JP2010118414A - Semiconductor inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor inspection device capable of electrostatically charging a wafer without generating a defect, etc., in a substrate such as a wafer. <P>SOLUTION: There is provided the semiconductor inspection device that evaluates a contact hole interface state and a thin film of the wafer 23 by using an absorption current measuring method using an electron beam, wherein the wafer 23 and a thin film periphery are indirectly irradiated with electrons emitted from outside the wafer 23 and then a measurement point of the wafer 23 or thin film, etc., is irradiated with the electron beam to take a measurement. <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 a sample is irradiated with an infrared laser to generate electron-hole pairs and a current flowing through these generated carriers is measured is often used. Are known. The EBIC method (Electron Beam Induced Current) (refer to Patent Document 2, Non-Patent Documents 2 and 3) that measures the current flowing by irradiating EB onto the sample surface in the same manner, or a part of the EB irradiation current is absorbed. An EBAC method (Electron Beam Absorbed Current) (see Non-Patent Document 4) for measuring a phenomenon has been developed and put into practical use.
International Publication 2008-53524A1 Special table 2006-505114 gazette 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.

  LSI wiring defect analysis and defect detection using optical and electron beam (EB) have already been performed. For example, as an optical method, an OBIC method (Non-Patent Document 1) is well known in which a sample is irradiated with an infrared laser to generate electron-hole pairs and a current flowing through these generated carriers is measured. The EBIC method (Non-patent Documents 2 and 3) that measures the flowing current by irradiating EB onto the sample surface by the same method, and the EBAC method (Non-patent Document 4) that measures the phenomenon in which part of the EB irradiation current is absorbed. ) Has been developed and put to practical use. 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 about 40 nm (see Non-Patent Document 8), 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).

  As a result of evaluating the contact hole interface using EB-Scope, the substrate current value measured by EB-Scope (EB absorption current value; hereinafter referred to as EBS value) clearly shows information on the contact hole interface. The data considered to have been obtained. 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.

  On the other hand, as in Patent Document 2, for example, a substrate such as a wafer is irradiated with an electron beam in advance, and the substrate current value reaches a constant value (stable state), and the electron beam intensity is changed to make contact. Devices for measuring holes and the like are known.

  However, since it is necessary to continue irradiating the substrate such as a wafer with an electron beam until the substrate current value becomes stable, the surface of the wafer or the like is likely to be excessively charged or defective, and the substrate current value also fluctuates. The problem of end up occurs. As a result, there is a drawback that the wafer cannot be inspected accurately by measurement using the substrate current value.

  Therefore, in the present invention, before irradiating the contact hole or thin film portion with an appropriate electron beam size and measuring the absorption current value measured at that time, the electron beam is directly applied to the contact hole or thin film portion to be measured. Without irradiating and pre-charging, the wafer is irradiated with an electron beam indirectly from outside the periphery for a certain period of time, and then the above measurement is performed, so that excessive charging or defects may occur at the measurement point of the substrate such as a wafer. An object of the present invention is to provide a semiconductor inspection apparatus capable of accurately measuring an absorption current value of a wafer without causing the above.

The invention according to claim 1 is a semiconductor inspection apparatus for evaluating a contact hole interface state and a thin film of a wafer using an absorption current measuring method using an electron beam.
Irradiating the electron beam from the outside of the wafer, indirectly irradiating electrons around the wafer or thin film by this irradiation, and then irradiating the electron beam to a measurement point such as the wafer or thin film to perform the measurement. It is characterized by that.

  According to a second aspect of the present invention, a reference table using a material that generates a large amount of secondary electrons or reflected electrons is provided on a part of the stage on which the wafer or thin film is mounted, and the reference beam is irradiated with the electron beam. The wafer or thin film is irradiated with the secondary electrons or reflected electrons.

  According to a third aspect of the present invention, the surface of the reference table is inclined so that secondary electrons or reflected electrons generated by irradiation of the electron beam on the surface of the reference table are irradiated toward the center position of the wafer or thin film. It was made to be characterized.

  According to the present invention, before the absorption current measurement is performed, an electron beam is irradiated from the outside of the wafer, and electrons generated by the irradiation are charged to the wafer. Therefore, the electron beam is directly applied to the measurement point of the wafer or thin film. There is no need to irradiate, so it is possible to accurately measure the absorbed current value of the wafer or thin film without causing excessive charging or defects at the measurement point of the wafer or thin film during charging before measurement. Can do.

(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.

  It is already known that the hole diameter can be measured to 45 nm or less, 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.

  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. As a result, the position of the object to be measured can be determined. When the positioning is completed, the absorption current (substrate current) IAC is detected by, for example, irradiating (or scanning) the electron beam EB inside the contact hole CONH. The substrate current IAC is input to the substrate current amplification system SCAS, the 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 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 BLM (Blanket Mode; a mode in which measurement is performed in a stationary state with a beam diameter slightly larger than that of the contact hole) 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 smaller than the hole diameter).

  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, but when the contact hole CONH is a multihole, the profile of the substrate current IAC has an alternating 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 processing state, (d) is a CONH stopper penetration state, (e) is a small and strange shape. CONH and (f) show schematic views in which the thin film layer thickness state can be observed.

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, considering the generation of electron-hole pairs by EB irradiation and the electrons flowing to the Si substrate due to the generated carriers, and qualitatively the film The measurement results can be well explained up to a thickness of about 10 nm.

  In addition, the result of calculating the current flowing into the wafer substrate (WEH) is also shown in the charging simulation related to the insulating film sufficiently thicker than the EB penetration depth. 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.

[Semiconductor inspection apparatus to which the present invention is applied]
A semiconductor inspection apparatus to which the data processing method of the present invention is applied will be described below. The detailed configuration of this semiconductor inspection apparatus is described in Patent Document 1 (line numbers 0024 to 0062).

  FIG. 5 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. 5, a wafer identification device 20 is provided so as to read a unique ID that can identify what kind of feature wafer the measurement target wafer 23 is. 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 wafer 23 with the electron beam is measured by a substrate current measuring device (current measuring device) 30, and the secondary electrons and the reflected electrons are detected by the secondary electron reflected electron detecting device 24, respectively. The

  An XY stage 21 and a tray 22 for moving and supporting the wafer 23 at a fixed position are accommodated inside the chamber 26, 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 23 is relatively moved by the XY stage 21 with respect to the irradiation axis of the fixed electron beam EB. Is supposed to move. 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 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 nm.

  Further, a current measuring device 30 is connected to the tray 22 on which the wafer 23 is placed, and the substrate current flowing through 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.

  In general, it is known that when a wafer is transferred into a sample chamber, it is often charged positively. When the wafer surface is positively charged, the substrate current value is measured high. This is because the 2 o'clock electrons emitted from the wafer surface are pulled back. On the other hand, if the wafer is negatively charged, the emitted secondary electrons are not pulled back, and the emission of secondary electrons is less likely to be accelerated at the same time. Therefore, it is effective for stabilizing the measurement to eliminate the positive charge by irradiating the surface of the wafer with some electrons.

  FIG. 6 is an explanatory diagram conceptually showing a method for indirectly irradiating and charging electrons to the wafer 23. In FIG. 6, reference numeral 200 denotes a reference table provided on the stage 21. The reference table 200 is a material that generates a lot of secondary electrons or reflected electrons (elements with a large atomic number tend to emit more reflected electrons). The inclined surface 201 is formed on the surface that is irradiated with the electron beam EB. The angle of the inclined surface 201 is such that when the inclined surface 201 of the reference table 200 is irradiated with the electron beam EB, the direction R in which the generated secondary electrons (or reflected electrons) jump out faces the center position 23 a of the wafer 23. Is set to

  Here, assuming that the incident angle of the electron beam EB with respect to the inclined surface 201 of the reference table 200 is θ, the emission angle of secondary electrons can be regarded as approximately θ, and therefore the direction of jumping out from the vertical line H of the inclined surface 201. The angle α of the inclined surface 201, the height of the reference table 200 (the height of the irradiation position 201a), and the like are set so that R becomes an angle θ and faces the center position 23a of the wafer 23.

  First, before measuring the substrate current value (absorption current value of the wafer 23), the inclined surface 201 of the reference table 200 is irradiated with the electron beam EB, and the wafer 23 is indirectly irradiated with electrons. This irradiation amount is made appropriate by controlling the irradiation time.

  When the irradiation time reaches a predetermined time, the contact current of the wafer 23 is irradiated as described above to measure the substrate current value.

  As described above, since the inclined surface 201 of the reference table 200 is irradiated with the electron beam EB and the charge of the wafer 23 is controlled, the measurement at the measurement point of the wafer 23 which has been conventionally performed is performed at the time of the charge control. Direct charging of the electron beam does not cause excessive charging or damage. Further, when the substrate current value is measured, the positive charge is eliminated from the wafer 23, so that the speed of the electron beam EB colliding with the wafer 23 is reduced, and the secondary electron pullback phenomenon is reduced. And the measurement accuracy of the substrate current can be improved.

  In order to uniformly irradiate the wafer 23 with the electron beam, the reference table 200 is formed in a cylindrical shape, the wafer 23 is disposed in the cylinder, and the electron beam EB is irradiated along the circumferential direction of the inclined surface 201. Good to go.

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 the block diagram which showed the structure of the semiconductor inspection apparatus of the Example of this invention. It is explanatory drawing which showed notionally the method to charge a wafer.

Explanation of symbols

10 Electron gun (irradiation means)
23 Wafer 30 Current measuring device 140 Waveform image recognition processing device (arithmetic processing device)
200 Reference table 201 Inclined surface EB Electron beam

Claims (3)

In a semiconductor inspection device that evaluates the contact hole interface state and thin film of a wafer using an absorption current measurement method using an electron beam,
Irradiating the electron beam from the outside of the wafer, indirectly irradiating electrons around the wafer or thin film by this irradiation, and then irradiating the electron beam to a measurement point such as the wafer or thin film to perform the measurement. A semiconductor inspection apparatus.   A reference stage using a material that generates a large amount of secondary electrons or reflected electrons is provided on a part of the stage on which the wafer or thin film is mounted, and the electron beam is applied to the reference stage to apply the electron beam to the wafer or thin film. The semiconductor inspection apparatus according to claim 1, wherein secondary electrons or reflected electrons are irradiated.   The surface of the reference table is tilted so that secondary electrons or reflected electrons generated by irradiation of the electron beam on the surface of the reference table are irradiated toward the center position of the wafer or thin film. The semiconductor inspection apparatus according to claim 2.