Microelectronic integrated sensor and method of manufacturing the same

p0001The invention relates to a micro-electronic, integrated sensor in which a cantilever is formed in, and in particular has a support which extends to support the upper layers through a cavity. Furthermore, the invention relates to a method for manufacturing the sensor.

p0002Such sensors are used for example for measuring accelerations. The cantilever serves together with an upper and a lower electrode as a capacitor series circuit, wherein changes in capacitance are evaluated as a measured variable. Typically, the known cantilever through springs in the sensor are anchored. However, the process sequences in the manufacture of the sensor lead to stress, in particular mechanical stress, in the cantilever. In an incomplete relaxation of the springs, the cantilever can thus bend permanently. Furthermore, the forces absorbed in the springs can lead to a malfunction of the cantilever during operation. For mechanical stabilization of these sensors are top closure panels which are usually made of a polysilicon layer, supported by means of oxide pillars. Likewise, the shutter speed can be formed from a metallization and supported with Metallisierungsstützen. In the case of aluminum supports but there is the problem that they must be insulated from the lower electrode, for example by means of a diode. Still can still leakage currents occur that affect the functionality of the sensor. Oxide pillars are difficult to manufacture because their design is problematic and heavily dependent on the etching times.

p0003The invention has for its object to provide a sensor of the type mentioned, which is insensitive to mechanical stress. In addition, a method of manufacturing of such a sensor is to be created.

p0004This object is effected device standpoint on the one hand with the characterizing features of claim 1 and, secondly, with the characterizing features of claim 8. The method default occurs the solution of a hand with the features of claim 10 and, alternatively, with the features of claim 11.

p0005According to an essential idea of ​​the invention, the cantilever is placed on a support, side and upper limits of travel are present, which are spaced in the manner of the edge of the cantilever, that on one hand sufficient compensating movements of the cantilever mechanical stress are possible, and that on the other hand the compensating movements only in the region of the support are possible.

p0006In this way a complete and free relaxierbarer cantilever is created, which is on the support, for example, bearing points, placed on which it is free to move substantially and is applicable laterally and from above limited in its movement that shifting or slipping over the bearing supporting points is also prevented.

p0007The support is prepared in a particularly preferred embodiment of a polysilicon layer, so that the direct and constant contact of the cantilever with the storage only between the polysilicon of the cantilever takes place and the polysilicon of the support.

p0008Support and movement control may conveniently be formed as a unit, preferably a blind hole-shaped surrounding the cantilever outer edge receptacle is provided. Similarly, one can also speak of a slit-shaped or slot-like receptacle of the cantilever here. The movement restrictions and the support are preferably provided in the entire peripheral region of the cantilever. Similarly, however, a point-like storage may be present.

p0009The movement restriction can also be functionally integrated into the support that the cantilever is a stepped, so that on the one hand rests on the bearing point and the stage would strike at the bearing points in the event of slippage. Planisierung through the oxide layer on which the cantilever is formed, also the production of a straight cantilever is possible.

p0010In a preferred embodiment, the movement restriction is formed in the form of a support which is guided through a recess formed in the cantilever. The movement limiting thus does not attack in this case at the outer edge of the cantilever, but in the formed recess in the edge of the cantilever.

p0011According to a further essential idea of ​​the invention, the microelectronic sensor has an existing nitride support which extends through the cavity of the sensor, and thereby supports the upper generally consisting of polysilicon layers of the sensor to the ground. Characterized an increase in stability of the sensor is reached at which any electrical insulation problems.

p0012The Nitridstützen are preferably formed with a cavity, because this shape is particularly easy to manufacture.

p0013In the method for producing a micro-electronic, integrated sensor with a formed in a cavity of a cantilever, a first oxide is according to any essential idea of ​​the invention on a substrate generated, a first polysilicon layer deposited and patterned to form a Cantileverlager, deposited thereon, a second oxide layer, deposited in the next step, a second silicon layer for Cantileverbildung, doped and recrystallized, in the second polysilicon layer a hole array structure which serves for the passage of the performed at the end of the process sequence oxide etching, depositing a third and fourth oxide layer and structured, a third polysilicon layer to form a cover applied, in the third polysilicon layer is patterned and an array of holes except for a part of the first oxide layer which lies under the structure of the first polysilicon layer, carried out isotropic etching of the underlying four oxide layers to form the cavity through this array of holes.

p0014With this method, a cantilever is formed in a cavity within a sensor that rests on a formed of the first polysilicon layer bearing point.

p0015In order to avoid that sucks on the polysilicon layer or to another surface in cooperation with the Ätzflüsigkeit during the oxide etching to form the cavity, the cantilever formed from the second polysilicon layer, it is advantageous to provide during the Herstellunsprozesses resist pillars. They can be formed in a simple manner by a two-stage generation of the holes arrays in the third polysilicon layer. Here are structured with a first photographic technique distributed over the surface holes. About these holes an anisotropic oxide etching is first carried out with a partially isotropic component. In the voids generated thereby resist is introduced by a resist mask is applied again to generate the remaining holes of the hole array in the third polysilicon layer, which allows the now free to be generated holes, and the holes generated first covering. Here, the previously etched cavities fill with paint and engage below due to the isotropic component of the preceding etching the second polysilicon layer. For the formation of this resist pillars, it is necessary that the holes used for this purpose in the array of holes of the second polysilicon layer substantially coincide with the holes of the third polysilicon layer. Finally, the resist is removed from the fully etched cavity so that the cantilever is arranged to be freely movable.

p0016According to another essential aspect of the invention a process sequence for forming a support in the cavity of the sensor used, are applied in the different oxide layers, which later form the cavity, on the oxide layers a later forming the lid polysilicon layer is deposited, this with a photographic technique is patterned and then etched through the etched hole in the polysilicon layer, an anisotropic oxide etching is carried out with an isotropic component, a nitride coating is applied, which also fills the previously etched cavity and thus forms a Nitridstütze, and etched by others in the polysilicon layer holes an oxide etch is performed to form the cavity around the pillar around.

p0017In the formation of the cantilever, which is formed of an oxide layer disposed between the further polysilicon layer, it is preferable to structure at the site of later support a larger recess, so that the support is spaced from the cantilever passes therethrough.

p0018In the cover forming polysilicon layer an array of holes is conveniently generated by the later etchings are made. In this case, a hole for performing the steps for manufacturing Nitridstützen is selected and the lying therearound holes used for etching the oxide layers.

p0019In one development of the invention, the various oxide layers of materials having different etching rates are formed so that when the Hohlraumätzung shaping the desired cavity through the choice of an oxide layer with a suitable etch rate can be controlled. In this embodiment, however, by using the first polysilicon layer as a bearing point and at the same time as an etch stop for a portion of the underlying oxide also Vewendung of oxide layers with the same etching rate possible.

p0020In the following the invention with reference to an embodiment shown in the drawing will be further explained. In detail, the schematic representations in:<dl id="dl0001"><dt>figure 1</dt><dd>a schematic cross section of a microelectronic sensor with cantilever and Nitridstütze during the manufacturing process;</dd><dt>figure 2</dt><dd>a microelectronic sensor with cantilever and Nitridstütze towards the end of the manufacturing process; and</dd><dt>figure 3</dt><dd>a partially-sectioned plan view of a microelectronic sensor.</dd></dl>

p0021In Figure 1, applied and structured in different process steps material layers are shown. A first, relatively thick oxide layer 2 is produced starting from a substrate first In this a first polysilicon layer 3 is deposited, which is patterned with a photolithographic procedure, in order to later form a bearing point for the cantilever. Thereafter, a second oxide layer 4 is applied, whose main task is the support point formed from the first polysilicon layer 3 to cover the 18th Outside this range, the oxide layer is removed again, so that, as shown in Figure 1, in the next step, a second polysilicon layer 5 can be applied. However, it would also be possible not to etch said second oxide layer 4 in partial areas, so that the second polysilicon layer 5 would then completely formed at the level of the right side of the polysilicon layer 5 shown elevated level.

p0022The second silicon layer 5 is doped and recrystallized with a high temperature treatment, thereby activating the dopants. Then an array of holes 6 is generated in the polysilicon layer 5 by patterning using a photographic technique and subsequent etching. The array of holes 6 is used for subsequent passage of the etching liquid for generating the cavity in the spaces situated below the polysilicon layer 5 areas.

p0023In places where later Nitridstützen should be generated in the polysilicon layer 5 is a matched, ie, created to avoid a collision with the Cantilver sufficiently large hole. In this second polysilicon layer 5 a third oxide layer 7 is deposited, planarized and compacted. With a photographic technique, the oxide layer 7 is structured so that it ends in the region of the arrow 14 and a further, fourth oxide layer 8 is applied in the next step, which extends over the third oxide layer and the second polysilicon layer. 5 In the next step, a third polysilicon layer 9, is applied, which forms the cover of the sensor. This is doped and recrystallized in a high-temperature step. The dopants are activated.

p0024To define the outer dimensions of the sensor and for generating an array holes 10 in the third polysilicon layer 9, the polysilicon layer using a photographic technique 9 patterned and then etched at the appropriate places. a dry, anisotropic oxide etching is distributed over the surface in some holes of the hole array 10 made using an isotropic component to generate in the oxide layers a cavity in which a support can be formed. The cavity extends substantially perpendicularly from the third polysilicon layer 9 down to the substrate 1 and performs the matched and large hole in the array of holes 10 of the second polysilicon layer 5. In the following, a nitride layer 11 is deposited, which is also the cavity previously formed to form a Nitridstütze 12 fills. The nitride layered are predominantly on the walls on, whereby a cavity 13 is produced inside the Nitridstütze 12th Since the previous Hohlraumätzung has an isotropic component, the cavity and thereby also the Nitridstütze 12 extends under cross under the third polysilicon layer 9 and supports this from hence.

p0025To carry out the further process, the nitride layer 11 is dry etched to form holes 15 especially in the area of ​​the underlying holes arrays 10th In the next step can then take place through the holes in the Polsiliziumschicht 9 and the nitride layer 11 is an isotropic etch of the oxide layers to cavitation. However, it is first carried out in some places, an anisotropic dry oxide etching with an isotropic component, thereby further cavities 16 are formed. The isotropic component must be so large that the cavity also portions of the second polysilicon layer 5 is detected, which forms the cantilever. These cavities are filled at a following photo art with paint, so that form in the sensor resist pillars that hold during the following oxide etching the cantilever in a predetermined position and thereby avoid a decrease of the cantilever 17th In this way it is prevented that sucks the cantilever during the oxide etch under the influence of the etching liquid. After etching of the cavity, the resist pillars are removed.

p0026The holes of the hole array 10 formed in the third polysilicon layer 9 are geometrically smaller than the holes of the hole array 6 in the second polysilicon layer 5, because the first-mentioned holes have to be closed again at the end.

p0027This results in the structure shown in figure 2 with the supporting point 18, which is formed from the first polysilicon layer 3, which is also referred to as an auxiliary layer, the cantilever 17, which is formed from the second polysilicon layer 5 and the covering which substantially consists of the third polysilicon layer. 9 The remaining holes in the cover formed from the third polysilicon layer 9 are covered and sealed with an oxide or borophosphosilicate glass (BPSG). At a suitable location, a contact hole 20 is etched and passed through a metallic contact on the underlying cantilever 17th It should be ensured that the metallic contact is not in contact with the polysilicon layer 3 in the region of the holes arrays. 6 This is done by an interruption 19 of the polysilicon layer 3. The sensor can now work as intended by the changing capacitances between the cantilever 17 and the polysilicon layer 9 on the one hand and the cantilever 17 and the substrate 1 on the other.

p0028In figure 3 a top view is shown on the sensor, wherein the dotted line indicates the outer dimensions of which are determined by the third polysilicon layer. 9 The third polysilicon layer covers on the one hand the main portion of the cantilever 17, and for the extension shown on the bottom right of the cantilever 17, in which the bearing point formed from the first polysilicon layer 3 and 18 is arranged. The third polysilicon layer 9 formed separately in these two areas in order to prevent electrical contact with the cantilever 17th In the central portion of the cantilever 17, both the array of holes 6 times the polysilicon layer and overlying the array of holes 10 of the third Polysliziumschicht 9 is arranged.