JPH06151387A - Precision processing method of silicon - Google Patents

Abstract

PURPOSE:To create a mask made of a silicon oxide film even on a stepped silicon film with a small dimensional conversion difference, and to reduce a decrease in mask size while the silicon film is etched. CONSTITUTION:With the use of a photoresist 5 patterned on the main surface of a wafer 1 and an extremely thin silicon oxide film 40 as a mask, a silicon film 3 is previously etched by a plasma etching method including a halogenated gas, and is then etched by another plasma etching method including the halogenated gas and oxygen. At this time, the thickness of the oxide film 40 is set to less than a half of an allowable dimensional conversion difference of a processing dimension, that is, 50Angstrom . This renders a recess caused by the etching of a photoresist during silicon etching irrelevant with a processing accuracy of a silicon film. In addition, the thickness of the oxide film 40 is extremely thin, and hence the amount of a decrease in line width due to processing can be suppressed to 100Angstrom or thereabouts, which is twice the film thickness, even by elimination such as isotropic etching.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor and a method for manufacturing a micromachine, and more particularly to a method for precisely etching a silicon layer.

[0002]

2. Description of the Related Art For example, in the progress of MOS type integrated circuits, the pattern size has been miniaturized, and the processing accuracy also needs to be improved with the miniaturization. In order to improve the processing accuracy, it is necessary to improve the mask accuracy determined by the lithography technique and reduce the dimension conversion difference determined by the etching technique. Among these, the present invention mainly relates to an etching technique.

Conventionally, at the time of etching a silicon layer, a photoresist formed by patterning by an optical lithography technique is used as a mask, or a silicon oxide film or a silicon nitride film formed on the silicon layer (hereinafter, both are oxidized. A typical example is a film, which is processed using a photoresist as a mask, and then the photoresist is removed and the oxide film is used as a mask.

The advantage of using a photoresist as a mask is that it can be processed in a minimum number of steps.
Moreover, even if the surface of the object to be processed has irregularities, there is little trouble in patterning. On the other hand, the drawback is that
It is possible that the photoresist is etched during the processing of the silicon layer, which causes a difference in size conversion. The advantage of using an oxide film as a mask is that it is hardly etched during the processing of the silicon layer, which is advantageous in reducing the difference in dimension conversion.The disadvantage is that the number of steps required for processing is limited to photoresist. In comparison, there is a possibility that the unevenness may be left on the step portion when the oxide film mask is processed if the processed surface has irregularities.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
As a mask for fine processing, it is desirable to use a mask that satisfies both the simplicity of an etching mask of a photoresist, suitability for surface steps, and high etch resistance of an oxide film. The present invention has been made in view of the above points, and an object of the present invention is to achieve the precision of silicon which eliminates the above-mentioned defects of the photoresist and the oxide film by using an extremely thin oxide film of 50 Å or less as a mask for fine processing. It is to provide a processing method.

[0006]

In order to achieve the above-mentioned object, the present invention forms a silicon layer, a silicon oxide film (or a silicon nitride film), and a resist layer in sequence on the main surface of a wafer, and forms the resist layer by lithography. After forming the pattern by the technique, the silicon oxide film (or the silicon nitride film) is formed by etching using the resist pattern as a mask. Then, using the resist pattern and the silicon oxide film (or silicon nitride film) formed by the pattern as a mask, the silicon layer is preliminarily etched by a plasma etching method using a halogenated gas, and then a plasma etching method containing a halogenated gas and oxygen is performed. It is characterized by etching.

Further, according to another invention of the present invention, after removing the resist pattern in the above-mentioned one, the silicon layer is preliminarily plasma-etched with a halogenated gas by using the silicon oxide film (or silicon nitride film) formed as a mask. Characterized by the fact that it is etched by a plasma etching method containing a halogenated gas and oxygen, and the thickness of the silicon oxide film (or silicon nitride film) is less than half the allowable size conversion difference of the processing size. It is what

[0008]

In the present invention, the fact that an extremely thin silicon oxide film (or silicon nitride film) can be used as a mask and the etching rate ratio between the oxide film and the silicon film to be etched can be sufficiently large is utilized.
When etching the silicon film, plasma etching with a halogenated gas is performed in advance, and then plasma etching with a mixed gas of a halogenated gas and oxygen is performed to lower the mask of the silicon oxide film even on a stepped silicon film. It can be formed by the dimension conversion difference, and further, the reduction of the mask dimension can be eliminated during the etching of the silicon film.

[0009]

EXAMPLES Before explaining the examples of the present invention, the principle and operational effects of the present invention will be explained. The present invention is
Increasing the etching rate of the oxide film that serves as a mask by the reaction product silicon halide during the etching of the silicon film by the plasma etching method of the halogen gas, and the silicon by the plasma etching method containing the halogen gas and oxygen. In the etching of the film, the reaction product reacts with oxygen and deposits as silicon oxide on the mask oxide film exposed to the plasma, and in the mixed gas plasma of halogenated gas and oxygen, the silicon film of the silicon film is removed. It was made based on the finding that the maximum oxygen mixing ratio at which etching proceeds depends on the acceleration energy of ions to the silicon film and the density ratio of halogen and oxygen on the silicon film surface.

For example, when etching a silicon film with an oxide film as a mask in an ECR plasma etching apparatus, if a mixed gas of chlorine and oxygen is used as an etching gas,
When the oxygen mixing ratio is increased, the etching of the silicon film hardly changes, but since silicon oxide is deposited on the oxide film serving as a mask, the silicon film can be etched with almost no etching of the oxide film mask. In this case, etching with chlorine gas in advance and then etching with a mixed gas of chlorine and oxygen can prevent generation of etching residues due to natural oxides or the like on the surface of the silicon film.

Since the reaction product of silicon increases the etching rate of the oxide film during the etching with chlorine gas performed in advance, the balance with the oxide film thickness serving as a mask is experimentally determined by etching the patterned wafer. There is a need. According to the experiment, if the etching rate of the oxide film during the etching of the silicon film is 20 Å / min and the etching rate of the silicon is 350 Å / min for 1 minute, the silicon oxide is continuously deposited on the oxide film. Even if etching with chlorine and oxygen was carried out under the above conditions, residue-free etching was constantly obtained on the entire surface of the 4-inch wafer. Therefore, the film thickness of the oxide film required for etching the silicon film may be 20 Å or more.

In this case, even if the thickness of the oxide film serving as a mask with a margin is 50Å, when the oxide film is processed using the photoresist as a mask, anisotropic plasma etching or isotropic etching can be performed. Even if it goes, the conversion difference of the line width can be realized without exceeding 100Å. In particular, if there is a step on the surface of the silicon film, it may be necessary to carry out a large amount of over-etching to completely remove it by anisotropic etching of the oxide film. The required amount of over-etching may be small, or a slight isotropic etching of the oxide film can completely remove the portion including the step portion that needs to be removed. Generally, as a required value of pattern processing accuracy in an integrated circuit, a dimensional conversion difference within ± 15% of a minimum line width is a standard target, and a line width conversion difference is 10 or less.
A value of 0Å means that the minimum line width satisfies the required value of processing accuracy for a pattern of about 700Å.

Further, it is not necessary to remove the photoresist at the time of etching the silicon film. In that case, since the photoresist is etched and recedes at the time of etching the silicon, the end portion of the oxide film serving as the mask is exposed to the plasma. It At that time, the oxide film exposed to the plasma remains without being removed during the etching, so that there is no dimensional conversion difference due to the etching.

On the other hand, when the photoresist is removed and the silicon film is etched only by the oxide film for the mask, EC
Etching with a low acceleration energy (10 to 50 eV) like the R plasma etching method can enjoy the advantage of having a small mask thickness, and thus will be described in detail below.

Particles entering the silicon film from plasma include positive ions, negative ions, neutral particles, electrons, and photons. Among them, positive ions are accelerated by the sheath, and negative ions and electrons are decelerated by the sheath. The neutral particles include those having anisotropy in the velocity distribution neutralized by the collision of ions during acceleration and deceleration with electrons, and those having an isotropic velocity distribution. These particles affect the etching of the silicon film, but especially when the silicon film is over-etched, since it is an electrical insulator regardless of whether it is a photoresist or an oxide film, charge-up is likely to occur on the surface. However, when charge-up is likely to occur on the upper surface of the insulator exposed to plasma, particles with a conductivity opposite to the charge that is charged up by the action of maintaining charge neutrality come in, so the charge-up is resolved. It

However, since the velocity distributions of positive ions and electrons are different, the action of maintaining charge neutralization cannot completely eliminate charge-up on the side surface of the mask. Therefore, on the side surface of the mask, the amount of electrons having a wide velocity distribution is negatively charged due to deceleration in the sheath. As a result, the amount of positive ions incident on the side surface of the mask and the side surface of the silicon film during overetching increases due to Coulomb interaction and the inertia of the ions, which causes side etching. In this case, the thinner the mask thickness, the smaller the charge amount on the side surface of the mask, and the less the effect of causing side etching. Further, the thinner the mask thickness, the smaller the aspect ratio between adjacent patterns (the ratio of the etching interval to the etching depth), so that the so-called microloading effect can be reduced.

Further, since an oxide film having a thickness of 50 Å or less can be formed by the thermal oxidation of silicon with almost no influence on the impurity distribution in the silicon substrate, a fine MOS transistor and a radiation resistant structure which require a steep impurity distribution and low temperature treatment. Also suitable for device processing. Furthermore, if the silicon film doped with phosphorus or boron is activated by thermal oxidation to give conductivity, the side wall of the silicon film is also prevented from being charged, which helps prevent side etching.

Example 1 FIG. 1 shows a first example of a precision processing method for a silicon film according to the present invention.
FIG. 3 is a principle diagram for explaining the embodiment of FIG. A silicon oxide film 2 serving as an insulating film and a silicon film 3 serving as an electrode to be processed are formed on the main surface of the wafer 1, for example, 4000 Å (FIG. 1 (a)). This wafer is, for example, 750
The silicon oxide film 4 having a film thickness of 50Å is formed on the surface of the silicon film 3 by oxidizing at 1 ° C. for 1 hour (FIG. 1 (b)). Then, a photoresist 5 is patterned on the silicon film 3 to be an electrode by a lithography technique (FIG. 1 (c)). The main surface of the wafer is dipped in a buffered hydrofluoric acid solution to process the silicon oxide film 4 to form an etching mask 40 for the silicon film 3 (FIG. 1 (d)).

Cl ₂ gas was applied to the main surface of the wafer in an ECR plasma etching apparatus at 0.1 mTorr.
The silicon film 3 is etched by about 350 Å by exposing it to plasma having a microwave input of 350 W for 1 minute (see FIG. 1).
(e)). Subsequently, when Cl ₂ gas was added at 0.5 mTorr and O ₂ gas was added at 7% and etching was performed with a microwave input of 350 W at a silicon etching rate of 1000 Å / min and a SiO ₂ deposition rate of 30 Å / min, it took about 4 minutes. After that, the silicon film is etched and the etching product of silicon is not supplied to the plasma, so that the deposition of SiO ₂ on the oxide film mask 40 is completed, and then the oxide film 40 is used as a mask for etching. The pattern shape to be processed is sharply formed (Fig. 1 (f)).

In this case, the etching rate of SiO ₂ is extremely low, about 2Å / min. Moreover, the etching rate of the photoresist 5 is increased by adding oxygen gas,
Both the film thickness and line width of the resist are reduced, and the processing pattern of the mask 40 of the silicon oxide film exposes its end to the plasma, but since it is not etched, it acts as a mask for silicon etching.

As described above, according to this embodiment, the extremely thin silicon oxide film 4 of 50 Å, that is, the oxide film mask 40 is formed on the silicon film 3, and the silicon film 3 is preliminarily subjected to the plasma etching method using chlorine gas using this as a mask. By performing etching by the plasma etching method containing chlorine gas and oxygen after the etching, the recession due to the etching of the photoresist during the etching of the silicon film can be made independent of the processing accuracy of the silicon film. Further, since the silicon oxide film 4 is extremely thin, even if it is removed by isotropic etching, the line width reduction amount due to processing can be suppressed to about 100 Å, which is twice the film thickness. With etching, even if the surface of the silicon film 3 has irregularities, there is no possibility that processing residue will occur. Of course, if the surface step of the silicon film 3 is in a range that does not hinder the processing of the silicon film by anisotropic etching, a minute dimensional conversion difference of the angstrom order can be realized by anisotropic etching.

Embodiment 2 FIG. 2 is a process sectional view corresponding to FIG. 1 showing a second embodiment of the present invention. The difference from the embodiment of FIG. 1 is that after the silicon oxide film 4 of FIG. 2D (corresponding to FIG. 1D) is processed as a mask 40, the mixture of concentrated sulfuric acid and hydrogen peroxide solution is mixed. Dip in the solution for 5 seconds to remove the photoresist 5 (Fig. 2 (e)),
After washing with water, the silicon oxide 6 formed on the surface of the silicon film 3 is removed by dipping in dilute hydrofluoric acid at 0.5% and 22 ° C. for 5 seconds (FIG. 2 (f)). The point is that the silicon film 3 is plasma-etched later. In this case, the oxide film mask 40 is etched by 20Å by the first etching with Cl ₂ gas, and its film thickness is 30Å.
(Fig. 2 (g)).

Subsequently, during the etching of the silicon film 3 with the mixed gas of Cl ₂ and O ₂ , the reaction product of the etching product of silicon and oxygen is deposited on the oxide film mask 40, and the film of the oxide film mask is deposited. Thickness increases. When the silicon oxide film is over-etched, the oxide film mask 40 is again etched, but the etching rate is 2Å
Since it is as small as / minute, the function as a mask remains sufficiently during overetching (FIG. 2 (h)).

As described above, also in this embodiment, the silicon film can be etched using the extremely thin oxide film of 50 Å as a mask, as in the first embodiment. further,
Since the thickness of the oxide film mask is thin, the increase in aspect ratio can be small even if the pattern interval is narrowed.
Since the microloading effect is unlikely to occur and the side wall of the oxide film has no influence on the ion trajectory, undercutting is unlikely to occur on the side wall of the silicon film even during overetching.

Further, when plasma etching a silicon film with a mixed gas of chlorine and oxygen, the maximum amount of oxygen added for the etching of the silicon film is the silicon oxide formed on the surface of the silicon or the oxygen adsorbed by the incident ions. Depends on whether or not the particles can be sputtered or etched, so when the energy of the incident particles on the silicon side surface decreases due to the antistatic side wall, the etching of silicon oxide by the incident particles becomes dominant on the horizontal plane, and the etching progresses. However, there is a condition that the formation of silicon oxide or the adsorption of oxygen becomes dominant on the side surface to prevent the etching on the side surface and the side etching of the silicon layer does not occur.

The above embodiment has been described by using the ECR plasma device, but this is because the ion collision energy is low and the etching selection ratio between the silicon and the oxide film is easily obtained in the ECR plasma device. Further, although the above-mentioned embodiment has explained the case where the oxide film thickness is 50Å, this is performed by in-situ surface etching performed at the beginning of etching the silicon film for the purpose of suppressing generation of etching residue of the silicon layer due to a natural oxide film or the like. However, if the surface of the silicon layer is not exposed to the atmosphere, especially moisture, such that all the processing is performed in a vacuum container, etching can be performed with a thinner film thickness.

In this case, since the silicon oxide can be deposited on the oxide film while the silicon layer is being etched, the oxide film thickness may be one molecular layer, and the patterning means is not limited to the photoresist process. It is also possible to use drawing by directly removing the silicon oxide film using a particle beam of ions or electrons or STM, or conversely, drawing by directly forming the silicon oxide film can be used. I'll do it. The present invention is an EC
The invention is not limited to the R plasma apparatus and can be applied to various apparatuses without departing from the scope of the invention.

[0028]

As described above, according to the present invention, an extremely thin silicon oxide film having a thickness of 50 Å or less is used as a mask for fine processing, and the etching rate ratio between the oxide film and the silicon film to be etched is a sufficiently large value. By utilizing the fact that the silicon film can be etched with a plasma etching method using a halogenated gas in advance, and then a plasma etching method using a halogenated gas and an oxygen gas, the silicon film can be etched even on a stepped silicon film. It has become possible to form a mask of a silicon oxide film with a small size conversion difference, and to reduce the reduction of the mask size during etching of the silicon film.

Therefore, even with a lithography technique using a normal photoresist which is excellent in simplicity and versatility, it is possible to process a silicon film with high precision and a high etching selection ratio with an underlying oxide film. As a result, it is possible to improve the performance of the integrated circuit without drastically changing the manufacturing process, and it is possible to miniaturize the integrated circuit when applied to a micromachine.

[Brief description of drawings]

FIG. 1 is a structural cross-sectional view for explaining a first embodiment of a silicon precision machining method according to the present invention in the order of steps.

FIG. 2 is a structural sectional view corresponding to FIG. 1 for explaining a second embodiment according to the present invention.

[Explanation of symbols]

 1 Wafer 2 Insulating Film 3 Silicon Film 4 Silicon Oxide Film 5 Photoresist 6 Silicon Oxide 40 Silicon Oxide Film Mask

Claims (2)

[Claims] 1. A step of sequentially forming a silicon layer on a main surface of a wafer, a film made of silicon oxide or silicon nitride and a resist layer on the silicon layer, and a step of patterning the resist layer by a lithography technique. And a step of forming a film of the silicon oxide or silicon nitride by etching using the resist pattern as a mask, and the silicon using the resist pattern and the silicon oxide film or silicon nitride film formed by the pattern as a mask. And a step of etching the layer by a plasma etching method using a halogenated gas in advance, and then etching the layer by a plasma etching method containing a halogenated gas and oxygen. 2. A step of sequentially forming a silicon layer on the main surface of the wafer, a film of silicon oxide or silicon nitride and a resist layer on the silicon layer, and a step of patterning the resist layer by a lithography technique. And a step of forming a pattern by etching a film made of the silicon oxide or silicon nitride by using the resist pattern as a mask, a step of removing the resist pattern, a silicon oxide film formed by the pattern formation or a silicon nitride film. A step of etching the silicon layer with a film as a mask in advance by a plasma etching method using a halogenated gas, and subsequently etching the silicon layer by a plasma etching method containing a halogenated gas and oxygen; Thickness is the processing size Precision machining method of silicon, characterized in that less than half of the pattern shift.