KR100883028B1 - Wafer defect detection device through electrochemical copper decoration and defect detection method using same - Google Patents

Abstract

The present invention provides an apparatus for detecting defects by performing electrochemical copper decoration on a wafer on which an oxide film is formed on one surface and an ohmic contact layer on the other surface, and an electrolyte for copper decoration is received and the wafer is brought into contact with the electrolyte. A container disposed in a portion thereof; A counter electrode disposed in the container to be immersed in the electrolyte and connected to a power source together with the ohmic contact layer for supplying current for copper decoration; And a reference electrode disposed in the container so as to be spaced apart from the counter electrode and serving as a reference for measuring the voltage with the ohmic contact layer.

Description

Wafer defect detection apparatus using electrochemical copper decoration and defect detection method using same {defect delineation apparatus by the electrochemical Cu decoration and defect delineation method using the same}

The present invention relates to the detection of defects on and around the surface of a semiconductor wafer. More particularly, the present invention relates to a device for detecting defects present in an oxide film and a lower portion thereof by reducing and depositing copper (Cu) on a surface of an oxide film. It relates to a defect detection method used.

Widely used analytical techniques for showing quality influences of defects, particles, metal contamination, etc. on the wafer surface and near the surface of the wafer include gate oxide integrity (GOI) analysis using breakdown voltage, and DSOD using copper decoration. (Direct Surface Oxide Defect) method.

All of the above analysis techniques form an insulating oxide film on the wafer surface, and then apply a strong electric field of about 10 MV / cm to analyze the distribution and shape of the defect through the phenomenon in which the insulating oxide film is not able to withstand normally and breaks. However, these methods also have a weak point that it is virtually impossible to find the exact cause defect, as the defects that are supposed to be the cause of the oxide film are also damaged together.

Specifically, in the GOI analysis method, as illustrated in FIG. 1A, a simple MOS (Gate Oxide) 2 and a Gate Poly 3 formed on a Si wafer 1 is formed. Metal Oxide Semiconductor) structure, and a method of measuring the degree of complete integrity as an insulator with respect to the gate oxide (2). Here, the perfect integrity of the gate oxide 2 is affected by defects on the wafer surface, particles, metal contamination, etc., so that the current does not function properly as an insulator. At this time, as the atomic lattice is destroyed under the influence of the strong electric field, the current rapidly increases as shown in the fail mode graphs A, B, and C shown in FIG. In FIG. 1B, graph D shows normal I-V characteristics.

In the DSOD method, as shown in FIG. 2, a lower ohmic contact layer 13 of a silicon wafer 12 coated with a copper plate 10 on an anode (+) and an oxide film 11 on an anode (−) is connected. In this state, when a voltage of about 30 V is applied, oxidized copper ions flow out of the copper plate 10 to reduce-deposit the defects of the silicon wafer 12. As the deposition continues, current is concentrated at the point of failure, and at some point the atomic lattice breaks down, causing a rapid current flow. Since the defect point and its vicinity grow to a defect of a size that can be observed with the naked eye, it is possible to easily analyze the region, density, and the like of the defect. Related patents include, for example, a defect analysis method of a wafer disclosed in Korean Laid-Open Patent Publication No. 1998-67611.

In the conventional GOI and DSOD methods, both currents flow rapidly in unsafe areas where defects or contamination exist by applying strong electromagnetic fields and voltages, indicating defect points. There is a problem that it is impossible to identify the shape of the defect that is directly causing. In this regard, FIGS. 3 and 4 show cross-sectional views of fail spots (F) and copper (Cu) precipitation sites using transmission electron microscopy (TEM) after GOI and DSOD analysis, respectively. In both cases, it is possible to confirm a state in which an oxide film, which is an insulating film, and a defect in the silicon sub below it are destroyed.

In conclusion, GOI and DSOD methods are excellent at identifying the location and distribution of defects by revealing defects, but it is impossible to identify the cause of defects.

In the case of the GOI method, a MOS sample is manufactured and measured, and for this, gate oxidation, poly deposition, photo resist, exposure, and etching ( Etching) and so on has a disadvantage of requiring a lot of time, cost, and equipment.

In addition, in the case of the DSOD method, there is a weakness that the voltage and current on the surface where the actual reaction occurs cannot be controlled due to the nature of controlling only the voltage difference between the anode and the cathode. Therefore, the magnitude of the current varies according to the concentration of copper ions falling away from the anode copper plate, and as the current increases, the overvoltage becomes larger due to the voltage drop (IR-Drop), and under the same voltage, the overvoltage increases. As the current flows less, the problem of increasing the measurement error that occurs every measurement occurs.

The present invention has been made to solve the above problems, a wafer defect detection device having a structure capable of voltage regulation to detect a defect under the oxide film through copper decoration while preventing damage to the oxide film formed on the wafer and its It is an object to provide a defect detection method.

It is another object of the present invention to provide a wafer defect detection apparatus and a method for detecting the same, wherein the copper concentration of the electrolyte can be adjusted so that copper can be easily reduced on the wafer.

In order to achieve the above object, the present invention detects a defect in a wafer by performing electrochemical copper decoration using a counter electrode for current flow and a reference electrode for voltage measurement.

That is, according to the present invention, an electrochemical copper decoration is performed on a wafer on which an oxide film is formed on one surface and an ohmic contact layer is formed on the other surface to detect a defect. A container in which the wafer is disposed in a portion thereof; A counter electrode disposed in the container to be immersed in the electrolyte and connected to a power source together with the ohmic contact layer for supplying current for copper decoration; And a reference electrode disposed in the container so as to be spaced apart from the counter electrode and serving as a reference for measuring the voltage with the ohmic contact layer.

It is preferable that copper ion contains in the said electrolyte solution. At this time, the concentration of copper ions in the electrolyte is preferably 1 ~ 50ppm.

Preferably, the counter electrode is a copper electrode, and the reference electrode is an Ag / AgCl electrode.

Methanol, ethanol, ultrapure water or isopropyl alcohol may be used as the solvent of the electrolyte solution.

The voltage between the reference electrode and the ohmic contact layer is preferably within ± 5V. The voltage preferably has a stepped profile.

According to another aspect of the present invention, in the method of detecting defects by performing electrochemical copper decoration on a wafer having an oxide film formed on one surface and an ohmic contact layer formed on the other surface, the wafer is disposed so that the oxide film contacts the electrolyte. Doing; Disposing a counter electrode and a reference electrode to contact the electrolyte solution; Decorating copper on the oxide film by supplying a current between the ohmic contact layer and a counter electrode; And performing a voltage feedback control by measuring a voltage between the ohmic contact layer and the reference electrode.

According to the present invention, it is possible to perform a precise voltage feedback by providing a reference electrode in addition to the counter electrode, and to detect the defect of the wafer using a weak voltage within ± 5V through the copper concentration control, thereby preventing damage to the oxide film. In addition, there is an advantage that it is possible to identify the defect under the oxide film that causes the failure.

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.

5 shows a main configuration of a wafer defect detection apparatus according to a preferred embodiment of the present invention.

Referring to FIG. 5, a wafer defect detecting apparatus according to a preferred embodiment of the present invention is an apparatus for performing electrochemical copper decoration, and is filled in a predetermined container 104 to be in contact with the oxide film 101 of the wafer 100. An electrolyte 103 and a counter electrode 105 and a reference electrode 106 immersed in the electrolyte 103 to be spaced apart from each other are included.

In the wafer 100 to be detected as a defect, an oxide film 101 is formed on one surface and an ohmic contact layer 102 is formed on the other surface. As a preferred example, a silicon (Si) wafer 100 is used as the wafer 100, and the oxide film 101 is formed of SiO _x. The ohmic contact layer 102 is formed of a thin film made of gold (Au).

The predetermined container 104 in which the electrolyte solution 103 is accommodated is for fixing the area of the oxide film 101 of the wafer 100 in contact with the electrolyte solution 103 constantly, and its shape can be variously modified.

As a solvent constituting the electrolyte solution 103, it is preferable to employ methanol to prevent copper from adsorbing too easily on the surface of the wafer 100, and ethanol, ultrapure water, or isopropyl alcohol is employed depending on the magnitude of the voltage used. May be

Preferably, Cu (NO ₃ ) ₂ is injected into the electrolyte solution to contain copper ions. Here, the concentration of copper preferably has a composition of 1 to 50 ppm. Outside the lower limit of the numerical range, copper is not properly adsorbed on the surface of the wafer 100, and when the upper limit is exceeded, too much copper is adsorbed.

The counter electrode 105 is in contact with the electrolyte 103, while being connected to a direct current power source with the ohmic contact layer 102 to provide an electrode that participates in the current flow for copper decoration. As the counter electrode 105, a copper electrode is used, and as the copper decoration is performed on the surface of the wafer 100, it is desirable to correct the decrease in the copper concentration of the electrolyte 103.

The reference electrode 106 is in contact with the electrolyte 103, and serves as a reference for measuring the voltage difference with the ohmic contact layer 102. Preferably, an Ag / AgCl electrode having a voltage difference of 0.197 V with respect to a standard hydrogen electrode (SHE) is used as the reference electrode 106.

Hereinafter, a process of performing copper decoration on the wafer 100 on which the oxide film 101 is formed by using the wafer defect detection apparatus and cutting and analyzing the wafer 100 to observe the defect and determine the cause of the defect is described. Let's explain.

SiO ₂ on the front of the wafer 100 first The insulating oxide film 101 is grown, and the back surface of the wafer 100 is removed with the oxide film 101 by HF vapor, and then coated with gold (Au) to a thickness of 500 kPa to form an ohmic contact layer 102.

Subsequently, after placing the wafer 100 under the container 104, the methanol electrolyte 103 containing copper ions is poured on the wafer 100, and the counter electrode 105 and the reference electrode () are immersed in the electrolyte 103. 106 is installed and a current is flowed between the counter electrode 105 and the ohmic contact layer 102 while measuring the voltage between the reference electrode 106 and the ohmic contact layer 102. This is done. Here, Scheme 1 represents a reaction in which copper is reduced and adsorbed onto the SiO ₂ surface of the wafer 100, and Scheme 2 represents a reaction in which copper is oxidized at the counter electrode 105.

^{Cu 2 + + 2e - → Cu} / SiO 2

Cu ^{→ Cu 2 + (methanol) +} 2e -

As shown in FIG. 6, the current density characteristic, that is, the I-V characteristic according to the voltage change between the reference electrode 106 and the ohmic contact layer 102 is sensitively changed depending on the thickness of the oxide film 101. Referring to FIG. 6, as the thickness of the oxide film 101 increases from 80 kW to 150 kW, the current density decreases, and the position of the peak potential also moves to the right. It is analyzed that this is because the flow of the current is interrupted as the oxide film 101 becomes thicker, and thus the copper oxidation of the counter electrode 105 is interrupted.

When the thickness of the oxide film 101 is 300 kV, the film becomes a complete insulating film and the flow of current is interrupted. In view of such a point, it is preferable that the thickness of the oxide film 101 has a value within 200 kPa. At this time, the measurement voltage between the reference electrode 106 and the ohmic contact layer 102 is maintained within ± 5V, preferably about ± 2V. At this level of voltage, copper is sufficiently reduced or adsorbed to the oxide film 101, but the amount is small enough not to damage the oxide film 101 or the silicon lattice, so that defects under the oxide film 101 can be measured.

7 (a) and 7 (b) show the shape of copper adsorbed on the surface of the wafer 100 and the composition of each point after the potential sweep according to the stepped profile of increasing the voltage stepwise from -2V to + 2V. The result of the measurement is shown. In the SEM image, the black circular part of about 50 μm in diameter represents the part where copper is adsorbed, and the particularly bright part shows the point of high precipitation of copper, which can be seen from the EDS analysis graph on the right. .

The starting point at which copper ions are reduced and adsorbed on the surface of the wafer 100 becomes the point where the defect is located. Therefore, after growing copper on the wafer 100 for a predetermined voltage and time, find the starting point of the copper growth and cut in the longitudinal direction as shown in Figure 8 to observe the defect using a TEM, and find the cause of the defect I can make it. Referring to FIG. 8, the enlarged portion (see photo on the left) is the point where the precipitation of copper begins, and the defect is present in the silicon bulk below the copper deposited on the SiO ₂ oxide film 101. This defect is a zig-zag-shaped stripe defect, which indicates that current has concentrated at this point and precipitation of copper has begun.

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.

Figure 1 is a schematic diagram showing a GOI analysis method according to the prior art and I-V measurement graph.

Figure 2 is a schematic diagram showing a DSOD analysis method according to the prior art.

3 is a TEM photograph showing a fail point after GOI analysis.

4 is a TEM photograph showing a cross section of a copper precipitation site after DSOD analysis.

5 is a block diagram of a wafer defect detection apparatus according to a preferred embodiment of the present invention.

6 is an I-V measurement graph according to the thickness change of the oxide film.

7 is a SEM photograph showing the appearance of copper adsorbed on the wafer surface and an EDS analysis graph showing the composition of each point.

8 is a TEM photograph showing a partially enlarged wafer cross section of a portion where copper is adsorbed.

<Description of main reference numerals in the drawings>

100: wafer 101: oxide film

102: ohmic contact layer 103: electrolyte

105: counter electrode 106: reference electrode

Claims (13)

In the apparatus for detecting a defect by performing an electrochemical copper decoration on the wafer on which the oxide film is formed on one surface and the ohmic contact layer formed on the other surface, A container in which an electrolyte solution for copper decoration is received and the wafer is disposed in a portion thereof so as to contact the electrolyte solution; A counter electrode disposed in the container to be immersed in the electrolyte and connected to a power source together with the ohmic contact layer for supplying current for copper decoration; And And a reference electrode disposed in the container to be spaced apart from the counter electrode and serving as a reference for measuring a voltage with the ohmic contact layer. The method of claim 1, Wafer defect detection apparatus, characterized in that the electrolyte contains copper ions. The method of claim 2, Wafer defect detection apparatus, characterized in that the concentration of copper ions in the electrolyte solution 1 ~ 50ppm. The method according to claim 1 or 2, And the counter electrode is a copper electrode and the reference electrode is an Ag / AgCl electrode. The method of claim 1, Wafer defect detection apparatus, characterized in that the solvent of the electrolyte solution is methanol, ethanol, ultrapure water or isopropyl alcohol. The method of claim 1, Wafer defect detection apparatus, characterized in that the voltage between the reference electrode and the ohmic contact layer within ± 5V. The method of claim 6, And wherein the voltage has a stepped profile. In a method of detecting defects by performing electrochemical copper decoration on a wafer having an oxide film formed on one surface and an ohmic contact layer formed on the other surface, Arranging the wafer such that the oxide film contacts the electrolyte solution; Disposing a counter electrode and a reference electrode to contact the electrolyte solution; Decorating copper on the oxide film by supplying a current between the ohmic contact layer and a counter electrode; And And performing a voltage feedback control by measuring a voltage between the ohmic contact layer and a reference electrode. The method of claim 8, Methanol, ethanol, ultrapure water or isopropyl alcohol is used as a solvent of the electrolyte solution, Wafer defect detection method characterized in that the step of initially injecting copper ions into the electrolyte. The method of claim 9, Wafer defect detection method characterized in that the concentration of copper ions in the electrolyte solution 1 ~ 50ppm. The method according to claim 8 or 9, And the counter electrode is a copper electrode, and the reference electrode is an Ag / AgCl electrode. The method of claim 8, And a voltage within ± 5 V having a stepped profile between the reference electrode and the ohmic contact layer. The method of claim 8, Wafer defect detection method, characterized in that the thickness of the oxide film is less than 200Å.

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