JP2874263B2 - Etching method of film to be etched composed of silicon compound - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for etching a film to be etched made of a silicon compound.

[Summary of the Invention] The present invention relates to a method for anisotropically etching a film to be etched made of a silicon compound such as silicon oxide (SiO ₂ ) formed on a substrate such as a silicon (Si) substrate. At least immediately before the substrate to be etched is exposed by etching the film to be etched, C and H are added to the etching gas selected from C _X F _{2X + 2} and C _X F _2X (an integer of X ≧ 2). After etching the film to be etched by adding a gas containing, or forming a thin film for etching on the film to be etched by irradiating a downflow plasma comprising a gas containing NF ₃ and NH ₃ , for example, Irradiating short wavelength light such as laser light to sublimate the etching thin film and etch the film to be etched by chemical reaction with components in the etching thin film. Without causing an impact of ions, anisotropic etching by chemical methods, by etching the film to be etched, without causing a trouble in an etching rate and to Si selectivity ratio,
The substrate damage can be reduced to such an extent that it does not hinder practical use.

[Prior art] In the etching of ULSI, VLSI, etc. manufacturing processes, as the diameter of a substrate increases and the design rules become finer, the equipment must be changed from a batch type to a uniform one in the processing surface of the substrate. It is changing to a leaf type. In this case, in order to maintain the same productivity (throughput) as that of the batch type, the etching rate must be increased by the small number of processings at one time, and a higher density plasma is formed than in the conventional RIE. As means, a microwave plasma etching apparatus and a magnetron RIE apparatus using an ECR discharge have been developed and put into practical use. For example, an SiO ₂ film is formed as a film to be etched made of a silicon compound on a substrate such as a silicon substrate, and the above magnetron RIE apparatus supplies 46 _{SCCM of a} high-order Freon gas of C ₃ F ₈ as a raw material gas. Etching was performed with the pressure set to 2 Pa. As shown in FIG. 2, when the power density was increased, the etching rate was increased. Here, the SiO ₂ film to be etched is etched until the underlying substrate is exposed, C and F polymer deposits are removed, and the substrate is excited by irradiating the substrate with an Ar laser to generate a heat wave. The substrate was irradiated with a He laser, and the reflectance of the He laser was examined to measure the damage on the substrate surface (substrate damage). The thermal wave signal (Thermal Wave Signa) shown in FIG.
l) got. This thermal wave signal is
-Measured by the Wave Inc. THERMA-PROBE TP-2000 system, indicating about 25 silicon substrates that have not been refined and have not undergone any subsequent processing. I have. From FIG. 2, it can be seen that in the magnetron RIE using C ₃ F ₈ gas, the power density was increased to increase the etching rate, and the power density was 1 W
It was found that when it was at least / cm ² , the thermal wave signal was at least 100, which caused substrate damage that could not be put to practical use.

Further, in the above magnetron RIE, when CHF ₃ gas is used as a source gas, the F radical is too much, and the selectivity with respect to the silicon substrate (to Si selectivity) is low.
The amount of CFx ⁺ ions was too small to obtain an etching rate suitable for the batch method.

Furthermore, in the magnetron RIE, as a source gas, CHF ₃ gas was added to C ₂ H ₄ gas, thermal Wave signals and to Si selectivity to supply the amount of C ₂ H ₄ gas (Si
O ₂ / Si selectivity), the results shown in FIG. 6 were obtained. From this Figure 6, the addition of deposition gas into CHF ₃ gas comprising C ₂ H _4, although it is possible to obtain a high-to-Si selective ratio, increase the thermal Wave signal 100 or more which corresponds to the substrate damage You can see that it is doing. On the other hand, when the substrate exposed from the SiO ₂ film by this etching method was observed with a transmission electron microscope, as shown in FIG. 7, a high-density defect layer was formed in a range of 40 nm from the substrate surface.

[Problems to be Solved by the Invention] In the various magnetron RIEs described above, when the etching of the film to be etched proceeds and the substrate is exposed, the substrate is damaged by ion bombardment. The surface of the diffusion layer formed on the substrate to be removed is removed to a depth at which the substrate is damaged. However, as design rules have become more refined,
Since the depth of the diffusion layer becomes shallow, anisotropic etching capable of preventing substrate damage without affecting the etching rate and the selectivity to Si is desired.

[Means for Solving the Problems] Accordingly, a first invention is a method for anisotropically etching a silicon compound-based film formed on a substrate, comprising: C _X F _{2X + 2} , C _X F _2X A first gas containing at least one selected from (X ≧ 2) is used to etch the film to be etched until immediately before the substrate is exposed;
The remainder of the film to be etched is etched by a second gas obtained by adding a gas containing at least C and H in molecules to the first gas.

According to a second aspect of the present invention, there is provided a method for anisotropically etching a silicon compound-based film formed on a substrate, wherein the thin film to be etched is irradiated with downflow plasma comprising a gas containing NF ₃ and NH _3. And a second step of sublimating the etching thin film by irradiating light to the etching thin film formed in the first step and etching the film to be etched.

[Operation] At least immediately before the etching of the film to be etched proceeds and the substrate is exposed from the film to be etched,
The film to be etched is etched at a low power density under the addition of a gas containing C and H, which has an etching property for the film to be etched and has a deposition property for the substrate, or By irradiating the thin film for etching formed in the process with short-wavelength light such as a laser to sublimate the thin film for etching and etching the film to be etched with the components in the thin film for etching sublimating,
Without affecting the etching rate and the selectivity to Si,
The film to be etched is etched by anisotropic etching with very little ion bombardment on the substrate to expose the substrate.

Example 1 Example 1 (corresponds to an example of the first invention.
First, as shown in FIG. 1A, an SiO ₂ film as a film to be etched made of a silicon compound is formed on the entire surface of a substrate 1 such as a silicon substrate on which a diffusion layer 2 is formed. An opening 3 is formed on the film 3 to be etched by photolithography at a portion corresponding to the diffusion layer 2 of the substrate 1.
A resist pattern 4 having 4a is formed.

Next, the first step etching and the second step etching are performed by magnetron RIE.

In the first etching step, C _X F _{2X + 2} , C _X F
_The power density is set to 1.3 W / cm ² or more using a high-order fluorocarbon gas as the first gas containing at least one selected from _2X (an integer of X ≧ 2) as shown in FIG. 1 (B). Then, using the resist pattern 4 as a mask, the film 3 to be etched is etched until just before the diffusion layer 2 of the substrate 1 is exposed, thereby forming a hole 5 in the film 3 to be etched. More specifically, in the etching of the first step, the thickness of the film 3 to be etched is, for example, 5000 ° while the variation of the etching depth ± 3 to 5% is taken into consideration.
Holes 5 having a depth of 90-98% were formed. Specific conditions for etching of the first step, the raw material gas; was 100G (on the substrate _{1); C 3 F 8 46} SCCM Pressure: 2 Pa Power density; 2.76W / cm ² magnetic field. In the etching of the first step, as shown in FIG. 2, high-speed anisotropic etching is performed based on the source gas and the power density.

In the etching in the second step, while maintaining a load lock in the etching in the first step, a second gas obtained by adding a gas containing at least C and H in molecules to the first gas is used as a source gas. The power density was set to 1.3 W / cm ² or less, and as shown in FIG. 1 (C), a portion (remaining portion) 3a remaining at the bottom of the hole 5 of the film 3 to be etched was formed using the resist pattern 4 as a mask. Etching including over-etching is performed until the diffusion layer 2 is exposed to form a contact hole 6 in the film 3 to be etched. Specific conditions for the etching in the second step are as follows: source gas; C ₃ F ₈ / C ₂ H ₄ 46/7 _SCCM pressure; 2 Pa power density; 0.88 W / cm ² magnetic field; ).

Here, FIG. 2 is a measurement result showing the etching rate and the thermal wave signal with respect to the power density in the etching of the first step. FIG. 3 is a measurement result showing the thermal wave signal and the selectivity to Si with respect to the addition ratio of C ₂ H ₄ in the etching in the second step. FIG. 4 shows the results of observation of the substrate 1 exposed at the bottom of the contact hole 6 with a transmission electron microscope in the etching in the second step.

Considering the etching of the first step and the second step based on the measurement results of FIGS. 2, 3 and 4, the etching rate of the first step is 900 nm / min or more. In the etching of the second step, it is found that the selectivity to Si is 15 or more and the thermal wave signal corresponding to substrate damage is 90 or less. From FIG. 2, the power density is 0.88 to 1.33.
It can be seen that there is a portion where the tendency of the power density dependence with the thermal wave signal changes between W / cm ² . From FIG. 3, it can be seen that when the addition of C ₂ H ₄ gas is in the range of 1 to 15% of the total gas flow rate, the thermal wave signal is generated due to the etching property of SiO ₂ of C ₂ H ₄ gas and the deposition property of Si. It can be seen that only the selectivity with respect to Si is improved without causing an increase in the ratio. From FIG. 4, it can be confirmed that the in-plane uniformity of the substrate is ensured and the substrate is not damaged.

The source gas for the first step etching in the first embodiment is other than C ₃ F ₈ , for example, C ₂ F ₆ , C ₄ F ₈ , C ₄ F
A gas such as ₁₀ may be used. The additional gas used in the etching in the second step may be a gas other than C ₂ H ₄ , for example, a gas such as ethylene, acetylene, methane, ethane, or methanol. A system gas is preferable. Further, the film to be etched 3 is made of PSG, B
It can be applied to S, SOG or SiN.

Second Embodiment (corresponding to one embodiment of the second invention. Fifth Embodiment
First, as shown in FIG. 5A, an SiO2 film 3 as a film to be etched made of a silicon compound is formed on the entire surface of a substrate 1 such as a silicon substrate on which a diffusion layer 2 is formed. Then, an opening is formed on the portion of the substrate 1 corresponding to the diffusion layer 2 by photolithography on the film 3 to be etched.
After forming the resist pattern 4 having 4a, the substrate 1 including the resist pattern 4 and the film 3 to be etched is formed on the substrate 1.
In the first step of irradiating a down-flow plasma composed of a gas containing NF ₃ and NH ₃ with the oxidation blocked, (NH
₄ ) Form a thin film 10 to be etched of ₂ SiF ₆ .

Next, the etching thin film 10 formed in the first step is formed.
Then, in a second step of irradiating short-wavelength light 11 such as an excimer laser in a vacuum, the etching thin film 10 is heated to about 100 ° C. Then, the portion of the etching thin film 10 on the ragist pattern 4 is sublimated, and the portion of the etching thin film 10 on the etching target film 3 located at the bottom of the opening 4a is sublimated, and at the same time, SiO ₂ constituting the etching target film 3 is sublimated.
Is chemically etched to form a hole 12 in the film 3 to be etched using the resist pattern 4 as a mask (for example, the meganism of this etching is described in, for example, IEICE; SDM89-48;
See page 6,36. However, the etching in this reference is isotropic). In the second step, the entire surface of the etching thin film 10 covering the hole wall surface of the opening 4a of the resist pattern 4 does not sufficiently rise to the sublimation temperature. The side portion remains as the side wall 13.

By performing the first step again, the etching thin film 10 of (NH ₄ ) ₂ SiF ₆ was formed on the resist pattern 4, the sidewalls 13, and the film 3 to be etched at the bottom of the hole 12. After that, by performing the second step, the etching thin film 10 is sublimated and the film 3 to be etched is chemically etched to form a hole 12A in the film 3 to be etched which is deeper than the previous time. The first and second steps are alternately performed until the diffusion layer 2 of the substrate 1 is exposed, so that the contact hole 6 is formed in the film 3 to be etched.
(See FIG. 1C). Also in the second step, the entire portion of the etching thin film 1 covering the side wall 13 and the hole wall surface of the hole 12 does not sufficiently rise to the sublimation temperature. The part of the hole 12 with the hole wall side is the side wall 14.
Will be left. Therefore, the first step and the second step
The etching in which the process and the process are alternately performed is anisotropic etching, and furthermore, the etching thin film 10 is heated and sublimated, and at the same time, reacts chemically with SiO ₂ but does not react with Si of the substrate 1. Therefore, even if the etching of the film-to-be-etched 3 proceeds and the diffusion layer 2 of the substrate 1 is exposed, substrate damage can be prevented.

In the second embodiment, since the irradiation light 11 in the second step is performed by an excimer laser, the time of alternately repeating irradiation and stop of the excimer laser is controlled, and the first step is performed during the stop. The etching thin film 10 can also be formed.

The film 3 to be etched in the second embodiment is
It may be one containing impurities such as PSG and BSG. In addition, irradiation light 11
Is a laser other than an excimer laser or a deuterium lamp,
It can be applied to short wavelength light such as a xenon mercury lamp and a high pressure mercury lamp. Further, until just before the substrate 1 is exposed, etching mainly with high-speed anisotropy as in the first embodiment is performed, and then the remaining portion at the bottom of the hole 5 of the film 3 to be etched shown in FIG. 3a, the first step and the second step can be performed alternately.

[Effects of the Invention] As described above, according to the present invention, at least immediately before the substrate is exposed from the film to be etched, the substrate is exposed by performing anisotropic etching with very little ion bombardment on the substrate. Therefore, damage to the substrate can be prevented without affecting the etching rate and the selectivity to Si. In addition, the substrate damage removal processing on the substrate surface after the completion of the etching can be omitted, and the productivity can be improved.

[Brief description of the drawings]

1 (A), 1 (B) and 1 (C) are process diagrams of a first embodiment corresponding to the first invention, and FIG. 2 is a graph showing power density in a first step of etching of the first embodiment. FIG. 3 is a characteristic diagram showing the measurement results of the etching rate of SiO ₂ and the thermal wave signal, and FIG. 3 shows the relationship between the thermal wave signal and the selectivity to Si with respect to the addition ratio of the additive gas in the etching in the second step of the first embodiment. FIG. 4 is a characteristic diagram showing measurement results, FIG. 4 is a measurement result diagram obtained by faithfully tracing a transmission electron micrograph of the substrate after etching in the first embodiment, and FIGS. 5 (A), (B), (C), and FIG. (D) is a process diagram of a second embodiment corresponding to the second invention, and FIG. 6 is an additional gas in a magnetron RIE using a gas obtained by adding C ₂ H ₄ gas to CHF ₃ gas as a conventional source gas. Thermal sig for percentage of Fig. 7 is a characteristic diagram showing the measurement results of the null and the selectivity to Si. Fig. 7 is a faithful trace of a transmission electron micrograph of a substrate etched by magnetron RIE using the same source gas as CHF ₃ / C ₂ H _4. It is the measurement result figure which performed. DESCRIPTION OF SYMBOLS 1 ... Substrate, 3 ... Etched film, 4 ... Resist pattern, 5, 12, 12A ... Hole, 6 ... Contact hole, 10
…… etching thin film, 11… laser light (short wavelength light or irradiation light), 13,14 …… side wall.

Claims (2)

(57) [Claims] In a method for anisotropically etching a silicon compound-based film formed on a substrate, at least one selected from C _X F _{2X + 2} and C _X F _2X (X ≧ 2). The film to be etched is etched with a first gas containing one kind until just before the substrate is exposed. Next, a second gas obtained by adding a gas containing at least C and H in molecules to the first gas is used. A method for etching a film to be etched comprising a silicon compound, comprising etching the remaining portion of the film to be etched. 2. A method for anisotropically etching a silicon compound-based film to be etched formed on a substrate, comprising: irradiating a thin film to be etched by irradiation with a downflow plasma comprising a gas containing NF ₃ and NH _3. The first step of forming and the second step of sublimating the thin film for etching by irradiating light to the thin film for etching formed in the first step and etching the film to be etched are performed alternately. A method of etching a film to be etched comprising a silicon compound.