JPS6129129A - Dry etching method - Google Patents

Abstract

PURPOSE:To anisotropically etch selectively a material to be etched by light emission by using a transparent mask material for a light as a mask layer, and opaquely treating the material for the light. CONSTITUTION:An SiO2 film 12 is accumulated on an Si substrate 11, no element-added polycrystalline Si film 13 is accumulated on the film, and an etching mask 14 is further formed on the film 13. The mask 14 is transparent for ultraviolet light. This sample is heated and annealed in oxygen gas atmosphere. Thus, since the mask 14 becomes opaque for the ultraviolet light, the light is emitted to etch it. The etching of the film 13 is proceeded only at the portion to which the light is emitted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an anisotropic dry etching method using photochemical reactions.

(Technical background of the invention and its problems) In recent years, integrated circuits have been becoming increasingly finer, and prototypes of ultra-LSIs with a minimum pattern size of 1 to 2 [μm] have recently been developed. Plasma etching technology is indispensable for microfabrication.As one of the plasma etching technologies, CF4
13.56 [MH
A sample is placed on the electrode (cathode) to which high-frequency power of [z] is applied, a glow discharge is generated between each electrode to generate plasma, and positive ions in the plasma are accelerated by the cathode drop voltage generated on the cathode. There is a method of etching the sample by bombarding it with these ions. This method is called reactive ion etching (RIE) and is currently the mainstream of microfabrication technology.

However, in this type of method, the sample to be etched is placed in plasma, which causes damage to the oxide film due to charging of charged particles such as ions and electrons, a shift in threshold voltage due to soft X-rays, and damage to the oxide film. In addition to inducing traps, various radiation damages such as metal contamination from the inner walls of the chamber occurred.

These radiation damages can be caused by ultra-L
There are many factors that can be fatal to SI,
Therefore, there is a strong need for a damage-free etching technique that does not cause radiation damage.

As a non-damage dry etching technique, anisotropic etching of Si and poly □3i (for example, 1-1, Akiya, etc.) using an atomic F beam whose kinetic energy is only equal to the gas temperature during glow discharge has recently been proposed.

proc, 3rd, Symp, on Dr
y processes, p119 (1981,
)) or etching using laser or ultraviolet light (e.g., T, J, Chuang; J, Chem,
phys.

74, 1453<1981); H, 0kano,
T. Yamazaki.

M, 3ekine and Y, Horiike,
proc, of 4 thsymp, on D
ry processes, P6 (19g2)
) have been reported, demonstrating the possibility of damage-free anisotropic etching.

Furthermore, according to research by the present inventors, in poly S1 etching in a CI2 atmosphere using ultraviolet irradiation emitted by a Hc+-Xe lamp, conventionally reported ion-assisted etching (e.g., J, W, Coburn
and H, F., Winters, J.

AI) l, phys, so, 3189 (197
9) Similar effects were found (for example, H,
0kano, T.

Yamazaki, M., 5ekine and
Y, Horiike.

prOc, of 4th Sy+++p, onl
) ry processes, p 5 (1982)
). That is, the effect is that the etching reaction on the light-irradiated surface is significantly accelerated compared to the non-irradiated surface. This effect is remarkable in undoped poly-Si, single-crystal Si, and P-type poly-Si added with boron, but it is also the same in, for example, n+ poly-St, MO, W, Ta, or their silicide compounds added with a high concentration of phosphorus. was recognized.

However, this type of method has the following problems. That is, due to the entry of reactive gas radicals photodissociated in the gas phase under the mask and a slight amount of scattered light from the surface to be etched, the etching mask 74 is removed as shown in FIG.
This results in an undercut 75 below. In particular, when a photoresist is used as the etching mask 74, the resist is transparent to the light and the light is irradiated even under the resist, making the undercut 75 more likely to occur. This undercut 75 becomes a major factor that hinders the miniaturization of elements.
This is a fatal flaw in ultra-LSIs. In the figure, 73 is a sample to be etched such as polySt, 72 is a SiO2 film, and 71 is a sample to be etched.
indicates a Si substrate.

On the other hand, FIG. 8 is for explaining the mechanism of anisotropic etching, which has been gradually revealed in recent RIE research. According to recent research, in the etching wall 76, a recombination reaction (for example, C, J, Mooab
and H, J.

Levinstein; J, Vac, Sci.
Technol, 17°721 (1980)
) to prevent lateral etching on the etching wall 76, or to prevent the attack of the etchant by adhering to the wall 76 various unsaturated materials such as decomposition products of resist, which is an etching mask, and discharge products. (For example, R8H
13ruceand G, P, Malafsky
; E, C, S.

Meeting, Abs, No. 288, [
) enver, 1981 or Takashi Yamazaki, Haruo Okano,
Kaburahiro Horiike, Proceedings of the 30th Applied Physics Society, Spring Committee, 198
3) and other mechanisms are considered to have validity.

[Purpose of the invention]

The purpose of the present invention is to be able to achieve anisotropic etching without causing radiation damage to the sample to be etched, and to use resists used in current processes as an etching mask. The object of the present invention is to provide a dry etching method that can contribute to miniaturization and high integration of devices.

[Summary of the invention]

The gist of the present invention is to use an etching mask that is currently commonly used as an etching mask when a sample to be etched is irradiated with light in an atmosphere of a reactive gas such as CI2 or a mixed gas containing at least carbon or hydrogen in the reactive gas. The purpose is to use the resist materials, etc. that are currently used.

That is, in the present invention, after a mask layer is formed on a sample to be etched, this mask layer is patterned to form an etching mask, and then the sample is exposed to a reactive gas atmosphere containing at least a halogen element. In a dry etching method in which the sample is selectively etched by irradiating the sample with light, a mask material that is transparent to the light is used as the masking layer, and the mask material is made opaque to the light in advance; Alternatively, after forming the etching mask, a process is performed to make the etching mask opaque to the light.

〔Effect of the invention〕

According to the present invention, a sample to be etched can be selectively etched anisotropically by light irradiation without using charged particles such as electrons or ions. Therefore, etching without radiation damage is possible, which is extremely effective in manufacturing semiconductor devices. Furthermore, since a resist material or the like that has been commonly used in the past can be used as an etching mask, there is little need to change the conventional manufacturing process, and it can be easily realized. Here, if metal or metal silicide is used as an etching mask,
This patterning is necessary, and it is also necessary to perform the patterning anisotropically, making the process extremely complicated. Furthermore, when these are used, there is a problem of contamination, making it extremely difficult to put them into practical use.

[Embodiments of the invention]

FIG. 4 is a schematic diagram showing a dry etching apparatus used in the embodiment method of the present invention. In the figure, 41 is a vacuum container (reaction container) forming an etching chamber, and this container 4
1 contains a susceptor 43 on which a sample 42 to be etched is placed.
is located.

Further, the container 41 is provided with a gas inlet 44 for introducing a reactive gas and a gas exhaust port 45 for evacuating the inside of the container 41. Then, a first reactive gas containing a halogen element such as CI2 and a second reactive gas (deposition gas) made of, for example, Si(CH3)4 containing carbon, oxygen, etc. are supplied to a gas flow rate controller 46. .47 into the container 41, respectively.

On the other hand, above the container 41, a first light source 48 is arranged for dissociating the first reactive gas. This light source 48 is, for example, a Cd--He laser having an emission center at a wavelength of 325 nm, or a Xe-CI excimer laser having an emission center at a wavelength of 308 nm. Light (first light) 49 from the light source 48 is perpendicularly irradiated onto the upper surface of the sample 42 on the susceptor 43 through an ultraviolet light passing window 50 provided in the clay wall of the container 41 . The first reactive gas is then dissociated by this light irradiation. For example, when using CI2 as the reactive gas, CI2
Because it well absorbs light around 330 [r1m], active C1 radicals are generated with very high quantum efficiency by irradiation with this light.

Note that the sample 42 is irradiated all at once by the light source 48.

Further, a second light source 51 for dissociating the second reactive gas is arranged on the left side of the container 41. This light source 51 is, for example, a YAG or CO2 laser that generates infrared light. Light (second light) 5 from light source 51
A beam 2 has a relatively large diameter and is irradiated into the container 41 from the lateral direction through an infrared light passing window 53 provided on the side wall of the container 41. The second reactive gas is dissociated by this light irradiation. For example, when 3i(CH3)4 is used as the second reactive gas, Si(C
By dissociating H3)4 by multiphoton absorption of infrared light,
Only the additive gas can be selectively dissociated without dissociating CI2 molecules.

Next, an etching method using the above apparatus will be explained.

<Example 1> Polycrystalline Si was used as the sample 42 to be etched.

That is, first, as shown in FIG.
An i02 film 12 is deposited, and an additive-free polycrystalline 3i film 1 is deposited on top of this.
Then, an etching mask was formed on the polycrystalline 3i film 13. Here, a photoresist sensitive to ordinary ultraviolet light was used as the etching mask 14, but this resist is transparent to ultraviolet light (short wavelength light having a wavelength of about 330 nm). Next, sample 42 was heated to 200 ['C] in an oxygen gas atmosphere and baked for 1 hour. This makes the etching mask 14 opaque to the ultraviolet light.

Next, the sample 42 was placed on the susceptor 43 of the etching apparatus, and etched as follows.

As the reactive gas introduced into the container 41, only chlorine gas was used. The second light source 51 is not used, and the first light source 4
8 was a Xe-CI excimer laser with a wavelength of 308 [nm]. When etched in this manner, in the additive-free polycrystalline S1 film 13, etching progressed only in the portions irradiated with light, so that anisotropic etching was achieved as shown in FIG. 1(b). Here, the etching mask 14
Because the above-mentioned heat treatment prevents ultraviolet light from passing through the resist, the polycrystalline Si film 13 under the mask 14 is not irradiated with light, thereby preventing undercuts.

Thus, according to the method of this embodiment, the polycrystalline S1 film 13 as a sample to be etched can be effectively etched by light irradiation without radiation damage without using charged particles such as electrons or ions.

Moreover, even though a resist is used as the material of the etching mask, it is possible to prevent light from entering under the mask, so it is extremely easy to realize this. That is, as in the past, metal (A
I, W, MO, etc.) and alloys of semiconductors and metals (AI-3i
, Mo-8i), similar effects are achieved with respect to etching, but a metal pattern processing process is required, and complete anisotropy must be achieved in the metal pattern. However, with metal patterns,
Normally, there is a problem in that the processed shape is tapered and diffused reflection occurs from the sidewalls, resulting in a decrease in processing accuracy when etching is performed by light irradiation. On the other hand, by using a resist material as in this example, these problems with the mask edge were solved and a pattern could be formed precisely. Furthermore, since the resist materials used in current processes are used as they are, serious contamination does not occur.

<Example 2> In this example, a single crystal 3i is used as the sample to be etched 42.
(100) wafer was used. That is, as shown in FIG. 2(a), a single crystal Si substrate 21 on which an etching mask 24 was formed was used as a sample. Similar to the previous example,
After forming the etching mask 24, the sample 42 was heat treated in an oxygen gas atmosphere to make the etching mask 24 opaque to ultraviolet light. Next, the sample 42 was placed on the susceptor 43 of the apparatus and etched. The types of gas and light used were the same as in the previous example.

In this case, as shown in FIG. 2(b), selective etching without undercuts is possible, and the same effects as in the previous embodiment can be obtained. Here, the sidewall 25 of the pattern is about 54
A (111) plane with an angle of .degree. has appeared, and this shape can be used to fill the trench with a 3io2 film, etc., and to apply it to device isolation technology.

<Example 3> This example is an example in which the present invention is applied to the anisotropic etching method previously proposed by the present inventors (Japanese Patent Application No. 59-20994). As the sample 42 to be etched, an n+ polycrystalline S protective film was used. That is, as shown in FIG. 3(a), <S++
N++ crystal 3i film (sample to be etched) 33 on plate 31
An etching mask 34 made of resist or the like was formed on the substrate. CI2 is used as the first reactive gas, and 5i(C+-1
3) 4 was used. Further, the first light from the first light source 48 is ultraviolet light with a wavelength of about 330 [nm], and the second light source 51
The second light from was infrared light with a wavelength of about 1 [μm].

The sample 42 shown in FIG. 3(a) was heat-treated in an oxygen gas atmosphere in the same manner as in the previous example to make the etching mask 34 made of resist opaque to ultraviolet light. Then,
placing a sample 42 in a container 41 of the etching device;
First and second reactive gases were introduced into the container 41, and first and second lights were introduced into the container 41. container 4
The first reactive gas introduced into C1, that is, CI2, is dissociated by irradiation with the first light to generate C1 radicals. This C1 radical is n++ as the sample to be etched.
The crystal 3i film 33 is etched.

On the other hand, the second reactive gas introduced into the container 41, that is, Si(CH3)4, is dissociated by the irradiation with the second light. The 5i(CHa)4 gas decomposed here forms a new thin film on the surface of the n+ polycrystalline S model film 33. This deposition reaction competes with the lateral entry of CI radicals as an etchant and the etching reaction of the pattern sidewalls due to reflected light, thereby preventing an increase in undercuts. On the other hand, on the light irradiated surface, the etching reaction progresses more than the deposition reaction due to the light assist effect, so that vertical etching progresses, and as a result, anisotropic etching without undercuts is achieved. Further, since the etching mask 34 does not allow the first light 49 to pass through the heat treatment, the eye light 49 does not pass through the etching mask 34.
There are no inconveniences such as 9 being irradiated.

Here, in FIG. 4(b), after the n+ polycrystalline S pattern film 33, which is the sample to be etched, has been etched to the middle, for convenience of explanation, the vertical irradiation of light is stopped and only the etching reaction is stopped.

In this case, since the deposition reaction continues to progress, the component of the second reactive gas, that is, the film (deposited film) 36, which is dissociated by the light incident from the side (second light 52), is the sample to be etched. It is uniformly deposited on the surface of a certain n++ crystal 3i film 33 and etching mask 34. When vertical light (first light 49) is irradiated again in this state, the deposited film on the light irradiated surface is quickly etched and etching of the n+ polycrystalline S pattern film 33 progresses, as shown in FIG. 3(C). On the other hand, since the deposition reaction is faster than the etching on the sidewalls that are not irradiated with light, the extremely thin deposited film 36 remains to protect the sidewalls, thereby achieving anisotropic etching. In addition, Fig. 3 (b
) The deposited film 36 shown in (c) is extremely thin, and there is almost no problem such as a decrease in pattern accuracy due to this film thickness.

Thus, according to this embodiment, the n+ polycrystalline S pattern film 33 as the sample to be etched can be selectively etched by light irradiation without using charged particles such as electrons or ions, and as in the previous embodiment. You can get the following effect. Also,
Due to the competitive reaction between etching by the first reactive gas and light and deposition by the second reactive gas and light, the n4' polycrystalline S
1 film 33 can be etched vertically. In other words, it is possible to achieve anisotropic etching, which is extremely effective in microfabrication, and is extremely effective in miniaturization and high integration of semiconductor devices.

<Modification> FIGS. 5 and 6 are schematic diagrams for explaining a modification of the third embodiment, respectively. The difference between these modified examples and the third embodiment described above lies in the light irradiation method. That is, the example in FIG.
The sample 131, 42 to be etched is irradiated with the light 49 at once, and the second light 52 for activating the added gas is, for example, a rectangular laser beam that covers the entire sample. In this case, since the second reactive gas on the sample 42 is dissociated uniformly, it is more effective to improve etching uniformity and throughput.

In the example shown in FIG. 6, the second light 52 is a linear beam with a small diameter. In this case, by uniformly scanning the linear beam 52 over the sample 42, uniform etching can be achieved as in the example of FIG.

Note that the present invention is not limited to the embodiments described above. For example, the process of making the resist material that is the etching mask opaque to the light is not limited to heat treatment, and the etching mask may be irradiated with ultraviolet light. Furthermore, the etching mask may be colored by adsorbing or penetrating the dye that is opaque to the light. Furthermore, it is also possible to mix the above-mentioned light-opaque dye into the resist material before forming the etching mask. In this case, the wavelength of the light used for exposure to form the etching mask and the wavelength of the light used for etching must be different.

Furthermore, since the transmittance of a photoresist for short wavelength light generally decreases when irradiated with ultraviolet light, it is also possible to form an opaque mask by irradiating far ultraviolet light after forming an etching mask. Furthermore, it is effective to perform heat treatment at a temperature of 200 [°C] or higher simultaneously or continuously with light irradiation.

At least in the second half of the heat treatment, the etching mask can be cured by using an oxygen atmosphere to prevent pattern deformation. Further, the mask material is not necessarily limited to a resist material, and any material can be used as long as it is transparent to the light used for photoetching and is compatible with the manufacturing process of semiconductor devices.

In addition, the samples to be etched include single crystal Si and polycrystal S.
The present invention is not limited to i, but can be applied to high melting point metals such as tungsten and molybdenum, or silicides thereof.

Further, the first reactive gas is not limited to CI2, and may be a gas containing a halogen element such as fluorine or bromine, or a gas containing carbon, boron, hydrogen, or the like. Furthermore, when using a second reactive gas, this gas is not limited to Si(CH3)4, but may also be W(Go)s.

N i (Co)4, Mo (Co)e,
M.

A metal carbonyl compound such as (Co)6, or any other compound containing carbon and oxygen, even if it is not present, may be used.

Further, conditions such as the flow rates of the first and second reactive gases may be appropriately determined according to specifications. Furthermore, the wavelengths of the first and second lights may be determined as appropriate depending on the type of reactive gas to be dissociated, and are not limited to monochromatic light such as laser light.

In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the selective etching process according to the method of the first embodiment of the present invention, FIG. 2 is a cross-sectional view of the process for explaining the method of the second embodiment, and FIG. 4 is a schematic configuration diagram showing the etching apparatus used in each of the above-mentioned embodiment methods; FIGS. 5 and 6 are schematic diagrams for explaining modified examples, respectively; Figure 7 is a sectional view for explaining the problems of the conventional method;
The figure is a cross-sectional view for explaining the mechanism of anisotropic etching in RIE. 11.21.31...3i substrate, 12...SiO2
Film, 13.33... Polycrystalline SiM (sample to be etched), 23... Single crystal 5ill (sample to be etched),
14.24.34...Etching mask, 36...
Deposited film, 41... Vacuum container (reaction container), 42...
Sample, 43... Susceptor, 44... Gas inlet, 4
5... Gas exhaust port, 46.47... Gas flow layer controller, 48... First light source, 49... First light, 5o.
...Ultraviolet light passing window, 51...Second light source, 52...
Second light, 53...UV light passing window. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 2 Figure 5 Figure 6 Figure 7 Figure 8 Figure 7

Claims (8)

[Claims] (1) After forming a mask layer on the sample to be etched,
In a dry etching method, the mask layer is patterned to form an etching mask, and then the sample is exposed to a reactive gas atmosphere containing at least a halogen element, and the sample is selectively etched by irradiating the sample with light, A mask material that is transparent to the light is used as the mask layer, and the mask material is made opaque to the light in advance, or the etching mask is formed after the etching mask is formed and before etching by the light irradiation. A dry etching method characterized by performing a treatment to make the material opaque to the light. (2) The dry etching method according to claim 1, wherein a resist material is used as the mask material. (3) The dry etching method according to claim 1 or 2, wherein the process of making the mask material opaque includes mixing a dye that is opaque to the light into the mask material. (4) The dry etching method according to claim 1 or 2, characterized in that the process of making the etching mask opaque includes adsorbing or permeating the mask with a dye that is opaque to the light. . (5) The dry etching method according to claim 2, wherein the etching mask is heat-treated in an oxygen atmosphere to make the etching mask opaque. (6) The dry etching method according to claim 2, wherein the process of making the etching mask opaque includes irradiating the mask with ultraviolet light. (7) The dry etching method according to claim 1, wherein the reactive gas is a mixed gas of a gas containing at least a halogen element and a gas containing at least carbon or oxygen. (8) A patent claim characterized in that the light is two or more types of light having different wavelengths, and the light that dissociates the gas containing the halogen element is irradiated perpendicularly to the surface of the sample to be etched. The dry etching method according to item 7.