Abstract:
A method of etching a substrate and an article(s) formed using the method are provided. The method includes providing a substrate; coating a region of the substrate with a temporary material having properties that enable the temporary material to remain substantially intact during subsequent processing and enable the temporary material to be removed by a subsequent process that allows the substrate to remain substantially unaltered; removing a portion of the substrate to form a feature, at least some of the removed portion of the substrate overlapping at least a portion of the coated region of the substrate while allowing the temporary material substantially intact; and removing the temporary material while allowing the substrate to remain substantially unaltered.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly assigned, pending U.S. patent application Ser. No. 10/911,186 filed concurrently herewith, entitled “A FLUID EJECTOR HAVING AN ANISOTROPIC SURFACE CHAMBER ETCH”, in the name of James M. Chwalek, et al., the disclosure of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates, generally, to the etching of features in monocrystalline wafer substrates and, more particularly, to a method of forming an etched feature which is connected to at least one orientation dependent etched feature without compromising the dimensional control inherent in an orientation dependent etching process. 
     BACKGROUND OF THE PRIOR ART 
     Orientation dependent etching (ODE) is a wet etching step which attacks different crystalline planes at different rates. As is well known in the art of orientation dependent etching, etchants such as potassium hydroxide, or TMAH (tetramethylammonium hydroxide), or EDP etch the (111) planes of silicon much slower (on the order of 100 times slower) than they etch other planes. A well-known case of interest, described in U.S. Pat. No. 3,765,969, is the etching of a monocrystalline silicon wafer having (100) orientation. There are four different orientations of (111) planes which intersect a given (100) plane. The intersection of a (111) plane and a (100) plane is a line in a [110] type direction. There are two different [110] directions contained within a (100) plane. They are denoted as [011] and [01-1] and are perpendicular to one another. Thus, if a monocrystalline silicon substrate having (100) orientation is covered with a layer, such as oxide or nitride which is resistant to etching by KOH or TMAH, but is patterned to expose a rectangle of bare silicon, where the sides of the rectangles are parallel to [110] type directions, and the substrate is exposed to an etchant such as KOH or TMAH, then a pit will be etched in the exposed silicon rectangle. If the etch is allowed to proceed to completion, then the pit will have four sloping sides, each side being a different (111) plane. Because the (111) planes etch so slowly, the process is said to be self-terminating. The shape and dimensions of the pit are very predictable and reproducible, being relatively insensitive to the etch bath conditions or etching duration, as long as the etching has been allowed to proceed to completion. If the length and width of the rectangle of exposed silicon were L and W respectively, and if L=W, then the four (111) planes would meet at a point, and the pit would be pyramid shaped. The (111) planes are at a 54.7 degree angle with respect to the (100) surface. The depth H of the pit is half the square root of 2 times the width, that is, H=0.707 W. If L&gt;W, then the maximum depth H is still 0.707 W and the shape of the pit is a V groove with sloped sides and sloped ends. The length of the region of maximum depth of the pit is L−W. Of course, if the thickness of the substrate is less than 0.707 W, and if the etch is allowed to proceed to completion, then a hole will be etched through the substrate. 
     One constraint of orientation dependent etching of self-terminated pits in (100) wafers is that, if etched to completion, they will intersect the wafer surface as a rectangle whose sides are parallel to [110] type directions. Arbitrary shapes are not allowed.  FIG. 1A  is a top view of a self-terminated orientation dependent etched pit  11  having length L and width W in a (100) wafer. Region  12  has been covered by masking layer, such as an oxide or a nitride, so that the (100) wafer surface was not exposed to the etchant. Region  13  is a rectangle with sides parallel to [110] directions. In region  13 , the masking layer was removed prior to orientation dependent etching, so that the wafer surface was exposed.  FIG. 1B  is a cross-section of rectangular pyramid shaped pit  11  through line  1 B- 1 B. Maximum depth of pit  11  is H=0.707 W. 
       FIG. 2  shows one example of what occurs if the exposed region  23  is not a rectangle with sides parallel to [110] type directions. As seen in the top view of  FIG. 2A , all sides of the exposed region are parallel to [110] type directions, but the exposed region  23  has an abrupt change in width from W 1  to W 2 , as if a wide rectangle having length L 1  and a narrow rectangle having length L 2  had been exposed end to end. Stated in another way, the exposed region  23  is a polygon with at least one convex corner  24 . A convex corner is defined here as a region which bulges into the polygon. A convex corner has the property that if a line is drawn between adjacent sides of the corner, the line will lie outside the polygon. Line  25  in  FIG. 2A  is an example. There are two convex corners in  FIG. 2A , but only convex corner  24  is labeled.  FIG. 2B  shows a top view of the resulting pit  21  if etched to completion. The masking layer has been removed for greater visibility of the etched pit  21 . Etching continues at a rapid rate even under the masking layer  22 , until the final shape is a rectangular pyramid having width W 1 , length L 1 +L 2 , maximum depth H=0.707 W 1 , and no convex corners. 
       FIG. 3  shows a second example of what occurs if the exposed region is not a rectangle. In this case, the exposed region  33  consists of two rectangles, each having sides parallel to [110] type directions, which intersect in a T. Exposed region  33  has two convex corners, one of which is labeled as  36 . Line  37  is drawn between adjacent sides to the convex corner and lies outside exposed region  33 . The length and width of rectangle  34  are L 1  and W 1 , and the length and width of rectangle  35  are L 2  and W 2 , where L 2 &gt;L 1 .  FIG. 3B  shows a top view of the resulting pit  31  if etched to completion. Etching will continue at a rapid rate even under the masking layer  32  until the final shape is a rectangular pyramid having length W 1 +L 2 , width L 1 , maximum depth H=0.707 L 1 , and no convex corners. 
     Because of the precision and reproducibility of orientation dependent etched features in (100) wafers, a variety of applications have been developed. One family of applications is related to the formation of fluid passageways, including fluid inlet holes, fluid filters, fluid manifolds, fluid flow restrictors, and individual fluid channels. It is frequently desired to join one or more of such fluid passageway components in a fluidic device, such as an ink jet printhead. However, due to the constraints of orientation dependent etching described above, such different components typically cannot be joined together by means of orientation dependent etching to completion. 
     U.S. Pat. No. 4,601,777 discusses various processes for fabricating thermal ink jet printheads.  FIG. 4  shows a top view of a group of ink channels  41  which are desired to be fluidically connected to ink manifold  42 . In this case the V-shaped grooves which will comprise channels  41  are formed by a self-terminating orientation dependent etching process, which is preferred because it is desired to precisely control the channel dimensions. The ink manifold  42  is formed by a timed orientation dependent etching process. The grooves forming the channels are formed close to the manifold, but not connected to it in the initial etching process. A narrow region  43  initially isolates the channel grooves from the manifold. Two alternatives are disclosed for making fluidic connection between the manifold  42  and the channels  41 . The first alternative is to isotropically etch to undercut the nitride mask in the narrow isolation region  43 , followed by a brief orientation dependent etch to complete the opening of the channels to the manifold. A disadvantage of this approach is that during the timed orientation dependent etch to join the channels to the manifold, the walls  44  between channels  41  nearest to the ends of the channels closest to the manifold  42  etch at a rapid rate, so that the precision and reproducibility of the channel dimensions are compromised somewhat. A second alternative described by U.S. Pat. No. 4,601,777 is to remove the narrow region  43  by a subsequent dicing operation. A disadvantage of this alternative, which is disclosed in the patent, is that the dicing operation also removes material which is not desired to be removed and which must be replaced in a subsequent sealing operation. 
     A second configuration of joining of fluidic passageways formed by orientation dependent etching is described in U.S. Pat. No. 4,639,748. In this case it is desired to join an orientation dependent etched fluid manifold to a particle filter comprised of a pattern of recesses which have been orientation dependent etched. The method of making the connection is to use an isotropic etch followed by an orientation dependent etch, similar to the first alternative described above for U.S. Pat. No. 4,601,777. 
     A third instance of joining of fluidic passageways formed by orientation dependent etching is described in U.S. Pat. No. 4,774,530. In this case it is desired to connect ink jet channels to an ink manifold. The channels and manifold are etched in an upper substrate with is aligned and mated to a lower substrate. On the lower substrate is a thick film layer which is patterned in such a way that fluidic connection is made between the channels and manifold. Such a thick film layer, however, is not always available in devices where it is desired to make passageways to connect orientation dependent etched features. 
     In addition to the forming of fluidic passageways, orientation dependent etched features are also used various other different types of applications. For example, the capability of forming precision V grooves by orientation dependent etching has been frequently used as a means for precision alignment of optical components, such as the end-to-end alignment of optical fibers, or the alignment of a laser to optical fibers. 
     Furthermore, orientation dependent etched features have been used in processes for fabrication of integrated circuit components, for example providing electrical isolation while minimizing parasitic capacitance (U.S. Pat. No. 4,685,198). 
     Orientation dependent etching is also frequently used in fabrication of a variety of microelectromechanical systems (or MEMS) devices. 
     Recognizing that orientation dependent etching has a wide range of applications, and that methods are desirable for forming a passageway or recess which is connected to one or more orientation dependent etched feature, this invention is directed toward such methods. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a method of etching a substrate comprises providing a substrate; coating a region of the substrate with a temporary material having properties that enable the temporary material to remain substantially intact during subsequent processing and enable the temporary material to be removed by a subsequent process that allows the substrate to remain substantially unaltered; removing a portion of the substrate to form a feature, at least some of the removed portion of the substrate overlapping at least a portion of the coated region of the substrate while allowing the temporary material substantially intact; and removing the temporary material while allowing the substrate to remain substantially unaltered. 
     According to another aspect of the present invention, an article includes a first feature having a first width formed from a self-terminated orientation dependent etching process. A second feature having a second width and a third feature are provided. The second feature connects the first feature and the third feature with the first width being greater than the second width. 
     According to another aspect of the present invention, an article includes a first feature having a first depth formed from a self-terminated orientation dependent etching process. A second feature having a second depth and a third feature are provided. The second feature connects the first feature and the third feature with the first depth being greater than the second depth. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the detailed description of the embodiments of the invention presented below, reference is made to the accompanying drawings, in which: 
         FIG. 1A  is a top view of a self-terminated orientation dependent etched pit in a (100) wafer. 
         FIG. 1B  is a cross-sectional view of the rectangular pyramid shaped pit of  FIG. 1A , as seen along the direction  1 B- 1 B. 
         FIG. 2A  is top view of a mask pattern on a (100) wafer where the exposed region is two rectangles of different width which are joined end to end. 
         FIG. 2B  is a top view of an orientation dependent etched pit where the etching was done to completion through the mask pattern of  FIG. 2A . 
         FIG. 3A  is a top view of a mask pattern on a (100) wafer where the exposed region is two rectangles intersecting at a T. 
         FIG. 3B  is a top view of an orientation dependent etched pit where the etching was done to completion through the mask pattern of  FIG. 3A . 
         FIG. 4  is a top view of prior art application of orientation dependent etched ink jet channels adjacent to an orientation dependent etched manifold. 
         FIG. 5A  shows a top view of a step in a first embodiment in which a mask layer on the substrate has been patterned to expose the substrate for etching a recess. 
         FIG. 5B  shows a cross-sectional view of the substrate and patterned mask layer, as seen along the direction  5 B- 5 B. 
         FIG. 6A  shows a top view following the subsequent step of etching a recess by DRIE. 
         FIG. 6B  shows a cross-sectional view of the substrate, etched recess and patterned mask layer, as seen along the direction  6 B- 6 B. 
         FIG. 7A  shows a top view following the subsequent step of coating the substrate surface with a temporary material. 
         FIG. 7B  shows a cross-sectional view of the substrate, etched recess, temporary layer and patterned mask layer, as seen along the direction  7 B- 7 B. 
         FIG. 8A  shows a top view following the subsequent step of polishing the surface to remove the temporary material except in the recess. 
         FIG. 8B  shows a cross-sectional view of the substrate, etched recess, and temporary layer in the recess, as seen along the direction  8 B- 8 B. 
         FIG. 9A  shows a top view following the subsequent step of patterning a masking layer such that the exposed region at least partly overlaps the coated layer in the recess. 
         FIG. 9B  shows a cross-sectional view of the substrate, etched recess, temporary layer in the recess, and patterned masking layer, as seen along the direction  9 B- 9 B. 
         FIG. 10A  shows a top view following the subsequent step of orientation dependent etching. 
         FIG. 10B  shows a cross-sectional view of the substrate, etched recess, orientation dependent etched feature, temporary layer which is in the recess and which cantilevers over the orientation dependent etched feature, and patterned masking layer, as seen along the direction  10 B- 10 B. 
         FIG. 11A  shows a top view following the subsequent step of removing the temporary layer and the patterned mask layer. 
         FIG. 11B  shows a cross-sectional view of the substrate, the orientation dependent etched feature and the recess which is connected to it, as seen along the direction  11 B- 11 B. 
         FIG. 12A  shows a top view of a second embodiment in which the recess connects orientation dependent etched features at both ends. 
         FIG. 12B  shows a cross-sectional view, as seen along direction  12 B- 12 B. 
         FIG. 13A  shows a top view of a third embodiment in which a plurality of recess connects orientation dependent etched features at both ends. 
         FIG. 13B  shows a cross-sectional view, as seen along direction  13 B- 13 B. 
         FIG. 14A  shows a top view of a fourth embodiment in which the recess is formed by orientation dependent etching. 
         FIG. 14B  shows a cross-sectional view, as seen along direction  14 B- 14 B. 
         FIG. 15A  shows a top view of a fifth embodiment in which the recess is formed by isotropic etching. 
         FIG. 15B  shows a cross-sectional view, as seen along direction  15 B- 15 B. 
         FIG. 16A  shows a top view of a step of forming a recess in a surface of a substrate. 
         FIG. 16B  shows a cross-sectional view, as seen along direction  16 B- 16 B. 
         FIG. 17A  shows a top view of a subsequent step of filling the recess with a temporary material. 
         FIG. 17B  shows a cross-sectional view, as seen along direction  17 B- 17 B. 
         FIG. 18A  shows a top view of a multilayer stack over the filled recess. 
         FIG. 18B  shows a cross-sectional view, as seen along direction  18 B- 18 B. 
         FIG. 19A  shows a top view after a subsequent step of forming a nozzle hole through the multistack layer. 
         FIG. 19B  shows a cross-sectional view, as seen along direction  19 - 19 B. 
         FIG. 20A  shows a top view after a subsequent step of etching a fluid chamber and an impedance channel. 
         FIG. 20B  shows a cross-sectional view, as seen along direction  20 B- 20 B. 
         FIG. 21A  shows a top view after a subsequent step of removing the temporary material from the recess. 
         FIG. 21B  shows a cross-sectional view, as seen along direction  21 B- 21 B. 
         FIG. 22A  shows a top view after a subsequent step of forming a fluid delivery channel. 
         FIG. 22B  shows a cross-sectional view, as seen along direction  22 B- 22 B. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present description will be directed, in particular, to elements forming part of, or cooperating directly with, apparatus or processes of the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. 
       FIGS. 5-11  illustrate a first embodiment of a method of forming an etched recess which is joined to at least one orientation dependent etched feature, without compromising the dimensional control inherent in orientation dependent etching. The general approach is to first etch the recess, and then coat it (and optionally fill it) with a temporary layer; then expose an overlapping region of substrate and etch it with an orientation dependent etch process; and then remove the temporary material from the etched recess feature. 
       FIG. 5  shows a top view and a cross-sectional view of a (100) wafer substrate  112  having a top surface  116  upon which a masking layer  113  has been deposited and patterned to expose a region  114  of wafer surface. Note: region  114  is depicted as a rectangle, but it may be comprised of one or more contiguous or noncontiguous regions of somewhat arbitrary shape, including polygonal shapes or curved shapes. Masking layer  113  may be an oxide or nitride material for example. 
       FIG. 6  shows a top view and a cross-sectional view of the same region, after a recess  115  has been etched at location  114 . The lateral shape of the recessed feature will be determined largely by the patterned shape of region  114 , while the cross-sectional shape will be dependent largely on the etch process used. A deep reactive ion etch process (DRIE) will provide a recess with vertical sidewalls. An isotropic etch process will provide a more rounded structure. An orientation dependent etched process will provide an angled pit, similar to that shown in  FIG. 1 . In  FIG. 6 , the recessed feature is depicted as having vertical sidewalls characteristic of DRIE processing. 
       FIG. 7  shows a top view and a cross-sectional view of the same region, after the surface has been coated with a temporary material  120 . In  FIG. 7  the thickness of the temporary coating is sketched as being less than the depth of the recess  115 , so that the top of layer  120  in the recess  115  is lower than the wafer surface  116 . However, optionally the thickness of temporary coating may be equal to or greater than the depth of the recess  115 . The temporary material may, for example, be comprised of a blanket coated layer of TEOS which has been deposited by plasma-enhanced chemical vapor deposition. A second example of temporary material is a glass layer which is spun on and then heat treated to form a blanket coating. Although  FIG. 7  shows the temporary material  120  as being coated over the masking layer  113 , it is also possible to remove the masking layer  113  prior to coating the wafer  112  with the temporary material  120 . Optionally, a nitride masking layer  113  may be used as an etch stop in a subsequent step of chemical mechanical polishing, and then removed. 
       FIG. 8  shows a top view and a cross-sectional view of the same region, after the surface has been polished, for example by a chemical mechanical polishing process, to expose wafer substrate surface  116 . The temporary material  120  still covers the floor and sidewalls of the recess  115 . If the temporary material  120  had been deposited in a thickness greater than the depth of the recess  115 , the step of polishing would have resulted in the top of the temporary material  120  being at the same level as the top of the substrate  116 . 
       FIG. 9  shows a top view and a cross-sectional view of the same region, after a masking layer  130  has been deposited and patterned to expose a rectangular area  131  having its sides parallel to [110] type directions. Exposed rectangular area  131  overlaps the coated recess  115 . In other words, portion  122  of temporary material  120  is enclosed within exposed rectangular area  131 , while portion  121  of temporary material  120  is outside of rectangular area  131 , so that portion  121  is coated with masking layer  130 . In addition, width W 2  of the exposed rectangular area  131  is greater than width W 1  of the coated recess  115  in the area where these two overlap one another. 
       FIG. 10  shows a top view and a cross-sectional view of the same region, after orientation dependent etching to form feature  132 . Feature  132  and coated recess  115  have been designed with respect to one another so that feature  132  is both wider and deeper than coated recess  115  in the area where they overlap one another. As a result, if orientation dependent etching is allowed to proceed to completion, feature  132  will continue to etch below coated recess  115 , so that portion  122  of temporary material is left extending partially over feature  132  in cantilever fashion. 
       FIG. 11  shows a top view and a cross-sectional view of the same region, after the masking layer  130  and temporary material  120  (portion  121  as well as portion  122 ) have been removed. If masking layer  130  is an oxide, it may be removed at the same time as temporary material  120  by using a buffered solution of HF. Note that the composite etched region, comprised of the orientation dependent etched feature  132  and the formerly coated recess  115 , has two convex corners  119 , each of which is at the point of connection between feature  132  and recess  115 . Further note that the precise dimensions (width, depth and length) and shape of feature  132  (provided by the self-terminated orientation dependent etch process) have not been compromised in providing connecting recess  115 . 
     A second embodiment is shown in  FIG. 12 . In this case the method is the same as that described with reference to  FIGS. 5-11 . At the step corresponding to  FIG. 9 , regions which do not overlap one another in the masking layer have been made to overlap at each end of the coated recess  115 . In the subsequent orientation dependent etching step, (corresponding to  FIG. 10 ) temporary material  120  cantilevers over orientation dependent etched features at each end. Finally, when temporary material  120  is removed, the composite etched region shown in  FIG. 12  results. In this particular case, orientation dependent etched feature  133  is shown as wider and deeper than orientation dependent etched feature  132 . Both features  132  and  133  are wider and deeper than connecting recess  115 . 
     A third embodiment is shown in  FIG. 13 . In this case the method is again the same as that described with reference to  FIGS. 5-11 . At the step corresponding to  FIG. 5 , the mask pattern for the etched recess was patterned to expose a plurality of recesses  115   a ,  115   b  and  115   c . Similar to  FIG. 12 , orientation dependent etched features  132  and  133  are connected by recesses. 
     Although  FIGS. 1-13  have shown the recess  115  with vertical sidewalls, consistent with a DRIE process, other types of etching may be used to form the recess.  FIG. 14  shows the case where orientation dependent etching has been used to form the recess in the process sequence step which is similar to  FIG. 6 . This is an interesting case in that two orientation dependent etched features are made to connect directly end to end without compromising the width or depth of either feature. 
       FIG. 15  shows the case where the recess has been formed by using isotropic etching in the process sequence step which is similar to  FIG. 6 . 
     The embodiments discussed thus far have been described in the context of connecting a recess to an orientation dependent etched feature which is at the top surface of the substrate. The next embodiment will describe the connection of a recess to an orientation dependent etched feature where the feature and the recess are covered by a layer which forms a roof over them. Such a structure is useful as a fluid chamber and fluid passageway in a microfluidic device, such as an ink jet printhead. Copending U.S. patent application Ser. No. 10/911,186, entitled A Fluid Ejector Having An Anisotropic Surface Chamber Etch, describes such a microfluidic device in greater detail. 
       FIGS. 16-22  illustrate an embodiment for forming a constriction in a fluid path between the fluid delivery channel and the nozzle of a fluid ejecting device. In this embodiment, the constriction is formed by connecting an orientation dependent etched fluid chamber and an orientation dependent etched impedance channel by means of a previously formed recess, said recess having a temporary material removed from it after the orientation dependent etching of the fluid chamber and the impedance channel is completed. 
       FIG. 16  shows the first step of etching a recess  215  into first surface  216  of (100) orientation silicon substrate  212 . The recess  215  may be etched by a variety of isotropic or anisotropic means. However, in this embodiment, it is shown, for example, to be etched by reactive ion etching. This recess has lateral dimensions l and w, and a depth d. 
       FIG. 17  shows recess  215  substantially filled with temporary material  220  having the following properties: a) it must be capable of filling the recess  215 ; b) it must be able to withstand the subsequent processing steps; c) it must be etched slowly or not at all by the etchant used to etch the temporary material above the fluid chamber; d) it must be etched slowly or not at all by the ODE etchant used in the fluid chamber etch step; and e) it must be removable by an etch process which does not substantially attack exposed silicon. Examples of such a material are TEOS or glass. In  FIG. 17 , the top of the temporary recess-filling material  220  is shown to be at the same level as the first surface  216  of the silicon substrate. The excess temporary material  220  which may have been deposited on surface  216  has been removed, by steps which may include chemical mechanical polishing. 
       FIG. 18  shows the result of processing steps for a multilayer stack  240  over the recess filled with temporary material  220 . The multilayer stack  240  in the vicinity of the fluid chamber also serves as a nozzle plate. Containing several levels of metals, oxide and/or nitride insulating layers, multilayer stack  240  is typically on the order of 5 microns thick. The lowest layer of the multilayer stack  240 , formed directly on silicon surface  216  is an oxide or nitride layer  241 . Hereinafter layer  241  will be referred to as an oxide layer. Layer  241  has the property that it may be differentially etched with respect to the silicon substrate in the etch step that will form the fluid chamber. As part of the processing steps for the multilayer stack  240 , a region  242   a  of oxide is removed, corresponding to the subsequent location of the fluid chamber, and a region  242   b  of oxide is removed, corresponding to the subsequent location of the impedance channel. Layer  243  is a sacrificial layer which is deposited over the oxide layer  241 , and then which is patterned so that the remaining sacrificial layer material  243   a  is slightly larger than the window  242   a  in the oxide layer  241 , and remaining sacrificial material  243   b  is slightly larger than window  243   a  in the oxide layer  241 . In other words, there is a small region of overlap  244 , on the order of 1 micron, where the sacrificial layer  243  is on top of oxide layer  241  at the extreme ends of the fluid chamber and the impedance channel. Sacrificial layer  243  may be one of a variety of materials. A particular material of interest as a sacrificial layer  243  is polycrystalline silicon, or polysilicon. The patterned sacrificial layer  243  remains in place during the remainder of the processing of multilayer stack  240 , but is removed later during the formation of the fluid chamber. 
       FIG. 19  illustrates the step of etching the nozzle  252 .  FIG. 20  shows the result of etching of the sacrificial layer  243  as well as the fluid chamber  260 , and the impedance channel  261  by introducing an etchant through nozzle  252 . For the case where the sacrificial layer  243  is polysilicon, it may be etched in the same process step as the orientation dependent etching of the fluid chamber  260  and the impedance channel  261 . Alternatively, sacrificial layer  243  is removed using a first etchant. Then the fluid chamber  260  and the impedance channel  261  are orientation dependent etched using a second etchant. Recess-filling temporary material  220  is substantially not affected by either the etch of the sacrificial layer  243  or by the orientation dependent etch step to form the fluid chamber  260  and the impedance channel  261 . 
       FIG. 21  shows the result of etching the recess-filling temporary material  220  from the recess  215  using an etchant which does not substantially affect exposed silicon. The connection between the orientation dependent etched fluid chamber  260  and the orientation dependent etched impedance channel  261  has been made by the interposed recess  215  without affecting the dimensional precision of either feature. Convex corners  262  occur at the intersection of the recess  215  and the fluid chamber  260 , as well as at the intersection with impedance channel  261 . 
       FIG. 22  shows a subsequent step of formation of the fluid delivery channel  270  by deep reactive ion etching from the backside of the silicon substrate. The fluid delivery channel is not an inherent part of the present invention of connecting to at least one orientation dependent etched feature having a roof over it, but it does show the completion of a fluid ejecting device. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention. 
     PARTS LIST 
     In the following list, parts having similar functions in the various embodiments are numbered similarly.
       11  self-terminated orientation dependent etched pit     12  region protected by masking layer     13  rectangular region where mask layer pattern exposes substrate     21  self-terminated orientation dependent etched pit from end-to-end pit mask     22  region protected by masking layer     23  end-to-end rectangles where mask layer pattern exposes substrate     24  convex corner between two connecting rectangles of different widths     25  line between points on the two sides adjacent to convex corner     31  self-terminated orientation dependent etched pit from T intersection pit mask     32  region protected by masking layer     33  T intersection rectangles where mask layer pattern exposes substrate     34  one rectangle at T intersection     35  a second rectangle at T intersection     36  convex corner at the intersection of the two rectangles     37  line between points on the two sides adjacent to convex corner     41  group of ink channels     42  ink manifold     43  narrow region isolating ink channels from ink manifold     44  channel walls near ink manifold     112  wafer substrate with (100) orientation     113  masking layer     114  region where masking layer is removed to expose wafer substrate     115  etched recess     116  top surface of wafer substrate     119  convex corner between etched recess and orientation dependent etched feature     120  temporary material     121  portion of temporary material coated with masking layer     122  portion of temporary material from which masking layer has been removed     130  masking layer     131  rectangular region from which masking layer has been removed     132  orientation dependent etched feature, partly overlapping etched recess     133  second orientation dependent etched feature, partly overlapping etched recess     212  (100) orientation silicon substrate     215  etched recess     216  first surface of silicon substrate     220  temporary material     240  multilayer stack     241  oxide layer on silicon surface     242  regions of oxide layer which have been patterned away     243  sacrificial layer     244  overlap of sacrificial layer over oxide layer     252  nozzle hole     260  fluid chamber     261  impedance channel     262  convex corners at intersection of recess with fluid chamber and impedance channel     270  fluid delivery channel