JPH0691035B2 - Low temperature dry etching method and apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface fine processing technique, and more particularly to a low temperature dry etching method and apparatus suitable for anisotropic etching processing of a semiconductor wafer.

(Prior Art) As the degree of integration of semiconductor integrated circuits increases from LSI to VLSI, the dimensions of integrated devices become smaller and smaller. When using a resist image having a pattern of 1 μm or less as a mask to etch the substance thereunder, the reaction products can be easily removed by using low-pressure gas plasma.
Moreover, if the acceleration of ions due to the electric field is used as in the reactive etching, there is less problem of undercut, and it is expected that fine patterns can be easily formed.

So-called dry etching, which uses gas without using a solution, is an indispensable technique for VLSI manufacturing, but it is a known technique to cool the sample stage on which the sample is placed in order to prevent alteration of the resist mask. Water cooling is the most common for cooling, but some also use gas,
Nuclear Instruments and Methods 189 (1981) P169
~ 173]. In all of these, it is obvious that the sample stage is cooled to a temperature of 120 to 150 ° C. or lower at which the resist is deteriorated, and the temperature control range is in the range of 20 to 100 ° C. Furthermore, a prior art in which a sample is cooled to a temperature below room temperature, that is, a number of minus 10 ° C. or less using a heat pipe to prevent side etching is disclosed as JP-A-60-158627. In dry etching,
High energy particles such as ions and electrons on the horizontal surface of the sample,
While neutral particles such as radicals are simultaneously incident, only neutral particles are incident on the pattern side wall. In the above-mentioned prior art, when the sample is cooled to a low temperature of minus several tens of degrees Celsius, the reaction rate between the sample and the neutral particles is remarkably reduced and the pattern side wall is not etched. Since the energetic particles collide with each other, a pseudo high temperature state is created on the very surface and etching progresses. As a result, anisotropic etching with less side etching is achieved.

Further, in the invention disclosed as the invention of JP-A-60-50923, an etching gas containing a halogen element and a gas for forming a thin film on the surface of the material to be etched are alternately introduced into a vacuum container, and the gas is removed from these gases. In the excited plasma,
The technique includes performing anisotropic etching while alternately repeating etching and thin film formation on the surface of the material to be etched.

(Problems to be Solved by the Invention) In the above-mentioned conventional technique, in addition to the time for etching the surface of the material to be processed, it takes time to form a thin film on the surface, which tends to increase the processing time. . In the case of implementing the above-mentioned prior art, a heat pipe is used as a cooling device, and the allowable temperature range is narrow. For example, the temperature control range for a heat pipe using liquid nitrogen is approximately -203 to -160 ° C. But practically 0
It is desirable to set the optimum temperature for each material and etching gas within the range of -200 ° C.

The present invention has been made to solve the above-mentioned problems, and the material to be treated is cooled to a low temperature of 0 ° C, preferably -50 ° C or lower to improve the thin film forming efficiency and to shorten the thin film forming time. By the side etching prevention effect due to low temperature, the number of repeated cycles for thin film formation is reduced, and the low temperature range corresponding to changes in etching conditions is expanded.
It is an object of the present invention to provide a low-temperature dry etching apparatus equipped with a sample stage capable of arbitrarily setting a sample in a desired temperature range and a method thereof.

(Means for Solving Problems) The above-mentioned object is to cool the material to be etched to a range of 0 to −200 ° C., and a circuit for controlling the temperature of the sample stage by an apparatus that uses both cooling by a liquefied gas and a heater. At the same time, a means for alternately introducing the etching gas and the thin film forming gas into the vacuum container can be achieved by a low temperature dry etching method that is performed via a device that sets the timing of automatic opening and closing of the gas line valve.

(Function) By setting the material to be etched within the above temperature range with high accuracy and cooling, the composition particles of the film are easily adsorbed on the surface of the material to be etched, and neutral radicals that cause side etching are removed. The reaction efficiency with the side surface of the pattern decreases, and at the same time, the vapor pressure of the reaction product decreases. These synergistic effects increase the thin film formation rate and reduce the side etching amount. That is, even if the thin film formation time is shortened by increasing the thin film formation rate, side etching can be suppressed.

(Example) The present invention will be described below with reference to an apparatus according to an example. FIG. 1 is a schematic explanatory view showing an embodiment of low temperature dry etching using a RIE (reactive ion etching apparatus) according to the present invention, in which a processing chamber 1 is a load-lock type and a sample exchange chamber. By separating them from each other by the gate valve 3 and the gate valve 3, dew condensation on the sample table due to moisture in the atmosphere is prevented. 4 is a processing gas supply port, 24 is a device for setting and controlling the timing time of automatic opening and closing of the gas line valve in order to alternately introduce the etching gas and the thin film forming gas into the reaction vessel, and 7 is a sample stage, inside which Liquid nitrogen 10 is introduced, an electric heater 9 is used as a heater, and a temperature sensor 18 is arranged. 17 is a Teflon table, 19 is a thermometer, 20 is an insulator, and 21 is a liquefied gas container. In this embodiment, the sample table 7 is made of copper in order to enhance the cooling efficiency of the material to be etched 8, and in order to prevent contamination by spattering of copper, the sample table 7 is covered with the quartz cover 6 except the portion on which the material to be etched 8 is placed. Has been done. In order to prevent reaction gas and reaction products from adhering to the surface of the quartz cover 6 being cooled, it is preferable that the thickness of the quartz cover 6 be 5 mm or more. Since the electrode acts as a trap for SF ₆ gas, it was difficult to control the gas pressure. In addition, the quartz cover 6 can be replaced by a Teflon cover depending on the implementation conditions, and the vacuum seal portion where the inside of the sample stage 7 and the processing chamber 1 are in contact is kept airtight by using a metal O-ring 5. The voltage supplied to the electric heater 9 is a pulse voltage, and the pulse interval is 0.1 depending on the set temperature of the sample table 6.
Set to a range of ~ 60 seconds. In addition, the output signal from the temperature sensor 18 is fed to the heater power supply via the feedback circuit 22.
12 and the gas supply control system 23 to control heating and cooling of the sample table 7. As a result, the temperature of the sample table 7 could be controlled to the set value ± 2 ° C. Sample exchange room 2
Performs pre-cooling of the material to be etched 8 before it is conveyed to the processing chamber 1 and heating of the material to be etched 8 after the processing. On the surface of the sample table 13 in contact with the material 8 to be etched in the sample exchange chamber 2, a quartz table 16 (a Teflon substitute can be used) is provided. A gas cooled by liquid nitrogen flows from the cooling gas supply port 14 to cool the material 8 to be etched. In order to prevent the material to be etched 8 from being damaged, the flow rate of the cooling gas was gradually increased and gradually cooled until the temperature of the sample stage 7 of the processing chamber 1 was reached. The processed material 8 to be etched is conveyed again onto the sample table 13 and heated to room temperature by the heating lamp 15.

In the above device, the temperature is set to −
80 ° C. was set as etching gas SF _6, using CCl ₄ as a gas for film formation, and SF ₆ and setting time in one cycle of CCl ₄ and, respectively 40 seconds and 5 seconds, a total of 5 cycles 225
As a result of performing the etching treatment for 2 seconds, the etching depth was 1 μm and the side etching amount was 0.1 μm or less.
On the other hand, in order to obtain the same result as above without cooling the material to be etched, the setting time for each cycle of SF ₆ and CCl ₄ is set to 20 seconds, and 12 cycles require a total of 480 seconds of etching processing time. did. That is, by alternately introducing the etching gas and the film-forming gas to cool the material to be etched, the processing time could be shortened by about 47% in this example.

Next, the cooling temperature of the sample table 7 was changed in the range of 0 to −150 ° C., and the etching shapes of Si were compared. Fig. 3 is a characteristic diagram showing the relationship between the temperature of the sample stage and the side etching amount. A remarkable decrease in side etching is seen at a temperature of approximately -80 ° C or less, and the side etching amount at -100 ° C is 0.05.
It decreased to less than μm. On the other hand, if the temperature is lower than -120 ° C, the etching rate is lowered, which is not preferable. From these results, it can be seen that the optimum etching temperature in this example is -100 to -120 ° C.

When SiCl ₄ was used as the etching gas in place of SF ₆ in the apparatus of the embodiment shown in FIG. 1, the optimum temperature was −80 to −100 ° C., and the side etching amount was reduced to approximately 0.05 μm or less.

Further, when W was used as the material to be etched in the apparatus of the embodiment shown in FIG. 1, the effect of reducing the side etching amount was observed from -20 ° C, and the optimum temperature was in the range of -40 to -80 ° C. .

Other materials to be etched include Al, SiO ₂ , Si ₃ N ₄ , Mo, T
With respect to materials such as i, Ta, and photoresist, the effect of suppressing side etching by cooling was recognized, although there were differences to some extent.

When liquid helium was used instead of liquid nitrogen as the cooling liquefied gas in the apparatus of the embodiment shown in FIG. 1, the cooling efficiency was high, and the sample stage could be cooled in a shorter time than liquid nitrogen. Other gases such as liquid ammonia and trichloromonofluoromethane can also be used practically.

FIG. 2 shows another embodiment of the present invention, which is an apparatus using microwave plasma etching, and the elements having the same reference numerals as those in FIG. 1 have the same function. The microwave excited by the magnetron 25
It is guided to 26 and plasma is generated in the processing chamber 1. The magnet 27 functions to increase excitation efficiency by the ECR (electron cyclotron resonance) action. Si etching was performed using the apparatus having the above configuration, and the gas supply time for one cycle of SF ₆ and CCl ₄ was set to 20 seconds and 3 seconds, respectively. According to this apparatus, the ionization efficiency is high, and the density of active species is higher than that of the apparatus of the embodiment shown in FIG. 1, so that an etching amount of 1 μm in depth was obtained in a total processing time of 92 seconds for 4 cycles. When not cooled, the processing time for each cycle is set to 20 seconds, and 16 cycles are obtained by repeating this for 4 cycles.
Since the same etching amount was obtained in 0 seconds, the total processing time was reduced to 58%. The amount of side etching when the present apparatus was used to etch Si with SF ₆ gas in the temperature range of −80 to −120 ° C. was 0.05 μm or less.

Further, although the electric heater is used as the heating heater in the present embodiment, the use of the heater by other heat sources is not hindered.

(Effect of the invention) By carrying out the present invention, it is possible to set the optimum temperature for the material to be etched and the processing gas in a wide range, and it is confirmed that the etching processing time is shortened and the side etching is suppressed. It showed a remarkable effect in improving accuracy.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a low temperature dry etching apparatus showing one embodiment according to the present invention, FIG. 2 is a schematic explanatory view of another embodiment according to the present invention, and FIG. 3 is a sample stage temperature and side etching. It is a characteristic view which shows the relationship of quantity. 1 ... Treatment chamber, 2 ... Sample exchange chamber 3 ... Gate valve, 4 ... Processing gas supply port 5 ... O-ring, 6 ... Quartz cover 7 ... Sample stage, 8 ... Etching material 9 ... … Electric heater, 10 …… Liquid nitrogen 11 …… RF power supply, 12 …… Heater power supply 13 …… Sample stand, 14 …… Cooling gas supply port 15 …… Heating lamp, 16 …… Quartz stand 17 …… Teflon Platform, 18 …… Temperature sensor 19 …… Thermometer, 20 …… Insulator 21 …… Liquefied gas container, 22 …… Feedback circuit 23 …… Liquefied gas supply control system, 24 …… Reaction gas opening / closing control system 25… … Magnetron, 26… Waveguide 27… Magnet, 100… Plasma

Claims (5)

[Claims] 1. A gas for forming a thin film on a surface of a material to be etched placed in the vacuum container and an etching gas are alternately introduced into the vacuum container at predetermined intervals, and then introduced into the vacuum container. A method of etching a predetermined surface of the material to be etched using plasma of the gas to be etched, wherein the etching is performed by cooling the temperature of the sample stage on which the material to be etched is placed by cooling with a liquefied gas and a heater. A low-temperature dry etching method, characterized in that it is carried out while being kept at a predetermined temperature of 0 ° C. or lower by using heating in combination. 2. A vacuum container, a sample table on which a material to be etched is placed at a predetermined position in the vacuum container, a gas for forming a thin film on the surface of the material to be etched, and an etching gas,
Means for introducing into the vacuum container by switching at predetermined intervals, means for generating plasma of the gas introduced into the vacuum container, and temperature of the sample stage by cooling with a liquefied gas and a heater A low-temperature dry etching apparatus comprising at least a means for heating to a predetermined temperature of 0 ° C. or lower. 3. The surface of the sample table is covered with an insulating film except for the portion where the material to be etched is placed, and the insulating film prevents trapping of a gas introduced into the vacuum container. The low temperature dry etching apparatus according to claim 2, wherein the low temperature dry etching apparatus has a sufficient film thickness. 4. The low-temperature dry etching apparatus according to claim 2, wherein the plasma is generated by microwaves. 5. The low temperature according to claim 2, wherein the plasma is generated by applying electric power to parallel plate electrodes arranged in the vacuum container. Dry etching equipment.