KR20020012863A - Method for manufacturing a contact hole suppressing an overetch of silicon substrate - Google Patents

Abstract

PURPOSE: A method for forming a contact hole wherein an over-etch of a silicon substrate is controlled, is provided to increase a carbon component or reduce a fluorine component, by forming a SiN layer or SiON layer on a SiO2 layer formed on the substrate. CONSTITUTION: The silicon substrate(40) is prepared. A pad layer, a silicon oxide layer(44) and an etch selectivity buffer layer are sequentially formed on the silicon substrate. The silicon oxide layer and the etch selectivity buffer layer are patterned by using a photoresist mask. An ashing process is performed in an oxygen atmosphere regarding the structure in which patterned etch selectivity buffer layer and the patterned silicon oxide layer are formed, so that polymer and the photoresist pattern formed on the pad layer are eliminated. The pad layer is plasma-etched by using etch gas including a carbon component and a fluorine component to form a contact hole exposing the silicon substrate.

Description

Method for manufacturing a contact hole suppressing an overetch of silicon substrate}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a contact hole in a semiconductor device, and more particularly, to a method for forming a contact hole having a high selectivity with respect to a silicon component and suppressing excessive etching of a silicon substrate.

In the initial stage of integration of semiconductor devices, wet etching, which is isotropic etching, was used, but wet etching has been replaced by dry etching as the problem of undercut due to isotropic etching cannot be faithfully transferred to the pattern as semiconductor devices become highly integrated. . Dry etching has an advantage in that it is easy to handle because of anisotropic etching, which has high pattern transfer fidelity and considerably less toxic solutions than wet etching.

Such dry etching is based on physical action such as glow discharge sputtering, chemical action such as plasma etching, and combination of physical and chemical action such as reactive ion beam etching and reactive ion etching. There is.

Pattern formation by plasma etching takes about six steps: first reactive species are produced in the plasma state, second reactive species diffuse to the surface of the material to be etched, and third reactive species are absorbed at the surface of the material to be etched. In the fourth chemical reaction, volatile by-products are produced, the fifth by-product is released from the surface and diffuses into the sixth released paper gas.

In the case of plasma etching of silicon and silicon oxide, CF ₄ , SF ₆ , and NF ₃ containing fluorine components are generally used as etching gases, and volatile SiF ₄ is generated as a by-product.

The plasma etching process of the silicon substrate and the silicon oxide film will be described with reference to FIGS. 1A to 1C.

In FIG. 1A, a silicon nitride film (SiN) or a silicon oxynitride film (SiON) 12 as a pad film and a silicon oxide film (SiO ₂ ) as an interlayer insulating film are sequentially formed on the silicon substrate 10. Next, a predetermined photoresist pattern 16 of carbon, oxygen, and hydrogen compounds is formed on the SiO ₂ film. The silicon oxide film pattern 14 and the opening 20 are formed by plasma etching the interlayer insulating film SiO ₂ using the photoresist pattern 16 as a mask and using CF ₄ gas.

In the etching mechanism, part of CF ₄ is decomposed to form CF ₃ ^* and fluorine atoms. The fluorine atom reacts with the silicon component of SiO ₂ to produce volatile SiF ₄ . On the other hand, CF ₃ reacts with oxygen to produce COF ₂ and fluorine atoms, and COF ₂ again reacts with oxygen to produce CO and fluorine atoms. That is, since the number of fluorine atoms increases, the etching of the silicon oxide film continues to produce volatile SiF ₄ , CO, and CO ₂ . By the way, in the case of using SiN as the pad film, the polymer 18 made of CN compound and Si-C compound is formed on the surface of the pad film 12. This polymer 18 hides the contact hole and does not open it. On the other hand, even when SiON is used as the pad oxide film, a polymer of a CN compound and a Si-C compound is formed and deposited on the substrate 10, and oxygen reacts with carbon to volatilize to CO or CO ₂ .

In FIG. 1B, a plasma etching or cleaning process is performed in an oxygen atmosphere to remove the polymer 18. At this time, the photoresist pattern 16 is also removed to expose the SiO ₂ film 14.

Next, the contact hole 24 is formed by etching the SiN film 12 positioned on the silicon substrate 10 in FIG. 1C. The SiN film 12 is etched with a high selectivity with respect to the silicon substrate 10, but the silicon substrate 10 should be exposed while suppressing substantial damage of the silicon substrate. Substantial damage refers to a state in which leakage current of an element formed on the substrate due to excessive etching of the substrate deteriorates device characteristics or increases contact resistance. In general, in order to expose the silicon substrate without substantial damage, the SiN film 12 should have a selectivity of 2: 1 or less relative to the Si component of the silicon substrate 10. By the way, it is difficult to obtain a selectivity of 2: 1 or less in the absence of the photoresist pattern (see 16 in FIG. 1A).

That is, when the pattern 12a is formed by the etching process of the SiN film 12a, a recess 22 is formed in the silicon substrate 10 to deteriorate the characteristics of the semiconductor element to be formed on the silicon substrate. The photoresist mask pattern 16 includes a carbon component, and the photoresist mask pattern 16 is also removed at the time of removing the polymer 18, so that the contact hole of FIG. (24) The carbon content provided in the etching step for formation is reduced. Meanwhile, according to the F / C model (Flouirine-to-Carbon Rate Model), the etching rate increases as the carbon content decreases. Accordingly, as shown in FIG. 1C, the substrate 10 is excessively etched to form the recess 22.

Accordingly, a technical problem to be achieved by the present invention is a contact capable of suppressing excessive etching of a silicon substrate when etching a silicon nitride film or a silicon nitride oxide film formed on a silicon substrate to form a contact hole in the absence of a photoresist mask. It is to provide a hole forming method.

1A to 1C are cross-sectional views illustrating a method of forming a contact hole according to the related art.

2A to 2C are cross-sectional views illustrating a method of forming a contact hole according to the present invention.

In order to achieve the technical problem to be achieved by the present invention, a silicon substrate is prepared. A silicon nitride film (or silicon nitride oxide film), a silicon oxide film, and an etch selectivity relief film, which are pad films, are sequentially formed on the silicon substrate. The etching selectivity reducing film may use a silicon nitride film or a silicon oxynitride film. The thickness of the etch selectivity reducing layer is formed to be substantially the same as or thicker than that of the silicon nitride layer formed on the upper surface of the substrate. Next, the silicon oxide film and the etching selectivity reducing film are patterned by using a photoresist mask, and the resultant on which the patterned etching selectivity reducing film and the silicon oxide film are formed is subjected to an etching process in an oxygen atmosphere to form a polymer and a photoresist formed on the silicon nitride film. Remove the pattern.

Subsequently, the silicon nitride film is plasma-etched using an etching gas containing a carbon component and a fluorine component to form a contact hole exposing the silicon substrate.

Hereinafter, the present invention will be described in detail with reference to FIGS. 2A to 2C.

In FIG. 2A, a silicon nitride film (SiN) or silicon oxynitride film (SiON) 42 as a pad film, a silicon oxide film (SiO ₂ ) 44 as an interlayer insulating film, and a silicon nitride film (SiN) 46 are formed on a silicon substrate 40. ) Are formed sequentially. The silicon nitride film (SiN) 46 is an etching selectivity mitigating film provided to suppress excessive etching of the substrate when forming contact holes. The thickness of the upper SiN film 46 for reducing the etching selectivity is formed to be substantially the same as or thicker than the lower SiN film 42 serving as the pad film. A predetermined photoresist pattern 48 of carbon, oxygen, and hydrogen compounds is formed on the SiN film 46. Using photoresist pattern 48 as a mask and CF ₄ gas, SiN 46 and SiO ₂ 44 are plasma-etched to form patterns 46 and 44 and openings 52. In this case, as shown in FIG. 1A, the polymer 50 including the CN compound and the Si—C compound is formed on the upper surface of the SiN film 42 formed on the silicon substrate 40. This polymer 50 does not open the contact hole. On the other hand, even when SiON is used as the pad oxide film, polymers of carbon and nitrogen compounds and silicon and carbon compounds are formed and deposited on the substrate 40, and oxygen reacts with carbon and volatilizes to CO or CO ₂ .

In FIG. 2B, a plasma etching or cleaning process is performed in an oxygen atmosphere to remove the polymer 50 as in FIG. 1B. At this time, the photoresist pattern 48 is also removed to expose the SiN film 46 on the SiO ₂ film 44 and the SiN film 42 formed on the substrate 40 by the opening 52.

Next, a process of etching the SiN film 42 positioned on the silicon substrate 40 in FIG. 2C is performed to form the contact hole 56. At this time, the upper SiN film 46 and the lower SiN film 42 are etched simultaneously, so that the thickness of the upper SiN film becomes thin and a contact hole is formed in the lower SiN film 42. When the upper contact hole 56 is formed, the silicon substrate 40 under the SiN layer 42 is also partially etched to form the recess 54, but is formed to be considerably thinner than the recess 22 of FIG. 1C. Therefore, it is possible to suppress the occurrence of leakage currents that affect the characteristics of the semiconductor element to be formed on the silicon substrate 40, and to ensure good contact resistance.

Specifically, referring to the process of forming the contact hole 56, plasma etching is performed using CF ₄ etching gas. As described above, CF _{4, which} is an etching gas, is dissociated into CF ₃ ^* and a fluorine atom, and the fluorine atom is a silicon component of the SiN film 46 covering the SiO ₂ film 44 and a SiN film formed on the silicon substrate 40 ( As the SiN films 42 and 46 are etched while reacting with the silicon component of 42) to produce volatile SiF ₄ , polymers of nonvolatile CN-based and C-Si-based compounds are deposited on the SiN films 42 and 46. Is formed. However, such a polymer is destroyed by the radicals for etching in the plasma state, and the carbon component diffuses into the reaction gas. As a result, the carbon component of the etching gas is increased and the etching selectivity is reduced compared to the process of FIG. 1C.

Meanwhile, in forming the contact hole of FIG. 1C, the SiO ₂ film 14 is directly exposed to the etching gas, while in FIG. 2C, the SiO ₂ film 44 is not exposed to the etching gas and the SiN film 46 is exposed. The oxygen component of the SiO ₂ film 44 combines with the carbon component of the etching gas as described above and ultimately increases the number of fluorine atoms. Therefore, the etching selectivity increased. However, in FIG. 2C of the real name, the silicon component and the nitrogen component of the SiN film 46 react with the carbon component of the etching gas to generate a nonvolatile polymer, which does not increase the number of fluorine atoms. Accordingly, compared with the contact hole process of FIG. 1C, since the generation of fluorine atoms is blocked by the SiN film 46 during the contact hole process, the number of fluorine atoms is relatively small, thereby reducing the etching selectivity.

This phenomenon occurs even when SiON is used instead of SiN 46 on the SiO ₂ film 44. The difference from the case of using the SiN film 46 is that the material constituting the film contains oxygen, but the oxygen component of the SiON film reacts with the carbon component compared to the reaction rate at which the oxygen component of the SiO ₂ film 14 reacts with the carbon component. Since the reaction rate will be small, when the SiON is exposed to the etching gas, the generation of fluorine atoms is relatively low, and the etching selectivity is reduced.

In the present invention, the etching gas is limited to CF ₄ , but various gases C _x F _y including carbon and fluorine may be used. In addition, a hydrogen component may be included to further lower the etching selectivity, and further, an inert gas such as Ar and N ₂ may be added.

When forming a contact hole exposing a silicon substrate, a SiN film or a SiON film is formed on the upper surface of the SiO ₂ film formed on the substrate to increase the carbon content or reduce the fluorine content in the plasma etching process. Even if the contact hole is formed without the mask, the substrate is not excessively etched.

Although the present invention has been described by way of example only for the SiN film or SiON film etching process for forming contact holes, the present invention can also be applied to a residue treatment process for ensuring good contact resistance.

Claims (3)

Preparing a silicon substrate, Sequentially forming a pad film, a silicon oxide film, and an etch selectivity mitigating film on an upper surface of the silicon substrate; Patterning the silicon oxide layer and the etch selectivity reducing layer using a photoresist mask; Performing an etching process on the patterned etch selectivity reducing layer and the silicon oxide layer on the patterned product to remove the polymer and the photoresist pattern formed on the pad layer; and Forming a contact hole exposing the silicon substrate by plasma etching the pad layer using an etching gas containing a carbon component and a fluorine component. The method of claim 1, wherein the pad layer is formed of a silicon nitride layer or a silicon oxynitride layer, and the etching selectivity reducing layer is a silicon nitride layer or a silicon oxynitride layer. The method of claim 1, wherein the etch selectivity mitigating layer is formed to be substantially the same as or thicker than the thickness of the pad layer.