DE102018221102B4 - Inertial sensor with a movable detection element of a field effect transistor and method for producing the same - Google Patents

Abstract

Method for producing an inertial sensor (400) with a movable detection element (180) of a field effect transistor, comprising the steps: - providing a digital integrated circuit (100); - providing an analog integrated circuit (200); - functional connection of the digital integrated circuit ( 100) with the analog integrated circuit (200) by means of wafer bonding; and- freeing the movable detection element (180) of the field effect transistor in the analog and / or digital integrated circuit (200) after the wafer bonding.

Description

The invention relates to a method for producing an inertial sensor with a movable detection element of a field effect transistor. The invention further relates to an inertial sensor with a movable detection element of a field effect transistor.

State of the art

Micromechanical sensors, such as inertial sensors, are usually implemented using capacitive or piezoresistive transducers. So-called moving gate or moving channel inertial sensors are also known, although such sensors are not yet available on the market.

Normally, silicon dioxide is used for sacrificial layers in micromechanics, which can be dry and isotropically etched highly selectively to silicon. If silicon dioxide were used as gate oxide in moving-gate inertial sensors, this would lead to an open channel region between drain and source contacts and would furthermore also disclose the source and drain contacts themselves. With the exposed contact and channel areas, surface conditions are generated that have a negative impact on e.g. can have the drift stability and the signal-to-noise ratio of the sensor element.

In order to ensure the sensor function, a movable structure must be created in the sensor element. US 2009/0317930 A1 describes a procedure for how a deflectable structure can be produced using a heterogeneous sacrificial layer. This opens up two possibilities with regard to inertial sensors based on the mode of operation of field effect transistors: on the one hand, describes EP 0 990 911 A1 a method with which the gate region is designed to be movable with respect to the source and drain region. DE 10 2009 029 217 A1 and DE 10 2012 217 133 A1 describe methods for making the channel region between drain and source contacts movable relative to the fixed gate region. US 2011/0265574 A1 also describes how micromechanical functional elements can be combined with CMOS devices.

The publication DE 19619921 A1 shows a MOS transistor with a movable gate electrode made of a thin silicon layer. The publication DE 19537285 A1 shows a field effect transistor with a movable gate (MOGFET), which is worked out of a wafer.

Disclosure of the invention

An object of the present invention is to provide an improved method for producing an inertial sensor with a movable detection element of a field effect transistor.

• - Bereitstellen einer digitalen integrierten Schaltung;
• - Bereitstellen einer analogen integrierten Schaltung;
• - Funktionales Verbinden der digitalen integrierten Schaltung mit der analogen integrierten Schaltung mittels Waferbonden; und
• - Freistellen des beweglichen Detektionselements des Feldeffekttransistors in der analogen und/oder digitalen integrierten Schaltung nach dem Waferbonden.

According to a first aspect, the object is achieved with a method for producing an inertial sensor with a detection element of a field effect transistor, comprising:

• - Providing a digital integrated circuit;
• - providing an analog integrated circuit;
• - Functional connection of the digital integrated circuit with the analog integrated circuit by means of wafer bonding; and
• - Freeing the movable detection element of the field effect transistor in the analog and / or digital integrated circuit after the wafer bonding.

This advantageously enables movable structures of the field effect transistor to be exposed from the rear. This advantageously results in a simpler process design and electrical conductor tracks can be freely designed without having to take subsequent processes into account. Providing perforations in order to be able to implement structures from the front is therefore unnecessary and not necessary.

• - eine digitale integrierte Schaltung;
• - eine analoge integrierte Schaltung;
• - wobei die digitale integrierte Schaltung mit der analogen integrierten Schaltung mittels Waferbonden funktional verbunden ist; und
• - wobei das bewegliche Detektionselement des Feldeffekttransistors im Wesentlichen von aus der analogen und/oder digitalen integrierten Schaltung nach dem Waferbonden herausstrukturiertem einkristallinen Substratmaterial gebildet wird.

According to a second aspect, the object is achieved with an inertial sensor with a detection element of a field effect transistor, comprising:

• - a digital integrated circuit;
• - an analog integrated circuit;
• - The digital integrated circuit is functionally connected to the analog integrated circuit by means of wafer bonds; and
• - The movable detection element of the field effect transistor is essentially formed by single-crystalline substrate material structured out of the analog and / or digital integrated circuit after wafer bonding.

Preferred developments of the method are the subject of dependent claims.

An advantageous development of the method is characterized in that the analog integrated circuit by means of wafer bonding with a Cap element is connected. The inertial sensor can advantageously be equipped with a cap element, a suitable gas pressure being formed within the cap element for improved functionality of the movable detection element of the FET.

A further advantageous development of the method is characterized in that the analog or digital integrated circuit has at least one electrically conductive contact, which establishes an electrical connection to a cap element. In this way, electrical circuits can also be used in the cap element. This is particularly advantageous if electrical functions that are to be connected to the functions of the analog integrated circuit are also present in a cap element that is subsequently attached.

Another advantageous development of the method is characterized in that the movable detection element of the field effect transistor is freed from polysilicon of the analog integrated circuit by means of sacrificial layer etching. In this way, the movable detection element of the field effect transistor is formed from the rear. Conventional anisotropic dry etching steps are carried out to expose the sacrificial layer, which are not impeded by disruptive metallization layers on the front side. As a result, it is possible in a simple manner to provide a movable detection structure of the field effect transistor in the bonded state with the digital integrated circuit.

Another advantageous development of the method is characterized in that a getter material is applied to an inner surface of the cap element. The getter material, which can bind gas molecules, improves the consistency of the gas pressure inside a cavern of the cap element.

A further advantageous development of the method is characterized in that a suitable gas pressure in a cavity is set via an opening in the cap element, the opening being closed by means of a laser by melting substrate material. This also makes it possible to adjust the gas pressure after wafer bonding, this being carried out by opening the cap element, adjusting the gas pressure and then closing the opening by melting and solidifying substrate material. If several caverns are realized in one cap element, this method can also be used to set different gas pressures, the process being repeated several times and in each case only the cavern to be set being opened and closed.

Further advantageous developments of the method are characterized in that a movable gate or a movable channel of the field effect transistor is formed as the movable detection element. In this way, different detection principles in the sense of a moving channel sensor or a moving gate sensor are implemented.

A further advantageous development of the method is characterized in that circuitry functionalities are integrated in the cap element. In this way, a functionality of the initial sensor can advantageously be further improved.

The invention is described in more detail below with further technical features and advantages using several figures. For better clarity, it can be provided that not all reference numbers are drawn in all the figures. The figures are not necessarily drawn to scale.

Disclosed method features result analogously from corresponding disclosed device features and vice versa. This means in particular that features, technical advantages and designs relating to the method for producing an inertial sensor with a movable detection element of a field effect transistor result analogously from corresponding designs, features and advantages relating to the inertial sensor with a movable detection element of a field effect transistor and vice versa.

• 1 - 16 anhand von Querschnittsansichten ein prinzipielles Verfahren zum Herstellen eines Inertialsensors mit einem beweglichen Detektionselement eines Feldeffekttransistors; und
• 17 einen prinzipiellen Ablauf eines Verfahrens zum Herstellen eines Inertialsensors mit einem beweglichen Detektionselement eines F eldeffekttransi stors.

The figures show:

• 1 - 16 based on cross-sectional views, a basic method for manufacturing an inertial sensor with a movable detection element of a field effect transistor; and
• 17th a basic sequence of a method for manufacturing an inertial sensor with a movable detection element of a field effect transistor.

Description of embodiments

1 shows a cross-sectional view through a fully processed digital integrated circuit 100 (Digital IC, CMOS chip), which was generated using conventional process steps. A first substrate can be seen 10 in the form of a Si wafer, which is between a first oxide layer 20 and a second oxide layer 30th is embedded. You can also see electrical vias through the individual oxide layers (via) and through the substrate 10 (through silicon via, TSV) covering the three layers mentioned 10 , 20 , 30th penetrate and in the second oxide layer 30th to electrical rewiring elements 50 are connected. The TSV is used to make vias through the substrate 10 to realize. The individual vias serve to separate metal layers within the oxide layers 20 , 30th connect to. In total, the entire through-connection is done by the digital integrated circuit 100 through the series connection of all individual vias and the TSV, whereby all vias and the TSV itself are produced individually by the layered structure.

The oxide layer 20 is created by many individual, successive depositions with intermediate structuring processes in order to realize the through contacts. Furthermore, are within the first substrate 10 Doping areas 11 recognizable. Within a fourth oxide layer 31 are polysilicon elements 12th trained to implement electrical connections.

The following cross-sectional views show the formation of an analog integrated circuit (“analog IC”) 200 with known process steps. In this context, “analog” means that transistors and other electrical components such as resistors and capacitors are also manufactured that do not have exclusively logical (digital) functionality, but work analogously, ie that they do more than just high or low - Provide signal level.

2nd shows a cross-sectional view of a second substrate 110 (Si substrate).

3rd shows a cross-sectional view of the second substrate 110 with drain and source areas diffused into it 120 for a field effect transistor to be trained later (not shown).

4th shows a cross-sectional view of the second substrate 110 , whereby it can be seen that in an insulation layer 121 buried polysilicon elements 130 are trained.

The cross-sectional view of the second substrate 110 from 5 shows that on the insulation layer 121 also polysilicon elements 140 was deposited as a gate region of the field effect transistor to be formed (not shown) and as a sacrificial layer.

The cross-sectional view of the second substrate 110 from 6 shows that on the insulation layer 121 a sum of further oxide layers 150 was deposited in the electrical conduction elements 160 are designed in the form of wiring levels and vias.

The cross-sectional view of 7 shows the partially completed inertial sensor 400 , where partially completed means that the moving structures are not yet free. This means that the device is not yet functional and therefore not “finished”. Here are the digital integrated circuit 100 and the analog integrated circuit 200 functionally and mechanically connected ("bonded") using a conventional wafer bonding process (eg eutectic bonding). A bond interface can be seen B1 , about which the circuits mentioned 100 , 200 are connected. At this stage, in which the two circuits 100 , 200 are functionally and mechanically connected to each other, an exemption of the movable detection element (not shown) of the field effect transistor from the rear or from below, ie from the side of the analog integrated circuit 200 carried out. In this way, there are advantageously no metallization planes between the structure to be exposed and the component surface, so that there is a clear path for the required etching processes. As a result, this means technological advantages in the form of a simpler process design and the layout of electrical conductor tracks is also flexible.

It is therefore advantageously not necessary to release the movable detection element from the top by means of the analog integrated circuit 100 to perform through. Under certain circumstances, this would disadvantageously result in a perforated design of the electrical rewiring element 50 require. As a result, no complex assembly and connection technology (AVT) is required for later processing, by means of which the separately available circuits 100 , 200 must be functionally connected, since this has already been done through the design of the vias and TSVs (through silicon-via) by wafer bonding. With the proposed method, a large number of electrical wire bond contacts can thus be saved. All in all, this results in a space saving of the entire device and also possible performance increases, since wire bond contacts generally result in unwanted, higher parasitic electrical capacities.

In the cross-sectional view of 8th you can see that the second substrate 110 the analog integrated circuit 200 towards the 7 was thinned back to a thickness D, the thickness D of the second substrate 110 after thinning back is preferably about 10 microns to about 20 microns.

In the cross-sectional view of the initial sensor 400 from 9 you can see that in one optional step an electrically conductive connection element 170 , preferably a tungsten element (tungsten plug) in the back-thinned second substrate 110 for the purpose of a later electrical contacting of circuit structures of the analog integrated circuit 200 with circuit structures of a cap element to be applied later (not shown) is inserted.

In the cross-sectional view of 10 it can be seen that by means of anisotropic etching of the substrate 110 and the insulation layer 121 and sacrificial layer etching of the polysilicon element 140 the analog integrated circuit 200 the movable detection element 180 was designed with a movable channel.

The result is a distance between the gate electrodes 190 to the connecting part between drain and source area 120 , which is always due to the insulation layer 121 are covered, depending on one on the inertial sensor 400 mechanical stress acting variable. The position of the movable channel relative to the gate electrode 190 can depend on the inertial sensor 400 acting mechanical force or acceleration can be varied. In this way, the inertial sensor 400 acting force or acceleration are measured.

In the following 11 to 13 is a cross-sectional view of a production of an optional cap element 300 shown.

One recognizes in 11 a third substrate 300 preferably in the form of a Si wafer, which, as in 12th shown, is formed in a suitable manner by means of an etching or trench process. In the cross-sectional view of 13 it can be seen that in the recess in the third substrate 300 optionally a getter material 310 is introduced. Using the getter material 310 can create gas molecules within the later cap element 300 be bound, resulting in a defined gas pressure within a cavity 320 of the cap element 300 can be preserved.

For this purpose, it can be provided, for example, to open the cap element by means of an etching step, the gas pressure within the cavity 320 suitably set and then the opening by means of a laser beam by melting the substrate material of the third substrate 300 to melt again, as a result of which a laser reseal process is carried out and the desired gas pressure in the cavity 320 is set.

A closure element produced in this way 330 is basically in the cross sectional view of 15 shown.

In the cross-sectional view of the sensor element 400 from 14 it can be seen that the cap element 300 mechanical and functional with the analog integrated circuit 200 was bonded by means of a wafer bonding process, whereby a second bond interface B2 is realized. The connection element 170 can be used for an electrical connection of electronic circuit structures in the elements mentioned.

In the cross-sectional view of the sensor element 400 from 16 it can be seen that on the rewiring elements 50 the digital integrated circuit 100 still solder bumps 410 were applied in order to make electrical contact with the entire sensor element 400 to provide. Other types of electrical contacting are also possible, which are not shown in the figures.

The invention proposes an advantageous embodiment of a sensor and a manufacturing process for sensors which use field effect transistors (FETs) with a movable channel area for signal detection. Furthermore, the proposed method enables the possibility of integrating analog and digital integrated circuits in an overall component, which is associated with a significant saving in area and thus a possible cost reduction of the overall system. By dispensing with hybrid AVT methods, the sensor performance can also be increased since, for example, the use of wire bonds to connect the MEMS to the analog and digital IC can be dispensed with. These usually cause unwanted, increased parasitic capacities and the associated longer signal propagation times.
The proposed method opens up several advantages:

The use of wafer bond technologies enables full 3D integration of MEMS, analog and digital IC, which significantly reduces the space requirement of the overall system and, as a result, can potentially reduce costs.

By not using hybrid connection technology between MEMS and ICs (e.g. wire bonds), potentially parasitic capacitances can be reduced, which has a positive influence on the sensor performance.

In contrast to conventional methods, the micromechanical function is carried out according to the manufacturing steps for the digital and analog IC. As a result, it is no longer necessary to perforate the wiring layers in the IC in order to release the moving parts. The wiring layers can thus be implemented without taking into account the later MEMS process steps. The micromechanics can then be structured from the back of the substrate after wafer bonding.

Due to the proposed manufacturing process, it is not necessary, in comparison to the prior art, to provide perforation of different layers in order to be able to mechanically clear all the necessary buried areas. Furthermore, the proposed process means that the channel region and the drain and source region remain covered with the insulation layer even after the sacrificial layer etching. This prevents the penetration / migration of ions / charges from the outside into the field-sensitive area and thus reduces the sensor drift.

17th shows a basic sequence of a method for producing an inertial sensor with a movable detection element of a field effect transistor.

In one step 500 will provide a digital integrated circuit 100 carried out.

In one step 510 becomes a provision of an analog integrated circuit 200 carried out.

In one step 520 becomes a functional connection of the digital integrated circuit 100 with the analog integrated circuit 200 performed using wafer bonds.

In one step 530 becomes a freeing of the movable detection element 180 of the field effect transistor in the analog and / or digital integrated circuit 200 performed after wafer bonding.

It goes without saying that the steps mentioned 500 to 530 can be interchanged in a suitable manner.

For example, in one variant it is also conceivable that, instead of the moving channel sensor explained above, an inertial sensor with a movable gate (moving gate sensor) is formed (not shown in the figures).

Although the invention has been described above on the basis of specific exemplary embodiments, the person skilled in the art can also implement embodiments which have not been disclosed or only partially disclosed without departing from the essence of the invention.

Claims (9)

Method for producing an inertial sensor (400) with a movable detection element (180) of a field effect transistor, comprising the steps: - providing a digital integrated circuit (100); - providing an analog integrated circuit (200); - Functional connection of the digital integrated circuit (100) with the analog integrated circuit (200) by means of wafer bonding; and - Freeing the movable detection element (180) of the field effect transistor in the analog and / or digital integrated circuit (200) after the wafer bonding. Procedure according to Claim 1 , characterized in that the analog integrated circuit (200) is connected to a cap element (300) by means of wafer bonding. Procedure according to Claim 2 , characterized in that the analog or digital integrated circuit (200) has at least one electrically conductive contact (170) which establishes an electrical connection to a cap element. Procedure according to one of the Claims 2 to 3rd , characterized in that the movable detection element (180) of the field effect transistor is freed from polysilicon of the analog integrated circuit (200) by means of sacrificial layer etching. Procedure according to Claim 4 wherein a getter material (310) is applied to an inner surface of the cap element (300). Procedure according to one of the Claims 2 to 5 A suitable gas pressure in a cavity (320) is set via an opening in the cap element (300), the opening being closed by means of a laser by melting substrate material. Method according to one of the preceding claims, wherein a movable gate or a movable channel of the field effect transistor is formed as the movable detection element (180). Procedure according to one of the Claims 2 to 7 Circuitry functionalities are integrated in the cap element (300). Inertial sensor (400) with a movable detection element of a field effect transistor, comprising: - a digital integrated circuit (100); - an analog integrated circuit (200); - The digital integrated circuit (100) is functionally connected to the analog integrated circuit (200) by means of wafer bonding; and - wherein the movable detection element of the field effect transistor is essentially formed from single-crystal substrate material structured out of the analog and / or digital integrated circuit (200) after the wafer bonding.

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