Patent Application
20250232946
The present invention relates to a technique of performing a measurement by irradiating a sample with a charged particle beam.
A charged particle beam device such as an electron microscope or an ion microscope is used for observation of various samples having a fine structure. For example, for a purpose of process management in a manufacturing process of a semiconductor device, a scanning electron microscope, which is one of charged particle beam devices, is applied for a measurement such as a dimension measurement or a defect inspection of a semiconductor device pattern formed on a semiconductor wafer as a sample.
The following PTL 1 discloses an example of a technique of performing a measurement by irradiating a sample with a charged particle beam. PTL 1 discloses that a charged state of the sample is controlled by irradiating the sample with a light beam in addition to the charged particle beam.
When a semiconductor device (such as a transistor) is formed on a semiconductor material, it may be necessary to control the charged state at a specific position of the device. For example, when a gate of a specific transistor is turned on or turned off, on/off characteristics (how much electrical signal needs to be applied to turn the transistor on or off) of the transistor may be measured. Such a measurement is typically performed by electrically connecting a measurement probe to the device.
It is considered whether the same measurement can be performed by controlling the charged state of the semiconductor device (that is, by controlling the number of charges held by the semiconductor device). However, in the related art as disclosed in PTL 1, it is not possible to freely select (or not to consider) a portion where the charges are controlled according to a structure of the semiconductor device. Therefore, in the related art, it is difficult to implement the on/off characteristics of the semiconductor device by the irradiation with the charged particle beam and the irradiation with the light.
The invention has been made in view of the above problems, and an object thereof is to control a charged portion according to a structure of a transistor formed on a semiconductor material, so as to measure on/off characteristics of the transistor by irradiation with a charged particle beam and irradiation with light.
A charged particle beam device according to the invention turns on a transistor formed on a semiconductor material by irradiating a gate of the transistor with a charged particle beam, and initializes charges of the transistor by irradiating the transistor with light, thereby controlling a conductive state of the transistor.
According to the charged particle beam device of the invention, by controlling a charged portion according to a structure of a transistor formed on a semiconductor material, on/off characteristics of the transistor can be measured by irradiation with a charged particle beam and light.
The electron optical system 11 includes an electron gun 111, a deflector 112, an electron lens 113, and an electron detector 114. The stage mechanism system 12 is implemented by placing a sample 122 on an XYZ stage 121. An inside of a housing of the electron optical system 11 is controlled to a high vacuum, and the stage mechanism system 12 is provided. The light irradiation system 13 includes a light source 131 and a light adjustment unit 132, and the sample 122 is irradiated with light via a light introduction unit 133. The control system 14 includes an electron gun control unit 1411, a deflection signal control unit 142, an electron lens control unit 143, a detector control unit 144, a stage position control unit 145, a light control unit 146, a control command unit 147, and a calculation unit 148. The control command unit 147 controls a writing of a control value to each control unit based on input information received from a sequence control unit 151.
An electron beam accelerated by the electron gun 111 is focused by the electron lens 113, and the sample 122 is irradiated with the electron beam. An irradiation position on the sample 122 is controlled by the deflector 112. The electron beam is controlled according to an acceleration voltage, an irradiation current, a deflection condition, and an electron lens condition that are set by a measurement item setting unit 152.
The control command unit 147 is a functional block that controls components of the charged particle beam device 1. The control command unit 147 sends an operation command to the detector control unit 144, the electron gun control unit 141, and the like, based on observation conditions received from, for example, the sequence control unit 151. Each control command system controls the stage mechanism system 12 based on, for example, light or electronic conditions received from the sequence control unit 151 to move the sample 122 to a predetermined position. The control command unit 147 controls a detection process of emitted electrons by the electron detector 114 by controlling a supply of power to the electron detector 114, a supply of a control signal, and the like via the detector control unit 144. The control command unit 147 transmits information on light irradiation conditions such as a wavelength, a light amount, and an irradiation timing to the light control unit 146 based on conditions input by the measurement item setting unit 152, and controls operations of the light source 131, the light adjustment unit 132, and the like. More specifically, for example, the light control unit 146 controls the light amount and the wavelength of the light emitted from the light source 131. The light control unit 146 instructs the light adjustment unit 132 to adjust a traveling direction and polarization of the light emitted from the light source 131. The light control unit 146 may be implemented by, for example, a manual operation, or may be implemented by, for example, a program executed by a personal computer on which a processor such as a CPU is mounted. The control command unit 147 may be implemented by, for example, a field-programmable gate array (FPGA) or an application specific integrated circuit (ASIC).
The light emitted from the light source 131 is emitted to a position on a surface of the sample 122 via the light introduction unit 133. As the light source 131, a light source capable of emitting lasers having a plurality of wavelengths or a light source capable of emitting lasers having a single wavelength is mounted for each necessary wavelength in the present embodiment. The light introduction unit 133 has a slit configuration, and can freely control a light shape. Accordingly, it is possible to control a position to be irradiated and a position to be irradiated according to a pattern.
In addition to the above, the operation system 15 includes an output unit 154 and a display unit 155. The output unit 154 outputs a processing result obtained by the calculation unit 148 in, for example, an appropriate data format. The display unit 155 displays the processing result obtained by the calculation unit 148 on a screen, for example, on a user interface to be described later.
A device information input unit 153 of the operation system 15 is a block having a function of inputting a structure of a sample to be observed and circuit information. By inputting CAD information or the like used at the time of designing a pattern of a device, a size of each pattern and electrical circuit information are associated with each other, and accordingly, irradiation positions of the electron beam and the light are controlled. At this time, a form of inputting the circuit information of the pattern and information such as the size is not particularly designated as long as coordinates of the pattern, the circuit information, and information such as a connection relationship of the patterns can be known, and may be, for example, CAD data or only data of a character string whose coordinates and circuit structure can be known. Even when the CAD data is not used, a circuit designation of the patterns can be performed. An example of a designation procedure at this time is shown. (1) An SEM image of an inspection portion is acquired, and (2) a signal obtained from the electron detector 114 is replaced with gradation information by a processing unit and the calculation unit, and the gradation information is displayed on the display unit 155 via the output unit 154. (3) On a GUI to be described later, a user sorts types of the patterns, and information is sent to the device information input unit 153. According to this flow, it is also possible to designate the types of the patterns of the observation position.
The measurement item setting unit 152 refers to device information input by the device information input unit 153 and generates conditions of light and an electron beam necessary for implementing an inspection item designated on the GUI. The sequence control unit 151 creates a measurement sequence based on the conditions of the light and the electron beam set by the measurement item setting unit 152. The sequence control unit 151 generates an irradiation sequence, and transmits an instruction signal to the control system. When a test item to be inspected is selected by the measurement item setting unit 152, the irradiation sequences of the light and the electron beam are generated. At this time, the user can customize the conditions of the light and the electron beam on the GUI to be described later. By selecting a sequence visualization button on the GUI, flows of the irradiation sequences of the light and the electron beam can be visually checked. The user may freely set irradiation timings of the light and the electron beam by himself/herself.
The control command unit 147 controls the detector control unit 144, the electron gun control unit 141, the deflection signal control unit 142, the electron lens control unit 143, the stage position control unit 145, the light control unit 146, and the like according to the sequence designated by the sequence control unit.
The light control unit 146 controls light parameters such as the wavelength, the irradiation amount, and peak power of the light. The light control unit 146 includes the light source 131 and the light adjustment unit 132. The light source 131 may be a white light source, a semiconductor diode laser, or a solid-state laser, and may be a light source capable of emitting other light. The light parameters adjusted by the light adjustment unit 132 include, for example, a light amount, a wavelength, a polarization plane, an irradiation angle to the sample, a pulse laser/continuous wave (CW) laser, and a repetition rate (in a case of a pulse laser). The light adjustment unit 132 also has a function of controlling an irradiation timing of the light according to the sequence information generated by the measurement item setting unit 152 and the sequence control unit 151 and performing irradiation. A mechanism having a function of the irradiation timing of the light may be a mechanical shutter, may be blocked by an electro optical element or an acoustic optical element, or may be a mechanism capable of implementing switching control of other light.
The electron optical system 11 emits the electron beam under the acceleration voltage, the irradiation current, the deflection condition, and the electron lens condition that are set by the measurement item setting unit 152. An irradiation timing of the electron beam is controlled by controlling timings of irradiation and non-irradiation based on the sequence generated by the measurement item setting unit 152 and the sequence control unit 151. The electron beam accelerated by the electron gun 111 is focused by the electron lens 113, and the sample 122 is irradiated with the electron beam. A position where the sample 122 is irradiated with the electron beam, and an observation magnification are controlled by the deflector 112.
In a second configuration example in
A third configuration example in
The control command unit 147 determines a type, a pattern, and an inspection item of a device to be inspected. Data on the type of the device and the device pattern may be designated based on the CAD data or information obtained by actually observing an SEM image of an observation position.
The control command unit 147 designates a portion of the device pattern to be observed, a size of a field of view, the number of inspection chips, and the like (observation range) based on the device pattern and a chip layout.
The control command unit 147 sets a range of the number of charges to be injected and irradiation conditions of light. For the electron beam to be emitted, an irradiation energy of the electron beam to be injected into the designated pattern, a minimum value and a maximum value of the charges, and a step amount are determined. At this time, an electron beam condition for injecting the electron beam into the pattern and the condition of the electron beam for the observation may not be the same. These electron beams may be output from the same electron source and electron optical system, or may be output from different electron sources and optical systems. Alternatively, an electron beam output from one electron source may be divided into a plurality of electron beams, and each of the electron beams may be controlled and emitted.
In this step, the light irradiation condition as a recommended condition is set according to the inspection item input and selected in S100. Based on the information input in S100, the wavelength, the irradiation amount, and the irradiation timing of the light calculated by the sequence control unit 151 are output to the light control unit 146 according to the inspection item and the device inspection range set by the measurement item setting unit 152. If the condition is sufficient, the user checks, for example, a “light condition confirm” button on the GUI. If a correction is necessary, the light irradiation condition is corrected by alight condition input unit displayed on the GUI, and when the light condition is determined, the “light condition confirm” button is pressed. The light control unit 146 controls the light irradiation condition according to the light irradiation condition determined in the “light condition confirm”.
The control command unit 147 starts the measurement according to the inspection measurement items set in S100 to S102.
The light control unit 146 controls a potential by stabilizing or equalizing an initial charged state of the sample 122 by irradiating the sample 122 with light. For example, when the transistor is formed in a lattice shape on the sample 122 (semiconductor material), first, the observation position is scanned along an X direction, and an on/off state of the transistor at each observation position is measured (a specific example of measuring the on/off state based on the observation image will be described later). Next, the observation position is moved by one line in a Y direction. Every time the observation position is moved by one line in the Y direction, the light control unit 146 emits light for only resetting the charged state of the drain (and the source).
In addition to the above, the light control unit 146 may emit light for resetting the charged state of the gate when performing this step at a first time. Specific examples of the light for resetting only the drain and the light for resetting the gate will be described later.
The electron optical system 11 injects charges into the sample 122 by irradiating the sample 122 with an electron beam. Charge injection conditions are set in S102. A charge injection amount is changed by a step width each time this step is performed. This step width is set in S102. By charging the gate of the transistor according to the charge injection amount, a state similar to that in which a voltage is applied to the gate is obtained. The on/off characteristics (gate threshold voltage (Vth) characteristics) of the transistor can be measured by measuring at which stage the transistor is turned on while changing the charge injection amount.
The following is considered as a modification. Photoelectron emission caused by the light irradiation may be used as a method for accumulating charges in the gate portion. When a material of the gate portion is polysilicon, photoelectrons are emitted from the gate portion by emitting light of a wavelength having a light energy equal to or higher than an ionization energy of silicon or emitting light having a peak intensity at which multiphoton excitation occurs, and accordingly positive charging occurs. The gate may be turned on using the positive charging. Therefore, step S105 in
The electron optical system 11 moves the field of view to the observation position and emits the electron beam under the electron optical condition set in S103. Electrons emitted from the sample are detected by the detector 114. The calculation unit 148 generates an observation image of the observation position using a detection signal output from the detector 114. The observation image is output as data or on the GUI via the output unit 154 and the display unit 155. When the observation position is the same as the charge injection position in S105, the irradiation position may not be moved in S105 and S106. When the observation position is not the same as the charge injection position in S105, the observation position may be moved by stage movement, deflection shift of the electron beam, or the like.
The control command unit 147 repeats S104 to S106 until the number of steps set in S102 is completed.
The calculation unit 148 acquires a luminance level of the observation image for each injected charge amount into the sample 122 (S107). The calculation unit 148 performs this process for each observation position on the sample 122. Accordingly, an in-plane distribution of the injected charge amount and the luminance level can be obtained (S108). A specific example of the in-plane distribution will be described later.
When the n-type MOSFET is operated and inspected using the electron beam, the gate portion is irradiated with the electron beam having a region in which a yield of secondary electrons is 1 or more, so that the number of electrons emitted from the sample is equal to or more than the number of electrons incident on the gate portion, resulting in the positive charge. Due to the positive charge, a positive potential is applied to the gate portion. Therefore, the gate is turned on, and a flow of electrons is generated between the source and the drain. On the other hand, in the case of the P-type MOSFET, since a drain current can be generated by applying a negative voltage to the gate, the gate is negatively charged by setting the irradiation energy of the electron beam under the electron beam conditions such that the yield of the secondary electrons is less than 1, and the negative voltage is applied to the gate portion. As a method for controlling positive and negative of the voltage applied to the gate portion, the acceleration voltage of the electron beam injected into the gate portion may be controlled, or an electrode may be provided directly above the sample to indirectly apply an electric field from the outside. Further, a voltage may be applied by coming into direct contact with a terminal of a prober or the like. When the electron beam is injected into the gate portion using the electron beam, the whole pattern may be irradiated with the electron beam, or one point of the portion where the transistor is formed in designated pattern coordinates may be irradiated. Further, an irradiation method simulating a plurality of operation states may be performed by using a plurality of electron beams and simultaneously or alternately performing the irradiation under negative voltage application conditions and positive voltage application conditions according to the type of the transistors during the same observation.
When the charges accumulated in the gate portion are reset, the gate portion is generally formed on a gate insulating film, and thus the charges are removed by supplying electrons from a substrate material. Therefore, the light control unit 146 removes the charges accumulated in the insulating film by irradiating the substrate material with light having a wavelength 1 that is absorbed by the substrate material. At this time, portions formed on a joint structure are reset at the same time since the substrate materials are the same. For example, in a general dynamic random access memory (DRAM) implemented by the insulating film or the joint structure on a Si substrate, the entire accumulated charges of the DRAM structure can be controlled or reset by irradiation with light having a wavelength of 500 nm or less. In addition, the number of the charges accumulated in the gate portion can also be controlled by controlling the irradiation amount and the wavelength. When the charges of the gate portion are controlled, light having a wavelength that is directly absorbed by the gate insulating film may be emitted. By resetting the charges of the gate portion, the transistor is turned off.
A wavelength 2 is selected so as to remove charges only in a portion formed on the joint. Accordingly, only the charges accumulated in the source portion and the drain portion are reset while the charges are accumulated in the gate portion (while the gate portion is turned on).
When performing S104 for the first time, the light control unit 146 can reset the charged state of the gate portion by emitting the light having the wavelength 1. In the loop of S104 to S106, for example, the charged states of the source portion and the drain portion can be reset by emitting the light having the wavelength 2 every time the observation position is moved by one line in the Y direction. For example, when it is desired to observe characteristics such as a breakdown voltage failure and a recovery time of the joint, the detection signal from the detector 114 may be acquired after the light having the wavelength 2 is emitted. When it is desired to observe the on/off characteristic of the gate portion (how much applied voltage, that is, how much injected charge amount is required to turn on) or to reset the entire transistor, the wavelength 1 may be used.
Depending on whether the transistor is in the on state, a secondary signal level detected by the detector 114 (that is, the luminance level of the observation image at the observation position) differs. Therefore, the on/off state of the transistor can be acquired based on the detection signal level or a pixel value of the observation image. According to this, the calculation unit 148 can measure the on/off characteristics of the transistor.
The in-plane distribution as shown in
The charged particle beam device 1 according to the present Embodiment 1 measures the on/off characteristics (gate threshold voltage (Vth) characteristics) with respect to the injected charge amount into the transistor based on the wavelength 1 for initializing the charged state of the gate portion of the transistor formed on the sample 122 and the wavelength 2 for initializing only the charged states of the drain portion and the source portion. Accordingly, the on/off characteristics of the transistor can be measured using the light irradiation and the charged particle beam irradiation without connecting a measurement device such as an electrical probe to the transistor.
The control command unit 147 irradiates the sample 122 with the electron beam so as to turn on only the gate of one of the transistors. Accordingly, for example, a charge amount sufficient for the turn-on is injected into the gate portion on a right side of
The conduction of the transistor can be detected by the detection signal level when the transistor is irradiated with the observation electron beam. That is, the detection signal from the transistor in the conductive state and the detection signal from the transistor in a non-conductive state have different signal levels. The calculation unit 148 can measure whether the parasitic capacitance as indicated by a dotted line in
In this flowchart, the parasitic capacitance is calculated by acquiring the detection signal while varying the irradiation interval (interval step of the GUI to be described later) and a current amount (irradiation current amount or pulse electron width) of the electron beam emitted in the observation electron irradiation (S106).
In step S104-1, a potential state of the entire transistor is made uniform, and in step S105, charges are injected into one gate portion. The observation position is moved to the drain portion formed by a switch such as a joint, and only the drain portion formed by the joint structure is reset in step S104-2. According to the conditions set in S102, the parasitic capacitance is calculated by acquiring the detection signal while varying the irradiation interval (interval step of the GUI to be described later) and a current amount (irradiation current amount or pulse electron width) of the electron beam emitted in the observation electron irradiation (S106). At this time, the sample 122 is irradiated with the light set in step S104-2 every time the condition such as the irradiation interval changes.
The charged particle beam device 1 according to the Embodiment 2 measures the parasitic capacitance between wirings to the transistor based on the wavelength 1 for initializing the charged state of the gate portion of the transistor formed on the sample 122 and the wavelength 2 for initializing only the charged states of the drain portion and the source portion. Accordingly, it is possible to indirectly evaluate a distance between the wirings, film quality of the insulating film, and the like by measuring the parasitic capacitance between the wirings using the light irradiation and the charged particle beam irradiation without connecting a measurement device such as an electrical probe to the transistor.
The user can designate and input each irradiation condition in addition to viewing a measurement result on the GUI. The control command unit 147 controls each unit according to the designation input to perform the measurement sequence described with reference to
In the above embodiment, it is described that the in-plane distribution shown in
In the above embodiment, the light irradiation conditions for the wavelength 1 and the wavelength 2 that are described with reference to
In the above embodiment, the control command unit 147 and the calculation unit 148 are described as individual functional units. Alternatively, the control command unit 147 and the calculation unit 148 may be implemented as an integrated control unit. The control system 14 and the operation system 15 (and the functional units provided in the control system 14 and the operation system 15) may be implemented by hardware such as a circuit device having functions of the control system 14 and the operation system 15, or may be implemented by an arithmetic unit such as a central processing unit (CPU) executing software having the functions of the control system 14 and the operation system 15.
In the above embodiments, it is described that charges are injected into the sample or the observation image of the sample is obtained by irradiating the sample with the electron beam, but the invention is also applicable to cases where similar functions are implemented by emitting other charged particle beams.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/021468 | 5/25/2022 | WO |
