JP3067289B2 - Dry etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method in which a conventionally used RF power source having a frequency higher than 13.56 MHz is applied to a substrate electrode.

[0002]

2. Description of the Related Art The dimensional width of transistors, wirings, and the like plays a large role in increasing the density of semiconductor integrated circuits.
Fine patterns of 1 μm or less are being put to practical use due to the size reduction. However, in realizing such fine patterns, two technologies, photolithography technology and dry etching technology, largely depend on progress.

[0003] The dry etching method uses one gas in an appropriate gas.
It utilizes the phenomenon that a material to be etched is etched when placed in reactive plasma or radicals generated by applying a high frequency (RF) power supply of 3.56 MHz to form a fine pattern. Usually uses a photoresist pattern as a mask material. Recently, RIE (Reactive Ion Etching) in which reactive ions are extracted from plasma by using a self-bias voltage (V _dc ) to perform anisotropic etching has become mainstream.
The reason why 13.56 MHz is used as the frequency of the RF power source is that there is no problem even if radio waves leak to some extent because the frequency is assigned by the Radio Law, and the shield device can be simplified.

FIG. 10 is a schematic diagram showing a conventional dry etching apparatus (RIE). Reference numeral 1 denotes a metal chamber into which a reactive gas is supplied through a supply port 2. Further, since the gas is discharged through the discharge port 3, an appropriate pressure (several hundred mTorr) is set in the chamber.
Is controlled. At the top and bottom of the chamber are an anode 4 and a cathode 5, respectively. A material 6 to be etched having a resist pattern is placed on the cathode. Further, an RF power source 8 is connected to the cathode via a blocking capacitor 7 to supply power to the gas. The operation of the dry etching apparatus configured as described above will be described below.

When an RF power is applied to the reactive gas in the chamber, the anode and the cathode are connected as shown in FIG.
A glow discharge is generated between the electrodes, and electrons and ions are generated to generate plasma. At that time, the area of the electrode in contact with the glow discharge is larger in the anode because the sample is placed on the cathode, and at the same time, the mobility of the electrons and ions in the plasma is more overwhelming than that of the latter. Caso-because it is large
Electrons flow into the cathode and the blocking capacitor becomes negatively charged, thereby negatively biasing the cathode. This bias is called a self-bias voltage _Vdc . FIG. 11B shows the potential distribution in the plasma in this state.
As shown in FIG. 11B, the plasma is divided into a bulk region where the potential is constant and a sheath region where the potential changes abruptly near the electrode due to self-bias, and ions are mainly generated in the bulk region. . Ions generated in the bulk region enter the sheath region from the bulk sheath boundary 10 and
The material is accelerated by the negative voltage due to the self-bias of the sheath region and bombards the material to be etched to cause an etching reaction,
A so-called anisotropic etching having a strong directivity can be obtained.

The manner in which a negative self-bias voltage is applied to the cathode to generate a sheath will be described in detail. As described above, since the mobility of electrons and ions generated by discharge is large in the former, the current-voltage characteristics are generally similar to those of a rectifier having a large leak current. Therefore, when the RF power is first applied to the cathode, electrons having a high mobility largely flow toward the cathode of the positive potential in the positive half cycle of the RF power, but on the other hand, in the next half cycle. Only a small amount of ions having low mobility flow into the cathode which has become negative potential, and the number of electrons and ions becomes non-equilibrium. Accordingly, the blocking capacitor is negatively charged, and a negative voltage is generated on the cathode until the cathode generates a space charge of electrons and rebounds, thereby reducing excess electrons. After a few cycles, the number of electrons incident on the cathode equals the number of ions incident on the cathode, and the cathode is negative so that the net current is zero on time average. Generates a bias potential and reaches a steady state. This potential is called self-bias. Due to this self-bias, a region is created near the cathode where there are almost no electrons and only ions. This region is called a sheath region, where the potential changes abruptly. On the other hand, in the plasma, the electrons are diffused to the outside, and the electrons become slightly insufficient, and have a slightly positive potential. This potential is called the plasma potential (V _p ). The time change of the cathode potential in this state is as shown in FIG. FIG.
As shown, in the positive period than the ground potential + V _p Caso -
Electrons flow into the cathode, and ions flow in the negative cycle. However, the time during which only the ions flow is overwhelmingly long, and the ions incident on the cathode cause an etching reaction.

Incidentally, Goto et al. Have proposed a new dry etching apparatus as shown in FIG.
1990, P1147-1150). The feature of this device is that the RF power supply is connected not only to the cathode but also to the anode side, and the frequency of the RF power supply on the cathode side is 10 to 50 MHz.
z, the frequency of the RF power supply on the anode side is 150 MHz to 2
That is, a frequency as high as 00 MHz is used.
The anode-side RF power supply is used for plasma generation like ECR and MERIE, and generates plasma with high ionization by supplying power of about 1 kW. on the other hand,
The RF power source on the cathode side is for extracting ions, and plays a role in extracting ions necessary for etching from the plasma source generated by the RF power source on the anode side to the cathode side.

[0008]

Recently, as the degree of integration of semiconductors has increased, fine processing technology of submicron or less has been required. However, in the conventional etching method, the gate oxide film of the transistor has become thinner as the dimensions have been reduced, so that the dielectric breakdown of the gate oxide film generated during dry etching has become a problem. This is because, in the etching by the RIE apparatus, since anisotropic etching is performed by accelerated ions, a charge-up occurs during the etching, and a voltage applied to the gate oxide film increases to cause stress. In particular, the gate oxide film of the chip around the wafer is easily broken. Further, in the conventional etching method, high energy ions bombard the silicon substrate to break the bond, thereby deteriorating the device. Further, for example, when Cl ₂ gas is used in the dry etching of the gate electrode, the radical component of the gate electrode should not etch the SiO ₂ film, but the poly-Si constituting the gate and the underlying layer may not be etched. The selectivity of SiO ₂ can be secured only about 10 due to the presence of high energy ions, and is not suitable for etching the gate polysilicon. SUMMARY OF THE INVENTION In view of the above problems, the present invention reduces gas damage due to ion charge-up, suppresses the occurrence of dielectric breakdown of a gate oxide film, and eliminates the generation of high-energy ions. It is an object of the present invention to provide a dry etching method capable of ensuring the selectivity by the chemical reaction of the above.

[0009]

In order to solve the above-mentioned problems, generation of high-energy ions should be suppressed as much as possible. To suppress the generation of high energy ions, RF
Although the power may be reduced, the ionization degree of the plasma is reduced, and the generation of radicals is reduced. As a result, the etching rate is reduced, and the efficiency is reduced. Goto et al. Turned on the RF power supply to solve this problem.
To the anode side so that the generation of radicals does not decrease even if the cathode side RF power is lowered.
The power of the power source is increased to about 1 kW to maintain the plasma source. As described above, the apparatus of Goto et al. Extracts ions from the plasma generated by the RF power supply on the anode side of the high power by the electric field of the sheath generated by the RF power supply on the cathode side of the low power. , The substrate is etched with low energy.

However, the Goto et al. Apparatus still has the following problems unsolved. Generally, the energy distribution of ions reaching the substrate electrode is shown in FIG.
As shown in FIG. 4A, the distribution spreads in a saddle structure around the energy obtained by accelerating the ions by the self-bias. In the device of Goto et al., The RF on the cathode side
By reducing the power of the power supply, the self-bias is reduced, and the ion energy distribution is shifted to a lower energy side as a whole, as shown in FIG. However, for example, gate - when the etching of the gate electrode, etching rate of SiO ₂ is a poly-Si and the underlying a object to be etched - ion energy DOO - dependent is as shown in FIG 15. Than 15, the ion energy - but it is so bets even greater efficiently etched, ion energy - - the etching rate of the selected ratio is high and poly-Si is about 50~60eV is higher than this and the SiO ₂ As the etching rate increases, the selectivity deteriorates. Conversely, when the ion energy is low, poly-
The etching rate of Si becomes small, resulting in inefficiency and poor anisotropy. Therefore, in the energy distribution of FIG. 14B obtained by the apparatus of Goto et al., The average energy of arrival of ions is small, so that damage to the substrate can be suppressed, but the energy distribution width ΔE is so small. As a result, there has been little improvement in selectivity, anisotropy, and etching efficiency.
In addition, the apparatus of Goto et al. Has a drawback that matching is difficult because two power supplies and two matching boxes are required.

As another cause of the generation of high-energy ions, the frequency of the RF power supply is considered. When the frequency of the RF power source is low, such as 13.56 MHz, which is currently used, the self-bias becomes large and the energy of the ions reaching the substrate becomes small, as described in the section of (action) below. The distribution width of the distribution becomes large, and high-energy ions are generated. On the other hand, when the frequency of the RF power source is increased, the self-bias is reduced, and at the same time, the distribution width of the ion energy is reduced.
Since the energy distribution is as shown in (c), it is possible to suppress the generation of high-energy ions, which not only reduces the damage to the substrate, but also reduces the selectivity, Dry etching with high anisotropy and high etching efficiency is realized.

Generally, when the etching gas pressure is reduced to increase the anisotropy, the self-bias increases. However, when the self-bias is reduced by increasing the frequency of the RF power source, the self-bias is reduced while maintaining the anisotropy. Damaged dry etching can be performed. Further, in dry etching using halogen gas such as poly-Si, SiN or Al alloy, the ion energy required for etching the underlying SiO ₂ film is smaller than the ion energy required for etching these objects to be etched. since larger, high energy by increasing the frequency of the RF power source - - suppressing the generation of ions, SiO ₂ etching les - it is possible to a large selection ratio lowered bets can be obtained.

According to the present invention, by increasing the frequency of the RF power source, the self-bias is reduced to 100 eV or less, and at the same time, the ion energy distribution width is reduced to ± 5% or less of the average attained energy, and the RF power is reduced. In addition to lowering the etching efficiency by lowering the etching efficiency, the generation of high-energy ions is suppressed to reduce damage to the substrate. Higher, more poly-S
Provided is a method for realizing dry etching in which a sufficiently large selectivity can be obtained by lowering the etching rate of the underlying SiO ₂ etched by high energy ions when etching i, SiN and Al alloys. Is what you do.

[0014]

As described above, when the frequency of the RF power supply is increased, two effects can be obtained with respect to the energy that ions reach the substrate. One is that the self-bias of the plasma is lowered and the entire energy distribution of ions is shifted to a lower energy side, so that high-energy ions are not generated.
Since the distribution width of the distribution is narrowed and neither low-energy ions nor high-energy ions are generated with respect to the desired ion energy, the etching rate can be controlled and the etching can be performed efficiently. is there.

The reason why the self-bias decreases when the frequency of the RF power supply is increased will be described below. Generally, RF glow
As shown in FIG. 16, the plasma generated by the discharge can be approximated by a parallel circuit of resistance and inductance in the bulk portion and the capacitor in the sheath portion, so that the impedance of the sheath is 1 / jωC ( ω). RF
As the frequency of the power supply increases and ω increases, the sheath length decreases and the capacitance C (ω) between the sheaths increases. Therefore, the impedance of the sheath decreases, and the voltage applied between the sheaths, that is, the self-bias, decreases as the frequency of the RF power supply increases.

As described above, when the self-bias of the plasma is reduced by increasing the frequency of the RF power source, the energy distribution of ions reaching the substrate is shifted to a lower energy side as a whole, and the high energy ions are increased. Can be suppressed. If high-energy ions are not generated, it is a problem in dry etching.
Can solve two problems. One is the problem of damage to the substrate. If no high energy ions are present, the silicon substrate will not be impacted and crystal defects will not occur, so that deterioration of the device can be prevented. At the same time, charge-up can be suppressed, so that dielectric breakdown of the gate oxide film can be prevented. The other is a problem of a selectivity between an object to be etched and a base. At present, for example, in the etching of a gate electrode, the selectivity between poly-Si constituting the gate and the underlying SiO ₂ film is only about 10. However, poly-S
Since the Si—Si bond of i is etched only by radicals without ion assist, even if the ion energy is reduced, the etching rate is not significantly affected. Also, when securing anisotropy, the ion energy
Is possible even at 100 eV or less. In contrast, Si
In the case of an O ₂ film, the bonding energy of Si—O is high, and etching is not performed without the presence of high energy ions. Therefore, when high-energy ions disappear, poly-S
i of etching rate - DOO whereas the tapering, the SiO ₂ film of the etching rate - DOO selection ratio becomes large since extremely small, etching the poly-Si without hardly affecting the SiO ₂ film Becomes possible.

Next, the distribution width of ion energy with respect to the frequency of the RF power supply will be considered. FIG. 17 shows an ion energy distribution when ions generated in the bulk region of plasma by Monte Carlo simulation reach the substrate across the sheath. The horizontal axis represents the energy reached by the ions, and the vertical axis represents the number of ions. As plasma conditions, an ion temperature of 300 K, a sheath length of 1.2 mm, a voltage applied to the substrate of 100 V, a self-bias of 100 V, and an argon gas were assumed. Also, R
As the applied frequency of the F power source, 1
3.56 MHz was assumed. As shown in FIG.
At the RF power frequency, it can be seen that the ion energy distribution reaching the substrate is spread in a saddle structure.

The reason why the energy of the ions reaching the substrate is dispersed and the distribution is spread in a saddle structure will be described below. FIG. 18 shows how the energy of ions incident on the bulk sheath boundary changes over time while traversing the sheath. The graph of (a) shows the time change of ion energy, and the graph of (b) shows RF.
Indicates the change in power supply voltage. The solid line indicates that the phase of the RF power source is 2
Ions 1 incident on the bulk-seas boundary at the moment of π / 4
, And the dotted line is the case of ion 2 incident at the moment of 7π / 4. Energy reached by ion 1 and ion 2
In comparison with the above, in the case of ion 1, since the voltage (A) of the RF power supply in the final phase of reaching the substrate is almost 0, it reaches the substrate at a substantially constant speed without receiving acceleration. Does not increase. On the other hand, in the case of ion 2, since the voltage (B) of the RF power supply has almost reached the maximum value in the final phase, the energy reached by the acceleration is greatly increased due to the large acceleration.

In order to explain the reason why a large difference appears in the arrival energy of ions depending on whether or not acceleration is applied in the final phase, FIG.
This shows how the energy that can be obtained by the ions depends on the potential difference between the ions. For the sake of simplicity, FIG.
As shown in, shea - Between potential difference time Δt between scan constant velocity v ₁ of the ion 1 it is assumed much larger than the velocity v ₂ of the ion 2 (v ₁ "v _2). In this case, the time Δ
The travel distance of ion 1 during t is longer than that of ion 2. Since the acquired energy of the ions is equal to the potential difference between the distances in the case where the ions have moved, the ions 1 can acquire a larger energy than the ions 2. Further, as shown in FIG. 19 (b), the rate of ion 1 is the same, the ion 1 - potential V ₁ of the inter-scan is ion 2 - and greater than the potential difference V ₂ between the scan ( V ₁ >> V
₂ ). Assuming that the velocities of the ions 1 and 2 do not change during the time Δt for simplicity, the ion 1 at the time Δt
Is the same as that of ion 2, but since the potential difference between the movement distances is larger for ion 1, ion 1
Can obtain greater energy than the ions 2. As described above, the energy obtained by the ions is determined by the speed of the ions and the potential difference between the sheaths at that moment. That is, the higher the velocity of the ions and the greater the potential difference between the sheaths at that moment, the greater the energy obtained by the ions. Therefore, in the final phase in which the velocity of the ions is high, the greater the potential difference between the sheaths, the greater the energy obtained by the ions, and conversely, the smaller the potential difference, the smaller the energy gain.

Incidentally, whether or not ions undergo acceleration in the final phase is determined by the phase of the RF power supply when the ions are incident on the bulk-sea boundary. However, since the timing at which ions are incident on the bulk-sheath boundary is completely random, the energy that the ions reach the substrate depends on the incident phase as shown in FIG.
As a result, the distribution of ion energy is spread in a saddle structure as shown in FIG. When the distribution of ion energy is widened in this manner, ions on the high energy side damage the substrate, and ions on the low energy side do not contribute much to etching.
Efficient dry etching cannot be realized.

However, if the frequency of the RF power supply is made higher than 13.56 MHz conventionally used,
The distribution width of the spread of the ion energy can be narrowed, and the distribution width is small and uniform ion energy can be obtained. That is, when the frequency of the RF power source is increased, the number of times that the ions are accelerated by the RF power source while passing through the sheath is increased, so that the energy reached by the ions is not affected by the incident phase and averaged. This is for concentrating on appropriate values (self-bias). Figure 21
Shown in If the frequency of the RF power supply is as low as 13.56 MHz conventionally used as shown in FIG.
The distance over which the ions are accelerated and moved during one RF period increases, and the difference in the energy reached by the ions increases depending on whether or not they are accelerated in the final phase. On the other hand, when the frequency is high as shown in FIG.
The distance over which the ions are accelerated and moved during the period is reduced, and as a result, the difference in the energy of arrival of the ions is reduced, and uniform ion energy with a small distribution width is obtained.
In the case of such ion energy having a small distribution width, by controlling the value of the energy to a desired value, dry etching with low damage and high efficiency can be performed.

The present invention realizes low-damage and high-efficiency dry etching by increasing the frequency of the RF power supply to 13.56 MHz, which has been conventionally used, as described above. This realizes dry etching with high selectivity and high selectivity.

[0023]

FIG. 1 is a schematic diagram showing an example of a dry etching apparatus using a high-frequency RF power supply according to the present invention. The frequency of the RF power source is 13.56 MHz assigned by the Radio Law.
Use a frequency higher than z. For this reason, the RF power is completely shielded by the shield device 9 so that radio waves do not leak.

With the dry etching apparatus constructed as described above, the etching rate and selectivity of the poly-Si and SiO ₂ films of the gate electrode according to the first embodiment of the present invention are determined by the RF power supply. We examined how it changes with frequency. In the experiment, Cl ₂ was used as a gas system, the gas pressure was 100 mTorr, and the RF power was 300.
W. Cl ₂ as an etching gas for the gate electrode
Was used for the following reason. Table 1 shows the binding energies of Si and the main atoms. The binding energy of Si-Si is as low as 1.83 eV, and the binding energy of Si-O is as high as 8.33 eV. Therefore, F, Cl, Br, and I in the middle can be used for etching the gate electrode. That is, for example, in the case of Cl, the relation of the binding energy is Si-Si <Si-Cl <Si-
This is because poly-Si is easily etched by Cl, whereas SiO ₂ is hardly etched by Cl, because O is O and the higher the binding energy is, the more stable it is. Therefore, to ensure a higher selectivity, S
A gas system having a binding energy as small as possible compared to the binding energy of i-O may be used. However,
Br ₂ and I ₂ have drawbacks in that it is difficult to remove the exhaust gas and that the chamber and piping are easily corroded. Therefore, Cl ₂ was used as an etching gas.

[0025]

[Table 1]

FIG. 2 shows that the frequency of the RF power source is 13.56 MHz, 40 MHz, and 70 MHz under these conditions.
z, 100 MHz, poly-Si and Si
This is the result of measuring the etching rate of the O ₂ film. The horizontal axis represents the frequency of the RF power source, and the vertical axis represents the etching rate and the selectivity. FIG. 3 shows the frequency dependence of the self-bias at this time. The horizontal axis represents the frequency of the RF power supply.
The vertical axis is the self-bias. FIG. 2 shows that the selection ratio increases as the frequency of the RF power source increases.
This is considered to be due to the fact that the self-bias of the plasma decreases as the frequency of the RF power source increases, as shown in FIG. That is, when the frequency of the RF power source increases and the self-bias of the plasma decreases, and as a result the ion energy reaching the substrate decreases, p
As described above in oly-Si, the bonding energy of Si-Si - is 1.83eV low because low energy - against being etched in ionic, S is in the SiO ₂ film
This is because the low-energy ions are difficult to be etched because the binding energy of i-O is as high as 8.33 eV. It is possible to lower the self-bias by lowering the RF power. However, in this case, the ionization degree of the plasma is reduced, radical generation is reduced, and the etching rate is reduced. Etching is not possible. On the other hand, in the method of increasing the frequency of the RF power supply as described above, the self-bias can be reduced without lowering the etching efficiency. As described above, when a chlorine-based gas is used as an etching gas in etching the gate electrode, a conventional 13.56 MHz high frequency power supply can secure a selectivity of only about 10 as shown in FIG. When the high-frequency power supply is used, the selectivity becomes 40 or more even with a chlorine-based etching gas, and the gate electrode can be etched without substantially affecting the base.

Next, a gate according to a second embodiment of the present invention will be described.
The frequency dependence of the RF power of the dielectric breakdown of the oxide film will be described. In the experiment, four wafers were prepared and the frequency of the RF power supply was 13.56 MHz, 40 MHz, and 70 MHz.
z, 100MHz and poly of gate electrode
-Si etching was performed. As the etching conditions, Cl ₂ was used as a gas system, and the gas pressure was 300 mTo.
rr and RF power were 300W. For these four wafers, the ratio of chips in which the gate oxide film causes dielectric breakdown was determined by the FDDB (Field Dependent Dielectric
akdown). FIG. 4 shows the result. From FIG. 4, it is confirmed that when the frequency of the RF power source is increased, the ratio of chips that cause dielectric breakdown decreases. this is,
As described above, when the frequency of the RF power supply increases, the self-bias of the plasma decreases, the generation of high-energy ions is suppressed, the charge-up is reduced, and the stress applied to the gate electrode is reduced.

A method according to a third embodiment of the present invention, which suppresses generation of high energy ions while increasing anisotropy, will be described. FIG. 5 shows the change in the self-bias with respect to the etching gas pressure measured using the frequency of the RF power source as a parameter. Generally, to increase anisotropy, it is preferable to lower the etching gas pressure and increase the degree of vacuum. However, when the etching gas pressure is reduced, the self-bias is increased as shown in FIG. 5 and high-energy ions are generated. However, when the frequency of the RF power supply is increased, the self-bias can be reduced as shown in FIG. 5, and the anisotropy can be ensured.

As described above, according to Examples 1, 2 and 3 of the present invention, R
It has been found that when the frequency of the F power source is increased, the self-bias of the plasma is reduced to suppress the dielectric breakdown of the gate oxide film, and at the same time, the selectivity and the anisotropy are increased.

Next, the frequency dependence of the RF power source of the ion energy distribution according to the fourth embodiment of the present invention will be described. The ion energy distribution was determined using Monte Carlo simulation. Figure 6 is a sheet - the scan length L _sh parameters - ion energy as data - represents the dependence on -1/2 power of the mass M of the etching gas distribution width ΔE of the distribution, as the frequency f _RF of the RF power source Is 13.56M
Hz was assumed. FIG. 7 is a graph showing Δ using M as a parameter.
It represents the dependence on the reciprocal of L _sh of E, as the f _RF was assumed 13.56 MHz. Furthermore, Figure 8 is a M parameters - represents the dependence on the reciprocal of f _RF of ΔE as data, as the L _sh assumed a 3 mm. In any case, the condition of the plasma is that the ion temperature is 3
00K, self-bias 100V, RF power supply voltage 1
00V. 6, 7, and 8, the distribution width ΔE of the ion energy distribution is −1 / の of the mass M of the etching gas.
It can be seen that it is proportional to the square and the reciprocal of the _sheath length _{Lsh and} the reciprocal of the frequency f _RF of the RF power supply. That is, the distribution width ΔE of the ion energy distribution is expressed by Expression 1.

ΔE = k / (M ^1/2 · L _sh · f _RF ) Equation 1 where k is a proportionality constant, and is k from FIGS. 6, 7 and 8.
Is about 6830 [eV • amu ^1/2 • mm • MHz]
It is. Thus, ΔE is proportional to M ^−1/2 L _sh ⁻¹ f _RF ^{− 1} when the mass increases, the sheath length increases, or the frequency of the RF power source increases. ,
The transit time of the ions traveling through the case becomes longer, and as a result, the number of times the ions are swung by the RF power source increases as described in the section of (action), and the energy of the ions reaching the substrate becomes smaller. This is because the distribution width is narrowed irrespective of the incident phase and concentrated on an average value (self-bias).

As a design condition of the dry etching apparatus,
Assuming that the distribution width of the ion energy is ± 5% of the self-bias, the allowable condition of the energy width is 10 eV or less. Therefore, from equation 1, the frequency f _{RF of the} RF power supply must satisfy equation 2. f _RF > 683 / (M ^1/2 · L _sh ) Formula 2 As an example, when the sheath length is 3 mm, the applied frequency of the RF power source is 36 M in the case of Ar ⁺ ion (M = 40).
Hz or more, 20 M for SF ₆ ⁺ ion (M = 127)
Hz and above seems reasonable.

FIG. 9 shows the distribution of Ar ⁺ ion energy. FIG. 9A shows the case where the frequency of the RF power source is 13.56 MHz.
In the case of z, (b) is the case of 40.0 MHz. The horizontal axis represents ion energy, and the vertical axis represents the number of ions. The sheet length was 3 mm. As shown in FIG.
It can be seen that by increasing the applied frequency of the RF power source, the ion energy is concentrated on the desired energy (self-bias), the distribution width is narrowed, and a uniform ion energy distribution is obtained.

As described above, according to the fourth embodiment, 1
By providing a high-frequency power supply higher than 3.56 MHz, a uniform ion energy distribution with low energy can be obtained, and low-damage and high-efficiency dry etching can be realized.

[0035]

As described above, according to the present invention,
By using a high-frequency RF power supply higher than 13.56 MHz, the plasma self-bias is reduced while maintaining the anisotropy by lowering the etching gas pressure, and the ion energy is reduced.
The distribution is shifted to the low energy side as a whole, and at the same time, the energy distribution width is narrowed to ± 5% or less of the average attained energy to generate a uniform ion energy distribution. By realizing the etching and further lowering the etching rate of the underlying SiO ₂ film when etching poly-Si, SiN or Al alloy, it is possible to obtain a sufficiently large selectivity, and its practical effect is obtained. Is big.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a dry etching apparatus provided with an RF power supply having a frequency higher than 13.56 MHz according to an embodiment of the present invention.

FIG. 2 is a diagram showing the RF power frequency dependence of the etching rate and selectivity of polysilicon and an oxide film.

FIG. 3 is a diagram showing the RF power supply frequency dependence of plasma self-bias;

FIG. 4 is a diagram showing the RF power supply frequency dependence of the breakdown rate of a gate electrode.

FIG. 5 is a diagram showing the dependence of self-bias on etching gas pressure.

FIG. 6 is a diagram showing the mass dependence of an etching gas on the distribution width of ion energy by Monte Carlo simulation.

FIG. 7 is a diagram showing the sheath length dependence of the ion energy distribution width by Monte Carlo simulation.

FIG. 8 is a diagram showing the RF power supply frequency dependence of the distribution width of ion energy by Monte Carlo simulation.

FIG. 9A is a diagram showing the energy distribution of Ar ⁺ ions when the frequency of the RF power source is 13.56 MHz. (B) is a diagram showing the energy distribution of Ar ⁺ ions at 40.0 MHz.

FIG. 10 is a configuration diagram of a conventional dry etching apparatus (RIE).

FIG. 11A is a conceptual diagram of an RF plasma. (B) is a diagram showing a potential distribution in plasma.

FIG. 12 is a correlation diagram between a time change of a cathode potential and a plasma potential.

FIG. 13 is a configuration diagram of a dual-frequency excitation dry etching apparatus proposed by Goto et al.

FIG. 14A is a schematic diagram of an ion energy distribution by a conventional RIE apparatus. (B) It is a schematic diagram of the ion energy distribution by the device of Tohoku University. (C) is a schematic diagram of the ion energy distribution when the frequency of the RF power supply is increased.

FIG. 15 shows the etching rate of poly-Si and SiO _2.
FIG. 4 is a diagram showing the ion energy dependence of the laser beam.

FIG. 16 is a diagram showing a circuit model of RF plasma.

FIG. 17 shows a case where the frequency of the RF power source is 13.56 MHz in the related art.
FIG. 10 is a diagram showing an energy distribution when Ar ⁺ ions reach the substrate across the sheath in the case of FIG.

FIG. 18 is a diagram showing a change over time of the energy of ions incident on a bulk / sheath boundary.

FIG. 19 is a schematic diagram showing how the energy obtained by ions depends on the speed of ions and the potential difference between the sheaths.

FIG. 20 is a correlation diagram between the energy of Ar ⁺ ions reaching the substrate and the incident phase.

FIG. 21 is a schematic diagram showing that the difference in the arrival energy of ions is reduced by increasing the frequency of the RF power supply.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal chamber 2 Supply port 3 Outlet 4 Anode (anode) 5 Cathode (cathode) 6 Sample 7 Blocking capacitor 8 RF power supply 9 Shield 10 Bulk / Sheet boundary 11 Blocking capacitor 2 12 RF Power supply 2

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Kenji Hatto 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. In-company (56) References JP-A-58-186937 (JP, A) JP-A-62-125626 (JP, A) JP-A-1-149965 (JP, A) JP-A-63-202028 (JP, A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01L 21/3065 C23F 4/00

Claims (2)

(57) [Claims] A step of placing a semiconductor substrate on said cathode in a metal chamber having an anode and a cathode; and applying an RF power to said cathode to apply said anode. Plasma between the cathode and the cathode to generate bulk and sheath
A frequency range of 13.5 as the frequency of the RF power source.
Using a constant frequency higher than 6 MHz, the self-bias of the plasma generated between the anode and the cathode is reduced without lowering the power of the RF power source, and at the same time the light is incident on the semiconductor substrate. Ion energy
A step of narrowing the distribution width, the cathode - when the potential of the de falls below plasma <br/> Ma potential, the low-energy ions generated in the bulk region in the semiconductor substrate - and incident efficiency A dry etching method including a step of performing etching without dropping. 2. The dry etching method according to claim 1, wherein the maximum energy of the ions reaching the substrate is set to 100 eV or less by setting the frequency of the RF power supply to 100 MHz or more.