FR2792065A1 - Observation apparatus for semiconductors during manufacturing of PCBs has microscopes, plate and manoeuvre panel allowing corresponding displacement of specimens and microscopes - Google Patents

Abstract

Observation apparatus (10) comprises reflective optic microscope (14) in housing (12), camera (44) and light source (46) placed on same side of specimen (52 b), supporting means (50), such as rigid arm (54), keeping observation axis (X-X, Y-Y) of microscopes (14, 16) at interval separating two specimens (52 a, b). Apparatus also has plate (28) and manoeuvre panel (28a) allowing displacement between second specimen and first microscope, identical to displacement between first specimen and second microscope, so that both microscopes observe identical and matching areas of specimens. An Independent claim is also included for the microscopic observation method.

Description

The present invention relates to a micro-

  scopic of a first specimen, associated according to the same plan to a se-

  cond identical specimen, the two specimens being fixed relative to each other and having the same orientation, the two specimens being separated by an interval, of the type comprising, in a vacuum observation chamber: - a microscope with particular interaction by reflection;

  - means for supporting the first specimen opposite the micro-

  scope with particle interaction by reflection, and

  means for causing a displacement between the first spec

  cimen and the reflection particle microscope.

  This type of installation is particularly suitable for observing

semiconductor circuits.

  During manufacture or after completion of a semi-circuit

  conductor, also commonly called integrated circuit, it is essential to

  ensure its quality and proper functioning.

  Thus, observations of the integrated circuits are carried out, while these are still assembled to each other on a wafer of

  silicon or other composition, in which they were engraved side by side.

  An initial observation is made by reflection optical microscopy in order to detect large defects, such as particles that can

soil the surface of the circuits.

  Due to the increase in the complexity of the circuits, and the reduction

  tion of the size of the constituent elements, it is necessary to resort to scanning electron microscopy, or any other type of microscopy with particle interaction by reflection in order to highlight defects

  not detectable by an optical microscope.

  The scanning electron microscope, due to its very large

  solution, satisfactorily ensures possible detection

  small defects or impurities.

  In addition to the use of scanning electron microscopy, it is

  possible, for fault detection, to electrically stimulate,

  directly or induced the integrated circuit and locally observe an area of the integrated circuit so as to detect and measure the variations of the signal

  over time, corresponding to variations in voltages on the circuit.

  In the case of optical microscopy, it is also known to observe and measure the operation of the circuit by analyzing the signal reflected through the substrate (silicon for example) from below the circuit

  or through the oxide from above the circuit.

  In the case of reflection particle interaction microscopy,

  the reflected signal gives information about the electrical signals flowing

  rant the metal tracks which cover the surface of the circuit.

  In addition, it is possible to add a laser system to the optical microscope for focusing a laser beam with a high energy density on the surface of the circuit. The laser can have an ablative effect on the material

  and in the case of integrated circuits, this makes it possible to cut metal tracks

  or to make openings through silicon or oxide for example. In addition, by adding gas, the laser can be used under vacuum

  to deposit material to form metal tracks for example.

  The scanning electron microscope has a very limited field of vision. Thus, its positioning relative to the extremely extended surface of the electronic circuit is delicate. Likewise, the exact location

  of the area observed on the circuit, compared to the whole circuit is different

difficult to determine.

  The object of the invention is to allow easy identification of the area of ob-

  servation of a specimen, in particular of an electronic circuit, in a microscopic observation installation allowing the detection of small size defects, and the analysis of circuits made up of very small elements.

  To this end, the invention relates to a medium observation installation

  croscopic of a first specimen, associated in the same plane with a second specimen, the two specimens being fixed relative to each other and

  having the same orientation, the two specimens being separated by an inter-

  valley, of the aforementioned type, characterized in that it comprises, in said en-

  girdle, an optical reflection microscope comprising means for observing

  optical vation and means of illumination of the second specimen, the illumination means and the means of optical observation being arranged with the

  same side of the second specimen, the observation axes of the two microsco-

  pes being parallel, in that it comprises means for maintaining the observation axes of the two microscopes separated from said interval separating the first and second specimens, and in that it comprises means for

  cause a displacement between the second specimen and the optical microscope

  that on reflection, identical to the displacement between the first specimen and the

  particle interaction microscope by reflection, so that both

  croscopes observe identical and corresponding regions of the two

specimens.

  According to particular embodiments, the installation comprises one or more of the following characteristics: - the illumination means comprise a source of radiation in the near infrared, in ultra violet or in white light; - the particle interaction microscope with reflection is at least one of a scanning electron microscope, a secondary ion microscope, an electron beam tester and a beam system

of focused ions.

  - the optical reflection microscope is equipped with a laser beam observation and measurement device;

  - the optical reflection microscope is equipped with a processing means -

  laser ment for ablation and / or deposition of material; the means for causing a displacement between the specimens and each of the two microscopes comprise displacement means at

  translation of the microscopes relative to the enclosure in a plane perpendicular

  circular to the parallel observation axes of the two microscopes while the specimens are fixed relative to the enclosure;

  - Said means for maintaining the observation axes of the two mid

  croscopes spaced from said interval comprise a rigid arm connecting the optical observation means to an observation body of the microscope with particle interaction by reflection;

  - the means to maintain the observation axes of the two micro-

  scopes removed from said interval separating the first and second specimens,

  include means for adjusting said interval.

  The invention further relates to a microscopic observation process.

  spike of a first specimen, associated in the same plane with a second identical specimen, the two specimens being fixed relative to each other

  and having the same orientation, the two specimens being separated by an in-

  tervalle, comprising the steps of: - placing the two specimens in a vacuum observation chamber,

  - observe the first specimen with a interaction microscope

ticular by reflection;

  - cause a displacement between the first specimen and the micro-

  scope for particle interaction by reflection; characterized in that it further comprises the steps of:

  - observe the second specimen with an optical microscope by

  bending, having an observation axis parallel to that of the microscope to interact

particulate reflection;

  - illuminate, when observing the second specimen, the face of the se-

  cond specimen from means of illumination arranged on the observation side

  vation; - maintain the observation axes of the two microscopes separated from said interval separating the first and second specimens; and

  - cause a displacement between the second specimen and the micro-

  optical scope with reflection, identical to the displacement between the first speci-

  men and the reflective particle interaction microscope, so that the

  two microscopes observe identical regions of the two specimens.

  According to a particular mode of implementation, a provocation is caused.

  placement of the two microscopes in relation to the specimens so as to

  alternately observe each specimen with one and the other of the micro-

scopes.

  The invention will be better understood on reading the description which will

  follow, given only as an example and made with reference to the

  attached sins, in which: - Fig.1 is a schematic perspective view of an observation installation according to the invention;

  - Fig.2 is a perspective view of a silicon wafer

  carrying several identical circuits; - Fig.3 is a schematic view in longitudinal section of the observation means of the installation of Figure 1;

  - Fig.4 is a schematic view from below illustrating the position-

  observation axes of the two microscopes of the installation by

  compared to the circuits engraved in a silicon wafer.

  The installation 10 shown in FIG. 1 is intended for the observation

  microscopic tion of a silicon wafer or wafer 11 on which is engraved a set of identical semiconductor circuits constituting

each a specimen to observe.

  An example of such a wafer is shown in Figure 2. In this figure, the elements constituting the integrated circuits are exaggeratedly

  enlarged for reasons of clarity.

  As known per se, and as illustrated in FIG. 2, the integrated circuits

  stoneware are engraved side by side during their manufacture, on a silica cake

  cium about fifteen centimeters in diameter. On this wafer, all the circuits are identical and are arranged in a matrix arrangement. They

  are arranged in rows and columns and all have the same orientation.

  Thus, for two separate integrated circuits of the same silicon wafer

  cium, the identical and corresponding elements of the two circuits are all

  spaced by the same interval noted I. The interval I depends on the pair of cir-

  cooked considered, and can be defined as the distance between the corners

  analogs of the two circuits, for example their upper left corners.

  The observation installation 10 essentially comprises an enclosure

  observation chamber 12 in which an optical microscope is arranged

  than reflection 14 and a particle interaction microscope by reflection

  16, such as a scanning electron microscope.

  The optical microscope 14 and the scanning electron microscope 16 are arranged on the same side of the silicon wafer 11. Their axes

  of observation, denoted X-X and Y-Y respectively, are parallel. They stretch

  tooth perpendicular to the plane of the wafer 11, as shown in FIG. 3. The observation enclosure 12 is defined by an airtight vessel 20

  substantially parallelepiped. The tank 20 is carried by a frame 20A.

  The tank 20 opens at its upper end. It is blocked by

an airtight lid 22.

  In the tank 20, there are provided under the cover 22, means 24 for moving the silicon wafer 11 in a plane perpendicular to the observation axes X-X and Y-Y of the two microscopes. These means are

  adapted to ensure a displacement of the wafer 11 in rotation and,

  tually, in vertical and horizontal translation, in particular according to two

  directions perpendicular to the axes of the microscopes.

  The means 24 comprise a frame 26 made of conductive material.

  tor inside which the wafer 11 is supported, so that its main face in which the circuits are engraved is oriented inward

  of the enclosure and is arranged opposite the two microscopes.

  The wafer 11 is electrically connected to the frame 26 to allow

  evacuation of surface charges.

  An operating device 26A is provided between the frame 26 and the neck.

  circle 22 for moving the wafer 11.

  Opposite the cover 22, the bottom of the enclosure 12 is formed by a

  mobile stage 28 carrying the two microscopes 14 and 16.

  The plate 28 is movable in translation relative to the tank 20

  in a plane perpendicular to the X-X and Y-Y axes of the two microscopes.

  To this end, an operating device 28A, of any suitable type, is provided between the tank 20 and the plate 28 in order to ensure the movement of the

  plateau in particular along two perpendicular directions of the plane.

  A sliding seal 29 is interposed between the plate 28 and the tank 20

  to seal the enclosure 12.

  The scanning electron microscope 16 comprises, an obstructing body

  servation 30 received in enclosure 12. This contains as known per se,

  an electron gun 32 at the outlet of which an electronic lens is provided

  that 34 focusing electrons on the circuit to be observed. It further comprises a detector 46 of electrons reflected by the surface of the circuit. Of the-

  guard 36 is arranged outside the body 30 and is carried by the tank 20.

  The body 30 is secured to the plate 28 and is movable therewith.

  As shown in Figure 2, the electron microscope with ba-

  layage 16 is connected to an information processing unit 38 consisting of a computer implementing a suitable program. Display means 40, such as a display screen and control means 42 such as a keyboard, are provided for controlling the processing unit

  38 and the operation of the two microscopes.

  The optical reflection microscope 14 includes means for observing

  optical vation 44, of cylindrical shape, consisting for example of a camera

  ra associated with an adapted objective. In addition, it includes means 46 for

  lumination of the wafer 11, arranged on the same side thereof as the

  observation means 44. The optical microscope is also advantageous

  mentally equipped with a device 47 for emitting a laser beam for the

  configuration of the circuit with an ablative effect or deposit of matter in the presence

of a suitable gas.

  The illumination means 46 comprise a radiation source adapted to the type of observation desired. For example, for the observation and measurement of signals from a circuit in operation, a light source emitting in the near infrared is chosen. Indeed, this radiation

  can pass through silicon and then be reflected. This generally corresponds-

  lying at a wavelength of about 11 m.

  The observation means 44 are spaced a few millimeters from

  the etched side of the electronic circuit to be observed.

  The optical microscope 14 is connected to the information processing unit.

  38 for the generation of an image on the screen 40 or the production of

result of a measurement.

  A vacuum system 48 is connected to the tank 20 in which the two microscopes are housed. This system is suitable for creating

  sufficient vacuum in enclosure 12.

  According to the invention and as shown in FIG. 4, the installation comprises means 50 for maintaining the observation axes XX and YY of the two microscopes spaced from the interval I separating a first circuit 52A to be observed by the electron microscope scanning 16 and a second identical circuit 52B to be observed by the optical microscope

to think about 14.

  The means 50 comprise a rigid arm 54, one end 54A of which is rigidly linked to the observation body 30 of the scanning electron microscope and the other end of which 54B supports the observation means

optical 44 of the optical microscope.

  The arm 54 extends perpendicular to the axes X-X and Y-Y.

  In order to allow the adjustment of the interval I between the axes X-X and Y-Y, the rigid arm 54 advantageously comprises a screw-nut arrangement allowing the adjustment of its length. This screw-nut arrangement is driven by an electric motor controlled from the processing means.

information 38.

  It can be seen, as shown in FIG. 4, that it is possible to

  blir the interval I between the axes X-X and Y-Y, so that the two microsco-

  pes 14, 16 observe the same regions of the first and second integrated circuits

stoneware 52A and 52B.

  Thus, the scanning electron microscope 16 observes a given region of the first circuit 52A of the wafer, while the optical microscope 14 observes the corresponding identical region of the second circuit 52B offset by the interval I.

  In order to observe a circuit carried by the same garage

  lette 11, while the enclosure 12 is kept in the air, first place the

  wafer 11 on the frame 26. A rotation of the frame is carried out under the

  requires operating means 26A until the direction of alignment of the circuits is brought parallel to the axis of the rigid arm 54. In addition, the length of the rigid arm 54 is fixed approximately at the

length of interval 1.

  The enclosure 12 is then placed under vacuum. An image of the first cir-

  fired 52A placed opposite the scanning electron microscope 16 is then carried out. From this image, and in particular from the observation of the four corners of the circuit, the angular positioning of the galeftte 11 is

  adjusted from the operating device 26A.

  After immobilizing the wafer 11, the electron microscope at

  scan 16 is brought to one of the corners of the first integrated circuit 52A.

  The positioning of the scanning optical microscope 16 is relative-

  easy since the corners of circuit 52A are easily recognizable

on the image obtained.

  The optical microscope 14 is then brought to the corresponding corner.

  laying of the second integrated circuit 52B by fine adjustment of the length of the arm

54.

  The means 50 are then blocked in order to keep the interval I fixed.

  established between the observation axes X-X and Y-Y.

  It is therefore conceivable that during the subsequent displacement of the plate 28 carrying the two microscopes 14, 16 relative to the wafer 11, in the plane extending perpendicular to the axes X-X and Y-Y, the two microscopes constantly observe identical and corresponding regions of two

integrated circuits 52A, 52B.

  So, to analyze a given region of the first electronic circuit

  as 52A with the scanning electron microscope 16, the second electronic circuit 52B is first observed with the optical microscope 14 and the plate 28 is moved until the region of the second circuit 52B identical to that of the first circuit 52A to be observed, is located in the observation axis XX of the optical microscope 14. We then proceed

  directly to the examination of the first circuit 52A from the electron microscope

  scanning tronic 16 without the need to reposition the wafer 11, since the observation axis Y-Y of the scanning electron microscope 16

  is then correctly positioned in relation to the region to be observed

  vee, the two microscopes continuously observing simultaneously

  corresponding regions of circuits 52A and 52B.

  In addition, it is also possible to move the two linked microscopes relative to the wafer. Thus, it is possible to switch from one circuit to another by moving the two microscopes so as to observe alternately

  each circuit with the electron microscope and with the micro-

  optical scope. Such a configuration makes it possible for example to measure

  depth or thickness by optical interferometry.

  The field of vision of the optical microscope 14 being from 10 to 100 times

  larger than that of the scanning electron microscope 16, the localization

  tion of the region to be observed is facilitated in relation to the same location

  performed by a scanning electron microscope alone.

  As a variant, the optical microscope by reflection is advantageously

  equipped with means of measurement by laser beam, in particular from the

  positive 47. In this configuration the wavelength of the illumination means is chosen in the near infrared since the silicon and the silicon oxide are transparent at such a wavelength (1 μm

  about). Thus, it is possible to observe over time the radiation

  flexed through silicon or oxide and deduce the variations in

  current or voltages at certain points in an operating circuit.

  Likewise, the scanning electron microscope 16 is advantageous.

  sely equipped with electron beam test means. These means allow an analysis of the circuit in operation, the electrons projected onto the circuit being reflected along different paths as a function of the potential variations of some of the tracks of the circuit. In that case,

  the observation is made locally and the variations of the detected signal are ob-

  served over time. Thus, it is possible to measure by potential contrast for example the voltage variations for a track of a circuit and to trace over time the evolution of the measured potential. Current electron beam testers achieve accuracy much lower than one volt

and microsecond.

  Likewise, as a variant, the scanning electron microscope is replaced by a focused ion beam system. In this case, the source

  electronics is replaced by an ion source. The primary ion beam

  mayors causes secondary particles (electrons or ions) to be re-emitted

  from the surface of the specimen. Just like the electron microscope

  that with scanning, the observation of the variation of the secondary electrons

  tected allows you to make either an image or a measurement. Alternatively, the

  focused ion beam system can be equipped with a detection system

  tion of secondary ions, this is called a secondary ion microscope.

  The focused ion beam system is advantageously equipped

  of a circuit treatment device using a focused ion beam (FIB, focu-

  sed beam), allowing the ion beam to cut certain tracks of the

  cooked, or to carry out deposits thereon when the ion beam is applied in the presence of a plasma generated by the addition of a gas in the axis of the scanning beam. The gas is directly affected by the beam and behaves like a localized plasma. Depending on the nature of the gas and the energy of the ion beam, it is possible to dig or cut the material to

  the circuit surface or depositing material such as metal for example

  full. The invention is also applicable for other types of specimens than

  integrated circuits such as micro-systems (MEMS, micro-

electro-mechanical systems).

  Alternatively, the illumination source for the optical microscope pro-

  produces white light or ultraviolet radiation.

Claims (10)

  1. Installation (10) of microscopic observation of a first speci-   men (52A), associated in the same plane with a second identical specimen (52B), the two specimens (52A 52B) being fixed relative to each other and having the same orientation, the two specimens being separated from an interval (I), of the type comprising, in a vacuum observation chamber (12): - a microscope (16) with particle interaction by reflection; means (26) for supporting the first specimen (52A) facing the microscope (16) with particle interaction by reflection, and   - Means (28, 28A) for causing a displacement between the first   mier specimen (52A) and the microscope (16) with particle interaction by bending,   characterized in that it comprises, in said enclosure (12), a micro-   optical reflection scope (14) comprising optical observation means (44) and means (46) for illuminating the second specimen (52B), the illumination means (46) and the optical observation means (44 ) being arranged on the same side of the second specimen (52B), the observation axes   (X-X, Y-Y) of the two microscopes (14,16) being parallel, in that it comprises   carries means (50) for maintaining the observation axes (XX, YY) of the two microscopes (14,16) spaced from said interval (1) separating the first and second specimens (52A, 52B), and in that it includes means (28, 28A)   to cause movement between the second specimen (52B) and the micro-   optical scope with reflection (14), identical to the displacement between the first specimen (52A) and the microscope (16) with particle interaction by reflection, so that the two microscopes (14,16) observe identical regions   and corresponding of the two specimens (52A, 52B).   2. Installation according to claim 1, characterized in that the illumination means (32) comprise a source of radiation in the   near infrared, in ultra violet or white light.   3. Installation according to claim 1 or 2, characterized in that the microscope with particle interaction by reflection (16) is at least one   among a scanning electron microscope, a second ion microscope   daires, an electron beam tester and a focused ion beam system.   4. Installation according to any one of the preceding claims,   characterized in that the optical reflection microscope (14) is equipped with a laser beam observation and measurement device.   5. Installation according to any one of the preceding claims.   tes, characterized in that the optical reflection microscope (14) is equipped   a laser treatment means for ablation and / or deposition of material.   6. Installation according to any one of the preceding claims,   characterized in that the means for causing a displacement between the specimens (52A, 52B) and each of the two microscopes (14,16) comprise means (28, 28A) for translational displacement of the microscopes (14,   16) relative to the enclosure (12) in a plane perpendicular to the axes of ob-   parallel servation (X-X, Y-Y) of the two microscopes (14,16), while the -   specimens are fixed relative to the enclosure (12).   7. Installation according to any one of the preceding claims.   tes, characterized in that said means (50) for maintaining the observation axes (XX, YY) of the two microscopes spaced from said interval (I) comprise a rigid arm (54) connecting the optical observation means (30) to a particle interaction observation body (40) of the microscope (16) by reflection.   8. Installation according to any one of the preceding claims,   characterized in that the means (50) for maintaining the axes of observation   tion (X-X, Y-Y) of the two microscopes (14,16) separated from said interval (I) se-   covering the first and second specimens (52A, 52B), include means for adjusting said interval (I).   9. Method for microscopic observation of a first specimen (52A), associated in the same plane with a second identical specimen (52B), the two specimens (52A, 52B) being fixed relative to each other and having the same orientation, the two specimens (52A, 52B) being separated by an interval (I), comprising the steps of:   - place the two specimens (52A, 52B) in an observation enclosure vacuum (12),   - observe the first specimen (52A) with a microscope (16)   particulate teraction by reflection; - causing a displacement between the first specimen (52A) and the microscope (16) with particle interaction by reflection; characterized in that it further comprises the steps of: observing the second specimen (52B) with a reflection optical microscope (14), having an axis (XX) of observation parallel to that (YY) of the microscope (16) with particular interaction by reflection; - Illuminating, during the observation of the second specimen (52B), the face of the second specimen (52B) from illumination means (32) arranged on the observation side; - maintain the observation axes (X-X, Y-Y) of the two microscopes (14,16) separated from said interval (I) separating the first and second specimens; and - cause a displacement between the second specimen (52B) and the   reflection optical microscope (14), identical to the displacement between the first   mier specimen (52A) and the microscope (16) with particle interaction by   bending, so that the two microscopes (14,16) observe regions   identical of the two specimens (52A, 52B).   10.- Method according to claim 9, characterized in that one pro-   evokes a displacement of the two microscopes compared to the specimens so as to observe each specimen alternately with one and the other microscopes.