JPH03206613A - Low temperature dry etching apparatus - Google Patents

Abstract

PURPOSE:To obtain an apparatus having a wire control range, a high control accuracy and an excellent thermal efficiency by installing a heat transfer unit between an electrode for placing a wafer and a cold storage unit, and varying the pressure of gas to be supplied to a gap between a plurality of thermal conductors of the transfer unit to control thermal conductive characteristic. CONSTITUTION:A wafer 21 is placed on the electrode 27 of an electrode unit 26 in an etching chamber 22 through an electrostatic chuck 29, and dry etched at a low temperature. A heat transfer unit 30 having a plurality of heat transfer elements 32 spaced at a gap 33 of a distance D is installed between the unit 26 and a cold storage unit 35 having a fin 36 dipped in liquid nitrogen 37. When the pressure of gas filled in the gap 33 is varied, thermal conductive characteristic between the electrode 27 and the unit 35 is freely controlled to provide a low temperature dry etching apparatus having an electrode temperature control mechanism which has a wide control range, a high control accuracy and an excellent thermal efficiency.

Description

[Detailed Description of the Invention] [Summary] Regarding low-temperature dry etching equipment used in semiconductor device manufacturing processes, we have developed a practical low-temperature dry etching system that has a wide temperature control range, high control accuracy, and a thermally efficient electrode temperature control mechanism. The purpose is to obtain a dry etching device. A heat transfer body is provided between the electrode on which the wafer is placed and the cooled regenerator, and the heat transfer body is composed of a plurality of heat conductors that are thermally insulated from each other and have a gap, and includes at least two heat conductors. The heat conductors are thermally connected to the electrodes and the regenerator, respectively, and the gaps are filled with gas so that the heat transfer characteristics between the electrodes and the regenerator can be controlled by changing the gas pressure.

[Industrial application field]

The present invention relates to a low temperature dry etching apparatus used in the manufacturing process of semiconductor devices.

[Conventional technology]

High integration of semiconductor devices. As speeds increase, device patterns become finer and device structures become three-dimensional, making requirements for etching accuracy more stringent.

For example, in etching the conductive material of the gate,
It became necessary to simultaneously satisfy both precise control of pattern width through anisotropic etching and high selectivity to the underlying oxide film.

The reason for this is as follows.

(1) The underlying gate oxide film is thinner.

(2) Since patterning is performed on a substrate with large steps such as a stacked capacitor structure, the difference in film thickness is large depending on the location, necessitating long over-etching.

Furthermore, in trench etching of a silicon (Si) substrate, the aspect ratio (etching depth/etching width) is as large as 10 or more, so an etching method with better directionality is required.

Regarding the etching cross-sectional shape, there is a demand for completely vertical etching that follows the width of the mask pattern without any dimensional shift, and for Taber etching that allows for highly controllable taper angles.

Reactive ion etching is a dry etching method that combines anisotropy and selectivity.
E ton Etching, RIE) and ECR (
Electron Cyclotron Resonan
ce) In plasma etching, there is a so-called low-temperature dry etching method that realizes anisotropic etching by cooling the wafer temperature to a low temperature.

The reason why anisotropic etching can be obtained at low temperatures is as follows.

(1) The reaction probability of neutral reactive species on the side wall decreases.

(2) The side wall is protected by the deposition of reactive substances on the side wall.

With the low-temperature etching method, unlike conventional RH, there is no need to deposit carbon polymer on the sidewalls of the pattern to protect the sidewalls in order to obtain anisotropy, so carbon impurities are reduced and carbon supports etching of the underlying oxide film. It is possible to achieve high selectivity and anisotropy at the same time without any effect.

At this time, in the low-temperature etching method, it is important to precisely control the wafer temperature during etching.

This is because if the temperature is too high, sufficient anisotropy cannot be obtained, and if the temperature is too low, a sufficient etching rate cannot be obtained.

In addition. The optimal wafer temperature varies depending on the material to be etched and the type of etching gas, but SF. When etching monocrystalline Si or polycrystalline Si using a fluorine-based gas such as -100'
It is necessary to cool the material to be etched to below C.

Regarding the cooling method and low-temperature etching equipment in this case, JP-A-60-158627 (Tachi et al.), JP-A-63-
115338 (Tsujimoto et al.), JP-A-63-291423
(Kintomo et al.) etc. have been disclosed.

(1) In JP-A-60-158627 (Tachi et al.), a heat pipe is used as a cooling device.

(2) In JP-A-63-115338 (Tsujimoto et al.), the electrode temperature (the temperature of the substrate to be etched) can be adjusted from 0 to - by using both cooling with liquid nitrogen and heating with an electric heater.
The temperature is controlled at 150'C.

(3) In JP-A-63-291423 (Kanatomo et al.). By changing the height of the liquid nitrogen level, the cooling characteristics are changed and the electrode temperature is controlled.

[Problem to be solved by the invention]

The technique disclosed in the above publication had the following problems.

Regarding (1), there was a drawback that the temperature control range was narrow. For example, in the case of a heat pipe using liquid nitrogen, the temperature control range is -203 to -160°C, which is too low to be practical.

Regarding (2), there were drawbacks such as poor thermal efficiency and extremely large consumption of liquid nitrogen because cooling and heating were performed at the same time.

Regarding (3). Thermal efficiency is slightly better than (2), but since the range of change in cooling characteristics due to changes in liquid level is narrow, it is necessary to use a heater in combination to achieve high-precision temperature control over a wide temperature range. Nitrogen consumption increased.

An object of the present invention is to obtain a practical low-temperature dry etching apparatus having a wide temperature control range, high control accuracy, and an electrode temperature control mechanism with good thermal efficiency.

[Means to solve the problem]

The solution to the above problem is to use a heat transfer body between the electrode on which the wafer is placed and the cooled regenerator. The heat conductor is composed of a plurality of heat conductors that are thermally insulated from each other and have a gap, and at least two heat conductors are thermally connected to an electrode and a cool storage body, respectively. This is achieved using a low-temperature dry etching device that is configured to fill the gap with gas and control the heat conduction characteristics between the electrode and the regenerator by changing the gas pressure.

[Effect]

The present invention achieves temperature control with excellent thermal efficiency by inserting a heat transfer body that can control heat conduction characteristics between the electrode on which the wafer is placed and the cool storage body cooled with liquid nitrogen, etc. It is something.

A heat transfer body consists of layers of good thermal conductors stacked one on top of the other with a narrow gap between them. By filling the gap with gas and changing the pressure of this gas, the heat conduction characteristics can be changed significantly. Therefore, even if the amount of electrode heating from the plasma changes, by monitoring the electrode temperature with a temperature sensor embedded in the electrode and changing the gas pressure to change the heat conduction characteristics between the regenerator and the electrode. By balancing heating and cooling, temperature control can be performed with high precision.

Next, the heat conduction characteristics of the above heat transfer body will be explained using FIG. 3.

Two plates 1 and 2 are fixed with a distance D between them, and their respective temperatures are T, , T2 (T I > T z ).

If the plates have a low emissivity, such as polished metal, the heat transfer between the two plates by infrared radiation can be ignored.

If the gas pressure between the plates is p and the mean free path of the gas molecule 3 is λ, then if the distance D is small and D x λ. In other words, if gas molecules that bounce off one plate reach the other plate without colliding with other molecules, heat conduction depends on the number and speed of the gas molecules. The flow of thermal energy Q is. It can be expressed as Q=Cp(T+-T2)T-"". Here, T is the gas temperature and C is the proportionality constant.

That is, heat conduction does not depend on the temperature gradient or the distance D, but is proportional to the temperature difference (T.-T.) between the high temperature surface and the low temperature surface and the gas pressure p.

Figure 4 shows the case where the temperature difference (T.-TZ) between the high-temperature surface and the low-temperature surface is constant. The relationship between thermal energy flow Q and gas pressure p is shown. Now, if Pa is the pressure at which the mean free path λ of gas molecules is comparable to D, then at a gas pressure of p or less, the amount of heat transferred is proportional to the pressure p.

Therefore. In low-temperature etching, the heat conduction properties can be controlled by changing the gas pressure in the gap of the heat transfer body. The electrode temperature can be controlled by balancing the heat flowing into the electrode from the plasma and the heat flowing out through the heat transfer body to the cool storage body.

Here, if the amount of heat inflow is small, it may be heated by a heater as in the conventional example, but in the present invention, as shown in the embodiment, the control range of heat conduction is wide, so the amount of heating is much smaller than in the conventional example. Temperature control is possible.

Therefore, thermal efficiency is good. Low-temperature etching with low consumption of liquid nitrogen becomes possible.

The reason why the control range of heat conduction becomes wider when the heat conduction characteristics are controlled by changing the gas pressure as in the present invention is as follows.

When a narrow gap is filled with diluted gas, the range of change in heat conduction due to pressure change is two to three orders of magnitude, but when changing the length of the conductor by changing the liquid level of liquid nitrogen, the length of the conductor is shortened. Since the accuracy of the length depends on the height of the liquid level, it can only be changed by one order of magnitude at most.

〔Example〕

FIG. 1 is a sectional view of a low temperature etching apparatus according to Example (1) of the present invention.

The device is the same as a normal RIE device except for the electrodes that can be cooled to low temperatures.

A wafer 21, which is a substrate to be etched, is placed on an electrode 27. The electrode 27 is made of a good conductor both thermally and electrically, and the area other than the wafer placement area is covered with an electrode cover 28 made of a material with poor thermal conductivity that does not contain metal impurities, such as quartz glass.

In order to improve heat conduction between the wafer 21 and the electrode 27, the wafer 21 is attracted by an electrostatic chuck 29 provided on the electrode 27.

The electrostatic chuck 29 has a structure in which two electrodes are embedded in an electrical insulator, and by applying a DC voltage between the two electrodes, the wafer 21 is attracted by electrostatic force. The insulator of the electrostatic chuck 29 is a silicone resin mixed with alumina or boron nitride, an electrical insulator such as alumina ceramic, or a material with an electrical resistance of 10' to 1013 Ωcffl and high thermal conductivity. Good.

Further, in order to improve heat conduction, a gas such as He or the like may be filled between the wafer 21 and the electrostatic chuck 29 at a pressure of 2 to 20 Torr.

Furthermore, instead of adsorbing the wafer with the electrostatic chuck 29, a mechanism for mechanically pressing the wafer against the electrode may be used.

The electrode section 26 is thermally connected via a heat transfer body section 30 to a cool storage body section 35 cooled with liquid nitrogen.

The heat conductor portion 30 consists of thermal conductors 32 stacked with a gap 33 between them by a spacer 34 made of a poor thermal conductor such as Teflon.

The thermal conductor 32 is made of a metal with good thermal conductivity, such as aluminum alloy with a polished surface.

Although not shown, the gap 33 is connected to a gas supply and exhaust device so that the gas pressure within the gap 33 can be controlled while being measured.

As a result of actual measurements, by controlling the distance D of the gaps 33 from 5 to 100 μm, using He as the gas, and controlling the gas pressure to 0 to 200 Torr, the thermal conductivity could be reduced to 0.0 for each gap. OO1～
It was possible to control within a range of 0.5 W cm-"°c-1.

The above values were obtained from actual measurements of the wafer temperature and temperature of the cool storage body when the spacing and gas pressure were varied and the power applied to the RF electrode was varied.

If the power of the plasma that heats the electrode is low, the thermal conductivity control range can be further shifted to a smaller value by increasing the number of gaps.

That is, under the same conditions, if there are two gaps, the gap is 0. OO050~0.25 W cm-
”゜C-1 If there are three gaps, 0.OO033 to 0.17
It can be controlled within the range of W cm-"°c-1.

The cool storage unit 35 has a structure in which a cooling liquid such as liquid nitrogen 37 can be stored inside, and is made of a thermal conductor such as metal, and has a plurality of fins 36 to improve heat conduction with the internal liquid.
is provided. Although not shown. A supply port for cooling liquid and a discharge port for gas vaporized by heat are provided.

The heat transfer body part 30 and the cool storage body part 35 are covered with a heat shield 31 made of glass wool or the like for thermal insulation. Further, a cover 39 is provided over the entire structure, and dry air or dry nitrogen is introduced from a purge gas port 40 and discharged from a barge gas exhaust port 41 to prevent dew condensation.

In the figure, 23 is a counter electrode of the parallel plate type etching apparatus, 24 is a reactive gas inlet, and 25 is a reactive gas exhaust port. 38 is a radio frequency (RF) power source.

Here, the output of the RF power supply 38 is . It may be connected directly to the electrode 27 as is normally done, or it may be connected to the regenerator section 35 as shown. In the latter case, the narrow spacing 33 of the heat transfer body portion 30 has a large capacitance, so that the rf power is transferred to the electrode 27 through the spacing 33.

Next, control of the wafer temperature when actual etching is performed using the apparatus of the embodiment will be explained.

Liquid nitrogen is used as the cooling liquid. The wafer 21 is connected to the electrode 27
SF. 50
SCCM was introduced and etching was performed under the conditions of a pressure of 0.08 Torr and an RF power of 0.66 W/c-.

The wafer temperature was measured using a fluorescent optical fiber thermometer (not shown) two minutes after the start of etching, when the temperature stabilized. Fifth
As shown in the figure, the He pressure p in the gap is varied from 1 to 100 To
By changing to rr, the wafer temperature can be changed from -30 to -
It was possible to control the temperature within the range of 150°C.

In addition, the amount of liquid nitrogen consumed is constant and independent of temperature.
p. It was 7 hours.

FIG. 2 is a sectional view of a low temperature etching apparatus according to Example (2) of the present invention.

The structure other than the heat transfer body portion 30 is the same as that of Example (1).

This structure has only one gap 33. Since the thermal conductor 32 and the gap 33 are parallel to the heat transfer direction and the area of the gap is large, heat conduction is better than in Example (1).

When etching was performed under the same conditions as in Example (1) and the wafer temperature was measured, the results were as shown in Figure 5. gap lie
By varying the pressure p from 1 to 100 Torr, the wafer temperature could be controlled within the range of -100 to -160'C.

In addition, the consumption amount of liquid nitrogen is constant regardless of temperature as in Example (1), and is constant at lOI. / It was time.

Next, as a comparative example, a conventional control example by adjusting the coolant level will be explained using FIG. 6.

FIG. 6 is a sectional view of a low temperature etching apparatus of a comparative example.

O This is a structure in which the heat transfer body part is removed from Example (1), and the height of the cool storage body part 35 is increased.

By increasing or decreasing the height H of the liquid nitrogen in the cool storage body 35, the heat conduction characteristics between the electrodes connected to the fins 36 and the liquid nitrogen are changed to change the temperature of the electrodes.

Furthermore, a heater 50 is embedded within the electrode 27.

Etching was performed under the same conditions as in Example (1), and the wafer temperature was measured. As shown in Figure 5, by changing the liquid level height from 1 to 20 cm, the wafer temperature varied from -150 to -150 cm. It was possible to control the temperature within the range of -170°C.

However, since the range of temperature change is small, a current is passed through the heating heater 50 built into the electrode to lower the wafer temperature by -2.
It was possible to control the temperature within the range of 0 to -170°C.

In this case, the consumption of liquid nitrogen depends on the temperature and
301 in C! ．． /hour at -50°C, which is 501/hour, which is larger than Examples (1) and (2).

[Effects of the Invention] As explained above, according to the present invention, the temperature control range is wide and the control accuracy is high. We were able to obtain a practical low-temperature dry etching device equipped with a thermally efficient electrode temperature control mechanism.

In other words, the present invention makes it possible to greatly change the thermal conductivity characteristics, and as a result, heating can be achieved without using a heater as in the conventional method. It is possible to accurately control temperature over a wide temperature range by balancing heating and cooling.

Furthermore, even when heating is performed using a heater, the control range of heat conduction is wide, so the temperature can be controlled with a much smaller amount of heating than conventional methods. Therefore, low-temperature etching with high thermal efficiency and low consumption of liquid nitrogen has become possible.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a low-temperature etching apparatus according to an embodiment (1) of the present invention, Fig. 2 is a cross-sectional view of a low-temperature etching apparatus according to an embodiment (2) of the present invention, and Fig. 3 is a gas pressure characteristic of thermal conduction. A diagram explaining the principle of dependence. Figure 4 is a diagram showing the dependence of heat conduction characteristics on gas pressure. FIG. 5 is a diagram showing the temperature control characteristics of Examples (1), (2) and a comparative example, and FIG. 6 is a cross-sectional view of a low-temperature etching apparatus of the comparative example. In the figure, 21 is a wafer, 22 is an etching chamber, 23 is a counter electrode, 24 is a reaction gas inlet, 25 is a reaction gas exhaust port, 26 is an electrode section, 27 is an electrode, 28 is an electrode cover 29 is an electrostatic chuck, 30 31 is a heat conductor, 31 is a heat shield, 32 is a heat conductor, 33 is a gap, 34 is a spacer, 35 is a cool storage body, 36 is a fin, 37 is liquid nitrogen, 38 is an RF power source, 39 is a cover, 40 is Purge gas population, 41 is the purge gas exhaust port, 50 is the heating heater 3g Example (1) oUr side view Figure 1 Cross-sectional view of Example (2) No. 2 Explanation of how to bury the prisoner! PJS Diagram Gas pressure dependence of heat conduction characteristics Figure 4 Pressure p (to leaf) O ● 3 10 30 +00 300 H also stone height (cm) Δ ↓ 8 12 16 20 Figure 5 ．． ．． 56 L comparison I 32 ri cross section

Claims (1)

[Claims] A heat transfer body is provided between an electrode on which a wafer is placed and a cooled regenerator, and the heat transfer body is made up of a plurality of heat conductors that are thermally insulated from each other and have gaps. The at least two heat conductors are thermally connected to the electrode and the regenerator, respectively, and the gap is filled with gas so that the heat conduction characteristics between the electrode and the regenerator can be controlled by changing the gas pressure. A low-temperature dry etching device characterized by comprising: