JP4473051B2 - Etching apparatus and etching method - Google Patents

Description

  The present invention relates to an etching apparatus and the like, and more particularly to etching that can perform taper processing without generating an etch stop.

  In the process of forming a semiconductor device, polysilicon is etched and patterned. At this time, it may be required to form the obtained pattern in a shape that rises perpendicularly to the base substrate. In some cases, the rising portion (side wall) has an angle with respect to the vertical, and the upper portion is formed in a taper shape (referred to as “forward taper”) having a trapezoidal shape smaller than the base portion (lower portion).

  The following methods are known as techniques for making the etched shape of polysilicon tapered.

(1) Method using side etching (a) Chemical dry etching is performed with CF ₄ gas. In this method, taper is imparted by performing isotropic etching with F radicals.

(B) Etching is performed with SF ₆ / CCl ₄ gas. In this method, by forming a thin side wall protective film on the polysilicon side wall, side etching is appropriately performed, thereby providing a taper.

However, in these methods, the difference in etching conversion is large, and the width dimension of the pattern formed with respect to the width of the pattern forming mask does not accurately correspond. For this reason, fine processing cannot be achieved by these methods.
(2) Method of increasing taper by increasing the amount of sputtered product generated from resist This method is an etching apparatus using ECR (Electron Cyclotron Resonance). By increasing the energy, the adhesion amount of the sputtered product from the resist to the polysilicon side wall as the side wall protective film is increased, thereby obtaining a tapered shape.

However, this method reduces the selectivity with the base film. Further, in this method, in order to increase ion energy, for example, when the underlayer is SiO ₂ , the selectivity with respect to polysilicon cannot be increased, and the underlayer SiO ₂ is etched during overetching of polysilicon. become.

(3) Method of forming a sidewall protective film on a polysilicon sidewall by adding oxygen gas to bromine-based gas or chlorine-based gas This method solves the problems in the methods (1) and (2) above, Polysilicon can be satisfactorily etched into an arbitrary shape. For example, forward tapered etching without side etching is possible, and etching with a high selectivity with respect to the underlying material such as underlying SiO ₂ is possible. However, with the increase in the flow rate of oxygen as the processing gas, there may occur a situation (called an etching stop) where the etching of the polysilicon to be etched stops (does not proceed) (refer to Patent Document 1).
JP-A-6-168916

  As described above, when polysilicon is to be etched in a tapered shape, the difference in etching conversion becomes large, or the selectivity with respect to the underlying layer decreases, or etching stops and the polysilicon etching stops. Occurs.

  The present invention has been made in view of these problems, and provides an etching apparatus capable of performing taper processing without causing an etch stop.

  In order to solve the above problems, the present invention employs the following means.

A processing chamber, a sample stage arranged in the processing chamber, a source power source for generating plasma in the processing chamber, a high-frequency power source for applying high-frequency power to the sample stage, a gas supply pipe for supplying a processing gas into the processing chamber, and the gas In an etching processing apparatus having a mass flow controller for controlling a gas flow rate supplied to a processing chamber via a supply pipe, the processing gas is a mixed gas composed of bromine gas, chlorine gas and oxygen gas, and after the processing gas is introduced A control device that applies power of the source power supply and then applies bias power of the high-frequency power supply , and the mass flow controller is a mixed gas until a wafer bias voltage is applied from the start of introduction of the processing gas. The proportion of oxygen gas in the inside is less than the proportion required for etching the polysilicon layer in a forward tapered shape. To your.

  Since the present invention has the above-described configuration, taper processing can be performed without causing an etch stop.

  Hereinafter, the best embodiment will be described with reference to the accompanying drawings. FIG. 1 is a diagram for explaining a plasma etching apparatus according to an embodiment of the present invention. In FIG. 1, 1 is a magnetron that generates a microwave, 2 is a waveguide, 3 is a quartz plate, 4 is a solenoid coil, and 5 is plasma generated in a processing chamber 10.

  Microwaves generated by the magnetron 1 pass through the waveguide 2 and pass through the quartz plate 3 and enter the processing chamber. Reference numeral 4 denotes a solenoid coil provided around the processing chamber, and electron cyclotron resonance (ECR) is generated by a magnetic field generated by the solenoid coil 4 and a microwave incident through the quartz plate 3. Reference numeral 5 denotes plasma. The process gas can be efficiently converted to plasma by ECR.

  6 is a wafer as a sample, 7 is an electrostatic attraction power source, and 8 is a sample stage on which the wafer is placed. The wafer 6 can be electrostatically attracted to the sample stage 8 by applying a DC voltage of the electrostatic adsorption power source 7 to the sample stage 8. A high frequency power source 9 applies high frequency power to the sample stage 8. Thereby, an acceleration potential for accelerating ions in the plasma in a direction perpendicular to the wafer can be applied. Reference numeral 10 denotes a processing chamber, 11 denotes a gas supply pipe for supplying a processing gas to the processing chamber, and 12 denotes a mass flow controller for controlling a gas supply amount. 13 is a magnetron that generates microwaves, 12 is a mass flow controller, and 13 is a control device that controls a high-frequency power source and the like according to a recipe. The gas supply pipe 11 and the mass flow controller 12 are provided for each type of gas to be supplied.

  The processing gas after etching is exhausted from an exhaust port provided at the lower part of the processing chamber via a turbo pump, a dry pump, etc. (not shown). In the above example, the ECR has been described as an example of the plasma generation unit, but the plasma generation unit is not limited to this example.

2A and 2B are diagrams for explaining an etching process when taper processing is performed. FIG. 2A shows a state of the sample before the etching process, and FIG. 2B shows a state of the sample during the etching process. FIG. In these drawings, reference numeral 103 denotes an underlayer (SiO ₂ ), 102 denotes a polysilicon layer formed on the underlayer 103, and 101 denotes a photoresist as a mask formed on the polysilicon layer 102. In the etching process, a polysilicon electrode having a desired pattern can be obtained by etching the polysilicon 102 using the photoresist 101 formed on the polysilicon 102 as a mask. Reference numeral 104 denotes a sidewall protective film formed during etching, and θ represents a taper angle of the sidewall protective film.

In the present embodiment, plasma etching is performed using a mixed gas obtained by adding O ₂ gas to HBr gas as the processing gas. Note that a chlorine-based gas can be used instead of the HBr gas (bromine-based gas). As shown in FIG. 2B, a sidewall protective film 104 made of Si and Br reactive organisms SiBrx and Si and O products SiOx is formed on the sidewalls of the polysilicon 102 produced by the etching. By supplying oxygen gas under various conditions, a vertical or tapered polysilicon electrode cross section can be obtained.

  For example, an optimal value is selected for the oxygen flow rate according to the shape of the taper to be formed, that is, whether it is a forward taper or a reverse taper, and the taper angle. The optimum oxygen flow rate can be determined mainly for bromine-based or chlorine-based gases that cause the reaction to proceed. The preferable flow rate of oxygen varies depending on the etching conditions. For example, the oxygen flow rate is about 8% of the mixed gas flow rate, and etching with a taper angle of about 76 ° can be achieved without stopping the etching. Further, when the oxygen flow rate is about 10% of the mixed gas flow rate, etching with a taper angle of about 72 ° can be achieved without stopping the etching.

  Next, the etching conditions for the etching process performed to obtain the forward tapered etching shape using the plasma etching apparatus shown in FIG. 1 will be described.

(1) Etching condition 1
HBr gas flow rate: 100ccm
O ₂ gas flow rate: 8ccm
Pressure: 0.6Pa
Microwave power: 800w
Wafer bias: 55w
As a result, a forward tapered shape of about 76 ° was obtained as the etched shape of the polysilicon.

(2) Etching condition 2
(For the etching condition 1, the O ₂ gas flow rate was changed from 8 ccm to 10 ccm in order to obtain a tapered shape with a smaller taper angle (small θ)).
HBr gas flow rate: 100ccm
O ₂ gas flow rate: 10 ccm
Pressure: 0.6Pa
Microwave power: 800w
Wafer bias: 55w
Under these conditions, an etching stop occurred and the taper angle requirement could not be satisfied.

This phenomenon occurs because the surface of the polysilicon 11 is oxidized by the O ₂ gas before ions in the plasma collide with the polysilicon surface due to the wafer bias output. This is considered to be a phenomenon that occurs because the oxide film formed on the surface cannot be etched.

(3) Etching condition 3
(After performing the etching process under the following pretreatment conditions, the etching condition 2 was performed while the plasma discharge was continued.)
Pretreatment conditions Etching time: 1 second HBr gas flow rate: 100 ccm
O ₂ gas flow rate: 3ccm
Pressure: 0.6Pa
Microwave power: 800w
Wafer bias: 0
As a result, the polysilicon etched shape was a forward tapered shape of about 72 ° without causing an etching stop.

  FIG. 3 is a diagram for explaining the processing under the etching condition 3. In FIG. 3, “RF” indicates the output of the high frequency power source 9, “Microwave” indicates the output of the magnetron 1, and “Gas” indicates the ratio of the oxygen component in the processing gas. In addition, the horizontal axis represents time, T1 is the start time of introduction of the processing gas, T2 is the time when plasma is generated by the microwave, and T3 is the time when the bias voltage is applied, and the processing under the etching condition 2 is started from this time. The As shown in the figure, before the process under the condition 2 is started, that is, from the start time T1 of the introduction of the process gas to the start time T3 of the forward tapered etching according to the process condition 2, the oxygen gas occupying the mixed gas The ratio is controlled to be a value (3/103 in this example) less than the ratio (8/108 in this example) required to etch the polysilicon layer in a forward tapered shape. Thereby, taper processing can be performed without generating an etch stop.

FIG. 4 is a diagram for explaining the effect of this embodiment. As shown in FIG. 4, in the case of etching condition 3 (condition in which pretreatment is inserted before etching condition 2), no etching stop occurs even if the oxygen gas flow rate is increased to 12 ccm. For this reason, a taper shape with a smaller taper angle θ can be obtained. On the other hand, under the conventional etching conditions (conditions 1 and 2), an etching stop occurred when the oxygen gas flow rate was 10 ccm.
As described above, etching is performed by limiting the ratio of oxygen gas in the mixed gas from the start of introduction of the processing gas to the application of the wafer bias voltage to about 3% (3/103) or less as pre-processing. Taper processing can be performed without generating a stop.

As described above, according to this embodiment, polysilicon can be etched with a wide range of taper angles (forward taper and reverse taper). In addition, when polysilicon is etched at a forward taper angle, etching without side etching is possible. In addition, the selectivity with respect to the underlying material SiO ₂ can be set high.

It is a figure explaining the plasma etching apparatus concerning the embodiment of the present invention. It is a figure explaining the etching process at the time of giving a taper process. It is a figure explaining the process of the etching conditions 3. FIG. It is a figure explaining the effect by this embodiment.

Explanation of symbols

1 Magnetron 2 Waveguide 3 Quartz plate 4 Solenoid coil 5 Plasma 6 Wafer
7 Electrostatic adsorption power supply 8 Sample stage 9 High frequency power supply 10 Processing chamber 11 Gas supply pipe 12 Mass flow controller 13 Controller 101 Photoresist 102 Polysilicon 103 Base (SiO ₂ film)
104 Side wall protective film

Claims (4)

A processing chamber, a sample stage arranged in the processing chamber, a source power source for generating plasma in the processing chamber, a high-frequency power source for applying high-frequency power to the sample stage, a gas supply pipe for supplying a processing gas into the processing chamber, and the gas In an etching processing apparatus equipped with a mass flow controller for controlling a gas flow rate supplied to a processing chamber via a supply pipe,
The processing gas is a mixed gas composed of bromine gas or chlorine gas and oxygen gas, and includes a control device that applies the power of the source power source after the introduction of the processing gas and then applies the bias power of the high-frequency power source ,
In the mass flow controller, the ratio of the oxygen gas in the mixed gas is less than the ratio required for etching the polysilicon layer in a forward taper form until the wafer bias voltage is applied from the start of introduction of the processing gas. An etching apparatus characterized by controlling as described above. The etching apparatus according to claim 1, wherein
An etching apparatus characterized in that the ratio of oxygen gas in the mixed gas from the start of introduction of the processing gas to the application of the wafer bias voltage is about 3% or less. A sample in which a polysilicon layer and a photoresist layer are sequentially laminated on an SiO layer as an underlayer is placed on a sample stage placed in a processing chamber, and a photoresist layer is formed using plasma of a processing gas generated in the processing chamber. An etching method for etching the polysilicon layer in a forward taper shape using as a mask,
Using bromine gas or a mixed gas of chlorine gas and oxygen gas as the processing gas, applying source power after the introduction of the processing gas , and then controlling to apply bias power,
At the start of etching, the oxygen gas ratio in the mixed gas is less than the ratio required for etching the polysilicon layer in a forward tapered shape from the start of introduction of the processing gas until the wafer bias voltage is applied. An etching method characterized by the above. The etching method according to claim 1,
An etching method characterized in that the ratio of oxygen gas in the mixed gas from the start of introduction of the processing gas to the application of the wafer bias voltage is about 3% or less.

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