KR100611475B1 - Method of treatment a reagent for observation a SEM using electrochemical wet etching methodology and method of analysis a fail site for isolation pattern using the same - Google Patents

Abstract

The present invention relates to a sample processing method for scanning electron microscope observation using an electrolytic etching method and a defect analysis method of the separation pattern, and removes the compound attached to the end surface of the device after focusing ion beam (FIB) processing, Accordingly, in order to easily analyze the leaky fail site in the separation pattern, the sample is electrochemically etched after FIB ion milling to effectively remove the gallium compound attached to the sample surface, and the leaky fail site analysis is performed. In this case, electrolytic etching is performed so that only the defective part remains, so that the rapid and accurate monitoring of the process product can be activated, and thus the sample processing for scanning electron microscope observation using the electrolytic etching method can make a big contribution to the observation of the reliability of the product. A method and method for failure analysis of separation patterns are disclosed.

Electrolytic Etching, Leakage Fail Site

Description

Method of treatment a reagent for observation a SEM using electrochemical wet etching methodology and method of analysis a fail site for isolation pattern using the same}             

1 is a view for explaining a sample processing method for scanning electron microscope observation using the electrolytic etching method according to the present invention.

2 to 4 are views for explaining the results of sample processing for scanning electron microscope observation using the electrolytic etching method according to an embodiment of the present invention.

5 and 6 are views for explaining a failure analysis method of the separation pattern using the electrolytic etching method according to the present invention.

<Description of the symbols for the main parts of the drawings>

11, 51: Electrolyzer 12, 52: Electrolyte

13, 53: Sample 14: power supply

55: anode oxide film

60 substrate 61 gate oxide film

62 gate electrode 63 anode oxide film

The present invention relates to a sample processing method for scanning electron microscope observation using an electrolytic etching method and a defect analysis method of the separation pattern, and removes the compound attached to the end surface of the device after focusing ion beam (FIB) processing, Accordingly, the present invention relates to a sample processing method for scanning electron microscope observation using an electrolytic etching method and a defect analysis method of the separation pattern to easily analyze the leaky fail site in the separation pattern.

Focused ion beam (FIB) processing technology is an analysis technique usefully used for defect analysis of semiconductor devices. This means that the electrical measurement results in the analysis of the cause of the failure in the multilayer structure by easily processing the cross section of the localized area with an ion beam without breaking the sample at the fault isolation site. However, since FIB has a resolution of 10 nm, a high resolution (<2.5 nm) scanning electron microscope (hereinafter referred to as 'SEM') should be used to easily observe defects revealed after the fabrication of the cross section. However, when the crater is fabricated using FIB, chemical contamination is caused because the compound material is covered on the surface of the device during gallium ions (Ga ++) remaining on the sidewalls and during ion milling during etching. (Chemical Staining) It is difficult to maximize the contrast difference due to the difficulty of treatment, which makes it difficult to observe the cross section. Accordingly, a case may not occur in which a technique of decorating with polysilicon / oxide etching solution, which is a sample fabrication technique applied to maximize contrast effect in the conventional SEM, is not applied. That is, in the case of the SEM showing the shape with contrast, the conventional simple dipping condition is performed in the process of maximizing the difference between the interfaces between layers by dipping with chemicals, etc., when the cross section is observed. No decoration was possible. In addition, in the case of gate oxide pin-hole observation, it was common to track and analyze fault sites using a conventional emission microscope. However, this method makes it impossible to track fault sites because the site tracking for leakage at the gate, the bottom of a highly integrated device, which is complicated in a multilayer structure, is very scattered.

Therefore, the present invention maximizes the contrast effect when observing defects using SEM by electrochemically removing a compound attached to the device surface after FIB processing, and thus an electrolysis that can effectively analyze leaky fail sites in separation patterns. It is an object of the present invention to provide a sample processing method for scanning electron microscope observation using an etching method and a method for analyzing defects of a separation pattern.

Sample processing method for scanning electron microscope observation using the electrolytic etching method according to the present invention for achieving the above object is provided with a step to provide a sample to analyze the defect; Performing focused ion beam machining on the sample; And electrolytically etching the sample by an electrolysis method using a chemical having an excellent etching selectivity as an electrolyte.

In addition, the failure pattern analysis method of the separation pattern using the electrolytic etching method according to the present invention for achieving the above object, in the failure analysis method of the separation pattern, the focused ion beam for the sample formed with the separation pattern to analyze the defect Performing a machining process; Primary electrolytic etching of the sample by an electrolysis method using a chemical having an excellent etching selectivity as an electrolyte; Removing the polarity applied to the sample and performing the second electrolytic etching; After performing the cleaning process characterized in that it comprises a step of observing the defect.

Since Luigi Galvani discovered in 1785 that chemical reactions caused electrical phenomena during biodissection experiments, "Electrochemical Engineering" has been studied in various fields. Electrochemical Wet Etching (ECWE), which is applied in this field, is an etching method that combines chemical interaction with electrical reaction. In other words, when the micro-voltage is applied by exposing the material to be etched in an electrolyte having a high selectivity, the electrical polarization phenomenon in the sample increases the ionization effect. Excellent. The present invention applies this electrolytic etching method to semiconductor device analysis and SEM fabrication.

The resolution of the SEM is determined by the contrast between materials, and the contrast may be due to the topology. Therefore, in order to observe the cross-section of a semiconductor device having a multi-layer structure, a series of sample processing techniques for observing an interface in a state in which a step is maximized by selectively removing adjacent layers while exposing a specific layer is required. . In this respect, the electrochemical treatment method is combined with the conventional chemical etching method to maximize the etching selectivity and activate the dissociation mechanism of the thin film to be exposed to reveal a specific layer. The application technology that was accomplished was described. Also, in the case of gate oxide film pin-hole observation, in the electrolytic etching method, the polarity is connected to have an anode characteristic at the leaked portion by using the oxidation effect of the anode (+), and the fault portion is characterized by the oxidation effect. The chemicals are left unetched and traced to the fault, which is then revealed by conventional etching.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention;

1 is a view for explaining a sample processing method for scanning electron microscope observation using the electrolytic etching method according to the present invention.

As shown, the sample 13 is placed in the electrolyte 12 in the electrolytic cell 11, and the power is supplied from the power supply 14 with the sample 13 as a cathode. The electrolyte 12 uses chemicals having a high etching selectivity between the material to be etched and the material to be left, and the supply power is 8 V / 250 mA. By using the electrolysis method as described above, the electrochemical chemicals are accelerated by the potential difference to maximize the etching selectivity, and the materials mixed with gallium (Ga) by the mass transport are easily removed. Here, a gold coating is applied to the sample to prevent charge-up during electrolytic etching, which is applied with a 45 ° slope to prevent the coating action of the ion milling cross section due to normal incident from becoming weak. Process.

2 to 4 are diagrams for explaining the results of sample processing for scanning electron microscope observation using an electrolytic etching method according to an embodiment of the present invention, Hemispherical Poly Grain (HPS) polysilicon delineation (delineation) For example.

In the embodiment of Figure 2 the electrolytic etching conditions are as follows. 1.5HF (49%) + 200HNO ₃ is used as the electrolyte and the electrolytic etching time is 8 seconds. Supply 20V / 150mA of power from DC power supply and connect negative to sample. The sample is also coated with gold for 3 minutes at a 45 ° slope.

When the electrolytic etching is performed under these conditions, the exposed surface of the insulating film (BPSG / IPO) is slightly etched in addition to the polysilicon layer, and the hemispherical polygrain polysilicon layer and the metal layer are stored in a good state because of high etching selectivity. In the FIB ion milling process, the metal layer and the like are assumed to be protrusions, and the poly2 tungsten-silicide layer is also well preserved.

From the above results, it can be seen that the first embodiment is very easy to observe the hemispherical polygrain polysilicon layer, but since the etching selectivity with the insulating film is very low, it is necessary to supplement the conditions separately.

In the example of FIGS. 3A and 3B, electrolytic etching conditions are as follows. 3HF (49%) + 200HNO ₃ is used as the electrolyte and the electrolytic etching time is 7 seconds. Supply 20V / 150mA of power from DC power supply and make positive connection to EUT. Samples were also coated with gold for 5 minutes at a 45 ° slope.

When the electrolytic etching is performed under the above conditions, the insulating film is etched in addition to the polysilicon layer, and the metal layer is not damaged, but the barrier metal layer is etched.

From the above results, it can be seen that the etching selectivity with the insulating film is improved.

4A and 4B show the well profile and metal layer profile observed in SEM images after FIB ion milling.

Normally, 1.5HF + 200HNO ₃ has a very high etching selectivity compared to SiO ₂ , but as a result of the electrolytic etching, a peculiar phenomenon in which the etching selectivity is low occurs. This is because the electrolytic etching mechanism reacts with Si and NO ₂ to SiO ₂ , breaks a series of secondary reaction rings removed by bonding with HF, and promotes HF to react with SiO ₂ directly by ionizing it from the mixture. It is estimated. The chemical reaction formula at this time is as follows.

_{Si + 2HNO 3 → Si + 2NO} 2 + 2OH → Si 2 + + 2NO 2 → Si 2 + + 2OH - → SiO 2 + H 2 (1 -order reaction)

SiO ₂ + 4HF → SiF ₄ + 2H ₂ O (secondary reaction)

5 and 6 are views for explaining a failure analysis method of the separation pattern using the electrolytic etching method according to the present invention.

FIG. 5 is a view for explaining the reaction mechanism of the electrolytic etching. In the electrolyzer 51 containing the electrolyte 52, a sample 53 to be observed for gate oxide defects is placed and Pt 54 is used for the load.

6A and 6B are cross-sectional views of samples for which defects are to be observed, showing a state in which the gate oxide films 61 and the gate electrodes 62A and 62B are formed on the substrate 60. When the sample 53 is electrolytically etched, the anode oxide film 63 is grown on the surface of the gate electrode 62A of the defective portion as shown in FIG. 6B.

More detailed description is as follows. When a voltage of several V is applied to the sample 53 in the electrolyte 52, in the leakage gate 62A where the gate oxide film defect A is generated, the etching reaction is very slow at an initial stage, and then the formation point of the anode oxide film 63 is reduced. When the equilibrium point is reached, etching does not occur due to the oxidation reaction, whereas the etching reaction occurs normally at the normal gate 62B. That is, since the leaked site remains unremoved while the normal site is removed, the leaked site can be easily observed. This reaction can also be used to observe leak sites at storage nodes and at tungsten plug contacts. If a defect is generated and the remaining site is etched in the electrolyte with the polarity removed, the chemical isotropically etches the silicon substrate through the pin-hole for etching the polysilicon layer. In this state, if only the gate oxide film is removed with hydrofluoric acid or the like and observed with an SEM, an under-cut trace remains at the pin-hole site.

Here, KOH + H ₂ O or HNO + HF is used as the electrolyte.

As described above, the present invention combines the electrical and chemical aspects to maximize the selectivity of the etching mechanism to facilitate the failure analysis of the semiconductor device using a scanning electron microscope (SEM). In particular, it is possible to overcome the difficulty of the contamination treatment after the ion milling operation of the focused ion beam (FIB), which is highly dependent on the analysis technology, so that it can be linked in high resolution image analysis equipment such as a scanning electron microscope with high resolution. The processed part can be observed precisely. In addition, the gate oxide pin-hole defect site can be analyzed using the electrolytic etching principle, thereby improving reliability. This enables quick and accurate monitoring of process products, which can greatly contribute to observing the reliability of products and contributes to the development of quality products.

Claims (9)

Providing a sample to analyze the defect; Performing focused ion beam machining on the sample; Placing the sample in an electrolyte which is a chemical chemical having a high etching selectivity ratio between a material to be etched and a material to be left; And A sample for observing a scanning electron microscope using an electrolytic etching method comprising electrolytic etching of the sample by promoting electrolysis of the electrolyte by an electrolysis method of connecting a cathode to the sample to supply a predetermined power source Treatment method. The method of claim 1, The electrolyte is 3HF (49%) + 200HNO ₃ Sample processing method for scanning electron microscope observation using the electrolytic etching method. The method of claim 1, The electrolytic etching is a sample processing method for scanning electron microscope observation using an electrolytic etching method, characterized in that performed for 7 seconds. The method of claim 1, The electrolytic etching is a sample processing method for scanning electron microscope observation using an electrolytic etching method characterized in that the anode is connected to the sample, supplying a voltage of 20V and a current of 150mA. The method of claim 1, The sample processing method for scanning electron microscope observation using the electrolytic etching method characterized in that it further comprises the step of performing a gold plating on the sample at a 45 ° slope before the electrolytic etching. In the failure analysis method of the separation pattern, Performing a focused ion beam machining process on a sample having a separation pattern for analyzing the defects; The electrolysis of the electrolyte is promoted by an electrolysis method in which the sample is put into an electrolyte which is a chemical chemical having a high etching selectivity between the material to be etched and the material to be left, and a cathode is connected to the sample to supply a predetermined power source. Primary electrolytic etching of the sample; Removing the polarity applied to the sample and performing the second electrolytic etching; Defect analysis method of the separation pattern using the electrolytic etching method comprising the step of observing the defect after performing the cleaning process. The method of claim 6, The electrolyte is KOH + H ₂ O or HNO + HF characterized in that the failure analysis method of the separation pattern using an electrolytic etching method. The method of claim 6, In the first electrolytic etching, the failure pattern analysis method of the separation pattern using an electrolytic etching method, characterized in that for connecting the anode to the sample. The method of claim 6, Electrolytic etching method characterized in that the portion in which the defect occurs during the first electrolytic etching occurs during the initial etching reaction and the etching point does not occur when the equilibrium point with the anode oxide layer is formed, and all the portions in which the defect does not occur are etched. Defect analysis method of separation pattern using

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