JP6364282B2 - Charged particle beam equipment - Google Patents

Description

  The present invention relates to a charged particle beam apparatus such as a scanning electron microscope, and more particularly to a charged particle beam apparatus provided with an excitation mechanism that enables vibration suppression.

  Accompanying the recent miniaturization of semiconductor elements, manufacturing apparatuses and apparatuses for measuring, inspecting, or evaluating semiconductor elements are required to have high precision corresponding thereto. Usually, a scanning electron microscope (hereinafter referred to as SEM), which is one of charged particle beam devices, is used to evaluate the geometric dimensions of a pattern formed on a semiconductor wafer and inspect defects of the formed wafer. It is done.

  In the inspection of a wafer by SEM, a charged particle beam generated in an ultra-high vacuum environment is irradiated on the wafer inside a charged particle optical column (hereinafter referred to as an optical column), and the two emitted from the wafer. An observation image is acquired by detecting the secondary electrons, and a pattern edge is determined from the change in brightness to derive a dimension, or a defect is observed. In order to cope with the miniaturization of the semiconductor described above, it is important to obtain a secondary electron image with less noise at a high observation magnification. When the optical lens barrel vibrates with respect to the wafer to be inspected, the irradiation position of the charged particle beam changes, and the observed image is distorted or the pattern edge appears to vibrate. As described above, the vibration of the optical lens barrel causes a reduction in the image quality of the observation image, and further contributes to a reduction in the resolution of the SEM.

  In Patent Document 1, as a mechanism for realizing high-speed and high-precision vibration suppression, an acceleration sensor and a vibration actuator are mounted on an optical barrel, and the vibration actuator is driven based on vibration information acquired by the acceleration sensor. A vibration suppression technique that cancels out optical barrel vibration is disclosed.

Japanese Patent No. 5162417 (corresponding US Pat. No. 8,553,199)

  However, according to the technique disclosed in Patent Document 1, it is possible to suppress the vibration of the optical barrel due to disturbance vibration, but the influence of the fluctuation of the irradiation position of the charged particle beam on the vibration of the optical barrel has not been confirmed. For this reason, even if the main vibration (frequency component having a large amplitude) of the optical barrel is suppressed, there is a possibility that the fluctuation of the irradiation position of the charged particle beam is not reduced.

  In addition, it is true that fluctuations in the irradiation position of charged particle beams are greatly influenced by low-order optical lens barrel vibrations, but if we try to suppress fluctuations in the nanometer order, the effects of higher-order vibrations in the optical lens barrel are ignored. Depending on the position of the acceleration sensor, there is a possibility that a node of the optical lens barrel vibration may be detected, and the main vibration of the optical lens barrel may not be detected. In order to avoid this, it is not practical to arrange a large number of acceleration sensors because the cost increases and the control becomes complicated.

  In the following, a charged particle beam apparatus intended to perform appropriate excitation based on the detection signal of a detector that detects vibration is proposed.

As one aspect for achieving the above object, a charged particle optical column that irradiates a sample with a charged particle beam emitted from a charged particle source, a vibration detector that detects vibration, and a detection signal of the vibration detector The charged particle beam apparatus includes a vibration device that vibrates the charged particle optical column, and the image is based on the detection signal and the signal obtained by irradiation of the detection signal and the charged particle beam. based on the relevant information of the swing, and a control device for controlling the vibrating device, comprising a storage medium for storing the related information, the said storage medium, the detection signal and the vibration information of the vibrator A transfer function (G1) indicating the relationship between the excitation information and the image shake, and a transfer function (G2 / G1) indicating the relationship between the detection signal and the image shake. At least one is remembered To propose a charged particle beam apparatus.

  According to the above configuration, appropriate excitation control can be performed based on the vibration detection of the vibration detector.

It is a figure which shows the whole charged particle beam apparatus. Example 1 It is a top view of a charged particle beam device. It is a flowchart which shows the process of acquiring the vibration conditions by a vibration apparatus. It is a control system block diagram which performs excitation control with respect to a charged particle beam apparatus. It is a figure which shows the whole charged particle beam apparatus. (Example 2) It is a figure which shows the natural vibration mode of a charged particle optical lens-barrel.

  The influence of the vibration of the optical barrel on the SEM will be described. With the miniaturization of semiconductors, the defect size to be detected on the wafer must be reduced, and the optical column during charged particle beam irradiation is required to suppress vibrations on the order of nanometers. At the same time, the number of defects detected per hour must be increased. Furthermore, the mainstream of the wafer size of semiconductor devices is expected to shift from φ300 mm to φ450 mm. As described above, high resolution and high throughput must be realized as the SEM becomes larger.

  In the inspection of a wafer by SEM, it is necessary to move the sample stage on which the wafer is mounted to the observation position. The sample chamber is vibrated by the reaction force when the sample stage is stopped, and the optical barrel vibrates. Since the movement time of the sample stage greatly affects the throughput of the entire apparatus, the sample stage is required to move at a high speed in order to further improve the throughput. Along with the high-speed movement, while the reaction force when stopping the sample stage is further increased, it is necessary to quickly attenuate the vibration of the optical column and suppress the fluctuation of the irradiation position of the charged particle beam.

  The embodiment described below calculates the fluctuation of the irradiation position assumed from the vibration information of the optical barrel, suppresses the fluctuation of the actual irradiation position by controlling and exciting the optical barrel based on the value, The present invention relates to a charged particle beam apparatus capable of acquiring an observation image with high accuracy.

  In an embodiment to be described later, for example, a charged particle beam apparatus including a sample stage on which a sample is placed, a sample chamber that supports the sample stage inside, and an optical column that irradiates the sample with a charged particle beam on the sample chamber. The vibration detecting means for detecting the vibration of the optical barrel is arranged in the optical barrel, and the vibration means for exciting the optical barrel in the horizontal direction is arranged at one end on the barrel. A plurality of controllers are arranged so that the other end is fixed to the sample chamber, and a controller for controlling the excitation means is provided. The controller controls the amount of deviation of the charged particle beam (hereinafter referred to as image fluctuation) that irradiates the sample. Image fluctuation detecting means for calculating the transfer function, adjusting means for controlling the excitation means so as to calculate a transfer function from vibration of the optical barrel to image fluctuation, and transfer function calculating means for calculating the transfer function And a storage unit for storing the transfer function , Assumed image fluctuation calculation means for calculating an assumed image fluctuation based on the transfer function and vibration information of the optical barrel, and an excitation control means for controlling the excitation means so as to cancel the assumed image fluctuation. In the adjustment step for calculating the transfer function, the excitation unit is controlled so as to perform the excitation by setting a frequency range for suppressing image fluctuation, and the transfer function is calculated and stored by the controller, In an inspection process for inspecting a sample, vibration information of the optical column is input to the controller, and an assumed image shake based on the transfer function is calculated, and an excitation unit is provided to cancel the assumed image shake. A charged particle beam apparatus to be controlled will be described with reference to the drawings.

  According to the configuration as described above, it is possible to provide a charged particle beam apparatus that can reduce image fluctuation with high accuracy against reaction force and disturbance vibration when the sample stage is stopped. Further, the image shake can be reduced without increasing the structure of the lens barrel. Further, it is possible to reduce the image shake without suppressing the excitation source of the lens barrel.

  In this embodiment, the optical system can be applied to other charged particle beam devices such as an SEM and a focused ion beam device, or other measurement / inspection devices, particularly for the purpose of measuring, inspecting, or evaluating semiconductors. An optical barrel vibration suppression mechanism that is a lens barrel and can suppress image shake with high accuracy will be described below with reference to the drawings.

  FIG. 1 is a diagram showing the entire charged particle beam apparatus. In the present embodiment, a semiconductor inspection apparatus using an SEM that is a representative charged particle beam apparatus will be described as an example. However, the present embodiment is not limited to the semiconductor inspection apparatus.

  Although not shown, the sample 115 is inserted from a load lock chamber attached to the sample chamber 103. The load lock chamber is evacuated from the atmospheric state by a turbo molecular pump and a dry pump and reaches a vacuum state. Thereafter, the sample 115 is placed on a sample stage 116 having an X table 111 movable in the X direction and a Y table 112 movable in the Y direction inside the sample chamber 103. Although not shown, the sample chamber 103 is always maintained in a vacuum state by a turbo molecular pump and a dry pump. The sample 115 is moved to a position where the primary electron beam 105 can be irradiated by the sample stage 116, and inspection is started.

  Although not shown, the inside of the optical barrel 102 is maintained in an ultrahigh vacuum state by an ion pump. The primary electron beam 105 generated from the electron gun 104 inside the optical barrel 102 is focused by a converging lens 106, and the surface of the sample 115 observed by the scanning polarizer 108 in a state of being focused by the objective lens 107 is two. Irradiated while scanning in a dimension. Secondary electrons 109 emitted from the sample 115 irradiated with the primary electron beam 105 are detected by a secondary electron detector 110 and input to an image shake detection means 121. The image fluctuation detecting means 121 has a function of displaying the pattern shape of the sample 115 as an image based on the detected amount of secondary electrons, and for example, the vibration amplitude of the pattern edge is displayed from the displayed image information. It has a function of measuring and acquiring as vibration amplitude with respect to the frequency axis by FFT processing and determining the information as image shake.

  The base of the optical column 102 is supported by the sample chamber 103, and vibration detection means 113 is disposed in the optical column 102 so that vibration information of the optical column 102 can be detected. The vibration detection means 113 is, for example, an acceleration detector, and can acquire acceleration in the horizontal biaxial directions (X and Y directions).

  At the base of the optical barrel 102, vibration means 114 having one end fixed to the optical barrel 102 and the other end fixed to the sample chamber 103 are arranged in pairs in the horizontal direction as shown in FIG. The optical barrel 102 can be vibrated in the horizontal direction (X, Y direction). The excitation means 114 is, for example, a piezoelectric element, and can generate a generated excitation force as excitation information.

  In the present embodiment, the sample 115 is inspected after making adjustments for examining in advance the influence of image fluctuation due to vibration of the optical barrel 102. A control method of the adjustment process and the inspection process will be described. The controller 145 for controlling the vibration means 114 includes an adjustment means 120, the image fluctuation detection means 121, an assumed image fluctuation calculation means 122, an excitation control means 123, and a storage unit 207.

  In the adjustment step, the adjusting unit 120 controls the vibration unit 114 to vibrate the optical column 102, and the image shake information at that time, the vibration information of the vibration unit 114, and the optical column 102 Vibration information is input to the assumed image shake calculation means 122, a transfer function from vibration of the optical barrel 102 to image shake is calculated, and stored in the storage unit 207.

  In the inspection process, the optical column 102 is excited by reaction force or environmental disturbance when the sample stage 116 is stopped, and vibration information of the optical column 102 at this time and the transfer function stored in the storage unit 207 are used. An assumed image shake is calculated, input to the vibration control means 123, and the vibration means 114 is controlled by the vibration means 123 so as to cancel the assumed image shake. Suppress.

  A procedure for acquiring the vibration conditions by the vibration device will be described with reference to FIG. In step 300, in the adjustment means 120, the operator sets an adjustment range. The operation of the operator is as described above, and thereafter, adjustment is automatically performed.

  For example, if the adjustment value is 1 Hz from a frequency of 1 Hz to 100 Hz, the subsequent adjustment is performed 100 times every 1 Hz. In step 301, the optical barrel 102 is vibrated at 1 Hz. In step 302, vibration information of the vibration means 114, vibration information of the optical barrel 102, and image shake information are acquired.

  In step 303, the assumed image shake calculating means 122 calculates a transfer function (G1) from the excitation information to the vibration information of the optical barrel 102, and a transfer function G2 from the excitation information to the image shake information. Then, a transfer function (G2 / G1) 206 from vibration of the optical barrel 102 to image shake is calculated from the transfer function G1 and the transfer function G2. In step 304, the information is stored in the storage unit 207. In step 305, the process from step 301 is repeated until the adjustment to 100 Hz is completed.

  The transfer function (G2 / G1) is so-called information related to the detection signal obtained by the vibration detection means 113 (vibration detector) and the fluctuation of the image formed based on the charged particles emitted from the sample. If the relevant information is acquired in advance, the image shake can be predicted based on the detection of the detection signal of the vibration detecting means 113, and the optical barrel is vibrated so as to cancel the image shift. Thus, it is possible to appropriately suppress image shake. The related information may be stored as a relational expression indicating the relationship between the output value of the vibration detecting unit 113 and the control signal of the vibrating unit 114, or a table indicating the relationship between the frequency and the excitation condition. However, in this embodiment, an example in which the transfer function (G2 / G1) is used as related information and a control signal is generated from the related information will be described. .

  FIG. 4 is a block diagram of a control system that performs excitation control on the charged particle beam apparatus. The transfer function (G2 / G1) 206 calculated and stored in the adjustment step is used as a feedback element, and feedback control is performed to suppress image shake. A disturbance excitation force 210 and an excitation force 209 due to reaction force and disturbance vibration when the sample stage 116 is stopped are input to the optical barrel 102 and output as optical barrel vibration information 124. The optical barrel vibration information 124 is input to the assumed image shake transfer function (G2 / G1) 206 and outputs an assumed image shake 126. The target image shake value is zero, and the assumed image shake 126 is inverted in sign and input to the vibration control means 123 and output as an assumed image shake canceling excitation signal 127. The assumed image shake canceling excitation signal 127 is input to the excitation unit 114 and output as the excitation force 209. The above control is repeated to suppress image shake.

  According to the present embodiment, the assumed image fluctuation transfer function (G2 / G1) 206 calculated in the adjustment process is used to control the assumed image fluctuation based on the optical barrel vibration information 124 in the inspection process. By subjecting the optical barrel 102 to vibration control, the image shake can be suppressed with high accuracy. In addition, the image shake can be reduced without increasing the structural rigidity of the optical barrel 102. Further, it is possible to reduce the image shake without suppressing the excitation source of the optical barrel 102 and without insulating the vibration path.

  FIG. 5 is a diagram illustrating an example in which the excitation unit 114 is installed at a position different from the charged particle beam apparatus illustrated in FIG. 1. The control method is the same as in FIG. 1 and is not shown. At the base of the optical barrel 102, the vibration means 114 having one end fixed to the optical barrel 102 and the other end fixed to the sample chamber 103 is arranged in the vertical direction, and the optical barrel 102 is placed vertically. It is possible to vibrate in the direction (Z direction). By applying vibration in the vertical direction of the vibration means 114, a bending moment is generated in the optical barrel 102, and the shake of the optical barrel 102 is suppressed.

  According to the present embodiment, the addition of the excitation means 114 and the adjustment and change of the mounting height are facilitated. With respect to the vibration behavior of the optical barrel 102, for example, the optical barrel 102 is shown in FIG. When excited in a vibration mode as shown in Fig. 5, if one end of the vibration means 114 is fixed to the antinode of the vibration mode, vibration can be suppressed even with a small vibration force. The same applies to higher-order vibration modes. If the higher-order natural vibration mode of the optical column is confirmed and predicted in advance by experiments and calculations, the vibration means 114 having a minimum vibration force is provided. Can be estimated.

DESCRIPTION OF SYMBOLS 101 Charged particle beam apparatus 102 Optical barrel 103 Sample chamber 104 Electron gun 105 Primary electron beam 106 Converging lens 107 Objective lens 108 Scanning polarizer 109 Secondary electron 110 Secondary electron detector 111 X table 112 Y table 113 Vibration detection means 114 Exciting means 115 Sample 116 Sample stage 120 Adjusting means 121 Image fluctuation detecting means 122 Assumed image fluctuation calculating means 123 Excitation control means 124 Optical barrel vibration information 126 Assumed image fluctuation information 127 Assumed image fluctuation canceling excitation command 145 Controller 206 Assumed image transfer function (G2 / G1)
207 Storage unit 209 Excitation force 210 Disturbance excitation force

Claims (7)

A charged particle optical column that irradiates a sample with a charged particle beam emitted from a charged particle source, a vibration detector that detects vibration, and the charged particle optical column added based on a detection signal of the vibration detector. A charged particle beam device including a vibration exciting device,
And the detection signal, based on the relevant information of the image shake based on the signal obtained by the irradiation of the detection signal and the charged particle beam, and a control device for controlling the vibrator, a storage for storing the relevant information With media,
The storage medium includes a transfer function (G1) indicating a relationship between the vibration information of the vibration generator and the detection signal, a transfer function (G2) indicating a relationship between the vibration information and the image shake, and the detection. A charged particle beam apparatus , wherein at least one of transfer functions (G2 / G1) indicating a relationship between a signal and the image fluctuation is stored . In claim 1,
The charged particle beam apparatus, wherein the storage medium stores the related information in units of frequency. In claim 1,
The said control apparatus acquires the said relevant information for every vibration condition of the said vibration apparatus of a different frequency, The charged particle beam apparatus characterized by the above-mentioned. In claim 3 ,
The control device, for each excitation condition of the excitation device having a different frequency, the transfer function (G1) indicating the relationship between the excitation information of the excitation device and the detection signal, the excitation information, and the image fluctuation. And a transfer function (G2 / G1) indicating a relationship between the detection signal and the image fluctuation, and at least one of the transfer function (G2) indicating the relationship between the detection signal and the image fluctuation. In a charged particle beam apparatus comprising: a sample stage for placing a sample; a sample chamber that internally supports the sample stage; and an optical column that irradiates the sample with a charged particle beam at the upper part of the sample chamber;
A vibration detecting means for detecting vibration of the optical barrel is arranged in the optical barrel, and one end of the vibration means for exciting the optical barrel in the horizontal direction is fixed to the optical barrel, A plurality of controllers are arranged so that the other end is fixed to the sample chamber, and a controller for controlling the vibration means is provided, and the controller detects image fluctuations for obtaining an image fluctuation representing a deviation amount of the charged particle beam applied to the sample. Means, adjustment means for controlling the excitation means so as to calculate a transfer function from vibration of the optical barrel to image shake, transfer function calculation means for calculating the transfer function, and storing the transfer function Storage unit, an assumed image shake calculation unit that calculates an assumed image shake based on the transfer function and vibration information of the optical barrel, and an excitation control that controls the excitation unit to cancel the assumed image shake Having means,
In the adjustment step for calculating the transfer function, the excitation means is controlled so as to implement a vibration by setting a frequency range for suppressing image fluctuation, and the transfer function is calculated and stored by the controller,
In the inspection process for inspecting the sample, vibration information of the optical barrel is input to the controller, and an assumed image shake based on the transfer function is calculated, and an excitation means is used to cancel the assumed image shake. A charged particle beam device characterized by controlling In claim 5 ,
Wherein the vibrating means is a vibrating means of the piezoelectric type, the vibrating means is one end is fixed to the front Symbol optical science barrel, the other end is fixed to the sample chamber, the cylinder before Symbol optical science barrel A charged particle beam device, characterized in that it is disposed on a surface so as to face each other in two horizontal axes. In claim 5 ,
The vibration direction of the vibrating means, the charged particle beam apparatus which is a direction perpendicular to the front Symbol optical science barrel.