KR100912342B1 - Evaluation method of defect in wafer using reactive ion etching and wafer structure for the same - Google Patents

Abstract

An evaluation method of defect in wafer using reactive ion etching and wafer structure for the same are provided to collect the by-product generated in the RIE(Reactive Ion Etching) process by using an etch mask. A silicon wafer is prepared(S100). An etch mask thin film is formed on the silicon wafer(S110). An etch mask thin film is patterned(S120). The reactive ion etching(RIE) process is performed on the silicon wafer. The exposed wafer surface is etched. The by-product of the reactive ion etching is adhered to the etch mask pattern by the electrostatic potential difference(S130). The wafer defect is found by the reactive ion etching(RIE)(S140).

Description

{Evaluation method of defect in wafer using reactive ion etching and wafer structure for the same}

The present invention relates to a method for detecting wafer defects using Reactive Ion Etching (RIE), and more particularly, to a method for detecting wafer defects that can solve a problem of deterioration of measurement reliability caused by by-products generated during RIE. It relates to a wafer structure for this.

With the development of the semiconductor industry, the importance of detecting defects in silicon wafers is also increasing. In order to increase the degree of integration in semiconductor device technology, defect detection techniques of silicon wafers are required to detect even smaller and smaller defects. Accordingly, various techniques for measuring the distribution of defects in silicon wafers have been developed.

Defects of a silicon wafer can be classified into surface defects and internal defects depending on where the defects are present. Surface defects include foreign matters attached to the wafer surface, such as dust in the air, or corrosion defects (Pit) of the wafer surface caused by various causes, or crystal defects that are exposed on the surface by wafer mirror processing. In addition, the internal defects correspond to COP (Crystal Originated Particle), oxygen precipitates, etc. generated inside silicon according to silicon crystal growth or heat treatment for device fabrication. These defects are known to have a great influence on the quality of semiconductor devices.

As a method for detecting defects on the wafer surface, techniques using laser scattering method have been steadily studied, and recently, commercial inspection equipments capable of detecting defects of 50 nm size have been released. On the other hand, various techniques have been developed for detecting defects inside the wafer rather than on its surface. There is a classical BMD (Bulk Micro Defect) detection method that detects oxygen precipitates in the cross section by etching while cutting the wafer, and another method is to detect internal defects using scattered light by a laser beam penetrating into silicon. . However, the detection of silicon internal defects is common in that the detection power is lower than that of surface defects.

One important prior art that overcomes these limitations is the method using Reaction Ion Etching (RIE) proposed by Nakashima et al. Related documents include [J. Electrochemical Society, v. 147, (11) 4294-4296, (2000), (Nakashima et al., Toyota), J. Electrochemical Society, v. 152, (5) G339-G344, (2005) (Nakashima et al., Toyota), Patent No. US2004 / 0079962 A1, Korean Laid-Open Patent Publication No. 2004-46840, and the like. These techniques use a very high selectivity RIE method to etch the silicon away, leaving the internal oxide defects on the surface in such a way that the oxygen precipitate defects inside the silicon remain.

As shown in FIG. 1, when the RIE process having a very high selectivity and good straightness is applied to a wafer, the oxygen precipitate 1 inside the silicon crystal acts as a very small etch mask, and as the silicon is removed, this oxygen is removed. The precipitate 1 is exposed on the wafer surface S and the silicon below the oxygen precipitate 1 remains unremoved and finally a very pointed cone-shaped structure that is much larger than the size of the original oxygen precipitate 1. (2) is made so that it can be detected on the surface (see Fig. 2). 3 shows an SEM image of the conical structure. In general, the conical structure looks like a circular point when viewed from above (see FIG. 3 (A)), but the shape of the conical structure can be clearly seen when viewed from the side using the tilt function of the SEM device (see FIG. 3). (B) and (C)).

It is known that the size of the oxygen precipitates of major interest in the silicon wafer is several micrometers to several tens of nm, and the smaller the size, the lower the detectability. However, when the RIE method is used, even a very small oxygen precipitate of about 10 nm can be easily detected by a simple device such as an optical microscope because the conical structure made by it is exposed to the surface of several micrometers. See, supra. Electrochemical Society, v. 152, (5) G339-G344, (2005) (Nakashima et al., Toyota)] applied the RIE method to reduce oxygen deposits in the silicon to about 10 nm in size up to several micrometers. The result of detecting a precipitate also is shown (refer FIG. 4). In fact, the 10nm detection power is superior to the detection power (50nm level) of the latest commercial equipment using the transmission laser scattering method.

However, conventional silicon internal defect detection methods using the RIE method suffer from some problems due to the inherent limitations of the method itself. The key problem is that measurements can be measured more than they actually are. This is because the by-products generated during the RIE process attach to the surface where the etching is in progress and act as etch masks, creating new conical structures. This is not a conical structure originally made from an internal defect to be detected, but a so-called fake conical structure, but cannot be distinguished from the same shape in the end.

In this regard, FIG. 5 shows an image of a fake conical structure caused by a by-product. As shown in the figures, various types of structures are observed, either as an optical microscope image (see FIGS. 5A and 5B) or as an SEM image (see FIGS. 5C and 5D). It is not easy to determine whether or not the structure is due to an internal defect that originally exists inside the silicon. On the other hand, Figure 6 is a FIB image that can be confirmed that both the internal defects and by-products have a conical structure. In Figure 6 (A) is a cone due to internal defects, (B) is a fake cone due to by-products.

In order to solve the above problems, the by-products should not be re-adhered to the wafer surface, but in this case, the straightness of etching, which is an important requirement of the RIE technology, may be impaired. This is because side wall protection is required to secure straightness because the effects of reattachment of by-products are in conflict with each other.

Such by-products result in a lower density of defects to be detected and thus lower measurement reliability. Not surprisingly, the lower limit of the measurable range will be increased by the number of false defects. In addition, the deeper the depth inside the silicon wafer to be detected, the lower the measurement reliability. The deeper the etch depth, the more false defects there will be, of course.

The present invention has been made to solve the above problems, by-products generated during the RIE process by forming a structure capable of forming an electrostatic potential difference on the surface of the wafer to adhere to the by-products generated during the RIE process to the structure It is an object of the present invention to provide a wafer defect detection method and a wafer structure therefor that can solve the problem of deterioration in measurement reliability.

In order to achieve the above object, the present invention forms an etch mask separately on a silicon wafer and then performs reactive ion etching (RIE) by using the etch mask to produce by-products generated during the RIE process. Demonstrate techniques for clinging to

That is, the defect detection method of the wafer according to a preferred embodiment of the present invention, (a) forming an etch mask thin film on the silicon wafer; (b) patterning the etch mask thin film; (c) etching the wafer surface exposed by the transmission window of the etch mask pattern by performing a reaction ion etching (RIE) process on the silicon wafer inside the chamber; And (d) observing a wafer defect revealed by the reactive ion etching.

In the step (b), it is preferable to perform the patterning so that the boundary line interval of the etch mask pattern is in the range of 1 ~ 100㎛.

Preferably, the patterning may be performed by a photolithography process.

In the step (a), the etch mask thin film may be formed by applying an oxide film, a polysilicon thin film or a photoresist film.

According to another aspect of the present invention, a wafer structure used for wafer defect detection using reactive ion etching (RIE), comprising: a silicon wafer body; And a perforated window formed on the surface of the silicon wafer and repeatedly patterned with a perimeter window for performing reactive ion etching (RIE) on the silicon wafer and a boundary line for capturing RIE by-products by electrostatic force around the permeate window. There is provided a wafer structure for defect detection comprising a mask thin film.

According to the present invention, an etch mask may be previously formed on the surface of a silicon wafer to separately provide an attaching surface capable of collecting by-products generated during a reaction ion etching (RIE) process.

Therefore, it is possible to suppress a phenomenon in which the fake conical structure is formed on the wafer surface during the RIE process, thereby increasing the defect detection reliability of the wafer.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

7 is a flowchart illustrating a process of performing a wafer defect detection method according to a preferred embodiment of the present invention.

Referring to FIG. 7, the present invention forms an etch mask thin film on a silicon wafer and is then patterned (steps S100 to S120), followed by reactive ion etching (hereinafter, 'RIE') according to the pattern of the etch mask. After the process is performed (step S130), a process of observing defects revealed on the wafer surface is performed (step S140).

The etch mask provides a surface to which by-products generated in the RIE process (hereinafter referred to as 'RIE by-products') may be attached. Since the RIE process uses a method of etching silicon with plasma, by-products cannot be prevented. Instead, the present invention provides an etch mask that forms a separate attachment surface to prevent the RIE by-products from reattaching to the wafer surface.

In general, most of the by-products off the silicon surface during the RIE process are charged, so the direction of movement of the particles depends on the electromagnetic field distribution. In particular, by-products in the RIE chamber that are located far from the silicon wafer surface, ie in the middle of the chamber, will move along the macroscopic electromagnetic field that forms the plasma, but by-products located very close to the silicon surface will be It is in a condition susceptible to electromagnetic fields caused by a miracle effect. Thus, even if the silicon wafer surface has a small electrostatic potential difference, by-products adjacent to the surface reattach to the surface according to the electrostatic potential difference. In order to fundamentally eliminate this, it is necessary to keep the entire silicon at a uniform potential, but it is impossible to completely eliminate the minute potential difference because the specific resistance of the silicon wafer itself varies slightly from wafer to wafer. In addition, there are many potential microscopic potential differences such as surface roughness that may exist on the wafer surface, surface change due to surface etching by RIE, and local variation of RIE plasma.

In view of the above, in the present invention, by using an etch mask, an RIE by-product is attached to the structure by making a separate structure on the wafer surface where an electrostatic potential difference is easily formed.

In the etch mask thin film forming process (step S110), the thin film, which will serve as an etch mask, is covered with the silicon wafer surface. The material of the etch mask can be any one that can block the RIE. Preferably, an oxide film, a polysilicon thin film, or a photoresist (PR) film is used.

In the etch mask pattern forming process (step S120), an exposure and mask etching process according to a conventional photolithography process is performed to form a hole pattern having an appropriate shape for the etch mask.

As illustrated in FIG. 8, the wafer on which the etch mask 101 is patterned has a structure including a transmission window, which is a hole area through which RIE may proceed, on the wafer body 100, and a boundary line blocking the RIE. Here, the transmission window portion exposes the surface of the wafer body 100 to detect defects, and the boundary portion provides an attachment surface to which the RIE by-product 10 can be attached by electrostatic force. In order to increase the defect detection reliability of the entire wafer area, it is preferable that the boundary line of the etch mask 101 pattern is densely formed in the range of 1 to 100 μm.

In the RIE process (step S130), the etching gas is put into a plasma state while the silicon wafer on which the etch mask is formed is introduced into the RIE chamber, thereby etching the surface of the target silicon wafer. At this time, the wafer surface exposed by the transmission window of the etch mask is selectively etched, and RIE by-products generated by etching are attached to the boundary of the etch mask by electrostatic force.

After the RIE process is completed, wafer defects revealed by etching are observed using observation equipment such as an optical microscope to detect defects. 9 shows an example of an optical microscope image showing a result of defect detection.

Referring to FIG. 9A, the fake cones appear as small dots in most areas. On the other hand, a certain area (10㎛) along the boundary of the etch mask shows a clean area without any small dots. The by-products of the fake cone are controlled by the electrostatic potential difference along the boundary of the etch mask, which is different from the etch mask. Attached results. Cones that also exist in this clean area can be considered to be conical structures formed by actual silicon internal defects, thereby achieving the object of the present invention. Here, if the pattern of the etch mask is formed more closely as shown in (B), the detection reliability can be further improved. In view of such a point, it is preferable that the boundary line spacing of the etch mask pattern is designed in the range of 1 to 100 mu m.

Although the present invention has been described above by means of limited embodiments and drawings, the present invention is not limited thereto and will be described below by the person skilled in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of the claims.

The following drawings, which are attached to this specification, illustrate preferred embodiments of the present invention, and together with the detailed description of the present invention serve to further understand the technical spirit of the present invention, the present invention includes matters described in such drawings. It should not be construed as limited to.

1 is a cross-sectional view illustrating a principle of detecting a defect in a wafer using a conventional RIE process.

Figure 2 is a photograph showing the results of the detection of oxygen precipitates by the conventional RIE process.

3 is a transmission electron microscope (TEM) photograph showing an image of a silicon wafer internal defect detected according to a conventional RIE process.

4 is a scanning electron microscope (SEM) photograph showing an image of a conical structure formed according to a general RIE process.

5 is an optical micrograph and a SEM image showing the image of the conical structure formed by the by-products generated in the general RIE process.

FIG. 6 is a FIB (Focused Ion Beam) photograph showing an image of a cone structure caused by internal defects of a silicon wafer and a cone structure formed by a by-product.

7 is a flowchart illustrating a process of performing a wafer defect detection method according to a preferred embodiment of the present invention.

8 is a partial cross-sectional view of a wafer structure for defect detection in accordance with a preferred embodiment of the present invention.

9 is an optical micrograph showing a result of detecting a defect of a silicon wafer by applying the present invention.

<Description of Major Reference Marks in Drawings>

10: by-product 100: wafer body

101: etch mask

Claims (7)

(a) forming an etch mask thin film on the silicon wafer; (b) patterning the etch mask thin film; (c) performing a reactive ion etching (RIE) process on the silicon wafer in the chamber to etch the surface of the wafer exposed by the transmission window of the patterned etch mask pattern and to remove the reactive ion etching. Attaching a by-product to the etch mask pattern by an electrostatic potential difference; And (d) observing a wafer defect revealed by the reactive ion etching (RIE). The method of claim 1, wherein in step (b), The patterning method of the wafer, characterized in that for performing the patterning so that the boundary line interval of the etch mask pattern is in the range of 1 ~ 100㎛. The process according to claim 1 or 2, wherein in step (b), The method of detecting a defect of a wafer, characterized in that for performing the patterning using a photolithography process. The method of claim 1, wherein in step (a), The etch mask thin film is formed by coating an oxide film, a polysilicon thin film or a photoresist film. Wafer structure used for wafer defect detection using Reactive Ion Etching (RIE), A silicon wafer body; And An etch mask formed on a surface of the silicon wafer and having a permeation window for performing reactive ion etching (RIE) on the silicon wafer and a boundary line for collecting RIE by-products by electrostatic force around the permeation window repeatedly patterned. Wafer structure for detecting defects, characterized in that it comprises a thin film. The method of claim 5, Wafer structure for defect detection, characterized in that the boundary interval of the etch mask pattern is in the range of 1 ~ 100㎛. The method of claim 5, The etch mask thin film is an oxide film, a polysilicon thin film or a photoresist (Photoresist) film, the wafer structure for defect detection.

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