JPH0834200B2 - Etching method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an etching method. INDUSTRIAL APPLICABILITY The etching method of the present invention can be applied to, for example, an etching technique in a semiconductor manufacturing process, and can be applied to other etching techniques in various industries.

[Outline of Invention]

The etching method of the present invention comprises means for selectively adsorbing a fluorine-based etching gas on the surface of a layer made of a glass-based material on a semiconductor substrate, treating the adsorbed portion with water, and removing the adsorbed portion. Depending on the etching method, there is little damage or contamination.

[Conventional technology and its problems]

The etching technique has been used as a useful technique in various industries, but there are still problems to be solved.

For example, the reactive ion etching (RIE) method has become extremely important as a microfabrication technology for semiconductors that are becoming more and more VLSI, because anisotropic etching capable of obtaining selectivity with the underlying layer is possible. However, when the RIE method is used, the substrate (Si substrate, etc.) may be damaged by charged particles accelerated by the self-bias voltage.
There is a problem based on the essence of RIE, such that contamination may occur due to the constituent elements of the etching gas for E. Therefore, when a semiconductor device or the like is manufactured by using the RIE method as it is, there may be a serious defect in the electrical characteristics of the product.

For example, as a specific example, the SiO ₂ film on the Si substrate is CHF ₃
If RIE is performed using a gas and then a semiconductor device is manufactured, the contact resistance between the electrode (such as Al) and the diffusion layer will increase, and the recombination / rough time of the minority carriers in the Si substrate will decrease. This may have an adverse effect on the physical characteristics. In order to prevent this, the following measures have been conventionally taken.

Change the RIE conditions so that damage is small and contamination is unlikely to occur.

The RIE is stopped halfway, and several hundred liters of SiO ₂ are left, and this part is etched by other means that does not cause damage.

The Si substrate after RIE is etched by a method that does not cause contamination or damage to remove the contamination damage layer in the Si substrate.

Although there are measures such as above, if RIE is adopted, RIE that simultaneously satisfies all of the anisotropy of etching necessary for microfabrication, the selectivity with the underlying layer, the etching uniformity, and an appropriate process speed suitable for the process. Setting the conditions is extremely difficult and practically difficult to implement. It is difficult to keep a few 100Å SiO ₂ with good controllability, and the remaining SiO 2
_When solution etching is used as a means for removing ₂ , the SiO ₂ in the RIE processed part is also etched as a result,
Problems will remain in microfabrication. Has been put to practical use by various methods, but the depth of the damage layer in Si can reach up to 500Å, and the structure that takes a junction with a thickness of about 0.1 μ will become the mainstream semiconductor device in the future. In the technology, just because a contaminated layer / damaged layer is generated, it is not possible to remove it by 500Å, and if a means such as solution etching is used for this etching removal, as described in the above problems, The RIE-processed portion is also etched, which violates the demand for fine processing.

From the above background, in etching technology,
It is strongly desired to establish an etching method which is capable of anisotropic etching, has less damage than before, and has less pollution.

[Technical Means for Solving Problems] In order to solve the above problems, in the first invention of the present application, as shown in FIG. 1, a glass-based material that is a chemically active material on a semiconductor substrate is used. Material (Step I shown in FIG. 1
The surface of the layer formed by (see) is exposed to a fluorine-based etching gas (the same step II), the fluorine-based etching gas is adsorbed on the surface (the same step III), and the adsorbed portion is treated with water to remove the adsorbed portion. (Technical Step IV).

In the second invention of the present application, a glass-based substance layer containing impurities is formed on a semiconductor substrate (also step I), and at least one film is formed on the glass-based substance layer containing impurities. Forming (step IIa), the film on the glass-based material layer containing the impurities is anisotropically etched to form a groove (step IIb), and the glass-based material layer containing the impurities. Is exposed to an etching gas (IIc in the step), and the etching gas is adsorbed to the impurity-containing glass-based material layer at the bottom of the groove by changing the pressure of the atmosphere of the layer containing the impurity (step IIc). ) (The glass-based material layer is consequently exposed as the bottom of the groove), the adsorbed portion is treated with water to etch the adsorbed portion (step IV).

The structure of the etching method according to the present invention will be described below with reference to the examples of FIGS. 2 to 6. In addition, hatching is omitted although each drawing is in a sectional state.

First, in step 1, as shown in FIG. 2, a layer 2 made of a glass-based material (active material) (eg, As-doped glass containing impurities) is formed on the substrate 1. Next, as shown in FIG. 3, in step IIa, at least one film (two layers of silicon nitride film 31 and silicon oxide film 32 in the example of FIG. 3) is formed on the active material layer (glass material layer) 2. The silicon nitride forms a substance in which the ratio of Si to N cannot be specified, and the silicon oxide includes a substance in which the ratio of Si to O cannot be specified. Next, in step IIb, a groove is formed in the film. In the illustrated example, first, the photoresist layer 4 is formed on the films 31 and 32 as shown in FIG. In this case, patterning is performed so that the resist layer 4 is not provided on the portion where the groove is to be formed. Next, the silicon oxide film 32 is etched as shown in FIG. 4 (b), and the silicon nitride film is then etched as shown in FIG. 4 (c).
31 is etched to form the groove 5. In the state shown in FIG. 4 (c), the exposed active material layer (glass-based substance layer) 2 is exposed to a fluorine-based etching gas (step IIc). Next, a fluorine-based etching gas is applied to the surface of the active material layer (glass-based substance layer) 2 by changing the state of the atmosphere of the active material layer (glass-based substance layer) 2, particularly by changing the pressure of the atmosphere. Adsorb (Step III). This state is shown in FIG. Next, in step IV, the portion where the fluorine-based etching gas is adsorbed is treated with water to etch the adsorbed portion. Step IV yields the structure of FIG.

[Operation of the invention]

As described above, according to the present invention, a fluorine-based etching gas is adsorbed to a layer made of an active material or a glass-based material layer that is a layer containing impurities, and after adsorption, the adsorbed portion is treated with water to be adsorbed. Since the removed portion is removed, only the adsorbed portion can be selectively etched. Therefore, if the method of the present invention is used in combination with an etching method such as RIE technology, the required selective etching can be achieved without impairing the fine workability of RIE. Moreover, since the method of the present invention utilizes the adsorption phenomenon of the fluorine-based etching gas, the substrate is neither damaged nor contaminated.

Example of Invention

 An embodiment of the present invention will be described below.

In this example, a layer is formed using glass doped with phosphorus or arsenic as a glass-based substance (hereinafter referred to as "active material layer 2"), and this is etched using a fluorine-based reactive gas. The present invention is embodied in. This example is based on the following interesting phenomenon discovered by the present inventors.

That is, an impurity-doped oxide such as PSG (phosphosilicate glass) or AsSG (arsenic silicate glass) formed on a Si substrate is placed in the chamber of a reactive ion etching apparatus for SiO ₂ for several minutes. After standing, the chamber was purged to atmospheric pressure and the substrate was treated with running water, and the active PSG, AsSG, etc. on the Si substrate were etched to a depth of several hundred Å to several thousand Å. This phenomenon is caused by the residual gas (especially F ₂ which becomes an etchant of SiO ₂₎ resulting from the etching gas in the chamber in the RIE apparatus.
Of the system) is adsorbed on the surface of the active material due to a sudden pressure change when purging the inside of the chamber, and this becomes H _{2 in} running water.
It is interpreted that only gas-adsorbed portions are selectively etched by reacting with O to form HF.

In this embodiment, if the above-mentioned gas adsorption phenomenon is utilized, no contamination or damage layer is generated in the semiconductor substrate, and the RIE
It is based on the finding that etching can be performed without impairing its anisotropy and fine workability when using.

First, refer to FIG. As shown in the figure, in this example, the active material layer 2 is formed on the Si substrate 1 with AsSG (silicate glass containing arsenic as an impurity) which is an active material. This layer 2 has a thickness of several hundred liters. This step corresponds to step I in FIG.

Next, as shown in FIG. 3, a film of silicon nitride such as Si ₃ N ₄ (hereinafter referred to as Si ₃ N ₄ ) 31, and S
A film (hereinafter referred to as a SiO ₂ film) 32 made of silicon oxide such as iO ₂ is formed. This corresponds to step IIa in FIG.

Next, as shown in Fig. 4 (a), photoresist (PR in the figure)
Patterning). That is, the resist layer 4 is formed in a portion other than the portion where the groove is to be formed. In this state, the uppermost SiO ₂ film 32 is RIEed with a CHF ₃ -based reactive gas. At that time, S
If the etching end point of the iO ₂ film 32 is determined by an optical end point determination method, for example, with a laser or a spectroscope, the SiO ₂ film 32
After etching away, the etching can be stopped on the Si ₃ N ₄ film 31. As a result, the structure shown in FIG. 4 (b) is obtained. Next, the Si ₃ N ₄ layer of the intermediate layer is formed with a gas having a high silicon nitride / silicon oxide selection ratio, for example, a gas capable of selectively etching Si ₃ N ₄ / SiO ₂ such as Freon 32 and Freon 41. RIE is performed to stop the etching on the lower active material layer 2. The above corresponds to the step IIb in FIG.
As a result, the structure shown in FIG. 4 (c) is obtained.

As the gas having a high silicon nitride / silicon oxide selection ratio, a gas containing at least carbon and fluorine as constituent elements and having a low F / C ratio (that is, CF ₄ or CHF ₃ is used). Whereas F / C is rich in fluorine such as 4: 1 or 3: 1 and the F / C ratio is large, the F / C ratio is 2: 1 such as CH ₂ F ₂ or CH ₃ F. And the F / C ratio is small such as 1: 1), CO ₂ is excessive, that is, F 2
By removing ^* as COF, it is possible to employ a gas obtained by mixing it to such an extent that CHF ₃ ⁺ (acting as an SiO ₂ etchant) due to F ^* recombination can be suppressed. For example, CH ₂ F ₂ is used as a gas with a small F / C ratio, and CO ₂
Is set according to the equipment and conditions, for example, a flow rate ratio of 30
It can be used as an etching gas by mixing up to 70%.

By forming the groove 5, the surface 21 of the active material layer 2 is exposed as shown in FIG. Here, the surface 21 is exposed to an etching gas. In this embodiment, since the RIE process was performed in the previous stage, the etching gas is present in the atmosphere in the chamber of the RIE apparatus, and therefore it is sufficient to leave it after forming the groove 5. Of course, it may be exposed to another gas under other conditions. In this example, it was left for several minutes. This is the process IIc in Fig. 1.
Equivalent to.

Next, the chamber of the RIE device is purged to atmospheric pressure. Since the inside of the chamber has a vacuum of about 10 ^-2 to 10 ^-5 Torr, a sudden pressure change occurs here. Due to this pressure change, the etching gas is adsorbed to the surface 21 of the active material layer 2, in this case AsSG. This is the process shown in Fig. 1.
III, which schematically shows the pattern of etching gas adsorption
Shown in the figure. In this example, the purging was performed by sucking N ₂ gas, which is commonly used in this type of technique.

Next, pure water is used to perform running water treatment to selectively remove only the active material layer 2 by etching. It is considered that F in the etching gas becomes HF and dissolves AsSG. This is step IV in FIG. The structure obtained is shown in FIG.

When the above method is used, there is no possibility that the semiconductor substrate 1 is contaminated or damaged, while using charged particles such as plasma for the last etching of the active material layer 2. Therefore, Si etching or the like due to the subsequent post-treatment is not necessary. Moreover, since the etching is performed by pure water using the adsorption phenomenon, only the active material layer 2 (AsSG) is selectively etched, and there is no fear of impairing the miniaturization as in the case of using solution etching.

Although AsSG was used as the glass-based substance in the above-described examples, it may be a glass-based substance containing impurities other than As such as PSG, and in any case, it is adsorbed by the fluorine-based etching gas and is adsorbed by water in the adsorbed portion. What is necessary is that the adsorption portion is etched by the treatment. As the etching gas, any fluorine-based etching gas capable of exhibiting such an adsorption phenomenon can be adopted.

Naturally, the invention is not limited to the embodiments described above.

[Effects of the Invention] As described above, according to the present invention, it is possible to realize an etching method that does not impair the effect of anisotropic etching such as RIE and that damages or contaminates the product is smaller than conventional methods.

[Brief description of drawings]

FIG. 1 is a process drawing showing the method of the present invention. 2 to 6 are views showing an embodiment of the present invention, each being a sectional view in the order of steps. I ... Active material layer forming step, IIa ... Membrane forming step, IIb
…… Groove formation process, II c …… Process of exposing to etching gas,
III: Etching process of etching, IV: Etching process by treatment of adsorption part.

Claims (2)

[Claims] 1. A surface of a layer made of a glass-based material on a semiconductor substrate is exposed to a fluorine-based etching gas, the fluorine-based etching gas is selectively adsorbed on the surface, and the adsorbed portion is treated with water. An etching method for removing the adsorbed portion. 2. A glass-based material layer containing impurities is formed on a semiconductor substrate, and at least one layer is formed on the glass-based material layer containing impurities, and a glass-based material containing the impurities is formed. The film on the material layer is anisotropically etched to form a groove, and the pressure of the atmosphere of the glass-based material layer containing the impurity is changed to allow the fluorine-based etching gas to contain the impurity at the bottom of the groove. Etching method in which the adsorbed portion is treated by adsorbing it to the glass layer and treated with water.