JPH1027780A - Plasma treating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma treating method by which deposition of particles caused by DC voltage of an electrostatic chuck can be prevented. SOLUTION: In this method, plasma treatment is carried out while holding a wafer by an electrostatic chuck. After high-frequency discharge for plasma treatment is started, a DC voltage is applied to operate the electrostatic chuck for the plasma treatment. When a desired plasma treatment is finished, the high-frequency discharge for the plasma treatment is stopped after stopping the application of voltage for operation of the electrostatic chuck. Accordingly, since DC current is not applied to the electrostatic chuck when the wafer is mounted on a wafer stage and high-frequency discharge is not caused, high electric field is not produced by DC voltage near the wafer and the electrostatic chuck. As a result, deposition of particles on the wafer is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing method, and more particularly, to a plasma processing method capable of preventing particles from adhering to a wafer when performing a plasma processing by attracting a wafer using an electrostatic chuck. About the method.

[0002]

2. Description of the Related Art With the increase in the degree of integration of semiconductor devices, the miniaturization of semiconductor integrated circuits is rapidly progressing. Currently, 0.3
Mass production of semiconductor integrated circuit devices of the 5 μm rule has been performed. Further, a semiconductor integrated circuit device having a 0.25 μm rule has been developed. Further, as a semiconductor substrate wafer (hereinafter, referred to as a wafer) used for manufacturing a semiconductor integrated circuit device, a wafer having a diameter of 200 mm is currently used, but a wafer having a diameter of 300 mm has been studied in order to increase production efficiency. Has begun.

[0003] Under such circumstances, there are various conditions required for the plasma processing, and in particular, it is important to control the wafer temperature and to prevent particles from adhering to the wafer. In order to enhance the controllability of the wafer temperature, it is effective to use an electrostatic chuck that can control the wafer temperature uniformly, with high accuracy, and with good reproducibility. An electrostatic chuck is also effective in preventing particle adhesion. This is because, if the outermost peripheral portion of the wafer is mechanically pressed by a clamp or the like, particles are generated by direct and physical contact between the clamp and the wafer. On the other hand, in the electrostatic chuck, the back surface of the wafer and the wafer stage are attracted by electrostatic force, so that the back surface of the wafer can be attracted to the wafer stage without contacting the front surface of the wafer, and as a result, adhesion of particles is suppressed. be able to.

[0004] An electrostatic chuck is a device in which a DC voltage is applied to an internal electrode embedded in an insulating member mounted on the uppermost layer position of a wafer stage which is in direct contact with the back surface of a wafer, so that the wafer is electrically connected to the surface of the insulating member. The mechanism has a mechanism for adsorbing and fixing the wafer by utilizing the electrostatic force appearing on the wafer. There are several types of electrostatic chucks, for example, a monopolar type with one internal electrode applied with one polarity and a bipolar type with two or more internal electrodes applied with two polarity. There is a formula.

In the case of the monopolar type, since the opposing ground is provided on the side wall of the reaction chamber via the plasma, the attraction force does not occur unless plasma excitation by high-frequency discharge is started on the wafer. In addition, even after the high-frequency discharge is completed, static electricity tends to remain between the wafer and the surface of the insulating member. Therefore, in order to detach the wafer, the polarity of the voltage applied to the internal electrodes during plasma processing must be adjusted. Requires processing such as applying a voltage having the opposite characteristic or adding a high-frequency discharge for static elimination.

On the other hand, in the case of the bipolar type, two or more internal electrodes buried in an insulating member forming a part of the wafer stage are provided with positive and negative polarities for each of the internal electrodes adjacent to each other. Since the applied voltage is applied, electric lines of electric force in opposite directions are generated on the adjacent internal electrodes via the wafer, and the wafer can be adsorbed without starting plasma excitation by high-frequency discharge. When the wafer is detached, a voltage in the opposite direction to the voltage applied during the plasma processing may be applied.

However, the use of the electrostatic chuck causes a new problem that the amount of particles attached increases. This is by using an electrostatic chuck,
This is because the surface of the wafer is charged and causes particles to adhere. Techniques for avoiding this are disclosed in, for example, JP-A-4-320325 and JP-A-7-94500.

Japanese Patent Application Laid-Open No. Hei 4-320325 discloses that in a magnetron sputtering apparatus, a potential control conductor is provided beside a wafer stage having an electrostatic chuck mechanism to form a conductive thin film on a wafer. Discloses a technique for connecting a thin film on a wafer and a potential control conductor to independently control the surface potential of the thin film on the wafer, thereby reducing particle adhesion.

Further, Japanese Patent Application Laid-Open No. 7-94500 discloses that
In the plasma CVD apparatus, in order to remove the wafer by performing static elimination of the electrostatic chuck, particle adhesion generated when a voltage having a polarity opposite to the polarity of the voltage applied during the plasma processing is applied. For the purpose of avoiding the problem, after the film formation by the high-frequency discharge is completed, the wafer is detached by applying a voltage having a polarity opposite to the polarity of the voltage applied during the plasma processing to the electrostatic chuck. Previously, a technique has been disclosed in which a gas remaining in a reaction chamber is exhausted so that particles floating in the gas together with the gas remaining in the reaction chamber are also exhausted to reduce particle adhesion.

[0010]

Problems to be Solved by the Invention
The technique disclosed in Japanese Patent Application Laid-Open No. 5-205 is a technique applied only when a conductive thin film is formed.
The method cannot be applied to the case where an insulating film is formed by a device. Similarly, it cannot be applied to the case where various thin films are removed by etching with a plasma etching apparatus.

According to the technique disclosed in Japanese Patent Application Laid-Open No. 7-94500, the present inventors have found that many particles adhere to a wafer. Hereinafter, description will be given based on the drawings.

FIG. 5 schematically shows the potential distribution in the reaction vessel when a negative DC voltage is applied to the electrostatic chuck before etching, ie, before the application of high-frequency power, and the static charge state of each part in the reaction vessel. This is shown in FIG. In the figure, 1 is a semiconductor wafer, 2 is an internal electrode, 3 is an insulating member, 4 is a wafer stage, 9 is a reaction vessel, and 13 is an upper electrode. As shown in FIG. 5, positive charges are induced near the surface of the insulating member 3 by dielectric polarization, and negative charges are similarly induced on the lower surface of the wafer 1. On the lower surface of the wafer 1, the DC voltage of the electrostatic chuck is reduced. A negative potential of E _dc is generated.

FIG. 6 schematically shows a potential distribution in a reaction vessel during etching, ie, plasma discharge, and a static charge state of each part in the reaction vessel. In the figure, 5 is a high-frequency power supply, and 14 is plasma. As shown in FIG. 6, when the high-frequency discharge is started, a negative potential difference V _dc is generated just above the wafer 1 due to a difference in mobility between ions and electrons in the plasma. Given. On the back side of wafer 1, | E _dc -V _dc
A potential difference (hereinafter, referred to as an effective voltage) given by | is generated, and this effective voltage gives an attraction force to the electrostatic chuck of the wafer. After the etching, that is, after the end of the plasma discharge, the state returns to the state shown in FIG.

FIG. 7 shows V _dc , E _dc , effective voltage, wafer surface potential, and output of high-frequency discharge from before the start of etching to after the end of etching, including the transient state.
It is a time chart which showed a time change. In the related art, the DC voltage _Edc is applied to the electrostatic chuck before the high-frequency discharge starts, and the DC voltage _Edc is cut off after the high-frequency discharge ends. This will be described step by step with reference to FIG.

First, when only the DC voltage _Edc is applied before the start of the high frequency discharge, the wafer surface potential becomes equivalent to _Edc . E
_{Although dc} varies depending on the type of plasma processing, it is generally about several hundred volts to 1,000 volts. When the reactive gas is supplied to the reaction chamber, there is a problem that the reactive gas and the reaction product in the reaction container are ionized by the DC voltage _Edc itself, and adhere to the wafer as particles.

Next, immediately after the start of the high-frequency discharge, the wafer surface potential becomes equivalent to _Vdc . V _dc varies greatly depending on the type of plasma processing and the like, but in the case of plasma etching, it is equivalent to several tens to several hundreds of volts. In a state where plasma is generated, the number of reactive gas ions generated by the plasma discharge is overwhelmingly larger than the number of charged particles. Therefore, the potential V on the wafer surface
The proportion of charged particles among the charged particles attracted to the wafer by _dc is very small. Therefore,
The number of particles adhering to the wafer is reduced.

Further, immediately before the end of the high-frequency discharge,
A large amount of reaction products generated by the plasma discharge float on the wafer. If the high-frequency discharge is terminated before the DC voltage _Edc is turned off, the wafer surface potential becomes equivalent to _Edc again, and the reaction product floating on the wafer is ionized by the electric field due to the DC voltage _Edc , and the wafer surface potential is reduced. There is a problem that it adheres as a large amount of particles.

[0018] As described above, by applying a DC voltage E _dc to the electrostatic chuck before initiation RF discharge, in the conventional method after the high-frequency discharge ends off a DC voltage E _dc, the DC voltage E _dc
Forms a high electric field, which causes ionization of particles in the vicinity of the electrostatic chuck and a phenomenon of attracting particles. Therefore, there is a problem that a large amount of particles adhere to the wafer.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a plasma processing method capable of preventing the adhesion of particles caused by a DC voltage of an electrostatic chuck even when the electrostatic chuck is used. And

[0020]

As a result of various studies to achieve the above object, the present inventor has conducted a plasma treatment by applying a DC voltage to the electrostatic chuck after starting the high-frequency discharge, and performing a plasma treatment. By stopping the application of the DC voltage before the termination, it has been found that the particle adhesion can be effectively reduced, and the present invention has been proposed.

That is, the plasma processing method of the present invention comprises:
In a plasma processing method of performing plasma processing by attracting a wafer using an electrostatic chuck, a high-frequency discharge for plasma processing is started, and then a DC voltage is applied to operate the electrostatic chuck to perform plasma processing. After the desired plasma processing is completed, the application of the voltage for operating the electrostatic chuck is stopped, and then the high-frequency discharge used for the plasma processing is stopped.

According to the present invention, no DC voltage is applied to the electrostatic chuck in a state where the wafer is mounted on the wafer stage and no high-frequency discharge is performed. It does not occur near the wafer and the electrostatic chuck. As a result, it is possible to prevent particles from adhering to the wafer.

[0023]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic diagram showing a plasma etching apparatus to which the plasma processing method of the present invention is applied. Here, a parallel plate type reactive plasma etching apparatus is used as an example of the plasma processing apparatus.

As shown in FIG. 1, the wafer 1 is electrostatically attracted onto an insulating member 3 placed on the uppermost position of the wafer stage 4. The wafer stage 4 has a temperature control mechanism (not shown), and can control the temperature of the insulating member 3. Helium gas is supplied between the insulating member 3 and the wafer 1 from a gas supply pipe (not shown) in order to increase thermal conductivity. Therefore, the chucking force of the electrostatic chuck is less than the insulating member
It is necessary to make the pressure higher than the pressure of the helium gas between the wafer and the wafer 1.

An internal electrode is embedded in the insulating member 3. The internal electrode 2 is connected to a DC power supply 7 via a high-frequency cutoff filter 6. The DC power supply 7 can arbitrarily vary and apply DC voltages of positive and negative polarities within ± 1500 volts. The adjustment of the output voltage value, the output voltage polarity, and the ON / OFF timing of the power supply can be precisely controlled by an external controller (not shown).

A grounded high-frequency power supply 5 is connected to the wafer stage 4 holding the wafer 1. The oscillation frequency of the high frequency power supply 5 is 13.56 MHz. Wafer stage 4 functions as a lower electrode, and opposing upper electrode 13
Is grounded and installed in the reaction vessel 9. The upper electrode 13 also has a temperature adjustment mechanism (not shown). The reactive gas is supplied from a gas cylinder (not shown) through the gas introduction pipe 8 to the reaction chamber from the lower surface of the upper electrode 13.

A vacuum pump 12 is connected to the reaction vessel 9 via a gas exhaust pipe 10 and a pressure control valve 11. After supplying a desired reactive gas into the reaction vessel 9 and adjusting the pressure to a desired pressure, high-frequency power is supplied from the high-frequency power supply 5 to the wafer stage 4, whereby the plasma 14 is excited between the wafer stage 4 and the upper electrode 13. Is done.

Next, detailed conditions for performing the plasma processing method of the present invention will be described. First, a silicon substrate having a wafer diameter of 200 mm was used. The film to be etched is a tungsten film formed by a chemical vapor deposition method. Other setting conditions of the plasma etching apparatus when performing the etching are as follows.

[0029] Under these conditions, when a high-frequency discharge is performed by the plasma etching apparatus shown in FIG.
_dc was about -50 volts. The electrostatic chuck on which the wafer is mounted is of a monopolar type, and ceramics is used for the insulating member. A DC voltage E _{dv of} about -500 volts was applied to the internal electrodes of the insulating member. The setting conditions of the DC voltage E _dc are as follows: (1) The attraction force generated by | E _dc −V _dc | is larger than the helium gas pressure between the wafer and the insulating member. (2) Even if V _dc = 0 when the high-frequency discharge stops under some conditions, the attraction force generated only by | E _dc | is smaller than the helium gas pressure between the wafer and the insulating member. Be big.

[0030] In the present embodiment,
Since V _dc = -50 (volts) and a potential difference of about 300 volts or more is required for wafer adsorption, the DC voltage E _dc was set to -500 volts with a margin.

FIG. 2 is a time chart showing, as an example of the plasma processing method of the present invention, a change in output of a high-frequency discharge for performing plasma processing and a change in an absolute value of a DC voltage applied to the electrostatic chuck. As shown in FIG. 2, in the plasma processing method of the present invention, after starting high-frequency discharge for plasma processing, a DC voltage is applied to operate the electrostatic chuck to perform plasma processing. After the desired plasma processing is completed, the application of the voltage for operating the electrostatic chuck is stopped, and then the high-frequency discharge used for the plasma processing is stopped.

According to the present invention, no DC voltage is applied to the electrostatic chuck while the wafer 1 is mounted on the wafer stage 4 and no high-frequency discharge is performed. No electric field is generated near the wafer and the electrostatic chuck. As a result, adhesion of particles to the wafer 1 can be prevented.

Next, the timing of ON / OFF of the DC voltage _Edc and the timing of ON / OFF of the high-frequency discharge RF are experimentally changed to determine the amount of particles adhering to the wafer when performing the above-described plasma etching. The result of measurement and comparison will be described.

Particles were measured by processing a mirror-finished silicon wafer having a diameter of 200 mm with the above-described plasma etching apparatus, measuring particles having a diameter of 0.20 μm or more with a particle measuring machine using a laser, and increasing the number of particles by the processing. This was done by calculating the number.

FIG. 3 is an experimental level table when the amount of attached particles is comparatively evaluated. Level 1 is a conventional technique, in which first, _Edc is turned on, and after 3 seconds, high-frequency discharge is turned on.
Then, the plasma treatment is performed, the high frequency discharge is turned off, and _Edc is turned off after 3 seconds. Level 2 is E
_dc and high-frequency discharge are simultaneously turned on, plasma processing is performed, and high-frequency discharge and _Edc are simultaneously turned off. Level 3 is a level at which _Edc and high-frequency discharge are simultaneously turned on, plasma processing is performed, and high-frequency discharge is turned off three seconds after _Edc is turned off. Level 4 is a plasma processing method of the present invention, first, a high-frequency discharge in the ON ON the E _dc after 3 seconds, by plasma treatment, to OFF high-frequency discharge in 3 seconds after the E _dc to OFF It is a standard.

In the present experiment, no inconvenience due to the difference in the time for sucking the wafer between the levels, for example, no deformation of the resist or an abnormality in the etching shape due to the difference in the wafer temperature was observed.

FIG. 4 is a graph showing the result of measurement of the number of increased particles for each level shown in FIG. As can be seen from FIG. 4, at level 1, a large amount of about 240 particles adhered to one wafer. On the other hand, at level 4, which is the plasma processing method of the present invention, it can be seen that the adhesion of particles is very small, about 15 particles per wafer.

As described above, by using the plasma processing method of the present invention, even if an electrostatic chuck is used,
Plasma processing with less particles attached to the wafer can be realized.

The present invention is not limited to the above embodiment, and various changes can be made within the scope of the technical matters described in the claims.

For example, in the above description, the case where a single-pole type electrostatic chuck is used has been described. However, the present invention is not necessarily limited to this case, and the same effect can be obtained when a bipolar type electrostatic chuck is used. Needless to say,

The high-frequency discharge for performing the plasma processing has been described with reference to the parallel plate type plasma etching apparatus. However, the present invention is not limited to this.
It goes without saying that the same effects can be obtained not only in a plasma etching apparatus using an inductively coupled plasma source or etching but also in a CVD (chemical vapor deposition) apparatus or a sputtering apparatus.

[0042]

According to the present invention, a DC voltage is not applied to the electrostatic chuck when the wafer is mounted on the wafer stage and no high-frequency discharge is performed.
A high electric field caused by a DC voltage does not occur near the wafer and the electrostatic chuck. As a result, it is possible to prevent particles from adhering to the wafer.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a plasma etching apparatus to which a plasma processing method of the present invention is applied.

FIG. 2 is a time chart showing, as an example of the plasma processing method of the present invention, a change in output of a high-frequency discharge for performing a plasma process and a change in an absolute value of a DC voltage applied to an electrostatic chuck.

FIG. 3 shows a comparative evaluation of the amount of particles attached to a wafer when plasma etching is performed by experimentally changing the ON / OFF timing of the DC voltage E _{dc and} the ON / OFF timing of the high-frequency discharge RF. It is an experimental level table at the time.

FIG. 4 is a graph showing the results of measuring the number of increased particles for each level shown in FIG. 3;

FIG. 5 schematically shows a potential distribution in a reaction vessel when a negative DC voltage is applied to an electrostatic chuck before etching, that is, before application of high-frequency power, and a static charging state of each part in the reaction vessel. FIG.

FIG. 6 is a diagram schematically illustrating a potential distribution in a reaction vessel during etching, that is, plasma discharge, and a static charge state of each part in the reaction vessel.

FIG. 7 is a time chart showing temporal changes in V _dc , E _dc , effective voltage, wafer surface potential, and output of high-frequency discharge from before the start of etching to after the end of etching, including transitional states.

[Explanation of symbols]

 1: Semiconductor wafer 2: Internal electrode 3: Insulating member 4: Wafer stage 5: High frequency power supply 6: High frequency cutoff filter 7: DC power supply 8: Gas introduction pipe 9: Reaction vessel 10: Gas exhaust pipe 11: Pressure control valve 12: Vacuum pump 13: Upper electrode 14: Plasma

Claims (3)

[Claims] In a plasma processing method for performing plasma processing by attracting a wafer by using an electrostatic chuck, a voltage for operating the electrostatic chuck is applied after starting a high-frequency discharge for the plasma processing. Plasma treatment method. 2. A plasma processing method in which a wafer is attracted by using an electrostatic chuck to perform plasma processing, and after a desired plasma processing is completed, application of a voltage for operating the electrostatic chuck is stopped and then the plasma processing is performed. A plasma processing method comprising stopping high-frequency discharge. 3. A plasma processing method for performing plasma processing by attracting a wafer by using an electrostatic chuck and applying a voltage for operating the electrostatic chuck after starting a high-frequency discharge for the plasma processing. A plasma processing method comprising: stopping application of a voltage for operating an electrostatic chuck after plasma processing is completed, and then stopping high-frequency discharge used for plasma processing.