JPH07161696A - Substrate cooling equipment - Google Patents

Abstract

PURPOSE:To prevent dielectric breakdown of cooling gas due to high voltage for electrostatic attraction, increase cooling efficiency, and improve reliability. CONSTITUTION:The cooling equipment is provided with an electrode 1 for applying DC high voltage which generates electrostatic attractive force, a substrate mounting stand 2 which fixes a substrate 4 to be processed by the electrostatic attractive force, a cooling mechanism 5 which cools the substrate mounting stand, and a gas suppling mechanism which introduces cooling gas into a space part between the substrate to be processed and the substrate mounting stand. The gas supplying mechanism consists of helium supplying systems 7, 8, 9 for helium supply and other gas supplying systems 7, 10, 11 for mixing gas whose dielectric strength is large in helium. Mechanisms 9, 11 which control the mixing ratio of helium and gas whose dielectric strength is large and the supply pressure are installed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate cooling device,
In particular, the present invention relates to a substrate cooling device applied to a high frequency discharge reaction device that performs a surface treatment of a substrate using plasma generated by high frequency discharge. The high frequency discharge reactor is used, for example, in an apparatus for dry etching a silicon oxide film or the like in a semiconductor device manufacturing process.

[0002]

2. Description of the Related Art In etching, which is one of the steps for manufacturing a semiconductor device, a mixed gas containing a halogen-containing gas as a main component is converted into plasma by discharge, and various active species (for example, atomic chlorine, atomic Fluorine,
A dry etching technique is generally used in which a fluorocarbon compound or the like) is introduced to the surface of the substrate to be processed to cause the thin film on the surface to react and the thin film is removed. Recently, in particular, a dry etching apparatus using so-called helicon wave discharge has been used as a dry etching apparatus using low pressure and high density plasma.

Further, with the progress of etching technology for semiconductor devices, it has become clear that it is important in microfabrication to actively perform cooling for the purpose of lowering the surface temperature of a substrate to be processed during etching. However, in a dry etching device that applies high-density plasma such as helicon wave discharge, the amount of heat given to the substrate by plasma is much larger than that in the conventional dry etching device. It is an important issue to maintain the temperature, and an efficient substrate cooling device for keeping the surface temperature of the substrate to be processed low is required. Conventionally, a substrate cooling device to which an electrostatic attraction force is applied has been proposed.

FIG. 2 shows an example of the configuration of a conventional substrate cooling device to which electrostatic attraction is applied. In FIG. 2, 1 is the electrode body,
2 is an electrostatic attraction plate made of alumina, silicon carbide or the like, 3
Is a cover, and 4 is a substrate to be processed. A shield plate 21 is fixed around the electrode body 1 via an insulator 22. The electrode body 1 is provided with a coolant reservoir 5, a coolant inlet / outlet 6, and a gas introduction pipe 7. Reference numeral 8 is a gas inlet, and 9 is a gas flow rate control device. The gas introduction pipe 7 is divided into two parts, that is, the electrode body 1 side and the gas introduction port 8 side, and the two parts are separated into the insulating pipe 2
Connect so that there is no gas leak by 3. Further, the gas introduction pipe 7 has a pressure gauge 12 for measuring the gas pressure in the pipe.
To provide. Further, a high voltage DC power supply 13 for generating an electrostatic attraction force is connected to the electrode body 1 and a high voltage is applied.

The above-mentioned conventional substrate cooling device is used as a substrate cooling device for a dry etching device utilizing low pressure and high density plasma, that is, a dry etching device utilizing helicon wave discharge, and has an advantage of high cooling efficiency. Have.

In the conventional substrate cooling device, in order to improve the adhesion between the substrate and the electrostatic attraction plate, a negative high voltage is applied to the electrode body 1 to enhance the electrostatic attraction force. The purpose of enhancing the adhesion between the substrate and the electrostatic attraction plate is to enhance the thermal conductivity. However, in general, even when the substrate 4 to be processed is firmly adhered to the electrostatic attraction plate 2 by a high electrostatic attraction force, a slight gap is left between the substrate 4 and the electrostatic attraction plate 2. It is common to have Such a gap is
Even a slight amount significantly hinders heat conduction under the conditions used in vacuum. In addition, gaps due to minute adhered substances on the surface of the substrate 4 or the electrostatic attraction plate 2 are likely to be formed frequently.

Further, depending on the material of the electrostatic attraction plate 2, the attraction force may be firmly maintained even after the processing of the substrate 4, and this may hinder the removal of the substrate. In this case, a shallow groove is formed on the surface of the electrostatic attraction plate 2, and a gap is positively formed between the substrate 4 to be processed and the electrostatic attraction plate 2 to reduce the contact area, and the attraction force is required. It is also being suppressed to a minimum.

In any case, since the substrate 4 to be processed is processed in a vacuum of 10 ^-4 Torr to 10 ^-2 Torr, heat conduction in the gap portion is performed only by heat radiation of the substrate. In many cases, the efficiency of heat conduction is poor, and cooling of the substrate 4 to be processed is often hindered. In particular, a dry etching apparatus in which the amount of heat flowing into the substrate to be processed is particularly large,
In a substrate cooling apparatus applied to a dry etching apparatus that also uses a magnetic field to apply high-density plasma, which requires high-speed processing, the problem of poor heat conduction in the gap becomes noticeable.

In order to solve this problem, a gas flow path penetrating the electrostatic attraction plate 2 is provided inside the electrode, and a cooling gas is introduced to the back surface of the substrate 4 to be processed through the gas flow path, It is effective to improve heat conduction in the gap portion. This cooling gas has excellent thermal conductivity,
It is general to use helium, which is a highly safe gas with little influence on discharge.

[0010]

The conventional substrate cooling apparatus utilizing the above electrostatic attraction force generally has the following problems.

When helium is introduced into the gap on the back surface of the substrate 4 to be processed, it is preferable to reduce the flow rate of helium as much as possible in order to minimize the change in characteristics of the discharge plasma. Generally, the substrate 4 to be processed and the electrostatic attraction plate 2
The pressure of helium in the gap between and is measured by the pressure gauge 12, and the helium flow rate is set so as to be several Torr. Since the thermal conductivity of the gas does not depend on the pressure in the molecular flow region, it is not necessary to increase the helium pressure above several torr where the molecular flow condition is achieved in the gap. Therefore, the substrate cooling effect can be obtained with the minimum flow rate by setting the pressure to several torr.

On the other hand, since the withstand voltage of helium is small,
In some cases, a negative DC voltage applied to the electrode body 1 in order to obtain an electrostatic attraction force causes a discharge to cause dielectric breakdown. Actual locations where dielectric breakdown is likely to occur are the gas introduction portion on the back surface of the substrate 1 to be processed and the portion of the insulating tube 23.

According to a document (Yoshinori Hatta, Gas Discharge, 1968, Modern Science Co., Ltd., p. 159), for some gases, the product of the pressure and the electrode interval at which the discharge voltage becomes minimum and the breakdown voltage at that time. Is as follows.

[0014]

[Table 1] Helium: 2.5 Torr · cm 150 V Argon: 1.5 Torr · cm 265 V Nitrogen: 0.8 Torr · cm 275 V

Therefore, it can be seen that helium is most easily discharged at a distance of 2.5 cm at a pressure of 1 Torr, and the dielectric breakdown voltage at that time is very low as compared with other gases. It is often difficult in principle to avoid the discharge of helium, because the above-mentioned locations where dielectric breakdown is likely to occur are often designed so that the distance between the discharge points is several cm.

Although it is possible to increase the dielectric strength voltage by increasing the pressure of helium, the gas flow rate increases by increasing the pressure, so that the discharge characteristics are affected or the substrate to be processed is affected. The increase in the backside pressure causes a force to push up the substrate to be processed, which causes problems such as impairing the adsorptivity.

In view of the above problems, an object of the present invention is to provide a substrate cooling device which prevents the dielectric breakdown of a cooling gas due to a high voltage for electrostatic attraction and has a high cooling efficiency and a high reliability. To do.

[0018]

A substrate cooling mechanism according to the present invention comprises an electrode for applying a DC high voltage for generating an electrostatic attraction force, and a substrate mounting table for fixing a substrate to be processed by the electrostatic attraction force. And a cooling mechanism for cooling the substrate mounting table, and a gas supply mechanism for introducing a cooling gas into a gap between the substrate to be processed and the substrate mounting table, wherein the gas supply mechanism is helium. And a gas supply system for mixing helium with a gas having a large dielectric strength, and a mechanism for controlling the mixing ratio and supply pressure of helium and a gas having a large dielectric strength. It is characterized by

In addition to the helium gas supply mechanism for cooling the substrate, another independent gas supply mechanism capable of introducing a gas having a large withstand voltage is provided, and helium and a gas having a large withstand voltage are mixed and the back surface of the substrate is mixed. Is configured to be supplied to the gap portion of the. Further, in this case, the mixing ratio and supply pressure of helium and a gas having a large dielectric strength are adjusted to be appropriate.

The other gas supply system is preferably a sulfur hexafluoride supply system.

[0021]

According to the present invention, the cooling helium gas is mixed with another gas having a high dielectric strength to prevent the dielectric breakdown of the cooling gas due to the high voltage for electrostatic attraction, thereby improving the cooling efficiency of the substrate cooling device. And increase reliability.

[0022]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a typical embodiment of a substrate cooling device according to the present invention. In FIG. 1, the substrate cooling device is incorporated in a high frequency discharge reaction device using a helicon wave. Regarding the basic components of the substrate cooling device,
The same elements as those of the conventional apparatus shown in FIG. 2 are designated by the same reference numerals.

That is, in FIG. 1, an electrostatic attraction plate 2 made of alumina, silicon carbide or the like is provided on the upper part of the electrode body 1.
And the target substrate 4 is placed on the electrostatic attraction plate 2. The upper surface of the electrostatic attraction plate 2 serves as a substrate mounting surface. A cover 3 is arranged around the substrate 4 to be processed and the electrostatic attraction plate 2. Furthermore, around the side of the electrode body 1,
The shield plate 21 is fixed via the insulator 22. A coolant reservoir 5, a coolant inlet / outlet 6, and a gas introduction pipe 7 are provided inside the electrode body 1. The gas introduction port 8 of the gas introduction pipe 7 is provided below, and a gas flow rate control device 9 is provided in the middle of the gas introduction pipe 7. The gas introduction tube 7 is actually the electrode body 1
Side and the gas introduction port 8 side are divided into two parts, and the two parts are connected by an insulating pipe 23 so as to prevent gas leakage. Further, it is desirable to add a pressure gauge 12 to the gas introduction pipe 7 for measuring the gas pressure in the pipe. Further, the electrode body 1 is connected to a high-voltage DC power supply 13 for generating an electrostatic attraction force on the electrostatic attraction plate 2, whereby a high voltage is applied.

A second gas inlet 10 and a second gas flow rate control device 11 are further added to the above structure. The gas introduction port 10 and the gas flow rate control device 11 are arranged in parallel to the first gas introduction port 8 and the first gas flow rate control device 9.

The gas introduced through the first gas introduction port 8 is a cooling gas, typically helium, and the second gas has a large dielectric strength. The second gas having a large dielectric strength is mixed with helium which is a cooling gas, and the gas flow rate control devices 9 and 11 adjust the mixing ratio thereof to an optimum one. Further, the supply pressures of the first and second gases can be adjusted by the gas flow rate control devices 9 and 11.

A substrate cooling device for placing, supporting and cooling the substrate 4 to be processed is arranged inside the reaction chamber 30. The inside of the reaction chamber 30 is exhausted by an attached exhaust mechanism 31 and is maintained in a required reduced pressure state. The plasma generation chamber 3 is provided above the reaction chamber 30 and above the substrate.
2 is formed. An antenna 42 is provided in the plasma generation chamber 32.
And a solenoid coil 33 is arranged around the outside of the plasma generation chamber 32. High frequency power is supplied to the antenna 42 from the high frequency power supply 40 via the matching circuit 41. Further, the solenoid coil 42 is supplied with power from a power source (not shown) and is excited. Further, a magnetic circuit including a permanent magnet 34 and a yoke 35 is arranged around the outside of the reaction chamber 30.

The basic operation of the substrate cooling device having the above structure will be described.

First, the inside of the plasma generation chamber 32 and the reaction chamber 30 is evacuated by the exhaust mechanism 31 to a required decompressed state, and then the reaction gas introduction pipe 36 is used to bring the predetermined gas to a predetermined pressure. Installed in 32. The value of this predetermined pressure is an optimum value determined by the gas type, antenna shape, magnetic field strength, and the like.

Next, when the high frequency power generated by the high frequency power supply 40 is supplied to the antenna 42 through the matching circuit 41, a high frequency discharge is generated inside the plasma generation chamber 32 and plasma is generated. At this time, if a magnetic field is generated in the plasma generation chamber 32 by the solenoid coil 33, the plasma generation efficiency is improved, and discharge can be generated even at a low gas pressure as compared with the case without a magnetic field. Further, depending on the configuration of the antenna 42, plasma by so-called helicon waves can be generated and applied as an ultra-high density plasma device.

The ions and the activated gas molecules or atoms present in the plasma generated in the plasma generating chamber 32 as described above diffuse inside the reaction chamber 30 and form a thin film on the surface of the substrate 4 to be processed. React with and remove it.
Since the charged particles in the plasma move along the magnetic field in the reaction chamber 30, as shown in FIG. 1, due to the effect of the permanent magnet 34 and the yoke 35, the charged particles in the plasma in the reaction chamber 30 become The loss due to the collision of the plasma is reduced, and the plasma density in the reaction chamber 30 can be kept high.

At this time, by applying a negative high voltage to the electrode body 1 of the substrate cooling device by the high voltage power source 13, an electrostatic attraction force is generated between the electrostatic attraction plate 2 and the substrate 4 to be processed, The substrate 4 to be processed is brought into close contact with the electrostatic attraction plate 2. Further, helium gas is supplied from the gas introduction port 8 to the back surface of the substrate 4 to be processed through the gas flow rate control mechanism 9 and the gas introduction pipe 7 so that a gap between the substrate 4 to be processed and the electrostatic attraction plate 2 is formed. Helium gas flows, improving thermal contact.

The problem of the conventional device is the dielectric breakdown in the cooling gas introduction system as described above. The state of occurrence of dielectric breakdown greatly differs depending on the pressure and type of the cooling gas, and in general cooling using helium, the dielectric breakdown easily occurs as described above. However, the thermal conductivity of helium is 0.144 J / (m · s · K) at room temperature.
In comparison with other gases (for example, the thermal conductivity of nitrogen is only 0.024 J / (m · s · K) at room temperature), it plays an important role in cooling. It is not realistic to replace the gas with high dielectric strength.

In the substrate cooling device shown in this embodiment, the second
The second gas can be introduced from the gas introduction port 10 through the second gas flow rate control mechanism 11, mixed with the helium gas in the gas introduction pipe 7, and supplied to the space on the back surface of the substrate 4 to be processed. Then, the mixing amount of the second gas is set to an appropriate amount between several% and several tens%, and the mixing ratio is controlled by the gas flow rate control mechanism 9 and the second gas flow rate control mechanism 11. Further, the gas flow rate is determined so as to be a predetermined value by measuring the pressure in the gas introduction pipe 7 with the pressure gauge 12.

As the second gas mixed with helium,
It is necessary to select one with high dielectric strength. A representative gas with high dielectric strength is sulfur hexafluoride. This gas has the effect of preventing the growth of the discharge by generating a large amount of negative ions due to the attachment of electrons due to the discharge. For insulation of a device using a high voltage, it is generally used at atmospheric pressure or under pressure. However, in this embodiment, a method of using helium of several torr mixed with several to several tens of percent is adopted, and even in this case, the effect of preventing dielectric breakdown is great.

Sulfur hexafluoride is often used as a reaction gas or a reaction auxiliary gas in a dry etching process, and even if it is mixed with a cooling gas and supplied into the reaction chamber 30, it adversely affects the etching process. There is little danger. However, in the process of performing microfabrication, when sulfur hexafluoride adversely affects the process result, another gas having high dielectric strength can be used instead of sulfur hexafluoride. An example of gas with high dielectric strength is shown below. The dielectric strength is shown as a relative value when the dielectric strength of sulfur hexafluoride is 1.

[0037]

[Table 2] Gas name Insulation strength (relative value when SF ₆ is 1) CF ₄ 0.4 C ₂ F ₆ 0.8 C ₃ F ₈ 0.97 C ₃ F ₆ 1.03 C-C ₄ F ₈ 1.25 CCl ₃ F 1.84 CCl ₂ F ₂ 1.04 CCl ₄ 2.4 CCl ₂ FCClF ₂ 2.41

The example shown in Table 2 above is a part of the gas having a relatively high dielectric strength, but in general, a gas composed of carbon or sulfur and halogen easily produces negative ions and has a high dielectric strength. Furthermore, many of these gases are used as a reaction gas or a reaction auxiliary gas for dry etching, and the same gas as that used for the target dry etching process should be selected as a mixed gas for cooling. Thus, any adverse effects on the dry etching process can be ignored. If the mixing ratio of helium and a gas having a high dielectric strength can be determined in advance to a constant value, it is possible to prepare a gas having that mixing ratio in advance and supply it by a cylinder. According to this configuration, it is not necessary to provide the gas supply systems 7 and 11 and the like, and the same effect as that of the above embodiment can be obtained.

[0039]

As is apparent from the above description, according to the present invention, a gas supply system for mixing a gas having a large dielectric strength as a second gas with a helium gas for cooling a substrate to be processed is attached. By doing so, it is possible to realize a substrate cooling device in which helium for cooling does not cause dielectric breakdown even when a high voltage is applied for electrostatic attraction. Thereby, the cooling efficiency of the substrate to be processed in the cooling device of the cooling gas introduction system can be improved. INDUSTRIAL APPLICABILITY The present invention, when applied to a substrate cooling device in a device in which a large amount of heat flows into a substrate to be processed, such as a dry etching device that uses high-density plasma combined with a magnetic field that requires high-speed processing, has a cooling effect Becomes noticeable.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a typical embodiment of a substrate cooling device according to the present invention, showing a state of being mounted on a high frequency discharge reaction device.

FIG. 2 is a vertical cross-sectional view showing a structural example of a conventional substrate cooling device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrode main body 2 Electrostatic adsorption plate 3 Cover 4 Processing target substrate 5 Refrigerant reservoir 7 Gas introduction pipe 8,10 Gas introduction port 9,11 Gas flow controller 13 High voltage DC power supply 30 Reaction chamber 31 Exhaust mechanism 32 Plasma generation chamber

Claims (2)

[Claims] 1. An electrode for applying a DC high voltage for generating an electrostatic attraction force, a substrate placement table for fixing a substrate to be processed by the electrostatic attraction force, and a cooling mechanism for cooling the substrate placement table. A substrate cooling device comprising a gas supply mechanism for introducing a cooling gas into a gap between the substrate to be processed and the substrate mounting table, wherein the gas supply mechanism is a helium supply system for supplying helium. And another gas supply system for mixing the helium with a gas having a large dielectric strength, and a mechanism for controlling the mixing ratio and supply pressure of the helium and the gas having a large dielectric strength. Substrate cooling device. 2. The substrate cooling apparatus according to claim 1, wherein the other gas supply system is a sulfur hexafluoride supply system.