JP2000068227A - Method for processing surface and device thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve uniformity of irradiation ion energy to an object to be processed, to increase ion irradiation amounts, and to increase the upper limit of the irradiation ion energy by suppressing the spread of an ion sheath formed between a plasma and the object to be processed. SOLUTION: This device is provided with a porous electrode 40, arranged so as to face the processing face of an object 6 to be processed with an interval (a distance D) in between, and this porous electrode 40 is fixed through an electrode supporting body 46 to a ground potential. The porous electrode 40 can be provided with plural small holes, and plural metal thin wires can be arranged as mesh-like or interdigital wanner. A negative pulse-shaped bias voltage VB is impressed from a bias power source 26 to the object 6 to be processed, which is supported by the supporting body 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for generating plasma in the vicinity of an object to be processed and applying a bias voltage, for example, in the form of a negative pulse, to the object to cause ions in the plasma to flow to the object. The present invention relates to a surface treatment method and apparatus for irradiating and performing processes such as ion implantation, surface modification, and etching on an object to be processed, and more specifically, the spread of an ion sheath formed between the plasma and the object to be processed. The energy of the ions incident on the workpiece,
The present invention relates to means for improving the amount of ion irradiation and the like.

[0002]

2. Description of the Related Art Plasma immersion (Plasma immersion) is one of the techniques for treating an object by irradiating the object with ions.
Immersion Ion Implantation: PIII method or Plasma Source Ion Implantation: P
There is something called the SII) method. FIG. 16 shows an example of a surface treatment apparatus according to this method.

The surface treatment apparatus shown in FIG. 16 includes a vacuum container 2 evacuated by a vacuum exhaust device 4 and a conductive support 8 provided in the vacuum container 2 and supporting an object 6 to be processed. And a gas 1 for plasma generation in a vacuum vessel 2.
A gas supply unit 10 for supplying the gas 2, a plasma generating means for ionizing the gas 12 in the vacuum vessel 2 to generate a plasma 20 near the object 6 on the support 8, the treated 6 and a bias power source 26 for applying a negative pulsed bias voltage V _B. The vacuum vessel 2 is grounded. 32 and 34 are insulators.

In this example, the plasma generating means supplies a high-frequency power RF from a high-frequency power supply 16 to a high-frequency coil 14 provided in the vacuum vessel 2 via a matching circuit 18, and discharges a high-frequency power in a peripheral portion of the high-frequency coil 14. The plasma 20 is generated in a steady (continuous) manner by ionizing the gas 12. The high frequency power supply 16 outputs a high frequency power RF having a sinusoidal shape with a frequency of 13.56 MHz, for example.

When a negative pulse-like bias voltage V _B is applied to the object 6 from the bias power supply 26 while the plasma 20 is generated, positive ions in the plasma 20 are accelerated toward the object 6. The object 6 is irradiated. Thus, the surface of the workpiece 6 (including the surface layer in this specification) can be subjected to processes such as ion implantation and surface modification.

[0006] The surface treatment method or apparatus as described above includes:
It has the following advantages.

Since the ions in the plasma 20 are directly incident on the object 6 without using an ion source or the like, the ion irradiation amount per unit time is relatively high.

Since ions can be made to enter the object 6 from multiple directions, the object 6 having a complicated three-dimensional shape can be irradiated with ions relatively uniformly so as to be processed relatively uniformly. Can be applied.

Since an ion source and various power supplies for the ion source are not required, the apparatus configuration is simple and inexpensive.

[0010]

The above-mentioned surface treatment method or apparatus has the following problems.

The energy range of ions incident on the workpiece 6 is wide. That is, the uniformity of ion energy is poor.

Although there is a demand to increase the amount of ion irradiation on the workpiece 6, it cannot be easily increased.

The upper limit of the ion energy with which the object 6 can be irradiated is not so high. That is, it is difficult to irradiate the workpiece 6 with ions of too high energy.

The above problem will be described in detail with reference to FIGS. 18A is an illustration of an example of a negative pulse-shaped bias voltage V _B of the waveform output from the bias power source 26, practically is not a perfect square wave, the rise time t _r, as in this example And a fall time t _d .

Before the bias voltage V _B is applied to the object 6, no ion sheath 22 is formed between the plasma 20 and the object 6 (see FIG. 17A).

When the bias voltage V _B is applied to the object 6, electrons having a small mass are rapidly blown off from the periphery of the object 6 by the electric field, and the electrons between the plasma 20 and the object 6 are removed. Spreads rapidly (see FIG. 17B). In other words, the ion sheath surface 22a, which is the boundary surface between the plasma 20 and the ion sheath 22, rapidly moves away from the workpiece 6. During this time, the ion sheath 22
The positive ions 24a left in the firstly enter the object 6 to be processed,
The current I suddenly starts flowing through the object 6 (see a in FIG. 18B). However, since the bias voltage V _B from the bias power supply 26 is applied between the plasma 20 and the processing target 6, a potential gradient occurs in the ion sheath 22, and therefore, the positive ions 24 a remaining in the ion sheath 22. voltage applied to is lower than the bias voltage V _B. Of course during this time also, incident from the plasma 20 by positive ions 24b are accelerated in a normal bias voltage V _B to the object to be processed 6. Moreover, because of the actual bias voltage V _B is finite rise time t _r, as shown in FIG. 18A (for example, about 5 .mu.sec), the energy of ions incident on the object to be processed 6 during this time, the constant bias voltage V _B Lower than that corresponding to the value V _BM . For the reasons described above, the ion energy incident on the object to be processed 6 is within the rise time t _r of about time, lower than those corresponding to steady-state value V _BM, yet is irregular. This is the reason for the above-mentioned problem that the energy width of ions is wide. When the energy width of the ions is wide, for example, the ion implantation depths become uneven. This is inconvenient especially for impurity implantation into a semiconductor.

When the time for the bias voltage V _B to reach the steady value V _BM elapses, the spreading speed of the ion sheath 22 decreases, but continues to spread (see FIG. 17C). During this time, the positive ions 24a remaining in the ion sheath 22 are incident on the object 6 with irregular energy, but they are considerably reduced. Most of the current I flowing through the object 6 is ( _I.e. , corresponding to the steady-state value _VBM ).

The ion current that can be extracted from the plasma is represented by the following space charge limiting current J, which is generally called the child Langmuir equation. Where V
_P is the applied voltage, q is the amount of charge of the ions, s is the distance between the object to be processed and the plasma end surface (ion sheath surface), m is the mass of the ions, and ε ₀ is the dielectric constant of vacuum.

[0019]

J = (4/9) · ε ₀ (2q / m) ^1/2 · V _P
^3/2 / s ²

That is, as the ion sheath 22 spreads as described above, the amount of the positive ions 24b extracted from the plasma 20 attenuates in inverse proportion to the square of the distance s, and as shown in FIG. Then, the current I flowing through the workpiece 6 attenuates rapidly. That is, the amount of ions incident on the processing object 6 rapidly attenuates. This contributes to the above-mentioned problem that the ion irradiation amount cannot be increased.

Suppose that the steady value V _BM of the bias voltage V _B = 10
At 0 kV, although it depends on the plasma density, for example, 10 μsec after the bias voltage V _{B is} applied,
The ion sheath surface 22a is separated from the object 6 by 5 cm or more. Although the bias voltage V _B is applied between the plasma 20 and the processing object 6, a problem of abnormal discharge occurs here. The voltage V at which this abnormal discharge occurs is expressed by the following equation according to Paschen's law. Here, p is a pressure, γ is a secondary electron emission coefficient from the workpiece 6, λ is a mean free path of electrons at a pressure of 1 Torr, u is an ionization potential of an introduced gas, A = 1 / λ, and B = u / λ and d are distances at which the electric field is formed.

[0022]

V = Bpd / [ln (pd) + ln ｛A / ln
(1 + 1 / γ)｝]

From the above equation (2), for example, in a nitrogen gas, the product pd of the distance d between the two electrodes and the gas pressure p is 2 × 10 ^-2 To.
Above rr · cm, when a voltage of 100 kV is applied between the two electrodes, abnormal discharge (specifically, arc discharge) occurs between the two electrodes. That is, when the steady value V _BM of the bias voltage V _B is 100 kV and the nitrogen gas pressure is 4 mTorr, the ion sheath surface 22 a
If the distance is more than 1 cm, abnormal pulse-like discharge occurs in the ion sheath 22, and normal ion irradiation becomes difficult. If it is severe, sustain discharge will occur, and the bias power supply 26 and the like will be damaged.

The above-mentioned Paschen's law is basically a law in a vacuum. In the above-mentioned ion sheath 22, a large amount of secondary electrons from the processing object 6 exist while being accelerated toward the plasma 20. As a result, abnormal discharge is more likely to occur.

As described above, in the prior art, since the ion sheath surface 22a moves (that is, the width s of the ion sheath 22 increases) and abnormal discharge easily occurs, the bias voltage V _B applied to the workpiece 6 is increased. (Stationary value V _BM ) and the pulse width W cannot be made too large. The fact that the magnitude of the bias voltage V _B cannot be increased so much
This is the reason for the above-described problem that high-energy ion irradiation is difficult. The reason why the pulse width W cannot be made too large is that the ion sheath 22 continues to expand during that time, which constitutes another factor of the above-mentioned problem that the ion irradiation amount cannot be increased. For example, in a conventional device, typically, the steady-state value V _BM
Is about 100 kV and the pulse width W is about 10 μsec.

As described above, the large spread of the ion sheath formed between the plasma and the object to be processed is the main reason for the above-mentioned problems.

Therefore, the present invention suppresses the spread of the ion sheath formed between the plasma and the object to be processed, thereby improving the uniformity of the ion energy applied to the object to be processed, increasing the ion irradiation amount, and irradiating the object. The main purpose is to allow the upper limit of ion energy to be increased.

[0028]

According to one aspect of the present invention, there is provided a surface treatment method comprising: a porous electrode which is opposed to a treatment surface of an object to be treated with a space therebetween and has a fixed potential of a ground potential or a positive potential. And a pulsed or DC bias voltage is applied to the object to be processed (claim 1).

One of the surface treatment apparatuses according to the present invention is provided with a porous electrode which is opposed to the treatment surface of the object to be treated at an interval and whose potential is fixed to a ground potential or a positive potential, and The bias power supply is configured to apply a pulsed or direct-current bias voltage to an object to be processed supported on the support (claim 7).

According to the above configuration, when no bias voltage is applied to the object, the plasma exists near the object through the opening of the porous electrode.

When a negative pulse-like bias voltage is applied to the object to be processed, for example, the electric field reaches the plasma, and electrons in the plasma are repelled from the periphery of the object to be processed. Although an ion sheath is formed and this ion sheath expands rapidly, when the ion sheath surface comes to the position of the porous electrode, an electric field is applied between the object to be processed and the porous electrode. Since the effect of repelling electrons in the plasma is eliminated, the spread of the ion sheath stops. In this state, ions are extracted from the plasma through the opening of the porous electrode,
It is irradiated on the workpiece. The energy of the irradiation ions substantially corresponds to the magnitude of the bias voltage applied to the object.

As described above, since the spread of the ion sheath can be suppressed by the porous electrode, it is possible to improve the uniformity of the irradiation ion energy with respect to the object to be processed, increase the ion irradiation amount, and increase the upper limit of the irradiation ion energy. become.

[0033]

FIG. 1 is a sectional view showing an example of a surface treatment apparatus according to the present invention. Portions that are the same as or correspond to those in the conventional example in FIG. 16 are denoted by the same reference numerals, and differences from the conventional example will be mainly described below.

The surface treatment apparatus of this embodiment includes a porous electrode 40 arranged so as to face the processing surface (for example, the upper surface) of the above-mentioned workpiece 6 with an interval (distance D) therebetween. In this example, the porous electrode 40 is mounted on a conductive (for example, metal) electrode support 46, and is fixed to the ground potential via the electrode support 46. The electrode support 46 is attached to the grounded vacuum vessel 2 and is at ground potential.

It is preferable that the porous electrode 40 is fixed to the ground potential as in this example, since a power supply is unnecessary.
In short, since it is sufficient that the potential is fixed, the potential may be fixed at a constant positive potential. However, if the porous electrode 40 is fixed at a negative potential, the positive ions in the plasma 20 are drawn into the negative electrode, and sputtered particles are sputtered out of the porous electrode 40 by sputtering.

The porous electrode 40 may have, for example, a large number of small holes 42 as shown in FIG. 2 or a large number of fine metal wires 44 having a diameter of 1 mm or less as shown in FIG. They may be arranged in a lattice (in a mesh) or may be arranged in a large number, for example, 1 mm in diameter as shown in FIG.
The following metal thin wires 44 may be arranged in parallel (interdigital). In short, what is necessary is just to have many openings between conductive members.

In this example, the bias power supply 26 includes a DC power supply 28 for outputting a negative DC voltage and a DC voltage output from the DC power supply 28 intermittently to generate a negative pulse-like bias voltage V _B. And an output switch 30.

In the above-described surface treatment apparatus, when the plasma 20 is generated in the vacuum vessel 2 as described above, and when the bias voltage V _B is not applied to the workpiece 6, the plasma 20 is applied to the porous electrode 40. It is diffused through the opening to the vicinity of the workpiece 6 and exists.

When a negative pulse-like bias voltage V _B is applied to the object 6, for example, as in this example, the electric field reaches the plasma 20 and the electrons in the plasma 20 are removed as described above. 6, an ion sheath 22 (see FIG. 5) is formed between the plasma 20 and the workpiece 6, and the ion sheath 22 spreads rapidly, but as shown in FIG. Ion sheath surface 2
When the electrode 2a reaches the position of the porous electrode 40, an electric field is applied between the object 6 to be processed and the porous electrode 40, and there is no action to repel electrons in the plasma 20. The spread of 22 stops. In this state, the positive ions 24 are extracted from the plasma 20 through the opening of the porous electrode 40, and the positive ions 24 are irradiated on the workpiece 6. This drawn through the porous electrode 40 by positive ions 24 which is delivered to the object 6 is accelerated by the bias voltage V _B to be applied between the object to be processed 6 and the perforated electrode 40, the irradiated ion 24 The energy of
Substantially corresponds to the magnitude of the bias voltage V _B applied to the article to be treated 6. That is, it is almost V _B [eV].

As described above, the spread of the ion sheath 22 (that is, the movement of the ion sheath surface 22a) can be suppressed by the porous electrode 40, so that the uniformity of the irradiation ion energy with respect to the object 6 to be processed and the ion irradiation amount can be improved. And the upper limit of the irradiation ion energy can be increased.

More specifically, by suppressing the spread of the ion sheath 22, the volume (volume) of the ion sheath 22 can be suppressed smaller than that of the conventional example, and accordingly, the volume of the ion sheath 22 remains in the ion sheath 22. the amount of ions (see positive ions 24a shown in FIG. 17) which are incident on the object to be processed 6 is accelerated with a smaller acceleration energy than the bias voltage V _B can be reduced. As a result, it is possible to reduce the irregularity of the energy of ions incident on the processing target 6. This is one of the reasons why the uniformity of the irradiation ion energy with respect to the processing target 6 can be improved.

For example, in the conventional example, the width of the ion sheath 22 is widened to about 5 cm to 10 cm.
In this example, the distance D between the porous electrode 40 and the processing target 6 can be set to about 1 cm to 2 cm. In such a case, the volume of the ion sheath 22 becomes very small as compared with the conventional example. the ions incident to the object to be processed 6 with energy below the bias voltage V _B can be very small.

Further, by suppressing the spread of the ion sheath 22, it is possible to prevent an increase in the distance s in the above equation (1), so that it is possible to prevent a decrease in the space charge limiting current J. As shown by b in the figure, the attenuation of the current I flowing through the processing target 6 can be suppressed.
The ion irradiation dose to the object 6 is proportional to the product of the current I and the time (that is, the area S of the region surrounded by the curve in FIG. 6B or FIG. 18B). Since the area S is increased as compared with the conventional example (see FIG. 18B), the amount of ion irradiation on the workpiece 6 can be easily increased.

[0044] Moreover Thus the area S increases, the area in the bias voltage V amount of ions is delivered to the object 6 at a low energy during the rise time t _r and _B (Fig. And in Fig. 6B 18B S _r ) Will be relatively reduced,
That is, since the amount of non-uniform energy ions in the ions irradiated to the processing target 6 is reduced, the uniformity of the irradiation ion energy to the processing target 6 is also improved for this reason.

Further, by suppressing the spread of the ion sheath 22, it is possible to prevent the distance d in the above equation (2) from increasing (that is, stop at the distance D). Can be. As a result, the steady value V _BM of the bias voltage V _B applied to the processing target 6 is made larger than in the conventional example, so that the processing target 6 can perform high-energy ion irradiation. That is, the upper limit of the irradiation ion energy can be expanded, and ion irradiation of high energy of 100 keV or more can be performed.

Further, by suppressing the spread of the ion sheath 22, the distance d in the above equation (2) can be kept constant (that is, stopped at the distance D). application time limit of V _B is eliminated unlike the conventional example. That is, there is no upper limit of the pulse width W of the bias voltage V _B, it is possible to lengthen the pulse width W. For this reason as well, as can be seen from FIG. 6, it is possible to easily increase the amount of ion irradiation on the object 6 to be processed. Moreover, when the pulse width W is increased, the area S where the low-energy ion irradiation is performed is performed.
_Since the relative ratio of _r is further reduced, the amount of non-uniform energy ions in the ions irradiated to the processing target 6 is reduced, and the uniformity of the irradiation ion energy is further improved.

Since the pulse width W of the bias voltage V _B is not limited from the viewpoint of preventing abnormal discharge as described above, if it is within the allowable heat range of the object 6, the support 8 and the porous electrode 40, it is also possible to extremely long, it is also possible to apply a DC voltage as the bias voltage V _B.

In the conventional example, as described above, the spread of the ion sheath 22 is about 5 to 10 cm. Therefore, it is necessary to provide a further space around the object 6 to be processed, and the vacuum Although there was a problem that the size of the container 2 was large and the area occupied by the apparatus was large, in the present invention, the spread of the ion sheath 22 can be suppressed by the porous electrode 40 as described above. It is not necessary to provide a space as in the conventional example, and the area occupied by the device can be reduced accordingly.

It should be noted that the distance D between the object 6 and the porous electrode 40 is, as a matter of course, less than or equal to the distance derived from Paschen's law shown in Equation 2 above. 6 so that abnormal discharge does not occur. That is, the distance D is set to be equal to or less than the value determined by the following equation.

[0050]

V [ln (pD) + lnｐA / ln (1 + 1 /
γ)｝] = BpD

However, if the distance D is so small that the porous electrode 40 is too close to the object 6, a region to which the ions are hardly irradiated due to the shadow of the porous electrode 40 is formed.
It is not preferable because it occurs above. This can be considerably prevented by forming the porous electrode 40 with the thin metal wires 44 described above. For example, it is preferable to form the porous electrode 40 with a thin metal wire 44 having a diameter of about 0.5 mm or less, and arrange it at a position of a distance D of about 1 cm to 2 cm from the workpiece 6. The shadow problem is negligible.

The porous electrode 40 is exposed to the plasma 20, and the heat from the plasma 20 causes the porous electrode 40 to be exposed.
If the distortion of a problem, for example, such as or cooled by water cooling or the like periphery of the porous electrode 40, when no bias voltage is applied to V _B to be treated 6 is to stop the generation of the plasma 20, porous Preferably, measures are taken to reduce the heat input to the electrodes 40. The embodiment of turning on / off the plasma generation described later (see FIG. 7 and the like) also has an effect of reducing the heat input from the plasma 20 to the porous electrode 40.

The porous electrode 40 and the electrode support 46 are maintained at a ground potential (or a positive potential) and are not subjected to sputtering due to the incidence of accelerated ions from the plasma 20. If the generation of a small amount of impurities causes a problem, the porous electrode 40 and / or the electrode support 46 may be made of a material which does not cause a problem even if it is mixed into the processing object 6, or coated with such a material. It is preferable to keep it. The substance that does not cause a problem even if it enters the processing target 6 is, more specifically, a substance having the same system as the processing target 6. For example, when the object 6 is a silicon substrate, it is silicon or a silicon-based material.

[0054] become impurity generation factor, but rather, a support 8 in the case of applying a negative bias voltage V _B, case, as described above, mixed with the support 8 to be treated 6 However, it is preferable that the material to be treated is composed of a substance having no problem, more specifically, a substance having the same system as that of the object 6 to be treated or coated.

The object 6 is a flat substrate such as a semiconductor substrate. In this case, the porous electrode 40 may be flat. When the object 6 has a three-dimensional shape, the porous electrode 40 may have a shape conforming to the shape of the object 6. By doing so, it is possible to perform ion irradiation that exhibits the various effects described above even on the three-dimensionally processed object 6.

One suitable application of the apparatus and method of the embodiment shown in FIG. 1 is for impurity implantation into a semiconductor substrate. In the field of semiconductor devices, miniaturization progresses year by year, and in the near future, 50 n
It is required to dope (implant) impurities into a very shallow region of m or less. For this purpose, ions must be implanted with a low energy of about 1 keV or less. However, in an ion implantation apparatus using a conventional ion source, a reduction in beam current due to a reduction in extraction voltage (in short, the beam current). The current is proportional to the 3/2 power of the extraction voltage) and the beam divergence increases, so that the beam current decreases, and a sufficient throughput cannot be obtained.

On the other hand, according to the surface treatment apparatus using the conventional plasma immersion method shown in FIG. 16, a relatively high throughput can be obtained even in the case of the low energy ion implantation as described above. Further, according to the apparatus and method of the embodiment shown in FIG. 1, even in the case of the low energy ion implantation as described above, the ion irradiation amount can be easily increased as described above, so that the throughput can be further reduced. Can be enhanced. In addition, since the irradiation ion energy has good uniformity as described above, the controllability of the implantation depth is excellent.

Next, another embodiment will be described. However, the following mainly describes differences from the above-described embodiments or differences between the embodiments.

[0059] Example 7 is further development of the embodiment of FIG. 1, the turning on and off the plasma generation, a negative pulsed bias voltage V _B during the on-period shall be applied to the article to be treated 6 It is.

That is, in this embodiment, a switch 48 is inserted in series with the high-frequency power supply 16 as switching means for periodically turning on and off (intermittently) the generation of the plasma 20 by the plasma generating means. The switch 48 turns on / off the high-frequency power RF supplied between the support 8 and the high-frequency coil 14 to turn on / off the plasma generation.

Further, the switch 48 and the switch 30 in the bias power supply 26 are synchronized with each other, and the switch 3 is turned on within a predetermined period after the switch 48 is turned on.
A timing control circuit 50 that periodically turns on and off at a timing (time difference) when 0 turns on is provided.

FIG. 8 shows an example of changes over time of the high-frequency power RF, the emission intensity I _P from the plasma 20, the plasma density N _P and the bias voltage V _{B in} the embodiment of FIG. Immediately after the high-frequency power RF is turned on, the light emission intensity I _P and the plasma density N _P rapidly increase, and shift to a steady state after a lapse of time t ₃ . The plasma density N _P becomes equal to or higher than the value in the steady state after time t ₁ from the time when the high-frequency power RF is turned on.
After ₂ the maximum is reached. t ₁ is about 5 to 10 μsec, t
₂ about 100~200μsec, t ₃ is about 500μse
c to 1 msec.

Accordingly, the time t ₄ from the time when the switch 48 is turned on to the time when the switch 30 is turned on is defined as t ₁ ≦ t ₄ ≦ t
_By setting it to ₃ , specifically, t ₄ is preferably 5
μsec to 1 msec, more preferably 10 μsec to
By setting the time to 500 μsec, ions can be extracted from the plasma 20 having a higher density than that of the steady plasma and can be irradiated to the object 6, so that the amount of ion irradiation on the object 6 can be easily increased. . For example, when other conditions are the same, the ion irradiation amount can be increased by about 10 to 30% as compared with the embodiment of FIG.

The frequency and the bias voltage V _B at which the high-frequency power RF is turned on and off to turn on and off the plasma generation.
Frequency (both 1 / T in FIG. 8) for turning on and off the can, not completely extinguished plasma 20 in too high an off period, the spike and the plasma density N _P of the emission intensity I _P with the plasma generation described with reference to FIG. 8 No increase was obtained, and from experimental results, 100 kHz is the upper limit. Further, if the frequency is too low, the productivity is extremely reduced, so that 10 Hz or more is appropriate. That is, the frequency is 10 Hz to 100
It is preferably in the range of kHz, more preferably in the range of 100 Hz to 1 kHz.

The embodiment of FIG. 9 is a further development of the embodiment of FIG. 7 and is suitable for use as a CVD (chemical vapor deposition) apparatus.

That is, in this embodiment, the lamp heater 54 is used as an example of a heating means for heating the workpiece 6 such as a substrate.
Is provided. The electrode support 46 has a plurality of holes 52 through which heat from the lamp heater 54 passes. A source gas is introduced into the vacuum vessel 2 as the gas 12.

According to this embodiment, simultaneously with the dissociation of the source gas 12 such as TiCl ₄ by the plasma 20 and the deposition on the workpiece 6, a negative pulse-like bias voltage V _B is applied to the workpiece 6. Thus, it is possible to deposit a thin film on the workpiece 6 while controlling adhesion, crystallinity, orientation, and the like.

Further, since the porous electrode 40 is provided, it is possible to control the ion energy with high accuracy by preventing the irradiation ion energy from being irregular as described above.
The film characteristics can be controlled with high accuracy and high reproducibility.

Further, the raw material gas 12 such as SiH _{4 is used.}
Depending on the type, fine particles are generated in the plasma 20,
It is known that the growth of fine particles can be suppressed by periodically turning on and off the plasma generation, although this may adversely affect the film properties. Therefore, in this embodiment, the generation of fine particles is suppressed by periodically turning on and off the plasma generation, and the above-described film characteristics are controlled by irradiating the processing target 6 with positive ions during the on period. it can.

The embodiment of FIG. 10 is a modification of the embodiment of FIG. 7, in which plasma generation is periodically turned on and off, and a positive pulse-like bias voltage V _B is applied to the object 6 during the off period. Thus, the workpiece 6 is irradiated with negative ions.

For this purpose, in this embodiment, the polarity of the DC power supply 28 in the bias power supply 26 is reversed, and a positive pulse-like bias voltage V _B is applied to the workpiece 6 supported on the support 8. A bias power supply 27 is provided instead of the bias power supply 26. Also, instead of the timing control circuit 50 as described above, the two switches 4
8 and the switch 30 in the bias power supply 27 are synchronized with each other, and a timing control circuit 51 for periodically turning on and off at a timing (time difference) that the switch 30 is turned on within a predetermined period from the time when the switch 48 is turned off. Provided.

The high-frequency power RF in the embodiment of FIG.
Electron density N _E in the plasma 20, an example of time change of the negative ion density N _I and the bias voltage V _B shown in FIG. 11.
Electron density N _E radio frequency power RF in the plasma 20 with the off rapidly decreases (at about 5μsec), 1~2e
Low-energy electrons of about V become dominant plasma.
Molecules or excited molecules are attached to and dissociated from this, generating negative ions. Electron density N _E is rapidly attenuated as the negative ion density N _I and either inversely proportional to (i.e. negative ion density N _I
Rapidly increases), and after the RF power RF is turned off, about 10 μs
After ec, a unique plasma in which positive ions and negative ions are dominant is formed. Negative ion density N _I reaches a maximum at about 30~40μsec after high-frequency power RF off, then gradually attenuates, becomes substantially zero at 1msec about after high-frequency power RF off.

Even when a positive bias voltage V _B is applied to the object 6 when the plasma 20 is rich in electrons, the object 6
Most of the electrons that are incident on are light and have high mobility,
The workpiece 6 cannot be irradiated with negative ions. However, by turning on and off the plasma generation as described above, a unique plasma is formed, and its negative ion density N _I
More specifically, within a period in which the electron density N _E becomes approximately 1/10 or less of the negative ion density N _I , more specifically, 10 μsec to 1 m after the high-frequency power RF is turned off.
within a period of post-sec, by applying a positive pulse-shaped bias voltage V _B to the object to be processed 6, it is possible to perform the negative ion irradiated to the article to be treated 6. Therefore, the timing control circuit 51 is so as to turn the switch 30 from OFF switch 48 let delayed time t _5. This time t ₅ is 10 μsec to 1 m as described above.
sec is preferable, and 20 μsec to 200 μsec is more preferable. In the latter case, the irradiation amount of the negative ions on the object 6 can be further increased.

Further, by providing the porous electrode 40 as in the embodiment of FIG. 10, for the reasons described above, the uniformity of the irradiation ion energy, the increase of the ion irradiation amount, and the irradiation The upper limit of the ion energy can be increased.

In the apparatus and method shown in FIG. 10, for example, a buried oxide film layer is formed in a substrate by injecting oxygen ions into a substrate containing Si, such as a Si substrate, a SiC substrate, or a SiGe substrate. SIMOX (Separated
by IMplanted OXygen) A method of fabricating a substrate, or implanting hydrogen ions into a substrate containing Si such as a Si substrate, a SiC substrate, or a SiGe substrate, and then heating the substrate to 380 ° C. or higher to form voids (voids) in the substrate. It can be used for a forming method and the like.

In the above method for forming voids, helium ions may be implanted instead of hydrogen ions, but helium does not generate negative ions.
When helium ion implantation is performed, an apparatus or method for irradiating and implanting positive ions shown in FIG. 1 and the like may be used.

Further, in recent years, negative ions have attracted attention in the field of etching, particularly in the field of etching semiconductors.
This is because it has become clear that the etching rate is several times higher in etching with negative ions than in etching with positive ions. Therefore, it is convenient to use the apparatus and method shown in FIG. 10 for negative ion irradiation in the field of etching.

In particular, in recent years, with the increase in the degree of integration of semiconductor devices, there has been an increasing demand for high-speed etching of electrode materials such as high / ferroelectric materials and Pt which are difficult to etch. In the configuration of the twelfth embodiment, Cl ⁻ , F
^- By mass irradiated with energy control negative ions with high precision, such as, it is possible to speed and controllability good etching.

As for the negative ion generation, as another means, a porous electrode is provided between the plasma generation region and the substrate (object to be processed), and a current is supplied to the porous electrode within the surface of the porous electrode.
By generating a magnetic field of less than Gauss or setting the potential of this porous electrode to 0 V to -50 V or a floating potential, a plasma rich in low-energy electrons of 1 to 2 eV or less is generated between the porous electrode and the substrate. However, techniques for efficiently generating negative ions and generating plasma with high density of negative ions have already been proposed. For example, "Electron and Ion Ener
gy Control in a Radio Frequency Discharge Plasma w
ith Silane ", Jpn. J. Appl. Phys. Vol. 36 (1997) pp4547-4
See 550 Part1, No. 7B, July 1997.

The embodiment shown in FIG. 12 is a combination of the embodiment shown in FIG. 10 and the technique for generating a plasma in which the above-mentioned negative ions are dense.

That is, in this embodiment, the porous electrode 4 described above is used.
The second porous electrode 60 is provided on the opposite side of the object 6 to be treated away from the porous electrode 40, and a DC voltage of 0 V to −50 V is applied to the second porous electrode 60 from the DC power supply 66 to bias the second porous electrode 60. I have to. The second porous electrode 60 is supported apart from the porous electrode 40 by, for example, a cylindrical insulator 70. 68 is an insulator.

The second porous electrode 60 may have a large number of small holes as in the case of the above-described porous electrode 40, or may have a thin metal wire arranged in a grid or in a comb.

When such a second porous electrode 60 is provided and biased to the above potential, during the generation of the plasma 20, between the porous electrode 40 and the second porous electrode 60,
A low-energy electron-rich plasma of 2 eV or less is generated, which makes the generation of negative ions efficient,
A plasma 72 having a high density of negative ions is generated.

Further, by turning on and off the generation of the plasma 20, the negative ion density in the plasmas 20 and 72 is increased within a period of 10 μsec to 1 msec after the off time for the reason described above (see the description of FIG. 11). To rise. And by applying the bias power source 27 within the time a positive pulse-shaped bias voltage V _B to the object to be processed 6, allowing higher density of the negative ion irradiated to the article to be treated 6.

The second porous electrode 60 may have a floating potential. Also, as shown in FIG. 13, the second porous electrode 60 is formed of a thin metal wire 64, and a current _ID is supplied from a DC power supply (not shown) to the second porous electrode 60 so that 0 gauss is generated in the plane of the second porous electrode 60. A larger magnetic field 65 of 100 Gauss or less may be formed.

FIG. 14 shows an embodiment in which the technique shown in FIG. 12 is used for forming a thin film by MOCVD (metal organic chemical vapor deposition).

In the field of semiconductor devices, with the progress of miniaturization, the dielectric constant of capacitor materials has been increased. Also, a BST (ie, (Ba, Sr) TiO ₃ ) thin film is attracting attention as a leading candidate for a next-generation capacitor material, and research on the MOCVD method is being promoted due to its superior step coverage.

In the conventional ordinary MOCVD method, the substrate is
In order to lower the temperature of the substrate, oxygen radicals and metastable oxygen molecules are produced by ECR plasma (plasma generated by using electron cyclotron resonance). Attempts have been made to lower the substrate temperature by making the light incident on the substrate.

However, in the method of producing oxygen radicals using such ECR plasma, organic materials (DPM is dipivaloylmethane) such as Ba (DPM) ₂ and Sr (DPM) ₂ are mixed in the gas phase, This combines with oxygen radicals to generate a large amount of fine particles and deposits on the substrate, which deteriorates the crystallinity, composition ratio and the like of the film and causes deterioration of film characteristics such as dielectric constant.

On the other hand, in the embodiment of FIG. 14, Ba (DPM) ₂ , Sr (DP
M) An organic metal source gas 78 such as ₂ is introduced into the region between the porous electrode 40 and the second porous electrode 60 described above. 74 is a cylinder. O ₂ gas, N ₂ O gas or the like is introduced as the gas 12 from the gas supply unit 10 described above. Other configurations are the same as those of the embodiment of FIG.

As described in the embodiment of FIG. 12, in the region between the porous electrode 40 and the second porous electrode 60, the electron temperature is 1 to
Since it is as low as 2 eV or less, dissociation of the organometallic raw material gas 78 is suppressed. Although fine particles are generated, the plasma 20
By turning on and off the generation of periodic, by suppressing the growth of the fine particles, applying a bias voltage V _B of the object (e.g., a substrate) 6, for example, 1kV following positive pulse-shaped in the OFF period, the The processing object 6 is irradiated with negative ions. Thereby, O ^-, O ₂ ^- is irradiated oxygen negative ions are to be treated 6 such, since oxidation of the coating composition such as BST described above is promoted, to be capable of a lower temperature of the substrate temperature Become.

[0092] Moreover, the fine particles are negative ions are negatively charged in high-density plasma 72, the in growth developing (i.e. before growth) fine particles to be treated 6 pull a positive bias voltage V _B, The generation and deposition of large fine particles, which are problematic in film characteristics, can be suppressed.

Further, carbon-based impurities in the film may cause a problem. However, since carbon can be released as a CO _x -based gas by irradiating oxygen negative ions, an effect of reducing carbon-based impurities can be expected.

The apparatus and method shown in FIG. 14 can be used for forming a PZT (lead zirconate titanate) thin film,
Of course, the present invention can be applied to the formation of a BT (bismuth strontium tantalate) thin film, an oxide-based dielectric thin film and the like.

By the way, the negative ions are not only different from the positive ions in the charge, but also characterized in that the generated ion species ratio is different. The above-mentioned SIMOX substrate is also used for the production. For example, when hydrogen ions are implanted into a substrate containing silicon and then heated to 380 ° C. or more to form voids (voids) in the substrate, There are a plurality of types of hydrogen positive ions such as H ₂ ⁺ (molecular ions) and H ⁺ (atomic ions). Therefore, when ions are implanted by non-mass separation such as plasma immersion, the distribution of the implantation amount in the implantation depth direction Then, multiple peaks appear.

On the other hand, since the negative ions of hydrogen are physically only H ⁻ (atomic ions), if the negative ions are implanted by using the embodiment of FIG. 10 or FIG. Shows only a single peak, which allows very controllable (ie, high precision) injection. Moreover, the action of the porous electrode 40 described above makes it possible to make the implantation energy (that is, the implantation depth) uniform.

Using such hydrogen negative ion implantation,
For example, by bonding Si unbonded hands in a Si substrate or a Si thin film to H atoms, it is possible to repair defects, that is, to control so-called passivation with high accuracy. Particularly in recent years, in the field of manufacturing TFT-LCDs (thin film transistor type liquid crystal displays), polycrystalline silicon (p-
Studies have been made to reduce leakage current by passivating Si) thin films with hydrogen-based plasma, and to increase photoelectric conversion efficiency by passivating polycrystalline silicon substrates for solar cells. If the technique of FIG. 10 or FIG. 12 is used, the implantation depth and the implantation amount of hydrogen ions can be controlled with high accuracy, so that hydrogen defects can be repaired with high efficiency.

The support 8 to which the above-described bias voltage V _B is applied is, for example, as shown in FIG. It is preferable to cover with a shielding container 47 which is conductive (for example, made of metal) and has a ground potential. In this example, the shielding container 47 also serves as the electrode support 46 described above.

When such a shielding container 47 is not provided, if a high voltage (for example, 10 kV or more) bias voltage V _B is applied to the support 8 when the above-described plasma 20 is not generated, As can be seen from Paschen's law shown in the above equation (2), since the distance d where the electric field is formed becomes very large, abnormal discharge occurs between the support 8 and the vacuum vessel 2, thereby causing a large discharge. A current may flow and damage the bias power supplies 26, 27 and the like. In order to cope with this, the shielding container 47 as described above is provided, and the distance L between the shielding container 47 and the support 8 is set to be sufficiently shorter than the distance derived from Paschen's law shown in Expression 2 above. Is preferred. That is, it is preferable to make the distance L sufficiently smaller than the value determined by the following equation. For example, when applying a bias voltage V _B of 100kV is to keep setting the distance L to 10mm or less.

[0100]

V [ln (pL) + lnｐA / ln (1 + 1 /
γ)｝] = BpL

By performing the above, abnormal discharge between the support 8 and the vacuum vessel 2 can be reliably prevented regardless of the presence or absence of plasma around the support 8, thereby improving safety. I do.

Further, as can be seen from the above-mentioned Paschen's law, since the smaller the pressure, the more the abnormal discharge is less likely to occur, a vacuum exhaust means for locally exhausting the inside of the shielding container 47 may be further provided. If you do so, you can improve safety. In the example of FIG. 15, the evacuation unit is constituted by an evacuation pipe 80 connected to the shielding container 47 and a not-shown evacuation device connected thereto.

The plasma generating means may be other than the examples shown in the above examples, for example, a parallel plate type (capacitively coupled type) plasma generating means for generating plasma using two high frequency electrodes, a microwave For example, a microwave discharge type plasma generation unit that generates plasma by using a plasma, a DC discharge type plasma generation unit that generates plasma by using a filament, or the like may be used.

[0104]

Since the present invention is configured as described above, it has the following effects.

According to the first, second, seventh and eighth aspects of the invention, the spread of the ion sheath formed between the plasma and the object can be suppressed by the porous electrode. It is possible to improve the uniformity of irradiation ion energy, increase the amount of ion irradiation, and increase the upper limit of irradiation ion energy.

Further, since the spread of the ion sheath can be suppressed by the porous electrode, it is not necessary to provide a space around the object to be processed as in the conventional example, and the area occupied by the apparatus can be reduced accordingly. Can be.

According to the third and ninth aspects of the present invention,
Positive ions can be extracted from the plasma in a high-density state before transition to the steady state and can be incident on the object to be processed. The amount of ion irradiation can be easily increased.

In addition, compared to the case where plasma is constantly generated, irradiation with highly ionized ions having a high ionization state can be performed, so that ion implantation into a deep position becomes easy.

According to the fourth and tenth aspects of the present invention, it is possible to extract negative ions from a plasma state having a high negative ion density and irradiate the same to the object. Moreover, by using the porous electrode, even in the case of negative ion irradiation, it is possible to improve the uniformity of the irradiation ion energy, increase the ion irradiation amount, and increase the upper limit of the irradiation ion energy.

According to the fifth, sixth, eleventh, twelfth, and thirteenth aspects of the present invention, it is possible to generate high density plasma of negative ions between the porous electrode and the second porous electrode, and to turn off the plasma generation. Since the increase in the negative ion density can be used later, it is possible to irradiate the workpiece with a higher density of negative ions.

According to the fourteenth aspect of the invention, by providing the shielding container, abnormal discharge between the support and the vacuum container can be reliably prevented regardless of the presence or absence of plasma around the support. The safety can be improved.

According to the fifteenth aspect of the present invention, the pressure in the shielding container can be reduced to make it more difficult for abnormal discharge to occur between the support and the shielding container.
Safety is further improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a surface treatment apparatus according to the present invention.

FIG. 2 is a plan view showing an example of a porous electrode.

FIG. 3 is a plan view showing another example of a porous electrode.

FIG. 4 is a plan view showing another example of a porous electrode.

FIG. 5 is an enlarged view showing a portion of a porous electrode of the apparatus of FIG. 1;

FIG. 6 is a diagram illustrating an example of a waveform of a bias voltage and a current flowing through an object to be processed in the apparatus of FIG. 1;

FIG. 7 is a cross-sectional view showing another example of the surface treatment apparatus according to the present invention.

FIG. 8 is a diagram showing an example of a temporal change of a high-frequency power, a plasma emission intensity, a plasma density, and a bias voltage in the apparatus of FIG. 7;

FIG. 9 is a sectional view showing another example of the surface treatment apparatus according to the present invention.

FIG. 10 is a sectional view showing another example of the surface treatment apparatus according to the present invention.

11 is a diagram showing an example of a change over time in high-frequency power, electron density in plasma, negative ion density in plasma, and bias voltage in the apparatus of FIG.

FIG. 12 is a sectional view showing another example of the surface treatment apparatus according to the present invention.

FIG. 13 is a diagram illustrating an example of a state in which a current is applied to a second porous electrode.

FIG. 14 is a cross-sectional view showing another example of the surface treatment apparatus according to the present invention.

FIG. 15 is a cross-sectional view showing an example in which the shielding container is locally exhausted.

FIG. 16 is a sectional view showing an example of a conventional surface treatment apparatus.

FIG. 17 is a view showing a process of generating an ion sheath in the apparatus of FIG. 16;

18 is a diagram illustrating an example of a bias voltage and a waveform of a current flowing through an object to be processed in the apparatus in FIG. 16;

[Explanation of symbols]

Reference Signs List 2 vacuum vessel 6 workpiece 8 support 10 gas supply unit (gas supply unit) 14 high-frequency coil (plasma generation unit) 16 high-frequency power supply (plasma generation unit) 20 plasma 26, 27 bias power supply 40 porous electrode 48 switch (switching unit) 50, 51 Timing control circuit (timing control means) 60 Second porous electrode

Claims (15)

[Claims] In a surface treatment method, a plasma is generated in the vicinity of an object to be processed in a vacuum vessel, and a bias voltage is applied to the object to cause ions in the plasma to be incident on the object. Providing a porous electrode facing the processing surface of the processing object at an interval and having a fixed potential of the ground potential or the positive potential, and applying a pulsed or DC bias voltage to the processing object A surface treatment method characterized by the above-mentioned. 2. The surface treatment method according to claim 1, wherein a negative pulse-like bias voltage is applied to the object. 3. A method of periodically turning on and off the plasma generation, and applying a negative pulse-like bias voltage to the object to be processed within a period of 10 μsec to 500 μsec after the on time in synchronization with the on / off. 3. The surface treatment method according to claim 2, wherein the application is performed. 4. A positive pulse-like bias voltage is applied to the object to be processed by periodically turning on and off the plasma generation and synchronizing with the on / off, and within a period of 10 μsec to 1 msec after the off time. The surface treatment method according to claim 1, wherein the application is performed. 5. A second porous electrode is provided on the opposite side of the porous electrode from an object to be treated, separated from the porous electrode, and an electric current is applied to the second porous electrode so that the second porous electrode is in the plane of the second porous electrode. 0
The surface treatment method according to claim 4, wherein a magnetic field larger than Gauss and 100 Gauss or less is formed. 6. A second porous electrode is provided on the opposite side of the porous electrode from the object to be treated, and is separated from the porous electrode, and the potential of the second porous electrode is set to 0 V to −50 V or a floating potential. The surface treatment method described. 7. A vacuum vessel, a vacuum exhaust device for evacuating the vacuum vessel, a support provided in the vacuum vessel for supporting an object to be processed, and supplying a gas into the vacuum vessel. Gas supply means, plasma generation means for ionizing this gas to generate plasma in the vicinity of the object supported by the support, and a bias for applying a bias voltage to the object supported by the support In a surface treatment apparatus comprising a power supply, a porous electrode that is opposed to the processing surface of the object to be processed at an interval and is fixed at a ground potential or a positive potential, and the bias power supply is A surface treatment apparatus for applying a pulsed or DC bias voltage to an object to be processed supported by a support. 8. The surface treatment apparatus according to claim 7, wherein the bias power supply applies a negative pulsed bias voltage to the workpiece supported by the support. 9. A switching means for periodically turning on / off the plasma generation by said plasma generation means, and said bias power supply being synchronized with on / off by said switching means and within a period of 10 μsec to 500 μsec after the on time. 9. The surface treatment apparatus according to claim 8, further comprising: timing control means for outputting the negative pulse-like bias voltage. 10. A switching device for applying a positive pulse-like bias voltage to an object supported on the support, wherein the bias power supply is configured to periodically turn on and off plasma generation by the plasma generation means. Means for outputting the positive pulsed bias voltage from the bias power supply in synchronization with the on / off of the switching means and within a period of 10 μsec to 1 msec from the off time. Item 7. A surface treatment apparatus according to item 7. 11. A second porous electrode provided on the opposite side of the porous electrode from the object to be treated and separated from the porous electrode, and a current is supplied to the second porous electrode to cause the in-plane of the second porous electrode to flow. The surface treatment apparatus according to claim 10, further comprising: a DC power supply that generates a magnetic field greater than 0 Gauss and 100 Gauss or less. 12. A second porous electrode provided on the opposite side of the porous electrode from an object to be processed and separated from the porous electrode, and a DC power supply for biasing the potential of the second porous electrode to 0V to -50V. The surface treatment apparatus according to claim 10, further comprising: 13. The surface treatment apparatus according to claim 10, further comprising a second porous electrode having a floating potential provided on the opposite side of the porous electrode from the object to be processed, and provided at a distance from the porous electrode. 14. The conductive container according to claim 7, further comprising: a conductive shielding container having a ground potential, which covers a portion of the support other than the object support portion with a space between the support and the support. The surface treatment apparatus as described in the above. 15. The surface treatment apparatus according to claim 14, further comprising vacuum evacuation means for locally evacuating the inside of the shielding container.