JPH05267245A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To make it possible to form a silicon oxide film in a vertically specific configuration by using a heat-resistant thin film as a master mask when the silicon oxide film is etched. CONSTITUTION:After a silicon oxide film 2 and a polysilicon thin film 3 are formed on a silicon substrate 1 in that order, a photoresist 4 is formed in a desired pattern. Then, after the polysilicon thin film 3 is vertically processed with the photoresist 4 as a mask, the remaining resist 4 is removed by a down flow ashing by use of a CF4/O2, gas, for example, thereby to pattern the polysilicon thin film 3 on the silicon oxide film 2. Subsequently, while the silicon substrate 1 is kept at a given temperature of 120 deg.C or more almost constantly, the silicon oxide film 2 is etched anisotropically with the polysilicon thin film as a mask. In this way, it is possible to form the silicon oxide film 2 in a vertically specific configuration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device such as a semiconductor integrated circuit, and more particularly to improvement of dry etching of a silicon oxide film in a process of manufacturing a semiconductor device.

[0002]

2. Description of the Related Art In recent years, with the progress of semiconductor integrated circuits, the miniaturization of elements has been progressing, and the demand for higher precision of pattern dimensions is increasing. Generally, a semiconductor integrated circuit is formed by laminating an insulating thin film such as a silicon oxide film having a predetermined pattern and a conductive thin film such as polycrystalline silicon or aluminum on a semiconductor substrate such as a silicon substrate.

Conventionally, various techniques have been used to process a silicon oxide film into a desired pattern. For example,
After a photosensitive resist is applied on the silicon oxide film, the resist is exposed to light or ultraviolet rays in accordance with a desired pattern, and developed to selectively remove exposed or unexposed areas to form a resist pattern. A graphic technique, a dry etching technique for etching the underlying silicon oxide film using the resist pattern as a mask, and a peeling technique for removing the resist.

However, as the degree of integration of semiconductor devices increases, the required minimum size and dimensional accuracy of patterns are becoming smaller, and this is no exception in the processing of silicon oxide films. The problem in processing the silicon oxide film will be specifically described below.

Currently, using a fine resist pattern,
A reactive ion etching (RIE) technique using plasma is widely used as one of the methods for processing the underlying silicon oxide film. In this method, for example, a substrate on which a silicon oxide film to be processed is deposited is housed in a vacuum container equipped with a pair of parallel plate electrodes, and after the inside of the container is evacuated,
A method in which a reactive gas containing a halogen element such as CF ₄ or CHF ₃ gas is introduced, the gas is made into plasma by the discharge generated by the application of high-frequency power, and the silicon oxide film to be processed is etched using the generated plasma. is there.

According to this RIE, ions of various particles in plasma are accelerated by a DC electric field generated in the ion sheath on the electrode surface, bombard the film to be processed with large energy, and cause an ion-promoting chemical reaction. Wake up.
Therefore, etching proceeds in the ion incident direction, and directional etching without undercut is possible.

However, since all the materials are excited or activated by this ion bombardment, the difference in reactivity peculiar to the substance is less likely to occur as compared with etching using only radicals, and the etching rate ratio is generally different depending on the material. That is, there is a problem that the selection ratio becomes small. Therefore, in the etching of the silicon oxide film, the etching rate of silicon that is the base of the silicon oxide film is high,
The etching cannot be stopped accurately when the silicon surface is exposed.

Therefore, when a plurality of contact holes having different depths are formed by etching, there is a problem that the underlying silicon of the shallow holes is etched by a considerable amount and the device characteristics are deteriorated.

In order to solve this problem, in etching the silicon oxide film, CH, which is the main etching gas, is used.
There is a method of increasing the selection ratio between the silicon oxide film and silicon to 20 or more by adding CO gas to F ₃ gas.

In addition to this, in etching contact holes, it is required to make the hole shape vertical. That is, when a contact hole is formed by etching using CHF ₃ gas at room temperature, the side wall of the contact hole is tapered by about 80 degrees. This is because the CHF ₃ gas is dissociated in the plasma, and the resulting fluorocarbon is deposited on the side wall of the contact hole, whereby a tapered shape appears.

As described above, the conditions required for processing a contact hole used in a highly integrated device are a high selectivity to silicon (20 or more) and vertical processing.

While maintaining a high selection ratio for silicon,
As a method of realizing the verticalization of the processed shape, there is a method of etching while keeping the substrate at a high temperature. That is, as the temperature of the substrate is increased, the shape of the side wall becomes closer to vertical. At a substrate temperature of 160 ° C., the taper angle of the side wall of the silicon oxide film reaches 83 degrees, and the selectivity ratio to silicon at that time is 35 degrees.
Met. However, when the substrate temperature is raised to 160 ° C. or higher, the resist pattern is deformed by heat, so that it is impossible to process a pattern having a desired pattern size with high accuracy. Thus, it was difficult to form a vertical silicon oxide film while maintaining a high selection ratio (20 or more) with respect to silicon.

[0013]

As described above, as described above,
The following problems have been encountered when processing a silicon oxide film by the reactive ion etching technique.

That is, it is impossible to form a vertical silicon oxide film while maintaining a high selection ratio (20 or more) with respect to silicon because the resist mask has low heat resistance.

The present invention has been made in consideration of the above circumstances, and provides a method of manufacturing a semiconductor device capable of forming a vertical silicon oxide film having a constant shape without degrading an etching mask. With the goal.

[0016]

The essence of the present invention is that a heat resistant thin film pattern is formed on a silicon oxide film to be processed as an etching mask for dry etching, and this heat resistant thin film pattern is used as a mask. It is used to dry-etch the silicon oxide film while maintaining the silicon oxide film at a high constant temperature by plasma of a gas containing C atoms and F atoms.

That is, according to the present invention, a step of forming a heat-resistant thin film pattern on a substrate to be processed having a silicon oxide film formed on the surface thereof, and a reaction region containing the substrate to be processed are
Gas containing C atoms and F atoms, or gas containing C atoms and F atoms, CO, H ₂ , O ₂ and C atoms and H
While introducing a mixed gas with a gas selected from the group consisting of atoms and forming a plasma by causing an electric discharge, the substrate to be treated is kept substantially constant at a predetermined temperature of 120 ° C. or higher. And a step of anisotropically etching the silicon oxide film using the heat-resistant thin film pattern as a mask.

The heat-resistant thin film pattern used in the method of the present invention is made of Si, S when the predetermined temperature is 160 ° C. or higher.
It is preferably selected from i-nitride, Si carbide, metal, metal oxide, metal nitride, or boron nitride. If the temperature is less than 160 ° C., an ultraviolet curable resist can be used in addition to the above-mentioned ones.

[0019]

In the method of the present invention, the silicon oxide film is dry-etched at a high temperature of 120 ° C. or higher by plasma of a gas containing C atoms and F atoms using the heat-resistant thin film pattern as a mask. Therefore, the vertical processing shape can be etched without causing the deformation of the etching mask due to heat. Further, since the temperature during etching is kept substantially constant, the processed shape is also maintained to be a constant vertical shape.

In the method of the present invention, in order to investigate the characteristics of dry etching of the silicon oxide film using the heat-resistant thin film pattern as a mask, a CFC gas or CFC gas and CO
Using H ₂ , O ₂ , or a mixed gas of a gas containing C and H, the gas flow rate ratio and the substrate temperature were changed, and the silicon oxide film, the etching rate of the silicon substrate, and the processed shape of the silicon oxide film were measured. However, it has been found that the silicon oxide film can be processed vertically with a selection ratio to silicon of 20 or more by appropriately selecting the gas flow rate ratio and the substrate temperature.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing a manufacturing process of a semiconductor device according to an embodiment of the present invention.

First, a silicon oxide film 2 was deposited on a silicon substrate 1 by thermal oxidation to a thickness of 1.4 μm. Then
After forming a polysilicon thin film (film thickness 250 nm) 3 by a CVD method, a resist 4 having a desired pattern was formed by a usual photolithography technique.

Next, as shown in FIG. 1A, the polysilicon thin film 3 is vertically processed by a dry etching technique using chlorine gas, using the photoresist 4 (film thickness 1.5 μm) as a mask. The remaining resist 4 was removed by downflow ashing using CF ₄ / O ₂ gas. As a result, as shown in FIG.
A pattern of the polysilicon thin film 3 was formed on the silicon oxide film 2. Next, as shown in FIG. 1C, dry etching of the silicon oxide film 2 was performed using a dry etching apparatus. Here, the process of FIG. 1C will be described in detail. First, the dry etching apparatus used in this embodiment will be described with reference to FIG.

The etching chamber 20 is composed of a vacuum chamber 20a, in which a first electrode 22 is arranged, and a substrate 21 to be processed is placed on the first electrode 22. A blocking capacitor 29 is provided on the first electrode 22.
The high frequency power source 24 is connected via the high frequency power source 24, and the high frequency power of 13.56 MHz is supplied from the high frequency power source 24 to the first electrode 2.
2 is applied. Further, the first electrode 22 is internally provided with a heater 25 for raising the temperature of the first electrode 22 and controlling the substrate temperature of the target substrate 21 to a desired temperature.

A CHF ₃ gas supply line 28a and a carbon monoxide gas supply line 28b are attached to the vacuum container 20a, and CHF ₃ and CO are introduced into the vacuum container 20a from these gas supply lines 28a and 28b. Also,
The inner wall (upper wall) of the vacuum container 20a also serves as a second electrode, and a high frequency voltage is applied between the second electrode and the first electrode 22.

Here, the vacuum container 20a is connected to the ground. Each of the gas supply lines 28a and 28b is provided with a valve and a flow rate adjuster 29a and 29b so that the flow rate and the gas pressure can be adjusted to desired values.

[0027] Above the vacuum chamber 20a, the permanent magnet 26 is installed, it is caused to rotate eccentrically around the axis of rotation 27 by a motor, by a magnetic field of 100 to 500 Gauss generated by the permanent magnets 26 10 ^{- 3} Torr stand,
It is configured so that high-density plasma can be generated and maintained even in a high vacuum of less than that. A large amount of ions are extracted from the high-density plasma generated in this way, irradiated onto the substrate 21 to be processed, and etching is performed.

Using the dry etching apparatus shown in FIG. 2, the silicon oxide film 2 was dry-etched as shown in FIG. 1 (c). As the etching gas,
A mixed gas of CHF ₃ gas and CO gas was used. CHF
Flow rate of ₃ gas 45sccm, flow rate of CO gas 155sccm, power
2.6W / cm ² , Pressure 40mTorr, substrate temperature 50 ℃ to 50 ℃
Etching was performed by changing the temperature to 0 ° C. At this time, the substrate temperature was adjusted so that the temperature of the heater 25 was kept within + 20 ° C. from the set temperature in order to prevent the substrate temperature from rising due to plasma irradiation during etching.

FIG. 3 shows a scanning electron microscope (SEM) of the etching rate of the silicon oxide film 2, the selectivity to silicon, and the etching cross-sectional shape of the silicon oxide film 2 when etching is performed while changing the substrate temperature. It is a graph which shows the taper angle at the time of observing.

From the graph shown in FIG. 3, the taper angle is 80 ° when the substrate temperature is 50 ° C., the taper angle is 84 ° when the substrate temperature is 175 ° C., and the taper angle is 90 °, that is, the vertical shape when the substrate temperature is 270 ° C. It turns out that At a substrate temperature of 270 ° C. or higher, radicals in plasma accelerate etching of the silicon oxide film, resulting in undercuts under the polysilicon thin film mask. Therefore, the substrate temperature is preferably less than 270 ° C. The etching rate of the silicon oxide film decreases linearly as the substrate temperature rises. However, the etching rate of silicon is
From 0 ° C to around 500 ° C, it does not decrease so much, so that it is understood that the selection ratio to Si decreases almost linearly.

Then, as shown in FIG. 1D, the polysilicon thin film 3 was removed by down-flow etching using a mixed gas of CF ₄ gas and O ₂ gas as an etching gas. As a result, it is possible to process the silicon oxide film 2 with a high degree of accuracy from a tapered shape to a vertical shape.

For comparison, the resist was used as a mask to etch the silicon oxide film 2 under exactly the same conditions as described above. As the substrate temperature was changed from 50 ° C. to 160 ° C., the taper angle was changed from 80 ° to 83 °. It was possible to approach the vertical. However, if the substrate temperature is 160
When the temperature is raised to ℃ or more, the resist pattern is deformed by heat, so that it is impossible to process a pattern having a desired pattern size with high accuracy.

Next, an example in which the silicon oxide film is etched without controlling the temperature of the substrate during etching will be described.
FIG. 4A is a graph showing a change in the substrate temperature with respect to the etching time when the substrate temperature is set to 200 ° C. before the etching and then the etching is started. The substrate temperature rises when exposed to plasma, and after about 7 minutes it is about 380 ° C.
Reached On the other hand, FIG. 4B is a graph showing the substrate temperature when the substrate temperature is controlled to be constant during etching.

The substrate setting temperature before the start of etching is 250
C., and it is maintained at 270.degree. C. during etching. The processed shapes of the silicon oxide film corresponding to the case where the substrate temperature is not controlled and the case where it is controlled are shown in FIG.
It shows in (b). In both FIGS. 5A and 5B, reference numeral 1
Is a silicon substrate, 2 is a silicon oxide film, and 3 is a polysilicon mask. Since the temperature control is not performed in FIG. 5A, the temperatures at the start and end of etching are different, and the processed shape reflects this. On the other hand, FIG. 5B shows the case where the substrate temperature is controlled, and since the temperature is almost constant (270 ° C.) from the start to the end of etching, the shape according to the temperature as shown in FIG. There is no change, and the silicon oxide film is processed vertically from the top to the bottom.

From the above, CHF ₃ gas flow rate 45scc
m, CO gas flow rate 155sccm, power 2.6W / cm ² , Pressure 40m
In the case of Torr, the silicon oxide film processing shape is changed from 88 ° to 9
When it was set to 0 °, it was found from the relationship between the substrate temperature and the taper angle in FIG. 3 that it was necessary to control the substrate temperature from 250 ° C. to 270 ° C. even during etching. The temperature range to be controlled depends of course on the etching gas and the etching conditions, but in order to vertically process the silicon oxide film, it is necessary to control the temperature during etching to be constant within a certain temperature range.

Next, dry etching of the silicon oxide film was performed using only CHF ₃ gas as an etching gas without adding CO gas. CHF ₃ gas flow rate is 200scc
m, other conditions are exactly the same as above, power 2.6
W / cm ² , Pressure 40mTorr, substrate temperature 50 ℃ to 500 ℃
The etching was performed by changing the temperature.

As a result, in the case of CHF ₃ gas alone, 5
The taper angle was 74 ° at 0 ° C, the taper angle was 84 ° at 125 ° C, and the taper angle was 90 ° at 170 ° C.
It was found that a vertical shape can be obtained at a lower temperature as compared with the case where CO gas is added to the CHF ₃ gas described above. However, at any temperature, the selection ratio to silicon was slightly lower than that when gas was added. Other pressure and power changes were tried. However, both of them only slightly affected the taper angle and the silicon selection ratio. From the above results, it is possible to obtain not only the vertical processed shape but also the vertical shape and the silicon selection ratio 20.
In order to satisfy both of the above, it was found that an increase in substrate temperature and an additive gas for improving the selection ratio with respect to silicon are necessary.

Gases containing H ₂ , O ₂ , and C and H in addition to CO were effective as the additive gas for increasing the selection ratio to silicon. It was confirmed that the vertical shape of the silicon oxide film was obtained by raising the substrate temperature with any of these gases, and that it had the same effect as CO.

The main etching gas for the silicon oxide film is not limited to CHF ₃ , but a gas containing C, F, preferably a gas containing C, H, F, the silicon oxide film processing characteristics are The same as in the case of CHF ₃ . Fluorocarbon precipitates generated when the gas containing C, H, and F is dissociated adhere to the side wall of the silicon oxide film to be processed, and protect the side wall of the silicon oxide film, whereby the silicon oxide film is tapered. Is processed. Therefore, in the method of the present invention, in order to prevent the fluorocarbon from adhering to the side wall, the substrate is heated to a high temperature and etched to obtain a vertical shape. The degree of polymerization of the fluorocarbon attached to the side wall depends on the type of the main etching gas, and in the case of fluorocarbon having a high degree of polymerization, the adhesion cannot be prevented unless the substrate is heated to a higher temperature. Therefore, the temperature at which a vertical shape can be obtained differs depending on the type of main etching gas, and in general, the use of a gas having a high degree of polymerization requires a higher temperature to obtain a vertical shape.

As described above, high-temperature etching is required for vertical processing of the silicon oxide film, and in the method of the present invention, a heat resistant mask is used as an etching mask therefor. The heat-resistant mask is not particularly limited to a silicon mask as long as it can withstand high temperatures, and a Si nitride film, a Si carbide film, a metal film, a metal oxide film, a metal nitride film, a boron nitride film, and these A film containing two or more kinds may be used. Further, if the temperature of the high temperature etching is less than 160 ° C., an ultraviolet curable resist can be used.

[0041]

As described above, according to the method of the present invention, since the heat-resistant thin film is used as the mask pattern during the etching of the silicon oxide film, 160 ° C. or higher, which cannot be achieved by the conventional photoresist mask. It is possible to etch the silicon oxide film at the same time, and as a result, it has a vertical silicon oxide film processing shape and a selectivity ratio to silicon of 2
It has become possible to achieve zero or more. Therefore, a finer pattern can be processed with high accuracy in the semiconductor integrated circuit manufacturing process.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a pattern forming process according to an embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of an etching apparatus used in the process shown in FIG.

FIG. 3 shows a taper angle when the substrate temperature is changed,
FIG. 4 is a characteristic diagram showing the relationship between etching rate and etching selection ratio.

FIG. 4 is a characteristic diagram showing a temperature change during etching when the substrate temperature is not controlled and when the substrate temperature is controlled.

FIG. 5 is a cross-sectional view showing a difference in shape of a silicon oxide film obtained when the substrate temperature is not controlled and when the substrate temperature is controlled.

[Explanation of symbols]

1 ... Silicon substrate, 2 ... Silicon oxide film, 3 ... Polysilicon thin film, 4 ... Photoresist.

Claims (2)

[Claims] 1. A step of forming a heat-resistant thin film pattern on a substrate to be processed having a silicon oxide film formed on the surface thereof, and a gas containing C atoms and F atoms in a reaction region containing the substrate to be processed, Or introducing a mixed gas of a gas containing C atoms and F atoms and a gas selected from the group consisting of CO, H ₂ , O ₂ and gases consisting of C atoms and H atoms, and causing discharge. A step of anisotropically etching the silicon oxide film using the heat-resistant thin film pattern as a mask while forming plasma and holding the substrate to be processed at a predetermined temperature of 120 ° C. or above substantially constant. A method for manufacturing a semiconductor device, comprising: 2. The heat-resistant thin film pattern is made of Si, Si
Nitride, Si carbide, metal, metal oxide, metal nitride,
A method for manufacturing a semiconductor device selected from the group consisting of boron nitride and an ultraviolet curable resist.