Abstract:
A semiconductor device inspecting apparatus includes a chamber, a stage situated in the chamber for placing a semiconductor device thereon, a femtosecond laser apparatus, and an electron microscope. The femtosecond laser apparatus includes a laser generating section for generating laser beams disposed outside the chamber, and a laser optical system for introducing the laser beams generated at the laser generating section into the chamber. The laser generating section generates femtosecond width pulse and a strength so that the semiconductor device on the stage is cut by the laser beams introduced inside the chamber. The electron microscope is disposed inside the chamber for observing the semiconductor device cut by the laser beams.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor device inspecting apparatus which cuts a semiconductor device and observes a cut cross section by an electron microscope, thereby analyzing a defective portion and observing a structure, etc. More particularly, the present invention relates to a semiconductor device inspecting apparatus capable of generating a sharp cut cross section. 
     2. Description of the Prior Art 
     Conventionally, as an apparatus for analyzing a defective portion in a developing process of a semiconductor device (LSI and the like), there is a known semiconductor device inspecting apparatus comprising a combination of an FIB (Focused Ion Beam) apparatus and a scanning electron microscope (SEM: Scanning Electron Microscope) (see Japanese Patent Application Laid-open No. H11-273613 for example). 
     According to this inspecting apparatus, a surface of the semiconductor device such as a semiconductor wafer is irradiated with FIB, thereby forming a fine groove or hole of submicron to micron size in the surface, or cutting the wafer, and the cross section is observed by the SEM, and analysis of defective portion or analysis by high resolution observation can be carried out. 
     There is also a known semiconductor device inspecting apparatus comprising a combination of the FIB apparatus and a transmission electron microscope (TEM: Transmission Electron Microscope). With this inspecting apparatus also, a semiconductor device such as a semiconductor wafer is irradiated with FIB to form a thin film sample, the sample is observed by the TEM, and evaluation of the semiconductor device or analysis of the defective portion can be carried out. 
     According to the above conventional semiconductor device inspecting apparatus, however, since the precision of working (such as cutting) by the FIB is affected by the atmosphere in a chamber (e.g., a temperature, a pressure) and the like, a worked surface (cut surface) does not appear sharply. Further, experience is required for working a wafer by the FIB in some cases. Furthermore, it takes time to work using the FIB and as a result, efficiency of the evaluation and analysis of the semiconductor device are inferior. 
     Further, according to the above-described semiconductor device inspecting apparatus, since a beam generating source of the FIB apparatus must be disposed in the chamber, a structure of the entire apparatus becomes complicated, and a producing cost is increased. 
     In addition, during driving operation of the FIB apparatus, since the sample (semiconductor device) is irradiated with ion beams, observation can not be carried out in real time using the SEM while working a fine defective portion using the FIB in some cases. 
     Further, according to the FIB apparatus, although the output is the same, a cutting depth is affected by the atmosphere in the chamber, characteristics of electromagnetic lens and the like, it is not easy to adjust the cutting depth. 
     SUMMARY OF THE INVENTION 
     It is a first object of the present invention to provide a semiconductor device inspecting apparatus capable of inspecting a semiconductor device precisely by forming a sharp working surface. 
     It is a second object of the present invention to provide a semiconductor device inspecting apparatus capable of enhancing the inspecting efficiency by working a semiconductor device within a short time. 
     It is a third object of the present invention to provide a semiconductor device inspecting apparatus in which its structure is not complicated. 
     It is a fourth object of the present invention to provide a semiconductor device inspecting apparatus capable of cutting and observing a working surface at the same time. 
     It is a fifth object of the present invention to provide a semiconductor device inspecting apparatus capable of always cutting uniformly without being affected by atmosphere in the chamber so much. 
     The present invention provides a semiconductor device inspecting apparatus comprising a stage disposed in a chamber on which a semiconductor device such as an LSI is set, a femtosecond laser apparatus for generating laser beams which cut the semiconductor device, and an electron microscope for observing a cut surface of the semiconductor device which was cut by the laser beams. 
     As the femtosecond laser apparatus, laser beams (titanium sapphire laser) of several tens to several hundreds fsec time width is used. “Cutting” in this invention includes formation of a groove and a hole in a surface of a semiconductor device such as an LSI, and cutting of the semiconductor device. 
     The femtosecond laser apparatus is used in the present invention. Therefore, it is possible to cut the semiconductor device at high speed, to cut the semiconductor device deeply, to make the depth uniformly, and to form a groove whose depth is changed at a predetermined-distance by changing a focus, distance of the laser beams during scanning. Further, since one dimensional or two dimensional cutting line can be controlled by a mirror provided in a laser optical path, it is possible to extremely shorten time required for cutting. 
     It is possible to cut the semiconductor device and to observe the working surface at the same time, and influence of atmosphere in the chamber is small, and the semiconductor device can always be cut uniformly. 
     The semiconductor device inspecting apparatus of the present invention uses a scanning electron microscope (SEM) or a transmission electron microscope (TEM). 
     In the semiconductor device inspecting apparatus of the invention, since the femtosecond laser apparatus is used as a laser beam source (i.e., an ion beam laser is not used), at least the laser generating section can be provided outside the chamber. With this feature, a structure of the semiconductor device inspecting apparatus is not complicated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing an example of an outward appearance of a semiconductor device inspecting apparatus of the present invention; 
     FIG. 2 is a system block diagram showing a semiconductor device inspecting apparatus using a TEM as an electron microscope in detail; 
     FIGS.  3 (A) and  3 (B) show a cutting operation by femtosecond laser beams in the system shown in FIG. 2, wherein FIG.  3 (A) shows a case in which a cutting depth is made constant by adjusting focus of the femtosecond laser beams, and FIG.  3 (B) shows a case in which the cutting depth is changed; 
     FIG. 4 is a diagram showing a detecting operation of a cut wall surface by an SEM in the system shown in FIG.  2 : 
     FIG. 5 is a system block diagram showing the semiconductor device inspecting apparatus using a TEM as the electron microscope in detail; and 
     FIGS.  6 ( a )- 6 (D) are explanatory views of operations of the system shown in FIG. 5, wherein FIG.  6 (A) shows a cutting operation for taking out a predetermined portion of a sample, FIG.  6 (B) shows a picking up operation of a sample piece by a probe of a manipulator, FIG.  6 (C) shows an operation in which a sample piece is set on a sample fixer, and a thin film of the sample piece is worked by the femtosecond laser beams to form a thin film sample piece, and FIG.  6 (D) shows an operation in which the thin film sample piece is sent to an observing position, of the TEM, and electron beams are allowed to pass through the cut surface to observe the cut surface. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a diagram showing an example of an outward appearance of a semiconductor device Inspecting apparatus of the present invention. In FIG. 1, a semiconductor device inspecting apparatus  1  comprises a vacuum chamber  11 , a femtosecond laser apparatus  12  and an SEM (scanning electron microscope)  13 . 
     In FIG. 1, a semiconductor device that is a sample is accommodated in a vacuum chamber  11  (see FIG.  2 ). This semiconductor device is a wafer halfway through a formation of a circuit or a wafer before dicing after the circuit is formed. 
     The vacuum chamber  11  is provided with a front chamber for sample  11   b . A sample is set in the vacuum chamber  11  through the front chamber for sample  11   b . In this embodiment, the vacuum chamber  11  is provided at its lower portion with a vacuum pump  11   c , and at its upper portion with a glass window  11   a  for introducing laser beams. The glass window  11   a  is provided at its upper portion with an x-y scanning galvanometer mirror  121  which constitutes a portion of the femtosecond laser apparatus  12 . 
     In FIG. 1, the galvanometer mirror  121  is illustrated as two mirror elements  121   a  and  121   b  for the sake of convenience. By adjusting angles of these mirror elements  121   a  and  121   b , an optical path of the femtosecond laser beams FSLB can be finely adjusted, and a predetermined position on a sample surface can be irradiated with laser beams FSLB. 
     An SEM (scanning electron microscope)  13  is mounted to the vacuum chamber  11 . With this SEM  13 , it is possible to observe a cross section of the sample cut by the laser beams FSLB. 
     FIG. 2 is a system block diagram showing the semiconductor device Inspecting apparatus  1  in detail. 
     In FIG. 2. a stage  141  in which a sample S is set is provided in the vacuum chamber  11 . The stage  141  can move on an x-y plane (i.e. the stage  141  can move in +x, −x directions, +y, −y directions) with rough precision by means of an actuator  142 . This actuator  142  may be a piezo-actuator, and it may be possible to control its position in a z direction (e.g., vertical direction in FIG.  2 ). The actuator  142  is driven by a stage driving circuit  143 . 
     A glass window  11   a  is provided perpendicularly above the stage  141  of the vacuum chamber  11 . A focus adjusting lens system  123  of the femtosecond laser beams FSLB is provided between the glass window  11   a  and the stage  141 . Although the focus adjusting lens system  123  is provided in the vacuum chamber  11  in FIG. 2, a portion or all of the focus adjusting lens system  123  may be provided outside the vacuum chamber  11 . A galvanometer mirror  121  (shown as one mirror in FIG. 2) is provided outside the glass window  11   a . The galvanometer mirror  121  constitutes an x-y fine control system, and constitutes a laser optical system  124  together with the focus adjusting lens system  123 . 
     In this embodiment, a femtosecond laser generating section  122  for generating of femtosecond width pulse is provided outside the vacuum chamber  11 , and the femtosecond laser generating section  122  and the laser optical system  124  constitute the femtosecond laser apparatus  12 . 
     The femtosecond laser apparatus  12  is driven by a laser driving circuit  15 . The irradiation point control circuit  16  highly precisely controls the femtosecond laser beams FSLB. The Irradiation point control circuit  16  sends out an x-y control signal to the galvanometer mirror  121 , thereby x-y controlling the laser irradiation point (controlling plane), and sends a z control signal to the focus adjusting lens system  123 , thereby z controlling the irradiation point (controlling a depth). 
     A body of the SEM  13  is provided diagonally above the stage  141 . The body of the SEM  13  comprises an electron gun, system  131  and an electron lens system  132 . The SEM  13  is driven by an SEM driving circuit  17 . 
     Although it is not illustrated, the electron gun system  131  comprises a thermoelectric field discharge electron source, a suppressor, a pullout electrode, a control lens and ground. The electron lens system  132  comprises a two-stage electrostatic four-pole lens for beam-axis adjustment, an electrostatic capacitor lens, a two-stage electrostatic eight-pole lens for scan/non-point aberration correction, an electrostatic object lens and the like. 
     A detecting system  133  is provided diagonally above the stage  141  in a direction opposite from the body of the SEM  13 . The detecting system  133  comprises a scintillation and a photomultiplier tube, and can detect reflected beams from the sample S of electron beams emitted by the electron gun system  131 . A detection signal detected by the detecting system  133  is sent to the detection signal processing circuit  181 , and a signal from the detection signal processing circuit  181  (comprising A/D converter circuit, an image information generating circuit and the like) is sent to a display signal generating circuit  182 , and the display signal generating circuit  182  can display the cross section image of the sample S on a display  183 . 
     In FIG. 2, a host computer  2  collectively controls the irradiation point control circuit  16 , the laser driving circuit  15 , the SEM driving circuit  17  and the stage driving circuit  143 , and can store a detection signal (detection data) from the detection signal processing circuit  181  in an appropriate storing device (such as a hard disk). 
     In the system shown in FIG. 2, the sample S is set in the stage  141  in the vacuum chamber  11 , and a predetermined portion of the sample S is cut by the femtosecond laser apparatus  12 . 
     In this embodiment, the SEM  13  is used also as a position control monitor means at the time of cutting by adjusting the magnification. The cutting position is controlled by the actuator  142  and the galvanometer mirror  121 , thereby cutting the predetermined portion, and the cut surface is irradiated with electron beams by the SEM  13  thereby observing the cut surface, and the cut surface is observed. FIGS.  3 (A) and  3 (B) show this cutting operation. At that time, the cutting depth can be made uniform by focus adjustment of the femtosecond laser beams FSLB as shown in FIG.  3 (A), or the cutting depth can be changed as shown in FIG.  3 (B). 
     FIG. 4 shows a detecting operation of the cut wall surface by means of the SEM  13 . FIG. 4 shows a state in which a rectangular groove G is formed on the sample S formed with a circuit C by the laser beams FSLB from the femtosecond laser apparatus  12  shown in FIG. 2 and a wall surface W is observed using electron beams EB from the body of the SEM  12 . 
     Another embodiment of the present invention will be explained with reference to FIGS. 5 and 6. FIG. 5 is a system block diagram showing the semiconductor device inspecting apparatus using a TEM (transmission electron microscope) as the electron microscope. An outer appearance of the semiconductor device inspecting apparatus using the TEN (transmission electron microscope) is substantially the same as that of the semiconductor device inspecting apparatus  1  using the SEM (scanning electron microscope) and thus, explanation thereof is omitted. 
     In FIG. 5, a stage  341  on which a sample S is set is provided in a vacuum chamber  31 . The stage  341  and an actuator  342  which drives the stage  341  are respectively the same as the stage  141  and the actuator  142  shown in FIG. 2, and they are driven by a stage driving circuit  343 . 
     Like the vacuum chamber  11  shown in FIG. 2. a glass window  31   a  is provided perpendicularly above the stage  341  of the vacuum chamber  31 . A focus adjusting lens system  323  of the femtosecond laser beams FSLB is provided between the glass window  31   a  and the stage  341 . A galvanometer mirror  321  is provided outside the glass window  31   a , which constitutes a laser optical system  324  together with the focus adjusting lens system  323 . 
     In this embodiment, like the system shown in FIG. 2. a femtosecond laser generating section  322  is provided outside the vacuum chamber  31 . The femtosecond laser generating section  322  and the laser optical system  324  constitute a femtosecond laser apparatus  32 . The femtosecond laser apparatus  32  is driven by a laser driving circuit  35 . An irradiation point control circuit  36  highly precisely controls the femtosecond laser beams FSLB. The irradiation point control circuit  36  sends out an x-y control signal to the galvanometer mirror  321  to x-y control (plane control) of the laser irradiation point, and sends a z control signal to the focus adjusting lens system  323  to z control (depth control) of the irradiation point. A structure of the femtosecond laser apparatus  32  of this embodiment is the same as that of the femtosecond laser apparatus  12  shown in FIG.  2 . 
     In this embodiment, a manipulator  39  is provided in the vicinity of the stage  341 . The manipulator  39  can pick up a portion (sample piece S′) of the sample S cut by the femtosecond laser beams FSLB with a probe  391 , and can move the same to an observing position by a TEM  33 . The TEM  33  comprises an electron gun system  331 , an electron lens system  332  and a detecting system  333 . The detecting system  333  can detect electron beams from the electron lens system  332  through which the sample S passes. 
     A detection signal detected by the detecting system  333  is sent to detection signal processing circuit  381 . A signal from the detection signal processing circuit  381  (comprising an A/D converter circuit, an image information generating circuit and the like) is sent to a display signal generating circuit  382 , and the display signal generating circuit  382  can display a composition image of the sample piece S′ on the display  383 . 
     In FIG. 5, the host computer  2  collectively controls an irradiation point control circuit  36 , a laser driving circuit  35 , a TEM driving circuit  37  and the stage driving circuit  343 , and can store a detection signal (detection data) from the detection signal processing circuit  381  in a storing device (hard disk or the like). 
     Operation of the system shown in FIG. 5 will be explained with reference to FIGS.  6 (A) to  6 (D). 
     First, a sample S is set in the stage  341  in the vacuum chamber  31 . As shown in FIG.  6 (A), the femtosecond laser apparatus  32  cuts a predetermined portion of the sample S for taking out such a portion. In this embodiment, the femtosecond laser apparatus  32  can be provided with position control monitor means (not shown). The sample S is cut by controlling the cutting position using the actuator  342  and the galvanometer mirror  321  as mentioned above. 
     Next, as shown in FIG.  6 (B), a probe  391  of the manipulator  39  picks up a sample piece (S 1 ). Then, a sample piece S 1  is set on the sample fixer  4  as shown in FIG.  6 (C) and a thin film of the sample piece S 1  is worked by femtosecond laser beams FSLB, thereby forming a thin film sample piece S 2 . 
     Then, as shown in FIG.  6 (D), the thin film sample piece (S 2 ) is sent to the observing position of the TEM  33  as a sample piece S′ and electron beams are allowed to pass through the cut surface to observe the cut surface. 
     According to the present invention, since a sharp working surface can be formed, a precise inspection can be carried out, and a semiconductor device is worked within a short time and thus, the inspection efficiency can be enhanced. 
     Further, since the laser generating section of the femtosecond laser can be provided outside the chamber, a structure of the semiconductor devices inspecting apparatus can be simplified. And the working surface can be cut and observed at the same time easily. 
     Since laser is used for cutting a sample (i.e., ion beams are not used), influence on atmosphere in the chamber is small, and uniform cutting state can always be realized.