Ceramic ring for guiding a wafer down to the lower electrode of a dry etcher

A structural configuration for a ceramic ring for guiding a semiconductor wafer down to the lower electrode of a dry etcher having upper and lower electrodes. The ceramic ring includes a base ring, a wall ring rising perpendicular to one surface of the base ring, and more than ten projections located on the top edge surface of the wall ring. Each of the projections includes a first and a second triangular surface, each at one end of the prismatic body and rising from the top edge surface of the wall ring. An inner sloped surface rises from-the top edge surface of the wall ring and an outer sloped surface rises from the top edge surface of the wall ring. First and second oblique sloped surfaces rise from the top edge surface of the wall ring, connecting the first and second triangular surfaces to the inner sloped surface, respectively. A trapezoidal surface having four sides, one each joined to the inner and outer sloped surfaces and the first and second oblique sloped surfaces forms an apex surface of the projection.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates in general to a component of a dry etcher for 
semiconductor fabrication equipment, and more particularly to a ceramic 
ring for guiding a semiconductor wafer more smoothly down to a lower 
electrode of a dry etcher in a semiconductor fabrication process. 
2. Description of the Related Art 
Dry etching is an etching procedure that employs an etcher chamber 
containing a low pressure gaseous atmosphere placed under an applied 
electric field. Due to the presence of the electric field, charged ions or 
radicals are produced in the gas, creating a plasma. This 
plasma-containing etcher chamber is then suitable to etch, for example, 
silicon oxide or nitride layers of a semiconductor wafer. 
Dry etching is essential in semiconductor fabrication, because it results 
in anisotropic characteristics in the etched wafer. Excellent conformity 
to desired precession patterns in the processed semiconductor 
configuration result from such dry etching procedures. 
One widely used, commercially available, dry etcher is the Tegal 903 dry 
etcher. Two electrode plates, an upper and a lower, are provided in the 
etcher chamber for producing ionized gaseous molecules when an electric 
field is applied thereto. 
A brief description of the characteristics of a conventional ceramic ring 
used for the above-described purpose follows to assist in the 
understanding of the invention. 
Referring to FIG. 1, a perspective view of a prior art ceramic ring 100 
observed at approximately a 45-degree angle is shown. As shown, the 
ceramic ring 100 includes a base ring 101, a wall ring 102, and a number 
of prism-shaped projections 103,104, . . . , and 112. Typically, the 
entire ceramic ring is made in one single piece. 
With simultaneous reference to FIG. 2, which is a side view of the ceramic 
ring of FIG. 1, it can be seen that the base ring 101 is generally a 
disc-shaped ring while the wall ring 102 is a tube-shaped ring. The wall 
ring 102 rises generally perpendicularly from the inner edge of the 
disc-shaped base ring 101, and the ceramic ring reveals an L-shaped cross 
section when cut diametrically. In FIG. 2, it is shown that the two faces 
of the base ring 101 have different diameters. Essentially, the face of 
base ring 101 opposite the direction of the rise of the wall ring 102 has 
a diameter 114 that is smaller than the diameter 113 of the other face, 
and this forms a tapered outer edge of the base ring 101, as shown in the 
drawing. The wall ring 102 has an inner opening with a diameter 115. 
In one typical example, the base ring 101 has a thickness 126 of about 4.97 
mm. Its larger diameter 113 is about 172.40 mm and its smaller diameter 
114 is about 167.20 mm. The inner opening diameter 115 of the wall ring 
102 is about 151.30 mm. It should be noted that all these diameters 113, 
114, and 115 are measured and obtained from concentric circles of the 
ceramic ring. Wall ring 102 has a height 127 measured from the 
larger-diameter disc surface of the base ring 101 of about 9.11 mm and a 
thickness of about 4.00 mm. 
Then, as shown in FIG. 3, the top view of the ceramic ring of FIG. 1, a 
total often prismatic projections 103-112 are located on the top ring-edge 
surface of the wall ring 102. Arrangement of the locations of these ten 
projections is as follows. Each of the prismatic projection pairs 107 and 
108, 108 and 109, 109 and 110, 110 and 111, and 111 and 112 are separated 
by about 45-degrees measured from the center of the ceramic ring 100. The 
center point 116 between prismatic projections 103 and 104 along the top 
edge surface of the wall ring 102 is also separated by about 45 degrees 
from the projection 112. In a similar manner, the center point 117 between 
prismatic projections 105 and 106 along the top edge surface of the wall 
ring 102 is separated by about 45 degrees from the projection 107. 
Further, the center points 116 and 117 are also 45-degrees apart. The 
distance between the prismatic projections 103 and 104, as well as between 
105 and 106, is about 8.00 mm. 
FIG. 4 is an enlarged and detailed view of the portion IV identified in 
FIG. 3. Since all ten prismatic projections 103-112 have basically the 
same structural configuration, only one, projection 112, is detailed in 
this drawing. 
The base of prismatic projection 112 has a width that is substantially the 
same as the width of the wall ring 102 as it rises above the surface of 
the top edge of the wall ring 102 in the form of a triangular column lying 
on one of its side surfaces. Quantitatively, the width of the base of the 
prismatic projection 112 is about 4.00 min. The end triangular surface 118 
of the prismatic projection 112 rises from the base when observed from the 
counterclockwise direction identified by reference numeral 125, as shown 
in the detailed view. The height of the projection 112 above the top edge 
surface of the wall ring 102 is about 3.01 mm 
The two side surfaces 120 and 121 of the triangular column of the 
projection 112 have base line lengths of about 1.50 and 2.00 mm, 
respectively, along the longitudinal direction of the column body. The 
inner side surface 120 has a length shorter than the outer side surface 
121, since the prismatic column of the projection is curved substantially 
in accordance with the circular curvature of the wall ring 102. Two side 
surfaces 120 and 121 of the triangular column-shaped prismatic projection 
112 are joined at the apex line 119. 
These ten prismatic projections 103-112 are used to provide adequate and 
smooth guidance for the silicon wafer in traveling down to the lower 
electrode of the dry etcher. However, conventional ceramic rings, such as 
the one described above with reference to FIGS. 1-4 have a short base line 
length for their guiding sloped surfaces. In fact, in the case of the 
conventional ceramic ring of FIGS. 1-4, the lengths of the base lines of 
the inner and outer side surfaces 120 and 121 of the prismatic projection 
112 are too short. These short base lengths result in excessive stress 
generated against the guiding prismatic projections when wafers are 
sliding downward guided by these projections. The guiding projections are 
therefore easily broken, and broken guiding projections misguide, rather 
than properly guide the wafers. 
When such misguidance of the wafer down to the dry etcher lower electrode 
occurs, the continuous fabrication procedure must be disrupted, and, if 
the wafer has not reached its correct position over the surface of the 
bottom electrode of the etcher, photoresist burn may develop. Further, ten 
or fewer guiding prismatic projections do not smoothly guide the wafers to 
correctly descend to the lower electrode of the dry etcher. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention to provide a ceramic ring for 
more smoothly guiding a semiconductor wafer down to the lower of two 
electrodes of a dry etcher in a semiconductor fabrication process. 
The invention achieves the above-identified object by providing a 
structural configuration for a ceramic ring for guiding a semiconductor 
wafer down to the lower electrode of a dry etcher having upper and lower 
electrodes. The ceramic ring includes a base ring, a wall ring rising 
substantially perpendicular to one surface of the base ring, and more than 
ten projections located on the top edge surface of the wall ring. Each of 
the projections includes a first and a second triangular surface, each at 
one end of the projection rising above the top edge surface of the wall 
ring. An inner sloped surface of the projection rises above the top edge 
surface of the wall ring and an outer sloped surface of the projection 
also rises above the top edge surface of the wall ring. First and second 
small sloped surfaces rise above the top edge surface of the wall ring, 
each spanning between-the triangular surfaces and the inner sloped 
surface, respectively. A trapezoidal surface having four sides, one each 
joined to the inner and outer sloped surfaces and the first and second 
small sloped surface forms the top apex surface of the projection. 
More particularly, the invention is directed to an improvement in a dry 
etcher having an upper electrode and a lower electrode, and a ceramic ring 
for guiding a semiconductor wafer to be etched down to the lower 
electrode. The ring includes a base ring, a wall ring rising substantially 
perpendicular to one face of the base ring, and a number of projections 
located on the top edge surface of the wall ring. The improvement includes 
a first triangular surface at one end of the projection, rising above the 
top edge surface of the wall ring; a second triangular surface generally 
parallel to the first triangular surface at the other end of the 
projection rising above the top edge surface of the wall ring; an inner 
sloped surface rising above the top edge surface of the wall ring; an 
outer sloped surface rising above the top edge surface of the wall ring; a 
first oblique sloped surface rising above the top edge surface of the wall 
ring and connecting the first triangular surface to the inner sloped 
surface; a second oblique sloped surface rising above the top edge surface 
of the wall ring and connecting the second triangular surface to the inner 
sloped surface; and an apex surface having four sides, one each joined to 
the inner sloped surface, the outer sloped surface, the first small sloped 
surface, and the second small sloped surface.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 5 shows a perspective view of a ceramic ring 501 as observed at 
approximately a 45-degree angle according to a preferred embodiment of the 
invention. The ceramic ring 501 comprises a base ring 201, a wall ring 
202, and a number of projections 203, 204, . . . , and 219. The entire 
ceramic ring is generally made in one single piece integrally. 
With simultaneous reference to FIG. 6, the side view of the ceramic ring 
501, it can be seen that the base ring 201 is generally a disc-shaped ring 
while the wall ring 202 is a tube-shaped ring. The wall ring 202 rises 
generally (approximately) perpendicularly at the inner edge of the 
disc-shaped base ring 201, and the ceramic ring 501 reveals an L-shaped 
cross section if cut diametrically. In FIG. 6, it is shown that the two 
faces of the base ring 201 have different diameters. Essentially, the face 
opposite the direction of the rise of the wall ring 202 has a diameter 221 
that is smaller than the diameter 220 of the other disc face, forming a 
tapered outer edge of the base ring 201, as shown in the drawing. The wall 
ring 202 has an inner opening with a diameter 222. 
In one preferred embodiment, the base ring 201 has a thickness of about 
4.97 mm. Its larger diameter 220 is about 172.40 mm and its smaller 
diameter 221 is about 167.20 mm. The inner opening diameter 222 of the 
wall ring is about 151.30 mm. It should be noted that all these diameters 
220, 221, and 222 are measured and obtained from concentric circles of the 
ceramic ring. Wall ring 202 has a height measured from the larger-diameter 
disc surface of the base ring 201 of about 9.11 mm and a thickness of 
about 4.00 mm. This embodiment has these dimensions to accommodate a 
standard size wafer. The dimensions may be altered is a different size 
wafer is used. 
FIG. 7 shows the top view of the ceramic ring 501 of the invention, having 
a total of more than ten, e.g., 17, projections 203-219 located on the top 
ring-edge surface 701 of the wall ring 202. Arrangement of the locations 
of these 17 projections is as follows. Each of the projection pairs 207 
and 208, 208 and 209, . . . , and 218 and 219 are separated by about a 
22.5-degree angular distance. The center point 223 between projections 203 
and 204 along the top edge surface of the wall ring 202 is also separated 
by about 22.5 degrees from the projection 219. In a similar manner, the 
center point 224 between projections 205 and 206 along the top edge 
surface of the wall ring 202 is separated by about 22.5 degrees from the 
projection 207. Note, however, that the center points 223 and 224 are 
about 45-degrees apart. The distance between the projections 203 and 204, 
as well as between 205 and 206, is about 6.00 mm. 
FIG. 8 is an enlarged and detailed view of the portion VIII identified in 
FIG. 7. Since all 17 projections 203-219 have basically the same 
structural configuration, only one projection 218 is detailed in this 
drawing. 
The base of projection 218 has a width that is substantially the same as 
the thickness of the wall ring 202 as it rises from the surface of the top 
edge of the wall ring 202. In other words, the width of the base of the 
projection 218 is about 4.00 mm. The end triangular surface 225 of the 
projection 218 rises from its base when observed from the counterclockwise 
direction identified by reference numeral 240, as shown in the detailed 
view. The height of the projection 218 above the top edge surface of the 
wall ring 202 is about 3.01 mm. 
The two side surfaces 227 and 228 of the projection 218 have lengths of 
about 2.00 and 3.00 mm, respectively, along the longitudinal direction of 
the column body. The inner side surface 227 has a length shorter than the 
outer side surface 228, since the projection is curved substantially in 
accordance with the circular curvature of the wall ring 202. In addition, 
two smaller oblique sloped surfaces 229 and 230 are also provided between 
the inner side surface 227 and the two end triangular surfaces 225 at both 
ends of the projection 218. Essentially, this prevents the base line of 
the end triangular surface 225 from reaching the inner edge of the wall 
ring 202. The same applies to the other end triangular surface at the 
other end of the projection 218. The two large side surfaces 227 and 228 
of the projection 218, as well as the two smaller sloped surfaces 229 and 
230, all rise from the top edge surface of the wall ring 202, and all four 
surfaces are joined at an apex surface 231, which has a trapezoidal shape 
as shown in the drawing. The apex surface 231 is a trapezoid having a 
width of 0.6 mm between its two parallel edges. 
In accordance with the ceramic ring of the invention as described above 
with reference to the accompanying drawing of FIGS. 5-8, physical 
embodiments were made and tested, showing that the guidance down to the 
lower electrode of the dry etcher provided by the ring of the invention is 
smoother than that of the prior art counterpart for wafers. Photoresist 
burn situations were therefore avoided and the fabrication procedure 
operated more smoothly with improved processing efficiency. 
While the invention has been described by way of example and in terms of a 
preferred embodiment, it is to be understood that the invention is not 
limited to the disclosed embodiment. To the contrary, it is intended to 
cover various modifications and similar arrangements. The appended claims, 
therefore, should be accorded the broadest interpretation so as to 
encompass all such modifications and similar structures.