JP2007227829A - Apparatus and method for plasma etching - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control a shape of etching while securing the in-plane uniformity of an etching rate when performing silicon etching with a resist as a mask. <P>SOLUTION: On the lower surface 20b of a shower head 20, a large number of gas discharge ports 22 are formed. Around the gas discharge ports 22, an annular projection 40 is provided projecting toward an oppositely arranged support table 2. Moreover, the gas discharge ports 22 are formed concentratedly to the vicinity of the center of the lower surface 20b of the shower head 20, so that all the gas discharge ports 22 may be included in the area S of a smaller area than that of a wafer W. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a plasma etching apparatus and a plasma etching method, and more particularly, to a plasma etching apparatus and a plasma etching method used when an object to be processed is etched using plasma.

  In the process of manufacturing a semiconductor device, for example, in the manufacture of a three-dimensional mounting device, silicon etching is performed in which a through hole for wiring, a groove for mechanical structure, and the like are formed in a silicon substrate at a depth of 100 μm or more.

In the silicon etching, first, an oxide film such as a SiO ₂ film is etched using a patterned resist as a mask, and after the resist is removed, for example, SF ₆ / O ₂ gas is used as an etching gas, and the SiO ₂ film is used as a mask. A method of etching silicon has been generally employed. However, recently, in order to reduce the number of steps, a method of directly etching silicon using a resist as a mask has been studied.

  In addition, the shape of the etching hole is tapered, that is, in order to easily perform processes such as formation of an insulating film in the etching hole, seed metal layer formation, Cu plating and the like necessary after silicon etching in the manufacture of a three-dimensional mounting device. In some cases, it is required to form the side wall so that the diameter of the bottom is narrower than the top of the hole. However, when silicon etching is performed using a resist as a mask, the uniformity of the etching rate (that is, the depth of the hole) and the controllability of the shape within the semiconductor wafer surface, which is the substrate to be processed, are difficult to obtain. was there. More specifically, since the etching rate of the central part (center) is faster than the peripheral part (edge) of the semiconductor wafer, the hole in the central part tends to be formed deeper than the peripheral part. However, there was a tendency that a side wall was not inclined as compared with the central portion, and a near vertical hole was formed.

  By the way, as for etching of the insulating film, in order to realize fine etching at a high speed, a projecting portion projecting downward is provided on the shield ring around the upper electrode, and etching processing is performed while preventing plasma diffusion. A technique to be performed has been proposed (for example, Patent Document 1).

In addition, for the purpose of controlling the amount of gas blown from the shower head and the gas flow, a technique related to a shower head including a shutter device having an opening whose opening diameter can be freely reduced and enlarged has been proposed (for example, Patent Document 2). ).
JP-A-8-335568 (for example, FIG. 2) Japanese Patent Laid-Open No. 10-60673 (for example, FIG. 1)

  Patent Document 1 and Patent Document 2 propose a shield ring protrusion and a showerhead shutter device. In silicon etching using a resist as a mask, the etching rate is uniform and the etching shape is changed. No consideration is given to the taper control.

  An object of the present invention is to control an etching shape while ensuring in-plane uniformity of an etching rate when performing silicon etching using a resist as a mask.

In order to solve the above problems, a first aspect of the present invention is a processing chamber capable of being evacuated under reduced pressure for performing a plasma etching process on an object to be processed.
A mounting table for mounting an object to be processed in the processing chamber;
A shower head which is arranged opposite to the mounting table and introduces a processing gas for generating plasma in the processing chamber;
On the lower surface of the shower head, an annular convex portion projecting annularly toward the mounting table,
A plurality of gas discharge holes arranged in a region having an area smaller than the area of the object to be processed in the inner central portion of the annular protrusion on the lower surface of the shower head;
There is provided a plasma etching apparatus comprising:

  The plasma etching apparatus according to the first aspect is provided with an annular convex portion projecting annularly toward the mounting table on the lower surface of the shower head and concentrating the gas discharge holes at the inner central portion of the annular convex portion. Because it is arranged, the plasma density in the vicinity of the annular projection and the amount of deposits are mainly controlled by making the pressure in the plasma forming space inside the annular projection uniform, and the central portion of the gas discharge hole is concentrated. As a result, the gas flow rate above the center of the workpiece is increased, and the amount of etchant generated in the center is suppressed. As a result, the in-plane uniformity of the etching rate and the etching shape can be controlled.

  In the first aspect, it is preferable that the pair of counter electrodes be configured with the mounting table as a lower electrode and the shower head as an upper electrode. Moreover, it is preferable that the outer diameter of the said annular convex part is 1.1L-1.5L with respect to the diameter L of a to-be-processed object, and the internal diameter of the said annular convex part is larger than the diameter L of a to-be-processed object. It is preferable. As a result, a plasma forming space that covers the whole of the object to be processed is formed, and in-plane uniformity of etching is ensured.

Moreover, it is preferable that the height of the said annular convex part is 0.4 times or more with respect to the distance from the mounting stand to the said shower head. Thereby, the effect of reducing the conductance of the gas flow and making the pressure in the space surrounded by the annular convex portion uniform can be obtained.
The gas discharge holes are preferably formed in a region having an area of 0.3 L × 0.3 L to 0.7 L × 0.7 L with respect to the diameter L of the object to be processed. This makes it possible to sufficiently increase the gas flow rate in the space above the central portion of the substrate to be processed.

A second aspect of the present invention uses the plasma etching apparatus of the first aspect,
A processing gas containing SF ₆ and O ₂ is applied to an object to be processed having a layer to be etched containing silicon as a main component and a resist layer formed in a layer above the layer to be etched and patterned in advance. There is provided a plasma etching method in which plasma to be etched is applied to a layer to be etched using the generated plasma as a mask.

  In the second aspect, the etched layer is preferably a silicon substrate or a silicon layer.

  A third aspect of the present invention provides a control program that operates on a computer and controls the plasma etching apparatus so that the plasma etching method of the second aspect is performed at the time of execution.

A fourth aspect of the present invention is a computer-readable storage medium storing a control program that runs on a computer,
The control program provides a computer-readable storage medium for controlling the plasma etching apparatus so that the plasma etching method of the second aspect is performed at the time of execution.

  The plasma etching apparatus according to the present invention has an annular protrusion projecting annularly toward the mounting table on the lower surface of the shower head, and a small area relative to the area of the object to be processed at the inner central portion of the annular protrusion. Therefore, by using this plasma etching apparatus, the uniformity of the etching depth within the surface of the object to be processed and, for example, the taper of the taper can be obtained. Etching with excellent controllability of the etching shape such as formation becomes possible. Therefore, this plasma etching apparatus can be advantageously used in manufacturing a highly reliable semiconductor device, and can cope with miniaturization and high integration of design rules of the semiconductor device.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing a magnetron RIE plasma etching apparatus 100 according to the first embodiment of the present invention. The plasma etching apparatus 100 is hermetically configured, has a stepped cylindrical shape composed of a small-diameter upper portion 1a and a large-diameter lower portion 1b, and has a wall (processing vessel) 1 made of, for example, aluminum. .

  In this chamber 1, there is provided a support table 2 that horizontally supports a wafer W, which is a single crystal Si substrate, as an object to be processed. The support table 2 is made of aluminum, for example, and is supported by a conductor support 4 via an insulating plate 3. A focus ring 5 made of a material other than Si, for example, quartz, is provided on the outer periphery above the support table 2. The support table 2 and the support table 4 can be moved up and down by a ball screw mechanism including a ball screw 7, and a drive portion below the support table 4 is covered with a bellows 8 made of stainless steel (SUS). . A bellows cover 9 is provided outside the bellows 8. A baffle plate 10 is provided outside the focus ring 5 and is electrically connected to the chamber 1 through the baffle plate 10, the support 4 and the bellows 8. The chamber 1 is grounded.

  An exhaust port 11 is formed on the side wall of the lower portion 1 b of the chamber 1, and an exhaust system 12 is connected to the exhaust port 11. The inside of the chamber 1 can be depressurized to a predetermined degree of vacuum by operating a vacuum pump of the exhaust system 12. On the other hand, a gate valve 13 for opening and closing the loading / unloading port for the wafer W is provided on the upper side wall of the lower portion 1 b of the chamber 1.

  A high frequency power source 15 for plasma formation is connected to the support table 2 via a matching unit 14, and high frequency power of a predetermined frequency is supplied from the high frequency power source 15 to the support table 2. On the other hand, a shower head 20, which will be described in detail later, is provided in parallel with each other so as to face the support table 2, and the shower head 20 is grounded. Therefore, the support table 2 and the shower head 20 function as a pair of electrodes.

  An electrostatic chuck 6 for electrostatically attracting and holding the wafer W is provided on the surface of the support table 2. The electrostatic chuck 6 is configured by interposing an electrode 6a between insulators 6b, and a DC power source 16 is connected to the electrode 6a. When a voltage is applied to the electrode 6a from the power source 16, the wafer W is attracted by electrostatic force, for example, Coulomb force.

  A refrigerant chamber 17 is provided inside the support table 2. In this refrigerant chamber 17, the refrigerant is introduced through the refrigerant introduction pipe 17a, discharged from the refrigerant discharge pipe 17b and circulated, and the cold heat is supported. Heat is transferred to the wafer W via the table 2, whereby the processing surface of the wafer W is controlled to a desired temperature.

  Further, even if the chamber 1 is evacuated by the exhaust system 12 and kept in a vacuum, the cooling gas is supplied by the gas introduction mechanism 18 so that the wafer W can be effectively cooled by the refrigerant circulated in the refrigerant chamber 17. It is introduced between the surface of the electrostatic chuck 6 and the back surface of the wafer W via the gas supply line 19. By introducing the cooling gas in this way, the cooling heat of the refrigerant is effectively transmitted to the wafer W, and the cooling efficiency of the wafer W can be increased. For example, He can be used as the cooling gas.

The shower head 20 is provided on the top wall portion of the chamber 1 so as to face the support table 2. A number of gas discharge holes 22 are provided on the lower surface 20 b of the shower head 20, and a cylindrical shape protruding around the gas discharge holes 22 toward the support table 2 arranged opposite to the gas discharge holes 22. An annular convex portion 40 made of a wall body is provided. The annular protrusion 40 may be provided integrally with the shower head 20, or an annular member different from the shower head 20 may be attached to the lower surface of the shower head 20. The annular protrusion 40 is made of the same material as the shower head 20, such as aluminum. Further, if necessary, an alumite treatment or a ceramic sprayed film such as Y ₂ O ₃ can be formed on the surface of the annular convex portion 40 in the same manner as the shower head 20.

  Further, a gas introduction part 20 a is provided on the upper part of the shower head 20. And the space 21 is formed in the inside. A gas supply pipe 23a is connected to the gas introduction part 20a, and a processing gas supply system 23 for supplying a processing gas comprising an etching gas and a dilution gas is connected to the other end of the gas supply pipe 23a.

As an etching gas, it is preferable to use a gas containing SF ₆ and O ₂ . SF ₆ gas has a density of F atoms generated in plasma several times higher than other fluorine-based gases, and S ₆ contained in SF ₆ promotes etching by preventing oxidation of the Si surface. Therefore, it can be suitably used for silicon etching.
Further, the O ₂ gas reacts with silicon in the silicon substrate to form a silicon oxide film (SiO _x ) on the side wall, and has a function of promoting anisotropic etching in the vertical direction.
As an etching gas other than the above, for example, S ₂ F ₁₀ , NF ₃ , SiF ₄ or the like can be used.

  Such a processing gas reaches the space 21 of the shower head 20 from the processing gas supply system 23 via the gas supply pipe 23a and the gas introduction part 20a, and is discharged from the gas discharge hole 22.

  On the other hand, a dipole ring magnet 24 is disposed concentrically around the upper portion 1 a of the chamber 1. As shown in the horizontal sectional view of FIG. 2, the dipole ring magnet 24 is configured by attaching a plurality of anisotropic segment columnar magnets 31 to a ring-shaped magnetic casing 32. In this example, 16 anisotropic segment columnar magnets 31 having a cylindrical shape are arranged in a ring shape. In FIG. 2, the arrows shown in the anisotropic segment columnar magnet 31 indicate the direction of magnetization. As shown in this figure, the magnetization directions of the plurality of anisotropic segment columnar magnets 31 are gradually shifted. Thus, a uniform horizontal magnetic field B directed in one direction as a whole is formed.

  Accordingly, in the space between the support table 2 and the shower head 20, as shown schematically in FIG. 3, a vertical electric field EL is formed by the high frequency power source 15, and a horizontal magnetic field B is generated by the dipole ring magnet 24. The magnetron discharge is generated by the formed orthogonal electromagnetic field. As a result, plasma of an etching gas in a high energy state is formed, and the wafer W is etched.

  Each component of the plasma etching apparatus 100 is connected to and controlled by a process controller 50 having a CPU. The process controller 50 has a user interface 51 including a keyboard for a process manager to input a command for managing the plasma etching apparatus 100, a display for visualizing and displaying the operating status of the plasma etching apparatus 100, and the like. It is connected.

  In addition, the process controller 50 includes a storage unit 52 that stores a recipe in which a control program for realizing various processes executed by the plasma etching apparatus 100 under the control of the process controller 50 and processing condition data are stored. It is connected.

  Then, if necessary, an arbitrary recipe is called from the storage unit 52 by an instruction from the user interface 51 and is executed by the process controller 50, so that a desired one in the plasma etching apparatus 100 is controlled under the control of the process controller 50. Is performed. The recipe may be stored in a computer-readable storage medium such as a CD-ROM, a hard disk, a flexible disk, or a flash memory, or may be a dedicated line from another device. It is also possible to transmit and use it as needed.

Next, the arrangement of the annular convex portion 40 and the gas discharge hole 22 in the shower head 20 will be described with reference to FIGS. 4 and 5.
By providing the annular protrusion 40 on the lower surface of the shower head 20, the conductance of the gas flow discharged from the gas discharge hole 22 of the shower head 20 is reduced, and the pressure distribution in the space surrounded by the annular protrusion 40 is uniform. Can be. As a result, the amount of the sidewall protective film in the etching hole can be reduced by controlling the plasma density and the amount of silicon reaction product that is the source of the deposit, particularly in the vicinity of the convex portion in the space surrounded by the annular convex portion 40. It becomes possible to control the etching shape of silicon in a forward tapered shape.

  The protrusion amount (height; H) of the annular convex portion 40 is the distance between the upper and lower electrodes (gap) G, that is, the upper surface of the support table 2 (the upper surface of the electrostatic chuck 6 in the case of FIG. 1) and the lower surface of the shower head 20. It is preferably 0.4 times or more, for example, 0.4 to 0.8 times the distance to 20b. When the protrusion amount H of the annular protrusion 40 is less than 0.4 times the gap G, the gas flow conductance is not sufficiently lowered, and the effect of equalizing the pressure in the space surrounded by the annular protrusion 40 is achieved. Less is. On the other hand, when the protrusion amount H exceeds 0.8 times the gap G, the conductance of the gas flow is excessively decreased, and the dissociation of the etching gas component proceeds excessively, which may deteriorate the etching characteristics. The gap G is preferably 25 to 50 mm, for example.

In addition, the outer diameter L ₁ of the annular protrusion 40 is preferably 1.1 L to 1.5 L with respect to the diameter L of the wafer W from the viewpoint of reducing the conductance of the gas flow above the wafer W. The outer diameter L ₁ is preferably set smaller than the diameter of the horizontal mounting surface on which the wafer W is mounted on the support table 2. When the focus ring 5 is provided on the support table 2, the outer diameter L ₁ of the annular protrusion 40 is preferably set smaller than the outer diameter L ₄ of the focus ring 5.

On the other hand, the inner diameter L ₂ of the annular protrusion 40 is preferably set larger than the diameter L of the wafer W from the viewpoint of forming a uniform plasma space above the wafer W.

Further, in the present embodiment, as shown in FIG. 5, the gas discharge holes 22 are concentrated and provided near the center of the lower surface 20 b of the shower head 20. That is, on the lower surface 20b of the shower head 20, a rectangular region S in which one side (L ₃ ) is approximately 0.3L to 0.7L with respect to the diameter L of the wafer W (that is, S = L ₃ × L _3). ) And the gas discharge holes 22 are concentrated and distributed in the lower surface 20b of the shower head 20, and the gas discharge holes 22 are not provided in the region facing the peripheral edge of the wafer W. Thus, in this embodiment, the gas discharge holes 22 are concentrated near the center of the lower surface 20b of the shower head 20 so that all the gas discharge holes 22 enter the region S having a smaller area than the area of the wafer W. Yes. In FIG. 5, the gas discharge holes 22 to be formed outside the region S are indicated by phantom lines in the shower head having the normally arranged gas discharge holes 22 for reference purposes.

By forming the gas discharge holes 22 in a central portion of the shower head 20, the gas flow rate in the space above the central portion of the wafer W can be increased. As a result of increasing the gas flow rate in the space above the central portion of the wafer W, the residence time of radicals is shortened. In this space, dissociation into F radicals as etchants is suppressed, and the etching rate of silicon decreases. The uniformity in the plane of the wafer W is improved.
Note that the distribution of the gas discharge holes 22 in the shower head 20 may be adjusted by closing and closing a member that can be inserted into the gas discharge holes 22 in a region facing the peripheral edge of the wafer W. For example, by closing the gas discharge holes 22 at the positions indicated by phantom lines in FIG. 5, the arrangement (distribution region) of the gas discharge holes can be adjusted and concentrated in the center of the shower head 20.

Next, an etching method of the present invention for performing plasma etching on silicon (single crystal silicon substrate or polysilicon layer) using the plasma etching apparatus configured as described above will be described.
First, the gate valve 13 is opened and the wafer W is loaded into the chamber 1 and placed on the support table 2. Then, the support table 2 is raised to the position shown in the figure, and the exhaust port 11 is set by the vacuum pump of the exhaust system 12. The inside of the chamber 1 is exhausted through.

  Then, a processing gas including an etching gas and a dilution gas is introduced from the processing gas supply system 23 into the chamber 1 at a predetermined flow rate, and the chamber 1 is set to a predetermined pressure. Supply high frequency power. At this time, the wafer W is attracted and held on the electrostatic chuck 6 by, for example, Coulomb force when a predetermined voltage is applied to the electrode 6a of the electrostatic chuck 6 from the DC power supply 16, and the shower head which is the upper electrode. A high frequency electric field is formed between 20 and the support table 2 which is a lower electrode. Since a horizontal magnetic field B is formed between the shower head 20 and the support table 2 by the dipole ring magnet 24, an orthogonal electromagnetic field is formed in the processing space between the electrodes on which the wafer W exists, and is generated thereby. Magnetron discharge is generated by electron drift. Then, the wafer W is etched by the plasma of the etching gas formed by this magnetron discharge. At this time, the uniformity of the etching rate in the wafer surface and the etching shape are increased by the pressure increase in the inner space of the annular protrusion 40 and the gas flow rate increase due to the concentrated arrangement near the center of the gas discharge hole 22 as described above. Controllability is improved.

  In order to improve the etching shape, it is also effective to adjust the temperature of the wafer W. For this purpose, a refrigerant chamber 17 is provided, and the refrigerant is circulated in the refrigerant chamber 17, and the cold heat is transferred to the wafer W via the support table 2, whereby the processing surface of the wafer W has a desired temperature. Controlled.

  The frequency and output of the high-frequency power source 15 for generating plasma are appropriately set in order to form desired plasma. In silicon etching, from the viewpoint of increasing the plasma density immediately above the wafer W, the frequency is preferably set to 40 MHz or higher, for example.

  The dipole ring magnet 24 applies a magnetic field to the processing space between the support table 2 as the counter electrode and the shower head 20 in order to increase the plasma density immediately above the wafer W, but in order to effectively exhibit the effect. It is preferable that the magnet be strong enough to form a magnetic field of 10,000 μT (100 G) or more in the processing space. It is considered that the stronger the magnetic field is, the higher the effect of increasing the plasma density is. However, from the viewpoint of safety, it is preferably 100000 μT (1 kG) or less.

Suitable conditions for performing silicon etching using the plasma etching apparatus 100 are as follows. The flow rate of the etching gas is SF ₆ = 100 to 1000 mL / min (sccm), O ₂ = 0 to 500 mL / min (sccm), and the flow rate ratio is SF ₆ / O ₂ = 3 / from the viewpoint of etching shape control. It is preferably 1 to 2/1.
The processing pressure is preferably 10 to 60 Pa (75 mTorr to 450 mTorr) from the viewpoint of securing a sufficient etching rate and mask selection ratio.
In order to obtain a sufficient etching rate and mask selection ratio, it is preferable that the high frequency power of the high frequency power supply 15 is 40 MHz or more and the high frequency power is 0.5 to 2.0 kW.
The strength of the magnetic field formed by the dipole ring magnet 24 is preferably 10000 μT to 30000 μT.
Further, from the viewpoint of favorably controlling the etching shape, that is, the anisotropy, it is preferable to adjust the temperature of the wafer W to, for example, about −15 to 30 ° C.

6 and 7 schematically show a cross-sectional structure in the vicinity of the surface of the object 110 such as the wafer W in order to explain the plasma etching method using the plasma etching apparatus 100 of the present invention.
As shown in FIG. 6, the object to be processed 110 includes a resist 102 patterned in advance on a silicon substrate 101. Note that an antireflection film (not shown) may be provided immediately below the resist 102. Then, the plasma etching apparatus 100 is used for the object 110 to be processed, and silicon etching is performed by applying plasma of a processing gas based on the pattern using the resist 102 as a mask. For example, SF ₆ / O ₂ can be used as the processing gas. The etching conditions at this time are as described above.

By this silicon etching, holes 121 having a predetermined depth D corresponding to the pattern shape of the resist 102 are formed in the silicon substrate 101 as shown in FIG.
Here, when comparing the opening diameter L _{5 at} the top of the hole 121 and the diameter L _{6 at} the bottom, the side wall of the hole 121 is inclined as understood from the fact that the diameter L _{6 at} the bottom is smaller. Is formed. That is, the hole 121 is formed in a tapered shape when viewed in cross section. The angle formed by the side wall of the hole 121 with respect to the horizontal direction (180 ° −θ; hereinafter referred to as “side wall angle”) is preferably, for example, 83 ° to 87 °.

  As described above, the plasma etching apparatus 100 in which the shower head 20 is provided with the annular convex portion 40 and the gas discharge holes 22 are concentrated in the vicinity of the center portion of the lower surface 20b of the shower head 20 is used. By etching the substrate 101, the uniformity of the etching rate within the surface of the wafer W and the etching shape can be controlled, and the uniformity within the surface of the wafer W can be achieved. Therefore, it is possible to form a hole having a uniform shape while aligning the hole depth in the surface of the wafer W and controlling it to a predetermined side wall angle.

Next, although a test example, an Example, and a comparative example are given and this invention is demonstrated in more detail, this invention is not restrict | limited by these. In the following test examples and the like, an 8-inch diameter (200 mm diameter) wafer W was used.
Test example 1
Using the shower head 20 provided with the annular protrusions 40 of the two types A and B shown below, the distance between the upper and lower electrodes (gap G) is set to 22 mm, 27 mm, or 32 mm, and the same as FIG. A plasma etching process was performed on the target object 110 having a structure to form a hole 121 in the silicon substrate 101. In addition, as the shower head 20, what alumite-treated on the surface was used.

Annular projection A:
Protrusion (H) = 15mm
Outer diameter (L ₁ ) = 260 mm
Inner diameter (L ₂ ) = 240 mm
Width [(L ₁ −L ₂ ) × 1/2] = 10 mm
Annular convex part B
Projection amount (H) = 21 mm
Outer diameter (L ₁ ) = 270 mm
Inner diameter (L ₂ ) = 240 mm
Width [(L ₁ −L ₂ ) × 1/2] = 15 mm

Etching conditions are as follows.
Resist: film thickness = 7μm
Process gas: SF ₆ / O ₂ = 170/50 mL / min (sccm)
Pressure = 37.3 Pa (280 mTorr)
RF frequency (high frequency power supply 15) = 40 MHz
RF power = 840 W (2.68 W / cm ² )
Magnetic field = 17000 μT (170 G)
Back pressure (center part / edge part) = 1333/4000 Pa (10/30 Torr; He gas)
Temperature (lower electrode / upper electrode / chamber sidewall) = 0 ° C./40° C./40° C.
Etching time = 4 minutes and 11 seconds

  The in-plane uniformity of the wafer W was evaluated for the cross-sectional shape (etching shape) of the hole 121 formed by plasma etching under the above conditions. The results are shown in Table 1. In the table, ◯ indicates that the controllability for controlling the etching shape to be tapered is good, and X indicates that the controllability is poor.

  From Table 1, when the annular protrusion A having a projection length (H) as short as 15 mm was used, the controllability of the etching shape was not obtained even when the gap G was 22 mm, which is the shortest. Therefore, in order to obtain a good etching shape controllability, it was considered that a protrusion amount H exceeding 15 mm at least was necessary.

Test example 2
Next, the shower head 20 is provided with 49 gas discharge holes 22 in a region S of 108.7 mm × 108.7 mm at the center of the lower surface 20b, and the distance between the upper and lower electrodes (gap G). Is set to 22 mm, 27 mm, 32 mm, or 33 mm, and a plasma etching process is performed on the workpiece 110 having the same structure as in FIG. 6 under the same conditions as in Test Example 1 to form a hole 121 in the silicon substrate 101. did. Then, the in-plane uniformity of the wafer W was evaluated for the etching depth D of the hole 121. The results are shown in Table 2. In the table, ◯ indicates that the etching depth uniformity in the wafer surface was good, and x indicates that the etching was poor.

  From Table 2, in the shower head 20 provided with 49 gas discharge holes 22 in the area S of 108.7 mm × 108.7 mm, the gap G is 27 mm to 27 mm in both the annular protrusion A and the annular protrusion B. Although a uniform etching depth was obtained in the wafer surface in the range of 32 mm, the uniformity of the etching depth in the wafer surface was obtained even when the annular protrusion B having a protrusion amount H of 21 mm was used when the gap G was 33 mm. I couldn't. From this result, it was inferred that it is necessary to select the protrusion height H of the annular protrusion 40 in relation to the gap G in order to obtain the uniformity of the etching depth within the wafer surface.

Test example 3
Next, using the shower head 20 having a Y ₂ O ₃ sprayed film formed on the surface, the area of the region S where the gas discharge holes at the center of the lower surface 20b are distributed, and the gas discharge holes 22 formed on the inside of the area S The number was changed as shown in Table 3, and a plasma etching process was performed on the target object 110 having the same structure as in FIG. 6 under the same conditions as in Test Example 1 to form holes 121 in the silicon substrate 101. Then, the in-plane uniformity of the wafer W was evaluated for the etching depth of the hole 121. In this test, the distance between the upper and lower electrodes (gap G) was set to 37 mm, and the annular convex portion 40 was not provided. The results are also shown in Table 3. In the table, ◯ indicates that the etching depth uniformity in the wafer surface was good, and x indicates that the etching was poor.

From Table 3, for the wafer W having a diameter of 200 mm, the shower head 20 in which 25 gas discharge holes 22 are formed in the region S of 61.7 mm × 61.7 mm, and the region S of 96.96 mm × 96.96 mm In the shower head 20 having 37 gas discharge holes 22 formed therein, a uniform etching depth was obtained in the wafer surface, whereas 81 areas in a region S of 120.5 mm × 120.5 mm were obtained. In the shower head 20 provided with the gas discharge holes 22, the in-wafer surface uniformity of the etching depth was not obtained.
From this result, it was considered that the arrangement and the number of the gas discharge holes 22 need to be selected in order to obtain the uniformity of the etching depth within the wafer surface.

Based on the above test results, the following Comparative Examples 1 to 3 and Example 1 were carried out.
Comparative Example 1
A conventional shower head in which 153 gas discharge holes 22 are arranged in a region S of 210 mm × 210 mm without the annular convex portion 40 is used, and the object 110 having the same structure as in FIG. Plasma etching was performed under the conditions, and holes 121 were formed in the silicon substrate 101.

Etching conditions are as follows.
Resist: film thickness = 7μm
Process gas: SF ₆ / O ₂ = 170/50 mL / min (sccm)
Pressure = 37.3 Pa (280 mTorr)
RF frequency (high frequency power supply 15) = 40 MHz
RF power = 840 W (2.68 W / cm ² )
Magnetic field = 17000 μT (170 G)
Gap = 37mm
Back pressure (center part / edge part) = 1333/4000 Pa (10/30 Torr; He gas)
Temperature (lower electrode / upper electrode / chamber sidewall) = 0 ° C./40° C./40° C.
Etching time = 4 minutes and 11 seconds

Comparative Example 2
Protruding amount (H) = 21 mm, outer diameter (L ₁ ) = 270 mm, inner diameter (L ₂ ) = 240 mm, width [(L ₁ −L ₂ ) × 1/2] = 15 mm of annular convex portion 40 Using a shower plate in which 153 gas discharge holes 22 are arranged in a region S of 210 mm × 210 mm, a plasma etching process is performed on the target object 110 having the same structure as in FIG. A hole 121 was formed in the substrate 101.

Etching conditions are as follows.
Resist: film thickness = 7μm
Process gas: SF ₆ / O ₂ = 170/50 mL / min (sccm)
Pressure = 37.3 Pa (280 mTorr)
RF frequency (high frequency power supply 15) = 40 MHz
RF power = 700 W (2.23 W / cm ² )
Magnetic field = 17000 μT (170 G)
Gap = 37mm
Back pressure (center part / edge part) = 1333/4000 Pa (10/30 Torr; He gas)
Temperature (lower electrode / upper electrode / chamber sidewall) = 0 ° C./40° C./40° C.
Etching time = 4 minutes and 11 seconds

Comparative Example 3
Using a shower plate that is not provided with an annular convex portion 40 and that has 25 gas discharge holes 22 concentrated and disposed in a region S of 61.7 mm × 61.7 mm at the center of the lower surface of the shower plate. A plasma etching process was performed on the target object 110 having the structure under the following conditions to form holes 121 in the silicon substrate 101.

Etching conditions are as follows.
Resist: film thickness = 7μm
Process gas: SF ₆ / O ₂ = 170/50 mL / min (sccm)
Pressure = 37.3 Pa (280 mTorr)
RF frequency (high frequency power supply 15) = 40 MHz
RF power = 840 W (2.68 W / cm ² )
Magnetic field = 17000 μT (170 G)
Gap = 37mm
Back pressure (center part / edge part) = 1333/4000 Pa (10/30 Torr; He gas)
Temperature (lower electrode / upper electrode / chamber sidewall) = 0 ° C./40° C./40° C.
Etching time = 4 minutes and 11 seconds

Example 1
Protruding amount (H) = 21 mm, outer diameter (L ₁ ) = 270 mm, inner diameter (L ₂ ) = 240 mm, width [(L ₁ −L ₂ ) × 1/2] = 15 mm of annular convex portion 40 A shower plate in which 49 gas discharge holes 22 are concentrated and arranged in a 108.7 mm × 108.7 mm region S at the center of the lower surface of the shower plate is used for the object 110 to be processed having the same structure as FIG. A plasma etching process was performed on the following conditions to form holes 121 in the silicon substrate 101.

Etching conditions are as follows.
Resist: film thickness = 7μm
Process gas: SF ₆ / O ₂ = 170/50 mL / min (sccm)
Pressure = 33.3 Pa (250 mTorr)
RF frequency (high frequency power supply 15) = 40 MHz
RF power = 500 W (1.59 W / cm ² )
Magnetic field = 17000 μT (170 G)
Gap = 32mm
Back pressure (center part / edge part) = 1333/4000 Pa (10/30 Torr; He gas)
Temperature (lower electrode / upper electrode / chamber sidewall) = 0 ° C./40° C./40° C.
Etching time = 4 minutes 30 seconds

  After the plasma etching in Comparative Examples 1 to 3 and Example 1, the etching depth and the etching shape (side wall angle) of the hole 121 at a plurality of points in the surface of each wafer W are based on the image of the transmission electron microscope. Measured. The measurement points were the center (center) of the wafer W, the edge 50 mm, the edge 30 mm, the edge 20 mm, and the edge 10 mm. Here, “edge 50 mm” means that the position is 50 mm from the peripheral edge of the wafer toward the in-plane center. Similarly, “edge 30 mm”, “edge 20 mm”, and “edge 10 mm” mean that the positions are 30 mm, 20 mm, and 10 mm, respectively, from the peripheral edge of the wafer toward the in-plane center. The results of Comparative Examples 1 to 3 and Example 1 are summarized in Table 4.

  As shown in Table 4, in the plasma etching result of Comparative Example 1 in which the shower head having the conventional structure in which the annular protrusion 40 is not provided and the formation region of the gas discharge hole 22 is wide, the etching depth in the wafer surface ( Variation in the depth of the hole 121 is large. In particular, at the edge portion of the wafer W, the side wall angle of the hole 121 is close to 90 °, and the taper shape in cross section cannot be controlled.

  In the plasma etching result of the comparative example 2 in which the annular protrusion 40 is provided, but the shower area of the gas discharge hole 22 is wide as in the conventional structure, the side wall angle of the hole 121 is larger than that of the comparative example 1. The side wall can be slightly inclined, but the variation of the etching depth (depth of the hole 121) in the wafer surface is still large.

  In the plasma etching result of the comparative example 3 using the shower head in which the annular convex portion 40 is not provided and only the formation region of the gas discharge hole 22 is narrowly formed, the etching depth in the wafer surface is larger than that of the comparative examples 1 and 2. Variation in (depth of hole 121) was improved. However, the side wall angle of the hole 121 is close to 90 ° as in the first comparative example, and cannot be controlled to have a tapered shape in sectional view.

  In the plasma etching result of Example 1 using the shower plate in which the annular convex portion 40 is provided and the gas discharge holes 22 are concentrated in the center of the lower surface of the shower plate, the wafer is compared with Comparative Examples 1 to 3. The variation in the etching depth (depth of the hole 121) in the plane was greatly improved. Further, the side wall angle of the hole 121 was 83 ° to 85 °, and it was possible to control the taper shape in a sectional view all over the wafer surface.

From the comparison between Comparative Example 1 and Comparative Example 2, for the purpose of giving the sidewall of the hole 121 an inclination and controlling the etching cross section to a tapered shape, a temporary effect can be obtained by using a shower plate having an annular convex portion 40. Is understood to be obtained.
Further, from the comparison between Comparative Example 1 and Comparative Example 3, the uniformity of the etching depth within the wafer surface is temporarily improved by using a shower plate in which the gas discharge holes 22 are concentrated in the center of the lower surface of the shower plate. You can see that

  However, in comparison with Comparative Examples 2 and 3 and Example 1, in Example 1 using the shower plate in which the annular convex portion 40 is provided and the gas discharge holes 22 are concentrated in the central portion, the etching depth is increased. The wafer surface uniformity and the controllability of the sidewall angle of the hole 121 were clearly superior to those of Comparative Examples 1 and 2. That is, the result of Example 1 was not the sum of the results of Comparative Examples 1 and 2, but improved both the etching depth uniformity in the wafer surface and the controllability of the etching shape.

  As mentioned above, although embodiment of this invention was described, this invention is not restrict | limited to the said embodiment, A various deformation | transformation is possible. For example, although the dipole ring magnet is used as the magnetic field forming means of the magnetron RIE plasma etching apparatus in the above embodiment, the invention is not limited to this, and the formation of the magnetic field is not essential. Further, any plasma etching apparatus such as a capacitive coupling type or an inductive coupling type can be used as long as the plasma can be formed by the gas species of the present invention.

  The present invention can be suitably used in the process of manufacturing various semiconductor devices such as transistors.

Sectional drawing which shows the magnetron RIE plasma etching apparatus suitable for implementation of the etching method of this invention. The horizontal sectional view which shows typically the dipole ring magnet of the state arrange | positioned around the chamber of the apparatus of FIG. The schematic diagram for demonstrating the electric field and magnetic field which are formed in a chamber. The figure which uses for description of arrangement | positioning of an annular convex part and a gas discharge hole. The top view of the lower surface of the shower head with which it uses for description of arrangement | positioning of an annular convex part and a gas discharge hole. The typical sectional view near the surface of a semiconductor wafer which shows the state where plasma etching is performed. The typical sectional view near the surface of the semiconductor wafer after plasma etching.

Explanation of symbols

1; chamber (processing vessel)
2: Support table (electrode)
12; exhaust system 15; high-frequency power source 17; refrigerant chamber 18; gas introduction mechanism 20; shower head (electrode)
22; gas discharge hole 23; processing gas supply system 24; dipole ring magnet 40; annular projection 101; silicon substrate 102; resist W;

Claims (10)

A processing chamber capable of being evacuated under reduced pressure for performing a plasma etching process on an object to be processed;
A mounting table for mounting an object to be processed in the processing chamber;
A shower head which is arranged opposite to the mounting table and introduces a processing gas for generating plasma in the processing chamber;
On the lower surface of the shower head, an annular convex portion projecting annularly toward the mounting table,
A plurality of gas discharge holes arranged in a region having an area smaller than the area of the object to be processed in the inner central portion of the annular protrusion on the lower surface of the shower head;
A plasma etching apparatus comprising:   The plasma etching apparatus according to claim 1, wherein a pair of counter electrodes is configured with the mounting table as a lower electrode and the shower head as an upper electrode.   The plasma etching apparatus according to claim 1 or 2, wherein an outer diameter of the annular convex portion is 1.1L to 1.5L with respect to a diameter L of the object to be processed.   The plasma etching apparatus according to claim 3, wherein an inner diameter of the annular convex portion is larger than a diameter L of the object to be processed.   5. The plasma etching apparatus according to claim 1, wherein a height of the annular convex portion is 0.4 times or more with respect to a distance from the mounting table to the shower head.   The said gas discharge hole is formed in the area | region which has an area of 0.3Lx0.3L-0.7Lx0.7L with respect to the diameter L of a to-be-processed object. The plasma etching apparatus according to claim 1. Using the plasma etching apparatus according to any one of claims 1 to 6,
A processing gas containing SF ₆ and O ₂ is applied to an object to be processed having a layer to be etched containing silicon as a main component and a resist layer formed in a layer above the layer to be etched and patterned in advance. A plasma etching method in which plasma to be etched is applied to a layer to be etched using the generated plasma as a mask.   The plasma etching method according to claim 6, wherein the etching target layer is a silicon substrate or a silicon layer.   A control program that operates on a computer and controls the plasma etching apparatus so that the plasma etching method according to claim 7 or 8 is performed at the time of execution. A computer-readable storage medium storing a control program that runs on a computer,
A computer-readable storage medium for controlling the plasma etching apparatus so that the plasma etching method according to claim 7 or 8 is performed when the control program is executed.

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