United States Patent [19J
`Sandhu et al.
`
`[11] Patent Number:
`[45) Date of Patent:
`
`5,069,002
`Dec. 3, 1991
`
`[75)
`
`[54] APPARATUS FOR ENDPOINT DETECI'ION
`DURING MECHANICAL PLANARIZATION
`OF SEMICONDUCI'OR WAFERS
`Inventors: Gurtej S. Sandhu; Laurence D.
`Schultz; Trung T. Doan, all of Boise,
`I d.
`[73] Assignee: Micron Technology, Inc., Boise, ld.
`[21) Appl. No.: 686,686
`[22] Filed:
`
`Apr. 17, 1991
`
`Related U.S. Application Data
`
`[62] Division of Ser. No. 586,996, Sep. 24. 1990. 5.036,015.
`
`Int. CJ.s ..................... B24B 49/ 16; HOlL 21/304
`[51]
`[52] U.S. Cl . ............................... 51/ 165 R; 51/283 R;
`156/626; 156/645; 437/225
`[58] Field of Search ............... 437/8, 7, 225; 156/645,
`156/627, 654, 626; 51/165 R, 283 R, 165.76,
`165.77, I 18, 165.74, 131.1
`References Cited
`U.S. PATENT DOCUMENTS
`3,699,722 10/1972 Davidson et al. .................... 51/283
`3,841.031 10/1974 Walsh ............................... 511283 R
`3,979,239 9/1976 Walsh .................................. 437/225
`4,193.226 3/1980 Gillet al. .......................... 51/124 R
`
`[56]
`
`4,358,338 11/1982 Downey et at ..................... 156/627
`4,407,094 10/ 1983 Bermett ................................. 51/118
`4,663,890 5/1987 Brandt .............................. 51/283 R
`4,793,895 12/ 1988 Kaanta et al. ....................... 156/645
`· 4,811,522 3/ 1989 Gillet al . ........................... 51/131.1
`4,879,258 11/ 1989 Fisher .................................. 437/225
`4,910,155 3/1990 Cote et al . ........................... 437/225
`4,914,868 4/1990 Church et al . ................... 51/165.77
`4,956,313 9/1990 Cote et al. ........................... 156/645
`Primary Examiner-Roscoe V. Parker
`Attorney, Agent, or Firm-Albert M. Crowder
`
`ABSTRACI'
`[57)
`An apparatus for detecting a planar endpoint on a seq-~i­
`conductor wafer during mechanical planarization of the
`wafer. The planar endpoint. is detected by sensing a
`change in friction between the wafer and a polishing
`surface. This change of friction may be produced when,
`for instance, an oxide coating of the wafer is removed
`and a harder. material is contacted by the polishing
`surface. In a preferred form, the change in friction is
`detected by rotating the wafer and polishing surface
`with electric motors and measuring current changes on
`one or both of the motors. This current change can then
`be used to produce a signal to operate control means for
`adjusting or stopping the process.
`
`9 Oaims, 2 Drawing Sheets
`
`.
`
`"!)
`CL
`
`_r-·
`
`ROTATING A SEMICONDUCTOR
`WAFER IN A POLISHING AGENT
`ON A POLISHING PLATEN
`
`I ~32
`
`SENSING A CHANGE IN
`FRICTION BETWEEN THE
`PLANARIZED WAFER AND
`POLISHING PLATEN
`
`I
`
`_r--34
`
`MEASURING LOAD ON
`ELECTRIC DRIVE MOTORS
`WITH CURRENT METER
`
`001
`
`SONY 1010
`
`

`
`U.S. Patent
`
`bee. 3, 1991
`
`Sheet 1 of 2
`
`5,069,002
`
`SUBSTRATE
`
`AGURE 1
`(PRIOR ART)
`
`SUBSTRATE
`
`FIGURE 2
`(PRIOR ART)
`
`10
`
`10
`
`FIGURE 3
`(PRIOR ART)
`
`AGURE4
`(PRIOR ART)
`
`002
`
`

`
`U.S. Patent
`
`Dec. 3, 1991
`
`Sheet 2 of 2
`
`5,069,002
`
`CL 9 ~14
`I I
`
`28
`
`F
`
`26
`
`I
`
`~
`CL
`
`FIGURE 5
`
`30 ~·
`
`ROTATING A SEMICONDUCTOR
`WAFER IN A POLISHING AGENT
`ON A POLISHING PLATEN
`
`16
`
`20
`
`SENSING A CHANGE IN
`FRICTION BETWEEN THE
`PLANARIZED WAFER AND
`POLISHING PLATEN
`
`I ~32
`
`I ~34
`
`FIGURE 6
`
`'
`MEASURING LOAD ON
`ELECTRIC DRIVE MOTORS
`WITH CURRENT METER
`
`FIGURE 7
`
`003
`
`

`
`1
`
`5,069,002
`
`APPARATUS FOR ENDPOINT DETECfiON
`DURING MECHANICAL PLANARIZATION OF
`SEMICONDUCfOR WAFERS
`
`This is a division of application Ser. No. 586,996, filed
`Sep. 24, 1990~ now U.S. Pat. No. 5,036,015.
`
`FIELD OF THE INVENTION
`This invention relates to semiconductor manufacture
`and, more particularly, to a novel method and apparatus
`for detecting a planar endpoint in a semiconductor
`wafer during mechanical planarization.
`
`2
`In the past, this planarization process has been ac(cid:173)
`complished by control of the rotational speed, down(cid:173)
`ward pressure, chemical slurry, and time of the planari(cid:173)
`zation process. The planar endpoint of a planarized
`5 surface has been detected by mechanically removing
`the Semiconductor wafer from the planarization appara(cid:173)
`tus and physically measuring the semiconductor wafer
`by techniques which ascertain dimensional and planar
`characteristics. If the semiconductor wafer does not
`10 meet specification, it must be loaded back into the pla(cid:173)
`narization apparatus and planarized again. Alternately,
`an excess of material may have been removed from the
`semiconductor w~fer rendering the part as substandard.
`In general, however, there has been no provision in
`15 the art for in situ endpoint detection of a planarized
`surface during the planarization process. The present
`invention is directed to a novel method and apparatus
`for in situ endpoint detection of a planarized surface
`during the mechanical planarization process.
`
`35
`
`BACKGROUND OF THE INVENTION
`In semiconductor manufacture, extremely small elec(cid:173)
`tronic devices are formed in separate dies on a thin, flat
`semiconductor wafer. In general, various materials
`which are either conductive, insulating, or semicon(cid:173)
`ducting are utilized to form a semiconductor wafer. 20
`SUMMARY OF THE INVENTION
`These materials are patterned, doped with impurities, or
`In accordance with the present invention, a novel
`deposited in layers by various processes to form the
`integrated circuits. A completed device is referred to as
`method and apparatus for endpoint detection of a plana-
`a semiconductor.
`rized surface of a semiconductor wafer during mechani-
`·
`One process that is utilized in the manufacture of 25 .cal planarization of the wafer is provided. In general,
`the method and apparatus of the invention senses a
`semiconductors is referred to as chemical mechanical
`change of friction between the wafer and a polishing
`planarization (CMP). In general, chemical mechanical
`planarization involves holding or rotating a thin, flat
`surface to detect the endpoint of a planarized surface. A
`wafer of s~miconductor material against a wetted pol-
`change in friction occurs when, for example, a first
`ishing surface under controlled chemical, pressure, and 30 material or film of the wafer is removed and a planar
`temperature conditions. A chemical slurry containing a
`surface of the wafer formed of a different material or
`polishing agent such as alumina or silica is utilized as the
`film is exposed. An oxide or nitride coating, for in-
`abrasive medium. Additionally, the chemical slurry
`stance, may be removed to expose polysilicon or a base
`may contain chemical etches for etching various sur-
`metallic film.
`faces of the wafer.
`The method of the invention, generally stated, com-
`In general, a semiconductor wafer is subjected to
`prises:
`chemical mechanical planarization to remove topogra-
`rotating a semiconductor wafer against a rotating
`phy, layers of material, surface defects such as crystal
`polishing platen in a polishing slurry; and
`lattice damage, scratches, roughness, or embedded par-
`sensing a change in friction between the planarized
`ticles of dirt or dust. This process is utilized in the for- 40
`wafer surface and the polishing platen in order to
`mation of various integrated circuit devices of a semi-
`detect a planar endpoint of the wafer.
`conductor and to improve the quality and reliability of
`Apparatus for planarizing a semiconductor wafer in
`a semiconductor.
`accordance with the method of the invention com-
`In the mechanical planarization process, a rotating
`prises:
`polishing head is typically utilized to hold the wafer 45
`holding means in the form of a rotatable polishing
`under controlled pressure against a rotating polishing
`head for holding a semiconductor wafer;
`platen. The polishing platen is typically covered with a
`polishing means including a rotatable polishing platen
`relatively soft, wetted material such as blown polyure-
`and a polishing slurry for the contacting and plana-
`thane. The chemical slurry is metered onto the polish-
`rizing the topography of the wafer; and
`ing platen and is selected to provide an abrasive medium 50
`sensing means for sensing a change in the coefficient
`and chemical activity for the etching.
`offriction between the surface of the wafer and the
`Such apparatus for polishing thin, flat semiconductor
`polishing platen.
`wafer.s are well known in the art. U.S. Pat. Nos.
`In a preferred form of the invention, the polishing
`4,193,226 and 4,811,522 to Gill, Jr. and U.S. Pat. No.
`platen and polishing head are both rotated by electric
`3,841,031 to Walsh, for instance, disclose such appara- 55 drive motors. The sensing means comprises a current
`tus. Another such apparatus is manufactured by Wes-
`meter which senses a change in motor current of-either
`tech Engineering and designated as a Model 372 Pol-
`or both drive motors during the planarization process.
`isher.
`This load change can then be equated to a change in the
`A particular problem encountered in the use of such
`coefficient of friction between the surface of the wafer
`chemical mechanical polishing apparatus is in the deter- 60 and the polishing platen.
`mination that a part has been planed to a desired planar
`Other objects, advantages, and capabilities of the
`endpoint. It is often desirable, for example, to remove a
`present invention will become more apparent as the
`thickness of oxide material which has been deposited
`description proceeds.
`onto a substrate, and on which a variety of integrated
`circuit devices have been formed. In removing or plana- 65
`rizing this oxide, it is desirable to remove the oxide to
`the top of the various integrated circuit devices without
`removing any portion of a device.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is an enlarged side elevation view of a portion
`of a semiconductor wafer prior to mechanical planariza(cid:173)
`tion;
`
`004
`
`

`
`5,069,002
`
`4
`3
`polishing means in the form of a rotatable polishing
`FIG. 2 is an enlarged side elevation view of a portion
`platen 16 and a polishing agent 18 which is applied t the
`of a semiconductor wafer after mechanical planariza-
`surface of the polishing platen 16;
`tion;
`holding means for holding the semiconductor wafer
`FIG. 3 is a plan view of a semiconductor wafer;
`5 10 in the form of a rotatable polishing head 20 mounted
`FIG. 4 is a side elevation view of FIG. 3;
`for holding and rotating the wafer 10 against the polish-
`FIG. 5 is a schematic view of mechanical planariza-
`ing platen 16 under a controlled force F; and
`tion apparatus having endpoint detection apparatus
`constructed in accordance with the invention;
`endpoint detection means in the form of motor cur-
`rent meters 22,24 which measure the load or amperage
`FIG. 6 is a schematic plan view showing rotation of
`a polishing platen and polishing head for mechanical 10 on electric drive motors 26,28 for the polishing platen
`planarization of a semiconductor wafer; and
`16 and polishing head 20 and sense a change in friction
`FIG. 7 is a block diagram of a method of endpoint
`between the wafer 10 and the polishing platen 16.
`As s~own in FIG. 5, the polishing head 20 holds the
`detection in accordance with the invention during me-
`chanica! planarization of semiconductor wafer.
`wafer 10 for rotation against the polishing platen 16
`IS under a controlled force (F). A direction of rotation of
`the polishing platen 16 and polishing head 20 is prefera-
`bly the same. This is shown in FIG. 6. (Alternately, the
`polishing platen 16 and polishing head 20 may be ro(cid:173)
`tated in opposite directions). Additionally, the polishing
`head 20 is constructed to move across the polishing
`platen 16 as indicated by the double headed arrow in
`FIG. 6. The polishing agent 18 is dispensed as shown in
`FIG. 5 through a suitable valved conduit onto the sur(cid:173)
`face of the polishing platen 16. Such mechanical planar(cid:173)
`ization apparatus are well known in the art. One such
`apparatus is manufactured by W estech Engineering and
`designated as a Model 372 Polisher.
`In general, with such polishing apparatus, all func(cid:173)
`tions (speed, force (F), temperature, slurry, chemical
`components) are under computer control. Additionally,
`the wafer size may be varied and an environment enclo(cid:173)
`sure (not shown) may be provided to protect the sur(cid:173)
`roundings from particles or contamination.
`In general, the apparatus of the invention adds the
`current meters 22,24 to the drive motors 26,28 of the
`planarization apparatus of the prior art in order to de(cid:173)
`tect the amperage or load on the motors 26,28. Such
`current meters 22,24 must necessarily be sensitive to
`small variations in current, but are commercially avail(cid:173)
`able in the art. In effect, the current meters 22,24 con(cid:173)
`stantly monitor the force required to rotate the wafer 10
`on the polishing platen 16. Any change in this force will
`signal the change in friction of the exposed surface of
`the wafer 10, which occurs at a planar endpoint.
`The load or amperage draw of the motors 26,28 is a
`function of the force (F) exerted by the polishing head
`20 and wafer 10 on the polishing platen 16. Addition(cid:173)
`ally, the load is a function of the coefficient of friction
`between the wafer 10, polishing slurry 18, and polishing
`platen 16. A change in the coefficient of friction be(cid:173)
`tween these surfaces will change the load or amperage
`draw of the drive motors 26,28. If, for example, the
`oxide coating of a wafer 10, as shown in FIG. 1, is
`removed to the plane of the tops of the (IC) devices the
`change in coefficient of friction can be detected by a
`different amperage draw of the currant meters 22,24.
`The point at which the coefficient of friction changes is
`thus equated to a planar endpoint of the wafer 10.
`The current of either the polishing platen drive motor
`26 or the polishing head drive motor 28 or both may be
`monitored. This change can be utilized to generate a
`signal from the current meters 22,24 to a control means
`36 (FIG. 5), which stops or adjusts apparatus and the
`mechanical planarization process as required. As is ap(cid:173)
`parent to those skilled in the art, such control means 36
`could be formed by equipment and procedures known
`in the art and may include visual signals and manual
`controls.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`Referring now to FIG. 1, a portion of a semiconduc(cid:173)
`tor wafer is shown prior to mechanical planarization of
`the semiconductor wafer. A semiconductor wafer typi- 20
`cally includes a substrate on which a plurality of micro
`devices have been formed. The wafer substrate is typi(cid:173)
`cally formed of a single crystal silicon material. The
`micro devices are formed by patterning regions on the
`substrate and patterning layers on the substrate. A 25
`chemical mechanical planarization process may be uti(cid:173)
`lized, for instance, to remove a portion of a layer. Dif(cid:173)
`ferent layers are generally formed of different materials.
`puring formation regions or vias on the silicon sub(cid:173)
`strate may be patterned for contact with a plurality of 30
`IC devices as shown in FIG. 1. An insulating or oxide
`coating may then be formed or deposited on the sub(cid:173)
`strate and over the IC devices. As shown in FIG. 2, it
`may be necessary to remove the oxide coating to the
`level of the IC devices to form insulating spacers there- 35
`between. This can be accomplished by a chemical me(cid:173)
`chanical planarization process.
`In general, a chemical mechanical planarization pro(cid:173)
`cess involves mechanically polishing a thin, flat semi(cid:173)
`conductor wafer under controlled pressure, tempera- 40
`ture, time, and chemical conditions. Such a semiconduc(cid:173)
`tor wafer is shown in FIGS. 3 and 4 and is generally
`designated as 10. As shown, the wafer is generally cir(cid:173)
`cular in shape and includes a major flat 12. The size of
`the wafer 10 is typically about 5 inches in diameter but 45
`may be several inches smaller or longer. A plurality of
`patterned dies (not shown) are formed o the surface of
`the wafer, each having a micro topography. The micro
`topography of each patterned die can be altered as
`illustrated by the example of FIGS. 1 and 2 by the me- 50
`chanica! planarization process. Alternately, mechanical
`planarization can be utilized to form other wafer topog(cid:173)
`raphy and in the polishing, cleaning, and planing of the
`wafer surface.
`In general, different layers of the semiconductor 55
`wafer are formed of different materials (i.e. metallic
`film, polysilicon film, insulators) which have a different
`relative hardness. The IC devices formed in FIGS. 1
`and 2, for instance, are generally harder than the oxide
`coating formed thereon. In general, the method and 60
`apparatus of the invention utilizes this relative differ(cid:173)
`ence between materials to detect planar endpoints dur(cid:173)
`ing the mechanical planarization process.
`Referring now to FIG. 5, a mechanical planarization
`apparatus constructed with endpoint detection appara- 65
`tus in accordance with the invention is shown and gen(cid:173)
`erally designated as 14. The mechanical planarization
`apparatus 14 includes:
`
`005
`
`

`
`5,069,002
`
`5
`The method of the invention is adapted to detect the
`endpoint of a planarized wafer surface in such an appa(cid:173)
`ratus and can be summarized by the steps of:
`rotating a semiconductor wafer 10 in a polishing
`agent 18 on a polishing platen 16, step 30; and
`sensing a change in friction between the surface of the
`wafer 10 and the polishing platen 16, step 32.
`As previously explained, in a preferred form of the
`invention, sensing of a change in friction is accom(cid:173)
`plish_sd by measuring the load on electric drive motors 10
`26,28 with current meters 22,24, step 34. This change in
`friction between the surface of the wafer and the polish(cid:173)
`ing platen 16 can then be equated to a planar .endpoint of
`the wafer surface. This concept can be more fully ex(cid:173)
`plained with reference to FIGS. 1 and 2. As the semi- 15
`conductor wafer 10 is rotated and pressed against the
`polishing platen 16, the oxide surface (FIG. 1) of the
`wafer 10 contacts the surface of the polishing platen 16.
`The oxide surface has a hardness which produces a
`certain coefficient of friction by contact with the sur- 20
`face of the polishing platen 16 and polishing agent 18.
`As previously stated, the surface of the polishing platen
`16 may typically be formed of a relatively soft material
`such as blown polyurethane.
`This coefficient of friction is generally constant until 25
`the oxide is polished away to the point in which the
`surface of the IC devices is exposed (FIG. 2). At this
`point, the IC devices contact the surface of the polish(cid:173)
`ing platen 16. In general, the IC devices may be formed
`of a harder material than the oxide coating (for example, 30
`a metallic film may be contacted). A different coeffici(cid:173)
`ent of friction thus occurs between the surface of the
`wafer 10 and the surface of the polishing platen 16.
`Assuming the downward force F (FIG. 5) on the wafer
`10 and the rotational speed of the polishing head 20 and 35
`polishing platen 16 remains constant, this different coef(cid:173)
`ficient of friction will produce a different load on the
`electric drive motors 26,28. This load can be sensed by
`the current meters 22,24. A planar endpoint in which
`the oxide coating has been removed to the top of the IC 40
`devices is thus detected.
`This change in coefficient of friction between the
`planar surfaces, although relatively small, is subjected
`to a multiplying factor if the current draw on the drive
`motor 26 for the polishing platen 16 is monitored. The 45
`multiplying factor can be determined as follows.
`The electric drive motor 26 for the polishing platen
`16 produces a torque (T) which is opposed by the rotat(cid:173)
`ing polishing head 10. This torque (T) is also related to
`the force (F) (FIG. 5) pressing the polishing head 20 50
`against the polishing platen 16. As is apparent force (F)
`is also related to but is different than the coefficient of
`friction between the surface of the wafer 10, polishing
`slurry 18, and polishing platen 16. Additionally, the
`torque (T) is dependent on the distance "R" (FIG. 6) of 55
`the polishing head 20 from the center of rotation of the
`polishing platen 16. This well-known relationship can
`be expressed by the formula T = F X r. A small change
`in the coefficient of friction between the surfaces can
`thus be detected as a change in the torque (T) seen by 60
`the electric drive motors 26 (and, thus, the current flow)
`multiplied by the radius (r).
`Additionally, as is apparent, changes in the coeffici(cid:173)
`ent of friction on relatively larger diameter wafers are
`generally larger and thus easier to detect than on rela- 65
`tively smaller diameter wafers.
`The invention thus provides a simple yet unobvious
`method and apparatus for detecting the planar endpoint
`
`6
`of a semiconductor wafer during a mechanical planari(cid:173)
`zation process. While the process of the invention has
`been described with reference to a preferred embodi(cid:173)
`ment thereof, as will be apparent to those skilled in the
`5 art, certain changes and modifications can be made
`without departing from the scope of the invention as
`defined by the following claims.
`What is claimed is:
`1. In a mechanical planarization apparatus for a wafer
`having a polishing head for holding and rotating the
`wafer against a rotatable polishing platen in a polishing
`slurry, an endpoint detection apparatus comprising:
`sensing means for sensing a change in friction be(cid:173)
`tween the wafer and polishing platen by detecting
`a current change to a drive motor for rotating the
`polishing platen or polishing head whereby a pla(cid:173)
`nar endpoint on the wafer is detected.
`2. Endpoint detection apparatus as claimed in claim 1
`and wherein:
`a change in friction occurs when coating of the wafer
`is removed and a surface formed of a different
`material is contacted.
`3. Endpoint detection apparatus as claimed in claim 1
`further comprising:
`control means operable by a signal from a current
`meter for adjusting the mechanical planarization
`apparatus.
`4. Endpoint detection apparatus as claimed in claim 3
`and wherein:
`both the wafer and polishing platen are rotated and
`the wafer is moved across the polishing platen.
`5. Endpoint detection apparatus as claimed in claim 3
`and wherein:
`the control means measures a distances "r" from the
`center of the polishing head to the center of the
`polishing platen, as a multiplying factor for measur(cid:173)
`ing torque (T) on a drive motor and force (F) press(cid:173)
`ing the wafer against the polishing platen by the
`formula T = F X r.
`6. Apparatus for mechanically planarizing a semicon(cid:173)
`ductor wafer and for detecting a planar endpoint of the
`wafer comprising:
`a. holding means for holding and rotating the wafer
`including a polishing head rotated by a first electric
`drive motor;
`b. polishing means including a polishing platen ro(cid:173)
`tated by a second electric drive motor and a polish(cid:173)
`ing agent for contact with the wafer and with the
`polishing platen; and
`c. sensing means for sensing a change in friction be(cid:173)
`tween the polishing head and polishing platen in(cid:173)
`cluding a current meter for either the first or sec(cid:173)
`ond electric drive motors, whereby a change in
`friction can be detected by a change in motor cur(cid:173)
`rent and equated to a planar endpoint on the wafer.
`7. Apparatus as recited in claim 6 and wherein:
`a planar endpoint is detected between an oxide coat(cid:173)
`ing which is removed and a surface including a
`different material.
`8. Apparatus as recited in claim 6 and wherein:
`the wafer and the polishing platen are rotated in the
`same direction.
`9. Apparatus as recited in claim 6 and further com(cid:173)
`prising:
`control means responsive to a signal from the sensing
`means to adjust the apparatus.
`• • • • •
`
`006
`
`

`
`Adverse Decision In Interference
`
`Patent No. 5,069,002, Gurtej S. Sandhu, Laurence D. Schultz, Trung Tri Doan, AN APPARATUS FOR
`ENDPOINT DETECTION DURING MECHANICAL PLANARIZATION OF SEMICONDUCTOR WA(cid:173)
`FERS, Interference No. I 03,958, linal judgment adverse to the patentees rendered March 9, 2001, as to claims
`1-9.
`
`(Official Gazette May /5, 200/)
`
`007