JPH03276626A - Etching method for film to be etched composed of silicon compound system - Google Patents

Abstract

PURPOSE:To prevent the damage of a substrate without deteriorating etching rate and selectivity for Si, by a method wherein, just before etching is progressed and the substrate is exposed from a film to be etched, gas which has etching capability for a film to be etched and deposition capability for the substrate, and contains C and H is added, and etching is performed in this state. CONSTITUTION:Higher order Flon gas as first gas which contains at least one kind selected out of CxF2x+2CxF2x (x is integer larger than or equal to 2) is used as material gas. A resist pattern 4 is used as a mask. Thus a film 3 to be etched is etched just before a diffusion layer 2 of a substrate l is exposed, thereby forming a hole 5 in the film 3. Next, second gas wherein gas containing C and H in molecules is added to the first gas is used as material gas. The resist pattern 4 is used as a mask. Thus the residual part 3a in the bottom part of a hole 5 of the film 3 is subjected to etching containing over-etching until the diffusion layer of the substrate 1 is exposed, thereby forming a contact hole 6 in the film 3 to be etched.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for etching a film to be etched made of a silicon compound.

F. Summary of the Invention] The present invention provides a method for anisotropically etching a film to be etched made of a silicon compound such as silicon oxide (Stow) formed on a substrate such as a silicon (Sl) substrate, at least Immediately before the film to be etched is etched and the underlying substrate is exposed, CHF t
The film to be etched is etched by adding a gas containing C and 4 in the molecule to an etching gas selected from x"t+ CHF e- (an integer of
After a thin film for etching is formed on the film to be etched by irradiation with downflow plasma consisting of a gas containing Ps and NHs, the thin film for etching is irradiated with short wavelength light such as laser light to form the thin film for etching. Etching the film to be etched by anisotropic etching using a chemical method without causing ion bombardment, such as sublimation and etching by chemical reaction with components in the etching thin film. This makes it possible to reduce damage to the substrate to a practically acceptable level without causing problems in etching speed and selectivity to Si.

[Conventional technology]

In etching for manufacturing processes such as ULSI and VLST, as substrates become larger in diameter and design rules become finer, uniformity within the substrate processing surface is not achieved, and equipment changes from a batch type to a single wafer type. It's coming. In this case, in order to maintain the same productivity (throughput) as the batch method, the etching speed must be increased because the number of sheets processed at one time is small, and reactive ion beam etching (RIBE) is used.
has been adopted. For example, a raw material gas is excited by microwaves from a magnetron to generate plasma, and a magnetic field is applied to this plasma, causing the highly dense reactive gas ions (hereinafter simply referred to as ions) in the plasma to be exposed. This is a method of irradiating the etched film by increasing the power density to the magnetron and increasing the incident energy of the ions, thereby increasing the etching speed. Specifically, a 5iOy film is formed on a substrate such as a silicon substrate as a film to be etched made of a silicon compound, and this is subjected to reactive ion beam etching (hereinafter simply referred to simply as magnetron RIE) using the interaction of microwaves and a magnetic field. ), 4611 CCN of C8F, a high-order CFC gas, was supplied as the raw material gas, and etching was performed with the pressure set at 2 Pa. As shown in Figure 2, as the power density was increased, the etching speed also increased. The characteristics were shown. Here, the film to be etched, which is a SiO* film, is etched until the underlying substrate is exposed, and after removing the deposits of C and F-based polymers, the substrate is irradiated with an Ar laser to excite it, and a heat wave is generated. The damage to the substrate surface (substrate damage) was measured by irradiating a He laser onto the substrate and examining the reflectance of the He laser.
e Signal) was obtained. This thermal unibu signal is produced by Therma-Wave Inc.'s THER
The value measured by the MAPROBE TP-2000 system is about 25 for a silicon substrate that has not been subjected to any subsequent processes after purification, and a value of 100 or less is considered acceptable for use as a semiconductor device. From this figure 2, it can be seen that in magnetron RIE using C5Fs gas, when the power density is increased to increase the etching speed and the power density exceeds IW/cm, the thermal unibe signal exceeds 100, making it practical. It was found that this caused irreversible damage to the substrate.

In addition, in the above magnetron RIE, when CHFa gas is used as the raw material gas, there are too many F radicals, and the selectivity to the silicon substrate (selectivity to Si) is low.
Moreover, the amount of CFx' ions was too small to achieve an etching rate suitable for a batch process.

Furthermore, in the above magnetron RIE, Ct l-(, gas was added to the CHF s gas as the raw material gas, and the thermal uniform signal and the selectivity to Si (SiOt/S+ selectivity) with respect to the supply amount of Ct H- gas were determined. The results obtained are shown in Fig. 6.From this Fig. 6, CHF and CtH were added to the gas.

It can be seen that although a high selectivity to Si can be obtained by adding a deposition gas, the thermal unive signal corresponding to substrate damage increases to 100 or more. On the other hand, when the substrate exposed from the stow film by this etching method was observed using a transmission electron microscope, as shown in FIG. 7, a high-density defect layer was formed within a range of 40 nm from the substrate surface.

[Problems to be Solved by the Invention] In the various magnetron RIE methods described above, when the etching of the film to be etched progresses and the substrate is exposed, the substrate is damaged by ion bombardment. The surface of the diffusion layer formed on the substrate is removed by the depth of the substrate damage.

However, as design rules become increasingly finer, the depth of the diffusion layer becomes shallower, so anisotropic etching that can prevent substrate damage without compromising etching speed and selectivity to Si is desired. There is.

[Means for Solving the Problems] Accordingly, the first invention provides a method for anisotropically etching a film to be etched made of a silicon compound system formed on a substrate-L. ,.

The film to be etched is etched with a first gas containing at least one type selected from (an integer of X≧2) until just before the substrate is exposed, and then the first gas contains at least C and H in its molecules. The remaining portion of the film to be etched is etched using the second gas added thereto.

A second invention is a method for anisotropically etching a film to be etched made of a silicon compound formed on a substrate, in which the film to be etched is irradiated with downflow plasma made of a gas containing N Fs and N Hs. A first step of forming a thin pattern and a second step of irradiating the etching thin film formed in the first step with light to sublimate the etching thin film and etching the film to be etched are performed alternately.

[Effect: At least as the etching of the film to be etched progresses,
Immediately before the substrate is exposed from the film to be etched, the film is exposed at low power density while adding a gas containing C and 11, which has an etching property for the film to be etched and a depositing property for the substrate. Either the etching film is etched, or the etching film formed in the first step is irradiated with short wavelength light such as a laser to sublimate the etching film, and the etching film is covered with components in the sublimated etching film. By etching the etching film, the etching speed and selectivity to S1 are not affected.
The film to be etched is etched to expose the substrate using anisotropic etching that causes very little ion bombardment on the substrate.

[Example code] First embodiment (corresponds to one embodiment of the first invention).

(See Figures 1 to 4) First, as shown in Figure 1(A), a film to be etched made of a silicon compound is coated over the entire surface of a substrate 1 such as a silicon substrate on which a diffusion layer 2 is formed. SiO2 film 3
A resist pattern 4 having an opening 4a in a portion of the substrate 1 corresponding to the diffusion layer 2 is formed on the film to be etched 3 by photolithography.

Next, by magnetron RIE, (1) first step etching and (2) second step etching are performed.

■In the first step of etching, CxF *x*t.

A high-order fluorocarbon gas, which is a first gas containing at least one selected from C, F, (an integer of As shown in Figure (B), using the resist pattern 4 as a mask, the film to be etched 3 is etched until just before the diffusion layer 2 of the substrate l is exposed, thereby forming a hole 5 in the film to be etched 3. Specifically, In this first step of etching, the etching target M3 is etched at a depth of 90% to 98% of the thickness of, for example, 5000 people, by taking into account ±3 to 5% variation in etching depth. The specific conditions for this first step etching were as follows: Source gas: C5Fs 46SCC11 Pressure: 2Pa Power density: 2.76W/cm' Magnetic field: 100G (on substrate 1) As shown in FIG. 2, this first step etching is a high-speed anisotropic etching in view of the raw material gas and power density.

■In the second step of etching, while maintaining a load lock in the first step of etching, a second gas obtained by adding a gas containing at least C and H in the molecule to the first gas is used as a raw material gas. , the power density is 1, 3
W/cm" or less, and as shown in FIG. 1(C), using the resist pattern 4 as a mask, the portion (remaining portion) 3a remaining at the bottom of the hole 5 of the II3 to be etched is etched into the diffusion layer 2 of the substrate 1. Contact holes 6 are formed in the film to be etched 3 by over-etching and chamber etching until exposed.The specific conditions for this second step etching are as follows: Source gas; C-F-/ CtH446/7SCCN pressure
Force: 2 Pa Power density: 2,76 W/cm'' Magnetic field: 100 G (on substrate 1).

Here, FIG. 2 shows the measurement results showing the etching speed and thermal unibe signal with respect to the power density in the first step etching.

FIG. 3 shows the measurement results showing the thermal uniform signal and the selectivity to Si with respect to the addition ratio of C2H4 in the second step of etching. FIG. 4 shows the results of observation using a transmission electron microscope of the substrate 1 exposed at the bottom of the contact hole 6 during the second step of etching.

Considering the etching in the first step and the second step based on the measurement results of FIGS. 2, 3, and 4FyJ, the etching rate in the first step is 900 nm/min or more, and the etching rate in the first step is 900 nm/min or more. It can be seen that in the two-step etching, the selectivity to Si is 15 or more, and the thermal unidirectional signal, which corresponds to substrate damage, is 90 or less. Also, the 21st i! ! From 7 onwards,
It can be seen that when the power density is between 0.88 and 1.33 W/cm'', the tendency of the dependence of the etching rate and the thermal unibe signal on the power density changes.

From Figure 3, it can be seen that the addition of Ct H4 gas is 1% of the total gas flow rate.
It can be seen that in the range of ~15%, only the selectivity to Si is improved without causing an increase in the thermal uniform signal due to the properties of C, H, and gas, which are etched in 5iO1 and devoted in Si.

From FIG. 4, it can be confirmed that in-plane uniformity of the substrate is ensured and that there is no damage to the substrate.

Note that the source gas for etching in the first step in this first embodiment is other than C and F, such as CrFa,
Gases such as C4F a and CaF to may also be used. In addition, the additive gas in the 12-step etching was CtH
Gases other than 4, such as ethylene, acetylene, methane, ethane, and methanol, are also possible, and unsaturated gases containing multiple bonds between carbon atoms are particularly preferred. Furthermore, the film to be etched 3 may be made of PSG, BSG, SOG or SiN.

Second embodiment (corresponds to an embodiment of the second invention).

(See FIG. 5) First, as shown in FIG. 5(A), a 5i02 pattern 3 as a film to be etched made of a silicon compound is spread over the entire surface of a substrate l such as a silicon substrate on which a diffusion layer 2 is formed.
A resist pattern 4 having an opening D4a in a portion corresponding to the diffusion layer 2 of the substrate l is formed on the film to be etched 3 using a photolithography technique, and then this resist pattern 4 and the film to be etched are formed. 3 and a substrate l containing
(NH4)? in a first step of irradiating downflow plasma consisting of a gas containing NF and NH while blocking oxidation. A thin film 10 to be etched of S+Fs is formed.

Next, the thin IR for etching formed in the first step of Section 2.
In a vacuum, a short wavelength light I such as an excimer laser is applied to the IO.
In the second step of irradiating with f, the etching thin film lO is heated to about 100°C. Then, the etching thin film 10
At the same time, the portion on the resist pattern 4 sublimates, and the portion on the film to be etched 3 located at the bottom of the opening 4a of the etching thin film IO sublimates, and at the same time, the film to be etched 3
5 ift constituting the etched film 3, and a hole is formed in the etched film 3 using the resist pattern 4 as a mask! 2
(This etching mechanism is, for example,
See Signal Techniques, SDM89-48, page 36.36.

However, the etching in this reference is isotropic).

In this second step, the entire portion of the resist pattern 4 of the etching thin film IO that covers the hole wall surface of the opening 4a does not rise sufficiently to the sublimation temperature, so the surface side sublimes, but the hole wall surface of the opening 4a The side part is a side wall! It remains as 3.

Then, by performing the first step again, an etching thin film 10 of (NH,)tS + F@ is formed on the Lenost pattern 4, the sidewall 13, and the film to be etched 3 at the bottom of the hole 12. After the formation, a second step is performed to sublimate the thin film for etching IO and chemically etch the film to be etched 3 to form holes 12A in the film to be etched 3 which are deeper than the previous one. In this way, the first step and the second step are performed alternately until the diffusion layer 2 of the substrate I is exposed, and the etching target $1 is
A contact hole 6 (see FIG. 1(C)) is formed in 3. Even in this second step, the entire portion of the etching thin film 10 that covers the sidewall 13 and the hole wall surface of the hole 12 does not rise sufficiently to the sublimation temperature, so the surface side sublimes, but the sidewall 13 side A portion of the hole 12 on the hole wall side remains as a sidewall 14. Therefore, the etching in which the first step and the second step are performed alternately is anisotropic etching, and at the same time as the etching thin film IO is heated and sublimated, the SI
Since this etching is selective to Si in that it chemically reacts with O* but does not react with Si of the substrate 1, etching of the film to be etched 3 progresses and the diffusion layer 2 of the substrate 1 is etched.
Even if exposed, damage to the substrate can be prevented.

In this second embodiment, since the irradiation light 11 in the second step is performed using an excimer laser, the time between the alternating irradiation and stop of the excimer laser is controlled, and the first step is performed during the stop. It is also possible to form a thin film IO for etching.

Note that the film to be etched 3 in this second embodiment is P
It may also contain impurities such as SG and BSG. Further, the irradiation light 11 is a laser other than an excimer laser, a deuterium lamp, or a xenon mercury lamp.

It is also applicable to short wavelength light such as a high pressure mercury lamp.

Furthermore, just before the substrate l is exposed, etching is performed mainly using high-speed anisotropy as in the first embodiment, and then the first etching process is performed.
Remaining portion 3 of the bottom of the hole 5 of the etching target I13 shown in Figure (B)
In a, it is also possible to perform the first step and the second step 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, anisotropic etching is performed with very little ion bombardment to the substrate to expose the substrate. Therefore, damage to the substrate can be prevented without affecting the etching rate and selectivity to Si. Moreover, the process of removing damage to the substrate surface after etching is completed can be omitted, and productivity can be improved.

[Brief explanation of the drawing]

Figures 1 (A), (B), and (C) are process diagrams of the first embodiment corresponding to the first invention, and Figure 2 shows the power density in the first step of etching of the first embodiment. 5id
Figure 3 is a characteristic diagram showing the measurement results of the etching speed and thermal unibu signal of Example 3. FIG. 4 is a characteristic diagram showing the measurement results of the same. FIG. 4 is a measurement result diagram faithfully tracing a transmission electron micrograph of the substrate after etching in the first embodiment. FIGS. 5(A) and (B). (C) and (D) are process diagrams of the second embodiment corresponding to the second invention, and FIG. 6 is a conventional magnetron R using CHF as the raw material gas and Ct H4 gas added to the gas.
A characteristic diagram showing the measurement results of thermal uniform signal and selectivity to St with respect to the ratio of added gas in IE, and Figure 7 shows the same conventional etching with magnetron RrE using the raw material gas of CHF s/C*H-. It is a measurement result diagram that faithfully traces a transmission electron micrograph of a substrate. 1... Substrate, 3... Film to be etched, 4... Resist pattern, 5, 12.12A... L6... Contact hole, 10... Thin pattern for etching, 11...
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Claims (2)

[Claims] (1) In a method of anisotropically etching a film to be etched made of a silicon compound formed on a substrate, C_xF_2_x_+_2, C_xF_2_x (X≧2
etching the film to be etched until just before the substrate is exposed using a first gas containing at least one type selected from (an integer of A method for etching a film to be etched made of a silicon compound, characterized in that the remaining part of the film to be etched is etched with a second gas consisting of: (2) In a method of anisotropically etching a film to be etched made of a silicon compound formed on a substrate, the first step is to form a thin film to be etched by irradiation with downflow plasma made of a gas containing NF_3 and NH_3. and a second step in which the etching thin film formed in the first step is irradiated with light to sublimate the etching thin film and etching the etched film, the silicon compound is characterized in that the steps are alternately carried out. A method for etching a film to be etched consisting of a system.