JP2006221961A - Cross-sectional observation method of chip - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems that, when a three-dimensional image is formed by repeating a process of removing the surface of a chip 101 so as to be sliced and performing cross-sectional observation by a SEM 107, a protection film 102 on the surface of the chip 101 is removed at first and discharge route of electric charge is lost and a charge-up phenomenon is brought about. <P>SOLUTION: The slanted face 105 is formed by using an FIB so that electron beam from the SEM 107 may not be cut off when the observation face 106 at the opposed position to the surface of the chip 101 is observed. After the observation face 106 is observed by the SEM 107, the observation face 106 is removed so as to be sliced, and a new observation face is observed by the SEM 107. Since a conductive protection film 102 is formed at the surface part of the chip 101, even if it is sliced and removed up to the uppermost surface, runaway route of the charge is secured, thereby charge-up phenomenon can be prevented. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention irradiates a charged particle to a plane obtained by processing a side surface of a chip on which a semiconductor integrated circuit or the like is formed by irradiation of the focused ion beam to the side surface, and obtains the obtained signal. In particular, the present invention relates to a method for observing a cross section of a chip for observing a cross sectional structure.

  In one of the cross-sectional observation methods described above, as described in Patent Document 1, a focused ion beam (hereinafter abbreviated as “FIB”) and a scanning electron microscope (hereinafter abbreviated as “SEM”) or a scanning ion. A three-dimensional structure of the chip surface is observed using a microscope (hereinafter abbreviated as “SIM”). Here, SEM will be described as a representative example as an observation means.

  In this method, formation of an observation surface for performing observation with an SEM or the like, which is substantially perpendicular to the surface of the chip, is formed in an area adjacent to the observation area formed on the surface of the chip by FIB. A region that becomes a shadow when observing with an SEM or the like is removed.

  Next, the observation surface is observed with an SEM or the like, and two-dimensional image data of the observation surface is accumulated.

  Next, the observation surface is removed using FIB, and a new observation surface substantially parallel to the observation surface is exposed.

  Then, observation of the observation surface and exposure of a new observation surface are repeated as long as there is a region to be observed, and a three-dimensional cross-sectional image is obtained.

  In addition, as a known technique, the chip surface is installed so as to be substantially perpendicular to the FIB beam direction, and the chip surface is removed from the chip surface direction by slicing with the FIB to expose a new surface. A method of obtaining a three-dimensional image after SEM observation from a direction substantially perpendicular to the surface and collecting two-dimensional data is known.

JP-A-8-115699 (pages 2 to 4, FIG. 2)

  However, in the observation method described in Patent Document 1, when SEM observation is used, the resolution is excellent at about 1 nm. However, in the formation of a new observation surface by FIB, the slice thickness is the control limit of FIB. Can be controlled only with a resolution of about 20 nm, so that there is a resolution of 1 nm on the axis in the first direction of the chip surface, whereas only a resolution of 20 nm is obtained on the axis of the second direction perpendicular to that direction on the observation surface. I can't.

  Therefore, when observing a three-dimensional structure with an emphasis on the structure in the plane direction parallel to the surface, a resolution of 1 nm is obtained in the direction of one axis, whereas it is perpendicular to the one axis in the observation plane. Since only the resolution of about 20 nm is obtained in the direction of the other axis, the resolution difference in the parallel observation direction becomes large. For example, when the observation direction of the chip is different, the three-dimensional observation image is deformed in the plane direction. Sometimes it was observed.

  In addition, when the SEM observation is performed from a direction substantially perpendicular to the chip surface by removing the chip surface so as to slice, which is a known technique, the resolution in the plane direction parallel to the surface becomes uniform. Since the surface is removed first, even if a conductive film for preventing charge-up is formed on the chip surface, the observation of the chip starts after the conductive film is removed, and the electrons used for SEM observation A charge-up phenomenon that makes it difficult to observe due to the fact that the accumulated charge cannot be released due to the injection of the line and the electron beam for SEM observation is repelled from the observation surface and the observation surface shines white. It might happen.

  Therefore, the present invention obtains two-dimensional data obtained by observing information in the plane direction of the chip while suppressing the charge-up phenomenon that the resolution in the plane direction of the chip has substantially the same value and making observation difficult, and further An object of the present invention is to provide a chip cross-sectional observation method for collecting three-dimensional data and obtaining a cross-sectional structure of a three-dimensional structure.

  In order to achieve the above object, the method for observing a cross section of a chip according to the present invention has a region to be observed formed on the surface side, and is made of a conductor on the surface side for protecting the region to be observed. Using a chip on which a protective film is formed, a depth that is positive in a direction perpendicular to the back surface of the chip from the front surface of the chip, and perpendicular to one side surface of the chip, from the side surface of the chip to the chip A depth that is positive in the direction toward the inside of the chip, and a width that is parallel to the side surface and the surface of the chip and that is positive from the left to the right when viewed from the outside of the chip. The cross-section observation method of the chip in which the arrangement is specified, wherein at both ends in the width direction, one end has a value greater than or equal to the maximum value of the width of the observed region, and the other end is the width of the observed region. Less than or equal to the minimum value of An observation surface having a depth equal to or greater than the maximum depth of the observation region and a depth equal to or greater than the maximum depth of the observation region is positioned parallel to the surface and facing the observation region. When observing the observation surface by collecting and collecting secondary electrons, or secondary ions, or secondary rays from the observation surface obtained by irradiating the observation surface with primary charged particles, Irradiating a focused ion beam from the side surface of the chip to remove a region that prevents the primary charged particles from reaching the observation surface, and using the signal, observing the observation surface; Accumulating cross-sectional image data, removing the observation surface in parallel with the surface using the focused ion beam, and forming a new observation surface are repeated until all the observation region is observed. Or to interpret the observation surface If the information required is obtained on the way observed, characterized by a step of aborting the repetition.

  According to this observation method, the first step of observing the observation surface and accumulating the data of the cross-sectional image, the observation surface being in a position parallel to the surface and facing the observation region. And removing the observation surface so as to be sliced parallel to the surface using the focused ion beam, and forming a new observation surface, and the first step and the second step are the observation region. Therefore, the region to be observed can be observed from a deep position to a shallow position on the chip. Therefore, by forming a conductive film on the surface of the chip, the charge of the primary charged particles that have entered the observation surface has escaped through the protective film made of a conductor on the surface. It is possible to suppress the charge-up phenomenon that the contrast is lowered due to the accumulation of charges of the next charged particles.

  Further, in order to observe the observation surface in a position parallel to the surface and facing the observation region, a two-dimensional image observation means having the same resolution is assigned to the chip surface direction, and the depth direction Since the resolution corresponding to the slice amount of the focused ion beam can be assigned to the surface, when observing a three-dimensional structure giving priority to the resolution of the structure in the surface direction, the resolution difference in the surface direction can be eliminated, and the plane direction It is possible to observe a three-dimensional structure mainly composed of

  The above-described method for observing a cross section of a chip according to the present invention is characterized in that in the step of observing the observation surface, observation is performed using a scanning electron microscope or a scanning ion microscope.

  According to this observation method, since the structure of the chip is observed with a scanning electron microscope, a fine structure with a resolution of about 1 nm, which is the resolution of the scanning electron microscope, can be observed. In addition, by using a scanning ion microscope that has higher detection sensitivity of crystal grain boundaries than a scanning electron microscope, it becomes possible to observe the crystal grain boundaries of polysilicon or aluminum with high sensitivity.

  Further, the above-described chip cross-sectional observation method of the present invention includes a step of synthesizing and outputting the three-dimensional structure of the observed region from the data of the step of observing the observation surface.

According to this observation method, since the three-dimensional structure is synthesized and output using the cross-sectional image data, the observation result of the cross-sectional structure can be expressed in a format that is easily visually recognized.
In the above-described chip cross-sectional observation method of the present invention, the protective film is made of an insulator.
According to this observation method, when the material of the chip is made of a conductor, a high contrast can be obtained as compared with the case where a protective film made of a conductor is used.

  Hereinafter, a method for observing a cross section of a chip according to the present invention will be described with reference to the drawings. In each drawing, the scale is different for each film and each member in order to make the size recognizable on the drawing.

  FIG. 1 is a schematic sectional view showing a technique for processing and observing a chip using a focused ion beam (hereinafter abbreviated as “FIB”) and a scanning electron microscope (hereinafter abbreviated as “SEM”).

  A conductive protective film 102 is formed on the surface of the chip 101. The chip 101 is fixed using the conductive paste 104 on the stage 103 that is electrically grounded with the surface of the chip 101 facing the right side of the drawing. In addition, the conductive protective film 102 is electrically connected to the stage 103 using a conductive paste 104.

  On the side surface (upper surface in FIG. 1) of the chip 101, a slope 105 is formed which is obtained by removing a shadow area when observing with the SEM 107 using the FIB from the FIB source 108. The observation surface 106 created in a direction substantially perpendicular to the surface 101 can be observed by the SEM 107.

  Here, the observation with the SEM 107 is a method of irradiating the observation surface 106 with an electron beam for observation from the position deeper than the surface of the chip 101 (left side in FIG. 1) in order to observe the observation surface 106. Is done. Further, after the observation of the observation surface 106 by the SEM 107 is completed, the observation surface 106 of the chip 101 is removed by slicing using the FIB from the FIB source 108, and the new observation surface is exposed and observed.

  Therefore, the conductive protective film 102 formed on the surface of the chip 101 remains until the observation of the chip 101 is completed, and when the chip 101 is observed using the SEM 107, the observation of the chip 101 is completed. The charge can be discharged through the conductive paste 104 and the stage 103 through the conductive protective film 102.

  Therefore, negative charges are accumulated on the observation surface 106 formed on the surface of the chip 101, and the observation surface is white due to the electron beam for observation by the SEM 107 being repelled from the observation surface due to the influence of the accumulated negative charges. The charge-up phenomenon that makes observation difficult by shining can be suppressed.

  Next, the observation procedure will be described with reference to FIGS. 2 and 3 are process cross-sectional views for illustrating an observation procedure according to the present invention.

  (1) As shown in FIG. 2A, a chip 101 having a conductive protective film 102 formed on the surface is fixed on a stage 103 using a conductive paste 104. At this time, the conductive paste 104 is applied so that the conductive protective film 102 and the conductive paste 104 are electrically connected.

  (2) As shown in FIG. 2B, the region to be measured is processed by using Ga ions from the FIB source 108 as the FIB from directly above the chip 101 with the surface direction rightward, and observed by the SEM 107 The step of exposing the observation surface 106a for performing SEM observation is performed by forming the slope 105 from which the shadow area is removed.

  (3) As shown in FIG. 3A, the observation surface 106a is observed by the SEM 107 from an oblique direction to obtain two-dimensional image data.

  (4) As shown in FIG. 3B, the FIB is incident from directly above the observation surface 106a, the chip 101 is removed so as to be sliced in parallel with the observation surface 106, and a new observation surface 106b is formed.

  (5) Repeat the steps (3) and (4) until all the observed region is observed, or when data is obtained when information necessary for interpreting the cross-sectional image is obtained during observation To end the repetition.

  By observing using this procedure, the plane parallel to the surface of the chip 101 can be observed by the SEM 107, and therefore the chip 101 that requires high resolution for the plane parallel to the surface of the chip 101 is observed. Can be performed with high accuracy.

  Next, a case where a three-dimensional image is observed will be described with reference to FIG.

  FIG. 4 is a cross-sectional view showing nine cross-sectional observation results according to the measurement order (S1 to S9) for the chip in which foreign matter has entered.

  FIG. 5 is a three-dimensional view obtained by combining the nine cross-sectional views in FIG. 4 and performing three-dimensional display. Since SEM is used as a two-dimensional image observation means having substantially the same resolution with respect to a surface substantially parallel to the chip 101, a high resolution can be obtained with respect to a surface substantially parallel to the chip 101. From the data by a single SEM 107, it was found that what was observed as a spherical foreign object was actually a conical shape.

<Modification>
In place of the above-described SEM used for surface observation, a SIM may be used. In particular, in observing a crystal grain boundary in a region to be observed having a polycrystalline structure, the grain boundary can be set as compared with the observation by the SEM 107 by using the SIM. It can be observed with high contrast.

  In addition, the slope 105 is formed so as not to block the electron beam from the SEM 107, but this is not intended to be limited to the slope and is processed to prevent the electron beam from the SEM 107, such as a stepped shape or a rectangle. Any shape is acceptable.

  In addition, although an example in which the protective film 102 has conductivity has been described, an insulating protective film may be used depending on the material of the chip 101. In particular, when the chip is made of a conductor, high contrast can be obtained by using an insulating protective film.

  Moreover, although the method for processing to a three-dimensional shape was demonstrated, this may obtain the observation result about a single surface. In particular, when the portion near the surface of the chip 101 is observed with the SEM 107, since the conductive protective film 102 is formed on the outermost surface of the chip 101, the SEM 107 is used while suppressing charge-up because there is a charge escape path. Observation becomes possible.

  Next, the effect of this embodiment will be described.

  (1) Observation by the SEM 107 is performed by irradiating an observation electron beam from the position deeper than the surface of the chip 101 toward the observation surface 106 in order to observe the observation surface 106. Further, after the observation of the observation surface 106 by the SEM 107 is completed, the observation surface 106 of the chip 101 is removed by slicing using the FIB from the FIB source 108, and the new observation surface is exposed and observed.

  Therefore, the conductive protective film 102 formed on the surface of the chip 101 remains until the observation of the chip 101 is completed, and when the chip 101 is observed using the SEM 107, the observation of the chip 101 is completed. The charge can be discharged through the conductive paste 104 and the stage 103 through the conductive protective film 102.

  Therefore, negative charges are accumulated on the observation surface 106 formed on the surface of the chip 101, and the observation surface is white due to the electron beam for observation by the SEM 107 being repelled from the observation surface due to the influence of the accumulated negative charges. The charge-up phenomenon that makes observation difficult by shining can be suppressed.

  (2) Since the surface parallel to the surface of the chip 101 can be observed by the SEM 107, the observation of the chip 101 that requires high resolution with respect to the surface parallel to the surface of the chip 101 is observed in another cross section. Compared to the case, it can be performed with higher accuracy.

  (3) Since a three-dimensional image is created on the basis of a two-dimensional image observed at different depths, a more accurate interpretation is possible compared to the case where the observation result of the chip 101 containing a foreign object is interpreted only with a two-dimensional image. Can be performed.

  (4) When information necessary for interpreting the cross-sectional image is obtained during the observation, the observation is discontinued, so that the time required for the observation of the chip 101 can be shortened.

The schematic sectional drawing which shows the method of processing and observing a chip | tip. Process sectional drawing for demonstrating the observation procedure which concerns on this invention. Process sectional drawing for demonstrating the observation procedure which concerns on this invention. Sectional drawing which shows a cross-section observation result according to a measurement order (S1-S9). The three-dimensional figure which shows the three-dimensional display result formed combining sectional drawing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Chip, 102 ... Protective film, 103 ... Stage, 104 ... Conductive paste, 105 ... Slope, 106 ... Observation surface, 106a ... Observation surface, 106b ... Observation surface, 107 ... SEM, 108 ... FIB source.

Claims (4)

An observation region is formed on the front surface side, and a chip formed of a conductor on the front surface side and having a protective film for protecting the observation region is used. With a depth that is positive in the direction perpendicular to the back of the chip,
A depth perpendicular to one side surface of the chip and positive from the side surface of the chip toward the inside of the chip;
A method of observing the cross section of the chip, wherein the arrangement is specified using a width parallel to the side surface and the surface of the chip and viewed from the outside of the chip from the left to the right. Because
At both ends in the width direction, one end has a value greater than or equal to the maximum value of the width of the observed region, and the other end has a value equal to or less than the minimum value of the width of the observed region, An observation surface having a depth equal to or greater than the maximum depth and a depth equal to or greater than the maximum depth of the observed region is disposed in a position parallel to the surface and facing the observed region. When observing the observation surface by collecting secondary electrons, secondary ions, or secondary rays from the observation surface obtained by irradiating the observation surface with primary charged particles, Irradiating a focused ion beam from the side surface of the chip to remove a region that prevents charged particles from reaching the observation surface; and
Irradiating the observation surface with the primary charged particles, observing the observation surface, accumulating cross-sectional image data, and removing the observation surface in parallel with the surface using the focused ion beam Forming a new observation surface, repeatedly until all of the observed region is observed, or when the information necessary for interpreting the observation surface is obtained during observation, A method for observing a cross section of a chip, comprising:   2. The method for observing a cross section of a chip according to claim 1, wherein in the step of observing the observation surface, the observation is performed using a scanning electron microscope or a scanning ion microscope.   3. The method of observing a cross section of a chip according to claim 1, further comprising a step of synthesizing and outputting a three-dimensional structure of the region to be observed from data of a step of observing the observation surface.   The chip cross-sectional observation method according to claim 1, wherein the protective film is made of an insulator.

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