JPS6211492B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention detects changes in the ionization rate of the plasma atmosphere due to the generation of etching reaction products in sputter etching or reactive ion etching using active ions, and enables the control of the amount of etching. Regarding a control device.

Etching processing technology used in the manufacturing process of electronic devices such as semiconductor integrated circuits has a significant impact on product yield and product quality. In recent years, there has been a particular demand for an improvement in the degree of integration of semiconductor devices, and it has become clear that etching using chemical solutions has a limit in processing accuracy. On the other hand, it has become difficult to process the large amount of chemical solution required for etching due to pollution problems.

As a method to improve these problems, a method of placing the material to be etched in a reduced pressure gas plasma atmosphere and etching it has been studied. The method using the reduced pressure gas plasma atmosphere can be roughly divided into two methods that have been established so far.
One method is to use an atmosphere of inert gas (argon, etc.) at a reduced pressure of 10 ^-3 to ^{10 -2} Torr.
This is so-called sputter etching, in which a high voltage is applied to the atmosphere to maintain gas discharge, and ions accelerated by an electric field collide with the material to be etched, thereby physically etching the material. The other method uses a gas atmosphere containing components such as fluorine, chlorine, and bromine instead of the above-mentioned inert gas, generates plasma discharge in the same manner as above, and generates plasma discharge by the dissociation of gas molecules during the discharge. This is reactive ion etching, in which chemical etching is carried out by exposing the material to be etched to the chemically active ions produced. The latter reduces the pressure of the plasma atmosphere from 10 ^-3 Torr to several
Can be used in the Torr range, tentatively 10 ^-3 ~
When used at 10 ^-2 Torr, the sputter etching mechanism described above can also be included.

These etching methods have in common that the etching rate does not depend on the difference in materials as much as chemical etching using a chemical solution, that is, selective etching cannot be performed. Particularly in sputter etching, the etching rate is almost constant except for a few substances. Also, in reactive ion etching, it is difficult to increase the etching rate ratio except for a few combinations of substances. For example, the etching rate ratio of an aluminum film deposited by vacuum evaporation on a silicon dioxide film formed by heating and oxidation on a silicon single crystal substrate and the underlying silicon dioxide film is Easily in solutions containing phosphoric acid
While a ratio of 100:1 or more can be obtained, the ratio is about 10 to 30 in the reactive ion etching method and about 1 to 2 in the sputter etching method.

In the processing of semiconductor integrated circuit devices, it is becoming increasingly important to ensure the selectivity between the layer to be etched and the underlying layer. This is one of the reasons why it is difficult to put the etching method used into practical use.

An object of the present invention is to provide an etching control device that can detect changes in the ionization rate in a gas plasma atmosphere containing etching reaction product substances and accurately determine the end point of etching in sputter etching or reactive ion etching. There is a particular thing.

Another object of the present invention is to provide an etching control device that uses the detection signal as a control signal for the etching process and can automate the etching process.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of an etching detection control method in a reactive ion etching apparatus according to the present invention. In the figure, a vacuum vessel 10
A high-frequency electrode 11 is connected via an insulating ring 12, a lid 13 that also serves as a counter electrode plate for the electrode, and a detector 20 that detects changes in the ionization rate of the gas plasma atmosphere.
It consists of After the vacuum container 10 is evacuated by the exhaust pump 14, the flow rate is adjusted by the barrier leak valve 15, gas in the gas reservoir 16 is introduced and maintained at a predetermined pressure, and the high-frequency electrode 11 is connected to a high-frequency power source. High frequency power is supplied from 30 to generate gas discharge 18.

Active ions in the gas discharge enter the material to be etched 17 placed on the high frequency electrode 11,
By reacting, the reaction product becomes a gas discharge 18
be mixed into. By arranging the detector 20 at a position where it can directly collect the gas components of the gas plasma 18 mixed with the reaction product, the collector 2 installed inside the detector 20
By applying a constant high voltage from the high voltage power supply 50 between the collector 1 and the container of the detector, the collector 2
1 and the inner wall of the detector 20. In such a device, ionized ions are accelerated and incident on the collector 21, where they are detected as a collector ion current. However, if the reaction product is mixed into the discharge atmosphere, the ionization rate differs from the ionization rate when no reaction occurs. In this case, the amount of ions (ion current) incident on the collector changes. The amount of etching of the material to be etched 17 is controlled by detecting and processing changes in the ion current as data in the control power source 40 and controlling the output of the high frequency power source 30.

That is, in this embodiment of the present invention, the change in the amount of etching is detected as a change in the amount of ions due to the mixing of reaction products with different ionization rates, and as a change in the collector ion current, thereby controlling the amount of etching. It is in.

In this example, the material to be etched was a quartz plate with an area of 15 cm ² and a film thickness of 5000 Å on a 0.5 mm thick quartz plate.
A substrate on which aluminum was vacuum-deposited was used. Etching in this example was carried out at a pressure of 0.06 Torr and a high frequency power of 150 W.

FIG. 2 is a functional block diagram of the detection control power supply 40 shown in FIG.
Signal conversion is performed at If necessary, the signals are stored in a storage device 42, and some are used as reference signals in a comparison device 44. As the etching time elapses, the signals sampled at regular intervals are processed by a differentiator 43, and the differential value and information such as the sign of the slope are compared with previously set conditions in the next comparator 44. . The compared data is analyzed by a data processing device 45 to determine the etching state, and an output device 46 controls the high frequency output of the high frequency power source 30.

FIG. 3 is a chart showing changes in the ion current monitored by the detection control power source 40 when the material to be etched was etched under the above conditions. In the figure, the ion current value immediately after the start of discharge
V ₁ is stored in storage device 42 . The initial peak of etching after the start of discharge is due to gas release from the inner wall of the detector 20, the collector 21, etc., and is excluded from data sampling, and the ion current value is
The time when _V2 is reached is determined to be the time to start etching, and data sampling is started.

The relationship between the amount of etching and the ion current is inversely proportional to the amount of etching per unit time under constant etching conditions. In other words, the larger the etching amount per unit time, the smaller the ion current value.If the area to be etched is known in advance, the etching amount per unit time can be calculated by multiplying by the required etching speed. It can be calculated. From this relationship, in order to control a predetermined etching rate, the amount of etching can be controlled to be constant by setting the ion current _V3 in advance and controlling the output of the high frequency power source 40.

As etching approaches completion, the ion current begins to increase again. In FIG. 3, the point at which the ion current starts to increase from _V3 corresponds to the point at which etching of the peripheral portion of the material to be etched is completed. At this point, the control of the etching amount is released and the process shifts to detecting the end of etching. In other words, etching is completed when the ion current value reaches _V4 , which is larger than _V3 , and becomes constant.If the output of the high frequency power supply 30 is stopped by a signal from the output device of the detection control power supply 40, the discharge can be stopped. It stops and etching is completed. In this way, in this detection control method, the ion current value V ₁ , the value at the start of etching V ₂ , and the value at the end
An important point in control is that V ₄ is almost the same.

FIG. 4 is a block diagram of another embodiment of the etching control method in a reactive ion etching apparatus according to the present invention. In the figure, the same numbers as in FIG. 1 of the reactive ion etching apparatus indicate the same parts. Further, the function of the detection control power source 40 is also similar to that shown in FIG. 2 above. The feature of this embodiment is that, as shown in FIG. 1, there is no need for a mechanism for collecting the gas from the discharge 18 and ionizing it. That is, in this embodiment, the voltage change applied to the high frequency electrode 11 is detected by the detector 20 due to the change in discharge impedance due to the mixing of reaction products into the gas discharge 18 when the material 17 to be etched is etched. , the amount of etching of the material to be etched 17 is controlled by processing data with the detection control power source 40 and controlling the output of the high frequency power source 30.

In this example, the same substrate as that used in the previous example was used as the material to be etched, and the etching conditions were also the same. Figure 5 shows the change in discharge impedance of the high-frequency electrode 1 when etching the above-mentioned etching substance under the same conditions.
This is a chart recording the voltage change of 1.

According to FIG. 5, the high frequency electrode voltage V ₁₁ at the time when the discharge becomes stable after the start of discharge is stored in the storage device 42 of the detection control power source 40 . At the start of etching, the discharge impedance changes as the ionization rate changes due to the mixing of reaction products into the gas discharge 18. In this case, when the input power is controlled, the voltage applied to the high frequency electrode 11 changes, and the discharge impedance, that is, the high frequency electrode voltage changes depending on the amount of etching. In this application example, the electrode voltage decreases as the amount of etching increases.

Near the end of etching, etching tends to progress from the periphery to the center of the substrate, and as the amount of etching decreases, the electrode voltage begins to rise again. When etching is completely completed in the central part, the electrode voltage becomes constant at V ₁₃ . The voltage value V ₁₃ in this case almost matches the voltage value V ₁₁ previously stored as the discharge initial voltage. Such data is processed in the detection control power source 40, and when the power input to the high frequency power source 30 via the output device is stopped, the discharge is stopped and the etching is completed. As described above, the control feature of this embodiment is that the voltage at the initial stage of discharge is
It is at a point where V ₁₁ and the voltage V ₁₃ at the etching end point almost match.

As explained in the above two embodiments, the present invention detects the change in the ionization rate of the gas due to the mixing of the etching reaction product of the material to be etched into the discharge in etching using a discharge, in the form of a change in the ion current. However, the two detection methods are basically the same.

Therefore, the present invention is advantageously applied to etching processes in which the ions of the discharge are changed by the generation of etching products of the material to be etched.

Furthermore, the present invention enables proper etching processing by reliably and reproducibly detecting the end point of etching, which has heretofore been done by operators relying on their experience and intuition, and by controlling electric discharge.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the etching control device in reactive ion etching according to the present invention, FIG. 2 is a functional block diagram of the detection control power source 40 of FIG. 1, and FIG. A time chart of changes in detected ion current when aluminum on a quartz plate is etched, FIG. 4 is a block diagram of the second embodiment of the etching control device in reactive ion etching of the present invention, and FIG. It is a time chart of the voltage change of the high frequency electrode due to the impedance change when aluminum on the quartz plate of the example shown in the figure is etched. 10... Vacuum container, 11... High frequency electrode, 20
...Detector, 30...High frequency power supply, 40...Detection control power supply, 50...High voltage power supply.

Claims (1)

[Scope of Claims] 1. In an etching apparatus in which a material to be etched is placed in a reduced pressure gas plasma atmosphere and etched, the ionization rate of the atmosphere is reduced due to the mixing of an etching reaction product into the atmosphere. An etching control device comprising means for detecting a change and means for controlling etching using the detection signal. 2. The etching control device according to claim 1, wherein the means for detecting the change in the ionization rate is a detector equipped with an ionization mechanism. 3. The etching control apparatus according to claim 1, wherein the means for detecting a change in the ionization rate is a detector for detecting a change in impedance of a gas plasma atmosphere.