The present invention relates to methods of measuring potential differences and currents, and, more particularly, the invention relates to methods of measuring the potential difference or the plasma current developed on the surface of a semiconductor wafer sample, when it is under plasma processing, during semiconductor manufacturing processes, with the semiconductor wafer located inside a plasma reactor in order to surface-treat the wafer. Also, the present invention relates to an apparatus for monitoring processes in a plasma processing apparatus by use of the measured potential difference or plasma current, and to a sample processing method that uses the process monitoring apparatus.
In general, during the manufacture of semiconductors, semiconductor wafers need to be subjected to various surface treatment processes, such as etching, and a plasma reactor that applies electromagnetic waves to generate a plasma is most commonly used as the surface processing apparatus. For such a plasma reactor, the electromagnetic waves and the plasma generate a strong electric field not only in the space of the plasma reactor, but also on the surface of the semiconductor wafer mounted on a processing table (sample mount) within the processing apparatus. When a strong electric field is generated on the surface of the semiconductor wafer, the field strength will cause a potential difference on the surface of the semiconductor wafer, and if the potential difference exceeds a predetermined value, the semiconductor wafer may be damaged. It is therefore important to measure the potential difference on the semiconductor wafer surface when processing that surface using a plasma reactor.
In this case, probing (hereinafter referred to as the first known method) is available as one of the typical methods of measuring the electric field strength and potential differences occurring inside the plasma reactor. The first known method is intended to measure the electric field strength and potential differences inside the plasma reactor by inserting conductor probes into a plasma atmosphere and, then, after scanning with the probes, detecting the voltage-current characteristics thereof.
A method of measuring the potential of a semiconductor wafer inside a plasma reactor (hereinafter referred to as the second known method) is described on page 775 of a Japanese-Version Preliminary Article Collection at the 46th Association Symposium on Applied Physics, held in the spring of 1996. For the second known method, the potential difference on the semiconductor wafer surface is measured by searching with probes embedded directly in the semiconductor wafer (which is mounted on the sample mount, namely, the semiconductor wafer mounting table, inside the plasma reactor) at a portion where the potential difference is estimated to occur, instead of searching with probes embedded in the sample mount itself.
Since the first known method, which proposes to measure the potential difference on the semiconductor wafer inside the plasma reactor, is used to detect the voltage-current characteristics of the conductor probes by scanning in a plasma atmosphere, it is necessary to transmit detection output signals from the conductor probes to an external apparatus by using connection lead wires and to provide the vacuum chambers with connection lead wire relay terminals, because the plasma is generated inside the vacuum chamber. In addition, the total structure of the plasma reactor is complex, and this makes it impossible for the potential difference on the semiconductor wafer to be measured using a simplified means.
Furthermore, since the second known method, which proposes to measure the potential difference on the semiconductor wafer inside the plasma reactor, uses probes embedded in a sample mount on which the semiconductor wafer is to be mounted, it is not only necessary for the sample mount to be of special structure, but it is also difficult to process the surface of the semiconductor wafer on this sample mount after measuring the potential difference on the semiconductor wafer by use of the sample plate. In addition, the type of sample mount to be used will differ between measurement of potential difference on the semiconductor wafer and the surface-treatment processing thereof, and this results in increased plasma reactor costs and, hence, an increased number of treatment processes.
The present invention is directed to such a technical background, and one of its objects is to provide a potential difference and current measuring method that enables the DC potential difference on a target object to be measured using a simplified means via a potential difference and current measuring arrangement having a simplified configuration.
Another object of the present invention is to provide a method that enables samples to be efficiently processed while the processes are being monitored using an apparatus having a simplified configuration.
When a light-emitting diode or the like is left in a plasma-exposed atmosphere, the potential difference arising from the resulting flow of charged particles (ions and electrons) from the plasma will create the flow of an electric current into the light-emitting diode and activate it to emit light. The light emission intensity of the light-emitting diode has a constant correlation with the voltage and current of the diode. The present invention utilizes this property.
The present invention is characterized in that, in a method of measuring the potential differences for plasma processing with a plasma processing apparatus that processes a sample by introducing a gas into vacuum chambers and generating a plasma: a light-emitting portion is formed on a measurement sample; the potential difference generated according to the difference in the amount of plasma-incident charged particles is detected; a current flows into said light-emitting portion according to the potential difference that has been generated across said light-emitting portion; the intensity of the light emitted from said light-emitting portion according to the particular level of said current is measured; and the potential difference on said measurement sample according to the particular light intensity is measured.
The present invention is also characterized in that, in a method of measuring the plasma processing potential difference on the object to be plasma-processed by introducing a gas into vacuum chambers and generating a plasma: a light-emitting portion is formed on said object to be plasma-processed; the flow of charged particles from the plasma to the surface of said object is measured as the intensity of the light emitted from said light-emitting portion according to the level of the current flowing thereinto; and the amount of current flowing into said object according to the particular light intensity is measured.
For example, antennas for acquiring charged particles from plasma to the terminals of the light-emitting portion are connected first. These antennas are then installed inside the plasma processing apparatus or on the wafer, and the light emission intensity of the light-emitting portion is measured. It is possible to measure the potential difference between any two positions by establishing the correlation expression between the pre-calculated light emission intensity and voltage-current characteristics of the light-emitting portion and converting the light emission intensity into a voltage, or to measure the plasma current between any two positions by converting the light emission intensity into a current using the above-mentioned expression.
To measure the plasma potential difference, the circuit resistance value of a light-emitting diode needs to be greater than an external circuit resistance including the plasma, or, to measure the plasma current, the circuit resistance value of the light-emitting diode needs to be smaller than the above-mentioned external circuit resistance value. This method requires only a window for measuring light intensity, and does not require lead wires or lead wire lead-in terminals.
In order to fulfill the foregoing objects, a potential difference measuring method based on the present invention uses a potential difference and current measuring arrangement equipped with one pair of conductor antennas, a light-emitting portion connected between the conductor antennas, and an AC voltage bypass element connected in parallel to the light-emitting portion, and a means is provided for arranging/connecting the conductor antennas at/to the potential measuring positions on the object to be measured and for measuring the DC potential differences at these potential measuring positions by detecting the intensity of the resulting light output from the light-emitting portion.
According to the means described above, after the arrangement and connection of the conductor antennas at/to the potential measuring positions on the object to be measured, when DC potential differences exist at these potential measuring positions, the light-emitting portion or the light-emitting diodes will emit light. The DC potential differences at the potential measuring positions can therefore be measured by visually detecting the emitted light intensity from the unit containing the target object (for example, from the exterior of the plasma generating layer) through an optical unit, such as a charge-coupled device (CCD) camera. Thus, it is unnecessary to provide connection lead wires to acquire detection output signals, or a sample mount in which conductor probes for detection are embedded.
In this case, since an AC voltage bypass element (preferably, a capacitor) is connected in parallel to the light-emitting portion, any AC potential differences between potential measuring positions are bypassed by the AC voltage bypass element and only the DC potential differences at the potential measuring positions can be measured.
The present invention also makes it possible to supply a highly efficient sample-processing method that uses a potential difference and current measuring portion having a simplified configuration.