Patent Publication Number: US-2021188625-A1

Title: Semiconductor chip

Description:
TECHNICAL FIELD 
     The present invention relates to a semiconductor chip, in particular a semiconductor sensor chip having a sensor device and processing circuitry for processing signals of the sensor device. 
     BACKGROUND ART 
     Subject to the application, sensor devices tend to be integrated on semiconductor substrates. This kind of manufacturing is beneficial in that the size of the sensor device can significantly be reduced compared to discrete type sensor devices, and a corresponding sensing element can be arranged together with processing circuitry integrated on the same semiconductor substrate. The processing circuitry may include functions acting on a signal delivered by the sensor device such as amplification, evaluation, etc. 
     Multiple sensor chips are manufactured from a common wafer, where the individual sensor chips are separated from the wafer e.g. by dicing the wafer. During the process of dicing, a sensor device or processing circuitry if any may be impacted, for example, by cracks induced during the dicing process, or by contaminants infiltrated during the dicing process. 
     In order to avoid such damaging of the sensor chip, a seal ring may be provided at the edge of the chip around the sensor device and the processing circuitry if any. Such a seal ring may comprise a metal ring for protection purposes. 
     US 2014/0319693 A1 discloses a method of forming a semiconductor device. Provided is a substrate having at least one MOS device, at least one metal inter-connection and at least one MOS device formed on a first surface thereof. A first anisotropic etching process is performed to remove a portion of the substrate from a second surface of the substrate and thereby form a plurality of vias in the substrate, wherein the second surface is opposite to the first surface. A second anisotropic etching process is performed to remove another portion of the substrate from the second surface of the substrate and thereby form a cavity in the substrate, wherein the remaining vias are located below the cavity. An isotropic etching process is performed to the cavity and the remaining vias. 
     US 2006/0076651 A1 discloses an electronic device which has an element formed in the chip region of a substrate, a plurality of interlayer insulating films formed on the substrate, a wire formed in the interlayer insulating films in the chip region, and a plug formed in the interlayer insulating films in the chip region and connecting to the wire. A seal ring extending through the plurality of interlayer insulating films and continuously surrounding the chip region is formed in the peripheral portion of the chip region. A stress absorbing wall extending through the plurality of interlayer insulating films and discretely surrounding the seal ring is formed outside the seal ring. 
     It is an object of embodiments of the present invention to provide a semiconductor chip which further facilitates the integration of sensor devices together with processing circuitry on a common substrate. 
     It is a further object of embodiments of the invention to improve the reliability of semiconductor chips comprising sensor devices which are integrated with processing circuitry on a common substrate. 
     DISCLOSURE OF THE INVENTION 
     According to an embodiment of a first aspect of the invention, there is provided a semiconductor chip comprising a substrate and a stack arranged on the substrate. The stack comprises one or more insulating layers and one or more metal layers. The chip comprises a sensor device arranged in a sensor area of the semiconductor chip and processing circuitry arranged in a processing area of the semiconductor chip. The chip further comprises connection circuitry configured to provide an electrical connection between the sensor device and the processing circuitry. A first seal ring structure is arranged between an outer edge of the chip and an inner area of the chip. The first seal ring is in particular configured to protect the inner area of the chip from lateral impact. The inner area of the chip encompasses the sensor area and the processing area. A second seal ring structure is arranged between the sensor area and the processing area and is configured to constrain an infiltration of contaminants from the sensor area to the processing area. 
     Such a semiconductor chip facilitates the integration of sensor devices and corresponding processing circuitry on a single semiconductor chip. The arrangement of the second seal ring between the sensor area and the processing area improves the reliability of the processing circuitry. Aspects of the invention are based on a finding/discovery of the inventors of the present invention that sensor devices that are integrated together with processing circuitry on the same semiconductor chip may adversely affect the functioning and/or reliability of the processing circuitry as well as the functioning of the connection circuitry. This applies in particular to sensor devices that are configured to interact with the ambience of the sensor device, in particular the ambient air. More particularly, sensor devices that are configured to interact with the ambience of the sensor area/sensor device may comprise openings that may provide an infiltration path for contaminants to enter the stack. 
     This is of particular relevance for processing circuitry and connection circuity that is implemented in CMOS technology and is hence rather sensitive to such contaminants. 
     The term processing circuitry shall denote any kind of electronic circuitry that may be used to process sensor signals of the sensor device. 
     The term contaminants shall denote any kind of elements, compositions or materials that may adversely affect the components of the stack, in particular the processing circuitry. 
     Contaminants may include in particular humidity and ions. 
     Aspects of the invention are particularly advantageous for the integration of sensor devices and MEMS devices that comprise a cavity, a recess or an opening in the substrate and/or an opening in the passivation. The second seal ring structure according to embodiments of the invention may effectively shield or seal such recesses or openings of the substrate, thereby avoiding that contaminants such as chemicals, humidity or ions may enter the (oxide) stack during the lifetime of the chip. Hence embodiments of the invention prevent that contaminants may diffuse via the sensor device/sensor area into the CMOS-area of the semiconductor chip. 
     This may significantly improve the reliability of such integrated chips. 
     Generally, the terms first ring structure and second ring structure shall denote any kind of loops that surround or enclose the inner area and that surround or encloses the sensor area respectively. The loop may be a closed loop without any openings for connection circuitry or an open loop with openings for connection circuitry as will be explained further below in more detail. The loop may have various forms such as a circle, an annulus, a polygon or other suitable free form loops in dependence on the geometry of the respective chip. 
     According to an embodiment, the semiconductor chip comprises a passivation layer arranged at least partly on top of the stack. Furthermore, the first seal ring structure and the second seal ring structure are implemented in the stack between the substrate and the passivation layer. 
     This is an effective way to implement the first and the second seal ring. The substrate preferably comprises or consists of a material that provides a diffusion barrier, in particular bulk silicon. The passivation layer preferably comprises or consists of a material that provides a diffusion barrier as well. This provides a kind of top cover and bottom cover to shield against the infiltration of contaminants. The first seal ring and the second seal ring establish vertical side barriers or in other words vertical side walls between the edge of the chip and the inner area of the chip and between the sensor area of the chip and the processing area of the chip respectively. This protects the processing circuitry and the connection circuitry from external contaminants. Preferably the first and/or the second seal ring structure are directly connected to or attacked to the passivation layer and to the substrate. 
     Hence according to embodiments the passivation layer, the substrate/bulk silicon, the first seal ring structure and the second seal ring structure provide an enclosure for the processing circuitry that serves as a diffusion barrier. 
     According to an embodiment, the second seal ring structure is configured as open seal ring structure comprising one or more openings for one or more electrical feed through connections. The one or more electrical feed through connections are configured to provide an electrical connection between the sensor device and the processing circuitry. 
     This is an elegant, simple and efficient way to implement on the one hand an electrical connection between the sensor device and the processing circuitry and to constrain on the other hand any infiltration of contaminants. In this respect the second seal ring according to such an embodiment serves two purposes or in other words has a dual use. 
     According to an embodiment, the second seal ring structure comprises a conductive structure arranged in the stack and the electrical feed through connections are implemented by two or more different metal layers of the stack. The two or more different metal layers of the stack are electrically connected by interconnect elements, which may also be denoted as vias. The feed through connections are arranged in such a way that a direct diffusion path between the sensor area and the processing area is blocked. Such a blocking of the direct diffusion path results in an extension or elongation of the remaining diffusion paths, decreases a possible contamination and hence increases the reliability of the components of the CMOS stack. 
     According to an embodiment, the electrical feed through connections comprise a plurality of elbow connections, in particular 90° elbow connections. Thereby walls are formed, in particular vertical walls, which block the direct diffusion path between the sensor area and the processing area. 
     According to embodiments, the one or more openings may comprise lateral projections configured to increase the diffusion length between the sensor device and the processing circuitry. Such lateral projections may in particular extend in a direction parallel to the surface of the substrate and the surface of the passivation layer. The lateral projections are in particular configured to prevent that that contaminants may disperse in several directions after the opening. Rather the lateral extension constrain the diffusion/infiltration path to an area between the lateral extensions. This increase the diffusion length and as a result reduces the diffusion of contaminants. 
     According to an alternative embodiment, the second seal ring structure is a closed seal ring structure. The closed seal ring structure provides a closed seal ring between the substrate and the passivation layer. The closed seal ring structure does not comprise any openings for electrical feed trough connections and is electrically insulated from the sensor device and the processing circuitry. Such a closed seal ring structure may completely seal the sensor area/sensor device from the processing area/processing device for any diffusion. 
     In order to provide an electrical connection between the sensor device and the processing circuitry, the semiconductor chip with the closed seal ring structure comprises as electrical connection circuitry a contact layer arranged on top of the passivation layer. The contact layer is configured to contact the sensor device through an opening of the passivation layer. This provides an electrical connection between the sensor device and the processing circuitry outside of the CMOS stack and by bypassing the closed seal ring structure. 
     According to a further embodiment, the second seal ring structure is a conductive structure arranged in the stack and the second seal ring structure is formed by a plurality of metal layers which are electrically connected by interconnect elements. 
     Such an embodiment of the closed seal ring structure can be efficiently and reliably fabricated by standard CMOS processes. 
     According to a further embodiment, the semiconductor chip comprises a further passivation layer arranged between the sensor area and the processing area and configured to shield the processing area from the sensor area, in particular to shield the processing area from diffusion of contaminants. 
     Such an additional passivation layer may be used to further reduce or constrain possible diffusion paths and may provide an additional barrier for contaminants to enter the CMOS stack. Such a further passivation layer may be arranged in particular adjacent to recesses, openings or cavities of the sensor device. 
     As described above, the second seal ring structure may effectively block or reduce diffusion paths from the ambiance, in particular the ambient air, into the CMOS stack. 
     Hence embodiments of the invention encompass in particular semiconductor chips with a sensor area that comprises recesses, openings and/or cavities in the substrate. More particularly, according to embodiments, the recesses, openings or cavities are provided in the bulk substrate and are etched from the bulk side or in other words from the bottom side of the semiconductor chip. 
     According to some embodiments, the etching of the substrate may be performed in such a way that it just stops at the vertical lower edge of the stack. According to other embodiments, the etching may also remove a part of the stack in addition to the etching of the substrate such that the recess or opening extends from the substrate into the stack. 
     Further embodiments encompass sensor devices with sensor areas having a passivation layer with at least one opening in the sensor area. 
     Furthermore, embodiments of the invention encompass sensor devices with bridge structures that carry one or more sensing elements of the sensor device. The diffusion paths that such recesses, openings, cavities, bridge structures or openings may provide can be effectively shielded with a chip architecture according to embodiments of the invention. 
     While generally the invention may be used for any kind of sensor device or MEMS device that shall be integrated with CMOS processing circuitry, particularly preferred embodiments encompass environmental sensor devices that interact with the environment of the sensor for measuring and/or sensing purposes. Sensor devices according to embodiments of the invention include in particular flow sensors, humidity sensors, MOX gas sensors, electro-chemical cells or infrared sensors. 
     A further aspect of the invention also applies to electronic devices, in particular portable electronic devices that comprise a semiconductor chip as described above. Using chips according to embodiments of the invention for such electronic devices provide advantages in terms of miniaturization, integration and reliability of the electronic devices. 
     Preferably, multiple semiconductor chips are manufactured from a common wafer. Hence, aspects of the invention also relate to a wafer comprising a plurality of semiconductor chips according to the first aspect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments defined above and further embodiments, features and advantages of the present invention can also be derived from the examples of embodiments to be described hereinafter in connection with the drawings in which the figures illustrate: 
         FIG. 1  shows a cross section of a semiconductor chip according to an embodiment of the invention; 
         FIG. 2  shows a 3-dimensional view of a semiconductor chip according to an embodiment of the invention; 
         FIG. 3  shows a schematic top view of a semiconductor chip according to an embodiment of the invention; 
         FIG. 4  shows a schematic top view of a semiconductor chip comprising a seal ring with openings for electrical feed through connections according to an embodiment of the invention; 
         FIG. 5  shows a cross section of a semiconductor chip according to an embodiment of the invention; 
         FIG. 6  shows a cross section of a semiconductor chip comprising a contact layer on top of the passivation layer according to another embodiment of the invention; 
         FIG. 7  shows a cross section of a semiconductor chip comprising an additional passivation layer according to another embodiment of the invention; and 
         FIG. 8  shows a schematic top view of a semiconductor chip comprising bridge structures according to another embodiment of the invention. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     The drawings are provided for illustration purposes and may be not to scale. Identical or similar elements are referred to by the same reference numerals. 
       FIG. 1  shows a cross section of a semiconductor chip  100  according to an embodiment of the invention. 
     The semiconductor chip  100  comprises a substrate  1  such as a silicon substrate. A stack of insulating/dielectric layers  2  and metal layers  3  is arranged on the substrate  1  and is collectively referred to by  4 . The dielectric layers  2  of this stack  4  may contain SiO or SiN and the metal layers  3  may contain Al, W or Cu. 
     According to this embodiment, a sensor device  5  is arranged on top of the stack  4 . However, according to other embodiments the sensor device  5  may also be embedded in the stack  4 , or arranged on the substrate  1 . 
     In addition, processing circuitry  6  is integrated in the stack  4  for processing signals of the sensor device  5  of the semiconductor chip  100 . The layers of the stack  4  are preferably CMOS layers. 
     The semiconductor chip  100  has a plane extending in an x/y direction and comprises a sensor area SA and a processing area PA in this plane. 
     The sensor device  5  is arranged in the sensor area SA and the processing circuitry  6  is arranged in the processing area PA. The semiconductor chip  100  further has an inner area IA that encompasses the sensor area SA and the processing area PA. 
     The semiconductor chip  100  comprises a recess or opening  15  in the substrate  1  and more particularly in the sensor area SA of the chip  100 . The recess or opening  15  may be etched from the bulk side/substrate side or in other words from the bottom side of the semiconductor chip  100 . Top and bottom refer in this context to the vertical z-direction. 
     According to the illustration of  FIG. 1 , the etching of the substrate  1  has been performed in such a way that the vertical top side/top plane of the recess or opening  15  corresponds to the vertical lower side/lower plane of the stack  4 . According to other embodiments, the recess or opening  15  may also encompass CMOS layers of the stack  4  or in other words the recess or opening  15  may extend into the stack  4 . The recess or opening  15  may be provided e.g. for thermal insulation purposes of the sensor device, e.g. for an MOX gas sensor device. 
     The semiconductor chip  100  further comprises connection circuitry  7  which provides an electrical connection between the sensor device  5  and the processing circuitry  6 . The connection circuitry  7  comprises as horizontal conducting elements (in the x-y plane) a plurality of metal layers  3  and interconnect elements  8 , embodied as vias, which provide an electric connection between metal layers of different planes in the vertical z-direction through corresponding insulating layers  2 . One or more of the metal layers  3  may also be used for building contact pads for contacting the semiconductor chip  100  from the outside. 
     The semiconductor chip  100  comprises a passivation layer  9  arranged at least partly on top of the stack  4 . The passivation layer  9  is inert and prevents the diffusion of contaminants such as humidity and ions into the stack  4 . 
     The semiconductor chip  100  comprises a first seal ring structure  10  arranged between an outer edge ED of the chip  100  and the inner area IA of the chip  100 . 
     The first seal ring structure  10  protects the inner area IA of the semiconductor chip  100  from lateral impact and in furthermore prevents the diffusion of contaminants such as humidity and ions into the stack  4 . The first seal ring structure  10  is implemented in the stack  4  and extends between the substrate  1  and the passivation layer  9 . It may be in particular formed as conductive and closed structure by metal layers  3  and interconnect elements  8 , thereby forming a closed barrier for the diffusion of contaminants. 
     The passivation layer  9  may comprise according to embodiments one or more openings  16  in the sensor area SA. The opening  16  is shown in  FIG. 1  in a schematic way. 
     The semiconductor chip  100  further comprises a second seal ring structure  11  arranged between the sensor area SA and the processing area PA. The second seal ring structure  11  constrains and preferably prevents an infiltration of contaminants from the sensor area SA or the ambiance of the sensor area SA to the processing area PA. 
     The second seal ring structure  11  is also implemented in the stack between the substrate  1  and the passivation layer  9 . It may be formed as conductive structure comprising metal layers  3  and interconnect elements  8 . 
     According to the embodiment of  FIG. 1 , the second seal ring structure  11  is configured as open seal ring structure and accordingly it comprises one or more openings  12  for one or more electrical feed through connections  13 . The feed through connections  13  form a part of the connection circuitry  7  and provide an electrical connection via the opening  12  between the sensor device  5  and the processing circuitry  6 . 
     The term sensor device shall be understood in a broad sense and shall in particular encompass any kind of microelectromechanical systems (MEMS) devices. 
     Hence the sensor device  5  may be in particular a microelectromechanical system (MEMS) device. In this respect, the terms MEMS shall be understood in a broad sense and shall include also devices without moving parts. Rather the term MEMS shall include devices and structures that are made using the techniques of micro-fabrication and in particular devices and structures that are fabricated with non-CMOS processes. The terms MEMS shall include in particular any kind of micro-sensors. According to preferred embodiments the sensor device  5  may be a flow sensor, a MOX gas sensor, a humidity sensor, an electro-chemical cell or an infrared (IR) sensor. 
     The processing circuitry  6  is in particular CMOS circuitry and hence sensitive to contaminants such as humidity and ions. 
       FIG. 2  shows a 3-dimensional partial view (cut away view) of a part of a semiconductor chip  200  according to an embodiment of the invention, which may partly correspond to the semiconductor chip  100  of  FIG. 1 . The semiconductor chip  200  is configured as gas sensor and hence configured to measure a gas concentration of a target gas in a sample of ambient air. 
     The semiconductor chip  200  comprises as sensor device  5  a gas sensitive component  210 . The gas sensitive component  210  comprises a gas sensitive layer  211 . The gas sensitive layer  211  comprise a gas sensitive sensing material. The sensing material is a material that changes at least one electrical property (in particular the real or imaginary part of its electrical impedance) as a function of the composition of the gas that surrounds it. The change of the property can be measured in order to obtain information on said composition. The sensing material of the gas sensitive layer  211  can e.g. contain at least one metal oxide material. Such metal oxide material may include one or more of tin oxide, zinc oxide, titanium oxide, tungsten oxide, indium oxide and gallium oxide. Such metal oxides may be used for the detection of various analytes as target gas such as ozone, VOCs, carbon monoxide, nitrogen dioxide, methane, ammonia, hydrogen, or hydrogen sulphide. 
     Metal oxide sensors are based on the concept that gaseous analytes interact with the metal oxide layer at elevated temperatures of the sensitive layer in the range of more than 100 ° C., and specifically between 250° C. and 450 ° C. As a result of the catalytic reaction, the conductivity of the gas sensitive layers may change, which change can be measured. Hence, such sensors are also denoted as high temperature chemoresistors for the reason that a chemical property of the analyte is converted into an electrical resistance at high temperatures of the gas sensitive layers. 
     The semiconductor chip  200  is integrated with CMOS circuitry  6  as processing circuitry. 
     The semiconductor chip  200  comprises a stack  4  of CMOS layers and a substrate  1  establishing a handle layer. Parts of the CMOS layers and of the handle layer are etched away to form a cavity  250  at the location of the gas sensitive layer  211 . The remaining CMOS layers form a thin membrane to support the gas sensitive component  210 . The cavity  250  may correspond to the recess or opening  15  illustrated in  FIG. 1 . 
     Embedded within the CMOS layers are heating elements  220  forming a heater to provide a local source of heat to heat the gas sensitive component  210  during operation. The temperature can rise rapidly around the gas sensitive component  210 , while the thicker part of the semiconductor chip reacts due to its thermal inertia with a slower rise of temperature. By controlling the heating elements  220  accordingly, the material, in particular the metal oxide, of the gas sensitive layer  210  can be activated for a measurement and subsequent regeneration. 
     The gas sensitive layer  210  is contacted by measuring electrodes (not shown) and hence acts as a resistor. In the presence of a target gas as analyte, the respective resistance of the gas sensitive layer  210  changes and thereby provides a measure of the concentration of the target gas in the sample of ambient air in the immediate vicinity of the gas sensitive layer  210 . 
     The semiconductor chip  200  comprises a first seal ring structure  10  and a second seal ring structure  11  as described with reference to  FIG. 1 . The second seal ring structure  11  constrains in particular an infiltration of contaminants from the cavity  250  to the processing circuity  6 . It should be noted that  FIG. 2  only shows a part of the seal ring structures  10 ,  11  extending in the y-direction due to the partial cut away view. However, the seal ring structures  10 ,  11  may also extend in the x-direction outside the shown area to provide a complete protection loop. 
       FIG. 3  shows a schematic top view of a semiconductor chip  300  according to an embodiment of the invention. The semiconductor chip  300  comprises processing circuitry  6  embodied as CMOS circuitry and a sensor device  5  embodied as MEMS circuitry. The processing circuitry  6  forms a processing area PA and the sensor device  5  forms a sensor area SA. The sensor device  5  and the processing circuitry  6  are electrically connected by connection circuitry  7 , schematically indicated by a double-arrow. A first seal ring  10  is arranged at an edge ED of the semiconductor chip  300  and more particularly between the edge ED and an inner area IA of the chip  300 . The first seal ring  10  is illustrated by a dashed line. 
     A second seal ring  11  is arranged around the sensor device  5  and more particularly between the sensor device  5  and the processing area PA of the CMOS processing circuitry  6 . Preferably the second seal ring  11  is arranged rather close around the sensor area SA. This provides the advantage that the second seal ring  11  can shield also other parts of the stack, in particular the connection circuitry  7 , from contaminants that may enter the stack via the sensor area SA. The second seal ring  11  is illustrated by a dotted line. 
       FIG. 4  shows a schematic top view of a semiconductor chip  400  according to an embodiment of the invention. The semiconductor chip  400  comprises three different processing circuitries  6   a,    6   b  and  6   c  which are arranged at different positions of the chip  400 . A sensor device  5  is embodied as MEMS circuitry. 
     The processing circuitries  6   a,    6   b  and  6   c  form three processing areas PA a , PA b  and PA c . The three processing areas PA a , PA b  and PA c  may be collectively referred to as processing area PA. 
     The chip  400  also comprises a first seal ring  10  which is arranged at an edge ED of the semiconductor chip  400  and more particularly between the edge ED and an inner area IA of the chip  400 . The first seal ring  10  is again illustrated by a dashed line. 
     According to embodiments the processing area PA may include the area of the connection circuitry  7  and according to embodiments the processing area PA may be the whole area of the stack inside the first seal ring  10  with the exception of the sensor area SA. 
     A second seal ring  11  is arranged around the sensor device  5  and more particularly between the sensor device  5  and the processing areas PA a , PA b  and PA c . 
     The second seal ring  11  is illustrated again by a dotted line. The second seal ring  11  comprises three openings  12   a,    12   b  and  12   c  for electrical feed through connections  13   a,    13   b  and  13   c  respectively. The openings  12   b  and  12   c  comprise lateral projections  18  that extend in the x-y plane from the sensor device  5  and increase the diffusion path for contaminants diffusing from the sensor area SA via the openings  12   b,    12   c  to the processing areas PA b  and PA c  respectively. 
       FIG. 5  shows a cross section of a semiconductor chip  500  according to an embodiment of the invention. More particularly,  FIG. 5  shows a cut out cross section of a second seal ring structure  511  and a part of the adjacent processing area PA and sensor area SA. The second seal ring structure  511  is implemented by a plurality of different metal layers M 1 , M 2  and M 3 . The plurality of different metal layers M 1 , M 2  and M 3  are electrically interconnected by interconnect elements  8 , embodied as vias  8 . 
     According to this embodiment the second seal ring structure  511  does not provide an electrical connection between the substrate  1  and the passivation layer  9 , but rather the substrate  1  and the passivation layer  9  are electrically insulated from each other. The second seal ring structure  511  comprises as connection circuitry an electrical feed through connection  13  which is illustrated with a dashed line. The electrical feed trough connection  13  electrically connects the sensor device  5  and the processing circuitry  6  of the semiconductor chip  600 . More particularly, the electrical feed through connection  13  does not provide a direct path between the sensor device  5  and the processing circuitry  6 , but is arranged with a plurality of elbow connections  530 , in particular 90° elbow connections. Thereby the electrical feed through connection  13  and the second seal ring structure  511  are formed with vertical walls  510  that block direct diffusion paths between the sensor area SA and the processing area PA. A vertical wall is understood as a wall that extends in the vertical z-direction or in other words orthogonal to the surface of the substrate  1 . Such a direct diffusion path is illustrated with a dotted line and the reference numeral  520 . The direct diffusion path  520  is blocked by a vertical wall  510   a.  A remaining diffusion path  521  which is also illustrated with a dotted line establishes an indirect diffusion path and is hence guided in an indirect manner around elbow connections through the second seal ring structure  11 . Due to the indirect and elongated diffusion path  521  the diffusion is effectively reduced compared with the direct diffusion path  520 . 
       FIG. 6  shows a cross section of a semiconductor chip  600  according to another embodiment of the invention. More particularly,  FIG. 6  shows a cut out cross section of a second seal ring structure  611  and a part of the adjacent processing area PA and sensor area SA. The second seal ring structure  611  is implemented as conductive structure and is formed by a plurality of different metal layers M 1 , M 2  and M 3 . The plurality of different metal layers M 1 , M 2  and M 3  are electrically interconnected by interconnect elements  8 , embodied as vias  8 . 
     According to this embodiment, the second seal ring structure  611  is a closed seal ring structure. The closed seal ring structure  611  provides a closed seal ring between the substrate  1  and the passivation layer  9  and hence a closed and complete diffusion barrier. The closed seal ring structure  611  is electrically insulated from the sensor device  5  and the processing circuitry  6 . 
     According to this embodiment, an electrical connection between the sensor device  5  and the processing circuitry  6  is provided by means of a contact layer  640 . The contact layer  640  may be a layer of metal and is arranged on top of a passivation layer  9 , the latter being arranged on the stack  4 . The contact layer  640  provides an electrical contact between the sensor device  5  and the processing circuitry  6  through an opening  630  of the passivation layer  9 . The contact layer  640  contacts the stack  4  and more particularly the first metal layer M 1 , the latter providing an electrical connection through the stack  4  via the metal layer M 2  and interconnect elements  8  to the processing circuitry  6 . 
     As illustrated with dotted lines, any diffusion path  620  between the sensor area SA and the process area PA is blocked by the closed second seal ring structure  611 . 
       FIG. 7  shows a cross section of a semiconductor chip  700  according to another embodiment of the invention. More particularly,  FIG. 7  shows a cut out cross section of a second seal ring structure  711  and a part of the adjacent processing area PA and sensor area SA. The second seal ring structure  711  is implemented by a plurality of different metal layers M 1 , M 2  and M 3 . The plurality of different metal layers M 1 , M 2  and M 3  are electrically interconnected by interconnect elements  8 , embodied as vias  8 . 
     According to this embodiment, the substrate  1  and the passivation layer  9  are electrically insulated from each other. The second seal ring structure  711  comprises an electrical feed through connection  13  which is illustrated with a dashed line. The electrical feed through connection  13  electrically connects the sensor device  5  and the processing circuitry  6  of the semiconductor chip  700 . The electrical feed through connection  13  is arranged with elbow connections and is formed with a vertical wall  710   a  that provides a bypath for a diffusion path  721  illustrated with a dotted line, thereby establishing an indirect diffusion path. 
     The semiconductor chip  700  comprises a further passivation layer  730  which is arranged between the sensor area SA and the processing area PA and more particularly adjacent to the sensor area SA and the second seal ring structure  711 . The further passivation layer  730  extends in the vertical z-direction along the substrate  1  into the stack  4  and in the horizontal x-y plane within the stack  4 . The passivation layer  730  seals the sensor area SA from the processing area PA and in particular blocks a direct diffusion path  720  between a recess  15  or opening  15  in the substrate and the stack  4 . 
       FIG. 8  shows a schematic top view of a semiconductor chip  800  according to another embodiment of the invention. The semiconductor chip  800  is a gas sensor for detecting and/or analysing a gas and comprises a sensor device  5  and CMOS processing circuitry  6 . 
     The semiconductor chip  800  comprises a substrate  1 , in particular a substrate of silicon. The substrate  1  has an opening or recess  15  arranged therein. The sensor device  5  comprises a plurality of separate bridge structures that span this opening or recess  15 . More particularly, the sensor device  5  comprises a first bridge structure  803   a  that forms a first hotplate  806   a,  a second bridge structure  803   b  that forms a second hotplate  806   b,  a third bridge structure  803   c  that forms a third hotplate  806   c  and a fourth bridge structure  803   d  that forms a fourth hotplate  806   d.  In the following it may be referred to the plurality of bridge structures collectively as bridge structures  803  and to the plurality of hotplates as hotplates  806 . 
     The sensor device  5  comprises a first patch  808   a  of sensing material arranged on the first hotplate  806   a,  a second patch  808   b  of sensing material arranged on the second hotplate  806   b,  a third patch  808   c  of sensing material arranged on the third hotplate  806   c  and a fourth patch  808   d  of sensing material arranged on the fourth hotplate  806   d.  The sensing material may be in particular a metal oxide material. 
     The sensing material is a material that changes at least one electrical property (in particular the real or imaginary part of its electrical impedance) as a function of the composition of the gas that surrounds it. The change of the property can be measured in order to obtain information on said composition. 
     The sensing material can e.g. contain at least one metal oxide material. Such metal oxide material generally may include one or more of tin oxide, zinc oxide, titanium oxide, tungsten oxide, indium oxide and gallium oxide. Such metal oxides may be used for the detection of analytes such as VOCs, carbon monoxide, nitrogen dioxide, methane, ammonia or hydrogen sulphide. 
     Each of the bridge structures  803   a,    803   b,    803   c  and  803   d  comprises a central region and two arms  807  extending between the central regions and the substrate  1 , thereby suspending the hotplates  806   a,    806   b,    806   c  and  806   d  over the recess or opening  2 . The arms  807  extend collinear to each other and with the central region with the hotplates being arranged between them. 
     Each of the bridge structures  803   a,    803   b,    803   c  and  803   d  comprises electrodes adapted to measure electrical properties of the patches. Furthermore, each of the bridge structures  803   a,    803   b,    803   c  and  803   d  comprises a heater adapted to heat the hotplates and a temperature sensor to measure the temperature of the respective bridge structure. The electrodes, heaters and temperature sensors are not shown in  FIG. 8  for visual clarity reasons. 
     The substrate  1  carries processing circuitry  6 , e.g. including circuitry for driving the heaters and processing signals from the electrodes and temperature sensors. For this, the processing circuitry  6  is electrically connected to the heaters, electrodes and temperature sensors via connection circuitry  7 . Advantageously, processing circuitry  6  is integrated in CMOS technology compatible with current CMOS manufacturing processes. Having the CMOS circuitry on-board of substrate  1  allows to reduce the number of bonds to the substrate and to increase signal-to-noise ratio 
     Structures of the type shown in  FIG. 8  can e.g. be built using techniques such as described in EP 2278308 or US 2014/0208830. 
     In particular, the process for manufacturing comprises the steps of forming a plurality of dielectric and metal layers on top of the substrate  1 . Some of these layers may be deposited in the course of the process for forming the CMOS circuitry  6 , e.g. as intermetal dielectric layer and metal layers, while other layers may be applied during post-processing, such as a tensile silicon nitride layer. Then, recess or opening  815  is formed using selective, anisotropic etching techniques. The patches  808   a,    808   b,    808   c  and  808   d  of sensing material can e.g. be applied using dispensing techniques where a drop or several drops of a liquid precursor of the sensing material is applied to the hotplates, such as e.g. described in EP 2952885. 
     The semiconductor chip  800  comprises a first seal ring structure  10  arranged between an outer edge ED of the chip  800  and the inner area IA of the chip  800  and a second seal ring structure  11  arranged between the sensor device  5  and the processing circuitry  6 . 
     As described above and illustrated in  FIG. 8 , the bridge structures  803   a,    803   b,    803   c  and  803   d  with the integrated hotplates are freely suspended and the material of the CMOS stack has been completely removed between the hotplates/bridge structures and the CMOS. This may result in a rather direct entering path for chemicals into the CMOS stack. Hence embodiments of the invention facilitate the integration of such structures together with CMOS circuitry on a common chip and the second seal ring structure  11  effectively shields a possible entering for chemicals into the oxide stack. 
     Semiconductor chips according to embodiments of the invention may be used in various electronic devices, in particular in portable electronic devices. Hence aspects of the invention also improve the reliability of the sensor functions of such electronic devices. 
     The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.