Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
2000-12-22
2003-09-23
Powell, William A. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C156S345370, C156S345480, C216S067000, C216S068000, C438S715000, C438S716000, C438S729000
Reexamination Certificate
active
06624084
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a plasma processing method and a processing device suited to perform processing, such as etching, using plasma for metallic materials, such as aluminum, copper, platinum, and others, for insulating materials, such as silicone oxide, silicon nitride, and others, and for organic materials, such as a low dielectric constant film (low-k film), in the manufacturing process of semiconductor devices; and, more particularly, the invention relates to plasma processing equipment and a plasma processing method for processing especially fine patterns in a damage-free manner.
In the process of manufacturing semiconductor devices, such as a DRAM, microprocessor and ASIC, plasma processing using a weak ionizing plasma is widely used. In the plasma process, ions and radicals generated by plasma are irradiated on a wafer to be processed. As a refinement of semiconductor device advances, for plasma etching equipment used for processing wires, gate electrodes and contact holes, finer processing characteristics, high selectivity, high processing uniformity and low damage are required.
As a plasma source for etching equipment which has been used for many years, there is a parallel plate type plasma source. The parallel plate type plasma is called a CCP (capacitive coupled plasma) because the coupling of the plasma and power is capacitive. The parallel plate type plasma source has a comparatively simple device configuration and performs anisotropic etching using a comparatively high self bias generated when a blocking capacitor is inserted on the anode electrode side. However, as the pattern size of semiconductor devices becomes smaller, it is difficult to generate high-density plasma at a low pressure.
As a result, Japanese Patent Application Laid-Open 7-297175,IEM (ion energy modulation) indicates that, by applying high frequency waves of several tens MHz to the upper electrode of a narrow electrode parallel plate type reactor, a comparatively high-density plasma is generated, and by applying a bias of several hundreds of kHz to the lower electrode on which a wafer to be processed is disposed, the ion amount to be irradiated to the wafer to be processed is controlled. The pressure for stably generating plasma using IEM is high, such as several tens Pa to 5 Pa. However, to achieve further refinement of the pattern size, it is desirable to generate a plasma at a lower pressure.
In recent years, to produce inductively coupled plasma (ICP), a coil is wound around the side or top of a dielectric container and plasma is maintained by an induction field generated by supplying an alternating current to the coil. The ICP process can generate high-density plasma at a low pressure.
As a plasma source for generating high-density plasma at a low pressure, there is a magnetic field microwave type plasma source using electron cyclotron resonance (ECR). At a magnetic flux density of 875 G, the electron Larmor frequency becomes 2.45 GHz, and by resonance with the power frequency, plasma can be generated efficiently even at a low pressure.
Furthermore, a new plasma source for high-density plasma at a low electron temperature has been proposed. For example, Japanese Patent Application Laid-Open 9-321031 describes a UHF-ECR device using the UHF band of frequency of 300 MHz to 1 GHz, instead of a microwave for exciting the plasma. With respect to plasma excited by electromagnetic waves of the UHF band, the electron temperature is low, and the dissociation of the processing gas can be kept to an optimum condition, and, furthermore, the magnetic flux density for causing the ECR can be controlled to a low value, so that it is also advantageous in preventing damage.
Although the aforementioned ICP process can generate high-density plasma at a low pressure, the high density invites a disaster depending on the process, in that the dissociation of the processing gas advances extremely, and a problem arises in that a favorable selection ratio to the mask material or substrate material is not obtained.
In the aforementioned ECR, the high density and high electron temperature invite a disaster depending on the process, in that the dissociation of the processing gas advances extremely, and a problem arises in that a favorable selection ratio to the mask material or substrate material is not obtained. The problems of bias non-uniformity caused by the magnetic field and charging damage cannot be ignored.
When an etching process is to be performed using each of the aforementioned plasma sources, under the condition that the processing speed on the wafer surface is uniform, only the processing speed is uniform, and, although the plasma parameters, such as the plasma density, electron temperature, and plasma potential, are almost uniform, it cannot be said that they are strictly uniform.
The etching speed is determined by the balance between ions generated by the plasma, radicals, and reaction products generated by the etching. The density of the reaction products in the neighborhood of a wafer is always high at the center of the wafer, if the etching speed on the wafer is uniform, so that, to cancel it, the ion distribution, under the condition that the processing speed is uniform, is always crowning.
As mentioned above, to make the processing speed uniform, the plasma distribution is adjusted to be slightly non-uniform. Even if the plasma density is uniform, the electron temperature and plasma potential may become naturally non-uniform.
Meanwhile, in order to achieve refinement of semiconductor devices, the minimum processing size at the time of manufacture of the devices is becoming smaller year by year, and in correspondence to this, the thickness of the oxide film of the gate becomes thin, for example, to about several nm.
When the oxide film of the gate becomes extremely thin, the withstand voltage of the oxide film becomes low, so that the semiconductor device becomes very sensitive to damage when the oxide film is exposed to plasma. One example of charging damage caused by plasma is macro damage. This phenomenon will be explained with reference to
FIGS. 14A
to
14
C.
At the time of etching, after the plasma is ignited, a high frequency bias is generally applied to a wafer. Ions are pulled in the wafer by the high frequency bias, and, hence, etching of high anisotropy is realized. When the high frequency bias is applied, depending on the difference in the displacement between the electrons and the ions, as shown in
FIG. 14A
, a self bias Vdc is generated on the wafer.
As described previously, the etching process is performed under the condition that the processing speed on the wafer surface is uniform. However, only the processing speed is uniform, and it cannot be said always that the plasma parameters are uniform. Therefore, the aforementioned self bias Vdc, as shown in
FIG. 14B
, may be different depending on the position on the wafer.
When the self bias voltage Vdc on the wafer surface is more than the withstand voltage of the oxide film of the gate, as shown in
FIG. 14C
, the current flows through the plasma as a part of the circuit and the device breaks. Namely, macro damage is generated.
FIG. 15
shows an example of the current-voltage characteristic of an oxide film of the gate. Although the characteristic is different depending on the conditions, such as the thickness of the oxide film of the gate, when a voltage between 7 V and 8 V or so is applied to the oxide film of the gate, the oxide film of the gate is subjected to a dielectric breakdown. When the thickness of the oxide film is made thinner, the withstand voltage will be naturally lowered. When the difference in the self bias potential on the wafer surface is more than 7 V, macro damage is generated.
The non-uniformity of the self bias as shown in
FIG. 14B
can be seen often when a magnetic field is applied to a plasma. The reason for this is that the motion of electrons is restricted by the magnetic field, and the impedance of the plasma is different between the crossing direction of the magn
Kawahara Hironobu
Maeda Kenji
Omoto Yutaka
Sasaki Ichiro
Hitachi , Ltd.
Powell William A.
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