JPH02177432A - Dry etching - Google Patents

Abstract

PURPOSE:To improve the etching rate of a polycrystalline silicon film and the etching selection ratio of the polycrystalline silicon film to a foundation oxide film and, further, avoid an undercut by a method wherein the polycrystalline silicon film is selectively etched with etching gas composed of bromine system reactive gas and oxygen or the like added to it while a substrate temperature is controlled. CONSTITUTION:A resist film 14 having a required pattern is formed on a polycrystalline silicon film 13 built up on a substrate 11. Then the polycrystalline silicon film 13 is selectively etched with etching gas composed of bromine system reactive gas such as bromine and hydrogen bromine which does not contain carbon and oxygen or gas containing oxygen which does not contain carbon and is added to the bromine system gas while the temperature of the substrate 11 is controlled. For instance, while the temperature of a sample 7 is controlled within a range of 50-150 deg.C, the etching gas composed of Br2 and O2 added to it is introduced into a reaction chamber 1 through a gas introducing tube 2 and discharged through a gas exhaust tube 3 and a pressure in the reaction chamber 1 is maintained at 0.1Torr and a radio frequency voltage is applied to the sample 7 by a radio frequency source 6 to subject the sample 7 to dry etching.

Description

[Detailed Description of the Invention] [Summary] Regarding a dry etching method suitable for forming fine patterns such as gate electrodes in semiconductor integrated circuits, the etching rate of polycrystalline silicon and the etching selectivity with respect to the underlying oxide film were investigated. In order to improve the quality of the film and to prevent the occurrence of undercurrent, the process involves forming a resist film with a desired pattern on the polycrystalline silicon film laminated on the substrate, and then applying bromine while controlling the temperature of the substrate. Alternatively, the step of selectively etching the polycrystalline silicon film using an etching gas that is a mixture of a bromine-based reaction gas that does not contain carbon such as hydrogen bromide, and oxygen or a gas that contains oxygen and does not contain carbon. Configure it so that it is included.

[Industrial application field]

The present invention relates to a dry etching method suitable for forming fine patterns such as gate electrodes in semiconductor integrated circuits.

Currently, semiconductor wafers tend to have larger diameters, and accordingly, single-wafer processing is becoming mainstream when performing etching.

Advantages in this case include improved uniformity, smaller etching equipment, and easier maintenance.

However, if this is done, the processing capacity will naturally decrease, so in order to compensate for this, it is desired to develop an etching technique that can obtain a high etching rate.

In addition, the formation of fine patterns is essential in order to realize multifunctionality, high speed, and high integration of semiconductor devices, and in order to realize finer patterns, it is necessary to have high selectivity and
There is a need for an etching technique that is free from undercuts and allows high precision and dimensional control.

[Traditional techniques, techniques]

Generally, etching speed is fast and anisotropic (vertical)
The following techniques are known as etching methods for obtaining shapes. Here, as an example, the case of forming a polycrystalline silicon gate electrode in an insulated gate field effect semiconductor device will be considered.

+1) A sputter etching method in which ions in plasma are perpendicularly incident on a semiconductor wafer, and ion bombardment is used to obtain anisotropy.

(2) An etching method that uses gas containing carbon to take advantage of its ability to protect the side walls of the object to be etched.

(3) Etching method performed while controlling the temperature of the semiconductor wafer.

In addition, as an etching method that can obtain a high selectivity,
The following techniques are known.

(4) Wet etching method using chemicals that are selective to the object to be etched.

(5) A chemical dry etching method that suppresses the impact of ions in plasma and uses radicals, which are neutral active species.

[Problem to be solved by the invention]

The etching methods explained in (11 to (5) above) will be discussed.

(a) (For the etching method 11, it is possible to give directionality to the ions and use the impact to obtain a high etching rate and anisotropic shape for polycrystalline silicon, for example, but it is possible to obtain a high etching rate and an anisotropic shape for polycrystalline silicon, for example. The disadvantage is that the selectivity with respect to the oxide film or mask material is small.

(b) Regarding the etching method in (2), gas containing carbon has the effect of increasing the etching rate of the underlying oxide film, so high selectivity cannot be expected. Since the area becomes narrow, there is a limit to the thickness of the sidewall protective film. Further, since carbon is easily deposited, it has the disadvantage of generating dust.

(C) Regarding the etching method in (3), etching
When polycrystalline silicon is etched using SF as the gas, the temperature of the semiconductor wafer is set to -130 ('), for example.
A vertical shape can be obtained by setting the degree C), and
The lower the temperature, the higher the selectivity with respect to the underlying oxide film.

Further, when C12 is used as the etching gas, a vertical shape can be obtained at a temperature of the semiconductor wafer of about -20 to 0 ('C).

However, at low temperatures below -20 ('C), especially at 130
Etching at ("C) is difficult from a practical standpoint, and it is not easy to modify or develop etching equipment (also, there is a drawback that the etching speed of polycrystalline silicon decreases as the temperature decreases. be.

(dl (Since the etching method in 41 uses a chemical reaction, etching progresses in the same direction, resulting in undercuts. In the future, as patterns become finer, the amount of undercuts will become larger. and microfabrication becomes impossible.

tel (Regarding the etching method in No. 51) This method can obtain a high selectivity by suppressing the influence of ions and utilizing radicals, which are neutral active species, but the etching rate of polycrystalline silicon is slow, and There are drawbacks such as undercutting and poor dimensional accuracy.

The present invention improves the etching rate of polycrystalline silicon and the etching selectivity with respect to the underlying oxide film, while also preventing the occurrence of undercuts.

[Means to solve the problem]

In the dry etching method according to the present invention, a resist film (for example, a photoresist film) having a desired pattern is formed on a polycrystalline silicon film (for example, a polycrystalline silicon film 13) laminated on a substrate (for example, a silicon semiconductor substrate 11). 14)
Next, in order to adjust the sidewall shape of the etching pattern in the polycrystalline silicon film, oxygen is added to a carbon-free bromine-based reactive gas such as bromine or hydrogen bromide while controlling the temperature of the substrate. Alternatively, the method includes a step of selectively etching the polycrystalline silicon film using an etching gas containing a mixture of oxygen-containing gas and carbon-free gas.

[Effect]

By adopting the above method, the sidewall shape of the etched pattern of the polycrystalline silicon film can be easily made into a vertical shape by controlling the temperature of the substrate. For example, by adding oxygen to the etching gas, etching of the underlying oxide film is suppressed. The etching selectivity with respect to the polycrystalline silicon film is improved, and good etching can be performed with no undercut (and high dimensional accuracy).Therefore, the etching rate of the polycrystalline silicon film, the selectivity with respect to the base oxide film, and the shape are improved. All the trade-off problems that occur between dimensional accuracy and dimensional accuracy have been resolved, and the etching equipment has been modified to one that can be used at low temperatures such as -130 ('C) to 20 ('C), and new etching equipment has been developed. There will be no need to do so.

〔Example〕

FIG. 1 shows the parallel plate reactive ion etching system used to practice the present invention.
FIG. 2 shows an explanatory diagram of the main parts of the RIE (etching: RIE) device.

In the figure, ■ is a reaction chamber, 2 is a gas introduction pipe, 3 is a gas exhaust pipe, 4 is an upper electrode, 5 is a lower electrode, 6 is a high frequency power supply,
7 indicates each sample.

In this RIE apparatus, etching gas is introduced into a reaction chamber l through a gas introduction pipe 2 and exhausted through a gas exhaust pipe 3.

FIG. 2 shows a cutaway side view of a main part for explaining the structure of the sample 7 shown in FIG. 1.

In the figure, 11 is a silicon semiconductor substrate, 12 is an oxide film made of silicon dioxide, 13 is a polycrystalline silicon film, 1
4 indicates a photoresist film, respectively.

Now, as sample 7, by applying the thermal oxidation method,
The surface of the silicon semiconductor substrate 11 has a thickness of, for example, approximately 1000 mm.
An oxide film 12 having a thickness of about 100 yen (200 cm) is formed, and then chemical vapor deposition
A polycrystalline silicon film 13 having a thickness of, for example, about 4,000 microns is formed on the oxide film 12 by applying a CVD method, and then a resist process in a normal photolithography technique is applied. A photoresist film 14 having a width of 1 μm is formed on a polycrystalline silicon film 13 by applying the above method, and this is set in a reaction chamber l.

Here, using a mixed gas of Br2 and 02 added as an etching gas, the etching gas is introduced into the reaction chamber 1 from the gas introduction pipe 2 and discharged from the gas exhaust pipe 3. is maintained at a pressure of 0.1 (Torr), and a frequency of 13. 56 (M
llz), and the power is 0. 66 (W/cm”
), dry etching is performed by applying a high frequency of 300 (W) in total.

FIG. 3 is an explanatory diagram showing various data obtained by performing dry etching under the settings described above with respect to FIGS. 1 and 2. Note that the temperature of the silicon semiconductor substrate 11 when obtaining this data was controlled by the temperature of the cooling water and the pressure of the He gas for gas conduction cooling that was flowed between the silicon semiconductor substrate 11 and the electrodes.

As is clear from the figure, changing the etching conditions was
This is because the flow rate was changed and the temperature of the silicon semiconductor substrate 11 was changed.

Now, when using Br2 alone, the etching rate of the polycrystalline silicon film 13 is 2000 (people/minute), and the etching rate of the oxide film 12 is 200 [people/minute], but if the amount of 02 added is increased. As the polycrystalline silicon film 1
The results show that the etching rate of the oxide film 12 increases, and that of the oxide film 12 decreases. In addition, the selection ratio,
In other words, when looking at the etching rate of polycrystalline silicon/etching rate of silicon dioxide, compared to the case of Br2 alone, 02 is 25 (sccm) for Br2.
．． When 0 (sccm) was added, the value increased from 1O10 to 11.8. At this time, the effect of O2 addition was observed until the abundance of O2 reached 10%,
If the temperature exceeds this level, the surface of the polycrystalline silicon film 13 will be oxidized, and etching will no longer proceed. Such a result can be achieved by keeping the temperature of the silicon semiconductor substrate 11 in the range of 5O-150 ('Ill:) for any amount of 02 added. Furthermore, looking at the shape, a vertical shape can be obtained by controlling the temperature of the silicon semiconductor substrate 11, and no undercuts are observed.

In addition to the above-mentioned points, the unevenness (jags) generated on the side surface of the etched polycrystalline silicon film 13 is smoothed by the addition of 02.

Figure 4 shows a diagram to explain that the amount of dimensional shift changes depending on the addition of 02, and the horizontal axis shows the amount of 02 added.
Also, the vertical axis shows the amount of dimensional shift. In addition, the amount of dimensional shift can be considered as the degree of unevenness, and
Etching gas in this case (Br2 or HBr)
The flow rate is 10100, which is the value displayed by the nitrogen mass flow.
(It was SCC.

As is clear from the figure, the etching gas is I(Br(
b) The sample and etching gas are Br2
For both samples with (Δ), the dimensional shift m decreases as the amount of 02 added increases.

FIG. 5 is an explanatory diagram showing various data obtained by performing dry etching under the settings explained in FIGS. 1 and 2, and the difference from the embodiment explained in FIG. 3 is as follows. , HBr was used as the etching gas. Note that the temperature of the silicon semiconductor substrate 11 when this data was obtained is the temperature of the cooling water and the temperature of the silicon semiconductor substrate 1.
The pressure was controlled by the pressure of He gas for gas conduction cooling, which was flowed between No. 1 and the electrode.

In this case as well, the etching conditions were changed by changing the O2 flow rate and changing the temperature of the silicon semiconductor substrate 11.

Now, with HBr alone, the etching rate of the polycrystalline silicon film 13 is 2800 [people/minute], and the etching rate of the oxide film 12 is 150 [people/minute], but as the substrate temperature is raised ( The results show that the etching rate of the polycrystalline silicon film 13 increases, and as the amount of O2 added increases, the etching rate of the oxide film 12 decreases.

Also, if we look at the selectivity ratio, that is, the etching rate of polycrystalline silicon/etching rate of silicon dioxide,
Compared to the case of HBr alone, 100100 (s
When 2.5 (sccm) of 02 is added to c, the value increases from 18.7 to 20.0. At this time, 0
The effect of the addition of 02 was observed until the proportion of 02 reached 5%, and beyond that point, the surface of the polycrystalline silicon film 13 was oxidized and etching stopped progressing.

These results indicate that the temperature of the silicon semiconductor substrate 11 is
5('C).

Further, the temperature of the silicon semiconductor substrate 11 was set to 90 (').
C) and then etched with HBr in the same manner, the etching rate of the polycrystalline silicon film 13 was as fast as 3200 people/min.
The selectivity ratio to 2 also increased to 21.3. Then add 02 to this. 5 (sccm), the etching rate for the polycrystalline silicon film 13 was 300 sccm.
0 (people/minute), but the etching rate of the oxide film 12 was 11O [people/minute], and the selectivity was 27.3.
It became high.

Furthermore, the temperature of the silicon semiconductor substrate 11 is set to 15
It has been confirmed that the etching rate and selectivity of the polycrystalline silicon film 13 are further improved when the temperature of the silicon semiconductor substrate 11 is increased to 0 ("C).
When the etching rate was lowered to 5 ('C) and etching was performed using HBr, the etching rate of the polycrystalline silicon film 13 was lowered, and the selectivity with respect to the oxide film 12 was also lowered.

The shape of the etching largely depended on the temperature of the silicon semiconductor substrate 11, and when the temperature was lower than 50 ('C), it became a tapered shape.

No undercuts were observed overall, and almost no unevenness was generated on the side surface of the etched polycrystalline silicon film 13, and the slight unevenness was caused by the addition of 02, as in the previous example. It can be easily smoothed and the same results as the data seen in FIG. 4 can be obtained in this case as well.

Incidentally, in the above-mentioned embodiment, the same effect can be obtained by adding H2O, NO2, or O3 instead of adding O2. However, gases containing carbon such as CO or 002 are not preferred because carbon increases the etching rate of silicon dioxide.

〔Effect of the invention〕

In the dry etching method according to the present invention, while controlling the temperature of the substrate, a carbon-free bromine-based reaction gas such as bromine or hydrogen bromide is mixed with oxygen or an oxygen-containing gas that does not contain carbon. The method includes a step of selectively etching the polycrystalline silicon film using the etching gas.

By adopting the above structure, the sidewall shape of the etched pattern of the polycrystalline silicon film can be easily made into a vertical shape by controlling the temperature of the substrate. For example, by adding oxygen to the etching gas, etching of the underlying oxide film is suppressed. The selectivity with respect to the polycrystalline silicon film is improved, and good etching can be performed without undercuts and with high dimensional accuracy. Therefore, all trade-off problems that occur between the etching rate of the polycrystalline silicon film, the selectivity with respect to the underlying oxide film, and the shape and dimensional accuracy are resolved. There is no need to modify or develop a new product that can be used at low temperatures such as ) to -20 ('C).

[Brief explanation of the drawing]

Figure 1 shows a parallel plate type RI used to carry out the present invention.
Figure 2 is a cutaway side view of the main parts to explain the structure of the sample shown in Figure 1. Figure 3 shows the settings explained in Figures 1 and 2. An explanatory diagram showing various data obtained by performing dry etching, Figure 4 is a diagram to explain that the amount of dimensional shift changes depending on the addition of oxygen, and Figure 5 is a diagram showing the changes in the amount of dimensional shift due to the addition of oxygen. 2 are explanatory diagrams showing various data obtained by performing dry etching under the settings described in connection with FIG. 2. In the figure, l is a reaction chamber, 2 is a gas introduction pipe, 3 is a gas exhaust pipe, 4 is an upper electrode, 5 is a lower electrode, 6 is a high frequency power supply,
7 is a sample, 11 is a silicon semiconductor substrate, 12 is an oxide film made of silicon dioxide, 13 is a polycrystalline silicon film, 14
indicate photoresist films, respectively.

Claims (1)

[Claims] A step of forming a resist film with a desired pattern on a polycrystalline silicon film laminated on a substrate, and then applying carbon-free bromine with bromine or hydrogen bromide while controlling the temperature of the substrate. A step of selectively etching the polycrystalline silicon film using an etching gas in which oxygen or a gas containing oxygen but not containing carbon is mixed as a reaction gas. Etching method.