JP2010103320A - Semiconductor inspection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor inspection apparatus capable of measuring an interface state on the bottom of a hole and capable of improving the SN ratio of beam irradiation without being affected by a displacement of an irradiating position. <P>SOLUTION: In the semiconductor inspection apparatus for evaluating an interface state of a contact hole of a wafer 23 by using an absorption current measurement method using an electron beam, an electron beam EB is applied to the contact hole of the wafer 23 to measure an absorption current of the wafer 23. In the measurement of the absorption current, the electron beam EB is defocused to a size slightly larger than the contact hole and the contact hole of the wafer 23 is scanned with the defocused electron beam EB to measure the absorption current. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a semiconductor inspection apparatus suitable for evaluating a semiconductor device manufacturing process.

  LSI wiring defect analysis and defect detection using an optical type or electron beam (EB) have already been performed (see Patent Document 1).

As an optical method, for example, an OBIC method (Optical Beam Induced Current) (Non-Patent Document 1) in which an electron beam is generated by irradiating a sample with an infrared laser and the current flowing through these generated carriers is measured is well known. Are known. The EBIC method (Electron Beam Induced Current) (see Non-Patent Documents 2 and 3) that measures the current that flows by irradiating EB onto the sample surface in a similar manner, and the phenomenon that a part of the EB irradiation current is absorbed are measured. An EBAC method (Electron Beam Absorbed Current) (see Non-Patent Document 4) has been developed and put into practical use.
International Publication 2008-53524A1 K. Haraguchi; Microscopic Optical Beam Induced Current Measurement and their Applications, Proc. IEEE (IMEC'94), May10-12, Vol.2, 1994, pp693-699. Tadashi Kondo, et al. GaAsMMIC failure location analysis example using EBIC / OBIC, LSI Testing Symposium, 2002, pp363268. Yusuke Ueki, et al .; Failure analysis by electron beam absorption current method, LSI testing symposium, 2007, pp303-307. Satoshi Nokuo, et al .: Consideration of semiconductor device failure location detection method using electron beam absorption current, LSI Testing Symposium, 2007, pp293-296. Susumu Yano, et al .: Potential contrast defect detection and simulation technology, LSI testing symposium, 2006, pp59-64. Hong Xiao, et al; A high Throughput Gray Level Measurement Method for Process Window Characterization / Production Monitor, LSI Testing Symposium, 2006, pp65-70. Topcon HP Keizo Yamada, Process management example using EB-Scope system, Electronic materials, June 2006, pp45-51. M. Honda, et al; Electron-beam Substrate Current Monitoring Technique for Contact Process Optimization & Yield Enhancement, 2007 Advanced Metallization Conference, October 9-11, 2007, pp185-186.

  With the future miniaturization of LSIs, the above-described inspection / evaluation method using an electron beam is considered to be a promising and promising method. The reason for this is the merits and controllability of EB convergence, permeability and absorption. However, although the above measurement method is effective for identifying the location of the defective part and identifying the cause process, it seems that it is not the optimal method for detecting an abnormality immediately after each wiring process (production line). . At the same time, it is necessary to form some electrode on the wafer in order to perform defect analysis and defect detection in the above method.

  On the other hand, EBI (Electron beam Inspection) (see Non-Patent Documents 5 and 6) is generally used for inspection immediately after each process, but it is limited to measurement of pattern dimensions and shapes. For example, a new measurement method must be proposed for failure analysis of the bottom interface of high aspect contact holes, which will be the most important in the future.

  The inventors of the present application have developed an EB-Scope that can measure the EB absorption current directly from the back surface of the wafer substrate, and can measure the thin film and contact hole diameter / interface evaluation (see Non-Patent Document 7). Have been evaluated. It has already been reported that the hole diameter can be measured to 40 nm (see Non-Patent Document 8), and the SiO2 thin film measurement can be measured in the order of nm, and a difference of about 50 to 250 Ω can be measured (Non-Patent Document 9). reference).

  In this report, we report the evaluation results of contact hole interface using EB-Scope. The substrate current value measured by EB-Scope (EB absorption current value; hereinafter referred to as EBS value) was clearly obtained as data that is considered to indicate information on the contact hole interface. At the same time, when the data was organized by a method of normalizing the measured EBS value with the hole diameter (normalized EBS value), it was found that the pattern considered to be a process abnormality exists in the normalized EBS value.

  Further, in the existing LSM (Line Scan Mode), the contact hole is scanned with a focused electron beam, the diameter of the contact hole is measured, and the opening / non-opening of the hole is measured, but the sensitivity to the thin film is low. There's a problem.

  On the other hand, BLM (Blanket Mode) irradiates a contact hole with a defocused electron beam and measures the interface state at the bottom of the hole, but simply irradiates a beam with a diameter larger than the diameter of the contact hole opening. The beam luminous flux is biased depending on the irradiation position, so that there is a large variation in measurement results depending on the irradiation position, and there is a problem that the S / N ratio due to the beam irradiation to the insulating region outside the hole is reduced. Furthermore, in order to cancel the influence of the surroundings, there is an operation in which reference data must be obtained using the same beam diameter in a place where there is no contact hole near the measurement point. As a result, there was a problem that the actual measurement time doubled at once.

  The present invention makes it possible to measure the interface state at the bottom of the hole with high sensitivity, and is not affected by the displacement of the irradiation position, can improve the S / N ratio of beam irradiation, and in the vicinity of the reference. It is an object of the present invention to provide a semiconductor inspection apparatus capable of eliminating the data collection and reducing the measurement time to half that of the prior art.

The invention of claim 1 is a semiconductor inspection apparatus for evaluating an interface state of a contact hole of a wafer using an absorption current measuring method using an electron beam.
When measuring the absorbed current of the wafer by irradiating the contact hole of the wafer with the electron beam, the electron beam is defocused to be slightly larger than the contact hole, and the contact hole of the wafer is scanned with the electron beam. And measuring the absorption current.

  According to the present invention, the electron beam is defocused to a size slightly larger than the contact hole, and the contact hole is scanned with this electron beam to measure the absorption current. Therefore, the interface state at the bottom of the hole is highly sensitive. In addition, the S / N ratio of the beam irradiation can be improved without being affected by the irradiation position shift. Also, the measurement time can be halved compared to the conventional method.

(Summary of Invention)
The present inventors can measure the absorption current (substrate current; EBS) directly from the back surface of the wafer substrate with high sensitivity, measure the thin film on the wafer surface, contact hole diameter, and evaluate the interface at the bottom of the contact. -Development of Scope (model name EBS3000) is underway.

  As described above, it is known that the hole diameter can be measured to 45 nm or less, the SiO2 thin film measurement can be performed in the order of nm, and a difference of about 50 to 250 Ω can be measured.

  Since EB-Scope can obtain information on the interface state at the bottom of the contact hole, it can be expected to be used for process control. As a result of measuring various wafers, it is considered that the absorption current (substrate current) clearly shows information on the contact hole interface. The possibility of process monitoring and control in the production line has also been found by using the normalized EBS technique.

The principle of the present invention will be described below with reference to the drawings.
(1) Measurement principle of EB-Scope FIG. 1 shows the measurement principle of EB-Scope according to the present invention. This EB-Scope has the same configuration as the SEM, but it can measure the absorption current (EBS value) from the backside of the wafer with high sensitivity and accuracy.

  In FIG. 1, WEH indicates a wafer, CONH indicates a contact hole, and CONHD indicates a bottom of the contact hole. There are a measurement mode in which the diameter of the contact hole CONH is measured by scanning the electron beam EB, and a mode in which the EBS value is measured by irradiating the contact hole CONH with a beam diameter slightly larger than the diameter of the contact hole CONH.

When the electron beam EB is irradiated onto the wafer WEH from the electron gun E-Beam Gun, the secondary electrons SE are detected by the electron detector PMT, and the output of the electron detector PMT is amplified by the preamplifier Pre-AMP and is displayed on the display device. The electron microscope image (SEM image) is displayed on the screen Gr of the display device. Also, an absorption current (substrate current) IAC is detected, this substrate current IAC is input to the substrate current amplification system SCAS, this substrate current IAC is also input to the display device, and an image based on the substrate current is displayed on the screen Gr of the display device. Displayed by a predetermined process.
Table 1 shows the basic specifications of EBS3000.

FIG. 2A and FIG. 2B are conceptual diagrams showing an EB-Scope measurement mode. FIG. 2A shows an LSM (Line scan mode) for measuring the size of the contact hole CONH. FIG. 2B shows a BLM (Blanket Mode; a mode in which measurement is performed in a stationary state by increasing the beam diameter) for evaluating the contact hole interface. There are mainly two measurement modes, but it is also possible to perform measurement having both of these (scanning with the beam diameter enlarged).

  As shown in FIG. 2A, a substrate current IAC is obtained by scanning with the electron beam EB. When the profile of the substrate current IAC is differentiated, a differentiated waveform BW is obtained, and the diameter φ of the contact hole CONH and the shape of the edge can be determined from the differentiated waveform BW. When the contact hole CONH is a single hole, the substrate current IAC has a single profile. However, when the contact hole CONH is a multihole, the profile of the substrate current IAC has an AC shape.

  As shown in FIG. 2B, when the beam diameter of the electron beam EB is increased and the contact hole CONH of the wafer WEH is irradiated in a stationary state, a substrate current IAC is obtained. The substrate current IAC is a DC component current although it fluctuates slightly. When the contact hole CONH is a single hole, it is desirable that the diameter of the electron beam EB is slightly larger than the diameter φ of the contact hole CONH. In the case where the contact hole CONH is a multi-hole, the diameter of the electron beam EB is preferably a diameter including several contact holes CONH.

  The state of the thin film and the contact hole CONH shown in FIG. 3 is measured while making full use of these measurement modes.

  In FIG. 3, (a) is a CONH insulating layer residue, (b) is a CONH polymer residue, (c) is a CONH etch stopper processed state, (d) is a CONH stopper penetration state, (e) is a small and strange shape. CONH and (f) show the thin film layer thickness state, respectively.

In general, the current IAC absorbed in the wafer substrate WEH is as shown in FIG.
IAC = Ip−IS−IBS (1)
It can be expressed using the following formula.

  Here, Ip is an initial current incident on the wafer WEH, IS is a current caused by secondary electrons emitted outside the wafer substrate WEH, and IBS is a current caused by reflected electrons. Since EB-Scope has an acceleration voltage of about several kV, IBS can be ignored. Further, defining IS as “secondary electrons emitted outside the wafer substrate WEH” means that it is necessary to consider the influence of secondary electron pullback due to the charging of the wafer substrate surface WEHS.

  The thin film measurement (SiO2 film) has already been compared with the simulation results (see Fig. 11), and the generation of electron-hole pairs by EB irradiation and the electrons flowing to the Si substrate due to these generated carriers are considered. Qualitatively, the measurement results can be well explained up to a film thickness of about 10 nm.

Also, in the charging simulation for the insulating film sufficiently thicker than the EB penetration depth, the result of calculating the current flowing into the wafer substrate (WEH) is shown (see FIG. 12). Since the electron flow to the wafer substrate WEH occurs even if the insulating film INS is present, it can be expected that the EB-Scope can measure various phenomena.
(2) Measurement example of LSM, BLM, D-LSM (2-1) Measurement example of LSM FIG. 5 shows a measurement example of the diameter of the contact hole CONH by LSM. As shown in FIG. 5, when the EB scan is performed, a substrate current IAC is obtained, and special data processing is performed on the LSM profile based on the substrate current IAC to calculate the diameter φ of the contact hole CONH.

  An example of the measurement reproducibility of the calculated diameter φ of the contact hole CONH is shown in FIG. FIG. 6 shows the result of 10 repetitions. Further, FIG. 6 shows five line graphs. The five line graphs are the diameter φ of the contact hole CONH obtained by each one of the five scanning lines in FIG. The line graph connecting the maximum values corresponds to the diameter φ of the contact hole CONH obtained by the central scanning line in FIG.

Next, FIG. 7 shows an example of measurement linearity. The measurement reproducibility was about 1 nm for a contact hole diameter φ in the range of 45-130 nm. In the measurement result of the contact hole diameter, R2 = 0.9944 was obtained in correlation with the CD-SEM measurement, and a result with good linearity was obtained. By using EBS3000, the process abnormality can be monitored by investigating the deviation of the contact hole diameter φ and the distribution in the wafer surface.
(2-2) BLM measurement example In the BLM, the EBS value is measured by irradiating a beam diameter slightly larger than the contact hole diameter without scanning. For this reason, information outside the contact hole is also measured. In order to cancel unnecessary information in the vicinity, a method (referred to as “Base line offset”) is adopted in which the peripheral information without the reference hole is measured in the same manner and the peripheral information is canceled by subtraction, as will be described later. .

BLM measurement examples are shown in FIGS. 8 (a) and 8 (b). FIG. 8A shows the interface state at the bottom of the contact hole after etching. The portion with a high EBS value is considered to have cleaning residue. Further, as shown in FIG. 8 (b), it has been found that evaluation such as Under / Over etching of an etch stopper at the bottom of Via is possible. Thus, the state of the contact hole interface can be easily observed. However, there are drawbacks as described above (measurement instability, measurement time, etc.).
(2-3) Measurement Example of D-LSM (Defocus-Line Scan Mode) FIG. 21 shows a measurement example of D-LSM. In this D-LSM, the electron beam is defocused, and this defocus is performed. The size of the electron beam EB1 is slightly larger than the contact hole CONH, the electron beam EB1 is line-scanned on the contact hole CONH, and the absorption current at this time is measured. According to this measurement, the absorption current flows most when the center of the electron beam EB1 comes to the center of the contact hole CONH, and the interface state at the bottom of the hole is not affected by the periphery of the hole and the internal structure. It can be measured with high sensitivity.

  That is, as shown in FIG. 22A, when the periphery or the inside of the contact hole CONH is, for example, stepped, that is, has a large-diameter hole portion H1 and a small-diameter hole portion H2, As shown, when measured by BLM, the absorption current value varies depending on the position of the irradiated electron beam EB1 (eccentric position with respect to the contact hole CONH), and interface evaluation cannot be performed correctly. However, as shown in FIG. 22C, the defocused electron beam EB1 (in FIG. 22A, for convenience of explanation, the diameter of EB1 is smaller than that of the large-diameter hole portion H1) is scanned. When the absorption current is measured, the absorption current becomes maximum when the center of the electron beam EB1 comes to the center of the contact hole. That is, the absorption current can be detected with the maximum sensitivity, and by detecting this maximum absorption current, the interface evaluation can be performed with a high sensitivity without being influenced by the internal structure of the contact hole CONH.

  When the data of the part without the peripheral contact hole is acquired, the peripheral data can be obtained by widening the scan to a part not affected by the hole. That is, the hole bottom data and the peripheral data can be acquired with a single operation, which is efficient.

  Further, as shown in FIG. 23, the shape of the electron beam is matched with the shape of the contact holes Ha and Hb, the electron beam is scanned, and interface evaluation is performed from the maximum absorption current obtained by the scan.

  That is, as shown in FIG. 23A, the shape of the defocused electron beam Ba is changed to an ellipse whose left and right are major axes in accordance with the shape of the elliptical contact hole Ha whose left and right are major axes. The maximum absorption current is detected by scanning Ba as shown in the figure. Further, as shown in FIG. 23B, the shape of the defocused electron beam Bb is changed to an ellipse whose upper and lower sides have a long diameter according to the shape of an elliptical contact hole Hb whose upper and lower sides have a long diameter. Bb is scanned as shown to detect the maximum absorption current.

  As described above, since the elliptical shapes of the contact holes Ha and Hb and the elliptical shapes of the defocused electron beams Ba and Bb are matched, the S / N ratio with respect to the electron beams Ba and Bb can be improved.

  Incidentally, as shown in FIG. 23C, when measurement is performed by irradiating the contact hole Ha with a circular electron beam Bc as in the prior art, the irradiation area of the surrounding insulating region outside the contact hole Ha is as follows. It becomes larger and the loss of current increases. For this reason, the S / N ratio with respect to the electron beam Bc deteriorates (decreases).

As shown in FIG. 24A, the D-LSM measurement is performed first by measuring the LSM, and after that without performing the BLM measurement shown in FIG. 24B. Will be measured.
(3) Measurement method It was found that the LSM / BLM measurement described in (2) can understand the situation of the contact hole bottom to some extent. However, the measurement result of BLM that can measure the state of the bottom of the contact hole with high sensitivity is affected by the hole size. Therefore, in order to obtain “more accurate information”, it is necessary to normalize by the hole area. Therefore, the “normalized EBS” method is adopted for evaluation. Fig. 9 shows the outline.

  First, as shown in FIG. 9, the diameter φ of the contact hole CONH is accurately measured by LSM. Next, the EBS value at the bottom of the hole is measured by BLM. In order to eliminate the influence of the hole diameter, the EBS value at each measurement point is divided by the hole area to obtain the EBS value per unit area. At this time, normalization is performed by determining a representative area as a reference and taking a ratio with this. Formula (2) shows the calculation formula.

FIG. 10 (a) shows a map obtained by measuring the contact hole diameter φ after the etching and cleaning process using LSM, and FIG. 10 (b) shows the EBS value after the etching and cleaning process. FIG. 10C shows a map of EBS values normalized by BLM, and FIG. 10D shows the relationship between the diameter of the contact hole CONH and the normalized EBS value. It is graphed and shown as information. Each map (or digitized information) provides useful information for line management.
(4) Normalized EBS pattern Generally, if each process is uniform, a substantially constant normalized EBS value independent of the hole size can be obtained as shown in the standard pattern of FIG. In fact, such data is obtained for a wafer WEH with a good yield.

  However, as a result of evaluating various wafers WEH, the normalized EBS pattern includes patterns 1, 2, and 3 (Pattern1, 2, and 3) shown in FIG. 11 and their composite patterns 1-2 and 2-3 (Pattern1). -2,2-3) has been found to exist.

  Currently, pattern 4 (Pattern4) and pattern 3-4 (Pattern3-4) have not been confirmed yet.

  The value of the normalized EBS value when the process is properly performed shows a substantially constant value, but the value varies slightly depending on the process conditions, device structure, and materials used. For reasons of the production line, if the value rises or falls below this fixed value, it is considered that some abnormality has occurred in the contact hole CONH.

  For example, when the contact hole CONH does not penetrate (Under etching) or when a residual film such as a SiO2 film is generated, the normalized EBS value tends to be small. In the case of under-etching, it is close to a state in which conduction cannot be achieved, and when a residual film is generated, secondary electrons are generated due to the presence of the SiO2 film, resulting in a small EBS value.

  On the other hand, when an organic substance (polymer material) such as a resist is present at the bottom of the hole, since the generation efficiency of secondary electrons is smaller than that of Si, the normalized EBS value tends to increase. Even if the hole bottom is large, the normalized EBS value tends to be low when a TiN film is present at the hole bottom. Further, when etching progresses and reaches the stopper and reaches the silicide, generation of secondary electrons of the silicide is large, so that the normalized EBS value is expected to be further lowered.

  Therefore, when the normalized EBS value increases as the contact hole diameter decreases, the presence of organic substances is suspected. Conversely, when the contact hole diameter decreases, processing defects are suspected, and as the hole diameter increases, the normality increases. When the converted EBS value is small, it can be estimated that there is an influence of the remaining film or an over-etched state.

However, since these differ depending on each process condition, device structure, and material used, a uniform cause cannot be derived. Verification in each case is necessary. A method that utilizes normalized EBS while understanding a certain degree of causality is considered to be extremely useful for process management.
(5) Measurement Example / Operation Example of Normalized EBS Value FIG. 12A shows a map of the normalized EBS value in the wafer surface. FIG. 12 corresponds to the wafer WEH corresponding to the pattern 2-3 of FIG. FIG. 12B shows the relationship between the size of the contact hole CONH and the normalized EBS value. A range of the normalized EBS value having a high probability of non-defective product is determined under a certain assumption, and a normal value that is smaller than that is determined. When the converted EBS value is color-coded, the distribution chart shown in FIG. 12B is obtained. Clearly, the normalized EBS value is considered to indicate a process abnormality.

  In at least the case shown in FIG. 12, it is considered that there are two factors in the process abnormality. This is a portion where a problem of a remaining film at a relatively large portion of the hole distributed on the edge of the wafer WEH and an organic residue scattered on the entire surface of the wafer with a small hole diameter are assumed. Incidentally, a difference is recognized also by TEM observation of each area | region.

  An example of a process management method using normalized EBS will be described with reference to FIG. FIG. 13 shows the result of examining the change in the normalized EBS value by changing the recipe. First, a range of normalized EBS management values that seems to be optimal is set. For example, we measured and set the normalized EBS for golden chips, and saw changes when the control values were exceeded in recipes 1, 2, and 3. At the same time, the yield estimated from the number out of the control range was estimated.

  Recipe 1 has many parts with high normalized EBS values, Recipe 2 has parts with slightly low normalized EBS values, and Recipe 3 has many low EBS values, and there is clearly an abnormality at the bottom of the hole due to process changes. I was able to estimate. Moreover, as a result of obtaining the yield estimated from the normalized EBS value, the actual and qualitative tendencies coincided.

  Further, as shown in FIG. 13, it can be seen that even in the POR wafer, a portion having a slightly high normalized EBS value is generated. Elucidation of POR recipe issues, search for optimal recipes, and confirmation of improvement results can be confirmed quickly by using the normalized EBS method.

  From the above, it can be seen that process management using the normalized EBS method is possible. It is possible to monitor the variation of each process equipment by sample inspection on the production line. Furthermore, the influence of a recipe change or the like can be managed. It is considered effective for tool matching management of each process equipment.

  EB-Scope that can measure EB absorption current directly from the back side of wafer substrate WEH, measure thin film and contact hole diameter, and evaluate interface, and evaluate contact hole interface, which is considered to be the most effective application . The substrate current value (EB absorption current value) IAC obtained data that is considered to clearly show information on the interface of the contact hole CONH.

  At the same time, various data were arranged by a method of normalizing the measured EBS value with the contact hole diameter, and it was found that there was a pattern considered to be a process abnormality in the normalized EBS value. At the same time, the possibility of process management using normalized EBS values could be shown.

    Further, from FIG. 12 showing a map of the normalized EBS value in the wafer surface, the type, size, etc. of the contact hole are displayed as dots on the wafer, and the distribution graph of the normalized EBS value is the same when corresponding to that point. It is also possible to classify by color or graphic symbols such as x, o, and △. Thereby, it can be known at a glance to which position on the wafer the normalized EBS value corresponds. For example, a red dot or the like (not shown) is displayed on the wafer map MA of FIG. )). At this time, the size of this point is also increased in accordance with the size of the contact hole, and it becomes easy to understand when shown on the map.

  When the operator instructs to surround the red line frame S1 of the normalized EBS value graph (b), the normalized EBS value in that range is displayed on the wafer map (a). Corresponding to the intermediate region of the normalized EBS value graph (b), a blue dot (not shown) is shown on the wafer map MA. Similarly, when the operator designates an area, the normalized EBS value in that range is displayed on the wafer map (a). Similarly, a portion with a low normalized EBS value in the graph (b) is displayed on the wafer map (a) by specifying the range. Such an operation allows the wafer map (a) to be completed by designating an area by the operator or designating a predetermined numerical range. The range specification described above may be specified at the EBS height distribution of the vertical bars on the left side of the wafer map (a) if only the normalized EBS value is specified.

  However, by using the graph (b), the wafer map (a) can be created by setting the range of the normalized EBS value and the range of the contact hole diameter. By easily creating such a color-coded wafer map, process issues can be easily visualized.

The range specification of the graph (b) can be arbitrarily set, and it is convenient to be able to operate in various cases if the measurement points 11 and 11 can be specified.
(6) Semiconductor inspection apparatus to which the present invention is applied Hereinafter, a semiconductor inspection apparatus to which the data processing method of the present invention is applied will be described. The detailed configuration of this semiconductor inspection apparatus is described in Patent Document 1 (line numbers 0024 to 0062).

  FIG. 14 shows a configuration of a semiconductor inspection apparatus according to an embodiment of the present invention. This semiconductor inspection apparatus irradiates a semiconductor substrate (hereinafter referred to as a wafer), which is an object to be measured (sample), with an electron beam, measures the substrate current induced in the wafer by the electron beam, The basic principle is to obtain an evaluation value of the fine structure formed on the wafer. For pattern matching, emitted secondary electrons or reflected electrons are also used.

  As shown in FIG. 14, a wafer identification device 20 is provided so that a unique ID that can identify what feature wafer the measurement target wafer 23 is can be read. Various semiconductor devices are formed on the measurement target wafer 23, and the shot coordinates and the chip coordinates of these semiconductor devices are uniquely determined according to a global alignment coordinate system provided in advance on the wafer 23. By specifying the position using these coordinate systems, all semiconductor elements formed on the semiconductor wafer 23 can be uniquely determined.

  On the contrary, the position of the detected defect is uniquely determined by using this coordinate system. By using these coordinate systems, it is possible to collate with CAD information, which is an inspection result output from another apparatus, a result of an electrical test, or design information.

  An electron gun (irradiation means) 10 that generates an electron beam EB is attached to a chamber 26 that accommodates a wafer 23 that is an object to be measured (sample), and the electron gun 10 includes an electron beam source 11. A high voltage power source 40 is connected to the source 11. Inside the electron gun 10, a condenser lens 12, an aperture 13, a deflection lens 14, and an objective lens 15 are arranged in this order along the emission direction of the electron flow from the electron beam source 11. Among these, the deflection lens 100 is connected to the deflection lens 14 so that the electron beam EB can be deflected with high accuracy. Also, below the objective lens 15, a wafer objective lens distance measuring device 16 for measuring the distance between the objective lens 15 and the wafer 23 is provided. Further, the energy, current amount, and focus state of the electron beam EB of the electron gun 10 can be arbitrarily controlled. The substrate current generated by irradiating the wafer 23 with the electron beam is measured by the substrate current measuring device 30, and the secondary electrons and the reflected electrons are detected by the secondary electron reflected electron detecting device 24, respectively.

  An XY stage 21 and a tray 22 for moving and supporting the wafer 23 at a fixed position are accommodated inside the chamber 20, and the wafer 23 is placed on the tray 22. The electron beam EB emitted from the electron gun 10 is directed to the surface of the wafer 23 placed on the tray 22, and the irradiation position of the electron beam EB on the wafer 23 is moved by moving the tray 22 by the XY stage 21. It is possible to adjust.

  Here, in order to irradiate the wafer 23 with the electron beam EB irradiated from the electron gun 10 with a position accuracy of the order of nm, the wafer is relatively moved by the XY stage 21 with respect to the irradiation axis of the fixed electron beam EB. It is supposed to move 23. As a driving device for the XY stage 21, a pulse motor, an ultrasonic motor, a linear motor, a piezoelectric element, or the like is used. By using a high-precision measurement technique such as a laser laser length measuring device or a laser scale, the positional accuracy of the wafer 23 placed on the XY stage 21 is controlled to about several nanometers.

  Further, a current measuring device 30 is connected to the tray 22 on which the wafer 23 is placed, and the substrate current induced in the wafer 23 is measured by the current measuring device 30 via the tray 22. . The current measuring device 30 is built in the tray 22 or arranged in the vicinity thereof, so that electromagnetic noise from the outside can be cut.

  As the current measuring device 30, various types such as a resistor, a voltage conversion type device, an AC amplifier, and a charge amplifier can be used. The current measuring device 30 includes an A / D converter that converts the measured substrate current value into a digital signal by A / D (Analog / Digital), and outputs the measured value as digital data.

  The semiconductor inspection apparatus includes a two-dimensional scanning control apparatus (including a pattern matching engine) 110, a secondary electron reflected electron signal processing apparatus 190, a current waveform storage apparatus 120, a waveform shaping apparatus 130, a waveform image recognition processing apparatus 140, A display device 150 and a database device 160 are provided, and these are constructed on an information processing device such as a computer.

  Among these, the two-dimensional scanning control device 110 controls the deflecting device 100 so that the electron beam EB scans the surface of the wafer 23 two-dimensionally, and at the same time, a pattern for adjusting the irradiation position of the electron beam EB with high accuracy. It is responsible for control related to matching. In the present embodiment, two-dimensional scanning means that line-shaped scanning is repeated a plurality of times at regular intervals. For example, the concept is the same as horizontal scanning and vertical scanning on a television screen. From the electron beam scanned in this way, a secondary electron or reflected electron image or a substrate current image is formed and used for pattern matching.

Here, supplementing the pattern matching, the positions of patterns such as holes formed on the wafer 23 are slightly different for each wafer even in the same lot. For this reason, XY
In combination with the alignment by the stage 21, pattern matching for comparing the actual pattern and the reference pattern for each wafer is performed, and the irradiation position of the electron beam is accurately adjusted with an accuracy of several nm for each wafer.

  When this pattern matching is performed, the center coordinates of the measurement target (hole or the like) are calculated. If the coordinates are different from the target value, the electron beam is shifted by an amount corresponding to the difference to irradiate the target beam with the electron beam. In order to realize this, the deflection apparatus 100 of this semiconductor inspection apparatus has a high resolution characteristic in order to accurately scan the electron beam EB in a straight line. Further, the two-dimensional scanning control device 110 includes an image recognition device and software for performing pattern matching.

  The current waveform storage device 120 stores the waveform of the substrate current value measured by the current measurement device 30 in association with the irradiation coordinates or time of the electron beam EB at that time. The waveform shaping device 130 shapes the waveform of the substrate current value to remove unnecessary noise components. The waveform image recognition processing device 140 calculates an evaluation value related to the shape of the fine structure formed on the wafer 23 by performing waveform processing on the waveform-shaped substrate current waveform. The display device 150 displays the evaluation value. The database device 160 stores the evaluation value.

  The outline of the operation of this semiconductor inspection apparatus will be described along the flow shown in FIG. In this example, a hole formed on the wafer 23 is a measurement target. At the time of measurement, first specify the position coordinates of the hole to be measured with respect to the control system of the XY stage 21 holding the wafer 23, move the XY stage 21, and center the hole formed on the wafer 23. Perform (alignment) (step 1).

  Specifically, the center of the hole is roughly adjusted to a position in a range where the electron beam EB can be irradiated by the XY stage 21. Subsequently, the distance between the wafer 23 and the objective lens 15 is measured using the wafer objective lens distance measuring device 16 provided at the lower end of the electron gun 10 (step 2), and the initial position of the electron beam focus is determined. Next, the electron beam EB is irradiated while scanning two-dimensionally within a predetermined region including holes, and secondary electrons generated at that time are collected to form a secondary electron image. Autofocus (step 3) is performed using the formed secondary electron image, and the strength of the objective lens is automatically adjusted so as to focus on the sample.

  Next, pattern matching is performed by comparing a secondary electron image obtained by scanning the focused electron beam with a template image stored in advance in the two-dimensional scanning control device 110 (step 4). The amount of deviation between the center of the image and the center of the hole is calculated. This calculated shift amount is input to the deflecting device 100, and the irradiation position of the electron beam EB is shifted, so that the irradiation position of the electron beam EB is accurately aligned with the center of the hole to be measured.

  Subsequently, under the control of the two-dimensional scanning controller 110, a predetermined region on the surface of the wafer 23 is two-dimensionally scanned by the electron beam EB with the hole center as a reference (step 5). That is, by controlling the objective lens 15 of the electron gun 10 so that the electron beam EB has a desired tip size and applying a control voltage to the deflecting device 100, the electron beam scanning is repeated in a line shape at a constant pitch. As a result, secondary electrons and reflected electrons are generated from a minute region on the surface of the wafer 23 irradiated with the electron beam EB, and a substrate current is induced in the wafer 23.

  Secondary electron, backscattered electron or substrate current induced on wafer 23 is measured by secondary electron backscattered electron detector 24 and current measuring device 30, and the measured value is immediately converted into a digital signal with the required resolution. Is done. For example, the resolution of this digital signal is 16 bits and the sampling frequency is 400 MHz.

  This speed can be changed as required. Secondary electrons and reflected electrons obtained by two-dimensional scanning of the electron beam EB include hole surface shape information, and the substrate current measurement value includes information about the two-dimensional shape of the bottom surface of the hole. (Irradiation position) or waveform information with respect to the time axis that is a function of measurement time (electron beam EB irradiation time) and is digitally recorded in the current waveform recording device 120 (for example, memory, flash memory, hard disk, magneto-optical disk, etc.) Is done.

  The signal waveform information acquired as described above is waveform-shaped by the waveform shaping device 130 in order to remove unnecessary noise and high-frequency components included in the waveform. Examples of the waveform processing include moving average filter processing, waveform processing for removing a specific frequency, filter processing for extracting only a signal of a specific frequency, Fourier filter processing, and the like. These waveform shaping processes may be performed by hardware or software.

  Subsequently, only useful waveforms are extracted from the waveform-shaped waveforms, and the hole bottom area is measured (step 6). In this case, there are cases where the electron beam irradiation area does not include a hole, or the waveform is dirty due to the edge of the hole. The accuracy of the edge coordinate value obtained by the processing is lowered. For this reason, a good current waveform useful for hole edge extraction is extracted only in the case of a signal having an absolute value larger than a certain value using a threshold method or the like. The electron beam is not only scanned in a line shape, but a current waveform is also obtained by irradiating the measurement point with the electron beam for a predetermined time. In these cases, similar waveform processing is performed, and necessary information is extracted.

  The wafer 23 to be used for measurement is recorded with an identification number provided on the wafer 23 or information so that it can be identified by a computer. More generally, there is an equipment operation management system called MES (Manufacturing Execution System) in a semiconductor factory, and it records all of what equipment, what time, and what processing each wafer received. By correlating with such information, it is useful for estimating the failure classification and its cause.

FIG. 18 lists information groups obtained by this semiconductor inspection apparatus. As described with reference to FIG. 14, this semiconductor inspection apparatus includes a wafer identification apparatus for identifying a wafer, a probe generation apparatus (electron gun 10 and electron beam source 11) for generating an electron beam probe for acquiring information, a probe Secondary electron backscattered electron detector 24, current measuring device 30, a wafer objective lens distance measuring device and an XY stage 21 for accurately irradiating the measurement target with a probe. A two-dimensional scanning control device 110 that performs pattern matching by correlating the two-dimensional properties of the obtained signal with a reference image is provided.
<Probe generator>
The electron gun 10 and the electron beam source 11 have a plurality of parameters for changing the electron beam state such as electron beam energy, irradiation current, probe size, probe shape, irradiation time, and the like. Suitable probes can be generated. Since the obtained information changes when the probe state is different, the measurement value obtained by this inspection apparatus and the probe condition are always paired to form one information.
<Secondary electron detector>
The secondary electron intensity generated by the probe irradiation can be obtained from the secondary electron detection device in the secondary electron reflected electron detection device 24. When the electron beam is scanned two-dimensionally over the hole to be measured, the secondary electrons generated as a result are guided to the MCP or electrode, and the intensity is signaled and arranged in two dimensions in the scanning order (position, time order). An electronic image is obtained. This is generally called an SEM image. Each pixel unit has contrast information, and its time change is also obtained as information. The pixel also has position information. The backscattered electron detection device in the secondary electron backscattered electron detection device 24 can also obtain a backscattered electron image, pixel-by-pixel contrast information, or a time change signal thereof. From the current measuring device 30, a substrate current image, contrast information for each pixel, and time change information of the substrate current value are obtained.
<Wafer objective lens distance measurement device>
In the wafer objective lens distance measuring device, the Z sensor (height sensor) and the focus value are responsible for the distance measurement function, and distance information between the objective lens 15 and the wafer 23 to be measured is obtained. Average height information in the range of several centimeters square is obtained from the Z sensor, and local height information on the wafer 23 within several microns is obtained from the focus value of the objective lens. The XY stage 21 has a high-accuracy position coordinate measurement capability, and the measurement point coordinates are always measured with an accuracy on the order of nm, and the measurement object can be distinguished using the electron beam shift amount.

This inspection apparatus has a function of electrically changing the strength of the objective lens 15 in order to focus the electron beam on the measurement target. A value indicating the strength of the objective lens necessary for just focusing on the measurement object is referred to as an electron beam focus value. The distance between the wafer 23 and the objective lens 15 can be obtained from the electron beam focus value or the Z sensor. In general, in consideration of the fact that the objective lens 15 and the wafer tray 22 are fixed to the apparatus housing and the distance thereof is not changed, information on the surface height of the wafer 23 can be obtained from the fluctuation of this value.
<Pattern matching engine>
The pattern matching engine in the two-dimensional scanning control device 110 compares the reference image with the graphic to be measured at high speed. A digital image consists of a collection of unit pixels called pixels, and has brightness and color attributes. The figure is recognized using the spatial connection of these two attributes. The pattern matching engine has two main functions. One is a function that calculates how similar two figures are, and the other is a search function that searches for similar figures. Of course, as an attached function, there is a function for calculating parameters representing characteristics of all figures such as area, length, angle, and distortion.

  In this inspection apparatus, a pattern matching search function is used to precisely position a measurement location. In this case, one or more standard images called templates registered in advance are compared with images obtained by measurement, such as secondary electrons, reflected electrons, or substrate currents. Then, the same coordinates as the standard image are extracted to calculate the center coordinates. It is also possible to compare the center coordinates with a standard value such as a design value. An alignment error can also be detected from the difference from the standard value. The distance between the plurality of measurement objects can be measured from the result of the pattern matching performed on the plurality of measurement objects. The alignment error can also be known from this value.

  Standard values can be extracted from CAD data that determines the layout of semiconductor devices. In order to use this function, CAD data and this inspection device are linked and used. This device has a function to import GDSII file of CAD data. The layer information of the measurement target is extracted from the GDSII file that is the CAD data, and the coordinates of the measurement target place are extracted. The alignment error information obtained by the measurement can be reflected in the CAD data through the reverse path. That is, by feeding back to the design data a place where an alignment error is likely to occur, prescriptions such as changing the design value to make the alignment error less likely can be executed.

On the other hand, in order to determine the surface shape, a function for calculating how much the image is similar to the reference is utilized. There are various algorithms in the image comparison method, such as a method of abstracting and comparing the measurement object in a contrast aggregate called a blob, and a method of extracting edges of the measurement object and comparing them by taking geometric correlation There are algorithms used for image recognition. Select and use the most appropriate of the known methods. When this pattern matching is performed, a value called a pattern matching score is obtained. This value indicates that, for example, 100 points is the highest in a certain apparatus, but in this case, the registered figure shape and the measured figure are completely the same. When the pattern matching score value is small, it indicates that the shape of the obtained figure is deviated from the standard image. Therefore, for example, by using the pattern matching score, it is possible to evaluate how much the measurement target image shape is similar to the standard image.
<Blanket mode>
Measure the average current value of the substrate current obtained when the positioned measurement object is irradiated with the electron beam for a certain period of time, for example, about 1 second, at a predetermined electron beam energy, irradiation current amount, and focus size. The method is called a blanket mode, and information such as the hole bottom size, the hole bottom residual film, and the relative change in the hole bottom surface state can be obtained.
<Line scan mode>
A method of measuring a substrate current waveform obtained by two-dimensionally scanning an electron beam focused on a measurement object at a predetermined interval and speed is called a line scan mode. The hole bottom size and shape can be obtained from the edge information of the substrate current waveform. From the height of the waveform, it is also possible to know the state of the hole bottom residual film. An alignment error or the like can also be known by comprehensively comparing the design values including the hole bottom size and shape, and the position information where the hole should exist.
<Hole area normalized substrate current>
If the substrate current value obtained in the blanket mode is normalized using the hole area on the design layout or the hole area based on actual measurement, the normalized measurement value becomes the substrate current value per unit area. The amount is independent of the sheath size. The value obtained by standardizing the measured values obtained by the blanket method universally indicates the surface state of the hole bottom, and it becomes possible to compare the state of the hole bottom surface between various holes of different shapes and sizes. . In some cases, area standardization may be performed using the hole surface area for comparison. FIG. 19 shows a method for normalizing the substrate current value area. For example, first, an electron beam is irradiated so as to include one or several equivalent holes in the blanket mode, and the substrate current value is measured. Next, line scan mode measurement is performed on the representative hole of the same hole or a plurality of holes, and the hole bottom area is evaluated. In this case, an average area of a plurality of holes may be used. Using the obtained hole bottom area information, a blanket mode measurement value obtained in advance is divided and normalized to a substrate current value per unit area. Since the obtained value is the substrate current value per unit area, it is an amount irrelevant to the hole area. Therefore, by comparing the substrate current value per unit area of each measurement object, the remaining state of the film at the bottom of the hole, the surface state of the hole, and the like can be compared. Here, the hole size is calculated using the line scan mode, but when the hole size is known by other means, the value may be used. Further, it is not always necessary to perform the blanket mode measurement first, and it may be performed after the line scan mode.

  FIG. 20 discloses another method for obtaining the substrate current amount per unit area in this inspection apparatus. The tip shape of the electron beam can be changed to various shapes and sizes by controlling the objective lens and the like. The relationship between the electron beam focus value and the electron beam tip area is measured in advance by other means, and preparation is made so that a known electron beam tip size can always be realized as shown in FIG. Next, the substrate current value is measured by controlling the measurement target so that the electron beam has a desired size and irradiating the electron beam. This electron beam irradiation may be performed by scanning or by controlling the irradiation position so that the electron beam only hits the hole.

  When the electron beam irradiation is a scanning method, the height of the substrate current waveform corresponds to the substrate current per unit area as shown in FIG. In this way, when the electron beam is applied only to the contact hole, the average value of the substrate current value generated by irradiation becomes the substrate current value per unit area. In this method, the substrate current value per unit area can be known even if it is not a contact hole. Although it can be applied to a contact hole, it is not necessary to measure the area of the hole at that time, so that the measurement speed can be increased.

  By using the substrate current value subjected to area standardization as described above as a measured value, it is possible to compare elements having different layout sizes. For example, providing a plurality of holes of different sizes on the mask, proceeding with the process, irradiating an electron beam with a known tip area for each size element, and comparing the normalized substrate current values to graph Thus, the state of the bottom of the hole can be estimated. Of course, holes with different sizes may be used by actually measuring holes with different hole diameters. It is possible to estimate the hole state more reliably than to estimate the hole state based on the information obtained from one hole.

    In addition, as is apparent from FIG. 11, the substrate current value normalized by the hole size (substrate current value per unit area) in the sample in which etching is normally performed is substantially constant even if the hole size is different. Show. On the other hand, in the sample in which the remaining film is generated at the hole bottom, for example, as the hole bottom size becomes smaller, the measured value after normalization becomes smaller or larger. That is, the substrate current depends on the secondary electron emission efficiency of the hole bottom material. When the silicon oxide film or the like is at the bottom of the hole, secondary electron emission increases, and the normalized substrate current value decreases as the hole bottom size decreases.

  On the other hand, a polymer containing a large amount of carbon such as a resist has a lower secondary electron emission efficiency than silicon or the like. Therefore, when an organic material such as a resist appears at the hole bottom, the substrate current value increases as the hole bottom size decreases. By plotting data obtained from holes having a plurality of hole diameters and using the slope as an index for process determination, it is possible to classify the cause of a process failure in detail.

  As described above, according to this inspection apparatus, it is possible to clearly detect whether there is a remaining film on the hole bottom or whether there is a residue such as an oxide film or a resist from the measured substrate current. With this detection device, the in-plane distribution of the normalized substrate current value can be known. Since the substrate current value after normalization by the hole area is invariable with respect to the measurement target size, the process distribution of only the state of the hole bottom can be known by evaluating the in-plane distribution with the value. For example, an etching apparatus has a process distribution unique to the apparatus. However, if there is a distribution in the exposure process, the hole surface diameter is also affected. For this reason, the process distribution obtained after etching is a combination of both, and if measured directly, it is not possible to extract only the distribution unique to the etching apparatus. However, by normalizing the substrate current with the hole surface diameter or the hole bottom diameter, it is possible to eliminate the influence of exposure and extract only the distribution unique to the etching apparatus.

  Further, the semiconductor inspection apparatus shown in FIG. 14 shows the residue distribution and the like on the wafer map MA shown on the display device (display unit) 150 from the data of the graph shown in FIG. For example, when an operation key (not shown) is operated, the waveform image recognition processing device (arithmetic processing means) 140 obtains the data of the graph shown in FIG. 12 and the position data of the contact hole obtained by the EBS value (position data obtained by pattern matching). ) And the like, the corresponding position on the wafer map MA is displayed in color according to the normalized EBS value. At this time, the display is not uniform, but a color map associated with the graph data and the wafer map MA is shown.

  In this embodiment, as shown in FIG. 12, for example, a red dot or the like (not shown) is displayed on the wafer map corresponding to (related to) the distribution of the EBS value graph with polymer residue, and there is an etching residue. Corresponding to (related to) the distribution of the EBS value graph, an orange dot (not shown) is displayed on the wafer map MA.

  Even if each measurement point of the EBS value graph is individually specified, that is, color is specified for each one according to the normalized EBS value and the contact hole diameter, or the color is specified for each block of the region by specifying the region. Good. The number of blocks can be specified arbitrarily.

  For example, on the wafer map shown in FIG. 12A, the type and size of the contact hole displayed in the distribution graph of the normalized EBS value, the distribution graph of the normalized EBS value in the same color, Display with dots. Thereby, it can be known at a glance to which position on the wafer the normalized EBS value corresponds. For example, a red dot or the like (not shown) is displayed on the wafer map of FIG. ). At this time, the size of this point is also increased in accordance with the size of the contact hole, and it becomes easy to understand when shown on the map.

  When the operator instructs to surround the red line frame S1 of the normalized EBS value graph (b), the normalized EBS value in that range is displayed on the wafer map (a). Corresponding to the intermediate region of the normalized EBS value graph (b), a blue dot (not shown) is shown on the wafer map MA. Similarly, when the operator designates an area, the normalized EBS value in that range is displayed on the wafer map (a). Similarly, a portion with a low normalized EBS value in the graph (b) is displayed on the wafer map (a) by specifying the range. Such an operation allows the wafer map (a) to be completed by designating an area by the operator or designating a predetermined numerical range. The range specification described above may be specified at the EBS height distribution of the vertical bars on the left side of the wafer map (a) if only the normalized EBS value is specified.

  However, by using the graph (b), the wafer map (a) can be created by setting the range of the normalized EBS value and the range of the contact hole diameter. By easily creating such a color-coded wafer map, process issues can be easily visualized.

  The range specification of the graph (b) can be arbitrarily set, and it is convenient to be able to operate in various cases if the measurement points 11 and 11 can be specified.

  Further, it can be seen at a glance where the residue distribution in the graph of the normalized EBS value corresponds on the wafer map.

  Further, if the area E1 showing a good yield range, the area E2 exceeding the area E1, and the area E3 below the area E1 are displayed in different colors on the graph shown in FIG. It is possible to see at a glance whether or not it is good, and it is possible to monitor the variation of each process apparatus by sample inspection on the production line.

  By the way, when normalizing the EBS value with the contact hole diameter, the standard hole diameter may be obtained from the measured plurality of contact hole diameters and normalized, but the average value of the contact hole diameter data of the portion with the best yield May be normalized as a standard hole diameter.

  The contact hole diameter of the wafer 23 is measured by scanning a focused electron beam over the hole.

  The absorption current value measurement of the contact hole of the wafer 23 is performed by irradiating a defocused electron beam slightly larger than the contact hole on the hole.

Further, the semiconductor inspection apparatus obtains the bottom current in the line scan mode LSM, normalizes the bottom current with the contact hole diameter, displays this on a graph similar to FIG. 12, and displays the same on the wafer map MA as described above. It has a function of displaying points P1, P2, frame lines S1, S2, etc. at corresponding positions.
<Normalization by D-LSM measurement>
Next, a case where the EBS value is normalized by D-LSM measurement will be described.

  First, the size and shape of the contact hole of the wafer 23 (see FIG. 14) and its internal structure are measured in the line scan mode.

  Next, a defocus-line scan mode is set by an operation key (not shown).

  In this defocus-line scan mode, the electron beam EB shown in FIG. 14 is defocused, and the size of the defocused electron beam EB is made slightly larger than the contact hole of the wafer 23. The electron beam EB is line-scanned (see FIG. 21) over the contact hole.

  At the time of this line scan, the shape of the electron beam EB is adjusted to the shape of the contact hole as shown in FIGS. When the elliptical long axis of the contact hole is oriented in the scanning direction, the major axis of the contact hole is matched with the major axis direction of the electron beam EB, and the electron beam EB is scanned along the major axis direction of the contact hole.

  When the elliptical minor axis of the contact hole is oriented in the scanning direction, the minor diameter of the contact hole and the minor axis direction of the electron beam EB are matched, and the electron beam EB is scanned along the minor axis direction of the contact hole. .

  Then, the absorption current during the scanning of the electron beam EB is measured by the current measuring device 30. In the case of measurement with LSM, it was difficult to obtain the average information of the hole bottom because it was a scan with a thin neem, but by making the beam diameter equivalent to the hole diameter, You can get an average top. There is also a state where the periphery is scanned other than the hole, and the reference signal can be obtained from the measured absorption current value at that time. For example, when the measurement is unstable due to charge-up of the wafer, etc. Corrections can also be made with reference to the absorption current measured when the periphery other than the hole is scanned.

  The current measuring device 30 detects the maximum absorption current when the line scan of the electron beam EB is performed, normalizes the maximum absorption current based on the hole bottom diameter obtained in the line scan mode, and obtains a normalized EBS value. . This normalized EBS value is performed by the waveform image recognition processing device 140, for example.

  As described above, since normalization is performed from the maximum absorption current, the interface evaluation can be performed with high sensitivity without being influenced by the internal structure of the contact hole. In addition, since the shape of the defocused electron beam is matched to the shape of the contact hole, the S / N ratio with respect to the electron beam EB can be improved.

  Further, the waveform image recognition processing device 140 creates the graph shown in FIG. 12 based on the obtained normalized EBS value and displays it on the display device 150, or the correspondence on the wafer map Ma as described above from the data of this graph. The position is displayed in color according to the normalized EBS value.

  In the above embodiment, the shape of the electron beam EB is matched with the shape of the contact hole. However, when the contact hole is an ellipse, the electron beam EB may be an ellipse slightly larger than the minor axis of the ellipse, or slightly larger than the major axis. It may be an ellipse.

It is the conceptual diagram which showed the measurement principle of this invention. It is a conceptual diagram which shows the measurement mode which measures the diameter of a contact hole. It is a conceptual diagram which shows the measurement mode which measures evaluation of the interface of a contact hole. It is explanatory drawing which showed the state of the contact hole. It is a conceptual diagram explaining the electric current absorbed by a wafer substrate. It is explanatory drawing which showed the relationship between the diameter of a contact hole, and an electric current. It is the graph which showed the frequency | count of a measurement and the diameter of the measured contact hole. It is the graph which showed an example of the measurement reality of the diameter of a contact hole. An example of measurement in the blanket mode is shown. It is the conceptual diagram which showed the measurement and normalization of the line scan mode. It is the map and graph of an EBS value measured in line scan mode. It is the graph which showed the pattern of the normalization EBS value. It is explanatory drawing which showed the normalization EBS value and the map. It is a graph which shows the result of having investigated change of normalized EBS value by change of a recipe. It is the block diagram which showed the structure of the semiconductor inspection apparatus of the Example of this invention. It is the flowchart which showed operation | movement of the semiconductor inspection apparatus. It is the wafer map which showed the board | substrate electric current value after normal of a normal wafer with the two-dimensional contour line. It is explanatory drawing which showed the wafer map with defect distribution. It is the table | surface which showed the information obtained by the semiconductor inspection apparatus of an Example. It is the flowchart which showed the method of the board | substrate electric current value area specification. It is explanatory drawing which showed another method of calculating | requiring the board | substrate electric current value per unit area. It is a conceptual explanatory view of the defocus-line scan mode. It is explanatory drawing which showed the internal structure of the contact hole, and the irradiation relationship of an electron beam. It is explanatory drawing which shows the shape of a contact hole, and the scanning of the defocused electron beam. It is explanatory drawing which showed line scan mode and blanket mode.

Explanation of symbols

10 Electron gun (irradiation means)
24 Secondary Electron Backscattered Electron Detector 30 Current Measuring Device 140 Waveform Image Recognition Processing Device (Calculation Processing Device)
150 Display device (display unit)

Claims (5)

In a semiconductor inspection apparatus that evaluates the interface state of a contact hole of a wafer using an absorption current measurement method using an electron beam,
When measuring the absorbed current of the wafer by irradiating the contact hole of the wafer with the electron beam, the electron beam is defocused to be slightly larger than the contact hole, and the contact hole of the wafer is scanned with the electron beam. A semiconductor inspection apparatus characterized by measuring an absorption current.   The semiconductor inspection apparatus according to claim 1, wherein the size of the electron beam is changed according to the size of the contact hole.   When the contact hole is an ellipse, the electron beam is made an ellipse slightly larger than the minor axis of the ellipse, the major axis of the contact hole is matched with the major axis direction of the electron beam, and the electron beam is aligned in the major axis direction of the contact hole. The semiconductor inspection apparatus according to claim 1, wherein scanning is performed along the scanning line.   When the contact hole is an ellipse, the electron beam is made an ellipse slightly larger than the major axis of the ellipse, the minor axis of the contact hole is aligned with the minor axis direction of the electron beam, and the electron beam is aligned with the minor axis of the contact hole. The semiconductor inspection apparatus according to claim 1, wherein scanning is performed along a direction.   5. The semiconductor inspection apparatus according to claim 1, wherein the shape of the contact hole and the state of the hole bottom are detected from a change in the absorption current according to the scanning of the electron beam.