Process for forming a semiconductor device

A buffer film (154, 164) is formed over an underlying film (153, 162) to protect that underlying film (153, 162) from damage during a removal sequence, such as polishing. Scratches, gouging, smearing that can occur to the underlying layer (153, 162) are less likely to occur because of the presence of the buffer film (154, 164). In some embodiments, an insulating film (162) is to be protected. The buffer film (164) is formed over the insulating film (162), and the insulating and buffer films (162 and 164) are patterned. During a subsequent conductive layer polishing operation in an embodiment, most of the buffer film (164) is removed. In still another embodiment, a buffer film (154) is formed over a conductive layer (153) to protect it during "gap fill" process sequence. Although residual portions of the buffer film (154, 164) are usually removed, in some instances, those residual portions can remain if there are no significant adverse affects.

FIELD OF THE INVENTION 
This invention relates in general to processes for forming semiconductor 
devices, and more particularly, to methods of processes for forming 
semiconductor devices using polishing. 
BACKGROUND OF THE INVENTION 
Semiconductor devices are requiring smaller dimensions as operational 
speeds of those devices increase. Currently, small dimensional devices 
require polishing in order to form the semiconductor devices. Single 
inlaid and dual inlaid interconnects are being used to provide the proper 
connections within the semiconductor device. A problem arises in that many 
interconnects include a barrier layer that is formed before forming the 
primary conductive fill material. When polishing the films to form the 
interconnect, typically scratches form within the underlying insulating 
layer. These produce visual and potentially electrical defects and are 
undesired. 
In still other devices, the interconnects can include materials that are 
difficult to polish, such as platinum and iridium, because they are not 
readily oxidized or hydroxylated using typical polishing slurries. 
Therefore, polishing these materials generally relies more on the 
mechanical component of chemical-mechanical polishing compared to copper, 
aluminum, tungsten, or other materials that are more readily oxidized or 
hydroxylated. The greater mechanical component increases the likelihood of 
forming undesired scratches in underlying layers. 
Attempts to remove of the scratches in the underlying layer have included 
using a short polish or removal step. The additional polishing or removal 
step increases cycle time or is only marginally effective in removing the 
scratches. Further, if the scratches are deep enough, too much of the 
underlying layer may need to be removed before the level of scratches is 
at an acceptable level. 
Another attempt to reduce particles includes using a relatively soft 
poromeric pad, such as a Polytex.TM. polishing pad made by Rodel, Inc. of 
Newark, Del. instead of a relatively harder pad, such a Suba.TM. polishing 
pad that is also made by Rodel. While the relatively softer polishing pad 
may reduce the magnitude of the scratches, it does not eliminate them 
because the particles from the barrier layer are still dragged across the 
surface during polishing.

Skilled artisans appreciate that elements in the figures are illustrated 
for simplicity and clarity and have not necessarily been drawn to scale. 
For example, the dimensions of some of the elements in the figures may be 
exaggerated relative to other elements to help to improve understanding of 
embodiments of the present invention. 
DETAILED DESCRIPTION 
A buffer film is formed over an underlying film to protect that underlying 
film from damage during a removal sequence, such as polishing. Scratches, 
gouging, smearing that may occur to the underlying film are less likely to 
occur because of the presence of the buffer layer. In some embodiments, an 
insulating film is to be protected. The buffer film is formed over the 
insulating film, and the insulating and buffer films are patterned. In an 
embodiment, most of the buffer film is removed during a subsequent 
conductive layer polishing operation. In still another embodiment, a 
buffer film is formed over a conductive layer to protect it during "gap 
fill" process sequence. In other embodiments, the process can also be used 
to form optical waveguides and buried or shielded interconnects. Although 
residual portions of the buffer film are usually removed, in some 
instances, those residual portions can remain if there are no significant 
adverse affects. 
FIG. 1 includes an illustration of a cross-sectional view of a portion of a 
semiconductor device substrate 100 that includes a transistor and an 
interconnect. The semiconductor device substrate 100 can be a 
monocrystalline semiconductor wafer, a semiconductor-on-insulator wafer, 
or any other substrate used to form semiconductor devices. Field isolation 
regions 102 and doped region 104 are formed within the substrate 100. A 
gate dielectric layer 106 and a gate electrode 108 overlie portions of the 
doped regions 104 and substrate 100. A first interlevel dielectric (ILD) 
layer 12 overlies the gate electrode 108 and other portions of the 
substrate 100. The first ILD layer 12 includes a lower insulating film 
120, an etch stop film 122, and an upper insulating film 124. The 
interconnect 14 is formed through the ILD layer 12 and contacts one of the 
doped regions 104. The interconnect 14 includes a barrier layer 142 and a 
conductive fill material 144. The device structure up to this point can be 
formed using a conventional processing method. 
A second ILD layer is formed over the interconnect 14 and first ILD layer 
12. The second ILD layer includes an insulating film 162, a buffer film 
164, and an optional hard mask film 166. The insulating film 162 can be a 
low-k dielectric material in the semiconductor industry. For the purposes 
of this specification, low-k means that the dielectric constant of the 
film is no greater than approximately 3.5. In some embodiments, the 
insulating film 162 is more susceptible to scratches and mechanical 
deformations compared to conventional silicon oxide films. Examples 
include highly porous materials, such as aerogels, xerogels, and some 
types of organic polymers. Other examples include other organic materials 
that tend to be susceptible to scratching or tearing. 
The buffer film 164 should be capable of withstanding polishing but also 
should be easily removed without adversely affecting exposed or underlying 
layers that could be exposed during a removal step. The buffer film 164 
includes benzo-cyclobutene, polyvinylacetate, polyvinylalcohol, 
polyethylene, polypropylene, polymethylmethacrylate, polyquinoline, 
Avatrel.TM., or the like. Avatrel.TM. is a polynorbornene-based material 
and is made by BFGoodrich Company of Richfield, Ohio. If a polymer is used 
for the buffer film 164, it should generally be a low molecular weight 
noncrosslinking hydrocarbon material capable of withstanding the process 
sequence for which the material will be subjected. 
Typically, the buffer film 164 is formed by coating the film over the 
substrate similar to a photoresist process. In other words, the material 
for the buffer film 164 is dissolved within a solvent, such as xylene, a 
ketone, or the like. After coating the film, it is typically soft baked to 
drive off carrier solvents. In the case of benzo-cyclobutene, the film may 
need to be cured to make the film more robust during the polishing step. 
However, if polyvinylacetate, polyvinylalcohol, polyethylene, 
polypropylene, or polymethylmethacrylate is used, curing is optional. If a 
cure step is performed, it is usually performed using a hot plate on a 
track system. The temperature of the cure is generally performed in a 
range of approximately 250-400.degree. C. The buffer film 164 typically 
has a thickness of at least approximately 100 nanometers, and usually, has 
a thickness in a range of approximately 200-600 nanometers. The buffer 
film 164 is typically thicker than polish-stop or antireflective films. 
The optional hard mask film 166 is typically a silicon oxide, silicon 
oxynitride, or silicon nitride film that is deposited using a chemical 
vapor deposition method. The chemical vapor deposition can be performed as 
a plasma assisted or a non-plasma assisted deposition. The hard mask film 
166 allows reworking an overlying subsequently formed photoresist layer 
(not shown) without attacking an underlying organic film (such as film 164 
if it includes an organic-based low-k film) before etching occurs. If the 
solvents used to remove a photoresist layer for rework are different from 
solvents that can remove the buffer film 164, the hard mask film 166 may 
not be necessary. 
An opening 22 is formed through the films 162, 164, and 166 to expose a 
portion of the interconnect 14 as shown in FIG. 2. A conductive layer is 
formed over the hard mask film 166 and includes a barrier film 32 and a 
conductive fill material 42. The barrier film 32 is formed overlying the 
hard mask film 166 and within the opening 22 as illustrated in FIG. 3. The 
barrier film can include any refractory metal compound, such as titanium, 
tantalum, tungsten, titanium-tungsten, titanium nitride (TiN), tantalum 
nitride (TaN), tungsten nitride (WN), titanium silicon nitride (TiSiN), 
tantalum silicon nitride (TaSiN), tungsten silicon nitride (WSiN), and the 
like. 
The conductive fill material 42 overlies the barrier film 32 and fills the 
opening 22 as shown in FIG. 4. The conductive fill material 42 can be 
formed by first depositing a seed film and then plating the balance of a 
similar material overlying the seed film. For example, in the case of 
copper, a very thin copper film is deposited by physical vapor deposition 
or electroless plating methods followed by electroplated copper. For 
simplicity, these two films are illustrated as the conductive fill 
material 42. Another material including tungsten or aluminum could be 
formed in place of copper. The conductive fill material 42 can be formed 
using one or any other number of steps. In this embodiment, films 32 and 
42 include different materials and have different properties. 
Polishing is performed to remove portions of the conductive fill material 
42 and barrier film 32 that overlie the insulating film 162 to form the 
interconnect 52 as illustrated in FIG. 5. The polishing also removes the 
hard mask film 166. Unlike polish-stop and etch-stop films where 
significantly less than half of the polish-stop or etch-stop film is 
removed, most of the buffer film 164 is removed. Because the barrier film 
32 may fracture into particles that are relatively hard, any scratches 
that may form are formed within the buffer film 164 instead of the 
insulating film 162. At this point in the process, a substantially planar 
surface 54 is achieved. 
The remaining portion of the buffer film 164 is then removed as shown in 
FIG. 6. Depending on the material used for the buffer film 164, one of 
many different types of removal processes can be used. For example, if the 
buffer film 164 is organic, a plasma ash using oxygen can be used. Still, 
other methods can be used. For example, in the case of benzo-cyclobutane 
or polyvinylacetate, a thermal decomposition can be performed. If the 
conductive fill material 42 includes copper, this decomposition is 
typically performed at a temperature of at least approximately 350.degree. 
C. in a substantially oxygen-free ambient to reduce the likelihood of 
oxidizing the surface of the copper. If the underlying material is 
resistant to oxygen interaction, or forms an oxide that is easily removed, 
then oxygen can be present during the decomposition. 
For polyvinylalcohol, an aqueous solution can be used. The aqueous solution 
can be at nearly any temperature including room temperature (approximately 
20.degree. C.) or even an elevated temperature close to boiling 
(100.degree. C.). If the underlying material includes copper, other 
chemicals can be added to the aqueous solution to passivate or reduce the 
likelihood of oxidizing or corroding the copper film. For example, organic 
amines or benzo-triozole can be added to the solution. In still other 
embodiments, an organic solvent, such as xylene (ortho-, meta-, or para-, 
or any combination thereof), a ketone, and the like can be used. Depending 
on the chemical selected, care may be necessary to reduce the likelihood 
of adverse interactions between the chemical and the underlying conductive 
fill material 42 and the insulating film 162. 
After the buffer film 164 is removed, the interconnect 52 lies at a higher 
elevation that the rest of the substrate as shown in FIG. 6. If the 
interconnect 52 is too high above the upper surface of the insulating film 
162, an optional buff polish can be performed to achieve a more planar 
surface as shown in FIG. 7. Although not shown, a passivation layer can be 
formed over the interconnect 52. Other ILD layers and interconnect levels 
can be added, if needed. 
In another embodiment, a buffer film helps to protect an underlying 
insulating film when a conductive film that is relatively difficult to 
oxidize is being polished. Usually, the mechanical component of 
chemical-mechanical polishing is more important to polish the film. 
Typically, a higher down force pressure or higher substrate or platen 
rotational speed is used. Turning to FIG. 8, a portion of a semiconductor 
device substrate 100 is illustrated having many of the same elements as 
previously described. In this particular embodiment, an ILD layer 80 is 
formed over the gate electrode 108 and substrate 100. The ILD layer 80 is 
patterned to form a contact opening 82 that includes a conductive plug 84. 
The conductive plug 84 includes a barrier film 86 and a conductive fill 
material 88. Typically, the conductive fill material 88 can be tungsten, 
although other materials could be used. An insulating film 162, buffer 
film 164, and hard mask film 166 are formed over the substrate 100. The 
films 162, 164, and 166 are made of the materials as previously described. 
The films 162, 164, and 166 are patterned to form an opening 92 that 
exposes a portion of the conductive plug 84 as shown in FIG. 9. A first 
capacitor electrode film 101 and a buffer film 103 are formed over the 
hard mask film 166 and within the opening 92 as shown in FIG. 10. In this 
embodiment, the first capacitor electrode film 101 includes a material 
that is more difficult to chemical-mechanical polish. For example, the 
first capacitor electrode film 101 includes a noble metal, such as 
platinum, palladium, iridium and the like, or another material including 
rhenium, ruthenium, osmium, oxides of those films or any combination 
thereof. 
The buffer film 103 can include any of the materials used that were 
described with respect to buffer layer 164. Because buffer film 103 can be 
removed separately from buffer film 164, the selection of materials that 
can be used is greater than for buffer film 164. Buffer film 103 can 
include an oxide, the same or similar material as insulating film 162, or 
even other materials. 
Polishing is performed to remove portions of the first capacitor electrode 
film 101 and buffer film lying outside the opening 92 and achieve a 
substantially planar surface 111 as illustrated in FIG. 11. Remaining 
portions of the hard mask film 166 and most of the buffer film 164 are 
also removed. The polishing is terminated before all the buffer film 164 
is removed. 
The remaining portions of the buffer films 103 and 164 are then removed as 
illustrated in FIG. 12. Films 103 or 164 can be removed during the same or 
different operations. If possible, films 103 and 164 should be removed 
simultaneously to reduce cycle time. If buffer film 103 includes the same 
or similar material as insulating film 162, film 103 should be removed 
before film 164. Still, buffer film 103 can be removed after buffer film 
164 if the removal does not adversely affect the insulating film 162 and 
first capacitor electrode film 101. 
A capacitor dielectric film 133 is formed over the first capacitor 
electrode film 101 and portions of the insulating film 162. A second 
capacitor electrode film 135 is then formed over the capacitor dielectric 
film 133. The capacitor dielectric film 133 and capacitor electrode 135 
are then patterned to finish formation of the capacitor 131 as shown in 
FIG. 13. The capacitor 131 is electrically connected to one of the doped 
regions 104 of the transistor shown in FIG. 13. 
Processing is continued to form a form a substantially completed 
semiconductor device as illustrated in FIG. 14. Insulating film 142, a 
buffer film (not shown), and a hard mask film (not shown) are formed over 
the capacitor 131 and insulating film 162. The insulating film 142, buffer 
film, and hard mask film can be formed using any of the materials or 
methods described previously regarding films 162, 164, and 166. A 
dual-inlaid opening 144 is formed. A barrier film 143 and conductive fill 
material 145, such as copper, aluminum, tungsten, and the like, are formed 
within the dual-inlaid opening 144. 
Portions of the barrier film 143 and conductive fill material 145 overlying 
the uppermost surface of the insulating film 142 are removed by polishing. 
The polishing also removes the hard mask film and most of the buffer film. 
The remaining portions of the buffer film are removed. This process 
sequence is similar to the process sequence described in forming the 
interconnect 52. A passivation layer 147 is formed over the interconnect 
141 and the insulating film 142. The passivation layer 147 can include one 
or more films. Although not illustrated in FIG. 14, other electrical 
connections are made to the gate electrode 108 and other doped region 104. 
Further, additional ILD layers and interconnects can be formed as 
necessary to make the proper electrical connections within the 
semiconductor device. 
In still another embodiment, a buffer film can be used to protect 
conductive materials from being scratched, smeared, or causing other 
defects during an insulating film polishing step. A gate electrode 108, a 
first ILD layer 80, and conductive plug 84 are formed over the substrate 
100 as shown in FIG. 15. A barrier film 151, a conductive film 153, such 
as aluminum, an aluminum alloy, and the like, and a buffer film 154 are 
formed over the conductive plug 84 and first ILD layer 80. The buffer film 
154 can include any of the materials previously described for buffer film 
164. The buffer film 154 needs to be removed selectively and without 
significantly adversely affecting a subsequently formed insulating film. 
The buffer film can also be an antireflective film or an optional, 
separate antireflective film (not shown) can be formed between the 
conductive and buffer films 153 and 154 or over the buffer film 154. Also, 
an optional hard mask film could be formed over the buffer film 154 but is 
not shown in FIG. 15. The barrier, conductive, and buffer films 151, 153 
and 154 are patterned using a conventional process as shown in FIG. 15. 
An insulating film 161 is formed over the first ILD layer 80 and patterned 
films in FIG. 16. The insulating film 161 fills the gaps between the 
remaining portions of films 151, 153, and 154. The insulating film 161 is 
polished to remove portions of the insulating film 161 and most of buffer 
film 154 overlying the remaining portions of the conductive film 153, 
thereby forming a substantially planar surface 172 in FIG. 17. The 
remaining portions of the buffer film 154 are removed to expose the 
conductive film 153 in FIG. 18. In this embodiment, a gap fill process is 
used without exposing the conductive film 154 during the insulating film 
161 polishing step. In an alternative embodiment, the buffer layer 154 may 
remain if it does not adversely affect performance. Unlike polish-stop 
layers, most of the buffer film 154 is typically removed during the 
polishing operation. 
Processing is continued to form a substantially completed semiconductor 
device shown in FIG. 19. A second ILD layer 191 is formed and patterned to 
form an opening. The opening is filled with a conductive plug 192 that 
includes a barrier film 193 and 194. A barrier film 195 and conductive 
film 196 are deposited and patterned. A passivation layer 197 is formed 
over the patterned films. Similar to prior embodiments, electrical 
connections are made to gate electrode 108 and doped region 104 but are 
not shown in FIG. 19. Also, additional ILD layers and interconnect levels 
can be added, if needed. 
FIGS. 20 and 21 include other embodiments that can be formed using a buffer 
film. FIG. 20 includes an illustration of a cross-sectional view of an 
optical waveguide. Films 200, 202 and 204 are insulative materials. Film 
202 has a higher refractive index compared to each of films 200 and 204. 
The optical waveguide can be formed in a manner similar to those 
previously described. A buffer film (not shown) is formed over film 200. 
Film 200 is typically gallium arsenide, silicon dioxide, indium phosphide, 
lithium niobate, or polymers including polymethylmethacrylate, polyimide, 
polyurethane, polyester, or the like. Film 202 is formed over the buffer 
film and within the opening. After polishing, only that portion of film 
202 within the opening remains. The remaining portion of the buffer film 
is removed, and film 204 is formed over films 200 and 202. Film 204 also 
has a lower index of refraction compared to film 202. Typically film 204 
is made of the same or a similar material as those listed for film 200. 
FIG. 21 includes an illustration of a cross-sectional view of a conductor 
buried within another conductor. Conductive films 210 and 218 form a 
conductor that surrounds conductive film 214. Conductive film 214 is 
separated from conductive films 210 and 218 by insulating films 212 and 
216. This structure can be used to form a capacitor or to protect 
conductive film 214 from radiation effects if films 210 and 218 are 
electrically connected to a fixed potential electrode (i.e., V.sub.SS or 
V.sub.DD). 
Similar to the prior embodiments, a buffer film (not shown) is formed over 
conductive film 210. An opening is formed through the buffer film but only 
partially (not completely) through film 210. An insulating film 212 and 
conductive film 214 are sequentially deposited to fill the opening. 
Polishing is performed to remove portions of the films 212 and 214 lying 
outside the opening. Most of the buffer film is removed during the 
polishing. Remaining portions of the buffer film is removed. Insulating 
film 216 is formed over the remaining portion of conductive film 214. 
Conductive film 218 is formed over the films 210 and 216 and contacts film 
210. Film 210, 214, and 218 can include the same or different materials. 
Typically, films 210, 214, and 218 include copper, aluminum, tungsten, 
polysilicon, or the like. 
Buffer films 154 and 164 are good at reducing the formation of scratches 
within films when polishing an overlying film, whether it is an insulating 
film or a conductive film. When an interconnect includes a barrier film 
and a conductive fill material, the barrier layer typically includes a 
refractory metal compound and is harder compared to the conductive fill 
material. If portions of the barrier film break off as particles, 
scratches are formed in the buffer film instead of the insulating film. 
Therefore, the insulating film 162 is protected from scratches that can 
cause physical and electrical defects. 
When polishing a layer difficult to remove, such as the first capacitor 
electrode film 101, additional force and other more aggressive mechanical 
parameters are used to remove the layer. Although the barrier film may or 
may not be present in this embodiment, the aggressive conditions are more 
likely to cause scratches and other defects within the underlying 
insulating film. Again the buffer layer absorbs the abuse and is 
subsequently removed. 
In the gap fill process illustrated in FIGS. 15-19, the buffer film 154 
reduces the likelihood of gouging the conductive film 153 or smearing it 
during polishing is reduced. Gouges are physical defects and can affect 
the resistance or electrical properties of the conductive film 153. 
Smearing may cause residual portions of the conductive film 153 to create 
an electrical short or leakage path between interconnects. 
Optical waveguides can be formed with a lower likelihood of scratches. 
Also, buried or surrounded conductors are formed without difficulty. 
More controlled thickness over the insulating film 162 can be achieved in 
some embodiments. If the buffer film 164 was not present, typically over 
polishing is continued which erodes a significant portion of the 
insulating film 162 to make sure that all residual portions of the 
conductive film or capacitor electrode film are removed (no stringers or 
other residual portions that may cause an electrical short or a leakage 
path within the semiconductor device). This erosion generally is undesired 
because it reduces the thickness of the insulating film between underlying 
and overlying conductors. The thinner insulating film increases the 
line-to-line capacitance within the structure (slower device) or the 
likelihood that a signal or potential in one of the conductors is 
significantly disturbed by the signal or potential in the other conductor. 
Still another benefit is that a buffer film can be integrated into a 
process flow without the having to obtain new equipment. The process 
integration is relatively straight forward. 
In the foregoing specification, the invention has been described with 
reference to specific embodiments. However, one of ordinary skill in the 
art appreciates that various modifications and changes can be made without 
departing from the scope of the present invention as set forth in the 
claims below. Accordingly, the specification and figures are to be 
regarded in an illustrative rather than a restrictive sense, and all such 
modifications are intended to be included within the scope of present 
invention. Benefits, other advantages, and solutions to problems have been 
described above with regard to specific embodiments. However, the 
benefits, advantages, solutions to problems, and any element(s) that may 
cause any benefit, advantage, or solution to occur or become more 
pronounced are not to be construed as a critical, required, or essential 
feature or element of any or all the claims.