`
`[19]
`
`[11] Patent Number:
`
`6,066,555
`
`Nulty et al.
`
`[45] Date of Patent:
`
`*May 23, 2000
`
`US006066555A
`
`........................... .. 43/639
`11/1995 Cronin et al.
`5,466,636
`.. 437/195
`1/1996 Havemann ..
`5,482,894
`29:23:31 1322:: 9 ~~~-£52232
`.
`u y ..... ..
`,
`,
`..
`5,569,628 10/1996 Yano et al.
`..
`. 437/190
`13332
`........H
`6/1998 Armacost et al.
`
`
`
`5:759:867
`
`.................... .. 438/634
`
`[54] METHOD FOR ELIMINATING LATERAL
`SPACER EROSION ON ENCLOSED
`DURING RF
`
`[75]
`
`SPUTTER CLEANING
`Inventors: James E. Nulty,‘ San Jose; Christopher
`J- P9159» Moumam V1°W> both Of Cam
`
`[73] Assignee: Cypress Semiconductor Corporation,
`San Jose, Calif.
`
`[ *] Notice:
`
`This patent issued on a continued pros-
`ecution application filed under 37 CFR
`1.53(d), and is subject to the twenty year
`patent
`term provisions of 35 USC.
`154(a)(2).
`
`OTHER PUBLICATIONS
`.
`.
`.
`.
`.
`.
`J. Givens et al., “Selective dry etching in a high density
`Plasma for 95 Mm Complemffmary meta1‘0Xide‘5emiC0n'
`ductor technology,” J. Vac. Sci. Technol. B 12(1), Jan./Feb.
`1994: PP~ 427‘432~
`K.K. Shih et al., “Hafnium dioxide etch—stop layer for
`phase—shifting masks,” J . Vac. Sci. Technol. B 11(6), Nov./
`Dec. 1993, pp. 2130-2131.
`
`[21] Appl‘ NO‘: 08/577751
`[22]
`Filed:
`Dee 22, 1995
`
`Primary Examiner—John F. Niebling
`Assistant Examiner—Lynne A. Gurley
`
`ABSTRACT
`[57]
`A process for minimizing lateral spacer erosion of an
`insulating layer adjacent to a contact region and an apparatus
`whereby there is provided a eomaet Opening with a Small
`alignment
`tolerance relative to a gate electrode or other
`structure are disclosed. The process includes the steps of
`forming a conductive layer on a semiconductor body, then
`depositing an insulating layer adjacent to the conductive
`layer. Next, substantially rectangular insulating spacers are
`.
`.
`.
`.
`formed adjacent to the gate electrode. An etch stop layer is
`fgvrgjnfigjgcggc:I;;;1h:,;nS‘;ft;I;g;f;:;;;°lgjfgdtgg
`th
`.
`.
`Th.
`t h .
`dp t Z;
`d
`d.t.
`h
`e
`region.
`ise c is con uc e un er con i ionsw erein
`etch removes the etch stop layer, but retains the substantially
`rectangular lateral Spacer Pr0fi1€_0f Eh? fifstjlnsulatlltg layer.
`The apparatus 1S capable of maintaining high quality con-
`tacts between the conductive material in the contact region
`and an device region, such as a source or drain, or some
`other layer or structure, and is an effective structure for small
`feature size structures, particularly self-aligned contact
`Structures
`'
`
`28 Claims, 8 Drawing Sheets
`
`Int. Cl.7 ................................................. H01L 21/4763
`[51]
`[52] U.S. Cl.
`438/634; 438/637; 438/639;
`_
`438/738; 438/740
`[58] Fleld Of Search ................................... .. 437/195, 190;
`438/595: 934> 639> 637> 738> 740
`_
`References cued
`Us. PATENT DOCUMENTS
`
`[59]
`
`A
`~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-
`13; E1011 et a1~
`2/1989 Mi‘;i;;i1';;';1:“7:::::.‘.':.‘.'::.‘.':::::::.‘: 438/595
`9/1990 Van Laarhoven .
`<37/180
`8/1991 Mele et al.
`.... N 43/639
`3/1992 Dennison .... N
`4 37/195
`11/1992 Davis et al.
`.......................... .. 437/190
`11/1992 Cote et al.
`............................ .. 438/595
`11/1993 Son et al.
`438/595
`1/1994 Ogawfi Ct a1~
`-- 43/639
`4/1994 Matsuum ct 31-
`257/195
`11/1994 L1” et 91'
`437/199
`11/1994 Cleeves et al.
`.. 437/195
`.
`1/1995 Huang et al.
`438/595
`1/1995 Young ......... ..
`430/5
`1/1995 Kenney et al.
`....................... .. 437/189
`
`
`
`-
`
`4:806:201
`4,956,312
`5,037,777
`591009838
`5,164,330
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`5,264,391
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`May 23, 2000
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`6,066,555
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`U.S. Patent
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`May 23, 2000
`
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`6,066,555
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`(PRIOR ART)
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`U.S. Patent
`
`May 23, 2000
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`6,066,555
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`Figure 3
`(PRIOR ART)
`
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`U.S. Patent
`
`May 23, 2000
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`May 23, 2000
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`May 23, 2000
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`6,066,555
`
`1
`METHOD FOR ELIMINATING LATERAL
`SPACER EROSION ON ENCLOSED
`CONTACT TOPOGRAPHIES DURING RF
`SPUTTER CLEANING
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The invention relates to semiconductor device processes,
`and more particularly,
`to improved methods for etching
`openings in insulating layers and a semiconductor device
`with well defined contact openings.
`2. Background of the Invention
`In the fabrication of semiconductor devices, numerous
`conductive device regions and layers are formed in or on a
`semiconductor substrate. The conductive regions and layers
`of the device are isolated from one another by a dielectric.
`Examples of dielectrics include silicon dioxide, SiO2, tet-
`raethyl orthosilicate glass (“TEOS”), silicon nitrides, SixNy,
`silicon oxynitrides, SiOxNy(HZ), and silicon dioxide/silicon
`nitride/silicon dioxide (“ONO”). The dielectrics may be
`grown, or may be deposited by physical deposition (e.g.,
`sputtering) or by a variety of chemical deposition methods
`and chemistries (e.g., chemical vapor deposition (“CVD”)).
`Additionally, the dielectrics may be undoped or may be
`doped, for example with boron, phosphorous, or both, to
`form, for example, borophosphosilicate glass (“BPSG”),
`phosphosilicated glass (“PSG”), and borophosphosilicate
`tetraethyl orthosilicate glass (“BPTEOS”).
`At several stages of the fabrication of semiconductor
`devices, it is necessary to make openings in the dielectric to
`allow for contact to underlying regions or layers. Generally,
`an opening through a dielectric exposing a diffusion region
`or an opening through a dielectric layer between polysilicon
`and a first metal layer is called a “contact opening”, while an
`opening in other oxide layers such as an opening through an
`intermetal dielectric layer is referred to as a “via”. For
`purposes of the claimed invention, henceforth “contact
`opening” or “contact region” will be used to refer to contact
`openings and/or via. The opening may expose a device
`region within the silicon substrate, such as a source or drain,
`or may expose some other layer or structure, for example, an
`underlying metallization layer, local interconnect layer, or
`structure such as a gate. After the opening has been formed
`exposing a portion of the region or layer to be contacted, the
`opening is generally cleaned with a sputter etch, e.g., a
`Radio-Frequency (“RF”) sputter etch, and then the opening
`is filled with a conductive material deposited in the opening
`and in electrical contact with the underlying region or layer.
`To form the openings a patterning layer of photoresist is
`first formed over the dielectric layer having openings cor-
`responding to the regions of the dielectric where the dielec-
`tric layer openings are to be formed.
`In most modern
`processes a dry etch is then performed wherein the wafer is
`exposed to a plasma, formed in a flow of one or more gases.
`Typically, one or more halocarbons and/or one or more other
`halogenated compounds are used as the etchant gas. For
`example, CF4, CHF3 (Freon 23), SF6, NF3, and other gases
`may be used as the etchant gas. Additionally, gases such as
`02, Ar, N2, and others may be added to the gas flow. The
`particular gas mixture used will depend on, for example, the
`characteristics of the dielectric being etched, the stage of
`processing, the etch tool being used, and the desired etch
`characteristics, i.e., etch rate, sidewall slope, anisotropy, etc.
`Many of the etch characteristics are generally believed to
`be affected by polymer residues that deposit during the etch.
`For this reason, the fluorine to carbon (F/C) ratio in the
`
`10
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`2
`plasma is considered an important determinant in the etch.
`In general, a plasma with a high F/C ratio will have a faster
`etch rate than a plasma with a low F/C ratio. At very low
`rates, i.e., high carbon content, polymer deposition occurs
`and etching ceases. The etch rate as a function of the F/C
`ratio is typically different for different materials. The dif-
`ference is used to create a selective etch, by using a gas
`mixture that puts the F/C ratio in the plasma at a value that
`leads to etching at a reasonable rate for one material, and that
`leads to no etching or polymer deposition for another. For
`example, an etchant that has an etch rate ratio or a selectivity
`ratio of two to one for silicon nitride compared to silicon
`dioxide is an effective stripper of silicon nitride from the
`semiconductor substrate, because it will selectively strip
`silicon nitride over silicon dioxide on a substrate surface. An
`etchant that has an etch rate ratio or a selectivity ratio of 0.85
`to one for silicon nitride compared to silicon dioxide is not
`considered an effective stripper of silicon nitride from the
`semiconductor substrate because the etchant will not effec-
`
`tively strip silicon nitride to the exclusion of silicon dioxide.
`The selectivity of the etch process is a useful parameter
`for monitoring the process based on the etch rate character-
`istic of the particular etchant. As noted above, particular
`etchants or etchant chemistries attack different materials at
`different etch rates. With respect to dielectrics, for example,
`particular etchants attack silicon dioxide, BPTEOS, TEOS,
`and silicon nitride dielectrics at different rates. To make
`openings in a substrate comprising a contact region sur-
`rounded by different dielectric layers, e.g., a dielectric layer
`of TEOS surrounded by a dielectric layer of silicon nitride,
`a process will utilize different etchants to make openings
`through the different dielectrics. Thus,
`the different etch
`rates of particular dielectric layers for an etchant may be
`used to monitor the creation of an opening through a
`dielectric layer.
`the taper of the
`Further, by adjusting the feed gases,
`sidewall in the etched opening of the dielectric can be
`varied. If a low sidewall angle is desired, the chemistry is
`adjusted to try to cause some polymer buildup on the
`sidewall. Conversely, if a steep sidewall angle is desired, the
`chemistry is adjusted to try to prevent polymer buildup on
`the sidewall. Varying the etch gas pressure, for example, has
`a significant effect on the shape of the opening. This is
`because the etchant
`ions generally arrive in a direction
`perpendicular to the substrate surface, and hence strike the
`bottom surfaces of the unmasked substrate. The sidewalls of
`
`etched openings, meanwhile, are subjected to little or no
`bombardment. By increasing the pressure of the etch gas, the
`bombardment directed toward the sidewalls is increased; by
`decreasing the pressure of the etch gas, the bombardment
`directed toward the sidewalls is decreased. The changing of
`the etch chemistry is also directly related to selectivity.
`Etchants that provide a near 90° sidewall angle are generally
`not highly selective while highly selective etches typically
`produce a sloped sidewall.
`Following the dielectric etch(es) and prior to any conduc-
`tive material deposition in a contact region, native oxide on
`top of the conducting layers in the contact region is removed
`or cleaned through a non-chemical sputter etch, e.g., an RF
`sputter etch. In addition to alleviating the contact region of
`native oxide,
`the sputter etch can erode any insulating
`dielectric layer or layers. Thus, the parameters of the sputter
`etch must be carefully monitored so as not to excessively
`erode the insulating dielectric layer(s) and expose other
`underlying conductive material. Exposing insulated conduc-
`tive material adjacent
`to the conductive material
`in the
`contact region results in poor quality contacts or a short
`
`
`
`6,066,555
`
`3
`circuit through the underlying conductive material. For a
`thorough discussion of oxide etching, see S. Wolf and R. N.
`Tauber, Silicon Processing for the VLSI Era, Vol. 1, pp.
`539-85 (1986).
`The preceding discussion focused on the making of
`openings, e.g., contact openings, in dielectric material on a
`semiconductor substrate. The same principles are used in
`constructing device regions with a dielectric layer or layers.
`As geometries shrink, the forming of discrete devices on a
`semiconductor substrate becomes more specialized. Special-
`ized deposition and etching techniques permit the density of
`semiconductor elements on a single chip to greatly increase,
`which translates into larger memory, faster operating speeds,
`and reduced production costs.
`A typical metal oxide semiconductor (MOS) transistor,
`e.g., NMOS or PMOS transistor, generally includes source/
`drain regions in a substrate, and a gate electrode formed
`above the substrate between the source/drain regions and
`separated from the substrate by a relatively thin dielectric.
`Contact structures can be inserted to the source/drain regions
`and interlays can overlie the contact structures and connect
`neighboring contact structures. These contact structures to
`the diffusion region are isolated from the adjacent gate by
`dielectric spacer or shoulder portions. The dielectric spacer
`or shoulder portions also isolate the gate from the diffusion
`region.
`the area of the
`Conventional contact structures limit
`diffusion region, because the contact hole is aligned to these
`regions with a separate masking step, and extra area must be
`allocated for misalignment. Proper alignment is necessary to
`avoid shorting the contact structure to the gate or the
`diffusion well. The larger contact area means a smaller
`density of elements on a structure. The larger contact area is
`also responsible for increased diffusion-to-substrate junction
`capacitance, which limits device speed.
`Aself-aligned contact eliminates the alignment problems
`associated with conventional contact structures and
`
`increases the device density of a structure. A self-aligned
`contact is a contact to a source or drain diffusion region. A
`self-aligned contact is useful in compact geometries because
`it can overlap a conducting area to which it is not supposed
`to make electrical contact and can overlap the edge of a
`diffusion region without shorting out to the well beneath.
`Consequently,
`less contact area is needed and gates or
`conductive material lines, e.g., polysilicon lines, can be
`moved closer together allowing more gates or lines on a
`given substrate than traditional contacts.
`FIG. 1 illustrates a self-aligned contact 130 between two
`gate structures. FIG. 1(A) is a planar top view of the contact
`130. FIG. 1(B) is a planar cross-sectional view of the
`self-aligned contact 130 between a pair of gates taken
`through line 1(B) of FIG. 1(A). FIG. 1(C) is a planar
`cross-sectional view of the self-aligned contact 130 between
`a pair of gates taken through line 1(C) of FIG. 1(A).
`The self-aligned contact 130 is a contact to a source or
`drain diffusion region (n+ or p+ silicon) 140 that can overlap
`a edge of the diffusion region 140 without shorting out to a
`well beneath the diffusion region 140. This can be seen most
`illustratively through FIG. 1(C). In FIG. 1(C), the contact
`130 does not lie directly in the diffusion region 140, but is
`misaligned and slightly overlaps the field oxide (designated
`by FOX in FIG. 10. In this illustration, the self-aligned
`contact 130 is not directly over the diffusion region but
`extends over (i.e., overlaps) a well portion 170. The self-
`aligned contact 130 does not short to the well portion 170
`because the self-aligned contact 130 is separated from the
`well 170 by the field oxide.
`
`10
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`The self-aligned contact130 is separated from a conduct-
`ing polysilicon layer 110 by an encapsulating dielectric layer
`120 such that the contact 130 can also overlap the polysili-
`con layer 110 without making electrical contact to the layer
`110 or gate. The polysilicon layer 110 is separated from the
`source/drain diffusion region 140 by a dielectric spacer or
`shoulder 150 of the same or different dielectric material as
`the dielectric layer 120 directly above the conducting poly-
`silicon layer 110.
`A distinct dielectric etch stop layer 125 overlies the
`encapsulating dielectric layer 120. The etch stop layer 125
`permits subsequent etching of the substrate without risk of
`exposing the device structures and layers because the device
`structuring and layers are protected from excessive etching
`by the etch stop layer 125. The diffusion contact is self-
`aligning because the structure can be etched to the substrate
`over the source/drain diffusion region 140 while the dielec-
`tric spacer 150 protects the polysilicon layer 110. Even if a
`photoresist that protects the polysilicon layer 110 from the
`etchant is misaligned with respect to the polysilicon layer
`110, the dielectric spacer 150 prevents shorts to the poly-
`silicon layer 110 when the contact 130 is provided for the
`diffusion region 140.
`to forming contact
`The current practice with respect
`regions, particularly self-aligned contact regions, that are in
`electrical contact with gates,
`interconnect
`lines, or other
`structures in small feature size structures is to utilize
`etchants with high selectivity to protect underlying regions,
`like the etch stop layer and the first insulating layer. FIG. 2
`illustrates a typical prior art process of forming a self-
`aligned contact region adjacent to a gate. In FIG. 2(A), a gate
`oxide layer 210 is formed on a substrate 200 with a con-
`ducting layer, for example a polysilicon layer 220, overlying
`the gate oxide layer 210, and an insulating layer, for example
`a TEOS layer 230, overlying the polysilicon layer 220.
`Adjacent to the polysilicon layer 220 is a contact opening
`region 270. The polysilicon layer 220 is separated from the
`contact region 270 by an insulating spacer portion, for
`example a TEOS spacer portion 235. Aseparate insulating or
`etch stop layer, for example a silicon nitride layer 240
`overlies the TEOS layer 230 and the contact region 270. A
`blanket layer, for example a doped insulating layer like a
`BPTEOS layer 270, planarly overlies the etch stop layer
`240.
`
`A layer of photoresist material 280 overlies the planarized
`BPTEOS layer 250 to expose the contact opening 270. In
`FIG. 2(A), a contact opening 270 has been opened through
`the BPTEOS layer 250. The etchant utilized to make the
`opening had a high selectivity toward BPTEOS relative to
`silicon nitride. When the contact opening 270 was formed
`through the BPTEOS material, the etchant did not etch or
`did not effectively etch the silicon nitride layer 240 material.
`Hence, the silicon nitride layer 240 is described as an etch
`stop layer. The silicon nitride etch stop layer 240 protected
`the underlying TEOS layer 230 and spacer portion 235 so
`that the polysilicon layer 220 remained completely encap-
`sulated.
`
`FIG. 2(A) illustrates an etch 260 to remove the silicon
`nitride etch stop layer 240. In the etch 260 illustrated in FIG.
`2(A), a high selectivity etch toward silicon nitride relative to
`the underlying TEOS layer 230 material is practiced to
`efficiently etch the silicon nitride layer 240 and to protect the
`underlying TEOS layer 230 from the etchant. An example of
`a high selectivity etch recipe to effectively strip silicon
`nitride as compared to the TEOS layer is 30 sccm CHF3 and
`30 sccm 02 at 60 mtorr and 100 watts of power. The result
`of the high selectivity etch is illustrated in FIG. 2(B).
`
`
`
`6,066,555
`
`5
`FIG. 2(B) shows that the silicon nitride selective etch
`effectively removed silicon nitride layer 240 from the con-
`tact opening 270. The selective etch for silicon nitride
`compared to TEOS material, however, left the TEOS layer
`230 with a spacer portion 235 wherein the spacer portion
`235 is sloping or tapered toward the contact opening 270.
`This result follows even where the spacer portion 235 is
`originally substantially rectangular as in FIG. 2(A). The
`properties of the highly selective etch of the overlying etch
`stop layer 240 will transform a substantially rectangular
`spacer into a sloped spacer. FIG. 2(B) presents a polysilicon
`layer 220 encapsulated in a TEOS layer 230 with a spacer
`portion 235 adjacent to the contact opening 270, the spacer
`portion 235 having an angle 290 that is less than 85°.
`In addition to providing stopping points or selectivity
`between materials, the use of high selectivity etches to form
`sloped spacer portions is the preferred practice because the
`sloped shape will result in good step coverage by the metal
`that is deposited into it. The filling of contact openings or
`gaps (i.e., gap fill) is an important consideration because it
`relates directly to the reliability of a device. If an opening is
`not completely filled with an insulative material,
`for
`example, and a gap is created, a subsequent conductive
`material deposit can fill the gap which can lead to shorting.
`Sloped contact openings are easier to completely fill than
`boxy structures because the transition between sloped struc-
`tures and openings is smooth compared to the abrupt tran-
`sitions between boxy structures and openings. Because of
`concerns for complete gap fill and good step coverage,
`industry preference is for sloped spacers and planar depo-
`sition layers similar to that shown in FIG. 2(b).
`Once the contact opening is made, the opening is cleaned
`with a sputter etch, e.g., an RF sputter etch, before conduc-
`tive material is added to fill the opening or gap. The RF
`sputter etch that is used to clean the contact opening in the
`process described above will attack and erode a portion of
`the insulating spacer surrounding the conducting portion and
`adjacent to the contact region. FIG. 3 illustrates a prior art
`substrate with a gate and a contact region undergoing an RF
`sputter etch 380. In FIG. 3, a gate oxide 310 is formed on a
`substrate 300 with a polysilicon layer 320 overlying the gate
`oxide 310 and an insulating layer, for example a TEOS layer
`330 overlying the polysilicon layer 320. Adistinct insulating
`layer, for example a silicon nitride etch stop layer 340,
`overlies the TEOS layer 330 and this etch stop layer 340 is
`covered by a third insulating layer, for example a BPTEOS
`blanket layer 350. Adjacent to the gate is a contact region
`360. An etch of the silicon nitride etch stop layer 340 with
`a high selectivity etch for silicon nitride relative to the
`underlying TEOS layer material produced a gate with a
`sloping or tapered spacer portion 370 of TEOS material,
`illustrated in ghost lines. A subsequent RF sputter etch 380
`is utilized to clean the contact region 360. Although brief
`and designed to clean the contact region, the RF sputter etch
`380 will erode a portion of the insulating TEOS spacer
`portion 370. The dynamics of the sputter etch are that it
`proceeds vertically, directing high-energy particles at
`the
`contact region. The sloping or tapered spacer portion 370
`adjacent the polysilicon layer 320 and separating the poly-
`silicon from the layer 320 contact region 360 is struck by the
`high-energy particles of the RF sputter etch 380. Because the
`spacer portion 370 is sloping or diagonal, a significant
`surface area portion of the spacer portion 370 is directly
`exposed to the high-energy particles from the RF sputter
`etch 380. Further, with sloping spacers, or spacers having an
`angle relative to the substrate surface of less than 85° the
`vertical portion of the dielectric layer (i.e.,
`that portion
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`above the polysilicon layer 320) decreases much less than
`the diagonal portion of the spacer. In terms of measuring
`TEOS material removal during the RF sputter etch 380 in
`FIG. 3, the difference between d1 and d2 is greater than the
`difference between V1 and V2. Thus, in conventional prior art
`self-aligned contact structures, the diagonal thickness of the
`TEOS spacer, portion 370 rather than the vertical thickness
`of the TEOS layer 330, determines the minimum insulating
`layer thickness for the gate.
`For gate structures having minimum diagonal insulative
`spacer portions of 500 A or less, the result of the sputter etch
`380 is that the sputter etch 380 laterally erodes the diagonal
`portion of the TEOS spacer portion 370 adjacent to the
`contact region to a point where the polysilicon layer 320 is
`no longer isolated from the contact region 360 by an
`insulating layer. In that case, there is a short circuit through
`the underlying conductive material when the contact region
`360 is filled with conductive material. This result follows
`
`because the conventional RF sputter etch 380 utilized for
`cleaning the contact region 360 results in an approximately
`200-500 A loss of the spacer material. Further, process
`margins generally require that the device spacer have a final
`minimum thickness (after all etches, doping, and deposits)
`of at least 500 A. Thus, to eliminating alignment sensitivity
`for conventional small feature size structures,
`including
`self-aligned contact structures, requires a final (i.e., at the
`time of contact deposition) minimum insulating spacer of
`more than 500 A and preferably on the order of 1000-1500
`A or greater to fulfill requirements for an adequate process
`margin, complete gap fill, and device reliability.
`To construct structures having a minimum insulative
`spacer portion of more than 500 A directly effects the
`number of structures that can be placed on a device, such as
`a chip. The construction of structures having a minimum
`insulative spacer portion of more than 500 A requires that
`the pre-etch-stop-etch spacer be bigger or thicker to yield an
`effective spacer after the etching processes. In such cases,
`the structures must be separated a distance such that the
`contact area opening is suflicient enough for an effective
`contact. This spacing requirement directly limits the number
`of structures that can be included on a device. In small
`feature size structures, particularly structures utilizing self-
`aligned contacts, the width of contact openings is approxi-
`mately 0.6 microns at the top of the planarized layer and 0.2
`microns at the base of the contact opening. FIG. 3 indicates
`the difference in contact opening widths for the same contact
`in prior art structures. wl represents the width at the top of
`the planarized layer and w2 represents the width at the base
`of the contact region 360. Further, an aspect ratio can be
`defined as the height of a structure (field oxide plus con-
`ductive layer plus first insulative layer plus etch stop layer,
`if any) relative to the width of the base of a contact opening
`(i.e., the distance between adjacent spacers). Typical aspect
`ratios for self-aligned contact structures target ratios of
`1.0-2.4. This prior art range is not achievable with any
`device reliability. To achieve aspect ratios of 1.0-2.4
`requires minimum spacer portions oof less than 1000 A and
`preferably on the order of 500 A. As noted above,
`the
`minimum spacer portions required for aspect ratios of
`1.0-2.4 cannot withstand the sputter etch and will result in
`the exposure of the underlying polysilicon gate and short
`circuiting with the contact.
`There is a need for cost effective structures wherein the
`
`individual devices are as close together as possible while
`maintaining device reliability and an adequate process mar-
`gin and assuring complete gap fill. There is a need for a
`device and for a process to manufacture such a device
`
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`7
`whereby there is provided a contact opening with no align-
`ment sensitivity relative to a gate electrode or other structure
`and whereby the gate electrode does not fall within the
`contact opening but remains isolated from the contact open-
`ing by an insulating layer. The process must be compatible
`with gate electrode insulating spacers of less than 500 A.
`The device resulting from the needed process should be
`capable of maintaining high quality contacts between the
`conductive material in the contact region and the adjacent
`conductive gate or other structure.
`SUMMARY OF THE INVENTION
`
`The invention relates to a process for minimizing lateral
`spacer erosion of an insulating layer on an enclosed contact
`region and a device including a contact opening with a small
`alignment tolerance relative to a gate electrode or other
`structure. The process provides high quality contacts
`between a conductive material in the contact region and a
`device region, such as a source or drain, or some other layer
`or structure. The process comprises the well known step of
`forming a conductive layer on the semiconductor body
`adjacent a contact region. This is followed by the forming of
`a first insulating layer adjacent said conductive layer and the
`contact region. A selected area is masked with photoresist
`and the first insulating layer and the conductive layer are
`etched to form a device structure, such as a gate, adjacent the
`contact region. Next, insulating lateral spacers are added to
`the device structure to isolate the conductive portion of the
`device. The insulating spacers are etched so that the device
`comprises an insulating layer overlying a conductive layer
`with a lateral spacer portion adjacent the contact region
`wherein the spacer portion has a substantially rectangular
`profile. A distinct insulating layer or etch stop layer is then
`formed adjacent to the first insulating layer and over the
`contact region. A third insulating layer or blanket layer is
`then optionally formed over the etch stop layer. The blanket
`layer may or may not be planarized.
`If a blanket layer is included, an etchant is utilized to etch
`a contact opening through the exposed portion of the blanket
`layer to the etch stop layer. Next, a second etch or etch-stop
`etch is performed to remove the etch stop layer material
`from the contact region. The etch-stop etch is also almost
`completely anisotropic, meaning that the etchant etches in
`one direction—in this case, vertically (or perpendicular
`relative to the substrate surface) rather than horizontally. The
`etch removes the etch stop insulating layer and retains the
`substantially rectangular lateral spacer portion of the first
`insulating layer. The anisotropic etch etches primarily the
`exposed etch stop material that lies normal to the direction
`of the etch. Thus, the etch removes the etch stop material
`covering the area of the contact region but does not signifi-
`cantly etch the etch stop material adjacent to the spacer(s).
`The etch stop layer on the spacer adds dielectric thickness
`between the conductive layer and any contacting conductor.
`In general, the etching conditions utilized for the etch-stop
`etch have a low selectivity for etching the etch stop layer
`compared to the underlying insulating material.
`The etch-stop etch may be followed by a sputter etch to
`clean the contact region. Unlike prior art processes whereby
`the sputter etch erodes the underlying sloping lateral spacer
`portion of the first insulating layer adjacent to the conduct-
`ing layer, the sputter etch does not significantly erode the
`substantially rectangular lateral spacer of the first insulating
`layer,
`thus allowing the conductive layer of the device
`structure to remain completely isolated or insulated by a
`spacer comprised of the first insulating layer and some etch
`stop layer material.
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`The structure contemplated by the invention is an effec-
`tive device for small feature size structures, particularly
`self-aligned contacts. The structure consists o