JP2007141918A - Dry etching method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dry etching method with which a deep trench with a sufficient shape can be obtained with faster forming speed. <P>SOLUTION: In the dry etching method; etching gas is made into plasma, and a workpiece formed of Si is dry-etched in a processing room. The dry etching method contains (a) a process for performing pre-processing by etching so that an inner wall of the workpiece formed of Si becomes an inverse tapered shape by using first etching gas, and (b) a second process for performing etching by using second etching gas. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a dry etching method for forming a trench or the like in an object to be processed made of Si. In particular, the present invention relates to a dry etching method for forming a trench having a deep depth and a good shape.

  In recent years, with the progress of miniaturization of electronic equipment, semiconductor devices used therein, such as integrated circuits and flat panel displays, are required to be miniaturized. In order to produce a semiconductor device, a trench (or groove), a via hole (or hole), and other structures (hereinafter, collectively referred to as “trench or simply trench”) may be formed in a silicon substrate. Due to the above-described requirements, trenches and the like formed in a silicon substrate are required to have a deeper overall depth, for example, a depth of 50 μm or more. Here, the total depth means the distance from the surface of the silicon substrate such as the finally formed target trench to the bottom, and means a value measured with an electron microscope.

  As a method for forming such a deep trench or the like in a silicon substrate, a dry etching method (or plasma etching method) for etching a silicon substrate in a plasma processing chamber (or simply referred to as “processing chamber”) is known. It has been. FIG. 1 shows a schematic diagram of an example of a dry etching apparatus (100) used in such a dry etching method. This apparatus is an ICP (inductively coupled plasma) type etching apparatus, which is a vacuum etching chamber (or etching processing chamber) (110), an upper electrode (120) and a lower electrode (130) in the etching chamber, and a high frequency power source (140). ) And (150), a gas inlet (160), and a gas outlet (170).

  First, a silicon substrate (200) to be etched is placed on the lower electrode (130). An etching gas is introduced into the etching chamber (100), which is turned into plasma to generate active species (ions, radicals, etc.). On the silicon substrate (200), a mask having a desired shape (for example, a photoresist and a hard mask, not shown) is arranged, and active species are made incident on the silicon substrate through the opening of the mask, so that the silicon substrate ( 200) is etched to form a trench or the like having a desired depth.

FIGS. 2A and 2B are schematic diagrams of ideal cross-sectional contours or shapes such as trenches.
In each of FIGS. 2A and 2B, a mask (210) is disposed on a silicon substrate (200), and a trench (220) is formed in the silicon substrate under the mask. A trench (220) is formed vertically downward from the opening of the mask (210).
The outline of the cross section of the trench (220) shown in FIG. 2 (a) is rectangular, the width of the trench (220) is constant, and the walls are not uneven.
The cross section of the trench (220) shown in FIG. 2 (b) has a tapered shape, the width of the trench (220) narrows downward at a constant rate, and the wall has no irregularities.

  FIG. 3 is a schematic diagram of a contour or shape of a cross section of a realistic trench or the like. Similar to FIG. 2, a mask (210) is disposed on a silicon substrate (200), and a trench (320) is formed in the silicon substrate under the mask. However, the outline of the cross section of the trench is significantly different from that of FIG. Below the mask (210) is a cut etched portion (330). This is also called undercut. In addition, the trench wall under the undercut (330) has an arcuately etched portion (340). This is also called Boeing. By producing these portions, the cross-sectional outline of the trench in FIG. 3 does not become rectangular, but has an opening wider than the opening of the mask, the width of the trench varies depending on the depth of the trench, and the wall Have curvature. Trench shape (or contour) irregularities that can occur in such trenches can lead to unacceptable results when actually using semiconductor devices.

Such irregularities in the shape of the trench are defined by the side etching ratio defined by the formula (I).
Formula I: Side etching ratio = (Undercut (330) + Boeing (340)) / Depth (d)
That is, the side etching ratio can be said to be an index indicating how much etching has progressed in the lateral direction with respect to the depth.
The side etching ratio is ideally 0, but is preferably 0.05 or less from the overall shape considering the depth of the trench.

  The reason why such irregularities in the shape of the actual trench are caused by the following mechanism. When the etching gas introduced into the plasma processing chamber is turned into plasma, two types of plasma, ions and radicals, are generated. Among these generated active species, ions are accelerated by a negative bias and incident on the silicon substrate (200) from a vertical direction, and etching proceeds in a direction perpendicular to the surface of the silicon substrate (200). On the other hand, since radicals are not affected by a negative bias, they do not have a specific directionality with respect to the surface of the silicon substrate (200) and are incident randomly, that is, isotropically. Also progress. Therefore, side etching such as undercut (330) and bowing (340) is generated directly under the opening of the mask (210).

Therefore, an etching method for forming a deep trench while keeping a good cross-sectional shape of the trench has been studied.
In Patent Document 1, a trench having a good shape is formed by forming a protective film made of a silicon compound on the sidewall of the trench by using C ₄ F ₈ before and / or during plasma etching. A method is disclosed. However, since this method uses C ₄ F ₈ , which can cause irregularities on the sidewalls of the trench due to the formation of a protective film derived from C ₄ F ₈ , the etching gas switching time is required and etching as a whole is necessary. Since the protective film is deposited on the inner wall of the processing chamber at a low speed, there are problems that the plasma state becomes unstable and the etching characteristics fluctuate as the number of processed silicon substrates increases.

Patent Document 2 discloses a method of performing etching by generating plasma using an etching gas in which helium having a relatively high flow rate is added to SF ₆ and O ₂ and performing etching in the vertical direction. However, this method has a problem that the etching rate is not sufficient or the mask on the silicon substrate can disappear before reaching a predetermined depth. The reason why the etching rate becomes insufficient is that a high flow rate of helium is continuously supplied, so that the residence time of the F radical is shortened. It is thought that it is done.

JP 2000-509915 A Japanese Patent Application No. 2004-340752

  The present invention has been made in order to solve such a problem, and the problems are that a trench having a good shape cannot be obtained, a trench having a deep depth cannot be obtained, and a trench formation speed is low. To provide a dry etching method in which at least one is alleviated, preferably substantially eliminated, more preferably all of the above problems are alleviated, and particularly preferably all of the above problems are substantially eliminated. .

  As a result of intensive studies, the present inventors performed pretreatment by etching on the object to be processed made of Si to form a pretreatment portion having an inversely tapered inner wall, and then etched the pretreatment portion. Surprisingly, by forming the entire target portion, it is surprising that at least the problem that the trench with a good shape cannot be obtained, the trench with a deep depth cannot be obtained, or the formation speed of the trench is slow is at least It is found that a catalyst can be obtained in which one is alleviated, preferably substantially alleviated, more preferably all of the above mentioned problems are alleviated, and particularly preferably all of the above mentioned problems are substantially eliminated. The invention has been completed.

According to one aspect of the present invention, a new dry etching method is provided,
In the processing chamber, the etching gas is converted into plasma, and the object to be processed made of Si is dry-etched,
(A) a first etching step in which pretreatment by etching is performed on a workpiece made of Si using a first etching gas to form a pretreatment portion having an inverted tapered inner wall; and (b) first This is a dry etching method including a second etching step in which etching is performed on the pretreatment portion using two etching gases.

  In one aspect of the present invention, the first etching step provides a dry etching method applied so that the depth of the pretreatment portion is less than 15% of the depth of the entire portion formed by etching.

  In another aspect of the present invention, the first etching step is performed such that an angle α formed between the reverse tapered inner wall of the pretreatment portion and the surface of the object to be processed is 70 ° <α <90 °. A dry etching method is provided.

  In a preferred embodiment of the present invention, the first etching gas reacts with an object to be processed made of Si, and a reaction product generated by the reaction is a component capable of forming a protective film on the side wall of the object to be processed made of Si. A dry etching method is provided.

  In a further aspect of the present invention, there is provided the dry etching method, wherein the first etching gas contains a fluorine compound and oxygen, and optionally a rare gas.

  In another aspect of the present invention, an electric field is generated around the object to be processed made of Si, and ions in the plasma generated from the first etching gas are attracted to the object to be processed, so that the ions collide with the object to be processed. A dry etching method for performing a pretreatment of an object to be processed by etching is provided.

  In still another aspect of the present invention, there is provided the dry etching method, wherein the ion energy source for generating an electric field around the object to be processed is an RF generator.

  In another preferable aspect of the present invention, there is provided a dry etching method in which an RF power input to the RF generator as an ion energy source is 30 to 200 W.

In a preferred embodiment of the present invention, there is provided a dry etching method in which, in the first etching step, the ion density in the plasma is 1 × 10 ¹¹ cm ⁻³ or more at a height of 10 mm from the workpiece.

  In another preferred embodiment of the present invention, a dry etching method for generating plasma by an ICP method is provided.

  In a further preferred aspect of the present invention, there is provided a dry etching method in which the plasma generation source for generating plasma is an RF generator, and the power of the RF generator is 2000 W or more.

  In a preferred embodiment of the present invention, there is provided a dry etching method in which the distance between the plasma generating portion and the object to be processed is 50 mm or less.

  In a further aspect of the present invention, there is provided a dry etching method in which the pressure in the processing chamber in the first etching step is 30 Pa or less.

  In another embodiment of the present invention, (b) the second etching step introduces a second etching gas containing a fluorine compound and oxygen, optionally containing a rare gas, into the processing chamber, and A dry etching method is provided which is a second etching step of etching.

  In another aspect of the present invention, there is provided a dry etching method in which the ratio of the flow rate of the fluorine compound and the flow rate of oxygen (fluorine compound / oxygen) in the second etching gas is 1/1 to 4/1.

  In a further aspect of the present invention, a dry etching method is provided wherein the flow rate of the fluorine compound in the second etching gas is 50 to 900 sccm.

  In a further preferred embodiment of the present invention, there is provided a dry etching method in which the oxygen flow rate of the second etching gas is 50 to 450 sccm.

  In the dry etching method according to the present invention, after pretreatment by etching is performed on a workpiece made of Si to form a pretreatment portion having a reverse tapered inner wall, the pretreatment portion is further etched. At least one of the problems that a trench having a good shape cannot be obtained, a trench having a deep depth cannot be obtained, and the formation speed of the trench is slow is alleviated, preferably substantially eliminated, and more preferably All of the problems are alleviated, and particularly preferably all of the above problems are substantially eliminated.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION

  The method of the present invention can be carried out using any dry etching apparatus as long as it is a dry etching apparatus capable of performing the method of the present invention, and is not particularly limited by the apparatus used. As such a dry etching apparatus, the ICP type etching apparatus, the RIE type etching apparatus, the two-frequency parallel plate type etching apparatus and the like shown in FIG.

  As described above, the ICP type etching apparatus (100) of FIG. 1 includes an etching chamber (110), an upper electrode (120) and a lower electrode (130) in the etching chamber, high-frequency power sources (140) and (150), and gas introduction. A port (160) and a gas exhaust port (170) are provided. In order to carry out the dry etching method of the present invention, the apparatus of FIG. 1 preferably further has the following specifications.

  The etching chamber (110) is a processing chamber in which an object to be processed is etched. The inner wall is preferably formed using an insulating material such as quartz, alumina, anodized aluminum base material, or yttrium oxide.

  The etching gas is supplied into the etching chamber (110) through the gas inlet (160), and the gas in the etching chamber (110) is exhausted from the etching chamber (110) through the gas exhaust port (170).

  Next, the dry etching method of the present invention using the above-described dry etching apparatus will be described as a part of the process in manufacturing a semiconductor device such as a transistor. In order to avoid obscuring the invention, description of other known manufacturing steps of the semiconductor device will be omitted.

  First, a first etching process will be described in which a pretreatment portion having an inversely tapered inner wall is formed by performing a pretreatment by etching on an object to be processed made of Si using a first etching gas. First, the reverse taper shape will be described.

FIG. 4 is a schematic view of a silicon substrate whose inner wall has been etched into a reverse taper shape. The width of the trench etched from the opening of the mask (210) on the silicon substrate (200) becomes wider as it goes down. For the sake of explanation, FIG. 4 emphasizes a considerable reverse taper, but in practice, it is not always necessary to have such an extreme reverse taper.
The depth of an inversely tapered portion (di: depth of an inversed tapered portion, see FIG. 4) formed in the first etching step is the entire etching portion to be finally formed, that is, the entire trench. Can be selected in various ways based on the depth (for example, see d in FIGS. 2A, 2B and 3). The depth (di) of the pre-processed portion formed in the reverse taper shape is preferably less than 15% of the depth (d) of the entire portion formed by the target etching, and is less than 10%. Is more preferable, and it is especially preferable that it is less than 5%. Note that di is not 0% of d, but is preferably 2% or more.
If necessary, after forming the entire trench or the like using the method of the present invention, the reverse tapered portion can be removed using a method such as full-surface etching or CMP.

The inclination of the inner wall formed with the reverse taper is preferably 70 ° <α <90 °, and more preferably 70 ° <α <85 °, where α is the angle between the silicon substrate surface and the inner wall. Preferably, 70 ° <α <80 ° is particularly preferable.
When α = 90 ° or> 90 °, the inclination of the inner wall is 90 ° or more, and thus no reverse taper is formed.
The above α may be directly measured by observing the trench shape with an electron microscope, but tan (90−α) is defined as the distance (wi, see FIG. 4) that the wall surface has retreated by forming an inverse taper. ) = Di / wi, it may be calculated from di and wi obtained by observing the trench shape with an electron microscope.

Before starting the first etching step, first, an object to be processed made of Si is placed on the lower electrode (130).
The object to be processed made of Si is not particularly limited as long as the object to be processed made of Si is usually subjected to dry etching. An example of such an adherend made of Si is a silicon substrate.

Next, the first etching gas is introduced into the etching chamber (110) through the gas introduction port (160) while the inside of the etching chamber (110) is maintained at a constant pressure, and is exhausted from the gas exhaust port (170). To do.
Next, high frequency power is supplied from the high frequency power sources (140) and (150) to the upper electrode (120) and the lower electrode (130), respectively, and the first etching gas is turned into plasma. For example, when the first etching gas contains a fluorine compound, active species in plasma such as F ⁺ ions, F ⁻ ions, and F radicals react with an object to be processed made of Si, for example, silicon on a silicon substrate, to form SiF. _4. Generate reaction products such as SiO ₂ and etch the silicon substrate to form trenches. Considering that the object to be processed is a silicon substrate, the RF power applied to the lower electrode (130) is preferably low.

  Etching conditions such as the composition of the first etching gas, the flow rate, the pressure inside the etching chamber, the power of the high-frequency power source, the frequency, the distance between the upper electrode and the lower electrode, etc. are conditions that can achieve the desired reverse tapered shape There is no particular limitation.

However, the first etching gas reacts with the object to be processed made of Si, and the reaction product generated by the reaction includes a component capable of forming a protective film on the side wall of the object to be processed made of Si. preferable.
The first etching gas preferably contains a fluorine compound and oxygen, and may optionally contain a rare gas.
The fluorine compound contained in the first etching gas is at least one selected from SF ₆ , NF ₃ , BF ₃ , PF ₅ and F ₂ , and the rare gas that can be optionally contained in the first etching gas is: More preferably, it is at least one selected from helium and argon.
It is particularly preferable that the fluorine compound is SF ₆ and the rare gas is helium.

The ratio of the flow rate of the fluorine compound contained in the first etching gas to the flow rate of oxygen (fluorine compound / oxygen) is preferably 1/1 to 4/1, more preferably 1/1 to 3/1. A ratio of 1/1 to 2/1 is particularly preferable.
The flow rate of the fluorine compound contained in the first etching gas is preferably 50 to 900 sccm, more preferably 50 to 300 sccm, and particularly preferably 50 to 150 sccm.
The flow rate of oxygen contained in the first etching gas is preferably 25 to 450 sccm, more preferably 25 to 150 sccm, and particularly preferably 25 to 75 sccm.

The flow rate of the rare gas contained in the first etching gas is preferably 50 to 95% of the total flow rate of the first etching gas, more preferably 65 to 90%, and 80 to 90%. Particularly preferred.
The flow rate of the rare gas contained in the first etching gas is preferably 2000 sccm or less, more preferably 500 to 1500 sccm, and particularly preferably 800 to 1000 sccm.

  In order to form a pre-processed portion having an inversely tapered shape, an electric field is generated around the object to be processed made of Si, and ions in the plasma generated from the first etching gas are attracted to the object to be processed. It is preferable to perform a pretreatment of the object to be processed by etching with energy that collides with the object to be processed. More specifically, it is preferable to perform the above treatment by applying an electric field to the lower electrode of the plasma treatment chamber. Accordingly, it is preferable to protect the inner wall of the pre-processed portion having an inversely tapered shape formed on the object to be processed.

An RF generator can be exemplified as an ion energy source that generates an electric field around the object to be processed.
Furthermore, the RF power input to the RF generator as the ion energy source is preferably 30 to 200 W, more preferably 30 to 120 W, and particularly preferably 40 to 60 W.

Moreover, in order to form the pre-processing part which has a reverse taper shape, in the 1st etching process, the ion density in plasma shall be 1 * 10 < ¹¹ > cm < ^-3 > or more in height of 10 mm from a to-be-processed object. Is preferred.
Here, the ion density in the plasma is a value measured by the Langmuir probe method, preferably 1 × 10 ¹¹ cm ⁻³ or more, more preferably 2 × 10 ¹¹ cm ⁻³ or more. It is especially preferable that it is more than ^x10 < ¹¹ > cm < ^-3 >.

  As long as the target dry etching is possible, any method may be used to generate plasma from the first etching gas. Examples of such a method include an ICP method, an RIE method, a magnetron RIE method, a dual frequency RIE method, an ECR method, a microwave excitation method, and the like, but the ICP method is preferable.

  An RF generator is preferable as a plasma generation source for generating plasma.

In order to set the plasma ion density to 1 × 10 ¹¹ cm ⁻³ or more at a height of 10 mm from the object to be processed, when an RF generator is used as the plasma generation source, the power of the RF generator must be 2000 W or more. Is preferred.
In this case, the distance between the plasma generating part (for example, RF generator) and the object to be processed is preferably 150 mm or less, and particularly preferably 100 to 150 mm.

Further, in the first etching step, in order to set the plasma ion density to 1 × 10 ¹¹ cm ⁻³ or more at a height of 10 mm from the object to be processed, a plasma generator (for example, an RF generator), The distance between the body is preferably 50 mm or less, more preferably 20 to 50 mm, and particularly preferably 20 to 30 mm.
In this case, the power of the RF generator as a plasma generation source is preferably 500 W or more and less than 3000 W, more preferably 500 W or more and less than 2500 W, and particularly preferably 500 or more and less than 2000 W.

  In the first etching step, the pressure in the processing chamber is preferably 30 Pa or less, more preferably 10 to 30 Pa, and particularly preferably 25 to 30 Pa.

  The first etching step using the first etching gas is performed for a desired time until a pretreatment portion having an inversely tapered inner wall is obtained. For example, it is preferably performed for 0.5 to 3 minutes, more preferably 0.5 to 2 minutes, and particularly preferably 0.5 to 1 minute.

  When the first etching process using the first etching gas is completed, the second etching gas is introduced into the etching chamber (110) through the gas inlet (160) while maintaining a constant pressure in the etching chamber (110). The second etching step is performed by introducing and exhausting from the gas exhaust port (170).

  The second etching step is not particularly limited as long as a trench having a good shape targeted by the present invention can be obtained. Examples of the second etching step include the following.

The second etching step may be performed by introducing a second etching gas containing a fluorine compound and oxygen and optionally containing a rare gas into the processing chamber and etching the pretreatment portion of the object to be processed. preferable.
The fluorine compound contained in the second etching gas is at least one selected from SF ₆ , NF ₃ , BF ₃ , PF ₅ and F ₂ , and the rare gas optionally contained in the second etching gas is helium and argon It is preferable that it is at least one selected from.
The fluorine compound of the second etching gas is particularly preferably SF ₆ and the rare gas is particularly preferably helium, but it is also particularly preferred that no rare gas is contained.

The ratio of the flow rate of the fluorine compound contained in the second etching gas to the flow rate of oxygen (fluorine compound / oxygen) is preferably 1/1 to 4/1, and more preferably 3/1 to 4/1. 2/1 to 4/1 is particularly preferable.
The flow rate of the fluorine compound contained in the second etching gas is preferably 50 to 900 sccm, more preferably 100 to 300 sccm, and particularly preferably 150 to 250 sccm.
The flow rate of oxygen contained in the second etching gas is preferably 50 to 450 sccm, more preferably 50 to 250 sccm, and particularly preferably 50 to 150 sccm.
The pressure in the etching chamber (110) is preferably 10 to 50 Pa, more preferably 25 to 50 Pa, and particularly preferably 30 to 50 Pa.

Similarly to the first etching gas, the second etching gas is turned into plasma.
The frequency of the high-frequency power (for plasma generation) supplied from the high-frequency power source (140) to the upper electrode (120) is preferably 2 to 60 MHz, and particularly preferably 13.56 MHz. The output of the high frequency power supplied from the high frequency power supply (140) is preferably 300 to 3000 W, more preferably 1000 to 2500 W, and particularly preferably 1000 to 2200 W.
The frequency of the high frequency power (for ion energy) supplied from the high frequency power source (150) to the lower electrode (130) is preferably 0.5 to 60 MHz, and more preferably 0.5 to 13.56 MHz. Particularly preferred is 13.56 MHz.
The output of the high frequency power supplied from the high frequency power source (150) is preferably 50 to 500 W, more preferably 75 to 200 W, and particularly preferably 100 to 150 W.
The distance between the upper electrode (120) and the lower electrode (130) is preferably 150 mm or less, and particularly preferably 100 to 150 mm.

  The etching process using the second etching gas is performed for a desired time. For example, it is preferably performed for 5 to 30 minutes, more preferably 5 to 20 minutes, and particularly preferably 5 to 12 minutes.

  In addition, in order to switch from the first etching process to the second etching process, the power output (for example, RF power) applied to the upper electrode (120) and the lower electrode (130) is both ON, and only one of them is ON. The both can be turned off and the first etching process can be switched to the second etching process by changing the etching conditions such as switching the second etching gas of the first etching gas. It is appropriate to switch from the first step to the second step with the output of power applied to the upper electrode (120) and the lower electrode (130) turned on, only one of them turned on, and both turned off. It is possible to change the etching conditions, such as switching from the first etching process to the second etching process, that is, switching from the first etching gas to the second etching gas, with both power outputs turned on. It is preferable to carry out.

  As described above, by using the dry etching method of the present invention including the first etching step and the second etching step, a trench having a good contour or shape on a workpiece made of Si, for example, a silicon substrate. In addition, a via hole or the like can be formed.

The side etching ratio of the obtained trench or the like is preferably greater than 0 and not greater than 0.05, more preferably greater than 0 and not greater than 0.04, and particularly preferably greater than 0 and not greater than 0.03.
The depth of the obtained trench or the like is preferably 50 to 400 μm, more preferably 50 to 300 μm, and particularly preferably 50 to 220 μm.
The diameter of the opening of the mask to be used is preferably 10 to 100 μm, more preferably 20 to 80 μm, and particularly preferably 30 to 50 μm.
In the dry etching method of the present invention, such trenches as a whole are preferably etched at an etching rate of 5 to 20 μm / min, more preferably at an etching rate of 10 to 20 μm / min, and particularly preferably 13 to 20 μm / min. For example, it can be formed on a silicon substrate at an etching rate.

  As described above, the dry etching method according to the present invention has a balance between the trench shape and the etching rate, such that a trench having a deep depth and a good contour can be formed at a higher etching rate. It is an excellent etching method.

The present invention has the above-described features and exhibits excellent effects. The reason for this is considered as follows. However, the present invention is not limited at all for the following reasons.
Based on various studies, the present inventors have noted that some etching gases generate reaction products that react with the target object made of silicon and become components that can protect the sidewalls of trenches and the like. did.
When a reverse taper is formed, reaction products that can serve as sidewall protection components in the second etching step are likely to be caught by the sidewalls when they exit from the bottom of the trench or the like to the opening of the trench, and a thick protective film continues on the sidewalls. It is thought that it can be formed. On the other hand, when the reverse taper is not formed, when the reaction product goes out from the bottom of the trench, since the width of the trench becomes wider from the bottom toward the opening, the reaction product is more easily discharged from the trench, The side wall protective film is also considered to be thin.
Further, if a reverse taper is formed, ions entering from the opening are unlikely to hit the side wall, but if no reverse taper is formed, ions entering from the opening are likely to hit the side wall.
Therefore, when a reverse taper is formed, a thicker protective film can be formed on the side wall. However, ions entering from the opening are less likely to hit the side wall, and when the reverse taper is not formed, the protective film on the side wall is thinner. It is considered that ions incident from the opening are more likely to hit the side wall. As a result, it is considered that the present invention has an effect of excellent balance between the trench shape and the etching rate, in which a trench having a deep depth and a good contour can be formed at a higher etching rate. .

The invention is explained in more detail by means of examples.
Example 1
As the first etching gas, SF ₆ / O ₂ / He = 120/60/820 sccm was used.
As the second etching gas, SF ₆ / O ₂ = 200/100 sccm was used.
A silicon substrate on which a mask having an opening with a diameter of 50 μm was formed was used as the object to be processed.
The first etching step was performed for 1 minute at a total pressure of 25 Pa, the upper electrode 3000 W, the lower electrode 55 W, the distance between the upper electrode and the lower electrode of 122 mm, and the lower electrode temperature of 15 ° C. At this time, the plasma ion density at a height of 10 mm from the silicon substrate was 2 × 10 ¹¹ cm ^{−3 as} measured by the Langmuir probe method.
This etched to a depth of about 7.5 μm (5% of the total depth of the trench).
A reverse taper shape with α = 78 ° was obtained.
The second etching step was performed for 5 minutes with the total pressure of the system being 40 Pa, the upper electrode 1500 W and the lower electrode 100 W, and the distance between the upper electrode and the lower electrode of 122 mm.
When switching between the first step and the second step, the power applied to the upper electrode and the lower electrode is not turned off (that is, both remain on), and the first etching condition is changed to the second etching condition. changed.
A trench having a depth of 148 μm and a side etching ratio of 0.011 could be formed as a whole at an etching rate of 18.4 μm / min.
A schematic diagram of a trench formed by the method described in Example 1 is shown in FIG. In addition, a reverse taper shape is recognized by the opening part of the trench of FIG.

Example 2
As the first etching gas, SF ₆ / O ₂ / He = 60/40/900 sccm was used.
As the second etching gas, SF ₆ / O ₂ = 200/100 sccm was used.
A silicon substrate on which a mask having an opening with a diameter of 50 μm was formed was used as the object to be processed.
The first etching process was performed for 30 seconds at a total pressure of 30 Pa, with the upper electrode 1500 W, the lower electrode 50 W, the distance between the upper electrode and the lower electrode of 20 mm, and the lower electrode temperature of 15 ° C. At this time, the plasma ion density at a height of 10 mm from the silicon substrate was 4 × 10 ¹¹ cm ^{−3 as} measured by the Langmuir probe method.
This etched to a depth of about 20 μm (10% of the total depth of the trench). A reverse taper shape with α = 74 ° was obtained.
The second etching step was performed for 12 minutes with the upper electrode 2200W and the lower electrode 100W at a total pressure of the system of 50 Pa and a distance between the upper electrode and the lower electrode of 122 mm.
When switching between the first step and the second step, the power applied to the upper electrode and the lower electrode is not turned off (that is, both remain on), and the first etching condition is changed to the second etching condition. changed.
A trench having a depth of 202 μm and a side etching ratio of 0.029 could be formed at an etching rate of 14.3 μm / min.

Comparative Example 1
As the etching gas, SF ₆ / O ₂ = 200/100 sccm was used.
A silicon substrate on which a mask having an opening with a diameter of 50 μm was formed was used as the object to be processed.
The etching process was performed continuously for 7.5 minutes at an upper electrode 1500 W, a lower electrode 100 W, a distance between the upper electrode and the lower electrode of 122 mm, and a lower electrode temperature of 15 ° C. with the total pressure of the system being 40 Pa.
A trench having a depth of 155 μm and a side etching ratio of 0.081 could be formed at an etching rate of 18.6 μm / min.
A schematic diagram of a trench formed by the method described in Comparative Example 1 is shown in FIG.
In the method of Comparative Example 1, only the second etching step of Example 1 is substantially performed. By comparing FIG. 5 with FIG. 6, it was found that a trench having a good shape can be formed by etching after forming a pre-processing portion having an inverse taper shape.

Comparative Example 2
As the etching gas, SF ₆ / O ₂ / He = 60/40/900 sccm was used.
A silicon substrate on which a mask having an opening with a diameter of 50 μm was formed was used as the object to be processed.
The etching process was continuously performed for 7.5 minutes at a total pressure of 30 Pa, with the upper electrode 1500W, the lower electrode 100W, the distance between the upper electrode and the lower electrode of 122 mm, and the lower electrode temperature of 15 ° C.
A trench with a side etching ratio of 0.025 could be formed at an etching rate of 5.2 μm / min, but the mask disappearance rate was large and the depth could reach only 85 μm.

FIG. 1 shows a schematic diagram of an example of an apparatus for carrying out the present invention. FIG. 2A is a schematic diagram of a cross section of an ideal trench formed in a silicon substrate, and shows a case where the cross section of the trench is rectangular. FIG. 2B is a schematic diagram of a cross section of an ideal trench formed in a silicon substrate, and shows a case where the cross section of the trench is tapered. FIG. 3 is a schematic cross-sectional view of a realistic trench having side etching formed in a silicon substrate. FIG. 4 is a schematic view of a silicon substrate whose inner wall has been etched into a reverse taper shape. FIG. 5 is a schematic view of a trench formed by the method described in the first embodiment. FIG. 6 is a schematic diagram of a trench formed by the method described in Comparative Example 1.

DESCRIPTION OF SYMBOLS 100 Dry etching apparatus 110 Etching chamber 120 Upper electrode 130 Lower electrode 140 High frequency power supply 150 High frequency power supply 160 Gas introduction port 170 Gas exhaust port 200 Silicon substrate 210 Mask 220 Trench 320 Trench 330 Undercut 340 Boeing

Claims (21)

In the processing chamber, the etching gas is converted into plasma, and the object to be processed made of Si is dry-etched,
(A) a first etching step in which pretreatment by etching is performed on a workpiece made of Si using a first etching gas to form a pretreatment portion having an inverted tapered inner wall; and (b) first A dry etching method comprising a second etching step of performing etching on the pretreatment portion using two etching gases. 2. The method according to claim 1, wherein the first etching step is performed such that a depth of the pretreatment portion is less than 15% of a depth of the entire portion formed by etching. 3. The first etching step according to claim 1, wherein the first etching step is performed so that an angle α formed between the reverse tapered inner wall of the pretreatment portion and the surface of the object to be processed is 70 ° <α <90 °. Method.   The first etching gas reacts with an object to be processed made of Si, and a reaction product generated by the reaction includes a component capable of forming a protective film on a side wall of the object to be processed made of Si. 4. The method according to any one of 3.   The method according to claim 1, wherein the first etching gas comprises a fluorine compound and oxygen, and optionally comprises a rare gas. The fluorine compound contained in the first etching gas is at least one selected from SF ₆ , NF ₃ , BF ₃ , PF ₅ and F ₂ , and the rare gas that may optionally be contained in the first etching gas is helium The dry etching method according to claim 5, which is at least one selected from argon and argon. The dry etching method according to claim ₆ , wherein the fluorine compound of the first etching gas is SF ₆ and the rare gas is helium.   An electric field is generated around the object to be processed made of Si, ions in the plasma generated from the first etching gas are attracted to the object to be processed, and the energy of the ions colliding with the object to be processed causes the front of the object to be processed by etching. The dry etching method according to claim 1, wherein the treatment is performed.   9. The dry etching method according to claim 8, wherein the ion energy source that generates an electric field around the object to be processed is an RF generator.   The dry etching method according to claim 9, wherein the RF power input to the RF generator is 30 to 200 W. ^11. The dry etching method according to claim 1, wherein in the first etching step, an ion density in plasma is 10 × 10 ¹¹ cm ⁻³ or more at a height of 10 mm from the object to be processed.   The dry etching method according to claim 11, wherein plasma is generated by an ICP method.   The dry etching method according to claim 11 or 12, wherein the plasma generation source for generating plasma is an RF generator, and the power of the RF generator is 2000 W or more.   The dry etching method according to claim 11 or 12, wherein a distance between the plasma generation unit and the object to be processed is 50 mm or less.   The dry etching method according to claim 1, wherein the pressure in the processing chamber in the first etching step is 30 Pa or less.   (B) The second etching step is a second etching step in which a second etching gas containing a fluorine compound and oxygen, and optionally containing a rare gas, is introduced into the processing chamber and etched into the pretreatment portion. The dry etching method according to claim 1. The fluorine compound contained in the second etching gas is at least one selected from SF ₆ , NF ₃ , BF ₃ , PF ₅ and F ₂ , and the rare gas optionally contained in the second etching gas is helium and argon The dry etching method according to claim 16, which is at least one selected from the group consisting of:   The dry etching method according to claim 16 or 17, wherein a ratio of the flow rate of the fluorine compound and the flow rate of oxygen (fluorine compound / oxygen) in the second etching gas is 1/1 to 4/1.   The dry etching method according to claim 16, wherein the flow rate of the fluorine compound of the second etching gas is 50 to 900 sccm.   The dry etching method according to claim 16, wherein a flow rate of oxygen of the second etching gas is 50 to 450 sccm. Fluorine compounds of the second etching gas, the dry etching method according to any one of claims 16 to 20 is SF _6.

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