JPH07147273A - Etching treatment - Google Patents

Abstract

PURPOSE:To attain an anisotropic etching, which is superior in shape efficiency, without reducing an etching rate even if a temperature is made low by a method wherein process gas containing one kind of a polarized halogen compound is introduced in a vacuum treating chamber to bring into a plasma state and a treatment of a material to be treated is performed. CONSTITUTION:A semiconductor wafer is placed on a lower electrode 4 of a hermetic container 1 for treatment as a material 6 to be treated and the wafer is cooled using liquid nitrogen. Then, HF gas 21, which is selected by a process gas feed system 2 and is a halogen compound having a polarization character, is introduced in the container 1. A high frequency is applied between an upper electrode 3 and the electrode 4 to generate plasma. At that time, H2O gas is fed via a nozzle 202 according to the need and the reaction of etching using HF plasma is made to accelerate. Accordingly, even if a chemical reaction rate constant is reduced in a low-temperature atmosphere, the adsorption of the wafer is not reduced and an etching rate can be maintained.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an etching method.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, a plasma etching apparatus using a reactive plasma is used for processing a processing surface of an object to be processed such as a semiconductor wafer. In particular, recently, the development of an etching method capable of performing ultrafine processing corresponding to the half-micron era and even the quarter-micron era has been under development, and among them, it is possible to achieve good anisotropic etching. Attention has been paid to possible low temperature etching methods.

In this low temperature etching method, for example, a cooling jacket such as a liquid nitrogen is supplied to a cooling jacket provided on a susceptor in a processing chamber to transfer cold heat to an object to be processed such as a semiconductor wafer placed on the susceptor. It is heated, the processed surface is cooled to a desired temperature, for example, an ultralow temperature region of −100 ° C., and an etching process is performed by reactive plasma.

[0004]

By the way, when the plasma etching process is performed in the low temperature atmosphere as described above, CH ₄ gas is used as a reaction gas (etchant) when etching a silicon oxide film as in the conventional case. Or when CCl ₄ is used as a reaction gas when etching an aluminum film, or when Cl ₂ is used as a reaction gas when etching polysilicon, the molecular structure of these reaction gases will be described later. However, since it does not exhibit polarizability, there is a problem that the etching rate decreases as the temperature decreases.

The present invention has been made in view of the above problems when selecting a reaction gas for a low temperature etching process, that is, an etchant. The object of the present invention is to lower the temperature. Even in the case, it is an object of the present invention to provide a new and improved etching treatment method capable of achieving anisotropic etching excellent in shape without lowering the etching rate.

[0006]

In order to solve the above-mentioned problems, an etching process for treating an object to be processed with a reactive plasma while cooling the temperature of the object to be processed in a vacuum processing chamber is constructed according to the present invention. The method is characterized in that a treatment gas containing at least one polarized halogen compound is introduced into a vacuum treatment chamber and plasma is generated to treat the object to be treated. Further, at that time, it is preferable to set the temperature of the object to be processed to −50 ° C. or lower, preferably −80 ° C. or lower.

[0007]

According to the present invention, the processing gas containing at least one polarized halogen compound is introduced into the vacuum processing chamber and turned into plasma, thereby enhancing the physical adsorption performance of the etchant to the processing portion and promoting the etching reaction. Therefore, even when the etching treatment is performed in a low temperature atmosphere, anisotropic etching can be performed without lowering the etching rate.

The operation will be described in more detail with reference to FIGS. 3 and 4. The mechanism of etching using plasma is as follows. As shown in FIG. 3 (a), after the etchant A is physically adsorbed on the surface of the object to be processed B, a reaction occurs due to the collision energy of ions as shown in FIG. 3 (b). It is considered that the etching proceeds by being removed as the reaction product AB. That is, the etching rate depends on the amount of the etchant adsorbed to the object to be processed and can be defined by the following equation.

(Etching rate) = (Chemical reaction rate constant) × (Adsorption amount)

According to the knowledge of the present inventors, the higher the treatment temperature, the larger the chemical reaction rate constant, but the smaller the adsorption amount, on the contrary, the lower the treatment temperature, the lower the chemical amount. It has been found that the reaction rate constant decreases but the adsorption amount increases. Therefore, when the treatment is performed in a low temperature environment, the etching can be performed without decreasing the etching rate if the increase in the adsorption amount is larger than the reduction in the chemical reaction rate constant.

Therefore, looking at the case where the silicon oxide film is etched as shown in FIG. 4, when F ₂ gas which is a non-polar molecule is used as an etchant as in the conventional etching method (see FIG. 4). In (a), although the surface of the silicon oxide film is negatively charged as shown in the figure, since F ₂ is non-polar, physical adsorption is not promoted. However, when a polar molecule polarized according to the present invention, for example, HF gas is used as an etchant, as shown in FIG. 4B, the positively charged H atoms of the HF molecule and the negative charge of the silicon oxide film are negative. Since the electrically charged O atoms are electrically attracted to each other, the adsorption amount of HF molecules can be increased. Therefore, according to the present invention, anisotropic etching can be realized without lowering the etching rate even when plasma processing is performed in a low temperature atmosphere.

Further, according to the knowledge of the present inventors, the adsorption amount of polar molecules increases as the treatment temperature atmosphere is closer to the boiling point of the treatment gas, and therefore generally, the lower the temperature is. Anisotropic etching can be more effectively realized by performing the treatment in an ultralow temperature atmosphere of −50 ° C. or lower, preferably −80 ° C. or lower, more preferably −120 ° C. or lower, and further −150 ° C. or lower.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which an etching method constructed according to the present invention is applied to a parallel plate type high frequency discharge plasma etching apparatus will be described in detail below with reference to the accompanying drawings.

First, the structure of the plasma etching apparatus shown in FIG. 1 will be described. This plasma etching apparatus includes a processing airtight container 1, a processing gas supply system 2 for the container 1, an upper electrode 3 and a lower electrode 4 for generating plasma, and an exhaust gas system for evacuating the inside of the container 1. 5, the object 6 to be processed is provided on the lower electrode 4.

At least the inner wall surface of the container 1 is made of a conductor such as aluminum, the inner wall surface is subjected to anodizing treatment, and the processing gas and reaction products are attached to the inner wall surface of the container 1. A means for setting a temperature for preventing such a phenomenon, for example, a heater (not shown) is built in the wall surface of the container 1 and is, for example, 50 ° C.
It is configured so that it can be set to an appropriate temperature in the range of ° C.

The gas supply system 2 uses a processing gas such as H 2.
A processing gas cylinder 21 for accommodating F gas, a gas supply pipe 22 connected to this, which is a bright annealing tube having a 1/4 inch diameter, and a mass flow controller 23 connected to this for controlling the supply amount of the processing gas, It is composed of a gas supply pipe 24 connected to this, which is a bright annealing pipe having a 1/4 inch diameter, and a needle valve 25 connected to this and provided in the vicinity of the processing gas inlet 31 of the upper electrode 3. ing. Further, a gas supply pipe 91 and a mass flow controller 9 are provided from a cylinder 90 containing H ₂ as an additive gas.
2 is connected to the HF gas supply pipe.

In order to set the processing gas temperature to a predetermined temperature throughout the gas supply pipes 22 and 24 for supplying the processing gas from the cylinder 21 to the processing gas inlet 31, for example, the supply pipes 22 and 24 described above. A temperature adjusting mechanism 80 for adjusting the temperature of, for example, a tape heater is provided so as to surround the outer circumferences of the supply pipes 22 and 24.

In particular, when HF, which is a halogen molecule having polarizability, is used as the processing gas according to the present invention, when water adheres to the supply pipes 22 and 24, the HF gas having a strong reactivity causes the supply pipes. Since 22 and 24 are corroded, in order to prevent this, it can be heated to about 100 ° C. by the temperature adjusting mechanism 80.

The side wall of the container 1 is provided with H ₂ O (not shown).
A valve 201 from the gas supply system via the supply pipe 100.
The H ₂ O gas, the supply amount of which has been adjusted in step ₂ , is supplied into the container 1 through the nozzle 202.

The upper electrode 3 is made of a material such as amorphous carbon or silicon and is hollow, and a plurality of processing gas exhausts are provided in a flat plate shape from the processing gas inlet 31 so as to face the object 6 to be processed. It is configured to have a port 32 and a gas passage port 33 that connects the introduction port 31 and the exhaust port 32. The upper electrode 3 is connected to the wiring 35 so as to be electrically grounded.

The processing gas exhaust port 32 of the upper electrode 3 is also provided.
The distribution of the openings is distributed in a range narrower than the size of the object 6 to be processed on the lower electrode 4 arranged oppositely, and by discharging the processing gas, it is distributed in a wider range than the size of the object 6. Compared with the case, it is configured so that a uniform plasma etching process can be performed.

At the outer edge of the processing gas discharge port 32 of the upper electrode 3 facing the object 6 to be processed, the focus ring 36 is provided with the focus ring 36 to concentrate the plasma flow of the processing gas toward the object 6 to be processed. It is provided so as to surround the processing body 6. The focus ring 36 is formed by coating the surface of aluminum, which is a conductor, with an insulator, such as Teflon, to prevent corrosion by the processing gas, and at a temperature of, for example, 50 ° C. to 150 ° C. by a heater incorporated in the focus ring 36. The reaction product is prevented from adhering in a film form.

At the uppermost part of the lower electrode 4, there is provided an adsorption means for adhering the semiconductor wafer 6, for example, an electrostatic chuck sheet 41 which is adsorbed by static electricity, and the electrostatic chuck sheet 41 has a conductive layer such as an electrolytic foil. Copper is sandwiched from both sides by an insulating layer such as a polyimide film, and a high voltage is applied from a charge supplying means such as a high voltage power source 42 through a wiring 43 to attract and hold the semiconductor wafer 6 to the upper surface of the lower electrode 4. It is possible to

An upper layer base 46 made of, for example, aluminum is provided below the electrostatic chuck sheet 41, and a lower layer base 47 is provided below the upper layer base 46. The lower substrate 47 is made of, for example, aluminum, has a refrigerant passage provided therein, and a refrigerant such as liquid nitrogen 42 is circulated therein.
The temperature of the semiconductor wafer 6 can be set to a predetermined temperature, for example, a temperature of −50 ° C. to −150 ° C. by the thermal cooling.

The upper layer substrate 46 is the lower layer substrate 4
It can be replaced separately from 7, and is constructed for convenience of maintenance. Between the upper base 46 and the lower base 47, the temperature of the liquid nitrogen 42 is kept between the upper base 46 and the upper base 46.
Helium gas 49 is configured to be fed from a helium gas supply system (not shown) via a pipe 50 for the purpose of conducting to.

Between the object to be processed 6 and the electrostatic chuck sheet 41, the temperature of the coolant 42 of the lower electrode 4 for cooling the object to be processed 6, for example, liquid nitrogen, is conducted to the object to be processed 6. The helium gas 44 is configured to be fed from a helium gas supply system (not shown) via a pipe 45.

The lower electrode 4 is connected to a high frequency power source 51 via a blocking capacitor 53, and for example, 1
It is configured so that high frequency energy of 3.56 MHz can be applied. The opposite pole of the high frequency power supply 51 is electrically grounded.

A focus ring 81 made of, for example, quartz is provided on the upper substrate 46 of the lower electrode 4 so as to surround the object 6 to be processed. The focus ring 81 protects the upper layer base 46 of the lower electrode 4 made of aluminum from the plasma generated between the upper electrode 3 and the lower electrode 4, and more than the surface to be processed of the object to be processed. Since the upper part of the focus ring is provided above the lower electrode 4, it is possible to concentrate the ions generated from the plasma on the object 6 to be processed and accelerate the progress of the etching process.

Further, the focus ring 81, when reaction products easily adhere depending on the type of processing gas,
In order to prevent the adhesion by heating at 50 ° C to 150 ° C, the reaction product is adhered by sandwiching the thin film heater formed by the CVD process on the ceramic plate with the ceramic. Therefore, it is possible to obtain a structure in which particles are less likely to be generated due to peeling of the adhered film.

The exhaust gas system 5 is provided with a plurality of gas discharge ports 54 provided in the peripheral portion of the bottom surface of the container 1, and an exhaust gas connected to the gas discharge ports 54 and provided in the vicinity of the container 1. A pipe 55, a vacuum exhaust valve 56 connected to the exhaust gas pipe 55, and a vacuum exhaust device 57 connected to the vacuum exhaust valve 56, for example, a rotary pump and a turbo molecular pump, are provided. For example 1x
It can be set to 10 ^-1 to 1 × 10 ^-8 Torr.

When HF gas is used as a processing gas before the vacuum exhaust device 57, means 58 for trapping the HF gas, such as a cooler or a filter, is provided, and the vacuum exhaust device uses HF gas having a strong reactivity. The corrosion of the can be prevented. As described above, the plasma etching apparatus to which the etching method constructed according to the present invention can be applied is constructed.

Next, referring to FIG. 2, the structure of the plasma etching apparatus in the semiconductor manufacturing process will be described. The components having the same functions as the components of the plasma etching apparatus described above are designated by the same reference numerals and detailed description thereof will be omitted.

When the object 6 to be processed is placed on the electrostatic chuck sheet 41 on the upper aluminum substrate 46 which has been cooled in advance by the transmission of cold heat, helium (not shown) is applied to the back surface of the object 6 to be processed. The helium gas 44 whose pressure is adjusted by the gas pressure control is supplied, and the pre-cooled electrostatic chuck sheet 41 moves the object 6 to be processed at −50 ° C.
Cool to a suitable temperature between -150 ° C.

Thereafter, the container 1 is evacuated to an appropriate vacuum atmosphere by the exhaust gas system 5, and the processing gas is supplied from the processing gas supply system 2, for example, a halogen compound having polarizability selected according to the present invention. The HF gas is supplied from the processing gas discharge port 32 of the electrode 3 into the processing container while the supply amount is adjusted by the valve 23 and the needle valve 25.

At the end of the processing gas supply system 2,
The needle valve 25 provided connected to the processing gas introducing port 31 of the upper electrode 3 has a higher pressure in the pipe 24 than the processing gas introducing port 31 of the upper electrode 3 and causes abnormal discharge.
The processing gas pressure is adjusted so that it does not occur inside.

A load lock chamber 62 is provided adjacent to the side wall of the container 1 of the plasma etching apparatus via a gate valve 61 that is openable and closable. The load lock chamber 62 is provided with a carrier device 63, for example, a carrier arm in which an arm made of aluminum is coated with conductive Teflon to prevent static electricity.
An exhaust pipe 64 is connected to the bottom surface of the load lock chamber 62 through an exhaust port, and is connected to the exhaust gas system 5 through a vacuum exhaust valve 65.

In this cassette chamber, there is provided a mounting table 69 for mounting a cassette 68 capable of accommodating, for example, 25 objects 6 to be processed. Also, this cassette room 67
An exhaust pipe 70 is connected to the bottom surface of the exhaust gas via an exhaust port, and is connected to the exhaust gas system 5 via a vacuum exhaust valve 71. As described above, the plasma etching apparatus to which the etching method according to the present invention can be applied is configured in the semiconductor manufacturing process.

Next, the operation of this plasma etching apparatus will be described. First, the gate valve 7 installed between the atmosphere
2 is opened, the cassette 68 accommodating the object 6 to be processed is mounted on the mounting table 69 in the cassette chamber 67 by a transfer robot (not shown), and the gate valve 72 is closed.

Next, the vacuum exhaust valve 71 connected to the cassette chamber 67 is opened, and the exhaust gas system 5 exhausts the cassette chamber 67 to a vacuum atmosphere, for example, 10 ^-1 Torr.

Next, the load lock chamber 62 and the cassette chamber 6
7, the gate valve 66 is opened between 7 and the object 6 to be processed is taken out from the cassette 69 placed in the cassette chamber and held by the transfer arm 63.
2 and the gate valve 66 is closed.

In the container 1, the vacuum exhaust valve 56 is opened and the exhaust gas system 5 allows a vacuum atmosphere, for example, 10 ⁻⁵ Torr.
Exhausted to. Then, a high frequency is applied between the upper electrode 3 and the lower electrode 4, and the processing gas containing a polarizable halogen compound introduced into the processing container according to the present invention is introduced into plasma, and the processed object is processed. 6 is plasma etched. At that time, if necessary, H ₂ O gas is supplied to the nozzle 20.
2 to accelerate the etching reaction by HF plasma.

When the plasma etching process is completed, the high frequency voltage 51 is stopped to stop the generation of plasma and the supply of the processing gas. After that, an inert gas such as nitrogen gas is replaced with a nitrogen gas cylinder 7 for the purpose of replacing the processing gas and the reaction product in the container 1.
3, the gas is introduced into the container 1 through the mass flow controller 74, and the exhaust gas system 5 exhausts the gas.

After the residual processing gas and reaction products in the container 1 are sufficiently exhausted, the electrostatic chuck sheet 41 of the lower electrode 4 is formed.
The high voltage source 42 is stopped, the gate valve 61 provided on the wall surface of the processing container 1 is opened, and the transfer arm 63 moves from the adjacent load lock chamber 62 to the position of the object 6 to be processed in the container 1. The object 6 to be processed is held and conveyed to the load lock chamber 61, and the gate valve 61 is closed. In the load lock chamber, the object to be processed 6 is heated to room temperature, for example, 18 ° C. by the heater, and then is discharged from the load lock chamber to the atmosphere via the cassette chamber 67. The above is the description of the operation in the semiconductor manufacturing process of the plasma etching apparatus.

Next, an embodiment of the plasma etching processing method performed based on the configuration and operation of the plasma etching apparatus described above will be described.

A silicon oxide film is formed on the cooled lower electrode 4 of the processing airtight container 1 of the plasma etching apparatus as the object 6 to be processed, for example, on a silicon wafer, and a resist pattern is formed on the silicon oxide film. The semiconductor wafer is placed on the wafer, and the wafer is -1 with liquid nitrogen.
Cool to 00 ° C.

A halogen compound having polarizability selected in the container 1 from the processing gas supply system 2 according to the present invention,
For example, HF gas is introduced at a flow rate of 50 cc / sec, and high frequency, for example, 13.56 MHz, 200 W is applied to the lower electrode 4 to generate plasma. Then, since HF gas has a strong reactivity to silicon oxidation,
The etching reaction shown by the following formula is performed. SiO ₂ + 4HF → SiF ₄ + 2H ₂ O

At this time, the HF gas has polarizability, the H portion is positively charged, and due to the presence of negatively charged oxygen atoms in the silicon oxide film, it is adsorbed on the surface of the silicon oxide film. Therefore, even if the chemical reaction rate constant decreases in the low temperature atmosphere, the adsorption amount does not decrease and the etching rate can be maintained. Particularly, according to the findings of the present inventors,
The amount of polar molecules adsorbed increases as the processing temperature atmosphere is closer to the boiling point of the processing gas, and thus generally at lower temperatures.
Preferably -80 ° C or lower, more preferably -120 ° C.
The anisotropic etching can be more effectively realized by performing the following ultra low temperature atmosphere.

FIG. 5 shows the relationship between the temperature of the object to be processed and the etching rate when the silicon oxide film is etched with HF gas. As shown in the figure, it can be seen that the etching rate is improved as it is closer to the boiling point of the polar molecule, that is, as the temperature is lower, for the above reason.

At this time, when the reaction product has a dew point below the processing pressure, for example, a pressure of 10 ^-5 Torr,
By cooling to 100 ° C., the H ₂ O generated by the above reaction becomes less than the dew point by thermal cooling from the wafer cooled to −100 ° C. on the side wall of the etching groove of the silicon oxide film, and the silicon oxide film Adsorption on the surface suppresses the reaction between the HF radical and the silicon oxide film on the side wall of the etching groove.

As described above, the process gas having a polarizability is adsorbed by the electric attraction force on the bottom surface of the etching groove of the silicon oxide film, and the etching reaction is promoted.
Since the etching reaction is suppressed at the side surface of the etching groove of the silicon oxide film, anisotropic etching with a high aspect ratio can be performed while maintaining a high etching rate.

When the plasma etching process is completed as described above, the object 6 to be processed is carried out of the processing container 1 and heated to room temperature while exhausting HF gas in the adjacent load lock chamber 62. , Shipped to the atmosphere.
In the process of returning to normal temperature and pressure, HF gas, which is a minute processing gas, and SiF ₄ and H ₂ O, which are reaction products, adhering to the surface of the wafer are diffused as a gas into the outside air. Can be carried out in a clean state and transferred to the next semiconductor processing step.

The etching method constructed according to the present invention has been described above by taking the case where the silicon oxide film is etched at a low temperature by using the HF gas which is a halogen compound having polarizability as an example. It is not limited to the example. In addition to HF gas, CHF ₃ , CH ₂ F ₂ , C ₂ H
The same effect can be obtained by using ₂ F ₄ , C ₄ H ₂ F _6, or the like.

Furthermore, the etching method according to the present invention is not limited to the case of etching a silicon oxide film, but can be applied to the case of processing an aluminum film, a polysilicon film, or an amorphous silicon film. It is possible, and in that case as well, anisotropic etching with a high etching rate can be performed by appropriately selecting a polarizable halogen compound according to the type of the object to be processed.

For example, the aluminum film is etched
In case of CHCl₃, CH₂Cl₂, SiHCl₃, BH
Cl₂, HCl, CCl₃F, SiH₂Cl₂Polarizability such as
Halogen compounds with can be used. Also
When etching the polysilicon film, HCl, C
HF₃, SiH₂F₂, SiHF₃, HBr, BHCl ₂,
SiHCl₃, SiH₂Cl₂Halo with polarizability such as
Gen compounds can be used.

[0055]

As described above, according to the etching method of the present invention, anisotropic etching having a high etching rate can be performed at a low temperature.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a plasma etching apparatus to which an etching method constructed according to the present invention can be applied.

FIG. 2 is an explanatory diagram showing an example in a manufacturing process of the plasma processing apparatus of FIG.

FIG. 3 is a schematic explanatory diagram showing an etching mechanism.

FIG. 4 is a schematic explanatory view showing a mechanism of physical adsorption.

FIG. 5 is a graph showing the relationship between temperature and etching rate when etching a silicon oxide film with HF gas.

[Explanation of symbols]

 1 Processing Airtight Container 2 Processing Gas Supply System 3 Upper Electrode 4 Lower Electrode 5 Exhaust Gas System 6 Object

Claims (2)

[Claims] 1. An etching treatment method for treating a target object with a reactive plasma while cooling the temperature of the target object in the vacuum processing chamber, wherein a processing gas containing at least one polarized halogen compound is supplied to the vacuum processing chamber. A method for etching treatment, characterized in that the object to be treated is treated by being introduced into a substrate and turned into plasma. 2. The etching processing method according to claim 1, wherein the temperature of the object to be processed is set to −50 ° C. or lower, preferably −80 ° C. or lower.