WO2002001626A1

WO2002001626A1 - Method and apparatus for evaluating semiconductor wafer

Info

Publication number: WO2002001626A1
Application number: PCT/JP2001/005399
Authority: WO
Inventors: Takeshi Kobayashi
Original assignee: Shin-Etsu Handotai Co., Ltd.
Priority date: 2000-06-27
Filing date: 2001-06-25
Publication date: 2002-01-03
Also published as: TW516245B

Abstract

A method and an apparatus for evaluating a semiconductor wafer by Cu deposition which enable a stable observation of defects and an accurate analysis of the distribution and density of defects, a suppression of variation of devices, batches, etc., and a stable evaluation by controlling and evaluating the Cu concentration and enables a shortening of the pretreatment time and a rapid evaluation by using a Cu reference liquid. The Cu deposition method comprises a step of forming an insulating film of a predetermined thickness on the surface of a semiconductor wafer and a step of breaking the insulating film on a defective part formed close to the surface of the semiconductor wafer and depositing Cu in a solvent on the defective part. The Cu concentration in the solvent is adjusted to a range of 0.4-30ppm and evaluation is performed.

Description

Description Semiconductor wafer evaluation method and equipment

Technical field

The present invention relates to a method for evaluating a defect of a semiconductor wafer such as a silicon wafer (hereinafter sometimes simply referred to as “a wafer”). The present invention relates to a semiconductor wafer evaluation method and apparatus using a Cu deposition method for accurately analyzing the distribution and density of surface defects. Background art

As the degree of integration of semiconductor devices increases, the quality of wafers has a significant effect on the yield and reliability of semiconductor devices. The quality of semiconductor wafers is determined throughout the crystal growth process, wafer processing process, and device manufacturing process. における Defects in wafers are mainly caused by crystal defects that occur during silicon ingot growth and crystal defects. It can be broadly divided into processing damage to be formed and defects due to external contamination sources.

In general, silicon wafers are manufactured using the Czochralski (CZ) method or the floating zone (FZ) method, a single crystal ingot is manufactured using a crystal growth process, and the single crystal ingot is sliced. However, at least one principal surface is processed into a mirror surface. More specifically, the wafer processing step includes a slicing step of slicing a single crystal ingot to obtain a wafer having a thin disk shape, and preventing cracking and chipping of the wafer obtained by the slicing step. A chamfering step for chamfering the outer peripheral portion thereof, a rubbing step for flattening the wafer, and a chamfering process for chamfering and remaining the wafer. There is an etching process to remove the distortion, a polishing (polishing) process to mirror the wafer surface, and a cleaning process to clean the polished wafer and remove the abrasive and foreign matter adhering to it. are doing. The above e-wafer processing step shows the main steps, and other steps such as a heat treatment step are added or the order of the steps is changed.

Generally, among the defects in wafers, external contamination such as dust is easily removed by the etching and cleaning process, but in the case of metals such as Cu, they are hardly removed by being taken into the inside of the wafer. There are also sources of pollution. This contamination can cause defects. In addition, crystal defects such as defects, oxygen precipitates, stacking faults, and metal precipitates existing in the grown single crystal mainly occur during the process of growing the single crystal and are not removed by the cleaning process. . In particular, among these, defects such as COPs (Crystal Originated Particles) known as micropits, which are surface defects of semiconductor wafers, are not removed by a conventional general cleaning process, and therefore, crystal growth. Its generation must be suppressed in the process or wafer processing process.

Defects such as COP continue to affect the oxide film breakdown voltage characteristic, that is, the process of forming a semiconductor device on a semiconductor wafer, and are factors that reduce the yield and reliability of the semiconductor device. Become. Therefore, it is very important to confirm the accurate distribution and density of these defects before forming the semiconductor elements on the wafer in the device manufacturing process, in terms of controlling the yield of the semiconductor elements.

Conventionally, the laser scattering method was mainly used to analyze surface crystal defects of wafers immediately after mirror polishing. For example, NH ₄ 0 H is said SC 1 _{_{_{Composition: H 2 0 2: H 2}}} 0 = 1: 1: After washing the Ueha with 8 chemical solution, the laser liked Yattaringu particle counter machine (Laser Scattering Particle Counter) using The surface of the wafer is irradiated with a laser having a certain wavelength, and the scattered signal is sensed to analyze defects on the wafer surface. However, the conventional method has the following problems. That is, when a conventional laser scattering particle counter is used, the detection limit for defects is about 0. Therefore, COPs smaller than this size cannot be detected. However, even a small defect of 0.12 or less that is not detected affects the quality such as the oxide film breakdown voltage.

In other words, since accurate information on surface defects of wafers could not be obtained, not only could the yield of semiconductor devices manufactured by the subsequent processes be controlled, but also Nor could we find an effective way to control the occurrence of defects. The Cu deposition method was considered as an evaluation method to solve this.

The Cu deposition method is an wafer evaluation method that accurately measures the position of defects in semiconductor wafers, improves the detection limit for defects in semiconductor wafers, and can accurately measure and analyze even finer defects. is there.

A specific wafer evaluation method is to form an insulating film of a predetermined thickness on the wafer surface, break the insulating film on the defective portion formed near the wafer surface, and place Cu or the like on the defective portion. This is to deposit (deposition) the electrolyte. In other words, in the Cu deposition method, when a potential is applied to the oxygen film formed on the surface of the wafer in a liquid (for example, methanol) in which the Cu ions are dissolved, a current is applied to a portion where the oxide film is deteriorated. This is an evaluation method that utilizes the fact that the Cu ions precipitate as Cu ions. It is known that defects such as COP exist in the area where the oxide film deteriorates.

The Cu-deposited defect site of the wafer can be analyzed under the condensing light or directly with the naked eye to evaluate its distribution and density.Furthermore, it can be observed by microscope, transmission electron microscope (TEM) or scanning electron microscope (TEM). (SEM) etc. Disclosure of the invention In the Cu deposition method described above, it takes a long time to season, and in order to use methanol efficiently, it is necessary to process multiple wafers using the same methanol. And the sensitivity was good, but the stability of the measured values was difficult. In particular, there were large variations in the values immediately after the start of the evaluation and between devices.

It was found that the Cu concentration in the solvent used for Cu deposition is important for this stability. However, it was confirmed that the evaluation became unstable when Fe, Ni, etc. were present. When processing multiple wafers, the use of the same methanol may bring in or accumulate impurities, causing a problem such as the incorporation of such instability-causing metals.

The first object of the present invention is to control and evaluate the copper concentration, thereby enabling stable observation of defects, accurate analysis of defect distribution and density, suppression of variations between devices, patches, and the like, and stable operation. In addition, it is an object of the present invention to provide a method and an apparatus for evaluating semiconductor wafers by the Cu deposition method, which can shorten the pretreatment time and enable quick evaluation by using a Cu standard solution by using a Cu standard solution. .

A second object of the present invention is to enable the solvent to be exchanged for each wafer and to efficiently process the solvent, to evaluate the wafer in a short time, and to evaluate the wafer due to contamination. It is an object of the present invention to provide a semiconductor wafer evaluation apparatus and method using a Cu deposition method, which can accurately evaluate a wafer defect by eliminating an instability factor.

In order to solve the above-described problems, a first aspect of the method for evaluating a semiconductor wafer according to the present invention includes: a step of forming an insulating film having a predetermined thickness on a surface of the semiconductor wafer; A step of destroying an insulating film on a defective portion formed in the vicinity and depositing copper in a solvent at the defective portion using a Cu deposition method. The semiconductor wafer is evaluated by adjusting it to the range of ~ 30 ppm. With the current method, it was found that the measured values were large and fluctuate early in the patch, and that very few defects were detected. This is thought to be due to insufficient concentration of copper in the solvent, for example methanol. The present inventors have conducted intensive studies and have found that it is preferable that 0.4 ppm or more of copper is present in methanol. When the concentration of copper in methanol exceeded 30 ppm, electric field concentration occurred in some defects, and other defects became difficult to see. Therefore, a Cu concentration of about 0.4 to 30 ppm is preferable.

This concentration can also be adjusted by adjusting the seeding time using a dummy wafer. A dummy wafer is a wafer used to start up the equipment (especially cleaning the electrodes) before processing the wafer (evaluated wafer) to be actually evaluated. Oxide film is formed on the wafer before the oxide film is formed. Conventionally, processing (seasoning) of a dummy wafer has been performed for the purpose of cleaning electrodes and ionizing Cu. However, the degree to which Cu was ionized in the solvent is not normally controlled, and it is usually treated by treating for a certain period of time (for example, about 1 hour).

However, even if the treatment was performed for about one hour, the measured values fluctuated greatly and sometimes became unstable. This fluctuated significantly between the effect of the container being measured, the differences in the measuring equipment and the repeated measurements. In such a situation, accurate evaluation could not be performed, and measures to stabilize the evaluation value were urgently needed. According to the study of the present inventors, it has been found that the Cu ion concentration in the solvent is particularly important, and that stable evaluation can be performed by setting the Cu concentration within a certain concentration range. is there.

This concentration can be dealt with by confirming how much eluted, taking into account the size of the container (evaluation container), etc., by processing the dummy wafer (seasoning) described above and then processing. In other words, the processing time in the dummy wafer may be adjusted for each evaluation device and managed so as to be within the above-mentioned concentration range. However, this method requires a particularly long time for the treatment of the dummy wafer (ionization of Cu), and a quick evaluation is performed. It ’s difficult. Seasoning for about one hour may not be enough and may require longer processing.

The present inventor has found that the Cu ion concentration in the solvent is more important than the time for treating the dummy wafer to stabilize the evaluation. Therefore, in order to shorten the evaluation time, a Cu standard solution with a known copper concentration such as copper sulfate or copper nitrate is added in advance to the solvent methanol without performing dummy-amber treatment (seasoning). It was confirmed that it could be done. Thus, it is preferable to adjust the copper concentration because quick evaluation can be performed. The measured values are also stable.

In addition, if the concentration is initially higher than a certain level by adding the Cu standard solution, there is almost no need to adjust thereafter, but the evaluation may be performed while controlling the conductivity in the solvent. Since the conductivity changes depending on the Cu concentration, it is necessary to maintain the conductivity above a certain value. However, care must be taken because metals (ions) other than Cu may change the conductivity.

In addition, in performing Cu deposition, it was confirmed that Fe and Ni hindered copper deposition and hindered accurate defect evaluation. In particular, it is remarkable when Fe and Ni are contained in the solvent at 10 ppb or more. Therefore, it is preferable to control and evaluate the Fe concentration and the concentration of Ni or Ni in the solvent to be 5 ppb or less.

An apparatus for evaluating a semiconductor wafer by a conventional Cu deposition method includes a processing container, a lower electrode provided in the processing container, and an upper electrode provided at a predetermined distance from the lower electrode. And an external power supply for generating an electric field between these electrodes. A semiconductor wafer is placed on the upper surface of the lower electrode, a solvent is injected into the processing vessel, and copper ions are removed from the target wafer.デ Evaluate the ゥ ha.

In this conventional evaluation device, an upper electrode made of copper to which an external voltage can be applied was used. In the conventional Cu deposition method, it was essential to ionize copper from the upper electrode by seasoning (dummy wafer processing). Therefore, it was necessary to use a copper electrode as the upper electrode. On the other hand, the use of copper electrodes required seasoning to clean the copper electrodes. In the first aspect of the evaluation method of the present invention described above, when a Cu standard solution is added to a solvent, a glass electrode, an electrode formed by plating gold on copper, a platinum electrode, a gold electrode or a carbon electrode is used as an upper electrode. It is possible to use electrodes. A glass electrode is a glass substrate with a transparent electrode film made of tin oxide, ITO (indium-tin oxide), or the like. In this case, there is an advantage that it is not necessary to use an electrode, and it is not necessary to perform seasoning for cleaning the electrode.

An i-th embodiment of the semiconductor wafer evaluation apparatus of the present invention includes a processing container, a lower electrode provided in the processing container, an upper electrode provided at a predetermined distance from the lower electrode, An external power supply for generating an electric field is provided between these electrodes, a semiconductor wafer is placed on the upper surface of the lower electrode, a solvent is injected into the processing vessel, and the semiconductor wafer is evaluated by a Cu deposition method. In the apparatus, the upper electrode is a glass electrode, an electrode plated with gold on copper, a platinum electrode, a gold electrode or a carbon electrode.

This device is used when adding a Cu standard solution to a solvent.If an electrode made of a material other than the above-mentioned copper is used, cleaning is easy and time-consuming seasoning is omitted. Processing time can be greatly reduced. In particular, by using a transparent electrode such as a glass electrode, it is possible to improve the sensitivity by using an optical effect, such as applying ultraviolet light to the surface of the wafer through the electrode. A second aspect of the semiconductor wafer evaluation apparatus of the present invention is an apparatus for evaluating a semiconductor wafer by a Cu deposition method, wherein an upper electrode is provided at a predetermined distance from the upper electrode. A lower electrode, an external power supply for generating an electric field between these electrodes, and a solvent injected into the surface of the semiconductor wafer mounted on the upper surface of the lower electrode. It is characterized in that it can be held on the wafer surface. Specifically, the distance between the wafer and the upper electrode The solvent is stored on the surface of the wafer by the surface tension by bringing the surface closer.

If a solvent injection port is formed in the upper electrode and the solvent is injected from the solvent injection port, there is the convenience that the injection operation is facilitated.

It is preferable that the distance between the upper electrode and the lower electrode can be adjusted and maintained by an electrode distance adjusting member. This interval may be appropriately adjusted in consideration of the range within which the solvent can be maintained at the surface tension, the thickness of the sheet, and the like. In other words, it can be set according to the properties of the solvent used and the measurement environment (room temperature, etc.). For example, when methanol whose Cu concentration is adjusted is used as a solvent, it is preferable to adjust the distance from the wafer surface by about 0.3 mm to 1.5 mm. If the distance is more than 1.5 mm, it is difficult to maintain the surface tension, and the solvent may spill due to slight inclination. On the other hand, if the interval is smaller than 0.3 mm, the Cu concentration (absolute amount of Cu) in methanol decreases, and sufficient precipitation may not occur. The force at which the thickness of the wafer varies depending on the size of the wafer 6 inch wafer — For 8 inch wafer, the distance between the upper electrode and the lower electrode may be set to about lmm to 2.3 mm. Further, even a large diameter wafer may be appropriately set in consideration of its thickness.

By further providing a horizontal holder having an adjustment function for maintaining the lower electrode in a horizontal state, the entire apparatus can be maintained horizontal, and good wafer evaluation can be realized.

As the above-mentioned upper electrode, it is possible to use a glass electrode provided with a transparent electrode film such as tin oxide or ITO (indium tin oxide) on a glass substrate, or an electrode plated with copper.

By additionally providing a means for fixing the semiconductor wafer mounted on the upper surface of the lower electrode, there is no inconvenience such as floating of the wafer due to surface tension. · A second aspect of the method for evaluating a semiconductor wafer according to the present invention includes a step of forming an insulating film having a predetermined thickness on the surface of the semiconductor wafer, and a step of forming an insulating film on a defect portion formed near the surface of the semiconductor wafer. And depositing copper in a solvent on the defect site using a Cu deposition method, and depositing copper while holding the solvent on the semiconductor wafer surface by surface tension. It is characterized by the following.

The basic process flow of the second embodiment of the method of the present invention can be said to be the same as that of the conventional method. In the second embodiment of the method of the present invention, seasoning is not required, and the solvent is applied to the wafer surface by surface tension. Because it is kept, the configuration of the equipment used in the Cu deposition process is different from the conventional one and the procedure is also different.

In the second embodiment of the method of the present invention, it is preferable to adjust the copper concentration by adding a Cu standard solution to the above solvent. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a flowchart showing an example of a process order of the first embodiment of the semiconductor wafer evaluation method of the present invention.

FIG. 2 is a schematic explanatory view showing one embodiment of the first aspect of the semiconductor wafer evaluation apparatus of the present invention.

FIG. 3 is a flowchart showing another example of the process order of the first embodiment of the semiconductor wafer evaluation method of the present invention.

FIG. 4 is a schematic explanatory view showing one embodiment of the second aspect of the semiconductor wafer evaluation apparatus of the present invention.

FIG. 5 is a graph showing the change in the Cu concentration in methanol and the change in evaluation according to the number of processed sheets in Experimental Example 1.

FIG. 6 is a photograph showing the result of the first microscope observation in Experimental Example 1.

FIG. 7 is a photograph showing the result of the second and third microscope observations in Experimental Example 1. Fig. 8 shows the evaluation of Cu standard solution added in Experimental Example 2 (Cu concentration in methanol). 0. 383 ppm).

FIG. 9 is a photograph showing the results of microscopic observation of the evaluation (Cu concentration in methanol: 4.45 ppm) obtained by adding the Cu standard solution in Experimental Example 2.

FIG. 10 is a photograph showing the results of microscopic observation of the evaluation (Cu concentration in methanol: 34. Oppm) of adding Cu standard solution in Experimental Example 2.

FIG. 11 is a photograph showing the results of microscopic observation evaluated in Experimental Example 3 at a Cu concentration of 0.857 ppm in methanol.

FIG. 12 is a photograph showing the results of microscopic observation in which the Cu concentration in methanol of 0.857 ppn ^ Ni200ppb in Experimental Example 3 was added and evaluated.

FIG. 13 is a photograph showing the results of microscopic observation in which the Cu concentration in methanol of 0.857 ppn: Fe 200 pppb was added and evaluated in Experimental Example 3.

FIG. 14 is a photograph showing the results of microscopic observation of the copper precipitate on the sample C in Example 2. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 4 in the accompanying drawings, but it goes without saying that various modifications other than the illustrated examples are possible without departing from the technical idea of the present invention. ,.

FIG. 1 is a flowchart showing one example of the process order of the first embodiment of the semiconductor wafer evaluation method using the Cu deposition method according to the present invention. First, an evaluation target wafer w to be evaluated is prepared [Step 100 in FIG. 1]. Necessary pre-processing is performed on this wafer W. As a pretreatment, the wafer is cleaned (step 102 in FIG. 1), and then the wafer W is put into an oxidation furnace, and thermal oxidation is performed to form an oxide film F on the wafer [FIG. Step 104 of 1). The thickness of this oxide film is not particularly limited, but is usually about 25 nm.

Next, with respect to the wafer W whose surface is covered with an insulating film F called a thermal oxide film, 1 To secure an electrical path between the wafer and the lower electrode, a part of the backside of the wafer is etched (step 106 in FIG. 1). The entire pack side of the wafer can be etched, but in the evaluation method of the present invention, it is sufficient to secure the minimum electric passage. Normally, this etching may be performed using hydrogen fluoride (HF) vapor.

The wafer is then washed with pure water to remove residues such as etching gas (step 108 in FIG. 1). Thereafter, Cu deposition is performed on the wafer to be evaluated on which the oxide film is formed [Step 1 12 in FIG. 1].

FIG. 2 is a schematic explanatory view showing one embodiment of the first aspect of the semiconductor wafer evaluation apparatus of the present invention. In FIG. 2, reference numeral 10 denotes an apparatus for evaluating a semiconductor wafer according to the first embodiment of the present invention, which is used as an apparatus for performing Cu deposition.

The evaluation device 10 has a processing container 12. In the processing container 12, a lower electrode (plate) 14 made of gold plating on copper and an upper electrode (plate) 16 made of a material described later are arranged at predetermined intervals. The wafer W whose surface is covered with the oxide film F is set in the wafer holding part 18 so as to be located between the lower electrode 14 and the upper electrode 16.

In the conventional Cu deposition apparatus, a copper electrode was used as the upper electrode, and seasoning was indispensable for cleaning the copper electrode. However, as will be described later, in the first embodiment of the method of the present invention, when a Cu standard solution is used to adjust the copper concentration, it is not necessary to adjust the Cu concentration by seasoning, and the upper electrode 1 As the electrode 6, a non-copper electrode such as a glass electrode, an electrode plated with gold on copper, a platinum electrode, a gold electrode or a carbon electrode can be used. This eliminates the need to use a copper electrode, eliminates the need to perform seasoning for cleaning the electrode, and has the advantage of greatly reducing the processing time.

Connection terminals 14a and 16a are connected to the lower electrode 14 and the upper electrode 16, respectively. The connection terminals 14 a and 16 a are connected to a DC external power supply 20. The 2 A voltage is applied to the lower and upper electrodes 14 and 16 in a variable state by the external power supply 20 so that a constant electric field is formed between the electrodes 14 and 16. I have. A solvent (electrolytic agent) 22 is injected into the processing container 12. Methanol is suitably used as the solvent 22. In the method of the present invention, it is necessary to adjust the copper concentration in the solvent 22 in the range of 0.4 to 30 ppm. The copper concentration can be adjusted by adjusting the time of the series jung, but is preferably adjusted by adding a Cu standard solution to the solvent. When the Cu standard solution is used, a glass electrode or the like can be used as the upper electrode 16 as described above, so that it is not necessary to use a copper electrode and seasoning is not required.

Usually, seasoning is performed with dummy # 18 at the stage of starting Cu deposition. Seasoning is usually performed for about one hour (step 110 in FIG. 1). The reason why such a long time is required is to clean the electrodes and to secure enough time for the copper to ionize. Specifically, for example, methanol is injected as a solvent (electrolytic agent), and a copper plate immersed in methanol is negatively biased to ionize the copper.

Then, after detaching the dummy wafer, the target wafer (evaluated wafer) W is mounted on the wafer holder 18. Next, an external voltage is applied to the lower electrode 14 and the upper electrode 16 to deposit copper ions on the target defect portion of the wafer W [step 112 in FIG. 1]. The strength of the electric field applied at the stage of depositing the prison is usually in the range of 3 to 1 O MVZ cm.

The wafer after such Cu deposition is washed, dried, and [Step 1 14 in FIG. 1] The wafer is visually inspected with a microscope (for example, 50-fold, one-horizontal scanning of about 3.5 mm field of view). Evaluate the number and distribution of deposited copper (precipitated at the defect location) formed in [Step 1 16 in Fig. 1].

FIG. 3 is a flowchart showing another example of the process order of the first embodiment of the evaluation method of the present invention. In the case of Fig. 3, a solution obtained by adding a Cu standard solution to solvent 22 is used. Accordingly, in the Cu deposition apparatus 10 shown in FIG. 2, an electrode other than copper is used as the upper electrode 16, for example, a glass electrode, an electrode plated with copper, a platinum electrode, a gold electrode, or carbon. An electrode or the like can be used. As a result, seasoning (step 110 in FIG. 1) becomes unnecessary, and the processing time can be greatly reduced.

FIG. 4 is a schematic explanatory view showing one embodiment of the second aspect of the semiconductor wafer evaluation apparatus of the present invention. In FIG. 4, reference numeral 30 denotes a semiconductor wafer evaluation device according to the second embodiment of the present invention, which is used as a device for performing Cu deposition.

The evaluation device 30 has a lower electrode 32. As the lower electrode 32, copper-plated copper is used. Above the lower electrode 32, an upper electrode 34 is provided so as to face a predetermined interval. The facing distance between the lower electrode 32 and the upper electrode 34 is maintained by the electrode spacing adjusting member 36 provided at the edge of the electrodes 32 and 34 and can be adjusted as appropriate. . The electrode gap adjusting member 36 is made of glass or the like.

The connection terminals 32 a and 34 a are connected to the lower electrode 32 and the upper electrode 34. The connection terminals 32a and 34a are connected to a DC external power supply 20. A voltage is applied to the lower and upper electrodes 32, 34 in a variable state by the external power source 20, so that a constant electric field is formed between the electrodes 32, 34. The wafer W whose surface is covered with the oxide film F is set on the upper surface of the lower electrode 32 so as to be located between the lower electrode 32 and the upper electrode 34. Reference numeral 38 denotes a wafer holder made of silicone rubber or the like, which is provided on the upper surface of the lower electrode 32 between the wafer W and the electrode gap adjusting member 36 so as to support the side surface of the wafer W.

In the example of FIG. 4, the wafer holder 38 is formed on a flat plate, and the upper side of the wafer holder 38 is the lower surface of the upper electrode 34, the side surface of the electrode gap adjusting member 36, and the wafer. It is a space 4 4 surrounded by the side of W. This space 4 4 does not need to be formed entirely above the wafer holder 38, for example, as shown in FIG. Auxiliary supports 45 made of fluororesin or the like are arranged as shown by the line 4 to support the wafer W and the upper electrode 34 in an auxiliary manner. A protection cover (not shown) may be provided so as not to touch the electrodes 34, 36 and the like.

Reference numeral 40 denotes a solvent injection hole formed in the upper electrode 34. There is no particular limitation on the position of the solvent injection port 40, but it is preferable that the solvent injection port 40 is formed at the center as shown in the illustrated example. The solvent 22 is injected from the solvent injection port 40 onto the surface of the wafer W. The injected solvent 22 is applied to the surface of the wafer W by the force of the surface tension as shown in FIG. 4 by setting the distance between the surface of the wafer W and the upper electrode 34 to a suitable close interval. The solvent 22 can be maintained.

A horizontal holder 42 is attached to the lower surface of the lower electrode 32. The horizontal holder 42 has a horizontal adjustment function so that the lower electrode 32 can be held horizontally, in other words, the entire evaluation device 30 can be held horizontally. As described above, in the evaluation device 30 of the present invention, since the solvent 22 is held on the surface of the wafer W by surface tension, when the evaluation device 30 is tilted, the solvent 22 becomes Although the evaluation device 30 is held horizontally by the horizontal holders 42, the accident that the solvent 22 spills from the surface of the wafer W can be prevented. it can. Therefore, in the present invention, it is important to start Cu deposition in a state where the evaluation device 30 is in the horizontal position in advance.

Since the wafer W may float under the influence of the surface tension acting between the upper electrode 34 and the wafer W, the wafer fixing means for fixing the wafer W placed on the upper surface of the lower electrode 32 may be used. For example, as shown by a virtual line in FIG. 4, it is preferable to provide a suction mechanism 46 for holding the rear surface of the wafer W by vacuum suction so that the wafer W can be fixed.

Thus, in the present evaluation apparatus 30, the processing container (reference numeral 12 in FIG. 2) described above is used. Do not use containers to store solvents. For this reason, since unnecessary contact with a container or the like is not required, metal contamination caused by contamination of the container or the like can be avoided. In this evaluation device 30, a solvent (methanol) to which a constant concentration of Cu standard solution is added is used. As a result, it is not necessary to use a Cu electrode as the upper electrode 34, so that it is possible to save time for seasoning such as a step of cleaning the Cu electrode.

A solvent whose concentration is controlled to a constant Cu concentration is used, and as the upper electrode 34, a glass electrode or an electrode plated with gold on copper can be used. By using a solvent with a constant Cu concentration in this manner, the upper electrode 34 does not need to be particularly limited.

That is, as the upper electrode 34, the same electrode as the lower electrode 32 obtained by plating copper on gold, a glass electrode, a gold electrode, a platinum electrode, a carbon electrode, and other electrodes can be used.

As described above, by using an electrode other than copper as the upper electrode 34, the seasoning time for cleaning the electrode, which has conventionally taken a long time, can be omitted. That is, the electrode is easier to clean than the Cu electrode, which is preferable. In addition, the surface of the Cu electrode is oxidized during use, and becomes a non-conductive state. By using a glass electrode or an electrode in which gold is coated on copper, long-term evaluation can be performed stably without oxidation.

In particular, by using a glass electrode as the upper electrode 34, the state in which the injected solvent spreads over the wafer can be observed, the solvent can be supplied stably, and ultraviolet rays can be passed through the electrode to the wafer surface. For example, optical effects can be used to increase sensitivity. The glass electrode is obtained by attaching a transparent electrode film to a glass substrate such as a quartz plate. This electrode may be one in which an electrode film is formed on a transparent substrate other than glass. Next, a second embodiment of the semiconductor wafer evaluation method of the present invention will be described. The order of the steps in the second embodiment of the semiconductor wafer evaluation method of the present invention is not specifically described. 6 is the same as the flowchart of the other example of the process order of the first embodiment of the evaluation method of the present invention shown in FIG. 3 described above, but the drawing is not repeated, and FIG. 3 is omitted. It will be described using FIG.

A second aspect of the semiconductor wafer evaluation method of the present invention is characterized in that copper is deposited while a solvent is held on the wafer surface by surface tension. As a whole, the evaluation method for semiconductor wafers is basically the same as the method shown in Fig. 1 before seasoning. In other words, an evaluation target wafer W to be evaluated is prepared (step 100 in FIG. 3), and necessary preprocessing is performed on this wafer W. As a pretreatment, the wafer is cleaned (step 102 in FIG. 3), and then the wafer W is put into an acid furnace and subjected to thermal oxidation to form an oxide film F on the wafer. (Step 104 in FIG. 3). Next, in order to secure an electrical path between the upper and lower parts of the wafer W, a part of the back side of the wafer W is etched with hydrogen fluoride (HF) vapor or the like (step in FIG. 3). 1 0 6) ₀ then washed with pure water residues such as etching gas to divided (step 1 0 8 in FIG. 3), then to be evaluated Ueha this acid I arsenide film is formed Cu deposition is carried out (step 1 1 2 in FIG. 3). In the second embodiment of the method of the present invention, the method of performing Cu deposition is different from that of the first embodiment of the method of the present invention, and the Cu deposition apparatus used in the second embodiment of the method of the present invention (FIG. 4). ) Is completely different from the Cu deposition system in Fig. 1. In the second embodiment of the method of the present invention, using the Cu deposition apparatus of the present invention shown in FIG. 4, first, the wafer to be evaluated W is set, and the upper electrode 34 and the surface of the wafer to be evaluated W Set to mm. This interval is appropriately adjusted depending on the thickness of the wafer W, the surface tension of the solvent 22 and the amount of the solvent required for Cu deposition.

Next, a methanol solution (solvent) 22 whose Cu concentration is controlled is injected from the solvent injection port 44 of the upper electrode 34. At this time, methanol (solvent) 22 gradually spreads along the surface of the wafer W and the electrodes 32, 34.保持 Hold so that methanol (solvent) 22 exists only on the surface of wafer W. 7 At this time, there is a possibility that ゥ AW may stick to (float) the upper electrode 34 side due to the surface tension of methanol (solvent) 22, and 裏面 The back surface of ハ W may rise due to the surface tension. It is preferable to hold by suction by a vacuum suction mechanism 46 or the like so as not to cause the problem.

In this state, (Step 1 1 2 in Figure 3) the upper electrode 3 4 and by applying an external electrode to the lower electrode 3 2 thereby depositing a copper Ion on the defect site Ueha W is ₀ By doing this,銅 Copper is deposited on the surface of the wafer.

The wafer subjected to such Cu deposition is washed and dried (steps 114 in FIG. 3), and the number of copper deposits (deposited at defect locations) formed on the wafer by a visual microscope. And the distribution (steps 1 and 16 in Fig. 3).

After Cu deposition, the solvent 22 was discarded, and the test wafer was evaluated sequentially using a new solvent. That is, the method of the present invention can be said to be an evaluation method using methanol (solvent) in a single wafer.

In the second aspect of the present effort method, methanol (solvent) is present only on the wafer W by making good use of the surface tension as described above, so that there is little external contamination. In addition, since methanol (solvent) is discarded each time Cu deposition is performed once, there is an advantage that there is no accumulation of impurities.

In the conventional method, a large amount of methanol (solvent) was used from the beginning. When there are many wafers to be evaluated, the amount of methanol (solvent) used is not particularly problematic. However, when evaluating several wafers, a large amount of methanol is required as well. Often wasted. In the second mode of the method (apparatus) of the present invention, the solvent (methanol) only needs to be supplied onto the wafer in an amount that can be maintained at the surface tension, and there is an advantage that the solvent is reduced.

Further, in the second embodiment of the method (apparatus) of the present invention, wafers having different diameters can be easily processed by the same apparatus because a conventional processing vessel is not used. Conventionally, processing vessels are prepared for each diameter, or the processing vessels are adjusted to large diameters beforehand. 8 In some cases, the solvent had to be used and wasted. In the apparatus of the present invention, since only the solvent is retained on the wafer surface, there is basically no need to change the size of the apparatus itself. For example, if the apparatus is made for an 8-inch wafer, Electrode spacing adjusting member ゃゥ A wafer of other diameter can be easily evaluated with a slight adjustment of the wafer holding (fixing) means.

Further, in the second embodiment of the method of the present invention, by using a solvent in which the Cu concentration is adjusted in advance, it is possible to omit the time for seeding, such as cleaning of the electrode and ionization of the Cu electrode, which have conventionally taken a long time. This allows for efficient and short-time wafer evaluation.

Example

Hereinafter, the method of the present invention will be described in more detail with reference to examples. However, it is needless to say that these are mere examples and should not be construed as limiting.

(Experimental example 1)

(Confirmation of the stability of the Cu concentration and Cu deposition measurement results in methanol) A 6-inch CZ mirror-polished wafer was used as the wafer to be inspected. Using the apparatus shown in Fig. 2 (however, a copper electrode was used as the upper electrode), 23 wafers were processed according to the above procedure shown in Fig. 1 and evaluated.

However, the thickness of the oxide film formed in the thermal oxidation (step 104 in FIG. 1) was 25 nm, and the etching in the backside etching (step 106 in FIG. 1) was hydrogen fluoride (HF). The applied electric field in Cu deposition (steps 11 and 12 in FIG. 1) was performed at 5 MVZ cm for 5 minutes. In this experimental example, seasoning was performed for 1 hour in advance under 5 MVZ cm.

After seasoning, the test wafers were processed one by one, and the number of defects appearing in Cu deposition and the copper concentration in methanol were confirmed.

The number of defects is determined by observing the defects by scanning them in a straight line in the diameter direction of the wafer by microscopic observation (50 ×, about 3.5 mm field of view), and the number of precipitated copper (defects) per unit area. (Piece Zcm ² ) was calculated.

The copper concentration in methanol was evaluated by ICP-MS after sampling 100 μl of the solvent and placing it in 100 ml of 1% nitric acid.

Figure 5 shows the results. As the number of substrates increased, the Cu concentration increased, and defects in Cu deposition were clearly observed. Although there is some variation, it can be seen that the evaluation was stable after the fourth sheet.

Figures 6 and 7 show the results of microscopic observations of typical defect states. Fig. 6 shows the observation result of the first sheet, and Fig. 7 shows the observation result of the 23rd sheet. No defect can be observed on the first sheet, but a permanent defect can be observed on the 23rd sheet. Defects similar to those in Fig. 7 are seen from the fourth sheet onward. From this, it can be seen that in order to stabilize the Cu deposition, the initial Cu concentration has an effect on the copper concentration in methanol, especially on the dispersion at the start of the evaluation.

However, when the Cu concentration exceeds a certain level, it is considered that the number of Cu deposition itself can be stably measured without change. The critical concentration is considered to be about 0.4 ppm, below which defects are not clearly observed and the measurement becomes unstable.

(Experimental example 2)

(Confirmation of Cu deposition using methanol with Cu standard solution added) According to Experimental Example 1 above, it is clear that control of the copper concentration in methanol is important to stabilize the measurement. Became. However, as mentioned above, it takes a lot of time if the measurement is repeated or the time of seasoning is increased and the concentration of copper in methanol is increased. Therefore, before evaluating the test sample, it was confirmed whether the evaluation could be performed by adding a solution having a known Cu concentration.

Using a commercially available Cu S0 ₄ · 5H ₂ 0 (manufactured by Kanto Chemical Co., Inc.) as a Cu standard solution. Using this standard solution, the concentration and concentration of Cu in methanol were adjusted to about 0.3, 0.8, 4.0, and 30 ppm, and the same apparatus and procedure as in Experimental Example 1 were used. Rated by Was done. In this experimental example 2, seasoning (processing for cleaning the electrode) was performed in 30 minutes.

As a result, the actual Cu concentration in methanol was 0.383 ppm, 0.886, 4.45, and 34 ppm. With the result of Cu deposition of 0.383, as shown in Fig. 8, the defect appeared only in a thin state, and the defect was not counted in some cases. At 0.886 and 4.45 ppm, clear defects can be observed as shown in Figure 9. When a Cu standard solution with a very high concentration of 34 ppm is added, abnormal defects as shown in Fig. 10 may be observed. This is thought to be caused by the electric field concentration. Even in such a state, the evaluation value may vary, so the upper limit is preferably about 30 ppm.

As described above, when the Cu concentration is less than 0.4 ppm, it is clear that the measurement varies, and a higher Cu concentration is required. The Cu concentration may be adjusted by seasoning or by adding a Cu standard solution from outside. Such a method is particularly effective because the pre-processing (seasoning) time for evaluation is reduced.

Next, it became clear that there were other factors in the instability factor of Cu deposition. As is clear from the experimental example 1 described above, it was clear that the measured values were stable when the Cu concentration was 0.4 ppm or more, but there was some variation among the stable data. A close investigation into the cause revealed that there were substances that hindered Cu deposition. This is a heavy metal other than Cu, such as Fe or Ni.

(Experimental example 3)

The evaluation was performed by setting the Cu concentration in methanol to 0.857 ppm. To this, Fe and Z or Ni were added for evaluation. Using the same apparatus as in Experimental Example 1, the basic Cu deposition method is also the same as in Experimental Example 1.

(1) When nothing is added, the defect can be observed as shown in FIG. Two

(2) When Ni was added at 200 ppb, no defect was observed as shown in FIG.

(3) When Fe was added at 200 ppb, no defect was observed as shown in FIG.

(4) When? ^ 1 is 89.78 ppb and Fe is 57.36 ppb, no defects are observed as in FIGS. 11 and 12.

(5) When the Cu concentration is 1.17 ppm, the Ni concentration is 20 ppm, and the Fe concentration is 10 ppm, no defects are observed as in FIGS.

Therefore, it was found that more stable evaluation of Cu deposition can be achieved by controlling the concentrations of Fe and Ni in methanol, and in particular, controlling the concentration to be 5 ppb or less.

(Example 1: First embodiment of the method of the present invention)

As the wafer to be inspected, a 6-inch CZ mirror-polished wafer was used. In this example, the wafer to be inspected was processed and evaluated according to the procedure shown in FIG. 3 using the apparatus shown in FIG. 2 in which the upper electrode was a glass electrode. The glass electrode is made by attaching a transparent electrode film to a quartz plate.

Using methanol containing 10 ppm of a Cu standard solution as a solvent, copper was immediately deposited (without seasoning), and wafer defects were evaluated. In other words, seasoning for 1 hour or 30 minutes under 5 MV / cm, which was performed when a Cu electrode was used, was not performed. The conditions for depositing copper and the method of evaluating defects are the same as those in Experimental Example 1 above.

As a result, a clear defect similar to that shown in FIG. 9 was observed without using a copper electrode as the upper electrode and without performing seasoning.

(Example 2: Second embodiment of the method of the present invention)

6-inch CZ silicon wafer as the wafer to be evaluated

(Mirror-polished wafer) was prepared. For this wafer, as pre-processing, After washing the wafer, the wafer is put into an oxidation furnace, and then heat-treated at 900 ° C for 95 minutes in an oxygen atmosphere to form a 25 nm thermal oxide film.

Next, in order to secure an electrical path between the wafer and the lower electrode, a part of the pack side of the wafer is etched with hydrofluoric acid vapor. Next, the substrate was washed with pure water to remove a residue such as an etching gas. Then, Cu deposition was performed on the wafer to be evaluated on which the oxide film was formed.

In this embodiment, using the Cu deposition apparatus shown in FIG. 4, the outer periphery of the wafer to be evaluated is first held with silicone rubber or the like so as not to be displaced, and the electrodes are spaced about 1.6 mm apart from each other. Set at about lmm from the evaluation surface. Adjustment of this interval may be performed by holding glass having a constant thickness through which no current flows between the upper and lower electrodes. Next, a solvent having a controlled Cu concentration (in this example, a methanol solution) is injected into the center of the wafer from a solvent injection port formed in the upper electrode.

By doing so, it is possible to maintain the presence of methanol only on the surface of the wafer under the influence of surface tension.

Use a methanol solution whose Cu concentration is controlled in advance. Cu standard solution Specifically, for example, a commercially available Cu S0 ₄ '5H ₂ 0 (manufactured by Kanto Chemical Co., Ltd.) was prepared by adding the solvent. It is preferable to use this standard solution to adjust the Cu concentration to be about 0.4 to 30 ρρπι.

In this example, methanol having a Cu concentration of about 1 ppm was used. This methanol was dropped using a pipette, and was dropped by using surface tension to such an extent that the methanol did not spill out of the wafer. Methanol spreads across the wafer between the wafer and the upper electrode. In this example, approximately 18 milliliters of solvent was dropped per wafer.

Then, an applied electric field was applied between the upper electrode and the lower electrode at 5 MVZcm for 5 minutes. After Cu deposition, wash with pure water, air dry, and observe the copper deposit on the wafer under a microscope. The wafer was scanned in a straight line in the diameter direction of the wafer at a magnification of 50 times (field of view of about 3.5 mm), defects were observed, and the number of precipitated copper per unit area (pieces / cm ² ) was calculated. Figure 14 shows the results of microscopic observation. As is clear from FIG. 14, donut-shaped precipitated copper was observed.

As described above, according to the second embodiment of the method of the present invention, it was confirmed that the inspection time was significantly reduced because seasoning was not performed. In addition, the above operation was repeated to evaluate a plurality of wafers. As a result of the repeated measurement, a defect was stably observed.

(Comparative Example 1)

Using a conventional Cu deposition system, one liter of solvent was placed in the processing vessel and Cu deposition was performed. In addition, seasoning is performed for one hour before depositing at the eha you want to evaluate. As a result of Cu deposition, defects similar to those shown in Fig. 14 were detected in this conventional device.

This operation was repeated without changing the solvent (methanol), and multiple wafers were evaluated. As a result of the repeated measurement, defects were sometimes hard to see. Examination of the cause revealed that the concentrations of Fe and Ni increased. It is probable that these metals were brought in from the evaluated wafers, or that those that had adhered to the processing vessel were eluted.

As described above, in the second embodiment of the method of the present invention, since the process is performed without using a processing container for storing the solvent, external contamination is reduced, and the solvent is exchanged and processed for each sheet. As a result, the accumulation of contamination brought in from other wafers is reduced, and the instability factors due to contamination can be significantly reduced. Also, the amount of solvent can be reduced.

Furthermore, by using a solvent whose Cu concentration has been adjusted in advance, it is not necessary to clean the electrodes or to have a time for seeding jungling such as ionization of the Cu electrodes, thus enabling quick evaluation. Also, use a glass electrode and a gold plated copper electrode as the upper electrode The electrode degradation and contamination sources were further reduced. Industrial applicability

As described above, according to the first aspect of the method of the present invention, by controlling and evaluating the copper concentration, stable defects can be observed, the distribution and density of defects can be accurately analyzed, and between devices, between batches, etc. This has the effect of minimizing the fluctuations in the evaluation and ensuring a stable evaluation. Further, according to the first embodiment of the method of the present invention, the use of the Cu standard solution has the effect that the pretreatment time can be shortened and the evaluation can be performed quickly.

Further, according to the first aspect of the method of the present invention, the first aspect of the present invention using a Cu standard solution as a solvent and using an electrode other than copper such as a glass electrode as an upper electrode is described. By using it, the copper concentration can be easily controlled, stable defects can be observed, and the distribution and density of defects can be accurately and quickly analyzed.

On the other hand, according to the second aspect of the method (apparatus) of the present invention, the wafer can be evaluated in a short time, and further, the instability factor of the wafer evaluation due to contamination can be eliminated, and the wafer defect can be accurately evaluated. .

Claims

The scope of the claims

1. a step of forming an insulating film having a predetermined thickness on the surface of the semiconductor wafer; and destroying the insulating film on a defective portion formed near the surface of the semiconductor wafer. Using a Cu deposition method comprising the step of depositing copper in a solvent, adjusting the copper concentration in the solvent to a range of 0.4 to 30 ppm for evaluation. Eight evaluation methods.

2. The method for evaluating semiconductors and wafers according to claim 1, wherein methanol is used as the solvent.

3. The method for evaluating a semiconductor wafer according to claim 1, wherein the Fe concentration and the Ni or Ni concentration in the solvent are controlled and evaluated to be 5 ppb or less.

4. The method for evaluating a semiconductor wafer according to any one of claims 1 to 3, wherein the copper concentration is adjusted by adding a Cu standard solution to the solvent.

5. A processing container, a lower electrode provided in the processing container, an upper electrode provided at a predetermined distance from the lower electrode, and an external power supply for generating an electric field between these electrodes. An apparatus for placing a semiconductor wafer on the upper surface of the lower electrode, injecting a solvent into the processing vessel, and evaluating the semiconductor wafer by a Cu deposition method, wherein the upper electrode is a glass electrode, 5. The method for evaluating a semiconductor wafer according to claim 4, wherein the evaluation is performed without performing seasoning using a semiconductor wafer evaluation apparatus that is an electrode plated with gold on a copper, a platinum electrode, a gold electrode, or a carbon electrode.

6. A processing container, a lower electrode provided in the processing container, an upper electrode provided at a predetermined distance from the lower electrode, and an external power supply for generating an electric field between these electrodes. An apparatus for placing a semiconductor wafer on the upper surface of the lower electrode, injecting a solvent into the processing vessel, and evaluating the semiconductor wafer by a Cu deposition method, wherein the upper electrode is a glass electrode, Gold-plated copper electrode, platinum electrode, An apparatus for evaluating a semiconductor wafer, which is a gold electrode or a carbon electrode.

7. An apparatus for evaluating a semiconductor device by a Cu deposition method, comprising an upper electrode, a lower electrode provided at a predetermined distance from the upper electrode, and an electric field between these electrodes. And an external power supply for generating electric power, injecting a solvent into the surface of the semiconductor wafer mounted on the upper surface of the lower electrode, and holding the injected solvent on the surface of the semiconductor wafer by surface tension. A semiconductor wafer evaluation apparatus characterized in that it can be used.

8. The apparatus for evaluating a semiconductor wafer according to claim 7, wherein a solvent injection port is formed in the upper electrode, and a solvent is injected from the solvent injection port.

9. The semiconductor wafer evaluation apparatus c10 according to claim 7 or 8, further comprising an electrode gap adjusting member for adjusting and maintaining the gap between the upper electrode and the lower electrode. 10. The apparatus for evaluating a semiconductor wafer according to claim 7, further comprising a horizontal holder having an adjusting function for maintaining a stable state.

11. The apparatus for evaluating a semiconductor layer according to claim 7, wherein a glass electrode or an electrode plated with copper is used as the upper electrode. 12. The evaluation of the semiconductor wafer according to any one of claims 7 to 11, further comprising means for fixing the semiconductor wafer mounted on the upper surface of the lower electrode. apparatus.

13. A step of forming an insulating film having a predetermined thickness on the surface of the semiconductor wafer; breaking the insulating film on a defect site formed near the surface of the semiconductor wafer; Using the Cu deposition method comprising the step of depositing copper, and depositing copper while holding the solvent on the surface of the semiconductor wafer by surface tension.

14. The method for evaluating a semiconductor wafer according to claim 13, wherein the copper concentration is adjusted by adding a Cu standard solution to the solvent.