JP3923733B2 - Sample preparation method for transmission electron microscope - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a specimen preparation method for a transmission electron microscope, and more particularly to a specimen preparation method for a transmission electron microscope using a focused ion beam suitable for evaluating a manufacturing process of a highly miniaturized semiconductor device. is there.
[0002]
[Prior art]
2. Description of the Related Art Conventional sample preparation methods for a transmission electron microscope (hereinafter referred to as TEM; Transmission Electron Microscopy) include processing a desired sample using a focused ion beam (hereinafter referred to as FIB). .
[0003]
First, referring to FIGS. 5 and 6, a first method that occurs when a conventional method for manufacturing a TEM sample using FIB is applied to a manufacturing process evaluation of a highly miniaturized semiconductor device having a processing dimension of 100 nm or less. The problem of will be described.
[0004]
FIG. 5 is a schematic view showing a method for producing a TEM sample used for manufacturing process evaluation of a conventional semiconductor device having a processing dimension of several hundred nm or more. For example, a case where a step of embedding a circular contact plug 103 in the insulating film 101 on the semiconductor substrate via the barrier layer 102 is evaluated by TEM observation will be described. This example does not necessarily show a partial structure of an actual semiconductor device, but is shown as a schematic diagram for showing conventional problems.
[0005]
FIG. 5A is a top view of a partial structure to be evaluated. In order to evaluate the embedded state in the contact hole by the barrier layer 102 and the contact plug 103, as shown in FIG. 5A, the evaluation portion is a thin film portion having a thickness of about 100 nm perpendicular to the center line of the contact hole. Then, a sample for TEM observation is prepared, and evaluation is performed by analyzing a TEM image transmitted through the thin film portion.
[0006]
A vertical sectional structure of the thin film portion is shown in FIG. Thus, when the size of the partial structure to be evaluated is sufficiently larger than the thickness of the thin film portion of 100 nm, FIG.
Since the cross section of the partial structure to be evaluated is clearly shown as a two-dimensional pattern in the cross section of the thin film portion shown in (b), good TEM observation can be performed.
[0007]
In recent years, microfabrication technology for semiconductor devices has progressed, and TEM observation has become increasingly important as a method for accurately evaluating the manufacturing process of highly miniaturized semiconductor devices with a processing dimension of 100 nm or less. If the thickness of the thin film portion of the sample used for TEM observation remains at the conventional value of about 100 nm, it is practically impossible to perform good TEM observation.
[0008]
Next, this problem will be described in detail with reference to FIGS. 6 (a) and 6 (b).
[0009]
The top view of the partial structure to be evaluated shown in FIG. 6A includes an insulating film 101 on the semiconductor substrate, a barrier layer 102, and a contact plug 103, as in FIG. 5A. However, it is different from FIG. 5A in that the manufacturing process is further miniaturized and the inner diameter of the contact hole is reduced to 100 nm or less (in FIG. 6A, the inner diameter of the contact hole is just 100 nm. It is shown).
[0010]
In order to evaluate the embedding condition and the internal structure inside the contact hole thus miniaturized, as shown by the broken line in FIG. 6 (a), the evaluation portion has a thickness of about perpendicular to the center line of the contact hole. If a sample for TEM observation is prepared with a thin film portion of 100 nm, the cross section of the target partial structure is not two-dimensionally displayed on the cross section of the sample shown in FIG.
[0011]
When the size of the partial structure to be evaluated is 100 nm or less and is highly miniaturized, as shown by the solid line in FIG. The thickness of the thin film portion to be made must be at least as thin as about 20 nm. If the thickness of the thin film portion is about 20 nm, as shown in FIG. 6 (b), the vertical cross section of the thin film portion shows the cross section of the partial structure to be evaluated two-dimensionally, and a highly accurate TEM Observation becomes possible.
[0012]
Next, with reference to FIG. 7, a second problem that occurs when the conventional method for manufacturing a TEM sample using FIB processing is applied to the evaluation of a manufacturing process of a highly miniaturized semiconductor device will be described. To do. A method for manufacturing a TEM sample using conventional FIB processing is specifically shown in FIG.
[0013]
FIG. 7A is a cross-sectional view showing a method for manufacturing a TEM sample. The TEM sample 101 to be subjected to TEM observation and the non-conductivity generated on the side surface of the thin film portion to be subjected to TEM observation by irradiation with FIB made of gallium ions. It is composed of a crystalline layer (damage layer) 104.
[0014]
As shown in FIG. 7A, FIB made of gallium ions accelerated by voltage is selectively irradiated by scanning in a direction perpendicular to the upper surface of the TEM sample 101, and the TEM sample 101 to be subjected to TEM observation. Remove both sides of the thin film part. At this time, the acceleration voltage value of the FIB is in the range of 30 kV to 50 kV. However, when the side surface of the thin film portion is damaged by the accelerated FIB gallium ions, the thickness per side is 20 nm to 30 nm (see FIG. Is shown in the case of 30 nm).
[0015]
As shown in FIG. 7B, in the TEM observation, an electron beam is incident perpendicularly to the side surface of the thin film portion along the surface of the TEM sample 101 on which the thin film portion is formed, and the electron lens system 105 is used. This is performed by forming an electron beam that passes through the thin film portion as a TEM image 106. TEM sample for TEM observation 101 It is necessary to remove the upper surface of the thin film portion by about 10 μm in the depth direction. At this time, since the amorphous layer 104 having a thickness of about 30 nm is formed on both sides of the thin film portion, the thickness of the thin film portion is reduced to 100 nm. On the other hand, a total of 40 nm to 60 nm (in the figure, the case of 60 nm is shown) is changed to the amorphous layer 104 on both sides.
[0016]
As described above, the portion reaching the thickness of 60 nm on both sides of the thin film portion having a thickness of 100 nm to be subjected to the TEM observation is changed to the amorphous layer 104 different from the original structure of the TEM sample 101. The image is greatly affected by the amorphous layer, making it difficult to analyze a good TEM image. In particular, in order to evaluate the manufacturing process of a highly miniaturized semiconductor device, for example, if the thickness of the thin film portion is reduced to about 60 nm, the entire thickness of the thin film portion to be subjected to TEM observation becomes amorphous. Therefore, the evaluation of the manufacturing process becomes almost impossible.
[0017]
Next, this problem will be described more specifically with reference to FIG.
FIG. 8 is a TEM image obtained to evaluate a part of the manufacturing process of the semiconductor device at an acceleration voltage of FIB of 30 kV and a thickness of the thin film portion of the TEM sample of 60 nm.
[0018]
The TEM image shown in FIG. 8 includes a silicon substrate 107, an STI (Shallow Trench Isolation) insulating film 108, a polysilicon layer 109, an interlayer insulating film 110, a tungsten plug 111, and a carbon layer 112. Here, the carbon layer 112 prevents charge-up by an electron beam during TEM observation, and is not included in the constituent elements to be evaluated.
[0019]
As shown in FIG. 8, since the metal film has a low electron beam transmittance in TEM observation, the tungsten plug 111 still forms an image with strong contrast even through an amorphous layer reaching a thickness of about 60 nm on both sides. However, the silicon substrate 107, the STI insulating film 108, the polysilicon layer 109, and the interlayer insulating film 110, as indicated by arrows A in FIG. Therefore, the structure cannot be evaluated by TEM observation.
[0020]
As described above, the reason why the contrast of the components made of different materials disappears from the TEM image is that the thickness of the amorphous layer reaches 60 nm, the entire thin film portion becomes amorphous, and the difference in the crystal structure of the materials. This is because there is no difference in electron beam transmittance.
[0021]
In the example of FIG. 8, since the left side of the figure tends to be slightly thicker, it is possible to barely distinguish each component on the left side of the figure, but as indicated by arrows B and C, the silicon substrate 107 A contrast of light and shade is generated in a portion that should be uniform. The reason is considered that the processing speed of FIB in the upper tungsten plug is slightly low, so that the other constituent elements immediately below it are thick, and a layer that does not become amorphous remains slightly in the thin film portion. .
[0022]
In this way, if a conventional FIB having an acceleration voltage of about 30 kV to 50 kV is used as it is and an attempt is made to evaluate the manufacturing process of a highly miniaturized semiconductor device by simply reducing the thickness of the thin film portion, an amorphous structure is obtained. The formation of the quality layer not only makes it impossible to distinguish the constituent elements of different materials, but variations in the TEM sample preparation process may cause the contrast of the TEM image to appear as an image that originally does not exist.
[0023]
In addition, the entire thickness of the thin film portion does not become amorphous, and a TEM image can be obtained by transmitting an electron beam through the thick amorphous layer even if the constituent elements of the TEM sample exist inside the thin film portion. There is a problem that the quality of the product is significantly reduced.
[0024]
In other words, the side face of the thin film portion to be observed by TEM becomes amorphous due to the damage of the FIB, and generally causes the following problems.
(1) About 1/2 of the thickness of the thin film portion 5 becomes amorphous, and the original structure of the TEM sample is destroyed, so that the amount of information of a required TEM image obtained from the original structure of the TEM sample is reduced. As a result, the quality of the TEM image is degraded.
[0025]
(2) When the thickness of the thin film portion is smaller than about 100 nm in normal TEM observation and becomes 40 nm to 60 nm or less, the entire thickness of the thin film portion becomes amorphous, and the TEM observation The original structure of the TEM sample cannot be known.
[0026]
(3) In the case of the above (2), in order to avoid the destruction of the original structure of the TEM sample from the thin film portion, for example, even if the thin film portion is formed thick, the desired portion to be subjected to TEM observation Since the structure (amorphous layer) other than the structure is included in the TEM image, it is difficult to interpret the TEM image.
[0027]
[Problems to be solved by the invention]
As described above, the conventional method for preparing a TEM sample is such that the side surface of the thin film portion used for TEM observation becomes amorphous due to the damage of the FIB, and the original structure of the sample is known particularly when the thin film portion is thin. There was a problem that it became difficult.
[0028]
The present invention has been made to solve the above-described problems, and provides a method for preparing a TEM sample in which a TEM image showing the original structure of the sample can be obtained by TEM observation even when the thickness of the thin film portion is small. Objective.
[0029]
[Means for Solving the Problems]
The main feature of the method for manufacturing a TEM sample of the present invention is that the acceleration voltage of the FIB is lowered in order to avoid the side surface of the thin film portion used for TEM observation from becoming amorphous due to the damage of the FIB.
[0030]
Specifically, the method for producing a TEM sample of the present invention includes a first FIB process using a first acceleration voltage that leaves a TEM sample upper surface region extending in the longitudinal direction and removes both sides thereof to a certain depth. The second FIB processing using a second acceleration voltage lower than the first acceleration voltage for further removing both sides of the upper surface region along the side surfaces formed on both sides of the upper surface region by the first FIB processing is performed. Including Thus, in the second FIB processing, the second FIB diameter is reduced to the first FIB diameter by lowering the acceleration voltage value of the second FIB compared to the acceleration voltage value of the first FIB. Increased compared to reduce the number of scans in the second FIB processing It is characterized by that.
[0031]
Preferably, in the method for producing a TEM sample according to the present invention, the acceleration between the first FIB processing and the second FIB processing is lower than the acceleration voltage of the first FIB processing and higher than the acceleration voltage of the second FIB processing. A third FIB process using a voltage is performed.
[0032]
In the method for manufacturing a TEM sample of the present invention, the first acceleration voltage value is 25 kV or more, preferably 30 kV to 50 kV, and the second acceleration voltage value is 25 kV or less, preferably 5 kV to It is in the range of 15 kV.
[0033]
Preferably, in the first FIB processing, the thickness of the amorphous layer formed on the side surface is in the range of 20 nm to 30 nm per side, and in the second FIB processing, the non-layer formed on the side surface is formed. The thickness of the crystalline layer is characterized by being in the range of 7.5 nm to 15 nm per side.
[0034]
Preferably, in the second FIB processing, when the thickness of the amorphous layer formed on the side surface is d per side and the thickness of the sample after the TEM sample is made D is D> 2d It is characterized by being satisfied.
[0036]
Further, preferably, following the second FIB processing, the amorphous layer formed on the side surface in the second FIB processing is removed by etching.
Preferably, the step of removing the amorphous layer by etching is performed by any one of wet etching containing either hydrofluoric acid or ammonium fluoride, sputtering using argon gas, or chemical dry etching. Features.
[0037]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1A to 1C are a bird's-eye view and a process cross-sectional view showing a method for manufacturing a TEM sample according to the first embodiment of the present invention.
First, an outline of a method for manufacturing a TEM sample according to the first embodiment will be described using the bird's-eye view of FIG.
[0038]
As shown in FIG. 1A, dicing processing for removing both sides of the TEM sample 1 is performed using, for example, a diamond cutter or the like. This dicing process is a pre-processing step for processing the shape of the TEM sample 1 so as to be convenient for creating a TEM sample by FIB, and does not particularly form the main part of the present invention.
[0039]
Next, FIB is irradiated perpendicularly to the 1a portion of the diced TEM sample, both sides of the 1a portion of the TEM sample remaining after the dicing are further removed, and a thin film portion that transmits an electron beam in TEM observation is obtained. Form. FIG. 1A is a schematic diagram, and the actual thickness / depth ratio is significantly different from that shown in the figure (for example, see the dimensions in FIG. 7A).
[0040]
The feature of the TEM sample manufacturing method according to the first embodiment is that the thin film portion is formed by FIB in a plurality of stages. With reference to FIGS. 1B and 1C, a detailed description will be given of a two-stage thin film portion forming method by FIB as an example.
[0041]
FIG.1 (b) is a figure which shows the XX cross section of Fig.1 (a).
The TEM sample shown in FIG. 1B includes a substrate portion 1a, a thin film portion 1b connected to the substrate portion 1a remaining after FIB processing with an acceleration voltage of 30 kV, a side surface 2 of the thin film portion 1b, and a thin film portion 1b formed by FIB processing. The amorphous layer 3 generated on the side surface 2, the upper surface region 4 of the thin film portion 1 b composed of a part of the upper surface of the TEM sample 1 before processing, and the upper surface 5 of the TEM sample 1 after FIB processing. In FIG. 1B, the lower part of the dicing surface of the TEM sample 1 in FIG.
[0042]
As shown in FIG. 1B, the TEM sample 1a is irradiated with FIB made of gallium ions accelerated at a voltage of 30 kV perpendicularly to the upper surface of the TEM sample 1a, leaving the thin film portion 1b to be subjected to TEM observation. Is processed in the depth direction. As described above, if the acceleration voltage of FIB is set to 30 kV, the thickness of the amorphous layer 3 is about 20 nm per side of the amorphous layer 1b. If TEM observation is performed using this, the TEM image is obtained. The quality is significantly reduced.
[0043]
Next, as shown in FIG. 1C, the acceleration voltage of the FIB is lowered to 5 kV, and the side surface of the thin film portion 1b is FIB processed again. Hereinafter, the FIB processing performed by lowering the acceleration voltage is referred to as FIB finishing processing. Here, the problem of FIB processing when the acceleration voltage of FIB is reduced from 30 kV to 5 kV will be described in detail.
[0044]
Conventionally, in the FIB processing using gallium ions, the optimum acceleration voltage range is 30 kV to 50 kV, and no practical attempt has been made to significantly reduce this range. The reason is as follows.
[0045]
(1) If the acceleration voltage of the FIB is lowered, the acceleration energy of the gallium ions is reduced, so that the processing speed is reduced substantially in proportion to the acceleration voltage.
[0046]
(2) If the acceleration voltage of the FIB is lowered, the beam width of gallium ions is expanded, so that the machining accuracy is lowered and the machining speed is further reduced.
[0047]
However, as shown in FIG. 1C, if the FIB finishing process is performed with the acceleration voltage lowered to 5 kV on the side surface of the thin film portion 1b in the first embodiment, the acceleration voltage at 30 kV in FIG. The amorphous layer 3 having a thickness of about 20 nm generated by the FIB processing can be efficiently reduced.
[0048]
That is, since the amorphous layer 3 is a damaged layer generated by FIB processing, the bonding force of the constituent atoms is weak, and this can be easily removed with gallium ions having low acceleration energy. Also, in the FIB finishing process with the acceleration voltage lowered, the amorphous layer 3 is formed on the side surface of the thin film portion 1b. The thickness of the amorphous layer 3 is the thickness of the FIB process with a high acceleration voltage. It can be made extremely small compared to. Further, if the acceleration voltage is lowered to 5 kV, the beam width of gallium ions is expanded to about 50 nm. Therefore, the number of times of ion beam scanning in the FIB finishing process for reducing the thick amorphous layer 3 in FIG. It becomes possible to decrease.
[0049]
FIG. 1C shows a FIB finishing method at an acceleration voltage of 5 kV.
Since the configuration of the FIB finishing method shown in FIG. 1C is the same as that of the FIB processing method of FIG. 1B, the same reference numerals are assigned to the corresponding portions, and detailed description thereof is omitted.
[0050]
As shown in FIG. 1C, following the FIB processing in FIG. 1B, the FIB made of gallium ions accelerated at a voltage of 5 kV is irradiated perpendicularly to the upper surface of the TEM sample 1a, and the TEM observation is performed. The side surface of the target thin film portion 1b is finished in the depth direction. As described above, after the FIB processing of FIG. 1B, the thickness of the amorphous layer 3 is about 20 nm per one side of the thin film portion 1b, but the FIB finishing processing shown in FIG. By doing so, the thickness of the amorphous layer 3 can be reduced to 7.5 nm per side of the thin film portion 1b.
[0051]
As described above, the method for forming a TEM sample has been described using the FIB two-stage thin film portion forming method as an example. However, the method for manufacturing a TEM sample according to the first embodiment is not necessarily limited to two stages. Absent. For example, the same purpose can be achieved by decreasing the FIB acceleration voltage from 30 kV to 5 kV in steps of n (n is an integer of 3 or more). The method for reducing the acceleration voltage of the FIB does not necessarily have to be stepped, and may be continuously reduced so that the best result is obtained under a certain program.
[0052]
Note that the value of the acceleration voltage in the FIB processing of FIG. 1B is not necessarily limited to 30 kV, and can be set within the optimum range of 25 kV or more, preferably 30 kV to 50 kV. Further, the value of the acceleration voltage in the FIB finishing shown in FIG. 1C is not necessarily limited to 5 kV, and can be set within the optimum range of 25 kV or less, preferably 5 kV to 15 kV.
[0053]
Next, a second embodiment will be described with reference to FIG.
In the second embodiment, the observation result of the TEM image of the vertical cross section of the amorphous layer 3 formed on one side of the thin film portion 1b made of the silicon substrate by FIB processing with an acceleration voltage of 30 kV in FIG. explain.
[0054]
That is, in the TEM image shown in FIG. 2, the amorphous layer 3 is formed on the side surface of the thin film portion 1b made of the silicon substrate as shown in FIG. 1B, and the amorphous layer 3 and the thin film portion 1b are further formed. One side of a TEM image obtained by performing FIB processing at an acceleration voltage of 30 kV and FIB finishing processing at an acceleration voltage of 5 kV from the upper surface of the substrate along a vertical plane (a plane parallel to the paper surface) to obtain cross sections of the thin film portion 1b and the amorphous layer 3 Part. In FIG. 2, the position of the processed surface of the amorphous layer 3 is indicated by a broken line. From the TEM image shown in FIG. 2, it is determined that the thickness of the amorphous layer 3 is about 30 nm per one side of the thin film portion 1b.
[0055]
Next, a third embodiment will be described with reference to FIG.
In the third embodiment, the observation result of the TEM image of the vertical cross section of the amorphous layer 3 formed on one side of the thin film portion 1b made of the silicon substrate by the FIB finishing with the acceleration voltage of 5 kV in FIG. Will be described.
[0056]
The method for observing the TEM image shown in FIG. 3 is the same as that of the second embodiment shown in FIG. From the TEM image shown in FIG. 3, it is determined that the thickness of the amorphous layer 3 is about 7.5 nm per one side of the thin film portion 1b.
[0057]
In the second and third embodiments, the thickness range of the amorphous layer when the acceleration voltage of FIB processing is changed from 30 kV to 50 kV is in the range of 20 nm to 30 nm per side of the thin film portion 1b. In addition, the thickness range of the amorphous layer when the acceleration voltage of FIB finishing is changed from 5 kV to 15 kV is in the range of 7.5 nm to 15 nm per one side of the thin film portion 1b.
[0058]
Next, a fourth embodiment will be described with reference to FIG.
In the fourth embodiment, the result of TEM observation showing the excellent features of the TEM sample manufacturing method described in the first embodiment will be described in detail.
A sample used for the TEM observation is a gate electrode of a MOS transistor including a gate oxide film 7 having a thickness of 10 nm or less formed on the upper surface of the silicon substrate 6 and a polysilicon gate 8 formed on the gate oxide film 7. It is a lower structure, and this gate electrode lower structure is used as the thin film portion 1b. FIG. 4A is a TEM image of the thin film portion 1b subjected to FIB processing at an acceleration voltage of 30 kV in the stage of FIG. The gate oxide film 7 is arranged in parallel with the upper surface of the thin film portion 1b.
[0059]
The TEM image shown in FIG. 4A shows the microstructure of the thin film portion 1b through the thick amorphous layer 3 of 40 nm in total (20 nm × 2 on one side) formed on both sides of the thin film portion 1b in FIG. As a result of the observation, the pattern information inherent to the fine structure is reduced, resulting in a totally blurred TEM image.
[0060]
On the other hand, the TEM image shown in FIG. 4B is obtained by TEM observation of the thin film portion 1b in the stage of FIG. 4B after the FIB finish processing at an acceleration voltage of 5 kV. At this time, since the fine structure of the thin film portion 1b is observed by TEM through the thin amorphous layer 3 of 15 nm in total (7.5 nm × 2 on one side) formed on both sides of the thin film portion 1b in FIG. The original pattern information is clearly shown.
[0061]
As shown by an arrow in the TEM image of FIG. 4B, the boundary between the silicon substrate 6, the gate oxide film 7 and the polysilicon gate 8 becomes very clear, the microcrystalline structure inside the polysilicon gate 8, Even the arrangement state of silicon atoms on the silicon substrate 6 can be read.
[0062]
Next, a fifth embodiment of the present invention will be described.
As described in the fourth embodiment, in TEM observation, a TEM image with higher resolution can be obtained as the amorphous layer 3 is thinner. Further, as described in the first embodiment, when a TEM sample is manufactured, acceleration is performed as a method for thinning the thick amorphous layer 3 formed on the side surface of the thin film portion 1b in FIB processing at a normal acceleration voltage. It is extremely effective to perform FIB finishing with a greatly reduced voltage.
[0063]
However, the method for thinning the amorphous layer is not necessarily limited to FIB finishing. Since the amorphous layer formed on the side surface of the thin film portion 1b has a large crystallinity with the base TEM sample, the etching rate is low between the amorphous layer and the base TEM sample with respect to wet etching or dry etching. A difference (etch selectivity) occurs. It is considered that the amorphous layer can be removed by appropriately using this etching selectivity.
[0064]
If the removal of the amorphous layer by etching is applied to the preparation of a TEM sample, the thickness of the thin film portion to be observed by the TEM is extremely thin, several tens of nm or less, and the thickness of the amorphous layer is usually the thin film portion. Since it occupies a large portion of the overall thickness, it is generally very difficult to control etching.
[0065]
On the other hand, since the thickness of the amorphous layer after the FIB finishing described in the first embodiment is smaller than the thickness of the entire thin film portion, the etching method with a low etching rate and the etching selectivity are appropriately set. If used, the amorphous layer after FIB finishing can be removed with good controllability.
[0066]
As a method for etching an amorphous layer after FIB finishing, wet etching using a dilute solution containing either hydrofluoric acid or ammonium fluoride, sputtering using argon gas, or chemical drying with a low etching rate is used. Etching or the like can be preferably used.
The present invention is not limited to the above embodiment. Various other modifications can be made without departing from the scope of the present invention.
[0067]
【The invention's effect】
As described above, according to the TEM sample manufacturing method of the present invention, even if the side surface of the thin film portion used for TEM observation becomes amorphous due to the damage of the FIB and the thickness of the thin film portion is small, the thin film is further thinned. The side surface of the part is finished with FIB having a low acceleration voltage, so that a TEM image showing the original structure of the sample in the thin film part can be obtained and used suitably for process evaluation of highly miniaturized semiconductor devices. It becomes possible.
[Brief description of the drawings]
FIG. 1 is a diagram showing a TEM sample manufacturing method according to a first embodiment,
(A) is a bird's-eye view which shows the process of a dicing process and FIB process.
(B) is a figure which shows formation of the thick amorphous layer in FIB process with a high acceleration voltage.
(C) is a figure which shows thinning of the amorphous layer by FIB finishing process with a low acceleration voltage.
FIG. 2 is a TEM photograph showing the formation of a thick amorphous layer on a silicon substrate in FIB processing with a high acceleration voltage.
FIG. 3 is a TEM photograph showing the formation of a thin amorphous layer on a silicon substrate in FIB finishing with a low acceleration voltage.
FIG. 4 is a TEM photograph showing a lower structure of a gate electrode of a MOS transistor,
(A) is a TEM photograph when a thick amorphous layer is formed.
(B) is a TEM photograph when the amorphous layer is thinned.
FIG. 5 is a diagram showing a situation in which a thin film portion for TEM observation is formed from a conventional large evaluation sample,
(A) is a top view of an evaluation sample.
(B) is sectional drawing of a thin film part.
FIG. 6 is a diagram showing a conventional problem when a thin film portion for TEM observation is formed from a highly miniaturized evaluation sample,
(A) is a top view of an evaluation sample.
(B) is sectional drawing which shows the condition which made thin the thickness of a thin film part.
FIG. 7 is a diagram showing a method for manufacturing a TEM sample using FIB processing with a conventional high acceleration voltage,
(A) is sectional drawing which shows formation of the thick amorphous layer of the thin film part in FIB process.
(B) is a figure which shows the preparation method of the TEM image using a thin film part.
FIG. 8 is a photograph showing degradation of TEM image quality by a conventional thick amorphous layer.
[Explanation of symbols]
1 ... TEM sample
1a: FIB processing part of TEM sample
1b ... Thin film part
2 ... Side film side
3. Amorphous layer
4. Top surface of thin film
5 ... TEM sample top surface removed by FIB processing
6 ... Silicon substrate
7 ... Gate oxide film
8 ... Polysilicon
101: Insulating film
102 ... Barrier metal
103 ... Tungsten plug
104: Amorphous layer
105 ... Lens system
106 ... TEM image
107: Silicon substrate
108 ... STI insulating film
109 ... polysilicon layer
110 ... Interlayer insulating film
111 ... Tungsten plug
112 ... carbon layer

Claims (7)

A first focused ion beam processing using a first acceleration voltage that leaves a sample upper surface region extending in the longitudinal direction and removes both sides thereof to a certain depth;
A second acceleration voltage lower than the first acceleration voltage for further removing both sides of the sample upper surface region along side surfaces formed on both sides of the sample upper surface region by the first focused ion beam processing is used. Second focused ion beam processing
In the second focused ion beam processing, by reducing the value of the acceleration voltage of the second focused ion beam compared to the value of the acceleration voltage of the first focused ion beam, A transmission characterized in that the diameter of the second focused ion beam is made larger than the diameter of the first focused ion beam and the number of scans in the second focused ion beam processing is reduced. Of electron microscope sample preparation.   Between the first focused ion beam processing and the second focused ion beam processing, the second focused ion beam is lower than the acceleration voltage of the first focused ion beam processing. The method for preparing a sample for a transmission electron microscope according to claim 1, wherein the third focused ion beam processing is performed using an acceleration voltage higher than the processing acceleration voltage. The value of the first acceleration voltage is in a range of 30 kV to 50 kV, and the value of the second acceleration voltage is in a range of 5 kV to 15 kV. The sample preparation method of the transmission electron microscope as described in one.   In the first focused ion beam processing, the thickness of the amorphous layer formed on the side surface is in the range of 20 nm to 30 nm per side of the upper surface region, and the second focused ion beam processing is performed. The thickness of the amorphous layer formed on the side surface in the ion beam processing is in the range of 7.5 nm to 15 nm per side of the upper surface region. The sample preparation method of the transmission electron microscope as described in one.   In the second focused ion beam processing, the thickness of the amorphous layer formed on the side surface is d per side, and the thickness of the sample after the preparation of the transmission electron microscope is D. The method for preparing a sample for a transmission electron microscope according to claim 1, wherein a relationship of D> 2d is established.   The amorphous layer formed on the side surface in the second focused ion beam processing is removed by etching following the second focused ion beam processing. The sample preparation method of the transmission electron microscope as described in any one of these.   The step of removing the amorphous layer by etching is performed by any of wet etching containing either hydrofluoric acid or ammonium fluoride, sputtering using argon gas, or chemical dry etching. A method for preparing a sample for a transmission electron microscope according to claim 6.

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