JPS63174320A - Low-temperature etching - Google Patents

Abstract

PURPOSE:To obtain a favorable etch rate and etching cross-sectional shape by setting the voltage between the plasma and the sample surface so that the departure speed by an etching reaction becomes larger than the deposition speed by the adsorption of the etching gas to the sample surface. CONSTITUTION:In a vacuum vessel 1 wherein a discharge is formed by introducing an etching gas, a sample stand 4 for holding a sample 5 within the vessel 1 is maintained at a low temperature, an a.c. current is applied to the sample stand 4, and an etching is performed. At that time, the voltage generated between the plasma within the vessel 1 and the sample 5 surface is set so that the departure speed by the etching reaction becomes larger than the deposition speed by the adsorption of the etching gas to the sample 5 surface. Whereupon, even in a low-temperature etching at 0 deg.C or a lower temperature, a favorable dry etching capable of controlling the cross-sectional shape is available without lowering the etch rate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a low-temperature etching method, and more particularly to a bias-applying low-temperature etching method suitable for the etch rate and etching cross-sectional shape.

[Conventional technology]

Conventional low-temperature etching, as described in Japanese Patent Application Laid-open No. 80-158627, discusses the control range of sample temperature.

Regarding the sample bias application method, please refer to Japanese Patent Application Laid-Open No. 56-13
480, the frequency of the radio frequency bias is discussed.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology does not take into consideration the energy of ions, that is, the bias voltage, which is important in low-temperature etching methods, and there is a problem in that the etch rate decreases. Furthermore, the bias-applying etching method does not take into consideration gas adsorption that occurs during low-temperature etching, resulting in a problem of reduced etch rate.

Furthermore, the conventional low-temperature etching described above does not take into account the non-uniformity of the etching rate within the plane, which occurs when the self-bias of the etched material is lowered and high selectivity etching is performed. 1 because it is selective etching
If there is a degraded layer or contaminated area on the surface, there are problems such as significant etching surface roughness.

In addition, in the conventional dry etching described above, changing the input power was effective in increasing the etching speed and improving the selectivity, but consideration was not given to the formation of a surface-altered layer due to significant adsorption and material deposition that occur during low-temperature etching. Therefore, it was necessary to improve the uniformity of the in-plane etching rate.6 The purpose of the present invention is to lower the sample temperature to below ℃.

Even when there is a gas adsorption phenomenon, the object is to obtain a suitable etch rate and a suitable etched cross-sectional shape by controlling the applied high frequency bias or the self-bias voltage generated between the plasma and the sample.

[Means for solving problems]

The above object is achieved by controlling the voltage generated between the sample stage that holds the sample and the plasma.

The other object described above is achieved by increasing and decreasing the negative bias voltage applied to the etching target material during the processing time when the cooled etching target material is etched by plasma.

[Effect]

When the temperature of the solid surface to be etched is lowered, the probability that the residual gas in the vacuum container and the reactive gas introduced for etching will be adsorbed onto the solid surface increases. On the other hand, since the surface of the hedron is at a low temperature, the probability of reaction with adsorbed gas is small, and the etching reaction is significantly reduced. When an etching gas is introduced into a vacuum container until a predetermined gas pressure is reached and a plasma state is created, the gas undergoes dissociation, monopolymerization, and ionization, and enters the solid surface. Here, the unionized etching gas easily adsorbs to the solid surface, and the ionized excitation gas
Each dissociated ion is accelerated by the plasma and the bias generated on the solid surface and impinges on the surface. At this time, when the acceleration energy is low, the layer adsorbed on the solid surface cannot be used efficiently, but when the acceleration energy is higher than a predetermined value, the temperature rises locally on the solid surface, and the solid Reactive gases adsorbed on the surface are excited and dissociated. As a result, etching is promoted by the reaction between the solid surface and the dissociated or excited highly reactive particles.

In addition, residual gas components are adsorbed and deposited from plasma on the surface of the material to be etched in a low temperature state, and modified areas are likely to be formed on the surface. , the surface-modified portion is difficult to be etched, and the etching rate is significantly reduced. As a result, unevenness occurs on the surface, but if the bias is increased to a negative value during etching, the energy of the ions incident on the surface of the etched material increases, and due to the synergistic effect of the physical sputtering effect and the chemical reaction promotion effect, The thin modified portion is easily removed. In other words, by periodically increasing and decreasing the bias during etching,
In addition to maintaining high selectivity, uniformity of etching rate within the surface can be ensured.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. Vacuum container 1 and etching gas inlet 2. Exhaust port 3. Cooled sample stage4. Sample 5. High frequency power supply 6. Sample stage cooling medium source7. It consists of a sample stage temperature control heater power supply of 8°. Here, the cooled sample stage 4 is insulated from the vacuum vessel by an insulator 9 that is a high-frequency power insulator and a material with low thermal conductivity (here, Teflon is used). The plasma 1O generated by the high frequency power source 6 comes into contact with the inner wall of the vacuum container 1 and the ground electrode 11 facing the sample stage, and has a potential close to the ground potential via a floating potential. On the other hand, the sample potential becomes a high-frequency potential due to the high-frequency power, but the plasma potential also changes with the phase of the high-frequency power, and the potential difference between the sample potential and the plasma changes with time. This fluctuation is averaged over time, and the average potential difference expressed as a DC potential is called Voc. The value of Voc varies depending on the gas pressure and the ratio of the area of the sample stage to the area of the inner wall at earth potential, but
Directly, the higher the high frequency power is, the larger it becomes.

In this embodiment, an example in which a silicon single crystal substrate is used as a sample and SFs is used as an etching gas will be explained below. The sample temperature was uniformly 100°C, and the SFa gas pressure was 0.
, When I Torr, the etch rate is extremely low when Voc is below 30V (less than 1/10 of the etch rate at normal temperature), and it is 100% when Voc is 50V.
n m/win or more, Voc = 100V or more, 3
00 nm/+++in or more. Vnc=l
At 50 V, the etch rate is 500 mm/win
Therefore, especially when it is necessary to improve throughput, VDC! It is effective to increase the thickness of polycrystalline silicon for normal gate electrodes (!I!i thickness ~ 300
Since the characteristics were almost the same even with 300 nm / 300 nm / 300 nm / 300 nm /
Win or higher can be processed in 1 minute, so if you estimate the time required for automatic wafer transfer to within 1 minute, it will be possible to process 30 wafers per hour, which is inferior to the processing capacity of conventional batch methods. Therefore, when etching silicon or polycrystalline silicon at around -100°C, Voc
It is preferable that Voc
Even if Voc is as low as 100V or less, the etch rate does not decrease significantly; for example, when Voc is 3 when the sample temperature is -30°C.
Even at around 0V, the elatin velocity is 300 nm/
It was +ain.

However, in this case, the etched cross-sectional shape is not vertical;
A so-called undercut, in which the area beneath the photoresist mask is etched, has occurred.

In other words, even if the Voc is the same, about 30V, the sample
When the temperature was 130°C, the deposition rate of the etching gas was relatively low, and the rate of desorption due to etching reaction was high, resulting in an etch rate of 300 nm/win; however, when the sample temperature was 1100°C, This shows that the rate of desorption due to etching cannot be increased when Voc is about 30 V, since the gas deposition rate becomes high.

At E-100° C. and Voc=100V or more, the cross-sectional shape was almost vertical, which was a shape suitable for microfabrication.

<Example 2> An example using a microwave plasma etching apparatus will be described with reference to FIG. Magnetron 13° electromagnetic coil 1
4. The waveguide 159 and the quartz discharge tube 16 are unique components of the microwave plasma etching apparatus, and the other components, such as the sample stage 4 and external power sources 8 and 6, are almost the same as those described in FIG. A feature of microwave plasma etching is that essentially non-polar discharge is possible, so there is a slight difference in the concept of VDC explained in Example 1 above. That is, plasma is generated by microwaves, and the sample has an induced potential within the plasma. The sample bias is applied by a high frequency power source 6, but when the frequency of the power source is 10 MHz or less, the above Voc is 0.
Even if the high frequency voltage Vpp (paak to p
This means that a voltage of 172 (eak voltage) is applied to the sample. Therefore, Vo explained in Example 1
Setting c to 100v or more means - V p p to 100v
The above is essentially the same thing. Furthermore, if Voc is not O, if -Vpp+Voa is defined to be 100V or more, the result will be the same as the experimental result of Example 1.

However, since the ionization rate is high in the case of microwave plasma, the etch rate is higher than that in Example 1.

For example, with SFe gas at -100℃, Q, 1 Torr,
Frequency: 800 KHz When Vpp+Voc is 100V, silicon etch rate is 600 nm/m
It became in. In other words, the etch rate was approximately twice that of Example 1. The frequency of the high frequency power supply 6 is 10MHz
As described above, it has been found that, for example, when the frequency is 13.56 MHz, ions cannot follow the frequency, and the determination can be made based on the value of Voc as in Example 1.

In Examples 1 and 2 above, the etching gas was F
2. It was found that almost the same sample bias is required when Cax and Brz are used, but as the mass number of the gas increases, the etch rate tends to decrease unless the sample bias is made a little more crystalline.

Also, the sample was 5iOz, and the etching gas was CF4°C2F.
B, when CsFδ is used, the sample bias is win; when the sample is An and the etching gas is CQx, the sample bias is 300 nm/mi at 100 V or more.
It is recognized that the sample bias may be larger than n, and it goes without saying that the sample bias varies somewhat depending on the combination of sample material and etching gas. In either case, low temperature etching requires a higher sample bias than the sample bias in conventional etching equipment, which typically uses a water-cooled sample stage.

<Example 3> In this example, 5iO on a Si substrate was etched using SFe gas in a parallel plate high frequency discharge plasma etching apparatus.
Polysilicon film formed on the Z film (5000 layers thick)
This figure shows the time change of the input power (13.56 MHz) applied to the sample stage on which the material to be etched is placed when etching is performed using the shift pattern as a mask. At this time, the material to be etched was kept at -100°C, and the SFe gas pressure was 65 mTorr. The solid line in Fig. 3 shows the change in input power, and the broken line shows the change in input power.
It was found that the potential of the etched object on the sample stage, which is the high-frequency application electrode, changes due to changes in the input power.

When kept constant at 200 W, the etching rate of the polysilicon film becomes non-uniform depending on the location, and in the most severe case, the maximum etching rate and the minimum etching rate within the plane are 1
The average etching speed with a 0% difference was 3500 people/w.
It was in. On the other hand, as in this example, 200W
When the power was changed from 1 to 400 W for a few seconds, the absolute value of the etching speed increased to 3,700 people/min, and at the same time, the uniformity of the etching speed could only be within 3% within the surface. That is, changing the bias of the material to be etched was extremely effective in improving the uniformity of the etching rate.

The method is applicable to other polarities such as Si, GaAs.

Semiconductors such as InPGe, An, Ca, Ti, Ni.

Metal materials such as Co, Mat wy and their silicides, SiOx, Tax○5. A n xos+S
It can also be used to process insulating materials such as iN and diamond. Furthermore, this method can be applied to any gas used for etching. Furthermore, the frequency of the input power used may be any frequency.

Furthermore, this method can be used with any plasma etching apparatus that has a mechanism for keeping the material to be etched at a low temperature, and the effect of improving in-plane uniformity is extremely large. Particularly in microwave etching equipment, a method in which a high frequency voltage is applied to the substrate and the bias is varied is excellent.

〔Effect of the invention〕

According to the present invention, even in low temperature etching below 0°C,
Since suitable dry etching with cross-sectional shape control is possible without reducing the etch rate, sub-μm
It is effective in improving practical throughput in high-grade microfabrication.

Further, according to the present invention, the uniformity of the etching rate within the surface is improved, which is effective in improving the economical efficiency of etching.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the low-temperature etching apparatus used in the present invention.
FIG. 2 is a cross-sectional view of the low-temperature microwave plasma etching apparatus used in the present invention, and FIG. 3 is a diagram showing an example of a time change in the high-frequency force and the bias voltage of the material to be etched. 1...Vacuum container, 2...Gas inlet, 3...Exhaust port. ... Cooling sample stage, 5... Sample, 6... High frequency power supply, 7 Cooling medium source, 8... Sample stage temperature control heater power supply,
... Insulator, 1o... Plasma, 11... Opposing electricity 13... Magnetron, 14... Electromagnetic coil,
15 waveguide, 16... quartz discharge tube.

Claims (1)

[Claims] 1. In a vacuum container in which an etching gas is introduced to form a discharge, a sample stage holding a sample in the vacuum container is kept at a low temperature, and an alternating current voltage is applied to the sample stage. In the etching apparatus, the voltage generated between the plasma in the vacuum container and the sample surface is set so that the desorption rate due to the etching reaction is greater than the deposition rate due to adsorption of the etching gas onto the sample surface. Characteristic low-temperature etching method. 2. In a microwave plasma etching device that uses microwaves to form a discharge, the sample stage is kept at a low temperature, and the negative component voltage of the AC voltage applied to the sample stage is controlled so that the desorption rate due to the etching reaction is the deposition rate. 2. The low-temperature etching method according to claim 1, wherein the etching method is set to be larger. 3. Using a surface treatment device consisting of a mechanism for introducing gas into a vacuum chamber, a mechanism for discharging the introduced gas using AC power to form plasma, and a cooling mechanism for keeping the material to be etched at a low temperature, In an etching method in which an etching material is etched by plasma, the material to be etched is cooled below the water cooling temperature, and the DC component of the negative bias voltage during etching of the material to be etched changes in voltage value depending on the time during the processing time. A low-temperature etching method characterized by heating the change.