WO2011115008A1

WO2011115008A1 - Etching method and etching device

Info

Publication number: WO2011115008A1
Application number: PCT/JP2011/055767
Authority: WO
Inventors: 泰宏森川; 貴英村山; 学吉居; 直樹水谷
Original assignee: 株式会社アルバック
Priority date: 2010-03-16
Filing date: 2011-03-11
Publication date: 2011-09-22
Also published as: TW201203352A; JPWO2011115008A1

Abstract

Disclosed is an etching method in which a substrate (S) mounted on a stage electrode (3) in a vacuum chamber (1) is etched in the thickness direction of the substrate (S), and in which: an etching gas is supplied to the vacuum chamber (1); high frequency electric power is supplied to the stage electrode (3) at a frequency between 60 MHz and 150 MHz inclusive; and etching is carried out at a pressure such that the energy distribution of ions incident on the substrate (S) has a pair of first peaks which occur at the edge of the high-energy side of the energy distribution and which are caused by different electric field accelerations in accordance with the frequency of the high frequency electric power, and a second peak which occurs in a lower energy range than the pair of first peaks and which has a higher intensity than the pair of first peaks.

Description

Etching method and etching apparatus

The present invention relates to an etching method, in particular, a method related to reactive ion etching and an apparatus used for carrying out the etching method.

2. Description of the Related Art Conventionally, as described in, for example, Patent Document 1 and Patent Document 2, a parallel plate etching apparatus is known as one form of an apparatus that performs dry etching on a substrate formed of a semiconductor material, an insulating material, or the like. ing. A parallel plate type etching apparatus usually has a stage electrode on which a substrate is placed and an upper electrode arranged to face the stage electrode in a vacuum chamber into which an etching gas is introduced. A high-frequency power source for applying a bias voltage to the substrate is connected to the stage electrode via a matching box for impedance matching.

When an etching process is performed in such a parallel plate type etching apparatus, an etching gas is first introduced through a gas introduction hole provided in the upper electrode. Next, plasma is generated from the etching gas in the vacuum chamber by applying a high-frequency voltage to the substrate from a high-frequency power source. Then, positive ions in the plasma are attracted toward the stage electrode that is negatively biased with respect to the plasma, whereby the substrate is chemically or physically etched. Thus, in the parallel plate type etching apparatus, a recess having a predetermined shape is formed in the thickness direction of the substrate by so-called reactive ion etching.

JP-A-6-53191 JP 2004-128236 A

Incidentally, in the process of attracting positive ions toward the substrate as described above, a sheath having a substantially uniform thickness is first formed on the surface of the substrate. Thereafter, the positive ions entering the sheath are accelerated by the electric field formed in the sheath, and the positive ions collide with the surface of the substrate in a state having energy corresponding to the electric field acceleration.

At this time, if all of the positive ions that have entered the sheath fly along the normal direction of the surface of the substrate, the positive ions may be applied to the electric field regardless of the thickness of the sheath. It is drawn in the normal direction which is the direction of. For this reason, etching proceeds only in the thickness direction of the substrate.

However, the particles that enter the sheath include positive ions and radicals that fly in a direction different from the normal direction, in addition to positive ions that fly in the normal direction. Then, positive ions and radicals flying in a direction different from the normal direction are less likely to reach the bottom surface of the concave portion as the distance between the bottom surface of the concave portion being formed and the upper end portion of the sheath increases. As a result, when the flight distance of the particles is increased by increasing the thickness of the sheath or the depth of the recess, the normal direction while the positive ions flying in the normal direction etch the bottom surface of the recess. The positive ions and radicals flying in different directions continue to etch only near the opening of the recess. As a result of an increase in the etching amount on the side wall of the recess, so-called CD (Critical Dimensions) loss increases. In particular, such a problem becomes conspicuous in a process that increases the etching amount in the thickness direction of the substrate, for example, a process that forms a through hole in a silicon substrate.

Note that these problems can be alleviated by increasing the plasma density and decreasing the sheath thickness, but even if the plasma density is increased, this is limited. Further, the problem of CD loss does not occur only in the parallel plate type etching apparatus, and a high frequency power source that applies a bias voltage to the substrate is mounted on the substrate, which is an object to be etched. If it is an etching apparatus which has the structure connected to this electrode, it will occur in general.

The present invention has been made in view of the above-described conventional situation, and an object thereof is an etching method capable of increasing the anisotropy of an etching shape formed in the thickness direction from the surface of a substrate, and the etching. It is to provide an apparatus for use in carrying out the method.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
A first aspect of the present invention is an etching method for etching a substrate placed on a stage electrode in a vacuum chamber in the thickness direction. The etching method includes supplying an etching gas into the vacuum chamber, supplying high-frequency power to the stage electrode at a frequency of 60 MHz to 150 MHz, and energy distribution of ions incident on the substrate is the high-frequency power. A pair of first peaks that appear at the ends of the high energy side of the energy distribution by different electric field accelerations determined by the frequency of the pair, and an energy region that is lower than the pair of first peaks, and the pair of first peaks Etching at a pressure such that the second peak has a higher intensity than the second peak.

A second aspect of the present invention is an etching apparatus for etching a substrate in the thickness direction thereof, a vacuum chamber, a stage electrode disposed in the vacuum chamber and mounting the substrate, and the vacuum chamber An etching gas supply unit that supplies an etching gas to the substrate, a high-frequency power source that supplies high-frequency power to the stage electrode, an exhaust unit that evacuates the vacuum chamber, and an energy distribution of ions incident on the substrate is 60 MHz or more and 150 MHz. Expressed in a pair of first peaks expressed at the high energy side ends of the energy distribution by different electric field accelerations determined by the frequency of the high frequency power below, and in an energy region lower than the pair of first peaks, And a second peak having a higher intensity than the pair of first peaks, and the pressure in the vacuum chamber is controlled to a pressure having a second peak. And a control unit for, a.

When ions reach the substrate without colliding with other particles in a sheath formed with a predetermined thickness on the surface of the substrate, in the frequency band from 60 MHz to 150 MHz that the ions follow, the ions Depending on the phase of the high-frequency power when it reaches the substrate, ions that receive a large electric field acceleration and ions that do not. As a result, an energy difference is generated between ions that have reached the substrate. As a result, a pair of peaks due to different electric field accelerations determined by the frequency of the high-frequency power, so-called bimodal peaks, are recognized at the end on the high energy side in the ion energy distribution.

Also, new positive ions may be generated in the above-described sheath. For example, positive ions may be generated by charge exchange between positive ions that have entered the sheath and neutral particles. In this case, newly generated positive ions are accelerated by the electric field from the generated position. Therefore, when a new positive ion is generated in the sheath, a peak different from the bimodal peak is recognized in an energy region lower than the bimodal peak described above.

According to the first and second aspects of the present invention, the etching is performed in a pressure region in which the bimodal peak and the peak in the energy region lower than the bimodal peak are recognized in the ion energy distribution. . In such a pressure region, ions that fly in the sheath and are drawn into the substrate, that is, ions that contribute to etching, are constituted by the following four types of [first ion] to [fourth ion].

[First ion] Ions flying in the sheath along the normal direction of the substrate surface [Second ion] Ions flying in the sheath along a direction different from the normal direction of the substrate surface [Third ion] sheath Ions generated in the air and flying in the normal direction of the substrate surface [Fourth ion] Ions generated in the sheath and flying in a direction different from the normal direction of the substrate surface Among the ions attributed to the modal peak, the [second ion] that reaches the substrate from a direction different from the normal direction of the substrate reaches the bottom surface of the target region as the depth of the target region increases. It becomes difficult. On the other hand, the [third ion] and the [fourth ion] are more likely to reach the substrate than the [first ion] and [second ion] flying from the upper end of the sheath toward the substrate. The shorter the flight distance, the easier it is to reach the bottom surface of the etching target area. Therefore, in the etching method using the above-mentioned [first ions] to [fourth ions], the [third ions] and [fourth ions] are newly generated in the thickness direction of the substrate. It is possible to increase the anisotropy of the formed etching shape. In particular, if the processing increases the etching amount in the thickness direction of the substrate, the effect becomes more remarkable.

Moreover, according to the etching method described above, since the [first ion] and [second ion] having relatively high energy exist, the anisotropy of the etching shape is changed by excessively increasing the pressure. Loss can be suppressed.

According to a third aspect of the present invention, in the etching method according to the first aspect, the pressure is 50 Pa or more and 150 Pa or less, and the plasma density is 1 × 10 ¹⁰ / cm ³ or more and 5 × 10 ¹² / cm ³ or less. That is the gist.

According to a fourth aspect of the present invention, in the etching apparatus according to the second aspect, the control unit has the pressure of 50 Pa to 150 Pa and a plasma density of 1 × 10 ¹⁰ / cm ^{3 to} 5 × 10. ^The gist is to control the flow rate of the etching gas supplied into the vacuum chamber so as to be ¹² / cm ³ or less.

The thickness of the sheath formed on the substrate is defined by the plasma density, which is the density of ions and electrons contained in the plasma. In general, the higher the plasma density, the thinner the sheath, and the lower the plasma density, the thicker the sheath. Therefore, in the case where reproducibility is required not only in the magnitude relationship between the first peak and the second peak but also in the ratio of the intensity of the first peak to the intensity of the second peak, etc., such a plasma is used. Preferably, a density range and a pressure range are defined. In this regard, according to the third and fourth aspects of the present invention, the pressure is set to 50 Pa or more and 150 Pa or less, and the plasma density is 1 × 10 ¹⁰ / cm ³ or more and 5 × 10 ¹² / cm ³ or less. Therefore, it is possible to obtain reproducibility in the ratio of the intensity of the first peak to the intensity of the second peak as described above.

In addition, as a method of adjusting the pressure of the space where the plasma is generated to a predetermined value, adjusting the flow rate of the etching gas and adjusting the exhaust amount of the etching gas can be mentioned. In this regard, according to the fourth aspect of the present invention, since the pressure of the space in which the plasma is generated is adjusted by the flow rate of the etching gas, the surface of the substrate is compared with the method of adjusting the exhaust amount of the etching gas. It is possible to increase the speed of the fluid. Therefore, if the pressure in the space where plasma is generated is increased, it is possible to carry out the etching in a so-called reaction-limited region where the etching rate is controlled by the progress of the etching reaction. As a result, it is possible to increase the anisotropy of the etching shape while suppressing a decrease in the etching rate.

According to a fifth aspect of the present invention, in the etching method of the first or third aspect, the substrate is a silicon substrate, and the etching gas is at least one of fluorine-containing gas, chlorine, bromine, and iodine. The gist of the present invention is that it is a mixed gas containing hydrogen halide gas having two.

In general, etching of a silicon substrate uses a gas containing fluorine that forms silicon fluoride, which is a highly volatile compound, by combining with silicon. On the other hand, silicon halides in which chlorine, bromine, and iodine, which are halogen elements other than fluorine, are bonded to silicon are less volatile than the above silicon fluoride, and silicon hydrides in which hydrogen is bonded to silicon are fluorine. More volatile than siliconized silicon.

Therefore, in the fifth aspect of the present invention, a hydrogen halide gas containing at least one of chlorine, bromine, and iodine is used as the etching gas for the fluorine-containing gas that is the main component of etching. Thus, the etching progressing in the thickness direction of the substrate is promoted by hydrogen ions, and the peripheral wall of the recess formed in the same thickness direction is hardly etched by the silicon halide deposit. Therefore, anisotropy of the etching shape is more easily obtained.

The schematic block diagram of the etching apparatus used for implementation of the etching method concerning one embodiment of this invention. The figure which shows distribution of ion energy of the ion which reaches | attains a board | substrate when the frequency of high frequency electric power is 40 MHz. The figure which shows distribution of the ion energy of the ion which reaches | attains a board | substrate when the frequency of high frequency electric power is 60 MHz. The figure which shows distribution of the ion energy of the ion which reaches | attains a board | substrate when the frequency of high frequency electric power is 150 MHz. The figure which shows distribution of the ion energy of the ion which reaches | attains a board | substrate when the frequency of high frequency electric power is 250 MHz. The schematic diagram which shows the track | orbit of the positive ion in reactive ion etching. (A) (b) The schematic diagram which shows the etching shape formed by reactive ion etching. (A) to (c) Images obtained by photographing a recess formed in a silicon substrate by etching with a scanning electron microscope (SEM).

Hereinafter, an embodiment in which an etching method according to the present invention and an etching apparatus used for carrying out the etching method are embodied will be described with reference to FIGS.
FIG. 1 shows a schematic configuration of an etching apparatus according to this embodiment, which is generally called a parallel plate type or a capacitive coupling type. The parallel plate type etching apparatus has a stage electrode 3 disposed in the vacuum chamber 1 via an insulating spacer 2. A substrate S, which is an object to be etched, is placed on the stage electrode 3, and a high frequency power source 4 that supplies high frequency power to the stage electrode 3 is connected via a matching box 5 that matches impedance. . The high frequency power supply 4 sets the frequency of the high frequency power supplied to the stage electrode 3 to 60 MHz or more and 150 MHz or less.

Also, an ion energy analyzer 6 for analyzing the energy of positive ions incident on the substrate S is disposed near the stage electrode 3. The ion energy analyzer 6 collects a part of particles flying toward the stage electrode 3 and classifies positive ions contained in the particles for each electron temperature (eV), and also has positive ions having each electron temperature. Measure the number of

Above the stage electrode 3 is a shower plate 7 that functions as a ground electrode facing the stage electrode 3 and is provided with a gas introduction hole for introducing an etching gas supplied from the outside of the vacuum chamber 1 into the vacuum chamber 1. It is arranged. A gas supply unit 8 that supplies various gases used for etching the substrate S is connected to the shower plate 7. In addition, an exhaust unit 9 that exhausts various gases such as etching gas and air in the vacuum chamber 1 is connected to the vacuum chamber 1. In the present embodiment, the flow rate of the gas per unit time supplied from the gas supply unit 8 to the vacuum chamber 1 is adjusted by the gas supply unit 8 or the exhaust amount per unit time of the exhaust unit 9 is adjusted. By adjusting with the exhaust part 9, the pressure in the vacuum chamber 1 is adjusted to a predetermined value (in this embodiment, 50 Pa or more and 150 Pa or less). Alternatively, the pressure in the vacuum chamber 1 is adjusted to the predetermined value by the cooperation of the gas supply unit 8 and the exhaust unit 9.

When etching is performed by the parallel plate type etching apparatus, the substrate S to be etched is first transferred into the vacuum chamber 1 and placed on the stage electrode 3. Next, the air in the vacuum chamber 1 is exhausted by the exhaust unit 9, and a predetermined flow rate of etching gas is supplied from the gas supply unit 8 into the vacuum chamber 1. At this time, the inside of the vacuum chamber 1 is adjusted to a predetermined pressure by the flow rate of the etching gas supplied from the gas supply unit 8 and the exhaust amount of the exhaust unit 9. When the high frequency electrode is supplied from the high frequency power supply 4 to the stage electrode 3 after the etching gas is supplied, the etching gas is discharged by the discharge between the substrate S placed on the stage electrode 3 and the shower plate 7. Plasma is generated. Various processes executed in the etching apparatus such as the exhaust process by the exhaust unit 9, the gas supply process by the gas supply unit 8, and the power supply process by the high frequency power source 4 are performed by the control unit 10 connected to the etching apparatus. Is executed by being driven.

When the plasma is generated, electrons in the plasma collide with the surface of the substrate S and the vacuum chamber 1, so that these surfaces are negatively biased with respect to the plasma, and the surfaces have a predetermined thickness. The sheath is formed almost uniformly. When positive ions in the plasma reach the boundary between the sheath and the plasma excluding the sheath (the upper end of the sheath), the positive ions are attracted to the surface of the negatively biased substrate S. The positive ions drawn into the surface of the substrate S etch the substrate S chemically or physically, so that etching with a predetermined etching shape proceeds from the surface of the substrate S in the thickness direction of the substrate S. To do. And the recessed part extended in the thickness direction of this board | substrate S from the surface of the board | substrate S is formed.

In this embodiment, the substrate S is a silicon substrate, for example, and the etching gas is composed of sulfur hexafluoride (SF ₆ ) gas, oxygen (O ₂ ) gas, and hydrogen bromide (HBr) gas. A mixed gas is used. However, the etching gas is not limited to such a combination, and any etching gas may be used as long as it is a gas in which a fluorine-containing gas and a hydrogen halide gas containing at least one of chlorine, bromine, and iodine are mixed. Can do. More specifically, examples of the fluorine-containing gas constituting the etching gas include sulfur hexafluoride gas, iodine pentafluoride (IF ₅ ) gas, chlorine trifluoride (ClF ₃ ) gas, and boron trifluoride (BF). ₃ ) At least one of gas, thionyl fluoride (SOF ₂ ) gas, sulfuryl fluoride (SO ₂ F ₂ ) gas, and carbonyl fluoride (COF ₂ ) gas can be employed. Also. As the hydrogen halide gas, for example, at least one of hydrogen chloride (HCl) gas, hydrogen bromide, and hydrogen iodide (HI) gas can be employed.

In this embodiment, a mixed gas containing sulfur hexafluoride gas, which is a fluorine-containing gas generally used for etching a silicon substrate, and hydrogen bromide gas, which is a hydrogen halide gas, is used as an etching gas. Yes. Thereby, the etching progressing in the thickness direction of the substrate S is promoted by hydrogen ions that form silicon hydride having higher volatility than silicon fluoride. Further, the peripheral wall of the concave portion extending in the thickness direction of the substrate S is difficult to be etched by the silicon halide deposit. Therefore, anisotropy of the etching shape is easily obtained as compared with the case where etching is performed using other gas species.

Incidentally, in this embodiment, the etching gas further contains an oxygen gas in addition to the fluorine-containing gas and the hydrogen halide gas. According to such an etching gas, silicon oxide having lower volatility than any of the silicon hydride, silicon fluoride, and silicon halide is formed during the etching. For this reason, the peripheral wall of the recess extending in the thickness direction of the substrate S is more difficult to be etched.

Here, it is assumed that positive ions flying toward the substrate S in the sheath reach the surface of the substrate S without colliding with other particles during the reactive ion etching described above. In this case, if the frequency band of the high frequency power is 60 MHz or more and 150 MHz or less, positive ions follow the electric field formed by the high frequency power. As a result, when positive ions reach the substrate S, positive ions that undergo a large electric field acceleration and positive ions that do not, are generated according to the phase of the high-frequency power. This causes an energy difference between these positive ions. For this reason, a pair of peaks due to different electric field accelerations determined by the frequency of the high-frequency power, so-called bimodal peaks, are recognized at the high-energy side end in the positive ion energy distribution.

When such a bimodal peak is recognized as a dominant peak in the energy distribution of positive ions, most of the positive ions fly from the upper end of the sheath formed on the surface of the substrate S to the surface of the substrate S. It will be. The positive ions flying through the sheath in this way include positive ions flying in a direction different from the normal direction, in addition to positive ions flying in the normal direction. Thus, the positive ions flying in a direction different from the normal direction are less likely to reach the bottom surface of the concave portion as the depth of the concave portion being formed increases. As a result, while positive ions flying in the normal direction increase the depth of the recess, positive ions flying in a direction different from the normal direction continue to expand the opening of the recess. Therefore, when the bimodal peak is recognized as a dominant peak in the positive ion energy distribution, the etching amount on the side wall of the recess increases as the depth of the recess increases. As a result, so-called CD loss increases.

Therefore, in the present embodiment, etching is performed under the condition that the second peak having a lower energy than the first bimodal peak in the positive ion energy distribution is dominant, particularly the pressure condition. I am doing so.

Next, the dependence of the frequency of the high-frequency power on the distribution of the positive ion energy drawn into the substrate S and the dependence of the pressure in the vacuum chamber 1 will be described with reference to FIGS. I will explain. FIGS. 2 to 5 illustrate positive ion energy distributions under the following etching conditions, and sequentially illustrate the energy distributions when the frequency of the high-frequency power is 40 MHz, 60 MHz, 150 MHz, and 250 MHz.
(Etching conditions)
Etching gas: mixed gas composed of SF ₆ gas, O ₂ gas, and HBr gas Output value of high-frequency power at the stage electrode 3: 10 W / cm ²
-Pressure in the vacuum chamber 1: 0.2 Pa, 25 Pa, 50 Pa, 150 Pa, 250 Pa
・ Plasma density during etching: 1 × 10 ¹¹
The ion energy distributions shown in FIGS. 2 to 5 are obtained from the output values output from the ion energy analyzer 6 provided in the etching apparatus. Moreover, in each figure, the ion energy when the pressure in the vacuum chamber 1 is 0.2 Pa is shown by a solid line, and the ion energy when the pressure is 25 Pa is shown by a broken line. Also, the ion energy when the pressure in the vacuum chamber 1 is 50 Pa is indicated by a two-dot chain line, the ion energy when the pressure is 150 Pa is indicated by a one-dot chain line, and the ion energy when the pressure is 250 Pa is indicated by a thick line. ing.

As shown in FIG. 2, when the frequency of the high frequency power is 40 MHz, the first high energy peak P1 recognized at about 140 eV is obtained under the condition where the pressure is 0.2 Pa and the condition where the pressure is 25 Pa. , A bimodal peak BP constituted by the second high energy peak P2 recognized at about 65 eV is recognized at the end on the high energy side. On the other hand, when the pressure is higher (50 Pa, 150 Pa, 250 Pa), the bimodal peak BP is not recognized. In particular, when the pressure is 250 Pa, almost no positive ions having an energy of 65 to 140 eV, which is an energy region sandwiched between the bimodal peaks BP, are recognized.

As shown in FIG. 3, when the frequency of the high frequency power is 60 MHz, the first high energy peak P1 recognized at about 125 eV and the pressure other than 250 Pa (0.2 Pa, 25 Pa, 50 Pa, 150 Pa) and , A bimodal peak BP constituted by the second high energy peak P2 recognized at about 80 eV is recognized at the end on the high energy side.

Furthermore, in the condition where the pressure is 50 Pa and the condition where the pressure is 150 Pa, the low peak which is the second peak having higher intensity than the bimodal peak BP on the lower energy side than the bimodal peak BP. An energy peak P3 is observed. The positive ions showing such a low energy peak P3 have an energy lower than that given by the electric field acceleration. Therefore, positive ions having a low energy peak P3 are generated in the sheath and positively generated by electric field acceleration from the middle of the sheath, for example, positive ions generated by charge exchange between neutral particles and positive ions. It can be assigned as an ion. In addition, the said tendency that the low energy peak P3 which has intensity | strength higher than the intensity | strength of bimodal peak BP is recognized by the low energy side of this bimodal peak BP is a tendency recognized in the whole range of 50 Pa or more and 150 Pa or less. .

As shown in FIG. 4, when the frequency is 150 MHz, as in the case of 60 MHz, the first pressure that is recognized at about 110 eV is obtained under conditions other than the pressure of 250 Pa (0.2 Pa, 25 Pa, 50 Pa, 150 Pa). A bimodal peak BP constituted by the high energy peak P1 and the second high energy peak P2 recognized at about 90 eV is recognized at the end on the high energy side. As in the case of 60 MHz, the conditions where the pressure is 50 Pa and the conditions where the pressure is 150 Pa have higher intensity on the lower energy side than the bimodal peak BP and higher than the bimodal peak BP. The low energy peak P3 which is the second peak is recognized. At 60 MHz, only one low energy peak P3 is recognized for each pressure condition of 50 Pa and 150 Pa, whereas for 150 MHz, three low energy peaks are obtained for each pressure condition of 50 Pa and 150 Pa. P3 is accepted. Moreover, the said tendency that the low energy peak P3 which has intensity | strength higher than the intensity | strength of the bimodal peak BP is recognized by the low energy side of this bimodal peak BP is 50 Pa or more and 150 Pa or less similarly to the case of said 60 MHz. This tendency is observed in the entire range.

As shown in FIG. 5, when the frequency is 250 MHz, as in the case of 40 MHz, the first condition, which is recognized at about 95 eV, is obtained under the condition where the pressure is 0.2 Pa and the condition where the pressure is 25 Pa. A bimodal peak BP composed of the high energy peak P1 and the second high energy peak P2 recognized at about 105 eV is recognized at the end on the high energy side. On the other hand, when the pressure is higher (50 Pa, 150 Pa, 250 Pa), the bimodal peak BP is not recognized.

Thus, in the energy distribution of ions incident on the substrate S, the conditions under which the bimodal peak BP and the low energy peak P3 in the energy region lower than the bimodal peak BP and having high intensity are recognized. The frequency band is 60 MHz or more and 150 MHz or less, and the pressure in the vacuum chamber is 50 Pa or more and 150 Pa or less. In this embodiment, when etching is performed with the above etching apparatus, the frequency band is determined to be 60 MHz or more and 150 MHz or less, and the following [First Condition] and [Second Condition] are satisfied. A range is defined. For example, under the above-described etching conditions, the frequency band is set to 60 MHz to 150 MHz, and the pressure range is set to 50 Pa to 150 Pa.
[First condition] The bimodal peak BP is recognized at the end on the high energy side.
[Second condition] A low energy peak P3 having a lower energy side than the bimodal peak BP and having an intensity higher than that of the bimodal peak BP is recognized.

Examples of a method for adjusting the pressure of the space where the plasma is generated to such a predetermined value include adjusting the flow rate of the etching gas and adjusting the exhaust amount of the etching gas. From the viewpoint of adjusting the speed of the fluid, it is preferable to adjust the pressure according to the flow rate of the etching gas. According to this, since the etching is easily performed in a so-called reaction rate limiting region in which the etching rate is controlled by the progress of the etching reaction, anisotropy of the etching shape is increased while suppressing a decrease in the etching rate. It is possible.

The thickness of the sheath formed on the substrate S is defined by the plasma density, which is the density of ions and electrons contained in the plasma. In general, it is known that a thinner sheath is formed as the plasma density is higher, and a thicker sheath is formed as the plasma density is lower. Therefore, not only the above [first condition] and [second condition] but also when the reproducibility is required for the ratio between the intensity of the low energy peak P3 and the intensity of the bimodal peak BP, such a plasma density. A method in which the range and the pressure range are defined is preferable. Therefore, in this embodiment, the flow rate of the etching gas and the high-frequency power are adjusted so that the pressure is 50 Pa or more and 150 Pa or less and the plasma density is 1 × 10 ¹⁰ / cm ³ or more and 5 × 10 ¹² / cm ³ or less. Output value is set.

Hereinafter, an etching shape obtained by the frequency band and pressure range determined as described above will be described with reference to FIGS. FIG. 6 shows the trajectory of positive ions near the surface of the substrate S when the reactive ion etching is performed. FIG. 7 schematically shows an etching shape formed by reactive ion etching.

As FIG. 6 shows, after the board | substrate S is accommodated in the said etching apparatus, supply of the etching gas to the vacuum chamber 1, and supply of the high frequency current to the stage electrode 3 are implemented in this order, A plasma Rp containing electrons E and positive ions IP is generated from an etching gas composed of neutral particles NP. Next, the electron E having a higher moving speed generated following the electric field formed by the high-frequency current reaches the surface of the substrate S, so that the surface of the substrate S is negatively biased with respect to the plasma. Thereby, on the surface of the substrate S, the electrons E are repelled and bounced back to the side away from the surface of the substrate S. Therefore, at a predetermined distance Da from the surface of the substrate S, more positive ions IP than the number of electrons E are present. A sheath Rs that is a region having a large number of is formed. A region farther from the substrate S than the sheath Rs is a region of the electrically neutral plasma Rp while the positive ions IP, the electrons E, and the neutral particles NP exist. When the positive ions IP in the plasma Rp reach the boundary surface BP between the plasma Rp and the sheath Rs, the positive potential positive ions IP are drawn into the surface of the negatively biased substrate S. In other words, the positive ions The IP flies to the surface of the substrate S.

Here, the positive ions IP incident on the surface of the substrate S can be roughly classified into the following two.
First positive ions IPa that reach the surface of the substrate S without colliding with other particles.
A second positive ion IPb newly generated from the neutral particle NP by charge exchange between the neutral particle NP and the positive ion IP in the sheath Rs.

The first positive ion IPa is subjected to electric field acceleration by high-frequency power and maintains the energy obtained by the acceleration until it enters the substrate S. That is, the first positive ion IPa is a positive ion belonging to the bimodal peak BP composed of the first high energy peak P1 and the second high energy peak P2 shown in FIGS. As shown in FIG. 6, the first positive ions IPa fly in the direction normal to the surface of the substrate S, and the first positive ions fly in a direction different from the normal direction. IPa is included. The first positive ions IPa flying in the normal direction and the first positive ions IPa flying in a direction different from the normal direction do not collide with other positive ions IP and neutral particles NP. The surface of S is reached. However, the first positive ion IPa flying along the direction different from the normal direction among the first positive ions IPa reaches the bottom surface of the concave portion as the depth of the concave portion formed in the substrate S increases. It becomes difficult to do.

On the other hand, the second positive ion IPb is a positive ion whose energy given by the electric field acceleration is smaller than that of the first positive ion IPa, that is, a positive energy attributed to the low energy peak P3 shown in FIGS. Ion. Similarly to the first positive ion IPa, the second positive ion IPb also includes a second positive ion IPb flying in the normal direction and a second positive ion IPb flying in a direction different from the normal direction. It is included. The positive ions generated in the sheath Rs in this manner have the same velocity direction distribution as that of the first positive ions IPa when the electric field acceleration is started, but the positions when the electric field acceleration is started are the first. It is closer to the substrate S than the positive ion IPa. That is, the flight distance of the second positive ion IPb is the distance Db from the point where the charge exchange is performed, and the charge exchange occurs in the sheath Rs. Therefore, the distance Db corresponds to the thickness of the sheath Rs. It becomes smaller than the distance Da. Therefore, the second positive ion IPb generated by the charge exchange reaches the substrate S more than the first positive ion IPa even if the flight direction deviates from the normal direction for the same reason as the first positive ion IPa. Since the flight distance until the time is shortened, it becomes easier to reach the bottom surface of the recess formed in the substrate S.

7A and 7B schematically show etching shapes formed when reactive ion etching is performed by the first positive ions IPa and the second positive ions IPb, respectively. As shown in FIG. 7, when a predetermined etching shape, for example, a recess H is formed on the substrate S by reactive ion etching, a mask M having a predetermined opening is formed on the substrate S prior to reactive ion etching. Formed on the surface. Then, the positive ions IP are incident on the substrate S from the opening, whereby the substrate S is etched.

As shown in FIG. 7A, when etching is performed with the first positive ion IPa, the method of the opening Ma of the mask M is performed with the first positive ion IPa flying in a direction different from the normal direction. Etching proceeds outward from the line direction. As a result, the maximum diameter DiaB in the recessed portion H that is an etching shape is larger than the diameter DiaA of the opening Ma.

On the other hand, as shown in FIG. 7B, when etching is performed with the second positive ions IPb, the second positive ions IPb are accelerated in the electric field from the vicinity of the substrate S. Etching is likely to proceed along the normal direction. Therefore, the diameter of the recessed portion H that is an etching shape is substantially equal to the diameter DiaA in the opening Ma.

Therefore, the ratio of the second positive ions IPb to the positive ions IP incident on the substrate S is increased. That is, as shown in FIGS. ] And [Second condition] are performed under such conditions that the anisotropy of the recess H is increased.

As shown in FIGS. 3 and 4, the second positive ion IPb belonging to the low energy peak P3 has lower ion energy than the first positive ion IPa belonging to the bimodal peak BP. If etching is performed under conditions where only the second positive ions IPb are present, the etching rate may decrease. In this regard, according to the present embodiment, the etching is performed under the condition in which the first positive ion IPa belonging to the bimodal peak BP and the second positive ion IPb belonging to the low energy peak P3 coexist. Therefore, a decrease in the etching rate can be suppressed by the first positive ions IPa while maintaining the anisotropy of the etching shape by the second positive ions IPb.
[Example 1]
After a mask having an opening with a diameter of 50 μm is applied to an 8-inch silicon substrate with a thickness of 750 μm, it is composed of SF ₆ gas, O ₂ gas, and HBr gas using the parallel plate etching apparatus. Etching was performed using a mixed gas as an etching gas. At this time, the frequency of the high frequency power output from the high frequency power source was 60 MHz, and the output value was 10 W / cm ² . In addition, various gases contained in the mixed gas are made of SF ₆ gas so that the plasma density is 1 × 10 ¹⁰ / cm ³ or more and 5 × 10 ¹² / cm ³ or less and the pressure during etching is 120 Pa. , O ₂ gas, and HBr gas were supplied to the vacuum chamber at flow rates of 150 sccm, 150 sccm, and 30 sccm, respectively.

And the recessed part H of Example 1 was obtained by implementing etching on the said conditions for 300 second. FIG. 8A shows a cross-sectional image of the recess H of Example 1 taken using a scanning electron microscope (SEM). Moreover, the maximum value (maximum depth) of the depth of the recessed part H measured based on the cross-sectional image of Fig.8 (a) and the maximum value (maximum internal diameter) of the internal diameter of the recessed part H are shown below.
・ Maximum depth: 154μm
・ Maximum inner diameter: 67μm
[Comparative Example 1]
The total flow rate of the mixed gas was changed so that the pressure during etching was 25 Pa, and the other conditions were the same as in Example 1 to obtain the recess H of Comparative Example 1. FIG. 8B shows a cross-sectional image of the recess H of Comparative Example 1 taken using a scanning electron microscope (SEM). Moreover, the maximum depth and the maximum internal diameter of the recessed part H measured based on the cross-sectional image of FIG.8 (b) are shown below.
・ Maximum depth: 88μm
・ Maximum inner diameter: 68μm
[Comparative Example 2]
The total flow rate of the mixed gas was changed so that the pressure during etching was 250 Pa, and the other conditions were the same as in Example 1 to obtain a recess H of Comparative Example 2. FIG. 8C shows a cross-sectional image of the recess H of Comparative Example 2 photographed using a scanning electron microscope (SEM). Moreover, the maximum depth and the maximum internal diameter of the recessed part H measured based on the cross-sectional image of FIG.8 (c) are shown below.
・ Maximum depth: 150μm
・ Maximum inner diameter: 71μm
From these results, the maximum depth of Example 1 is about twice the maximum depth of Comparative Example 1, and the maximum inner diameter of Example 1 is substantially the same as the maximum inner diameter of Comparative Example 1. Was recognized. According to this difference in the maximum depth, it was found that positive ions are more likely to reach the bottom surface of the recess H in the pressure region where the low energy peak P3 is recognized than in the low pressure region where it is not recognized. Further, according to the difference in the maximum inner diameter, it is understood that the positive ions reaching the side surface of the recess H are approximately the same in the pressure region where the low energy peak P3 is recognized and the low pressure region where it is not recognized. It was.

In addition, while changing the pressure of Comparative Example 1 to another pressure lower than 50 Pa, and measuring the etching shape under the same conditions as Comparative Example 1 as other conditions, the pressure during etching becomes lower than 50 Pa. The above-mentioned decreasing tendency of the maximum depth was remarkable.

From the above results, it was confirmed that the maximum depth of Example 1 was slightly larger than the maximum depth of Comparative Example 2, and that the maximum inner diameter of Example 1 was slightly smaller than the maximum inner diameter of Comparative Example 2. According to the difference in the maximum depth, even in the pressure region where the low energy peak P3 is recognized, positive ions hardly reach the bottom surface of the recess H in a high pressure region where the bimodal peak BP disappears. I found out. Further, according to the difference in the maximum inner diameter, even in the pressure region where the low energy peak P3 is recognized, in the high pressure region where the bimodal peak BP disappears, the positive ions reaching the side wall of the recess H I found out that it was going to increase.

In addition, while changing the pressure of Comparative Example 2 to another pressure higher than 150 Pa and measuring the etching shape under the same conditions as Comparative Example 2 as the other conditions, the pressure during etching becomes higher than 150 Pa. The above-mentioned decreasing tendency of the maximum depth became remarkable and the increasing tendency of the maximum inner diameter was remarkable.

As described above, according to the etching method and the etching apparatus of the present embodiment, the effects listed below can be obtained.
(1) Pressure region where the frequency of the high frequency power is 60 MHz or more and 150 MHz or less, and the bimodal peak BP and the low energy peak P3 having higher intensity and lower energy are recognized in the distribution of ion energy. Etching is performed. Therefore, the anisotropy of the etching shape formed in the thickness direction of the substrate S can be increased by the amount of the second positive ions IPb newly generated in the sheath Rs.

(2) Since the etching with the first positive ion IPa having relatively high energy also proceeds, it is possible to suppress the loss of etching shape anisotropy due to excessively high pressure. is there.

(3) Since the etching is performed under conditions where the pressure is 50 Pa or more and 150 Pa or less and the plasma density is 1 × 10 ¹⁰ / cm ³ or more and 5 × 10 ¹² / cm ³ or less, the intensity of the low energy peak P3 It is also possible to obtain reproducibility in the ratio of the intensity of the bimodal peak BP with respect to.

(4) As an etching gas, sulfur hexafluoride gas that is one of fluorine-containing gases and hydrogen bromide that is one of hydrogen halide gases containing at least one of chlorine, bromine, and iodine are included. A mixed gas was used. As a result, the etching progressing in the thickness direction of the substrate S is promoted by hydrogen ions, and the side walls of the recesses formed in the substrate S are less likely to be etched by silicon halide deposits. Therefore, anisotropy of the etching shape is more easily obtained.

(5) The etching gas contains oxygen gas in addition to sulfur hexafluoride gas and hydrogen bromide gas. As a result, during etching, silicon oxide having lower volatility than any of the silicon hydride, silicon fluoride, and silicon halide is formed. Therefore, the peripheral wall of the irradiation surface is more difficult to be etched.

It should be noted that the above embodiment can be implemented with appropriate modifications as follows.
The plasma density range in the above embodiment may be a range in which the above [first condition] and [second condition] are satisfied by the energy distribution of ions incident on the substrate, and the low energy peak P3 If a particular reproducibility is not required for the ratio between the intensity and the intensity of the bimodal peak BP, it is possible to omit the determination of the plasma density range.

-The pressure range in the said embodiment should just be a range with which said [1st condition] and said [2nd condition] are satisfy | filled by the energy distribution of the ion which injects into a board | substrate, According to the kind of etching gas For example, it may be 50 Pa or less or 150 Pa or more. With such an etching method, it is possible to expand the type of etching gas and the range of materials to be etched.

The ion energy distribution in the above embodiment is acquired by the ion energy analyzer 6 provided in the vicinity of the stage electrode 3. The method used for this is a method capable of analyzing the energy of positive ions incident on the substrate S, such as a method using a single probe (Langmuir probe), a method using decomposition ion mass spectrometry, a method using emission spectroscopy, or the like. There is no particular limitation. In addition, the method is not limited to the method actually mounted on the etching apparatus, and an apparatus for obtaining the distribution of ion energy is separately used, and the pressure range in which the [first condition] and the [second condition] are satisfied is the etching apparatus. The method may be determined by a different device.

-The above etching method was carried out using a parallel plate type etching apparatus. However, the present invention is not limited thereto, and the etching is performed using another etching apparatus having a configuration in which a substrate that is an object to be etched is placed above the electrode and a high-frequency power source that applies a bias voltage to the substrate is connected to the electrode. You can also.

Claims

An etching method for etching a substrate placed on a stage electrode in a vacuum chamber in the thickness direction,
Supplying an etching gas into the vacuum chamber;
Supplying high-frequency power to the stage electrode at a frequency of 60 MHz to 150 MHz;
From the pair of first peaks, the energy distribution of ions incident on the substrate is expressed at the high energy side ends of the energy distribution by different electric field accelerations determined by the frequency of the high frequency power, and the pair of first peaks. Etching at a pressure such that the second peak is expressed in a low energy region and has a second peak having a higher intensity than the pair of first peaks,
An etching method comprising:
The etching method according to claim 1,
The pressure is 50 Pa or more and 150 Pa or less, and
The etching method is characterized in that the plasma density is 1 × 10 10 / cm 3 or more and 5 × 10 12 / cm 3 or less.
The etching method according to claim 1 or 2,
The substrate is a silicon substrate;
The etching method, wherein the etching gas is a mixed gas containing a fluorine-containing gas and a hydrogen halide gas containing at least one of chlorine, bromine, and iodine.
An etching apparatus for etching a substrate in its thickness direction,
A vacuum chamber;
A stage electrode placed in the vacuum chamber to place the substrate;
An etching gas supply unit for supplying an etching gas into the vacuum chamber;
A high frequency power supply for supplying high frequency power to the stage electrode;
An exhaust section for exhausting the inside of the vacuum chamber;
A pair of first peaks appearing at an end on the high energy side of the energy distribution due to different electric field accelerations determined by the frequency of the high-frequency power of 60 MHz to 150 MHz, the energy distribution of ions incident on the substrate; A controller that controls the pressure in the vacuum chamber to a pressure that is expressed in an energy region lower than the first peak of the second peak and has a second peak having a higher intensity than the pair of first peaks;
An etching apparatus comprising:
The etching apparatus according to claim 4, wherein
The control unit is an etching gas supplied into the vacuum chamber so that the pressure is 50 Pa or more and 150 Pa or less and the plasma density is 1 × 10 10 / cm 3 or more and 5 × 10 12 / cm 3 or less. An etching apparatus characterized by controlling the flow rate of.