KR100265768B1 - Method - Google Patents

Abstract

PURPOSE: A method for applying an RF(Radio Frequency) bias of plasma etching equipment is provided to improve problems of a peak to peak voltage and a self bias voltage of an RF bias by composing a capacitor of a transfer path of an RF bias. CONSTITUTION: A bias is generated from an RF bias source(100). The RF bias is transferred through an impedance matching network(102) connected directly with a chuck for loading a wafer. The RF bias is applied by using only a wafer back capacitor(Cback) as a direct capacitor. The wafer back capacitor(Cback) uses the wafer and the chuck of a plasma chamber as an electrode and an insulating layer coated on the chuck as a dielectric layer. A range of the RF bias is 20 to 200 MHz.

Description

Application method of R.F bias in plasma etching equipment

The present invention relates to a facility used in the manufacturing process of a semiconductor integrated circuit, and more particularly, to an egg of a plasma etching facility used for dry etching. F (Radio Frequency, hereinafter referred to as "RF") relates to a bias application method.

Several types of etching equipment are used for dry etching of semiconductor integrated circuits. Recently, low-pressure high-density plasma is mainly used, and such etching facilities include ICP type (Inductive Coupled Plasma), TCP type (Transformer Coupled Plasma), ECR type (Electron Resonance Plasma), HWP type (Helicon Wave Plasma), and SWP type ( Surface Wave Plasma). These etching facilities apply an RF bias to the chuck on which the wafer is placed using a power source that is independent of the power generating plasma. The reason for applying the RF bias to the chuck is to increase the energy of ions incident on the substrate to perform anisotropic etching. Therefore, the RF bias can be controlled independently of the power source generating the plasma, thereby easily controlling the ion energy in the plasma chamber. In applying such an RF bias, a blocking capacitor is used in series with a chuck that is subjected to an RF bias. The reason is to increase the direct current offset caused by the difference in mobility between ions and electrons present in the plasma of the plasma chamber. As the direct current offset increases, ion energy incident on a wafer, which is a semiconductor substrate, increases, thereby increasing anisotropic etching.

Prior arts have been registered in US Pat. No. 4557819 (Date: December 20, 1985) under the title System for igniting and controlling a wafer processing plasma.

In the prior art, a blocking capacitor is usually constructed with a capacity of several hundreds of microwatts. In this case, if the plasma density in the plasma chamber is increased to 10 ¹¹ / cm 3 or more, the peak to peak voltage and the self bias voltage of the RF bias are reduced, and the DC offset is decreased. Tend to. Therefore, there is a limit in controlling the energy of ions incident on the substrate in the plasma etching process.

The technical problem to be solved by the present invention is to improve the problem of falling the peak to peak voltage and the self bias voltage of the RF bias by configuring a capacitor in the path through which the RF bias is delivered. The present invention provides a method of applying an RF bias to a plasma etching apparatus.

1 to 3 are diagrams for explaining the RF bias applying method of the plasma etching apparatus according to the present invention.

Explanation of symbols on the main parts of the drawings

100: RF bias power supply, 102: impedance matching box,

104: plasma chamber, 106: chuck,

108: RF power line, 110: wafer,

112: insulating material on the wafer, 114: insulating film coated on the chuck,

: Plasma region, C _back : wafer back capacitor,

C _sh : Sheath Capacitor

Vp: plasma potential.

In order to achieve the above technical problem, the present invention provides an impedance matching network that does not include a capacitor connected in series when generating an RF bias in an RF bias power supply and connecting the RF bias with a chuck on which a wafer in a plasma chamber is placed. And transmitting the RF bias using a wafer back capacitor using a wafer and a chuck of a plasma chamber as electrodes and using an insulating film coated on the chuck as a dielectric film as a series capacitor. Provided is an RF bias application method for a plasma etching facility.

According to a preferred embodiment of the present invention, the frequency of the RF bias is suitably in the range of 20 to 200 MHz, and the wafer back capacitor may increase the capacitance by thinning an insulating film or coating a material having a high dielectric constant.

Preferably, the chuck is ESC (Electro Static Chuck) type, the plasma etching equipment is ICP type (Inductive Coupled Plasma), TCP type (Transformer Coupled Plasma), ECR (Electron Cyclotron Resonance) type, HWP (Helicon) It is suitable to be one selected from Wave Plasma) and SWP (Surface Wave Plasma) types.

Further, according to a preferred embodiment of the present invention, the impedance matching network is preferably provided with an impedance matching box including a capacitor and an inductor, where the capacitor is suitably configured in parallel with the chuck.

According to the present invention, only the wafer back capacitor is configured to be connected in series to the chuck, thereby implementing an efficient RF bias application method that reduces the peak-to-peak voltage and the self-bias voltage of the RF bias.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic diagram illustrating an RF bias transmission path of a plasma etching apparatus according to the present invention. Equipment that applies RF bias independently, such as ICP type (Inductive Coupled Plasma), TCP type (Transformer Coupled Plasma), ECR (Electron Cyclotron Resonance) type, HWP (Helicon Wave Plasma) type and SWP (Surface Wave Plasma) type Although there is a slight difference in the configuration of applying the RF bias depending on the equipment is schematically shown in FIG. The RF bias generated by the RF bias power supply 100 is caused by the chuck 106, for example the force of static electricity, on which the wafer inside the plasma chamber 104 is placed via the RF power line 108 including the impedance matching box 102. It is applied with a chuck of ECS (Electro Static Chuck) type to fix the wafer. Here, the impedance matching box 102 is composed of a circuit including a capacitor and an inductor. Here, the impedance matching network represents an intermediate path through which an RF bias including an impedance matching box 102 and an RF power line 108 is delivered. The capacitor in the impedance matching box 102 is then configured in parallel to the chuck. RF power line 108 is again grounded. In addition, an area in which plasma is formed is formed on the chuck 106 of the plasma chamber. There is).

FIG. 2 is a schematic representation of a reconstruction of FIG. 1 to illustrate a wafer back capacitor and sheath capacitor. Since the insulating film 114 is coated on the ECS type chuck 106 which fixes the wafer by the force of static electricity, when the RF bias is applied from the RF bias power supply 100, the chuck 106 and the wafer 110 are separated. It can be seen that the capacitor is always operating because it acts as an electrode and the insulating film 114 acts as a dielectric. This is called a wafer back capacitor. And the plasma region ( ) Can also act as an electrode because of its conductivity, and the insulating material 112 on top of the wafer can also act as a dielectric. Therefore, the wafer 110 and the plasma region ( ) Is a vacuum electrode between the plasma region and the wafer or a capacitor having an insulating material 112 on the wafer as a dielectric, which is referred to as a sheath capacitor.

3 is an equivalent circuit diagram of FIG. 2. Plasma area ( ) And the RF bias power supply, the wafer back capacitor C _back controls the RF bias.

At this time, if the capacity of the wafer back capacitor (C _back ) is small, a voltage drop occurs while the wafer back capacitor is charged in a short time due to the ion current coming in during the half cycle of the RF bias, thereby causing the original RF. The bias waveform is distorted and the peak to peak voltage and the self bias voltage are reduced. When the frequency of the wafer back capacitor (C _back ) is constant, the frequency decreases, that is, the longer the period of the RF bias waveform, the longer the time to charge the wafer back capacitor (V _back ) is, so that the peak to The phenomenon of decreasing the peak to peak voltage and the self bias voltage also appears. Therefore, if the wafer back capacitor (C _back ) is configured with a sufficiently large capacitor capacity, the potential changes before the capacitor is fully charged by the incoming ion current during the half cycle of the RF bias, so the peak to peak voltage of the RF bias is increased. And a phenomenon in which the self bias voltage decreases does not occur.

However, if the blocking capacitor of several to several hundreds of capacitance and the wafer back capacitor of several capacitance are connected in series to the plasma chamber chuck as in the prior art, the overall capacitance value is determined by the blocking capacitor having a small capacitance. The peak to peak voltage and the voltage drop of the self bias voltage are affected by the blocking capacitor with small capacitance. Therefore, if the RF bias is controlled by using only the wafer back capacitor as the blocking capacitor without additionally configuring the blocking capacitor in series as in the present invention, sufficient capacitance can be secured. In other words, if the RF bias having a frequency of 20 to 200 MHz is used when the wafer back capacitor C _back is several GHz, the distortion of the RF bias waveform, the peak to peak voltage of the RF bias, and the magnetic bias are used. RF bias can be applied without reducing the self bias voltage. That is, the RF bias application method of the plasma etching apparatus according to the present invention, first generates an RF bias in the RF bias power source, and then an impedance matching network that does not include a capacitor configured in series with the RF bias chuck of the plasma chamber (impedance matching network) ). Finally, RF bias is applied using only the wafer back capacitor (C _back ) to secure a sufficiently large capacitance, and the RF bias is reduced without reducing the peak to peak voltage and the self bias voltage of the RF bias. Can be applied. Therefore, it is possible to control the ion energy incident on the wafer with only RF bias power without being affected by the source power that generates the plasma. When the RF bias frequency is 20 MHz or less, the capacitance of the wafer back capacitor may be increased by reducing the thickness of the insulating film coated on the chuck or by using a material having a high dielectric constant as the insulating material. In the figure, V _sh denotes a sheath capacitor, and Vp denotes a plasma potential, respectively.

The present invention is not limited to the above embodiments, and it is apparent that many modifications can be made by those skilled in the art within the technical spirit to which the present invention belongs.

Therefore, according to the present invention described above, only the wafer back capacitor is configured to be connected in series to the chuck to control the ion energy incident on the wafer with only the RF bias power supply without the problem that the peak-to-peak voltage of the RF bias and the self-bias voltage fall. It is possible.

Claims (8)

Generating an RF bias at an RF bias power supply; Delivering the RF bias through an impedance matching network that does not include a capacitor component in series with the chuck on which the wafer of the plasma chamber is placed; And applying the RF bias as a series capacitor using only a wafer back capacitor using the wafer and the chuck of the plasma chamber as electrodes and the insulating film coated on the chuck as a dielectric film. RF bias application method. The method of claim 1, wherein the frequency of the RF bias is in the range of 20 to 200 MHz. The method of claim 1, wherein the chuck is of an electro static chuck (ESC) type. The method of claim 1, wherein the wafer back capacitor has a thin film or a high dielectric constant coated thereon to increase capacitance. The method of claim 1, wherein the impedance match network includes an impedance matching box. The method of claim 5, wherein the impedance matching box includes a capacitor and an inductor. 7. The method of claim 6, wherein the capacitor is configured in parallel with the chuck of the plasma chamber. The plasma etching apparatus of claim 1, wherein the plasma etching facility is an ICP type (Inductive Coupled Plasma), a TCP type (Transformer Coupled Plasma), an ECR (Electron Cyclotron Resonance) type, a HWP type, and a Wave Wave Plasma type RF bias applying method of the plasma etching equipment, characterized in that one selected from.