Patent Publication Number: US-2021170399-A1

Title: 3D Nanochannel Interleaved Devices

Description:
FIELD OF THE INVENTION 
     The present invention relates to nano-fabricated devices, and more particularly, to three-dimensional (3D) nanochannel interleaved devices for molecular manipulation using dipole moments. 
     BACKGROUND OF THE INVENTION 
     Molecular-level control of compounds has important applications in a variety of fields. In medicine, for instance, manipulation of molecules at the molecular level can be used to control the composition of medications. Such a fine-tuned control over the composition of medications can enable the creation of customized medicines and specific dosing. Further, molecular-level control can provide more efficient delivery systems for medications, thus advancing treatment options and efficacy. 
     However, the ability to effectively manipulate molecules at the molecular level remains challenging and difficult. Technology does not currently exist for production-scale molecular manipulation. 
     Accordingly, improved techniques for efficient and effective manipulation of molecules at the molecular level would be desirable. 
     SUMMARY OF THE INVENTION 
     The present invention provides three-dimensional (3D) nanochannel interleaved devices for molecular manipulation. In one aspect of the invention, a method of forming a device for molecular manipulation is provided. The method includes: forming a pattern on a substrate of alternating mandrels and spacers alongside the mandrels; selectively removing the mandrels from a front portion of the pattern forming gaps between the spacers; selectively removing the spacers from a back portion of the pattern forming gaps between the mandrels; filling i) the gaps between the spacers with a conductor to form first electrodes and ii) the gaps between the mandrels with the conductor to form second electrodes; and etching the mandrels and the spacers in a central portion of the pattern to form a channel (e.g., a nanochannel) between the first electrodes and the second electrodes, wherein the first electrodes and the second electrodes are offset from one another across the channel, i.e., interleaved. 
     In another aspect of the invention, a device is provided. The device includes: a channel (e.g., a nanochannel); first electrodes disposed in between spacers on a first side of the channel; and second electrodes disposed in between mandrels on a second side of the channel, wherein the first electrodes and the second electrodes are offset from one another across the channel, i.e., interleaved. 
     A more complete understanding of the present invention, as well as further features and advantages of the present invention, will be obtained by reference to the following detailed description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a three-dimensional diagram illustrating mandrels having been formed on a substrate according to an embodiment of the present invention; 
         FIG. 2  is a three-dimensional diagram illustrating spacers having been formed on opposite sides of the mandrels according to an embodiment of the present invention; 
         FIG. 3  is a three-dimensional diagram illustrating spaces between the spacers alongside adjacent mandrels having been filled with additional mandrel material according to an embodiment of the present invention; 
         FIG. 4  is a three-dimensional diagram illustrating a mask having been formed over back and central portions of the pattern, and an etch having been performed to selectively remove the mandrels from a front portion of the pattern creating gaps between the spacers according to an embodiment of the present invention; 
         FIG. 5  is a three-dimensional diagram illustrating the gaps between the spacers having been filled with a sacrificial material according to an embodiment of the present invention; 
         FIG. 6  is a three-dimensional diagram illustrating the mask having been removed according to an embodiment of the present invention; 
         FIG. 7  is a three-dimensional diagram illustrating a channel spacer having been formed over the central portion of the pattern according to an embodiment of the present invention; 
         FIG. 8  is a three-dimensional diagram illustrating the spacers having been removed from the back portion of the pattern creating gaps between the mandrels according to an embodiment of the present invention; 
         FIG. 9  is a three-dimensional diagram illustrating the sacrificial material having been selectively removed according to an embodiment of the present invention; 
         FIG. 10  is a three-dimensional diagram illustrating that the gaps between the spacers (in the front portion of the pattern) are offset from the gaps between the mandrels (in the back portion of the pattern) according to an embodiment of the present invention; 
         FIG. 11  is a three-dimensional diagram illustrating the gaps between the spacers and the gaps between the mandrels having been filled with a conductor according to an embodiment of the present invention; 
         FIG. 12  is a three-dimensional diagram illustrating the channel spacer having been removed forming a trench in the conductor according to an embodiment of the present invention; 
         FIG. 13  is a three-dimensional diagram illustrating the spacers and the mandrels in the central portion of the pattern having been removed through the trench forming a channel according to an embodiment of the present invention; 
         FIG. 14  is a three-dimensional diagram illustrating the conductor having been recessed forming first/second electrodes on opposite sides of the channel according to an embodiment of the present invention; 
         FIG. 15  is a top-down diagram illustrating that the first electrodes are offset from the second electrodes across the channel according to an embodiment of the present invention; 
         FIG. 16  is a three-dimensional diagram illustrating that the first electrodes are offset from the second electrodes across the channel according to an embodiment of the present invention; and 
         FIG. 17  is a three-dimensional diagram illustrating that, during operation, an electric field applied to the first/second electrodes will electrokinetically orient and/or locomote a polar molecule in the channel according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Provided herein are three-dimensional (3D) device structures for molecular manipulation that leverage the dipole within the molecule, as well as current nanofabrication techniques to precisely manufacture extremely small features, e.g., dimensions ranging from several micrometers (μm) to 10&#39;s of nanometers (nm). Further, the present techniques improve resolution through the interleaving of 3D spirally located electrodes enabling a much finer level of control and manipulation. 
     Namely, as will be described in detail below, advanced patterning techniques are leveraged herein to place the (interleaved) electrodes for field generation at precise locations at a molecular scale. Advanced etching techniques are used to precisely place channels of a nanoscale size at the center of the electrodes. By ‘interleaved’ it is meant that, instead of being directly opposite one another, the electrodes on opposite sides of the nanochannel are offset from one another. 
     Advantageously, the present 3D device structures permit the electro-kinetic control of individual molecules using the dipoles inherent in the subject material. For instance, during operation, applying a field selectively to portions of a molecule (via the electrodes) will electrokinetically orient and/or locomote the molecule in the nanochannel as a result of dynamic electric field application. Individual electrodes can be controlled individually and intelligently. 
     An exemplary methodology for forming a 3D device for molecular manipulation is now described by way of reference to  FIGS. 1-17 . As shown in  FIG. 1 , the process begins with the formation of mandrels  104  on a substrate  102 . 
     According to an exemplary embodiment, substrate  102  is a bulk semiconductor wafer, such as a bulk silicon (Si), bulk germanium (Ge), bulk silicon germanium (SiGe) and/or bulk III-V semiconductor wafer. Alternatively, substrate  102  can be a semiconductor-on-insulator (SOI) wafer. A SOI wafer includes an SOI layer separated from an underlying substrate by a buried insulator. When the buried insulator is an oxide it is referred to herein as a buried oxide or BOX. The SOI layer can include any suitable semiconductor, such as Si, Ge, SiGe, and/or a III-V semiconductor. Substrate  102  may already have pre-built structures (not shown) such as transistors, diodes, capacitors, resistors, isolation regions (e.g., shallow trench isolation (STI) regions), interconnects, wiring, etc. 
     To form the mandrels  104  on substrate  102 , a mandrel layer is first deposited onto the substrate  102  and then patterned into the individual mandrels  104  shown in  FIG. 1 . According to an exemplary embodiment, mandrels  104  are formed from an undoped oxide material. Suitable undoped oxide materials include, but are not limited to, undoped silicon oxide (SiOx). A process such as chemical vapor deposition (CVD), atomic layer deposition (ALD) or physical vapor deposition (PVD) can be used to deposit the mandrel material. 
     Mandrels  104  can be patterned using a patterning technique such as lithography followed by an etching process. With a lithography and etching process, a lithographic stack (not shown), e.g., photoresist/organic planarizing layer (OPL)/anti-reflective coating (ARC), is typically used to pattern a hardmask (not shown). The pattern from the hardmask is then transferred to the underlying substrate (in this case the mandrel layer). The hardmask is then removed. Suitable etching processes include, but are not limited to, a directional (anisotropic) etching process such as reactive ion etching (RIE). Alternatively, the mandrels  104  can be formed by other suitable techniques, including but not limited to, sidewall image transfer (SIT), self-aligned double patterning (SADP), self-aligned quadruple patterning (SAQP), and other self-aligned multiple patterning (SAMP) techniques. It is notable that the patterning of four mandrels  104  on substrate  102  in the present embodiment is merely provided as an example meant to illustrate the present techniques. For instance, embodiments are contemplated herein where more or fewer mandrels  104  than shown are formed on substrate  102 . 
     According to an exemplary embodiment, mandrels  104  have nanoscale dimensions. Advantageously, use of the above-described pitch multiplying techniques such as SIT, SADP, SAQP or SAMP, permits the patterning of mandrels at a sub-lithographic pitch (i.e., a pitch smaller than what is achievable using direct lithography. For instance, in one exemplary embodiment, mandrels  104  have a height H of from about 20 nanometers (nm) to about 50 nm and ranges therebetween, a width W of from about 5 nm to about 10 nm and ranges therebetween, and a pitch p of from about 10 nm to about 20 nm and ranges therebetween. See  FIG. 1 . Pitch is defined as the distance from a given point on one mandrel to the same point on the adjacent mandrel. 
     Spacers  202  are then formed on opposite sides of the mandrels  104 . See  FIG. 2 . Preferably, the spacers  202  are formed from a different material than the mandrels  104  to provide etch selectivity between the spacers  202  and the mandrels  104 . This etch selectivity will be leveraged later on in the process to remove (portions) of the mandrels  104  selective to the spacers  202 . As provided above, the mandrels  104  can be formed from an undoped oxide material such as SiOx. In that case, a nitride material such as silicon nitride (SiN) and/or silicon oxynitride (SiON) can be used for the spacers  202  to provide etch selectivity vis-à-vis mandrels  104 . 
     According to an exemplary embodiment, spacers  202  are formed by depositing a spacer material (e.g., SiN and/or SiON—see above) onto the mandrels  104 . A process such as CVD, ALD or PVD can be used to deposit the spacer material. A directional (anisotropic) etching process such as RIE is then used to pattern the spacer material into the individual spacers shown in  FIG. 2 . In one exemplary embodiment, spacers  202  have a width Wspacer of from about 5 nm to about 10 nm and ranges therebetween. 
     As shown in  FIG. 2 , following placement of spacers  202  alongside the mandrels  104 , there is a space S present between the spacers  202  alongside adjacent mandrels  104 . As will be described in detail below, this space S will be filled with additional mandrel material in the next step. 
     It is notable, that the above-described process of placing mandrels  104  and then spacers  202  alongside the mandrel can be repeated (in one or more iterations), if so desired, to achieve denser patterning. In that case, although not explicitly shown in the figures, an oxide-selective etch can be used to remove the mandrels  104  selective to the spacers  202  (see above). Additional spacers (not shown) can then be placed alongside spacers  202 , effectively doubling the pitch of spacers  202 . 
     The spaces S between the spacers  202  alongside adjacent mandrels  104  are then filled with additional mandrel material, forming mandrels  302 . See  FIG. 3 . According to an exemplary embodiment, mandrels  302  have the same dimensions (i.e., height, width, pitch, etc.) as mandrels  104 . For clarity, mandrels  104  and mandrels  302  may also be referred to herein as first mandrels and second mandrels, respectively. As provided above, suitable mandrel materials include, but are not limited to, undoped oxide materials such as undoped SiOx. A process such as CVD, ALD or PVD can be used to deposit the mandrel material into the spaces S. Following deposition, the mandrel material can be planarized using a process such as chemical-mechanical polishing (CMP). 
     As shown in  FIG. 3 , an alternating pattern  304  of spacers  202  and mandrels  104 /mandrels  302  is now present on the surface of substrate  102 . Using the configuration above where the spacer material is a nitride material (such as SiN and/or SiON) and the mandrels material is an oxide material (such as undoped SiOx) as an example, an alternating nitride/oxide pattern is now present on the surface of wafer  102 . 
       100391  The next task is to selectively remove portions of the mandrels  104 /mandrels  302  from a (first) portion  402  of the pattern  304 . To do so, a mask  406  is next formed masking/covering a (second) portion  403  and a (third) portion  404  of the pattern. See  FIG. 4 . As shown in  FIG. 4 , in the present example, the first portion  402  encompasses a front portion of the pattern  304 , the second portion  403  encompasses a central portion of the pattern  304 , and the third portion  404  encompasses a back portion of the pattern  304 . As will be described in detail below, the first/front portion  402  and the third/back portion  404  of the pattern  304  will be used to form interleaved/offset electrodes of the device. A channel of the device will be formed in the second/central portion  403 , between the first/front portion  402  and third/back portion  404  electrodes. 
     According to an exemplary embodiment, mask  406  is formed by depositing a hardmask material onto substrate  102  over the pattern  304 . Suitable hardmask materials include, but are not limited to, a carbon-containing hardmask material such as amorphous carbon. Use of a carbon-containing hardmask will enable the removal of mask  406  selective to the underlying (e.g., nitride) spacers  202  and (e.g., oxide) mandrels  104 /mandrels  302 . The hardmask material can be deposited using a process such as plasma-enhanced CVD (PECVD) or a casting process such as spin coating or spray coating. Lithography and etching techniques (see above) are then employed to pattern the hardmask material into the patterned mask  406  shown in  FIG. 4 . 
     An etch is next performed to selectively remove portions of the mandrels  104 /mandrels  302  from the first/front portion  402  of the pattern  304 . According to an exemplary embodiment, a directional (anisotropic) etching process such as RIE is employed to remove the mandrels  104 /mandrels  302  from first/front portion  402 . As provided above, mandrels  104 /mandrels  302  can be formed from an oxide material such as SiOx. In that case, an oxide-selective RIE can be used to remove the portions of the mandrels  104 /mandrels  302  from the first/front portion  402  of pattern  304  selective to spacers  202 . Notably, as shown in  FIG. 4 , mask  406  is present over and protecting the portions of the mandrels  104 /mandrels  302  in the second/central portion  403  and the third/back portion  404  of the pattern  304 . 
     Removal of mandrels  104 /mandrels  302  in this manner creates gaps  408  between the spacers  202  in the first/front portion  402  of pattern  304 . Ultimately, these gaps  408  will be filled with a conductor to form the electrodes on one side of the channel. However, at this stage in the process, gaps  408  are first filled with a sacrificial material  502 . See  FIG. 5 . The term ‘sacrificial’ as used herein refers to the notion that material  502  will be used early on in the process to place a channel spacer, and then later removed and replaced with the electrode conductor. See below. Suitable sacrificial materials include, but are not limited to, amorphous silicon and/or poly-silicon. A process such as CVD, ALD or PVD can be employed to deposit the sacrificial material  502  into the gaps  408 . As shown in  FIG. 5 , the deposited sacrificial material  502  overfills the gaps  408  and is then planarized to the top of mask  406 . The sacrificial material  502  can be planarized using a process such as CMP. 
     Mask  406  is next selectively removed from the second/central portion  403  and third/back portion  404  of the pattern  304  exposing the underlying spacers  202 /mandrels  104 /mandrels  302 . See  FIG. 6 . As shown in  FIG. 6 , sacrificial material  502  remains in the first/front portion  402  of pattern  304  filling the gaps  408  between the spacers  202 . As provided above, mask  406  can be formed from a carbon-containing hardmask material such as amorphous carbon. Amorphous carbon is an ashable material. Thus, according to an exemplary embodiment, mask  406  is removed selective to the underlying (e.g., nitride) spacers  202  and (e.g., oxide) mandrels  104 /mandrels  302  using oxygen-containing plasma ashing. 
     Removal of the mask  406  enables the placement of a channel spacer  702  over the second/central portion  403  of the pattern  304  adjacent to sacrificial material  502 . See  FIG. 7 . Namely, as provided above, mask  406  had been present over the second/central portion  403  and third/back portion  404  of the pattern  304  in which a channel and electrodes of the device will be formed, respectively. Removal of the mask  406  is needed so that the full height channel spacer  702  (relative to the top of sacrificial material  502 ) can be formed. Suitable materials for the channel spacer  702  include, but are not limited to carbon-containing spacer materials such as amorphous carbon. Use of a carbon-containing spacer material will enable the selective removal of sacrificial material  502  (e.g., amorphous silicon and/or poly-silicon) later on in the process (see below). The spacer material can be deposited using a CVD process such as PECVD or a casting process such as spin coating or spray coating. Lithography and etching techniques (see above) can then be employed to pattern the spacer material into the channel spacer  702  shown in  FIG. 7 . 
     In one embodiment, the channel of the device has nanoscale dimensions, i.e., the device has a nanochannel. In that case, according to an exemplary embodiment, channel spacer  702  has a width Wchannel spacer of from about 2 nm to about 10 nm and ranges therebetween. See  FIG. 7 . 
     With sacrificial material  502  covering the first/front portion  402  and channel spacer  702  covering the second/central portion  403  of pattern  304 , an etch is next performed to selectively remove portions of the spacers  202  from the third/back portion  404  of the pattern  304 . See  FIG. 8 . According to an exemplary embodiment, a directional (anisotropic) etching process such as RIE is employed to remove to the portions of the spacers  202  from third/back portion  404 . As provided above, spacers  202  can be formed from a nitride material such as SiN and/or SiON. In that case, a nitride-selective RIE can be used to remove the portions of spacers  202  from the third/back portion  404  of pattern  304  selective to (e.g., oxide) mandrels  104 /mandrels  302 . 
     Removal of spacers  202  in this manner creates gaps  802  between the mandrels  104 /mandrels  302  in the third/back portion  404  of pattern  304 . Later in the process, these gaps  802  will be filled with a conductor to form the electrodes on one side of the channel. Notably, the mandrels  104 /mandrels  302  in the third/back portion  404  of pattern  304  are offset from the spacers  202  present in the first/front portion  402  of pattern  304 . Thus, as will be described in detail below, electrodes formed in the gaps  802  too will be offset from the electrodes formed (on an opposite side of the channel) in the gaps  408  (see, e.g.,  FIG. 4 —described above) between spacers  202 . As highlighted above, having offset or interleaved electrodes is a unique aspect of the present device design that advantageously improves resolution thereby enabling a much finer level of control and manipulation of molecules. 
     Next, sacrificial material  502  is selectively removed from the first/front portion  402  of pattern  304  and from in between spacers  202 . See  FIG. 9 . As shown in  FIG. 9 , removal of sacrificial material  502  re-opens gaps  408  between spacers  202 . According to an exemplary embodiment, a directional (anisotropic) etching process such as RIE is employed to remove sacrificial material  502 . As provided above, suitable materials for sacrificial material  502  include, but are not limited to, amorphous silicon and/or poly-silicon. In that case, a silicon-selective RIE can be used to remove sacrificial material  502  selective to (e.g., nitride) spacers  202 , (e.g., oxide) mandrels  104 /mandrels  302 , and (e.g., amorphous carbon) channel spacer  702 . 
     As shown in  FIG. 9 , channel spacer  702  remains covering the second/central portion  403  of pattern  304 . However, for clarity, if one were to visualize the structure looking through the channel spacer  702  (see  FIG. 10  where channel spacer  702  is shown transparent for illustrative purposes only) it can be seen that the gaps  408  between spacers  202  (in the first region  402  of pattern  304 ) are offset from the gaps  802  between the mandrels  104 /mandrels  302  (in the third region  404  of pattern  304 ). Thus, when the gaps  408  and gaps  802  are filled with a conductor to form electrodes of the device, those electrodes formed in the gaps  408  and gaps  802  too will be offset from one another, i.e., interleaved. 
     Namely, following from  FIG. 9 , the gaps  408  between spacers  202  (in the first/front portion  402  of pattern  304 ) and the gaps  802  between the mandrels  104 /mandrels  302  (in the third/back portion  404  of pattern  304 ) are next filled with a conductor  1102 . See  FIG. 11 . Suitable conductors include, but are not limited to, copper (Cu), tungsten (W), cobalt (Co) and/or ruthenium (Ru). A process such as sputtering, evaporation, or electrochemical plating can be employed to deposit conductor  1102  into the gaps  408  and the gaps  802 . As shown in  FIG. 11 , the conductor  1102  overfills the gaps  408  and the gaps  802  and is then planarized to the top of channel spacer  702 . The conductor  1102  can be planarized using a process such as CMP. 
     As shown in  FIG. 11 , the channel spacer  702  now separates the conductor  1102  over the first/front portion  402  from the conductor  1102  over the third/back portion  404  of pattern  304 . The channel spacer  702  is then selectively removed. See  FIG. 12 . As shown in  FIG. 12 , removal of channel spacer  702  forms a trench  1202  in between the conductor  1102  over the first/front portion  402  and the conductor  1102  over the third/back portion  404  of pattern  304 . 
     As provided above, channel spacer  702  can be formed from a carbon-containing spacer material such as amorphous carbon. Amorphous carbon is an ashable material. Thus, according to an exemplary embodiment, channel spacer  702  is removed selective to conductor  1102  using oxygen-containing plasma ashing. 
     Opening of trench  1202  in conductor  1102  exposes the underlying portions of spacers  202  and mandrels  104 /mandrels  302  in the second/central portion  403  of the pattern  304 . An etch is then used to remove these portions of spacers  202  and mandrels  104 /mandrels  302  through trench  1202 . See  FIG. 13 . As shown in  FIG. 13 , this etch step forms a channel  1302  in between the first/front portion  402  and the third/back portion  404  of the pattern  304 . According to an exemplary embodiment, a directional (anisotropic) etching process such as RIE is employed for the channel etch. As provided above, the spacers  202  can be formed from a nitride material, and the mandrels  104 /mandrels  302  can be formed from an oxide material. Thus, in that case, an oxide/nitride-selective RIE (or combination of RIE steps) can be used to pattern channel  1302  through trench  1202 . Based on the dimensions of channel spacer  702  (see above), according to an exemplary embodiment, channel  1302  is a nanochannel having a width of from about 2 nm to about 10 nm and ranges therebetween. 
     The conductor  1102  is then recessed. See  FIG. 14 . A process such as CMP or a metal-selective etch can be used to recess conductor  1102  down to spacers  202  (in the first/front portion  402  of the pattern  304 ) and mandrels  104 /mandrels  302  (in the third/back portion  404  of the pattern  304 ). Recessing the conductor  1102  forms an array of electrodes on both sides of the channel  1302 . Namely, as shown in  FIG. 14 , first electrodes  1402  are present in between spacers  202  on a first side of channel  1302 , and second electrodes  1404  are present in between mandrels  104 /mandrels  302  on a second/opposite side of channel  1302 . 
     When viewed from the top-down (i.e., from viewpoint A), it can be seen that the first electrodes  1402  are offset from second electrodes  1404  across channel  1302 . See  FIG. 15 . This configuration is what is referred to herein as ‘interleaving’ the electrodes. 
     For instance, if one were to visualize the structure without the mandrels  104 /mandrels  302  and spacers  202  (see  FIG. 16  where mandrels  104 /mandrels  302  and spacers  202  are transparent for illustrative purposes only) it can be seen that the first electrodes  1402  are offset from second electrodes  1404  across channel  1302 , i.e., interleaved. According to an exemplary embodiment, each of first/second electrodes  1402 / 1404  has a width Welectrode of from about 5 nm to about 10 nm and ranges therebetween, and a height Helectrode of from about 20 nm to about 50 nm and ranges therebetween. See  FIG. 16 . 
     As highlighted above, the present 3D device structures permit the electro-kinetic control of individual molecules using the dipoles inherent in the subject material. See, for example,  FIG. 17 . As is known in the art, polar molecules have a partial negative end and a partial positive end. Dipole-dipole interactions occur when the partial positive end of one molecule is attracted to the partial negative end of another molecule, and vice versa. These interactions can also be used to control the orientation and movement of individual polar molecules with the nanochannel. 
     For instance, as shown in  FIG. 17 , during operation a field applied selectively to portions of a polar molecule  1702  will electrokinetically orient (see angle θ) and/or locomote (along x-direction) the polar molecule  1702  in the channel  1302  as a result of dynamic electric field applied to the first/second electrodes  1402 / 1404 . Polar molecule  1702  can be present in a fluid medium such as a solvent. Thus, in addition to electrokinetics, a positive pressure of the fluid can also be employed to move molecule  1702  through channel  1302 . 
     Advantageously, first/second electrodes  1402 / 1404  can be controlled individually to locomote and/or orient polar molecule  1702 . See, for example, the electric field being applied dynamically to the electrodes  1402 / 1404  on opposite sides of channel  1302 . Further, as provided above, first/second electrodes  1402 / 1404  are offset from one another on opposite sides of the channel  1302 . Interleaving the electrodes  1402 / 1404  in this manner enables a much finer level of control and manipulation of the molecule  1702 . 
     Although illustrative embodiments of the present invention have been described herein, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be made by one skilled in the art without departing from the scope of the invention.