JP3905870B2 - Plasma processing equipment - Google Patents

Description

The present invention relates to plasma processing, and more particularly to a parallel plate RIE type plasma processing apparatus .

2. Description of the Related Art Conventionally, a parallel plate type plasma etching apparatus is often used in etching processing in a manufacturing process of a semiconductor device or an FPD (Flat Panel Display). In a parallel plate type plasma etching apparatus, an upper electrode and a lower electrode are arranged in parallel in a processing vessel or a reaction chamber, a substrate to be processed (semiconductor wafer, glass substrate, etc.) is placed on the lower electrode, A high frequency voltage is applied to at least one of the upper electrodes via a matching device. Electrons are accelerated by the electric field formed between the two electrodes by this high-frequency voltage, plasma is generated by impact ionization between the electrons and the processing gas molecules, and the film on the substrate surface is etched by radicals and ions generated by the plasma. . In particular, in the parallel plate type RIE (Reactive Ion Etching) method, ions in plasma are accelerated by the electric field of the ion sheath generated near the substrate surface and incident perpendicularly on the substrate surface. Isotropic etching is also possible. Generally, this system employs cathode coupling, the upper electrode is grounded, and a high frequency for plasma excitation is applied to the lower electrode (see, for example, Patent Document 1).
JP 2000-12531 A

The conventional parallel plate type RIE plasma etching apparatus has a limit in terms of etching uniformity, etching ability, and the like in an application with a large substrate size, particularly etching of a large diameter (for example, 300 mm) wafer or FPD substrate. Specifically, since etching of aluminum, titanium, and titanium-containing metals requires high-density plasma under a low pressure, it is necessary to increase the RF power. However, when the RF power is increased, there is a problem that the plasma is concentrated near the center of the substrate and the uniformity of the plasma density distribution or the etching uniformity is lowered. In addition, etching of aluminum alloys and ITO (indium tin oxide) and etching of silicon oxide film (SiO ₂ ) did not provide a sufficient etching rate, and the selectivity was not good. Therefore, an inductively coupled plasma etching apparatus (ICP) that is advantageous for generating high-density plasma has been adopted for these materials to be etched.
In addition, the lower two-frequency superimposing method is a first high frequency of a relatively high frequency (generally 27 MHz or more) suitable for plasma generation in the lower electrode supporting the substrate in the above-described cathode-coupling type plasma processing apparatus. And a second high frequency wave having a relatively low frequency (generally 13.56 MHz or less) suitable for ion attraction. In the conventional plasma processing apparatus that employs the lower two-frequency superimposing application method, each of the two matching units provided in the first and second high-frequency power supply paths is configured by an L-type circuit, and each matching for different high frequencies is performed. In order to prevent malfunction of the unit, each matching unit is provided with an individual filter, which leads to an increase in the size and cost of the entire matching unit.

The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a plasma processing apparatus that realizes downsizing and cost reduction of a matching circuit in a two-frequency superimposed application method .

In order to achieve the above object, a plasma processing apparatus of the present invention places a substrate to be processed on a lower electrode arranged opposite to an upper electrode in a vacuumable processing vessel, and between the electrodes. A plasma processing apparatus that forms a high-frequency electric field and flows a processing gas into the processing gas to generate a plasma of the processing gas, and performs a desired plasma processing on the substrate to be processed under the plasma. A first high-frequency power supply for applying a first high-frequency power having a frequency, and the first high-frequency power supply for matching the impedance on the first high-frequency power supply side and the load impedance on the lower electrode side, A first matching circuit connected between the lower electrode and a second high-frequency power source for applying a second high-frequency power having a second frequency lower than the first frequency to the lower electrode; A second matching circuit connected between the second high-frequency power source and the lower electrode in order to match the impedance on the second high-frequency power source side and the load impedance on the lower electrode side; The second matching circuit is configured as a T-type circuit having a coil in the output stage, and the coil in the output stage constitutes a high-cut filter for blocking the first high frequency from the first high frequency power supply. .

  In the plasma processing apparatus, in the two-frequency superimposed application method in which the first and second high frequencies having different frequencies are superimposed and applied to the lower electrode on which the substrate to be processed is placed, the second on the second high frequency side having a low frequency is applied. And a matching circuit for performing coil matching adjustment and a high-cut filter for protecting the second high-frequency power source on the low frequency side. Thus, the size and cost of the second matching circuit can be significantly reduced.

  In the plasma processing apparatus, in order to minimize the number of elements constituting the second matching circuit, the second matching circuit is connected between the output terminal of the second high-frequency power source and the lower electrode. It is preferable to have a first capacitor in the input stage connected in series with the coil, and a second capacitor connected between the connection point of the first capacitor and the coil and the ground potential. In this case, when performing matching adjustment, it is preferable that at least one of the first and second capacitors is a variable capacitor whose capacitance can be variably adjusted. The output stage coil preferably has an impedance of 100 ohms or more to ensure a high frequency cutoff function.

In the plasma processing apparatus, the first frequency is set in the range of 10 MHz to 30 MHz and the second frequency is set in the range of 2 MHz to 6 MHz in order to optimize the distribution characteristics of the plasma density. Is preferred. The upper electrode may typically be connected to ground potential. The processing gas used in the plasma processing apparatus is one of Cl ₂ , BCl ₃ , HCl, SF ₆ , CF ₄ , CHF ₃ , CH ₂ , F ₂ , O ₂ , N ₂ , H ₂ , Ar, and He. It may be a single gas containing seeds or a mixed gas containing two or more kinds.

According to the plasma processing apparatus of the present invention , the matching circuit can be reduced in size and cost in the two-frequency superimposed application method by having the above-described configuration and operation.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a configuration of a main part of a plasma etching apparatus according to an embodiment of the present invention. This plasma etching apparatus is configured as a parallel plate RIE plasma etching apparatus, and has a vacuum chamber (processing vessel) 10 made of metal such as aluminum or stainless steel. The chamber 10 is grounded for safety.

  A support base 14 made of, for example, aluminum is installed on the bottom surface of the chamber 10 via an insulating plate 12 such as ceramic, and a lower electrode 16 made of, for example, aluminum is provided on the support base 14. The lower electrode 16 also serves as a mounting table for mounting a substrate to be processed (for example, an FPD substrate) G.

  An upper electrode 18 is disposed above the lower electrode 16 so as to face the electrode 16 in parallel. The upper electrode 18 is formed with a number of through holes or gas discharge ports 18a for constituting a shower head. A gas supply pipe 24 from a processing gas supply source 22 is connected to the gas inlet 20 provided behind the upper electrode 18. In the middle of the gas supply pipe 24, a flow rate regulator (MFC) 26 and an on-off valve 28 are provided.

  An exhaust port 30 is provided at the bottom of the chamber 10, and an exhaust device 34 is connected to the exhaust port 30 via an exhaust pipe 32. The exhaust device 34 has a vacuum pump such as a turbo molecular pump, and can depressurize the plasma space in the chamber 10 to a desired vacuum level. A substrate loading / unloading port (not shown) is provided on the side wall of the chamber 10, and a load lock chamber (not shown), for example, is connected to the substrate loading / unloading port via a gate valve (not shown).

  In this plasma etching apparatus, the lower electrode 16 is electrically cathode-coupled. The upper electrode 18 is connected (grounded) to the ground potential via the chamber 10. On the other hand, first and second high-frequency power sources 40 and 42 are electrically connected to the lower electrode 16 via first and second matching units 36 and 38, respectively.

The first high frequency power supply 40 is preferably a first high frequency (hereinafter, referred to as “high frequency for source”) having a frequency of 10 MHz to 30 MHz (for example, 13.56 MHz or 27.12 MHz) for mainly contributing to plasma generation. .) Output RF _s with desired power. The first matching unit 36 is for matching the impedance on the high-frequency power source 40 side and the load impedance on the lower electrode 16 side, and protects the matching circuit 44 for performing matching adjustment and the high-frequency power source 40. And a band-pass filter 46 for the purpose.

The matching circuit 44 is configured as an L-type circuit including two variable capacitors 48 and 50 and one coil 52. More specifically, _a capacitor 48 is connected between the input terminal (node N _a ) and the ground potential, and a coil 52 and a capacitor 50 are connected between the input terminal (node N _a ) and the output terminal (node N _c ). Are connected in series. By variably adjusting the capacitances of both the variable capacitors 48 and 50, the load impedance on the lower electrode 16 side including the matching circuit 44 can be apparently matched with the impedance on the first high frequency power supply 40 side including the band pass filter 46. It has become.

The band-pass filter 46 is configured as a series resonance circuit in which a coil 54 and a capacitor 56 are connected in series, and selectively passes only a frequency band near the source high-frequency RF _s . Even if a high-frequency RF _b from a second high-frequency power source 42 to be described later passes through the matching circuit 44, the band-pass filter 46 blocks the high-frequency RF _{b so} that the high-frequency RF _b is not transmitted to the first high-frequency power source 40.

The second high frequency power source 42 is preferably a second high frequency (hereinafter referred to as “bias high frequency”) preferably having a frequency of 2 MHz to 6 MHz (for example, 3.2 MHz) for mainly contributing to the adjustment of the self-bias V _dc . ) Output RF _b at a desired power. The second matching unit 38 is for matching the impedance on the high-frequency power source 42 side and the load impedance on the lower electrode 16 side. The second matching unit 38 is a T-type composed of two variable capacitors 58 and 60 and one coil 62. The circuit also serves as a matching circuit for matching adjustment and a filter circuit for protecting the high-frequency power source 42.

More specifically, a capacitor 58 and a coil 62 are connected in series between a matcher input terminal on the high-frequency power source 42 side and a matcher output terminal (node N _c ) on the lower electrode 16 side, and the capacitor 58 and the coil 62 are connected. A capacitor 60 is connected between the connection point (node N _b ) and the ground potential. In this T-type circuit, the coil 62 at the final output stage alone or in combination with the ground-side capacitor 60 constitutes a high-cut filter, and cuts off the source high-frequency RF _s from the first high-frequency power supply 40. Have In order to ensure this high-frequency cutoff function, it is preferable that the impedance of the coil 62 be 100 ohms or more. On the other hand, the load impedance on the lower electrode 16 side including the matching circuit (58, 60, 62) appears to be the impedance on the second high-frequency power source 42 side by variably adjusting the capacitances of both the variable capacitors 58, 60. It can be matched. The power supply line 64 between the matcher output terminal (node N _c ) and the lower electrode 16 may be formed of a power supply rod.

As described above, in the plasma etching apparatus of this embodiment, in the two-frequency superimposing application method in which the source high-frequency RF _s and the bias high-frequency RF _b are superimposed and applied to the lower electrode 16, the low-frequency side matching unit 38 is provided. It is composed of a T-type circuit of three elements (58, 60, 62) having a coil 62 at the final output stage, and the coil 62 protects the high frequency power source 42 on the low frequency side, that is, the bias high frequency RF _b side. The filter is also used. Thereby, the size and cost of the matching unit 38 are greatly reduced.

In order to perform etching in this plasma etching apparatus, first, the gate valve is opened and the substrate G to be processed is loaded into the chamber 10 and placed on the lower electrode 16. Then, a predetermined etching gas is introduced into the chamber 10 from the processing gas supply source 22 at a predetermined flow rate and flow rate ratio, and the pressure in the chamber 10 is set to a set value by the exhaust device 34. Further, when the source high-frequency RF _s is applied to the lower electrode 16 from the first high-frequency power source 40 at a predetermined power, the bias high-frequency RF _b is applied from the second high-frequency power source 42 at a predetermined power. Apply with a predetermined power. The etching gas discharged from the shower head (upper electrode) 18 is turned into plasma by high-frequency discharge between the electrodes 16 and 18, and the main surface of the substrate G is etched by radicals and ions generated by this plasma.

Here, the source high-frequency RF _s applied to the lower electrode 16 from the first high-frequency power supply 40 mainly acts on the high-frequency discharge between the lower electrode 16 and the upper electrode 18 and thus strongly acts on the generation of plasma. . In general, in the parallel plate type, the plasma density can be increased as the frequency of the high frequency applied between the two electrodes is increased, but the electrode center side tends to be higher than the electrode edge side. In addition, as the power of the high frequency RF _s for the source is increased, the energy applied to the plasma can be increased and the plasma density can be increased, but the plasma tends to concentrate at the center of the electrode, and the uniformity of the plasma density distribution is reduced. To do. In this embodiment, solves this problem by 2 frequency application of the bias RF RF _b as will be described later.

The bias high-frequency RF _b applied to the lower electrode 16 from the second high-frequency power source 42 is primarily set to the magnitude (absolute value) of the negative self-bias voltage V _dc generated on the lower electrode 16 or the substrate G. It acts on the strength of the electric field that draws ions in the plasma into the substrate G. In general, the self-bias voltage V _dc has a maximum point on the frequency axis, and if the frequency of the high-frequency bias RF _b is too high (at 6 MHz or more), the V _dc decreases, and the frequency of the high-frequency bias RF _b is low. Even if it becomes too much, _Vdc becomes small. From this point of view, in this embodiment, the bias high frequency RF _b is set in the range of 2 MHz to 6 MHz.

The present inventor has conducted extensive studies on the parallel-plate type RIE plasma etching apparatus of the two-frequency superimposing application method in this embodiment, and as a result, studied the frequency and power of the high frequency RF _s for source and the high frequency RF _b for bias. In addition, by appropriately selecting other etching conditions such as pressure and etching gas, radical-based chemical etching and ion-based physical etching can be controlled independently or optimized, respectively, as well as specific etching target It has been found that the uniformity of the plasma density distribution can be improved for the material and that an etching capability comparable to that of an ICP (inductively coupled plasma etching apparatus) can be obtained.

Next, an example of the plasma etching method in the plasma etching apparatus of this embodiment will be described.

The plasma etching apparatus of FIG. 1 is used, and in the etching of aluminum (Al), the source high frequency RF _s (13.56 MHz) power P _s and the bias high frequency RF _b (3.2 MHz) power P _b are parameters. The uniformity of plasma density distribution was evaluated.

In a multilayer wiring structure in which aluminum wiring is provided, taper etching is desired for the lower layer side, particularly the lowermost aluminum wiring, in order to facilitate embedding of an insulating film. In FPD aluminum taper etching, in order to enable anisotropic etching, it is desirable to increase the power P _s of the source high-frequency RF _s by lowering the pressure.

However, as shown in Comparative Examples 1, 2 and 3 in FIGS. 4-6, in a single frequency application type only source for high frequency RF _s no applied bias RF RF _b raises the power P _s of RF _s The lower the pressure in the chamber, the higher the plasma density at each position, but there is an inconvenient phenomenon that the vicinity of the center of the electrode abnormally protrudes and becomes higher. Moreover, as shown in FIG. 4, even if the gap between electrodes (GAP) is increased, the uniformity of the plasma density decreases. More specifically, in the inter-electrode gap of 210 mm (GAP), and the pressure of the following 5 mTorr, in the condition that the power P _s of the source frequency RF _s or more 1000W application, to obtain a good plasma density distribution uniformity Is impossible first.

On the other hand, in the first embodiment of the two-frequency superimposed application method, as shown in FIGS. 2 and 3, the bias is preferably proportional to the power P _s of the source high-frequency RF _s , preferably at a ratio of 1/10 or more. By selecting the power P _b of the high frequency RF _b for use, a substantially uniform plasma density distribution was obtained even in the application under the above conditions. Thereby, it was confirmed that the plasma etching apparatus of FIG. 1 can be used to perform a desired etching process with excellent etching uniformity on the aluminum film on the substrate G. Titanium and titanium-containing metals are materials to be etched that belong to the same category as aluminum, and these metals can be similarly etched with excellent etching uniformity.

  The data in FIGS. 2 and 4 are obtained by visually observing the plasma emission state inside the chamber (particularly between both electrodes) through a monitor window (not shown) provided on the side wall of the chamber 10, When a phenomenon in which the plasma emission region is concentrated in one place (usually the center) is observed, the uniformity is poor (x), and when a phenomenon in which the plasma emission region is distributed almost uniformly is observed Indicates good uniformity (O). On the other hand, the data of FIGS. 3, 5 and 6 are obtained by measuring the plasma density distribution as an electron density distribution by a plasma absorption probe (PAP) method using a network analyzer.

In Example 1 and Comparative Examples 1 and 2, chlorine gas Cl ₂ (flow rate 300 or 200 sccm) is used as an etching gas. As shown in the reference example of FIG. 6, Ar 2 is added to Cl ₂ gas. It was found that the uniformity of the plasma density distribution can also be improved from a method of mixing at an appropriate flow rate ratio (preferably Cl ₂ / Ar = 125/75 to 100/100).

Using a plasma etching apparatus of FIG. 1, in the etching of aluminum-neodymium which is a kind of aluminum alloy (AlNd) was the power P _b of a high frequency bias RF _b (3.2 MHz) to the parameter estimation the magnitude of the etching rate did. As other main etching conditions, the gap between electrodes (GAP) is 140 mm, the etching gas is Cl ₂ (flow rate 300 sccm), the pressure in the chamber is 5 mTorr, and the temperature (upper electrode (T) / lower electrode (B) / chamber side wall ( W)) = 60/20/60 ° C. The power P _b of the high frequency RF _s (13.56 MHz) for the source was set to 2000 W. As the etching gas, other chlorine-based gas such as BCl ₃ can also be used.

  Further, a glass substrate for LCD having a size of 550 × 650 is used as the substrate to be processed G, and the etching rate is measured at a large number of measurement points (1 to 14) on the substrate as shown in FIG. 8) and average values were determined for the intermediate portions (4, 5, 10, 11), and maximum values and minimum values were determined for the edge portions (1, 2, 3, 6, 9, 12, 13, 14). .

As shown in the graph of FIG. 8, the higher the power P _b of the high frequency RF _b (3.2 MHz) for bias, the higher the etching rate of aluminum / neodymium, which is approximately 2000 ＝ / min or more at P _b = 1000 W or more. It can be seen that the etching rate can be obtained. Thus, it was confirmed that by using the plasma etching apparatus of FIG. 1 for etching the aluminum alloy, a sufficient etching capability comparable to that of an ICP (inductively coupled plasma etching apparatus) can be obtained. Moreover, since the plasma density can be made uniform by the two-frequency superimposed application method of the present invention, the etching uniformity can be improved. In addition, ITO is also a material to be etched belonging to the same category as the aluminum alloy, and this alloy can obtain the same etching ability as that for the aluminum alloy.

In the etching of the silicon oxide film (SiO ₂ ) with the silicon substrate or the silicon layer (Si) as a base layer, the power P _b of the bias high frequency RF _b (3.2 MHz) is used as a parameter in the plasma etching apparatus of FIG. Each etching rate and selectivity were measured. As other main etching conditions, the gap between electrodes (GAP) is 140 mm, the etching gas is CHF ₃ (flow rate 200 sccm), the pressure in the chamber is 5 mTorr, and the temperature (upper electrode (T) / lower electrode (B) / chamber side wall ( W)) = 60/20/60 ° C. The power P _b of the high-frequency RF _s for the source (27.12 MHz) was set to 2500 W. Here, the reason why the frequency of the high-frequency RF _s for the source is set to 27.12 MHz is to obtain plasma with a higher density than 13.56 MHz. As the etching gas, not only CHF ₃ but also a mixed gas of any one or two gases of CF ₄ , CH ₂ F ₂ and C ₄ F ₈ and H ₂ and Ar can be used. Further, a mixed gas of SF6, O2, and a rare gas may be used.

As shown in the graph of FIG. 9, the higher the power P _b of the bias high frequency RF _b (3.2 MHz) is, the higher the SiO ₂ etching rate is, and the etching is almost 1000 Å / min or more when P _b = 1000 W or more. It can be seen that a rate is obtained and a selectivity of about 10 or more is obtained. As described above, it was confirmed that by using the plasma etching apparatus of FIG. 1 for the etching process of the SiO ₂ film, a sufficient etching capability comparable to an ICP (inductively coupled plasma etching apparatus) can be obtained. Moreover, since the plasma density can be made uniform by the two-frequency superimposed application method of the present invention, the etching uniformity can be improved.

  The basic form of the plasma etching apparatus (FIG. 1) of the above-described embodiment can be applied to other plasma processing apparatuses, and is modified to various plasma processing apparatuses that perform, for example, plasma CVD, plasma oxidation, plasma nitridation, sputtering, and the like. be able to. Further, the substrate to be processed in the present invention is not limited to an FPD substrate, and a semiconductor wafer, a photomask, a CD substrate, a printed substrate, and the like are also possible.

It is a figure which shows the structure of the principal part of the plasma etching apparatus in one Embodiment of this invention. It is a figure which shows the evaluation result of the plasma density distribution characteristic by visual observation in a 1st Example. It is a figure which shows the electron density distribution characteristic in a 1st Example. It is a figure which shows the evaluation result of the plasma density distribution characteristic by visual observation in a comparative example. It is a figure which shows the electron density distribution characteristic in a comparative example. It is a figure which shows the electron density distribution characteristic in a comparative example. It is a figure which shows the electron density distribution characteristic in a reference example. It is a figure which shows the bias power dependence of the etching rate in a 2nd Example. It is a figure which shows the bias power dependence of the etching rate in a 3rd Example.

Explanation of symbols

10 chamber (processing vessel)
16 Lower electrode 18 Upper electrode 22 Processing gas supply source 34 Exhaust device 36 First (for source) matching unit 38 Second (for bias) matching unit 40 First (for source) high-frequency power source 42 Second (for bias) ) High-frequency power supply 58 Variable capacitor 60 Variable capacitor 62 Coil

Claims (7)

A substrate to be processed is placed on a lower electrode disposed opposite to the upper electrode in a vacuumable processing container, a high-frequency electric field is formed between both electrodes, and a processing gas is flowed to generate plasma of the processing gas. A plasma processing apparatus that generates and performs a desired plasma process on the substrate to be processed under the plasma,
A first high frequency power source for applying a first high frequency having a first frequency to the lower electrode;
A first matching circuit connected between the first high-frequency power source and the lower electrode in order to match the impedance on the first high-frequency power source side and the load impedance on the lower electrode side;
A second high frequency power source for applying a second high frequency having a second frequency lower than the first frequency to the lower electrode;
A second matching circuit connected between the second high-frequency power source and the lower electrode in order to match the impedance on the second high-frequency power source side and the load impedance on the lower electrode side; The second matching circuit is configured as a T-type circuit having a coil in the output stage, and the coil in the output stage constitutes a high-cut filter for blocking the first high frequency from the first high frequency power supply. Plasma processing equipment.   The second matching circuit includes an input stage first capacitor connected in series with the output stage coil between the output terminal of the second high-frequency power source and the lower electrode; and the first capacitor The plasma processing apparatus according to claim 1, further comprising: a second capacitor connected between a connection point between the coil and the coil and a ground potential.   The plasma processing apparatus according to claim 2, wherein at least one of the first and second capacitors is a variable capacitor whose capacitance can be variably adjusted.   The plasma processing apparatus according to any one of claims 1 to 3, wherein the first frequency is set in a range of 10 MHz to 30 MHz, and the second frequency is set in a range of 2 MHz to 6 MHz.   The plasma processing apparatus according to any one of claims 1 to 4, wherein a coil of the output stage in the second matching circuit has an impedance of 100 ohms or more.   The plasma processing apparatus according to claim 1, wherein the upper electrode is connected to a ground potential. The processing gas is a single gas containing one of Cl ₂ , BCl ₃ , HCl, SF ₆ , CF ₄ , CHF ₃ , CH ₂ , F ₂ , O ₂ , N ₂ , H ₂ , Ar, and He, or It is a mixed gas containing 2 or more types, The plasma processing apparatus as described in any one of Claims 1-6.

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