JP4580982B2 - Charged particle beam apparatus, contamination removal method, and sample observation method - Google Patents

Description

  The present invention relates to a charged particle beam device, a contamination removal method, and a sample observation method, and more particularly, to a charged particle beam device, a contamination removal method, and a sample observation method that can suppress the occurrence of contamination in a short period of time.

  In a manufacturing process of a semiconductor device, observation of a sample by a charged particle beam device, measurement of a line width of a pattern, and the like are performed. In observation and measurement of a sample using a charged particle beam apparatus, scanning is performed while irradiating an observation part with an electron beam, and the amount of electrons such as secondary electrons is converted into luminance and displayed as an image on a display device.

  In general, a phenomenon in which contamination adheres to a sample occurs when the sample is irradiated with an electron beam. If contamination adheres to the sample, the sample cannot be observed accurately, and the line width of the pattern fluctuates and accurate measurement cannot be performed.

  FIG. 1 is a schematic diagram showing how the width of a pattern increases during observation of a sample by a charged particle beam apparatus. When the pattern shown in FIG. 1A is observed, scanning is performed while irradiating the observation portion with the electron beam EB. FIG. 1B shows a state in which contamination adheres to the surface of the pattern by electron beam irradiation. As the contamination adheres, the pattern width cannot be accurately measured. Further, when the same portion of the sample is observed, contamination further adheres as shown in FIG. 1C, and the width of the pattern changes greatly.

  In addition, with the miniaturization of semiconductor devices, the observation magnification is increased and a fine sample is observed. When the observation magnification is increased, the amount of electron beam irradiation per unit area increases, the contamination adheres to the sample, and the sample cannot be observed more accurately.

  Various methods for reducing the occurrence of contamination in the charged particle beam apparatus have been proposed for such problems.

As a technique related to this, Patent Document 1 discloses a method of cleaning the inside of a chamber with ozone in an electron beam exposure apparatus. Patent Document 2 discloses a method of removing dirt by introducing high-concentration ozone into a chamber with a small amount of oxygen used during exposure in a charged particle beam exposure apparatus.
JP 09-259811 A JP 2001-148340 A

  In the above-described method for preventing the occurrence of contamination in the chamber, the generation of contamination is prevented by injecting ozone into the apparatus while the apparatus is in operation. That is, ozone in an apparatus and an electron beam are collided to separate ozone into oxygen and active oxygen. And it reacts with the contamination which is going to adhere to the surface of each component in a sample or an apparatus with the separated active oxygen, and is evaporated as carbon monoxide gas.

  However, it is unclear how long it will take for contamination to occur after ozone is injected into the device and the device is operated. Further, when the same part of the sample is irradiated with the electron beam a plurality of times, the amount of electron beam irradiation increases. In this case, it is also unclear whether or not contamination occurs.

In general, the stage movement of the stage on which the sample is placed in the sample chamber is expected. Vacuum grease is used as a lubricant for a mechanism and a mechanism for transporting a sample. Further, vacuum grease is also applied to an O-ring used for vacuum sealing. It has been conventionally known that substances that cause contamination are volatilized from the vacuum grease. As described above, when a large amount of vacuum grease is used in the sample chamber, the amount of contamination generated increases accordingly. On the other hand, devices that do not use vacuum grease have been developed. It becomes very expensive.

  The present invention has been made in view of the problems of the prior art, and is a charged particle beam apparatus capable of efficiently suppressing the occurrence of contamination in a sample chamber even when vacuum grease is used, a contamination removal method, and It aims at providing the observation method of a sample.

The above-described problems include an electron gun that irradiates the surface of the sample with an electron beam, a wafer stage on which the sample is placed, a wafer stage moving unit that moves the wafer stage, and a sample chamber in which the wafer stage is housed. Ozone gas injection means for directly injecting ozone gas; ultraviolet irradiation means for directly irradiating ultraviolet rays into the sample chamber; and a shielding means capable of opening and closing between the column in which the electron gun is housed and the sample chamber. The charged particle beam apparatus has a control means for continuously moving the wafer stage simultaneously with the ozone gas injection and the ultraviolet irradiation .

In addition, the above-described problems include a step of closing between the column of the charged particle beam apparatus and the sample chamber in which the wafer stage is accommodated, a step of injecting ozone gas into the sample chamber, and irradiating the sample chamber with ultraviolet rays. A step of continuously moving the wafer stage when the ozone gas is injected and the ultraviolet ray is irradiated; a step of stopping the irradiation of the ultraviolet ray; and a step of stopping the injection of the ozone gas ; And a step of stopping the movement of the wafer stage .

Furthermore, the above-described problem is a sample observation method for observing the surface of a sample placed on a wafer stage in the sample chamber, the step of closing the column and the sample chamber, and injecting ozone gas into the sample chamber A step of irradiating ultraviolet rays into the sample chamber, a step of continuously moving the wafer stage when the ozone gas is injected and the ultraviolet rays are irradiated, and a step of stopping the irradiation of the ultraviolet rays A step of stopping the injection of the ozone gas, a step of stopping the movement of the wafer stage, a step of opening between the column and the sample chamber, and irradiating the sample with an electron beam on the sample And a step of generating an image of the surface.

  In the present invention, ozone gas is directly injected into the sample chamber of the charged particle beam apparatus and irradiated with ultraviolet rays. By injecting ozone gas, active oxygen decomposed from ozone reacts with a causative substance of contamination, and contamination such as C can be removed. In addition, irradiation with ultraviolet rays reacts with oxygen decomposed from ozone, and ozone is newly generated. Therefore, the amount of active oxygen that decomposes from ozone does not decrease rapidly. Thereby, it is possible to suppress the contamination such as C from adhering to the sample in the sample chamber in a short period of time.

  In addition, a shield plate that can be opened and closed is provided between the sample chamber and the column, and the shield plate is closed to clean only the sample chamber by irradiation with ozone gas and ultraviolet rays. As a result, it is possible to efficiently remove the contamination in the sample chamber and observe the sample without contamination. Furthermore, since ozone gas and ultraviolet rays are not introduced into the column, damage such as oxidation of parts in the column by ozone can be prevented.

  Embodiments of the present invention will be described below with reference to the drawings.

First, the configuration of the charged particle beam apparatus will be described. Next, a process for suppressing the occurrence of contamination in a short period, which is a feature of the present invention, will be described. Next, a contamination removal method and a sample observation method will be described. Finally, an embodiment in which the adhesion of contamination to the sample is reduced by the treatment for suppressing the occurrence of contamination according to the present invention will be described.
(Configuration of charged particle beam system)
FIG. 2 is a configuration diagram of the charged particle beam apparatus according to the present embodiment.

  The charged particle beam apparatus 100 includes an electronic scanning unit 10, a signal processing unit 30, an image display unit 40, and a control unit 20 that controls the electronic scanning unit 10, the signal processing unit 30, and the image display unit 40. Broadly divided. Among these, the electronic scanning unit 10 includes an electron column (column) 15 and a sample chamber 16. The electron column unit 15 includes an electron gun 1, a condenser lens 2, a deflection coil 3, and an objective lens 4, and the sample chamber 16 includes a wafer stage moving unit 5 and a wafer stage 6. The sample chamber 16 holds a motor 11 for moving the wafer stage 6, an ozone generator 12 for injecting ozone, an ultraviolet generator 13 for irradiating ultraviolet rays, and the sample chamber 16 in a predetermined reduced pressure atmosphere. The vacuum pumps 18 are connected to each other. A shield plate 17 that can be opened and closed is provided between the electron lens barrel 15 and the sample chamber 16.

  The charged particles 9 irradiated from the electron gun 1 are irradiated to the sample 7 on the wafer stage 8 through the condenser lens 2, the deflection coil 3 and the objective lens 4.

  The amount of secondary electrons or reflected electrons emitted from the sample 7 after being irradiated with the charged particles 9 is detected by an electron detector 8 composed of a scintillator or the like, and the detected amount is digitally converted by an AD converter in the signal processing unit 30. Is converted into a quantity, further converted into a luminance signal, and displayed on the image display unit 40.

  The electronic deflection amount of the deflection coil 3 and the image scan amount of the image display unit 40 are controlled by the control unit 20. The control unit 20 stores a program for executing length measurement.

  Wafer stage moving unit 5 moves wafer stage 6 by motor 11. A screw is used for the wafer stage moving unit 5, and vacuum grease is applied to the screw to lubricate the movement of the wafer stage 6. The ozone generator 12 generates ozone to be injected into the sample chamber 16, and the ultraviolet generator 13 is for irradiating the sample chamber 16 with ultraviolet rays. Further, the shielding plate 17 is for shielding the space between the sample chamber 16 so that ozone gas does not go to the electron column portion 15.

  In the charged particle beam apparatus configured as described above, prior to the observation of the wafer placed on the wafer stage 6, a vacuum state in which no contamination occurs is generated. Here, it is assumed that the vacuum grease containing the contamination-causing substance is used for the screw portion of the wafer stage moving unit 5. First, the space between the sample chamber 16 and the electron lens barrel 15 is shielded. Next, in order to uniformly distribute the vacuum grease, the wafer stage 6 is continuously moved for a predetermined time. While moving the wafer stage 6, ozone generated by the ozone generator 12 is injected into the sample chamber 16. Simultaneously, the sample chamber 16 is irradiated with ultraviolet rays generated by the ultraviolet generator 13. These processes are collectively managed by the control unit 20. These operations are performed continuously for one month, for example.

After performing the above processing, the sample is observed. In this embodiment, ozone is injected while the wafer stage 6 is moved. However, after the wafer stage 6 is continuously moved and the vacuum grease is uniformly distributed, ozone is injected. Also good.
(Description of processing to suppress the occurrence of contamination)
By performing the above treatment, it is possible to suppress contamination from adhering to the sample. This is considered to be due to the following reasons.

  A substance that causes contamination generated from vacuum grease is considered to be an organic substance composed of C and H. FIG. 3A is a diagram schematically showing the presence of such an organic material on the sample. By reacting active oxygen with the contamination-causing substance, organic substances C and H are combined with active oxygen and evaporated. Thereby, as shown in FIG.3 (b), C considered to be a contamination substance disappears from the surface of a sample. And even if an electron beam is irradiated on a sample, it will be suppressed that C adheres to a sample.

  Thus, it is considered that generation of contamination can be suppressed if C, which is considered to be contamination, can be removed from the causative substance of contamination using active oxygen.

  In order to generate active oxygen, ozone gas is injected into the sample chamber 16. Since ozone is an unstable substance, it is decomposed into oxygen and active oxygen over time. Thereby, active oxygen is generated and C can be removed from the causative substance of contamination.

  Furthermore, by irradiating the sample chamber 16 with ultraviolet rays, oxygen generated by decomposing ozone reacts with the ultraviolet rays to newly generate ozone. This ozone is decomposed into oxygen and active oxygen with the passage of time, and the active oxygen removes C from the contaminants and oxygen and ultraviolet rays react to generate ozone. By this series of reactions, it is considered that the rate of removing C from the contamination-causing substance is increased, and the sample chamber 16 can be made less contaminated in a shorter period of time than the conventional method.

  When the sample was observed after the above treatment, the adhesion of contamination to the sample was greatly reduced compared to the conventional method. Moreover, such a state with little contamination has continued for a long time. Therefore, once an initial state with little contamination is created before the observation of the sample, it is possible to prevent the occurrence of contamination thereafter. If such an initial state is performed in accordance with, for example, the overhaul of the apparatus, it is possible to observe the sample with a small amount of contamination without causing a decrease in the operation rate of the apparatus.

As a result, even a charged particle beam apparatus using vacuum grease, which has been considered impossible in the past, has less contamination and can accurately measure a minute pattern. Further, even when a specific place of the sample is observed a plurality of times, it is possible to prevent contamination from adhering to the pattern, and it is possible to perform accurate measurement.
(Contamination removal method and sample observation method)
Next, a method for observing a sample using the charged particle beam apparatus of the present embodiment will be described with reference to the flowchart of FIG.

  Here, it is assumed that the vacuum grease is applied to the screw portion of the wafer stage moving unit 5. Further, prior to step S <b> 11, the space between the sample chamber 16 and the electron lens barrel 15 is shielded by the shielding plate 17.

  First, in step S11, an operation of expanding the surface of the vacuum grease is performed. By uniformly spreading the surface of the vacuum grease, all the substances that cause contamination can be volatilized at an early stage. In the present embodiment, the vacuum grease is expanded by continuously moving the wafer stage 6. The method for expanding the surface of the vacuum grease is not limited to this.

  Next, in step S <b> 12, ozone gas is injected into the sample chamber 16. By injecting ozone gas, active oxygen produced by decomposing ozone reacts with the causative substance of contamination, and evaporates as carbon monoxide gas.

  Next, in step S13, the sample chamber 16 is irradiated with ultraviolet rays. By irradiation with ultraviolet rays, ozone reacts with oxygen formed by decomposition, and ozone is further generated.

  The above steps S11 to S13 are continued for a predetermined period.

  After generation of contamination in the sample chamber 16 is suppressed, irradiation of ultraviolet rays into the sample chamber 16 is stopped in step S14, and injection of ozone gas into the sample chamber 16 is stopped in step S15.

  Thereafter, the shielding plate 17 is opened, the sample is placed on the sample stage, and the sample is observed.

  In the sample observation method of this embodiment, ozone gas is injected into the sample chamber 16 and ultraviolet rays are irradiated, so that the occurrence of contamination in the sample chamber is suppressed in a short period of time, and the contamination adheres to the sample. Therefore, it is possible to accurately observe or measure the sample.

  In particular, a shield plate 17 that can be opened and closed is provided between the sample chamber 16 and the electron column section 15, and the shield plate 17 is closed so that only the sample chamber 16 is cleaned by ozone gas and ultraviolet irradiation. It is possible to remove the contamination in the sample chamber 16 and observe the sample without contamination.

  Further, when the electron lens barrel 15 is not separated from the sample chamber 16 by the shielding plate 17, ozone gas is also introduced into the electron lens barrel 15. At that time, since ozone is introduced in an amount necessary for cleaning the inside of the sample chamber 16 where a large amount of contamination is generated, there is a risk of damaging the components in the electron column section 15. On the other hand, in the present embodiment, since the shielding plate 17 is closed, ozone gas and ultraviolet rays are not introduced into the electron lens barrel 15 and damages such as oxidation of parts in the electron lens barrel 15 by ozone are caused. Can be prevented.

The ozone gas injection in step S12 and the ultraviolet irradiation in step S13 may be performed simultaneously. Further, the process of expanding the surface of the vacuum grease in step S11 may be performed simultaneously with the ozone gas injection and the ultraviolet irradiation.
(Example)
Hereinafter, the result of the reduction of contamination adhering to the sample will be described using the charged particle beam apparatus of the present embodiment. Here, the formed pattern was line & space, the pattern width was 250 nm, and the ratio of the line to space width was 1: 1.

  First, the sample was observed using the charged particle beam apparatus of this embodiment. 10 g of vacuum grease was applied to the screw portion of the wafer stage moving unit 5 and observed by the charged particle beam apparatus according to the sample observation method of this embodiment. That is, after applying vacuum grease, ozone was injected into the sample chamber 16 of the charged particle beam apparatus and irradiated with ultraviolet rays. At the same time, the wafer stage 6 was continuously moved so that the vacuum grease spread uniformly. This operation was continued for about 400 hours.

  Thereafter, the sample was observed according to the following procedure. The observation magnification of the charged particle beam apparatus was increased so that the electron beam was irradiated in the range of 1 μm × 1 μm, and then the sample was observed at an observation magnification of 2 μm × 2 μm. FIG. 5A is an explanatory view showing a state in which the adhesion of contamination to the sample is small, and FIG. 6A is an SEM (Scanning Electron Microscope) image of the observation result. The electron beam was applied to the inside of the broken line 51 in FIG. 5A, but contamination was hardly adhered. As can be seen from the SEM image in FIG. 6A, it was confirmed that almost no contamination occurred on the sample.

  Next, 1 g of vacuum grease was applied to the screw portion of the wafer stage moving unit 5, and the sample was observed without injecting ozone and irradiating ultraviolet rays into the sample chamber 16 of the charged particle beam apparatus. The sample was observed by increasing the observation magnification of the charged particle beam apparatus so that the electron beam was irradiated in a range of 1 μm × 1 μm, and then observing the sample at an observation magnification of 2 μm × 2 μm. FIG. 5B is an explanatory diagram showing a state in which contamination adheres to the sample, and FIG. 6B is an SEM image of the observation result. As a result of irradiating the inside of the broken line 52 in FIG. 5B with the electron beam, contamination due to adhesion of C occurred in the broken line 52. Further, the line width 53 is wider than that in FIG. 5A due to the adhesion of contamination. As can be seen from the SEM image in FIG. 6B, it was confirmed that contamination was attached to the sample.

  Thereafter, it is confirmed that no contamination occurs on the sample by performing the process of this embodiment such as injecting ozone into the sample chamber 16 again and irradiating with ultraviolet rays.

  As described above, in the contamination removal method and sample observation method of the charged particle beam apparatus according to the present embodiment, ozone gas is directly injected into the sample chamber 16 of the charged particle beam apparatus and irradiated with ultraviolet rays. . At the same time, an operation of stirring the vacuum grease existing in the sample chamber 16 is performed. By performing these operations only for a predetermined time, for example, a period corresponding to the amount of vacuum grease being used, it is possible to suppress the adhesion of contamination such as C on the sample.

  In addition, a shield plate 17 that can be opened and closed is provided between the sample chamber 16 and the electron column section 15, and the shield plate 17 is closed to clean only the sample chamber 16 by ozone gas and ultraviolet irradiation. As a result, it is possible to efficiently remove the contamination in the sample chamber 16 and observe the sample without contamination. Furthermore, since ozone gas and ultraviolet rays are not introduced into the electron lens barrel 15, it is possible to prevent damage such as oxidation of parts in the electron lens barrel 15 by ozone.

  Furthermore, it has been confirmed that when the contamination removal method of the present embodiment is used, a state in which no contamination occurs can be achieved about 100 times faster than the conventional method. Conventionally, when the line width is measured, the contamination is attached to the sample by about 1 nm. On the other hand, when the measurement was performed using the charged particle beam apparatus of the present embodiment, it was confirmed that the contamination adhered only to about 0.03 nm.

It is a figure which shows a mode that the width | variety of a pattern increases by irradiation of an electron beam. It is a block diagram of the charged particle beam apparatus used by embodiment of this invention. It is a figure explaining the principle by which the contamination of this invention is suppressed. It is a flowchart which shows the observation method of the sample of this invention. FIG. 5A is a diagram showing a state in which no contamination adheres to the sample. FIG. 5B is a diagram illustrating a state in which contamination adheres to the sample. FIG. 6A is an SEM image corresponding to FIG. FIG. 6B is an SEM image corresponding to FIG.

Claims (6)

An electron gun that irradiates the surface of the sample with an electron beam;
A wafer stage on which a sample is placed;
A wafer stage moving means for moving the wafer stage;
Ozone gas injection means for directly injecting ozone gas into the sample chamber in which the wafer stage is stored;
UV irradiation means for directly irradiating ultraviolet rays into the sample chamber;
Shielding means that can be opened and closed between the column in which the electron gun is housed and the sample chamber;
A charged particle beam apparatus comprising: control means for continuously moving the wafer stage simultaneously with the ozone gas injection and the ultraviolet irradiation.   The charged particle beam apparatus according to claim 1, wherein the control unit causes the ozone gas injection unit and the ultraviolet irradiation unit to simultaneously perform the ozone gas injection and the ultraviolet irradiation continuously for a predetermined time. A step of closing between the column of the charged particle beam apparatus and the sample chamber in which the wafer stage is stored;
Injecting ozone gas into the sample chamber;
Irradiating ultraviolet rays into the sample chamber;
Continuously moving the wafer stage when injecting the ozone gas and irradiating the ultraviolet light;
Stopping the ultraviolet irradiation;
Stopping the injection of ozone gas;
And a step of stopping the movement of the wafer stage. The contamination removal method according to claim 3 , wherein the ozone gas injection and the ultraviolet irradiation are performed simultaneously for a predetermined time. A sample observation method for observing the surface of a sample placed on a wafer stage in a sample chamber,
Closing between the column and the sample chamber;
Injecting ozone gas into the sample chamber;
Irradiating ultraviolet rays into the sample chamber;
Continuously moving the wafer stage when injecting the ozone gas and irradiating the ultraviolet light;
Stopping the ultraviolet irradiation;
Stopping the injection of ozone gas;
Stopping the movement of the wafer stage;
Opening between the column and the sample chamber;
And irradiating the sample with an electron beam to generate an image of a surface on the sample. The sample observation method according to claim 5 , wherein the ozone gas injection and the ultraviolet irradiation are simultaneously performed for a predetermined time.

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