DE102016214973A1 - Combined laser drilling and plasma etching method for producing a micromechanical device and micromechanical device - Google Patents

Abstract

The invention relates to a micromechanical device having a first substrate (11), with at least one first cavern (100), with a closed access (1) to the first cavern (100), the access (1) passing through the first substrate (11). 11) runs. The essence of the invention is that the access (1) has a laser drilled first section (12) and a plasma etched second section (13), wherein the plasma etched second section (13) has an opening to the first cavity (100), wherein the Access (1) in the first section (12) by a melt closure (5) made of melt of at least the first substrate (11) is closed. The invention also relates to a combined laser drilling and plasma etching process for the production of micromechanical devices.

Description

State of the art

The invention is based on a micromechanical device having a first substrate, with at least one first cavern, with a closed access to the first cavern, the access extending through the first substrate.

From the publication WO 2015/120939 A1 is a method for selectively adjusting an internal pressure in a cavern of a MEMS element known. In this case, a narrow access channel to a MEMS cavern is produced in a cap wafer or in a sensor wafer. The cavern is flooded with the desired gas and internal pressure via the access channel. The area around access channel is then heated locally via a laser. The substrate material liquefies locally and hermetically closes the access channel during solidification.

In most cases, such a method is used if one wishes to generate in a MEMS element with two caverns, wherein a different internal pressure is to be generated in the two caverns ( 1 ).

This is necessary if, for example, you would like to combine an acceleration sensor with a yaw rate sensor. The acceleration sensor requires a high internal pressure for optimum operation, whereas a rotation rate sensor requires a very small internal pressure. This method makes it possible to set the respective optimum internal pressure in each cavern.

Also, the method can be used, if caused by an outgassing during litigation, a very low internal pressure in a cavern can not be achieved, it can be subsequently adjusted.

In a discrete arrangement in which only one MEMS element is realized and the evaluation circuit is provided separately, the generation of the access channel ( 1 ) simultaneously with the blanking of the electrical contact surfaces ( 2 ) be made. In such an arrangement, a relatively thin cap wafer is usually used. After bonding the cap wafer ( 3 ) on the sensor wafer ( 4 ) can be generated via a photomask and a trench method in one step, both a narrow access opening to a first cavity, and a large access opening to the contact surfaces.

In the German patent DE 102011103516 B4 It is proposed to encapsulate a MEMS structure with a deposition of a polycrystalline silicon layer and then to create an access channel into the polycrystalline silicon layer by means of a laser drilling process. Then a defined atmosphere is set in the MEMS cavern and the access channel is closed with a laser sealing process. The creation of the access channel is cost-effective compared to a pure trench process with only one access channel applied. The disadvantage is that in a laser drilling process always creates smoke that can affect the MEMS structures. Another disadvantage is that the laser drilling process is not very selective to different materials. That is, irrespective of the material, laser drilling does not only create an access hole through the polycrystalline silicon layer, but also simultaneously drills a hole in the underlying layer.

Object of the invention

What is needed is a method or arrangement that allows inexpensive production of an access channel in a thick substrate. The access channel should end in a cavern and produce no smoke and other impurities in the manufacturing process. Also, the process should stop as soon as it reaches the cavern and not further drill into the underlying material under the cavern. Furthermore, the method should produce at the substrate surface very small access holes that can be closed by a laser reflow process.

Advantages of the invention

The invention is based on a micromechanical device having a first substrate, with at least one first cavern, with a closed access to the first cavern, the access extending through the first substrate. The essence of the invention is that the access has a laser-drilled first section and a plasma-etched second section, wherein the plasma-etched second section has an opening to the first cavity, wherein the access in the first section is closed by a melt-melt closure of at least the first substrate ,

An advantageous embodiment of the invention provides that the first substrate has an additional layer and the access is also closed by melt of the additional layer.

Advantageously, the micromechanical device is a hybrid integrated micromechanical device wherein the device has a second substrate with an ASIC circuit.

The invention also relates to a combined laser drilling and plasma etching method for producing micromechanical devices.

Advantageously, with the method according to the invention, smoke in the cavern is completely avoided. Advantageously, no expensive photomask for the plasma etching process is necessary. The laser drilling process generates the mask necessary for the trench process. Advantageously, the adjustment between the laser drilling process and the trench process via the additional layer is self-adjusting, an offset is excluded. Advantageously, by combining two removal methods, namely laser drilling and trench etching, a higher overall aspect ratio for the access channel can be achieved. By suitable choice of the additional layer, it is advantageously possible to achieve smaller access openings in the laser drilling process. Advantageously, the additional layer can be used simultaneously to produce a more stable laser reseal process, for example by making the material of the additional layer more readily fusible, or by forming a eutectic with the material of the substrate, in particular silicon. Advantageously, the combined laser drilling and plasma etching process according to the invention can be integrated with the defined introduction of a suitable atmosphere and sealing at any point in the entire MEMS production process. In particular, this sequence of steps can also be integrated at the very end of the wafer production process. So the actual manufacturing process does not have to be changed.

An advantageous embodiment of the method according to the invention provides that after step (c) the additional layer is removed. Advantageously, the additional layer can be removed immediately after step (c) or in a later process step.

An advantageous embodiment of the method according to the invention provides that after the step (e) in the first cavern, an atmosphere having a specific composition and a certain pressure is set.

An advantageous embodiment of the method according to the invention provides that laser melting of material of the additional layer takes place in step (f). Advantageously, the access is closed by melt of the additional layer.

An advantageous embodiment of the method according to the invention provides that step (c) and / or step (d) is carried out essentially at atmospheric pressure.

An advantageous embodiment of the method according to the invention provides that in step (c) the laser drilling is performed with a first laser or with first laser operating parameters, in particular with a very short wavelength or very strongly focused or with a very short pulse length, and that in step (d) the laser drilling with a second laser or with second laser operating parameters, which are different from the first laser operating parameters, in particular with a larger wavelength or less strongly focused or performed with a larger pulse length.

An advantageous embodiment of the method according to the invention provides that in step (d) the laser drilling is first performed with the first laser operating parameters to a certain depth and then the laser drilling is performed with the second laser operating parameters.

drawing

1 shows a micromechanical device with a cavern with a closed access in the prior art.

2A to G shows an embodiment of the combined laser drilling and plasma etching method according to the invention for producing a micromechanical device.

3 schematically shows the laser drilling and plasma etching process according to the invention for producing a micromechanical device.

description

1 shows a micromechanical device with a cavern with a closed access in the prior art. Schematically illustrated is a micromechanical device with a MEMS wafer 4 and a cap wafer 3 , The cap wafer 3 has an access channel 1 on top, with a melt closure 5 is closed. In recesses of the cap wafer 3 are electrical contact surfaces 2 arranged. The micromechanical device has a first cavity 100 which contains, for example, a rotation rate sensor, and a second cavity 200 , which contains, for example, an acceleration sensor on. The cavern 200 essentially contains an atmosphere with pressure and composition of the process gas in the bonding of the MEMS wafer 4 with the cap wafer 3 , As a result, a good damping of the acceleration sensor is ensured. The cavern 100 was through the access 1 evacuated and access 1 then by means of a melt closure 5 locked. This ensures a high quality of the oscillator of the rotation rate sensor. The arrow indicates the effective direction a laser closure process for making the fusion closure 5 ,

In a discrete arrangement of a micromechanical sensor or another micromechanical device, in which only one MEMS element is realized and the evaluation circuit or another electrical control circuit is provided separately, the access channel 1 simultaneously with the cropping of the electrical contact surfaces 2 getting produced. In such an arrangement is usually a relatively thin cap wafer 3 used. After bonding the cap wafer 3 on the sensor wafer 4 can use a photomask and a trench in a common step, both a narrow access opening 1 to the first cavern 100 , as well as a large access opening to the contact surfaces 2 , be generated.

Difficult is the production of the access opening 1 to the first cavern 100 with thick cap wafer. The access opening 1 must not be too large, otherwise it will no longer be possible to close it by means of a local melting and subsequent solidification. Trench methods that produce very narrow accesses and at the same time reach very low, ie have a high aspect ratio, are difficult and become increasingly slower and more complicated as the aspect ratio increases.

Will the access 1 to the first cavern 100 not at the same time as opening the contact areas 2 produced, a separate photomask must be provided for both processes. This is complicated and expensive and partly technically difficult to implement.

2A to G shows an embodiment of the combined laser drilling and plasma etching method according to the invention for producing a micromechanical device. 2A shows first a provided wafer composite with a MEMS wafer and a substrate with an ASIC evaluation circuit. For applications of so-called hybrid integration, wafer level becomes a second substrate 15 with an ASIC evaluation circuit 6 directly with a MEMS wafer 7 with a first substrate 11 combined. Alternatively, a MEMS element is applied to the ASIC evaluation circuit and this wafer is encapsulated with a cap substrate. In order to get as compact a component as possible, the ASIC substrate can be used 15 or the MEMS substrate 11 Vias (trans silicon vias, TSV's) 8th be provided to produce an electrical connection between the ASIC circuit, in particular a MEMS sensor evaluation circuit, and the environment. 2 B shows the application of an additional layer 9 on the first substrate 11 , Using a laser drilling method with pulsed laser energy is performed according to 2C in the additional layer 9 a hole 10 drilled. Next is then according to 2D into the underlying material of the first substrate 11 also deepened the hole with a pulsed laser and into a first section 12 of the first substrate 11 promoted. Before the underlying first cavern 100 is achieved, is switched to a plasma etching process, in particular a trench method, as in 2E is shown. The additional layer 9 serves as a mask for the plasma etching process. With this layer as a mask, the access channel becomes the plasma etching process 1 through a second section 13 of the first substrate 11 until the first cavern 100 , in which, for example, a MEMS functional element is etched. The arrows indicate here the direction of action of a trench method. In the cavern, especially at one of the access channel 1 opposite wall of the cavern, can optionally a stop layer 14 so that the plasma etching process does not further etch into the MEMS functional element or the ASIC circuit or into the second substrate. Then the cavern is flooded with the desired gas and the desired internal pressure via the access channel. 2F shows a variant of the method according to the invention, in which the additional layer 9 subsequently removed. The additional layer 9 may for example consist of oxide and be removed by etching. The arrows here indicate the action of an ore process for removing the additional layer 9 , Alternatively, the additional layer 9 be removed or persist in a later step. 2G shows how finally an area of the first substrate 11 around the access channel 1 is heated locally via a laser. The substrate material of the first substrate 11 liquefies locally and closes the access channel during solidification 1 in the laser drilled first section 12 hermetic with a melt closure 5 , If the additional layer 9 has not been removed, also a part of the additional layer can be heated by the laser. Material of the additional layer 9 liquefies locally and closes when solidifying also the access channel 1 ,

• (a) Bereitstellen eines mikromechanischen Vorläuferprodukts mit einem ersten Substrat 11 und wenigstens einer ersten Kaverne 100, wobei die erste Kaverne 100 wenigstens von dem ersten Substrat 11 begrenzt wird,
• (b) Aufbringen einer Zusatzschicht 9 auf das erste Substrat 11,
• (c) Laserbohren durch die Zusatzschicht 9 und somit Herstellen einer Maske,
• (d) Laserbohren eines ersten Teilabschnitts 12 des ersten Substrats 11 durch die Maske hindurch,
• (e) Plasmaätzen eines zweiten Teilabschnitts 13 des ersten Substrats 11 durch die Maske und durch den ersten Teilabschnitt 12 hindurch, derart, dass ein Zugang 1 durch das erste Substrat 11 zur Kaverne 100 geschaffen wird,
• (f) Laser-Schmelzen von Substratmaterial des ersten Teilabschnitts 12 und Verschließen des Zugangs 1 mit Schmelze.

3 schematically shows the laser drilling and plasma etching process according to the invention for producing a micromechanical device with the method steps:

• (a) providing a micromechanical precursor product with a first substrate 11 and at least a first cavern 100 , where the first cavern 100 at least from the first substrate 11 is limited,
• (b) applying an additional layer 9 on the first substrate 11 .
• (c) laser drilling through the additional layer 9 and thus producing a mask,
• (d) laser drilling a first section 12 of the first substrate 11 through the mask,
• (e) plasma etching a second subsection 13 of the first substrate 11 through the mask and through the first section 12 through, such an access 1 through the first substrate 11 to the cavern 100 is created
• (f) laser melting substrate material of the first section 12 and closing the access 1 with melt.

• 1. Ein MEMS-Wafer-Strack wird mit mindesten einer Zusatzschicht versehen.
• 2. Mit einem Laser-Bohr-Verfahren wird in die Zusatzschicht und das Substratmaterial ein Sack-Loch gebohrt.
• 3. Mit einem Plasma-Ätzverfahren insbesondere mit einem Trench-Verfahren wird das Loch weiter bis in die Kaverne geätzt.
• 4. Optional kann nun die Zusatzschicht entfernt werden (2F).
• 5. Die Kaverne wird mit den gewünschten Gas und dem gewünschten Innendruck über den Zugangskanal geflutet.
• 6. Der Bereich um den Zugangskanal wird lokal über einen Laser erhitzt, das Substratmaterial verflüssigt sich lokal und verschließt beim Erstarren den Zugangskanal hermetisch.

The essential process steps of the process according to the invention can be summarized as follows:

• 1. A MEMS wafer line is provided with at least one additional layer.
• 2. A sack hole is drilled in the additional layer and substrate material using a laser drilling method.
• 3. With a plasma etching process, in particular with a trench method, the hole is further etched into the cavern.
• 4. Optionally, the additional layer can now be removed ( 2F ).
• 5. The cavern is flooded with the desired gas and internal pressure over the access channel.
• 6. The area around the access channel is locally heated by a laser, the substrate material liquefies locally and hermetically seals the access channel upon solidification.

Further embodiments of the invention

It is convenient to perform the laser drilling process with two different lasers or laser settings. The first laser drilling process is optimized to drill a hole in the additional layer. For example, it is possible to deliberately use a laser with a very short wavelength, which is very focused and or has a very short pulse length. Thus, a very small access hole can be created in the additional layer. The second laser drilling process can be optimized to drill a hole in the substrate. In particular, the additional layer and the second laser can be combined in such a way that a part of the laser power is reflected. For example, as an additional layer, it is possible to use a metal layer, in particular aluminum, which is combined with a laser wavelength, so that a large part of the light is reflected. Or, a partially transparent layer such as oxide is used, but is selected in a thickness such that the laser light is largely reflected. By such an arrangement, the laser light can be further spatially localized by the additional layer in addition to the normal focus and it is thus able to drill very small access channels also at great depth. A favorable feature of this method is that the second laser drilling process can also use a laser with a longer wavelength and / or a longer pulse length, which allows faster drilling rates.

Furthermore, it can be beneficial with the first laser drilling process a hole not only in the additional layer 9 to drill, but also in the upper part of the first substrate 11 which is to be closed later via the reflow process. In the middle part of the substrate one can then use a second laser drilling process, which drills a larger opening and works faster. A narrow access opening in the upper substrate area is favorable for the subsequent closing process. Therefore, it is favorable to drill the first narrow bore as deep or deeper as the depth of the melting area in the sealing process in the substrate.

It is further advantageous if the laser drilling process is initially carried out in air, that is to say at atmospheric pressure, in order to allow simple, cost-effective process control. Subsequently, the plasma etching process is carried out in a vacuum chamber. Then, the wafer is directly, without bringing the wafer from the vacuum system, closed with the laser reseal process. A favorable feature of this process is that no impurities can enter the cavern during subsequent aerating. Furthermore, moisture and other absorbing gases can not enter the cavern. These gases could be removed in part only by heating. Since in this process management no annealing is necessary, the inventive method can be made at any point, especially at the very end of the process chain for the production of a micromechanical device. This is also possible, for example, if solder balls have already been placed on the wafer and therefore a temperature treatment is no longer possible.

With the method according to the invention, the MEMS substrate can be selected to be significantly thicker than the ASIC substrate. This is particularly favorable when the MEMS structures are mechanically coupled to the MEMS substrate.

The method is particularly favorable for hybrid integrated MEMS elements. It is particularly advantageous if a MEMS structure is provided on a substrate and an ASIC evaluation circuit is provided on a further substrate and both substrates are bonded to one another. Then it is convenient to choose access to the described method through the substrate with the MEMS structure. In this case, ASIC functional layers such as passivation layers (oxides) or wiring layers (Al or Cu) can be used as etchants. Stop layer can be used for the plasma etching process without additional layers must be applied in the system.

In particular, the method is favorable for the production of hybrid integrated MEMS elements with at least two caverns with different internal pressure.

Furthermore, the method is favorable for the production of hybrid integrated MEMS elements which are designed as bare die constructions, ie are provided directly with solder balls and are not potted in plastic material.

LIST OF REFERENCE NUMBERS

1

access channel

2

electrical contact surfaces

3

cap wafer

4

sensor wafer

5

melting closure

6

ASIC wafer

7

MEMS wafer

8th

TSV

9

additional layer

10

 laser drilled hole in additional layer

11

 first substrate

12

 laser drilled first section of the access channel in the first substrate

13

 plasma etched second section of the access channel in the first substrate

14

 stop layer

15

 second substrate

20

 solder ball

100

 first cavern

200

 second cavern

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2015/120939 A1 [0002]
• DE 102011103516 B4 [0007]

Claims (10)

Method for producing a micromechanical device comprising the steps of: (a) providing a micromechanical precursor product with a first substrate ( 11 ) and at least one first cavern ( 100 ), the first cavern ( 100 ) at least from the first substrate ( 11 ), (b) applying an additional layer ( 9 ) on the first substrate ( 11 ), (c) laser drilling through the additional layer ( 9 ) and thus producing a mask, (d) laser drilling a first subsection ( 12 ) of the first substrate ( 11 through the mask, (e) plasma etching a second subsection 13 of the first substrate ( 11 ) through the mask and through the first section 12 such that access ( 1 ) through the first substrate ( 11 ) to the cavern ( 100 ), (f) laser melting of substrate material of the first subsection ( 12 ) and closing access ( 1 ) with melt. Method according to claim 1, characterized in that after step (c) the additional layer ( 9 ) Will get removed. Method according to claim 1, characterized in that after step (e) in the first cavern ( 100 ) an atmosphere with certain composition and pressure is set. A method according to claim 1 or 3, characterized in that in step (f) also laser melting of material of the additional layer ( 9 ) he follows. Method according to one of the preceding claims, characterized in that the step (c) and / or the step (d) is carried out substantially at atmospheric pressure. Method according to one of the preceding claims, characterized in that in step (c) the laser drilling is performed with first laser operating parameters, in particular with a very short wavelength and / or very strongly focused and / or with a very short pulse length, and that in step (c) d) the laser drilling with second laser operating parameters, which are different from the first laser operating parameters, in particular with a larger wavelength and / or less focused and / or carried out with a larger pulse length. A method according to claim 6, characterized in that in step (d) the laser drilling is performed first with the first laser operating parameters to a certain depth and then the laser drilling is performed with the second laser operating parameters. Micromechanical device with a first substrate ( 11 ), with at least one first cavern ( 100 ), with a locked access ( 1 ) to the first cavern ( 100 ), whereby the access ( 1 ) through the first substrate ( 11 ), characterized in that the access ( 1 ) a laser drilled first section ( 12 ) and a plasma-etched second subsection ( 13 ), wherein the plasma etched second subsection ( 13 ) an opening to the first cavern ( 100 ), the access ( 1 ) in the first subsection ( 12 ) by a melt closure ( 5 ) of melt of at least the first substrate ( 11 ) is closed. Micromechanical device according to claim 8, characterized in that the first substrate ( 11 ) an additional layer ( 9 ) and the access ( 1 ) also by melt of the additional layer ( 9 ) is closed. Hybrid integrated micromechanical device according to one of claims 8 or 9, characterized in that the device comprises a second substrate ( 15 ) having an ASIC circuit.

Images