JPH088244B2 - Dry etching method - Google Patents

Description

The present invention relates to a dry etching method in which a thin film on a substrate is tapered and selectively etched, and in particular, the etching gas pressure and the substrate temperature are controlled. The present invention relates to an optimized dry etching method.

(Prior Art) Conventionally, a reactive ion etching method has been used for etching an electrode material such as polycrystalline silicon or a silicon oxide film. In the reactive ion etching method, a substrate to be processed (for example, a substrate on which a thin film to be etched is formed) is placed in a vacuum container provided with a pair of parallel plate electrodes, a reactive gas is introduced, and then high frequency power is applied to the substrate. This is a method in which a gas is discharged and the substrate to be processed is etched using the gas plasma generated by this discharge.

In addition to this reactive ion etching method, there are plasma etching ECR type dry etching method, ion beam etching method, photo-excited etching method, etc., but these etching methods also use reactive gas activated on the substrate to be processed in the vacuum container. Etching is performed by causing ions to chemically or physically act, and in this respect, it may be considered to be similar to the reactive ion etching method.

As a reactive gas for etching the silicon oxide film
Those containing carbon such as C ₂ F ₆ , CF ₄ and CHF ₃ are used.

When the underlying layer is Si and SiO ₂ is etched by CF ₄ + H ₂ gas, CF ₃ generated by electric discharge is adsorbed on Si.
This CF ₃ is pulled out of F by H, and CF _x (x = 1,2,
A polymerized film consisting of 3) is produced. On the other hand, CF ₃ is similarly adsorbed on the SiO ₂ surface. This CF ₃ is C and F due to ion bombardment.
And F reacts with Si to become SiF ₄ ↑, and the remaining C reacts with O remaining on the surface to become CO ↑. As a result, unlike Si, etching proceeds rapidly. At that time, the reaction proceeds only on the surface that receives the ion bombardment,
Etching does not occur on the side wall and the shape becomes vertical.

The etching of the silicon oxide film is used to form contact holes and via holes, but with the miniaturization of patterns, holes with small openings and large aspect ratios are formed. As a result, the metal film of Al or the like is buried in the contact hole in a hole having a vertical cross-section and a large aspect ratio, resulting in poor step coverage of the Al film. Then, when the opening becomes about 1 μm, there is a problem that Al is not connected in the hole.

Further, when forming a via hole, aluminum oxide or aluminum fluoride generated by etching is thickly deposited on a vertical side wall and cannot be removed in a subsequent resist removing step or the like. Since this deposit contains fluorine, it becomes a cause of Al corrosion embedded in the via hole, and in the selective burying of W into the via hole, not only the underlying Al but also the sidewall deposits grow, and the selectivity is increased. There is a problem of collapse.

(Problems to be solved by the invention) As described above, conventionally, in dry etching of an oxide film such as a contact hole or a via hole, the cross-sectional shape of the etching sidewall becomes vertical, so that an Al film for a hole with a small frontage and a high aspect ratio is formed. In formation, there was a problem that step coverage was poor and the hole was interrupted, or that aluminum oxide or aluminum fluoride deposited on the side wall could not be removed. In order to solve these problems, the sidewalls of contact holes and via holes are tapered, and the frontage 1
In the case of μm, etching may be performed with a taper angle of about 80 degrees, but a method of etching with such a taper has not yet been put into practical use.

The present invention has been made in consideration of the above circumstances, and an object thereof is to be able to control an etching shape in a taper shape, to improve step coverage of a metal film or the like and to remove a sidewall deposit. It is to provide a dry etching method that can be easily performed.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, in the present invention, a reactive gas containing at least C, F and H elements in a reaction container accommodating a substrate to be treated. In the dry etching method of activating the gas and selectively etching the substrate to be processed (specifically, the thin film to be etched on the substrate), in the etching region of the thin film, the opening width is 1 and the thickness is t. At this time, the etching pressure P (Torr) and the substrate temperature T (° C.) are set within a region defined by the following conditions to perform etching.

T <80logP + 240 ... T ≧ 80logP + 160 ... Here, the expression shows the condition that the taper angle of the side wall is 70 degrees or more, the expression shows the condition that the taper angle is smaller than 90 degrees, and the expression shows the condition that etching can be performed until the base is reached by taper etching.

(Action) Reactive gas containing at least C, F and H, eg C
When HF ₃ gas is excited by discharge, CF ₃ having strong adsorptivity is generated and adsorbed on the substrate surface. This adsorbed amount increases as the substrate is cooled and is deposited thickly on the substrate surface. The reaction proceeds on the etching thin film (for example, SiO ₂ ) subjected to ion bombardment, and the fluorocarbon film is not formed. However, the reaction does not proceed on the side wall where there is no ion bombardment, and the deposited fluorocarbon film serves as a mask, whereby the thin film such as SiO ₂ can be etched in a taper shape. To form a hole with a frontage of 0.8 μm and a depth of 1.2 μm, the taper angle must be 70 degrees or more. Etching can be performed.

The etching of the silicon oxide film after cooling the substrate is described in 1988 Applied Physics Autumn Meeting Proceedings P464-19a-K-1.
0, 1988 Autumn Meeting of Applied Physics Proceedings P463, 27P-L-6
And Japanese Patent Application Laid-Open No. 63-174322, the former two are descriptions outside the range of the relationship between temperature and pressure specified in the present invention, and the latter two are those using a gas containing no carbon. This is a description of etching a silicon oxide film. That is, none of the known examples describes the taper etching using the reactive gas containing C, F and H, let alone the optimum pressure P and temperature T for the taper etching.
The condition of is not even suggested.

(Examples) The details of the present invention will be described below with reference to illustrated examples.

FIG. 1 is a schematic configuration diagram showing a dry etching apparatus used in the method of one embodiment of the present invention. In the figure, 10 is a grounded container forming an etching chamber 11, and a cathode 20 is installed at the bottom of this container 10. High frequency power of 13.56 MHz is applied to the cathode 20 from a power supply 22 via a matching circuit 21. Further, the cathode 20 is cooled by a coolant through a cooling pipe 23, and this cooling pipe 23 is used as a lead for applying high frequency power. A copper plate 25 sandwiched between polyimide films 24 is attached on the cathode 20, and by applying a voltage of 4 kV from a power source 26 to the copper plate 25, the substrate 30 to be treated is electrostatically adsorbed on the cathode 20. It is supposed to be done.

Further, a reactive gas is introduced into the etching chamber 11 through the gas inlet 12, and the gas in the etching chamber 11 is exhausted.
Exhausted from 13. The anode facing the cathode 20 is formed by the upper wall of the etching chamber 10. A plurality of permanent magnets 14 and a drive mechanism 15 for the permanent magnets 14 are provided at the positions facing the back surface of the anode.
A magnetic field generator consisting of is installed to apply a magnetic field to the space facing the cathode 20 and the anode. 27 in the figure
Is a gas introducing tube for introducing heat into the back surface of the substrate 30 to be processed for heat conduction, 28 is an insulator for insulating the cathode 20 from the container 10, 29 is a copper plate 25 of the electrostatic chuck, and a cathode 20 shows an insulator for insulating 20 and.

This apparatus is a dry etching apparatus using magnetron discharge, but the method of the present invention is not limited to the apparatus configuration, and other apparatuses can be used. As an example of another device, FIGS. 2 and 3 are shown. The apparatus shown in FIG. 2 is a reaction vessel to which a magnetic field is applied by a magnetic field coil 47.
A microwave of 2.45 GHz generated by the magnetron 44 is introduced into the magnet 41 through the waveguide 45 and the quartz window 46 to excite the reactive gas by ECR discharge. 13.56 MH on the sample table 43
RF power of z is applied to control the ion irradiation energy on the wafer (sample) 42. Further, the sample cooling mechanism (not shown) cools the sample temperature. Also,
FIG. 3 shows that the sample 42 is irradiated with ions generated by exciting a reactive gas by using a Kauffman type ion gun 48. The sample temperature is controlled by a sample cooling mechanism (not shown).

Next, a dry etching method using the above apparatus will be described.

First, the temperature dependence of the etching rates of SiO ₂ and Si will be described with reference to FIG. Using the apparatus shown in FIG. 1, the flow rate of CHF ₃ gas was 50 sccm, the pressure was 40 mTorr, and the RF power was 450 W. At this time, the horizontal magnetic field strength on the substrate was 100 Gauss. In the figure, the vertical axis represents the etching rate and the horizontal axis represents the substrate temperature. The etching rate of the SiO ₂ film hardly changes with temperature. On the other hand, the etching rate of Si decreases with decreasing temperature.

As described above, the reason why the etching rate of Si changes is that the amount of CF _x adsorbed increases and the polymerized film of fluorocarbon becomes thicker as the substrate temperature decreases. On the other hand, Si
Since CF _x is rapidly removed by the reaction on O ₂ ,
The etching rate is almost independent of temperature.

The pressure dependence of the etching rate of the SiO ₂ film and Si will be described with reference to FIG. CHF ₃ flow rate 50sccm, RF power 450W, temperature 0
℃ was made. In the figure, the vertical axis represents the etching rate and the horizontal axis represents the pressure. The SiO ₂ etching rate does not depend on pressure, but the etching rate of Si decreases with increasing pressure. The cause is similar to the case of the temperature dependence described above. That is, when the pressure is increased, CF ₃ increases and the amount of adsorption on the surface increases.

Next, SiO ₂ actually etched by the method of this embodiment was used.
The cross-sectional shape of the film will be described with reference to FIG. First, a substrate to be processed as shown in FIG. 6 (a) is formed. That is, a CVD-SiO ₂ film 62 is formed on the underlying polysilicon film 61, a resist layer 63 is formed thereon, and the resist layer 63 is patterned by a normal exposure technique to open an opening. When this substrate to be processed was etched at a temperature of 120 ° C., FIG. 6 (b)
The SiO ₂ film 62 was vertically etched as shown in FIG. Further, when the etching was performed at a temperature of 30 ° C., the polymer film 64 was deposited on the etching side wall as shown in FIG. 6C, and as a result, the etching side wall was tapered.

The relationship between the magnetic field strength and the SiO ₂ etching rate will be described with reference to FIG. CHF ₃ 50sccm, RF power 900W, pressure 40mTor
It was r. It can be seen that the etching rate of SiO ₂ increases as the magnetic field strength increases, and that applying a magnetic field is effective in increasing the etching rate. The relationship between the magnetic field strength and the taper angle will be described with reference to FIG. When a substrate similar to that shown in FIG. 6 (a) was used, it was found that the taper angle does not depend on the magnetic field strength.

The relationship between temperature, pressure and taper angle will be described with reference to FIG. CHF _{3 was} 50 sccm, RF power was 900 W, and the same substrate as in FIG. 6 (a) was used. In the figure, the vertical axis represents the taper angle and the horizontal axis represents the temperature. The taper angle becomes closer to vertical when the temperature is raised, and becomes closer to vertical when the pressure is lowered. Further, the higher the pressure, the smaller the taper angle. This is because the amount of CF _x adsorbed increases due to the cooling of the temperature and the increase of the pressure, and a thick polymer film is formed on the surface. It should be noted that on the SiO ₂ surface, CF _x is decomposed by ion bombardment to produce F and become SiF ₄ ↑, and C reacts with the remaining O to become CO and the reaction proceeds rapidly, but polymerization occurs on the side wall without ion bombardment. The film remains, and this is used as a mask to etch SiO ₂ into a taper shape.

When forming a contact hole, for example, the frontage is 0.8μ
When forming a hole with a depth of 1.2 μm in m, the taper angle is 7
If it is not more than 0 degree, the hole will not be drilled down. Further, considering the miniaturization of the pattern, if the taper angle is too large, the opening width also becomes large, which is not desirable. Generally, the taper angle needs to be 70 degrees or more.

As a result of further studies based on the above-mentioned experimental data, the present inventors have found the relationship between the taper angle and the temperature and pressure. FIG. 10 is a diagram showing the relationship between the taper angle and the temperature and pressure. In the figure, the horizontal axis is the logarithm of the pressure P (Torr), and the vertical axis is the temperature T (° C). The upper straight line has a taper angle of 90 °, and the lower straight line has a taper angle of 70 °. From each straight line, the condition that the taper angle is 90 degrees is T
= 80logP + 240, and the condition that the taper angle is 70 ° is expressed as T = 80logP + 160. Then, if the etching is performed under the condition in the region between the upper straight line and the lower straight line, the SiO ₂ film can be etched in a taper shape of 70 to 90 degrees.

Further, depending on the relationship between the opening width and the film thickness, if the taper angle becomes small, etching may not be possible until the base is reached. As shown in FIG. 11, when the opening width (the length of the short side when the opening is not square) is l and the film thickness is t, if the opposite tapered sidewalls intersect on the underlying surface, the taper at this time is set. The angle θ is Becomes And if the taper angle becomes smaller than this,
The etching will not reach the underlying surface. Therefore,
The optimum condition for taper etching is T <80logP + 240 ... T ≧ 80logP + 160 ... Can be set to satisfy each. The tenth
The general formula of the straight line having the taper angle θ shown by the broken line in the figure is expressed as T = 80logP + α. In this formula, α is a function of θ, and α = 4θ−120 ... Becomes Therefore, good taper etching becomes possible by etching under the conditions defined by the formula.

Next, the effect of the method of this embodiment will be described with reference to the drawings. FIG. 12 shows a step in which an Al film 74 is sputtered in the contact hole 73 of the SiO ₂ film 72 formed on the Si substrate 71 to embed Al. FIG. 12 (a) shows an embedded shape of the Al film 74 in the contact hole 73 formed by the conventional etching method. Since the side wall of the contact hole 73 is vertical, the step coverage is poor and the contact between Al and Si cannot be made. FIG. 12B shows the embedding of the Al film 74 in the contact hole 73 formed by the above-described taper etching method. Since the contact hole 73 has a taper,
The step coverage of the Al film 74 is excellent.

Further, FIG. 13 shows the formation of via holes 83 in the SiO ₂ film 82 formed on the Al film 81. FIG. 13 (a) shows a via hole 83 formed by a conventional etching method. A thick deposit 84 remains on the vertical side wall and cannot be removed. FIG. 13B is a via hole 83 formed by the above-described taper etching method. The deposit 84 attached due to the taper of the side wall is ion-impacted and re-sputtered to be removed. Does not remain.

Thus, according to the present embodiment, in the etching of the silicon oxide film using the excited CHF ₃ gas, the contact hole having the tapered side wall is formed by etching the SiO ₂ film under the condition of the formula. be able to. Therefore, it is possible to easily remove the deposits on the sidewalls after etching, and it is possible to embed the metal film in the etched contact holes with good step coverage.

Next, another embodiment method of the present invention will be described. The method of this embodiment is to perform taper etching by two-step etching.

First, as shown in FIG. 14A, a resist 93 having an opening for forming a contact hole is formed on a SiO ₂ film 92 formed on a Si substrate 91. Next, as shown in FIG. 14B, the SiO ₂ film 92 is taper-etched halfway using the resist 93 as a mask. In this etching, only the above-mentioned conditions are required, and the conditions of and are not required.

Then, as shown in FIG. 14C, the SiO ₂ film 92 is taper-etched to the end using the resist 93 as a mask again. This etching may be performed under the condition that the taper angle is larger than that of the previous etching. For example, the substrate temperature is raised and etching is performed. Instead of raising the substrate temperature, the gas pressure may be lowered. The taper angle may be 90 degrees in the second etching.

The present invention is not limited to the above-mentioned embodiments. For example, the reactive gas introduced into the container is not limited to CHF ₃ , but any gas containing at least C, F and H elements can be used, and CH ₂ F ₂ or CF ₄ + H ₂ can be used. Is. In this case as well, the mechanism of forming the taper is the same as that of the embodiment, so the etching conditions are
, The range should satisfy the formula. The material to be etched is not limited to the silicon oxide film, but any material that can be etched with the above gas can be applied. Specifically, when applied to etching polysilicon, Cl ₂ + CHF ₃ , and when applied to Al etching, Cl ₂
+ BCl ₃ + CHF ₃ may be used. In addition, various modifications can be made without departing from the scope of the present invention.

[Effect of the Invention] As described in detail above, according to the present invention, a thin film on a substrate can be etched in a tapered shape, and the etching shape can be controlled. In addition, since the etching is performed in a taper shape, there is no deposit on the side wall, and further, the step coverage can be obtained by embedding the metal film in the etched groove.

[Brief description of drawings]

1 to 3 are schematic configuration diagrams showing a dry etching apparatus used for carrying out the method of the present invention, and FIGS. 4 to 4.
FIG. 13 is for explaining one embodiment method of the present invention.
4 is a characteristic diagram showing the relationship between the substrate temperature and the etching rate, FIG. 5 is a characteristic diagram showing the relationship between the gas pressure and the etching rate, and FIG. 6 is a sectional view showing the contact hole shape.
FIG. 7 is a characteristic diagram showing the relationship between the magnetic field strength and the etching rate, FIG. 8 is a characteristic diagram showing the relationship between the magnetic field strength and the taper angle, and FIG. 9 is a characteristic diagram showing the relationship between the substrate temperature and the taper angle. Fig. 10 is a characteristic diagram showing the relationship between the taper angle and gas pressure and substrate temperature, Fig. 11 is a schematic diagram for defining the taper angle, and Fig. 12 is a sectional view showing the Al-filled shape in the contact hole. , FIG. 13 is a sectional view showing the shape of a via hole, FIG.
The drawings are process cross-sectional views for explaining a method of another embodiment of the present invention. 61 ... Polysilicon film, 62,72,82,92 ... SiO ₂ film, 63,93 ... Resist, 64 ... Polymerized film, 71,91 ... Si substrate, 73 ... Contact hole, 74,81 ... Al film, 83 ... Beer hole, 84 ... Deposit.

Claims (4)

[Claims] 1. A substrate on which a thin film to be etched is formed is housed in a reaction vessel, and a reactive gas containing at least C, F and H elements is introduced into the vessel, and this gas is activated to form a substrate on the substrate. In the dry etching method of selectively etching the thin film, the gas pressure P (Torr) in the container and the substrate temperature T are defined when the opening width of the etching region of the thin film is l and the thickness is t.
(℃) is In addition, a dry etching method is characterized in that etching is performed within a region defined by the condition of T <80logP + 240. 2. The dry process according to claim 1, wherein the gas pressure P (Torr) in the container and the substrate temperature T (° C.) perform etching within a region defined by the condition of T ≧ 80logP + 160. Etching method. 3. A substrate on which a thin film to be etched is formed is housed in a reaction vessel, and a reactive gas containing at least C, F and H elements is introduced into the vessel, and this gas is activated to activate the gas on the substrate. In the dry etching method of selectively etching the thin film, the thin film is partially etched under the condition that the gas pressure P (Torr) in the container and the substrate temperature T (° C.) are T ₁ <80logP ₁ +240, and then
T ₂ > T ₁ , P ₂ = P ₁ , T ₂ = T ₁ , P ₂ <P ₁ , or T ₂ > T ₁ , P ₂ <P ₁
The dry etching method is characterized in that etching is performed to the end under the conditions of. 4. The dry etching method according to claim 1, wherein the thin film to be etched is a silicon oxide film, and CHF ₃ gas is used as the reactive gas.