JP2004119972A - Silicon etching method and etching device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a high aspect ratio and improvement of the etching rate in Si etching. <P>SOLUTION: Mixture gas of Cl<SB>2</SB>/O<SB>2</SB>/NF<SB>3</SB>is introduced from a process gas supply part 42 into a chamber 10 as an etching gas, and etching is performed under the condition, where the residence time is about 180 nsec or larger. High-frequency near 60 MHz is applied from a first high-frequency power source 58 to an upper electrode 30 at a specified power level. Further, a high frequency near 2MHz is applied from a second high-frequency power source 64 to a lower electrode (susceptor) 16 with a specified power level. The etching gas, discharged from a porous electrode plate or a shower head 36 of the upper electrode 30, is turned into a plasma during the glow discharge between the electrodes, and a Si wafer W is etched by radicals and ions generated in the plasma. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a technique for etching Si (silicon), and more particularly to an etching method and apparatus suitable for forming a deep trench having a small opening diameter in a Si substrate or a Si layer.

A common trench isolation method for element isolation in LSI (Large Scale Integrated circuit) is STI (Shallow Trench Isolation). In STI, a Si substrate is dry-etched using a resist or an insulating film as a mask to form a relatively shallow groove (trench) having a depth of 1 μm or less. This trench etching requires a technique for controlling the depth and shape of the trench, particularly the sidewall angle (taper angle).

Conventionally, a mixed gas based on Br (bromine), typically an HBr / O ₂ mixed gas, is often used as an etching gas for STI. HBr is relatively weak in aggressiveness to an oxide film (SiO ₂ ) formed on the trench side wall due to the action of O ₂ , and is easy to form a tapered shape. It is easy to control the thickness and taper angle. In STI, since the groove is shallow, the tapered shape is not so inconvenient. Rather, the tapered shape is preferable to the strict vertical shape in that the void can be prevented when the groove is buried with the insulating film. It has been.

By the way, DTI (Deep Trench Isolation) has been attracting attention as a trench isolation method having a high element isolation capability along with the increase in density and miniaturization of LSI. In DTI, a relatively deep trench (trench) having a depth of about 3 to 5 μm is formed in a Si substrate, so that a trench etching technique capable of coping with a much higher aspect ratio than STI is required.

The HBr / O ₂ mixed gas cannot perform DTI since trench etching with a high aspect ratio cannot be performed. There is also a problem that the etching rate is low and the processing efficiency or productivity is low.

The present invention has been made to solve the problems of the related art, and has as its object to provide a Si etching method and an etching apparatus which can cope with a high aspect ratio and improve an etching rate.

In order to achieve the above object, the Si etching method of the present invention uses a mixed gas containing Cl ₂ , O ₂ and NF ₃ as an etching gas when dry etching a Si substrate or a Si layer in a processing vessel. Then, the etching process is performed under the condition that the residence time τ represented by the following equation (1) is about 180 msec or more.
τ = pV / Q ‥‥‥ (1)
Here, p is the pressure (Torr) in the processing vessel, V is the volume (l: liter) of an effective etching space set on the object to be processed, and Q is the total flow rate of the etching gas (Torr · l / s). It is.

Further, the etching apparatus of the present invention is an etching apparatus for dry-etching a Si substrate or a Si layer, the apparatus having a gas inlet and an exhaust port, and capable of taking in and out an object to be processed including the Si substrate or the Si layer. An etching gas containing a processing vessel to be accommodated, a Cl ₂ gas, an O ₂ gas, and an NF ₃ gas mixed at a desired flow ratio, and supplying the mixed gas as an etching gas into the processing vessel through the gas inlet; A supply unit, a plasma generation unit that converts the etching gas into plasma, and an exhaust unit that exhausts the inside of the processing chamber through the exhaust port to provide a desired etching pressure. The etching process is performed under the condition that the residence time τ is about 180 msec or more.

In the present invention, a mixed gas containing Cl ₂ , O ₂ and NF ₃ is used as an etching gas. In this etching gas, Cl ₂ is a main etchant for etching Si, reacts with Si with a higher reaction probability than HBr, generates a highly volatile reaction product, and enables high-speed etching. O ₂ reacts with Si to form an oxide film or a protective film (SiO _x ) on the side wall of the groove to prevent side etching. NF ₃ suppresses excessive growth of the side wall protective film, allows the etchant to smoothly enter the inside or bottom of the groove, and promotes anisotropic etching.

た め In order to vertically and deeply etch a groove having a small opening diameter, it is important to balance the deposition rate and the etching rate near the bottom of the groove. In the present invention, the Si etching process is performed under the condition that the residence time τ is about 180 msec or more.

As an example, in a parallel plate type plasma etching apparatus, in order to set the residence time τ to 180 msec or more under the conditions that the diameter of an object to be processed, for example, a Si wafer is 200 mm, the pressure is 60 mTorr, and the distance between electrodes (gap) is 115 mm. The flow rate Q of the etching gas may be set to about 95 sccm or less.

In the present invention, preferably, the total flow rate of Cl ₂ and O _{2 in} the total flow rate of the etching gas (Cl ₂ / O ₂ / NF ₃ ) may be about 80% or less. Therefore, in the above example, the flow rate of Cl ₂ + O ₂ may be about 75 sccm or less.

Further, the ratio of the (Cl ₂ + O ₂ ) flow rate to the O ₂ flow rate, O ₂ / (Cl ₂ + O ₂ ), is also an important parameter, and O ₂ / (Cl ₂ + O ₂ ) is preferably 0.1 to 0.3. , More preferably within the range of 0.15 to 0.25. If O ₂ / (Cl ₂ + O ₂ ) is too large, the growth of the side wall deposition film is accelerated, and the taper angle is reduced and the etching rate is reduced. Conversely, if O ₂ / (Cl ₂ + O ₂ ) is too small, the protection of the side wall is weakened, and reverse taper or bowing is likely to occur.

Also, in the present invention, an inert gas such as Ar may be mixed as a diluting gas with the etching gas, and preferably, the total flow rate of the etching gas may be 100 sccm or less. Preferably, the etching pressure may be set in the range of 20 mTorr to 200 mTorr, and the distance between the electrodes in the parallel plate type may be set in the range of 30 mm to 300 mm.

In the etching apparatus according to the aspect of the invention, preferably, the plasma generating unit is disposed to face the first electrode for placing the object to be processed in the processing container at a predetermined interval from the first electrode. A configuration including the second electrode may be employed. In this case, high-frequency power may be applied to the first electrode to perform ion-assisted etching.

According to the present invention, a Cl ₂ / O ₂ / NF ₃ mixed gas is used as an etching gas at the time of Si etching and the gas flow rate is set in an optimum range, so that it is possible to cope with a high aspect ratio and to improve an etching rate. Can be done.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 shows a configuration of an etching apparatus according to an embodiment of the present invention. This etching apparatus is configured as a parallel plate type plasma etching apparatus, and has, for example, a cylindrical chamber (processing vessel) 10 made of aluminum whose surface is anodized (anodized). The chamber 10 is grounded.

A cylindrical deposition shield material 12 made of alumina is adhered to the inner wall surface of the chamber 10. At the bottom of the chamber 10, a columnar susceptor support 14 is disposed via an insulating plate 13 made of ceramic or the like, and a susceptor 16 made of, for example, aluminum is provided on the susceptor support 14. The susceptor 16 constitutes a lower electrode, on which, for example, a single crystal Si substrate or a Si wafer W is mounted as an object to be processed.

静電 An electrostatic chuck 18 for holding the Si wafer W with an electrostatic attraction force is provided on the upper surface of the susceptor 16. The electrostatic chuck 18 has an electrode 20 made of a conductive film sandwiched between a pair of insulating sheets, and a DC power supply 22 is electrically connected to the electrode 20. The DC voltage from the DC power supply 22 causes the Si wafer W to be attracted and held on the electrostatic chuck 18 by Coulomb force. A focus ring 24 made of, for example, quartz for improving the uniformity of the etching is arranged on the upper surface of the susceptor 16 around the electrostatic chuck 18.

{Circle around (4)} The susceptor support 14 is provided with a refrigerant chamber 26 extending in a circumferential direction, for example. A coolant at a predetermined temperature, for example, cooling water is circulated into the coolant chamber 26 from an external chiller unit (not shown) via pipes 26a and 26b. The processing temperature of the Si wafer W on the susceptor 16 can be controlled by the temperature of the coolant.

{Circle over (4)} A cooling gas, for example, He gas, from a cooling gas supply mechanism (not shown) is supplied between the upper surface of the electrostatic chuck 18 and the back surface of the Si wafer W via a gas supply line 28. The cooling gas supply mechanism is capable of independently controlling the gas pressure, that is, the back pressure at the central portion of the wafer and the peripheral portion of the wafer in order to increase the uniformity of the etching process within the wafer surface.

(4) Above the susceptor 16, an upper electrode 30 is provided so as to face the susceptor in parallel. The upper electrode 30 is supported by the chamber 10 via an insulating material 32, and has a lower electrode plate 36 having a large number of discharge holes 34 and made of a ceramic such as alumina, for example, and a conductive material supporting the electrode plate 36. For example, it has an electrode support 38 whose surface is made of anodized aluminum. A buffer chamber is formed inside the electrode plate 36 and the electrode support 38, and a gas inlet 40 is provided in the center of the upper surface of the buffer chamber. A gas supply pipe 44 from a processing gas supply unit 42 is connected to the gas inlet 40.

An exhaust port 46 is provided at the bottom of the chamber 10, and an exhaust device 50 is connected to the exhaust port 46 via an exhaust pipe 48. The exhaust device 50 has a vacuum pump such as a turbo-molecular pump, and can reduce the pressure of the etching processing space in the chamber 10 to a desired degree of vacuum. A gate valve 52 that opens and closes a loading / unloading port for the Si wafer W is attached to a side wall of the chamber 10.

A ground potential is connected to the upper electrode 30 via a low-pass filter (LPF) 54, and a first high-frequency power supply 58 is connected via a matching unit 56. The first high-frequency power supply 58 applies a high-frequency power of a frequency in the range of 50 to 150 MHz, typically around 60 MHz, to the upper electrode 30.

ア ー ス The susceptor 16 serving as the lower electrode is connected to a ground potential via a high-pass filter (HPF) 60, and is connected to a second high-frequency power supply 64 via a matching unit 62. The second high-frequency power supply 64 applies a high-frequency power of a frequency in the range of 1 to 4 MHz, typically about 2 MHz, to the susceptor 16.

In this embodiment, the distance between the upper electrode 30 and the lower electrode (susceptor) 16, that is, the distance between the electrodes, may be preferably set in a range of 30 mm to 300 mm.

To perform Si etching in this plasma etching apparatus, first, the gate valve 52 is opened, and the Si wafer W to be processed is loaded into the chamber 10 and placed on the susceptor 16. Then, an etching gas is introduced into the chamber 10 at a predetermined flow rate from the processing gas supply unit 42, and the pressure in the chamber 10, that is, the etching pressure is set to a set value (preferably a value in the range of 20 mTorr to 200 mTorr) by the exhaust device 50. I do. Further, a high frequency of about 60 MHz from the first high frequency power supply 58 is applied to the upper electrode 30 at a predetermined power, and a high frequency of about 2 MHz from the second high frequency power supply 64 is applied to the susceptor 16 at a predetermined power. Further, a DC voltage is applied from the DC power supply 22 to the electrode 20 of the electrostatic chuck 18 to fix the Si wafer W to the susceptor 16. The etching gas discharged from the perforated electrode plate of the upper electrode 30 or the shower head 36 is turned into plasma during glow discharge between the electrodes, and the Si wafer W is etched by radicals and ions generated by this plasma.

In this plasma etching apparatus, the plasma is densified in a preferable dissociated state by applying a high frequency to the upper electrode 30 in a much higher frequency region (50 to 150 MHz) than in the past (generally, 27 MHz). An appropriate plasma can be formed under the conditions. In addition, by applying a high frequency in a higher frequency range (1 to 4 MHz) than the conventional one (generally 800 kHz) to the susceptor 16 as the lower electrode, a moderate RIE (Reactive Ion Etching) is applied to the object to be processed at a lower pressure. Can be applied.

In the Si etching of this embodiment, a mixed gas containing Cl ₂ , O ₂ and NF ₃ is used as an etching gas. For this purpose, as shown in FIG. 2, the processing gas supply system 42 has, for example, a Cl ₂ gas source 66, an O ₂ gas source 68, and an NF ₃ gas source 70, and controls the respective flow rates to mass flow controllers 66a, 68a, 70a. And can be controlled individually and arbitrarily. Note that an inert gas such as Ar may be mixed with the etching gas as a diluent gas, and in that case, a diluent gas supply unit (not shown) is also provided.

Next, specific examples of the Si etching method of the present invention will be described.

Examples 1 to 8
In trench etching for DTI for forming a groove having an opening width of 0.3 μm and a depth of 3 to 6 μm in a Si wafer, a flow rate of an etching gas (Cl ₂ / O ₂ / NF ₃ ) is used by using the plasma etching apparatus of FIG. The etching characteristics were evaluated using the parameters and the flow rate ratio as parameters. Other major etching conditions are as follows. FIG. 3 and FIG. 4 show data of the experimental results.
Si wafer diameter = 200mm
Mask material = two-layer structure film of SiO ₂ (upper layer) / SiN (lower layer) Mask thickness (SiO ₂ / SiN) = 3000３1500Å
Pressure = 60mToor
RF power (upper electrode / lower electrode) = 500W / 600W
Distance between electrodes = 115 mm
Temperature (upper electrode / lower electrode / chamber side wall) = 80/60/60 ° C

Comparative Examples 1 and 2
In the trench etching for DTI for forming a groove having an opening width of 0.3 μm and a depth of 3 to 6 μm in a Si wafer, a HBr / O2 / NF ₃ mixed gas (Comparative Example 1) or a plasma etching apparatus of FIG. The etching characteristics were evaluated using an HBr / O2 mixed gas (Comparative Example 2) as an etching gas. Other etching conditions are the same as those of the embodiment except that the gap between the electrodes is 120 mm. FIG. 5 shows the data of the experimental results.

3 and 5, the etching rate (Si E / R) of Si is about 0.25 μm / min in Comparative Examples 1 and 2 based on HBr, whereas Example 1 is about 0.25 μm / min. ８8 is about 3 times or more at 0.78 μm / min or more.

As for the taper angle, Comparative Example 1 (92.3 °) has an inverted taper or bowing shape exceeding 90 °, and Comparative Example 2 (87.5 °) has a taper shape of less than 89 ° and has a vertical shape. The shape could not be obtained.

On the other hand, Example 1 (89.3 °), Example 2 (89.0 °) and Example 3 (89.2 °) all fall within the range of 89 to 90 °, and achieved a vertical shape. However, Example 4 (87.6 °), Example 5 (87.5 °), Example 6 (87.7 °), and Example 7 (87.8 °) have a tapered shape, and Example 8 (91.8 ゜) became a bowing shape.

When examined in Examples 1 to 8, Examples 1 to 3 are characterized in that the gas flow rate is reduced, and in particular, the total flow rate of Cl ₂ and O ₂ (Cl ₂ + O ₂ ) is reduced. It is. More specifically, in Examples 4 to 8, the total flow rate of the etching gas is 100 sccm or more and the residence time is less than about 180 msec, whereas in Examples 1 to 3, the total flow rate of the etching gas is less than 100 sccm and 45 sccm. The residence time is longer than 180 msec and longer than 380 msec. The flow rate of (Cl ₂ + O ₂ ) is 25 sccm or less.

The residence time τ is defined as in the following equation (1) with reference to FIG.
τ = V (= A × H) / S = pV / Q ‥‥‥ (1)
Here, V is the volume of the etching space (l: liter), S is the pumping speed (l / s), P is the pressure (Torr), Q is the total flow rate (Torr × l / s), A is the wafer area, H is the distance between the lower electrode and the upper electrode.

In order to vertically form a 3 to 6 μm deep groove with a fine opening width of about 0.3 μm, the etching gas residence time, that is, the flow rate of the etching gas (Cl ₂ / O ₂ / NF ₃ ) is limited; In particular, it is important to reduce the flow rate of (Cl ₂ + O ₂ ). From FIG. 3, it is preferable that the residence time is about 180 msec or more. To set the residence time to 180 msec or more, the flow rate Q of the etching gas may be set to about 95 sccm or less. Further, in the present invention, it is preferable that the total flow rate of Cl ₂ and O _{2 in} the total flow rate of the etching gas is set to about 80% or less, or about 75 sccm or less. It is considered that when the flow rate of (Cl ₂ + O ₂ ) is large, the devolution rate in the vicinity of the bottom of the trench exceeds the etching rate, and the taper is easily formed. However, if the flow rate of (Cl ₂ + O ₂ ) is too small, the etching rate is affected. Therefore, the flow rate is preferably set to 15 sccm or more.

In addition, the ratio of the O ₂ flow rate to the (Cl ₂ + O ₂ ) flow rate or the O ₂ ratio is also important. If the O ₂ ratio is too low as in Example 8 (0.09), the devotion rate falls below the etching rate. Boeing tendency. Conversely, if the O ₂ ratio is too high, the devotion rate tends to exceed the etching rate and tend to taper. The O ₂ ratio may be set preferably in the range of 0.1 to 0.3, and more preferably in the range of 0.15 to 0.25.

Although the flow rate of the Examples 1 to 8 in NF ₃ was 20 sccm (constant), within the scope of 10~30sccm etching characteristics of each embodiment it will probably not change much. Practically, it is desirable that the flow rate of NF _{3 be} about 20% or more of the total flow rate of the etching gas.

In Examples 1 to 8, the pressure was set to 60 mTorr (constant). From the above equation (1), the pressure is a parameter that affects the residence time and also affects the etching rate and the like. Therefore, it is desirable that the pressure be optimized according to other etching conditions and trench specifications. Incidentally, RF power (upper electrode = 500 W, the lower electrode = 600W) of Examples 1-8 in terms of the power density, the upper electrode = 1.6 W / cm ^2, a lower electrode = 1.9W / cm ^2. Preferably, the RF power or power density is also optimized according to other etching conditions and trench specifications.

Further, as shown in FIG. 3, the mask selectivity of Example 2 (etching rate of Si / etching rate of SiO ₂ ) was 28.70. In other examples and Comparative Examples 1 and 2, the same mask selection ratio can be obtained. In the Si etching of the present invention using a mixed gas of Cl ₂ / O ₂ / NF ₃ as an etching gas, a mask material having at least a surface layer of SiO ₂ is desirable.

Although the plasma etching apparatus of the above embodiment is a capacitively coupled parallel plate apparatus, it may be configured as another plasma etching method, for example, a magnetic field RIE or ECR (Electron Cyclotron Resonance) method. In the above embodiment, the etching of the Si wafer is described, but the Si etching method and the etching apparatus of the present invention can be applied to any object to be processed including the Si substrate or the Si layer.

FIG. 1 is a diagram illustrating a configuration of an etching apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration of a processing gas supply unit in the etching apparatus of FIG. 1. FIG. 3 is a diagram showing main etching conditions and etching characteristics in an example. It is a diagram showing a (Cl ₂ + O ₂₎ flow rate and _{O 2 ratio (O 2 / Cl} 2 + O 2) dependence of the taper angle in the embodiment. FIG. 9 is a diagram showing main etching conditions and etching characteristics in a comparative example. It is a figure showing the definition of residence time in an embodiment.

Explanation of reference numerals

10 chambers (processing vessel)
16 Susceptor (lower electrode)
Reference Signs List 18 electrostatic chuck 22 DC power supply 30 upper electrode 36 electrode plate 40 gas inlet 42 processing gas supply unit 46 exhaust port 58 first high frequency power supply 64 second high frequency power supply 66 Cl ₂ gas source 68 O ₂ gas source 70 NF ₃ Gas source 66a, 68a, 70a Mass flow controller

Claims (10)

When dry etching a Si substrate or a Si layer in a processing vessel, a mixed gas containing Cl ₂ , O _2, and NF ₃ is used as an etching gas, and a residence time τ represented by the following equation (1) is about A Si etching method for performing an etching process under a condition of 180 msec or more.
τ = pV / Q ‥‥‥ (1)
Here, p is the pressure in the processing chamber, V is the volume of the effective etching space set on the object, and Q is the flow rate of the etching gas. Cl ₂ and Si etching method according to claim 1 total flow rate of O ₂ is less than about 80% of the total flow rate of the etching gas. Si etching method of claim 1 the flow rate ratio of O ₂ is in the range of about 0.1 to 0.3 to the total flow of Cl ₂ and O ₂ in the etching gas. The method of claim 1, wherein the total flow rate of the etching gas is about 100 sccm or less. The method according to claim 1, wherein the pressure in the processing container is set in a range of 20 mTorr to 200 mTorr. 2. The Si etching method according to claim 1, wherein a distance between the electrodes in the processing container is set within a range of 30 mm to 300 mm. An etching apparatus for dry-etching a Si substrate or a Si layer,
A processing container having a gas inlet and an exhaust outlet, and accommodating the object to be processed including the Si substrate or the Si layer in a removable manner,
An etching gas supply unit for mixing a Cl ₂ gas, an O ₂ gas, and an NF ₃ gas at a desired flow rate ratio, and supplying the mixed gas as an etching gas into the processing container through the gas inlet;
Plasma generating means for converting the etching gas into plasma,
Exhaust means for exhausting the processing chamber through the exhaust port to provide a desired etching pressure,
An etching apparatus that performs an etching process under the condition that the residence time τ represented by the following equation (2) is about 180 msec or more.
τ = pV / Q ‥‥‥ (2)
Here, p is the pressure in the processing chamber, V is the volume of the effective etching space set on the object, and Q is the total flow rate of the etching gas. 8. The etching apparatus according to claim 7, wherein the etching gas supply means supplies the etching gas to the processing container at a flow rate of about 100 sccm or less. 8. The etching apparatus according to claim 7, wherein the exhaust means reduces the pressure inside the processing container to a range of 20 mTorr to 200 mTorr. 8. The etching apparatus according to claim 7, further comprising: an upper electrode and a lower electrode having a distance between the electrodes set within a range of 30 mm to 300 mm in the processing container.

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