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EP-4737388-A1 - TWO-STEP LASER PROCESSING FOR PRODUCING A MEMS CHIP COMPRISING AN ENVIRONMENTAL BARRIER STRUCTURE MADE FROM POLYMER NANOFIBERS

EP4737388A1EP 4737388 A1EP4737388 A1EP 4737388A1EP-4737388-A1

Abstract

A method for producing a MEMS chip (100) with an environmental barrier structure (150) made from polymer nanofibers (151), the method comprising providing a wafer substrate (110) having plurality of adjacent through holes (131, ..., 134). The environmental barrier structure (150) is created by applying polymer nanofibers (151) onto one of the front and back sides (111, 112) of the wafer substrate (110). A plurality of MEMS chips (100) are singulated from the wafer substrate (110) by applying a two-step laser process comprising: a first laser-processing step including guiding a laser beam (160) over the one side of the wafer substrate (110) at which the polymer nanofibers (151) are applied in order to locally remove the polymer nanofibers (151) from the wafer substrate (110) and to locally uncover an underlying surface, and a subsequent second laser-processing step including applying a stealth dicing process for singulating the MEMS chips (100) by guiding a stealth dicing laser beam over the locally uncovered surfaces.

Inventors

  • Anzinger, Sebastian
  • Wasisto, Hutomo Suryo
  • MAIER, DOMINIC
  • SOTNIKOV, ANATOLY
  • Füldner, Marc

Assignees

  • Infineon Technologies AG

Dates

Publication Date
20260506
Application Date
20241029

Claims (15)

  1. A method for producing a MEMS chip (100) with an environmental barrier structure (150) made from polymer nanofibers (151), the method comprising: providing a wafer substrate (110) having a front side (111) and an opposite back side (112), forming a plurality of adjacent through holes (131, ..., 134) in said wafer substrate (110), creating the environmental barrier structure (150) by applying polymer nanofibers (151) onto one of the front and back sides (111, 112) of the wafer substrate (110), such that the polymer nanofibers (151) are densely connected to form a connected web that covers the wafer substrate (110) including the through holes (131, ..., 134) formed therein, singulating a plurality of MEMS chips (100) from the wafer substrate (110) by applying a two-step laser process comprising: a first laser-processing step including guiding a laser beam (160) over the one side of the wafer substrate (110) at which the polymer nanofibers (151) are applied in order to locally remove the polymer nanofibers (151) from the wafer substrate (110) and to locally uncover an underlying surface, and a subsequent second laser-processing step including applying a stealth dicing process for singulating the MEMS chips (100) by guiding a stealth dicing laser beam over the locally uncovered surfaces.
  2. The method according to claim 1, wherein the laser being used in the first laser-processing step is different from the laser being used in the subsequent second laser-processing step.
  3. The method according to claim 2, wherein the laser beam (160) of the laser being used in the first laser-processing step is focused on the polymer nanofibers (151), and wherein the stealth dicing laser beam being used in the subsequent second laser-processing step is focused on the inside of the wafer substrate (110).
  4. The method according to claim 2 or 3, wherein the first laser-processing step includes applying a laser grooving process for removing the polymer nanofibers (151).
  5. The method according to any one of the preceding claims, wherein the laser being used in the first laser-processing step is adjusted to remove the polymer nanofibers (151) only without grooving the uncovered underlying surface.
  6. The method according to any one of claims 1 to 4, wherein the laser being used in the first laser-processing step is adjusted to remove the polymer nanofibers (151) and to groove the uncovered underlying surface.
  7. The method according to any one of claims 2 to 6, wherein the laser being used in the first laser-processing step is a short-pulsed Nd:YAG laser having a wavelength between 300 nm and 400 nm, and wherein the stealth dicing laser being used in the second laser-processing step is a pulsed Nd:YAG laser having a wavelength between 1000 nm and 1100 nm.
  8. The method according to any one of the preceding claims, wherein the first laser-processing step includes square-patterning the connected web formed by the polymer nanofibers (151) by guiding the laser beam (160) along straight lines between the adjacent through holes (131, ..., 134), the straight lines being offset by 90° to each other resulting in a square pattern.
  9. The method according to any one of the preceding claims, wherein a silicon oxide layer (120) is arranged between the bare wafer material and the polymer nanofibers (151), and wherein the underlying surface being uncovered during the first laser-processing step corresponds to the silicon oxide layer (120).
  10. The method according to any one of the preceding claims, wherein prior to the step of applying the polymer nanofibers (151) onto the one of the front and back sides (111, 112) of the wafer substrate (110), the method comprises a further step of providing a rigid mesh (141, ..., 144) covering at least one of the through holes (131, ..., 134), wherein the rigid mesh (141, ..., 144) is flush with the one of the front and back sides (111, 112) of the wafer substrate (110) at which the polymer nanofibers (151) are to be applied, and applying the polymer nanofibers (151) onto the one of the front and back sides (111, 112) of the wafer substrate (110) and onto the rigid meshes (141, ..., 144).
  11. The method according to any one of claims 1 to 9, wherein the step of applying the polymer nanofibers (151) onto the one of the front and back sides (111, 112) of the wafer substrate (110) includes applying the polymer nanofibers (151) over the non-obstructed open through holes (131, ..., 134).
  12. The method according to any one of the preceding claims, comprising a further method step of melting the polymer nanofibers (151) by applying a thermal laser treatment including guiding a laser beam (160) over the polymer nanofibers (151) for melting them, wherein, after curing of the molten polymer nanofibers (151), a bonding interface (152) is created for enhancing an adhesive force between the molten polymer nanofibers (151) and the underlying material.
  13. The method according to claim 12, wherein the step of melting the polymer nanofibers (151) by applying the thermal laser treatment includes using the same laser (160) as in the first laser-process step or using a laser being different from the lasers being used in the first and second laser-processing steps.
  14. The method according to claim 12 or 13, wherein the step of melting the polymer nanofibers (151) by applying the thermal laser treatment includes guiding the laser beam (160) over the wafer substrate (110) while omitting the through holes (131, ..., 132) formed therein, such that only polymer nanofibers (151) residing on the wafer substrate (110) are melted while other polymer nanofibers (151) residing over the through holes (131, ..., 134) remain substantially unmelted.
  15. The method according to claim 12 or 13, wherein the step of melting the polymer nanofibers (151) by applying the thermal laser treatment includes guiding the laser beam (160) over the wafer substrate (110) and over the through holes (131, ..., 134), such that polymer nanofibers (151) residing on the wafer substrate (110) as well as other polymer nanofibers (151) residing over the through holes (131, ..., 134) are melted.

Description

Embodiments of the present disclosure relate to a method for producing a MEMS chip (MEMS: Micro Electro Mechanical System) with an environmental barrier structure made from polymer nanofibers. TECHNICAL BACKGROUND Next generation MEMS chips, for example MEMS microphones and other sensors, are expected to have environmental barriers (EBs) in their package construction to be able to withstand harsh environmental conditions, including impacting solid objects (e.g., dust particles and hairs) and high water ingression. Currently available solutions from MEMS chip manufacturers rely on external and large environmental barriers (EBs) that are placed far away from the MEMS chip itself, leading to high production cost, large package size, low performance, and limited usage for applications. In addition, currently used materials are often based on per- and polyfluoroalkyl substances (PFAS). However, the European Chemicals Agency (ECHA) published a comprehensive dossier concerning a ban on around 10,000 PFAS, which are widely used in many industries and present in many consumer goods. The restriction proposal aims to restrict the manufacture, placing on the market and use of substances harmful to human health and the environment, and to limit their associated risks. To overcome the above restrictions, the applicant of the present disclosure presented an innovative approach of creating an environmental barrier structure by spinning polymer nanofibers onto MEMS chips, either on wafer level or on chip level. These innovative EB structures are described in EP 4 380 182 A1, EP 4 380 183 A1 and EP4 378 882 A1, the contents of which are incorporated herein by reference in their entirety. Creating the EB structures on wafer level is sometimes preferred over chip level production due to a higher yield in less time. However, during ongoing research it was discovered that singulating the single MEMS chips from the wafer by applying standard dicing processes, such as stealth dicing, may sometimes result in uneven dicing lines and incomplete separation of the nanofibrous EB structure. In some instances, the nanofibrous EB structures were peeled off from the underlying substrate, in particular in case of polysilicon substrate material, since there may be poor adhesion forces between polymer nanofibers and poly-silicon. Therefore, it would be desirable to provide a concept for reliably and repeatedly performing dicing for singulating MEMS chips with nanofibrous EB structures from a wafer, while at the same time improving adhesion of the nanofibrous EB structures with the underlying substrate material. This goal can be achieved by means of the herein disclosed method for producing a MEMS chip comprising an environmental barrier structure made from polymer nanofibers with all the features of the independent claim. Further embodiments and advantageous aspects are suggested in the dependent claims. The innovative method comprises a step of providing a wafer substrate having a front side and a back side, and a step of forming a plurality of adjacent through holes in said wafer substrate. The method further comprises a step of creating the environmental barrier structure by applying polymer nanofibers onto one of the front and back sides of the wafer substrate, such that the polymer nanofibers are densely connected to form a connected web that covers the wafer substrate including the through holes. According to the herein disclosed innovative approach, the plurality of MEMS chips are singulated from the wafer substrate by applying a two-step laser process. A first laser-processing step includes a step of guiding a laser beam over the one side of the wafer at which the polymer nanofibers are applied in order to locally remove the polymer nanofibers from the wafer substrate and to uncover an underlying surface. A subsequent second laser-processing step includes a step of applying a stealth dicing process for singulating the MEMS chips by guiding a stealth dicing laser beam over the locally uncovered surfaces. In the following, embodiments of the present disclosure are described in more detail with reference to the figures, in which Figs. 1A-8Bshow different method steps of a first embodiment of the herein disclosed innovative method for producing a MEMS chip,Figs. 9A-11Cshow optional further method steps of the first embodiment including melting the polymer nanofibers for creating a bonding interface between the molten polymer nanofibers and the underlying surface,Figs. 12A-15Bshow different method steps of a second embodiment of the herein disclosed innovative method for producing a MEMS chip, andFigs. 16A-17Bshow optional further method steps of the second embodiment including melting the polymer nanofibers for creating a bonding interface between the molten polymer nanofibers and the underlying surface. DESCRIPTION OF THE FIGURES Equal or equivalent elements or elements with equal or equivalent functionality are denoted in the following