral 17 is an inductively coupled plasma (ICP) system, reference numeral 18 is a ICP-enhanced Beamed-ICP system or MSC-ICP (Multi Spiral Coil: MSC) system, reference numeral 19 is a Magnetically Enhanced-CCP system, and reference numeral 20 is a capacity 21 shows a capacitively coupled plasma (CCP) method, and 21 indicates a high power impulse magnetic sputtering (HIPIMS) method or a magnetron method.

  In the dry etching apparatus 1 configured as described above, the process gas is introduced into the plasma generation chamber 10 from the hollow tube connected to the plasma termination plate 6, and at the same time, vacuuming is performed from the gas exhaust unit (not shown). Thus, the steady gas pressure is maintained in the range of 0.1 to 1.0 Pa in the plasma generation chamber 10 and the plasma processing chamber 11.

In addition, the gas residence time of the process gas in the vacuum chamber 2 is 0.5 to 60 msec, and the total amount of process gas supplied per minute is set to achieve an etching rate of ER _si = 50 μm / min or more. It is more than 1.0 × 10 ¹⁷ cm ^-3 .

In this state, while a high frequency signal of a predetermined high frequency voltage is applied to the plasma generation chamber 10 by the high frequency coupling antenna 3, a predetermined magnetic field is formed in the plasma generation chamber 10 by the magnetic coil 4. The electromagnetic field excited plasma of the helicon plasma is excited. At this time, the plasma density in the vicinity of the wafer 12 can be 10 ¹⁸ m ^-3 .

  The charged particles in the electromagnetic field excitation plasma are transported substantially parallel to the magnetic field lines B toward the wafer 12 mounted on the stage 5 of the plasma processing chamber 11 while being spirally moved so as to wind around the magnetic field lines B. Thus, the wafer 12 is etched.

  Further, by changing the RF bias applied to the stage 5 in accordance with the processing gas and atmosphere to be used, it is possible to control the ion acceleration in the sheath and to realize appropriate plasma processing according to the wafer 12 .

  The etching of the wafer 12 proceeds in principle by the reaction between radicals and the surface to be etched, but when ions are incident on the surface to be etched, the etching is accelerated by the ion assist effect.

  Since the acceleration of etching by the ion assist effect also occurs when the incident velocity of ions at the sheath end and the voltage drop in the sheath increase, the etching rate can be accelerated as the ion rushing rate to the wafer 12 is increased. Since the ion-assisted etching proceeds with anisotropy in the collision direction of the ions, the side wall shape of the etching hole can be smoothed by aligning the rush direction of the ion-assisting ions.

  Also, in the direction of etching by radicals, if the steady gas pressure is high, the radicals are scattered, the probability of oblique incidence increases, and the etching anisotropy decreases, but by lowering the steady gas pressure, the radicals and ions are reduced. The probability of particles being incident on the side wall surface of the through hole due to the scattering is reduced, and good anisotropic etching can be realized.

  In the dry etching method to which the present invention is applied, an efficient anisotropy is achieved by increasing the supply of gas particles as a radical generation source and lowering the steady state gas pressure to such an extent that the ion scattering probability due to collision with gas particles decreases. Etching can be realized.

  The ions rotate in the clockwise direction toward the traveling direction and move parallel to the magnetic field lines B. The ions spirally move around the magnetic flux along the direction of the magnetic field so as to wrap around the magnetic field line B, and are transported in a direction parallel to the magnetic field if scattering does not occur.

  As a result, the collision rate at which ions collide with other gas particles before reaching the bottom of the etching hole is suppressed, which contributes to the speeding up of etching and can reduce the collision of ions against the vacuum chamber sidewall. , The loss of plasma is reduced.

  Further, as the charged particles (here, ions) of the electromagnetic field excitation plasma increase in density as the magnetic flux density increases, the number of charged particles of plasma entering the wafer increases. This increases the probability of plasma charged particles entering the wafer and has the characteristic of increasing the etching rate.

  A linear magnetic field or converging magnetic field is formed between the plasma generation chamber 10 and the stage 5, and the ions are initially determined by the potential of the plasma sheath (area of several millimeters immediately above the wafer) from the plasma generation chamber 10 to the stage 5 Incident with speed. This improves the etch rate of the wafer.

  Further, a bias voltage application electrode 13 for applying a high frequency RF bias to the stage 5 is provided. The RF bias is also generated in a direction substantially perpendicular to the pedestal surface of the stage 5. The potential difference between the RF bias and the plasma potential described above further increases the ion rushing rate and further improves the etching rate of the wafer 12. .

In order to form through holes for TSV by etching at a high speed of 50 μm / min or more, the dry etching apparatus 1 increases the gas supply amount supplied per unit time as compared with the conventional case (generally 1000 times). Specifically, the total amount of gas supplied per minute of the process gas is 1.0 × 10 ¹⁷ cm ⁻³ or more.

  As the gas supply amount supplied per unit time increases, the amount of radicals generated along with plasma generation also increases. And if the amount of radicals increases, the etching rate will improve.

  However, even if the gas supply amount is increased, if the steady-state gas pressure is high, the mean free path of ions is shortened and the etching rate is lowered. Therefore, in the dry etching apparatus 1, by increasing the gas refresh rate of the vacuum chamber 2, the steady-state gas pressure in the vacuum chamber 2 is made lower than in the prior art. Specifically, the steady gas pressure is maintained in the range of 0.1 to 1.0 Pa.

On the other hand, the diameter of the cylindrical vacuum chamber 2 may be shorter than the gas mean free path in the chamber. The dry etching apparatus 1 uses the helicon wave type plasma generation method, and the high plasma density and the ability to introduce ions to the wafer with a linear magnetic field can reduce the probability that the plasma collides with the sidewall and disappears. It is for.
As described above, an ECR method can also be adopted as a plasma generation source.

  Further, the steady free gas pressure in the chamber ensures that the mean free path of the ions in the chamber is greater than the distance between the high frequency coupling antenna 3 and the stage 5 by making the above-mentioned Hall parameter h sufficiently larger than 1. The degree is adjusted.

  As a result, the probability that ions transported along the magnetic field lines B to the wafer 12 cause ion scattering before reaching the bottom of the etching hole of the wafer 12 is reduced as much as possible, and collides with the wall of the vacuum chamber. Loss of plasma can be reduced. As a result, in addition to the increase in the amount of radicals involved in etching, the digging power by ion assistance is also improved, and the etching rate is further improved.

  In the dry etching apparatus 1, magnetic lines of force B generated between the plasma generation chamber 10 and the stage 5 are substantially orthogonal to the pedestal surface of the stage 5. Therefore, the ions fly along the magnetic field lines B, and are perpendicularly incident on the pedestal of the stage 5. As a result, it is possible to realize smooth side walls of the etching hole.

  Furthermore, although the magnetic lines of force B intersecting the wafer 12 are substantially perpendicular to the plane of the wafer 12, the magnetic field is once converged at an intermediate position between the plasma generation chamber 10 and the stage 5, and the magnetic flux density near the stage 5 is It may be higher than the vicinity of the plasma generation chamber 10. When the magnetic flux density in the vicinity of the stage 5 is increased, the plasma density in the vicinity of the stage 5 is increased, and the etching rate is improved.

  Further, it is preferable to adjust the position of the stage 5 so that the wafer 12 mounted on the stage 5 is at the position of the antinode or node of the electromagnetic wave propagating in the electromagnetic field excitation plasma. When the axial boundary (stage 5) is an electrically insulating material (or an electrically insulating material as a whole), the wafer 12 is adjusted to the position of the antinode of the electromagnetic wave, and the axial boundary is a conductor material (or the whole) If it is a conductive material, the wafer 12 can be adjusted to be at the node position of the electromagnetic wave.

  Further, in the dry etching method to which the present invention is applied, it is possible to adjust the following points for application to an etching rate and fine-fine plasma etching of 100 nm or less.

  First, it is conceivable to adjust pulse power application using a pulse length (ms or less) in consideration of particle diffusion time, or a pulse length (1 s or less) shortened to suppress temperature rise. By controlling ON and OFF of pulse power, plasma is generated intermittently to reduce heat generation of the antenna.

  In addition, the voltage value of the bias voltage can be adjusted to change the speed at which ions enter the wafer. In particular, by increasing the bias voltage, the acceleration effect of ions can be enhanced, and the etching rate can be improved.

  Further, in accordance with the antenna configuration and the plasma generation source, it is considered to adjust the frequency of the high frequency power source in a range of several MHz to several GHz.

  In addition, the gas flow rate of the supplied process gas can be adjusted in the range of several sccm to 100 sccm to reduce the gas usage.

  Furthermore, it is also possible to adjust the steady-state gas pressure by adjusting the vacuum conductance by inserting a baffle plate or providing a gate valve opening / closing structure.

  As described above, the dry etching method of the present invention is capable of realizing an excellent etching rate and capable of processing at a high aspect ratio.

DESCRIPTION OF SYMBOLS 1 dry etching apparatus 2 vacuum chamber 3 antenna for high frequency coupling 4 magnetic coil 5 stage 6 plasma termination plate 7 matching box 8 RF power supply 9 stage shaft 10 plasma generation chamber 11 plasma processing chamber 12 wafer 13 bias voltage application electrode 14 permanent magnet 15 Helicon wave excitation plasma system 16 electron cyclotron resonance plasma (ECR) system 17 inductively coupled plasma (ICP) system 18 Beamed-ICP system or MSC-ICP (Multi Spiral Coil (MSC) system 19 Magnetically Enhanced-CCP system 20 capacitively coupled plasma ( Capacitively Coupled Plasma (CCP) method 21 High Power Impulse Magnetron Sputtering (HIPIMS) method or Magnetron method

Claims (6)

The steady-state gas pressure is in the range of 0.1 to 1.0 Pa by making the mean free path of the ions generated by the plasma generation unit for generating the electromagnetic field excitation plasma in the vacuum chamber longer than the sheath thickness generated on the surface of the workpiece And supplying the gas into the vacuum chamber such that the total amount of gas supplied per minute is 1.0 × 10 ¹⁷ cm ⁻³ or more.
An ion inducing step of directing ions generated by the plasma generation unit to a material to be treated located on a sample support placed in the vacuum chamber;
A dry etching method comprising: an etching process step of radicalizing the gas and etching the surface to be treated of the material to be treated by setting the plasma density in the vicinity of the material to be treated to 10 ¹⁸ m ^-3 or more. The dry etching method according to claim 1, wherein the gas supply step supplies a gas into the vacuum chamber such that a residence time of the gas is 0.5 msec or less. The dry etching method according to claim 1 or 2, wherein the gas supply step supplies a gas into the vacuum chamber such that a flow rate of the introduced gas is equal to or less than 100 sccm. The dry etching method according to claim 1, wherein the plasma generation unit generates a plasma using a helicon wave excitation plasma method or an electron cyclotron resonance plasma method. In the ion induction step, magnetic force lines of a magnetic field generated in the plasma generation unit and the vacuum chamber are drawn to the same sample support via the magnetic force lead-in portion provided on the sample support, and ions are transferred to the same sample support. 5. The dry etching method according to claim 1, wherein the light is incident substantially perpendicularly. The dry etching method according to claim 1, wherein the ion induction step controls ions by applying a high frequency electric field to the sample support.