WO2011019276A1

WO2011019276A1 - Method of manufacturing a micro unit and a micro unit for use in a microscope

Info

Publication number: WO2011019276A1
Application number: PCT/NL2010/050503
Authority: WO
Inventors: Jan Fredrik Creemer; Gregory Pandraud; Fabio Santagata
Original assignee: Technische Universiteit Delft
Priority date: 2009-08-10
Filing date: 2010-08-10
Publication date: 2011-02-17
Also published as: NL2003340C2

Abstract

The invention relates to a method of manufacturing a micro unit for use in a microscope. The method comprises the step of providing a planar substrate supporting structure and creating a chamber in the supporting structure for receiving a fluid containing a chemically reacting substance to be inspected. Further, the method comprises the step of coating an inner surface of the chamber with a thin layer. The method also comprises the step of locally removing material from the exterior of the supporting structure until the thin layer is reached for forming a window segment that is at least partially transparent to a beam of radiation generated by the microscope.

Description

Title: Method of manufacturing a micro unit and micro unit for use in a microscope

The invention relates to a method of manufacturing a micro unit for use in a microscope, comprising the steps of providing a planar substrate supporting structure on which the micro unit is based.

Such a micro unit is e.g. known from the International publication WO 2006/031104 disclosing a reactor for microscopy in the fields of analyzing heterogeneous catalysis, corrosion, chemical vapour deposition, materials science, biochemistry, biomedicine and electrochemistry. In principle, such reactors enable the imaging of chemical processes with high resolution, down to the atomic scale, i.e. circa 0.1 nm to circa 0.2 nm.

In realizing such a micro unit, an assembly step is performed for realizing a chamber in the micro unit for receiving the specimen to be inspected. Though such micro units operate properly, the manufacturing process might be enhanced in terms of ease of production. Further, the pressure in the chamber may vary in a restricted range, thereby limiting potentially interesting applications.

It is an object of the invention to provide a method of manufacturing a micro unit for use in a microscope according to the preamble that is easier to produce. Thereto, the method according to the invention further comprises the steps of creating a chamber in the supporting structure for receiving a fluid containing a specimen to be inspected, the chamber including a pair of mutually facing wall sections, coating an inner surface of the chamber with a thin layer, and locally removing material from the exterior of the supporting structure until the thin layer is reached for forming a window segment in a first wall section of the pair of mutually facing wall sections, the window segment being is at least partially transparent to a beam of radiation generated by the microscope. By coating the inner surface of the chamber with a thin layer that forms a window segment when locally removing material from the exterior of the supporting structure, a micro unit can be obtained that might be integrally formed with the supporting structure, thus eliminating the assemblage step wherein a chamber is formed. Since the chamber and the window segments can be formed in a single piece, using the internal coating process, the production process of the micro unit simplifies considerably, thereby reducing manufacturing costs.

Further, since the micro unit can thus be manufactured using micro electromechanical system (MEMS) or micro system manufacturing techniques, including thin film technology and photolithographic processing technology, any alignment of upper and lower windows can be performed with an accuracy that is much higher than is available when using conventional techniques. As an example, an accuracy of circa 0.1 micron can e.g. be reached, instead of circa 2 micron. Therefore, the lateral window size may be reduced from approximately 5 micrometer to approximately 1 micrometer, thereby considerably increasing the rigidity of the window segment. Therefore, the window segment can withstand much higher pressures in the chamber, thereby facilitating a measurement at relatively high pressure while maintaining high resolution accuracy. Moreover, a vertical and lateral scaling can be improved allowing a higher integration and a reduction of costs.

Preferably, the chamber includes a multiple number of

interconnecting members extending through the chamber and interconnecting said facing wall sections. By providing interconnecting members, such as pillars, the mechanical robustness can increase substantially since any bulging of the chamber ceiling induced by the application of a pressure in the chamber can efficiently be counteracted. As a result, the height of the chamber or channel is reduced, enabling a higher density of molecules to be inspected while transparency requirements can be maintained. Therefore, measurements at high pressure are possible while advantageously

maintaining high resolution accuracy.

Further, the invention relates to a micro unit for use in a microscope.

Other advantageous embodiments according to the invention are described in the following claims.

By way of example only, an embodiment of the present invention will now be described with reference to the accompanying figures in which

Fig. 1 shows a schematic cross sectional side view of a first embodiment of a micro unit according to the invention;

Fig. 2 shows a schematic top view of the micro unit of Fig. 1;

Fig. 3 shows a schematic perspective partial view of a second embodiment of a micro unit according to the invention; and.

Fig. 4 shows a flow chart of an embodiment of a method according to the invention.

The figures are merely schematic views of a preferred embodiment according to the invention. In the figures, the same reference numbers refer to equal or corresponding parts.

Figure 1 shows a schematic cross sectional side view of a first embodiment of a micro unit 100 according to the invention. The micro unit 100 comprises a supporting structure 1, also called substrate, typically made of silicon of 0.5 mm thick. However, the substrate may also be made from other materials, such as e.g. glass. Further, the substrate thickness might be smaller or larger than 0.5 mm. The substrate 1 is provided with a chamber 3, also called channel, which is arranged for receiving a specimen, in particular a fluid containing a chemically reacting substrate. As such, the micro unit is formed as a microreactor. The channel 3 comprises a multiple number of window segments 13. In Fig. 1, two window segments 13 are shown that are provided in opposite wall sections 23 a,b. The window segments 13 are at least partially transparent to a beam of radiation E generated by a microscope, thereby enabling that the fluid containing a chemically reacting substance is inspected by the microscope, especially in a channel section 3a that is located near the window segment 13. As an example, the beam of radiation E might be formed an electron beam or an X-ray beam. In the shown embodiments, the

supporting structure 1 includes a viewing hole that is in line with the multiple number of window segments 13a-c.

Figure 2 shows a schematic top view of the micro unit 100, and Figure 3 shows a schematic perspective partial view of an alternative embodiment of a micro unit 100 also including a multiple number of window segments 13. In order to provide the window segment 13 that is at least partially transparent to the microscope beam of radiation E, the micro unit 100 further comprises a thin layer 11 that is integrally formed with the window segment 13. The thin layer 11 extends along an inner surface of the channel or chamber 3, beyond the window segment 13. The thin layer 11 is typically made from SiN, SiC, SiCh and/or polycrystalline Si material and is typically circa 10 nm thick. However, also another thickness can be applied.

Preferably, the entire inner surface of the chamber 3 or

substantially the entire inner surface of the chamber 3, e.g. more than circa 50% or more than circa 90% is covered by the thin layer 11. The thin layer is locally integrally formed with a window segment to enable the microscope beam E, such as an electron beam, a light beam, an ion beam or an X-ray beam, to enter the chamber 3. In an embodiment according to the invention, the thin layer 11 forms the window segment at locations where the supporting structure 1 has been removed to realize blind holes 25a,b. In principle, however, the window segment might not only include the thin layer 11 but also a further layer.

In the embodiments shown in Figures 1-3, the chamber includes a pair of mutually facing wall sections, viz. a ceiling 4 and a floor 5 defining the cavity that forms the chamber or channel 3. Also the ceiling 4 and the floor 5 may be made from SiN or other thin film material, e.g. SiC, , SiCh and/or polycrystalline Si, having a typical thickness of e.g. 700 nm. Again, also another thickness can be applied. Further, the chamber includes a multiple number of interconnecting members, also called pillars or supports 8 extending through the chamber and interconnecting said facing wall sections. By joining the ceiling 4 and the floor 5 via the supports 8 any bulging of the chamber ceiling 4 and floor 5 that might be induced by the application of a pressure in the chamber, is efficiently counteracted. As a result, the height of the chamber or channel might be strongly reduced, e.g. to a value in a range from circa 0.1 micrometer to circa 1 micrometer. Decreasing the effective chamber height enables a higher density of molecules to be inspected while transparency requirements are maintained. Advantageously, decreasing the effective chamber height has a similar effect as increasing the inner pressure in the chamber or replacing any gas containing the chemically reacting substance by a liquid.

As a result, a low pressure limit for gas-solid reactors for microscopy is relaxed. Since, according to an aspect of the invention, a higher pressure in the chamber can be applied, even up to a range of circa 2 bar to circa 100 bar whereas a high resolution is maintained, thus enabling imaging of chemical processes with high resolution, down to the atomic scale, i.e. to a range of circa 0.1 to circa 0.2 nm. Further, by employing supports 8 interconnecting the mutually facing wall sections, a chamber height thinner than 1 micrometer can be realized so that a sufficient transparency can be obtained in a robust micro unit that is relatively cheap and reliable.

In this respect, it is noted that the micro unit according to the invention, including the thin layer that is integrally formed with the window segment and extends along an inner surface of the chamber beyond the window segment can in principle also be realized without the interconnecting members, e.g. when only moderate pressures will be applied in the chamber.

Due to a specific MEMS or micro system manufacturing technique, the supports may include a blind hole 16 a-e. By substantially evenly distributing the multiple number of interconnecting members 8 over the inner surfaces of the mutually facing wall sections 4, 5 a relatively large pressure can be applied since the forces can then also be transmitted to wall sections in an evenly distributed manner.

Preferably, the interconnecting members 8 are designed to resist a pull force so that a relatively large internal pressure in the channel 3 can be applied.

The one or multiple number of window segments can be comprised in the chamber ceiling 4 and/or chamber floor 5. By realizing window segments 13 in both the ceiling 4 and the floor 5, preferably in line, a transmission measurement can be performed. However, in principle, the one or more window segments can also be realized in either the ceiling 4 or the floor 5, thereby allowing a reflection measurement.

Further, the micro unit may include an input port 6 and an output port 7, also called inlet and outlet, for flowing the fluid into and from the channel 3, respectively. In principle, the micro unit may include a single port for allowing the fluid to flow into and from the channel. 17. The channel structure extending between the inlet 6 and the outlet 7 has a substantially elongated form, thereby providing an elegant design providing inflow and outflow regions as well as an inspection region including the viewing hole 2 with the window segments 13.

In addition, the micro unit optionally includes electrical contact pads 15 as well as a heating element 14 interconnecting the electrical contact pads 15 for the purpose of heating the unit to a desired temperature range.

During use of the micro unit 100, a solid specimen is deposited on the window segments, inside the channel, typically some kind of nanoparticles. Then, a gaseous and/or liquid environment that is different from the

environment outside in terms of pressure, temperature and/or molecular species is flown to the channel 3, e.g. by applying a pressure difference between the inlet and the outlet. As a result, the fluid contains a chemically reacting substance, e.g. a solid specimen. If desired, the specimen and its environment are brought to a higher temperature employing the heating element 14 to accelerate an expected chemical or physical reaction. In the channel a chemical reaction or physical transformation may take place to be monitored by use of a microscope, quite often in vacuum.

Figure 4 shows a flow chart of an embodiment of the method according to the invention. The method is used for manufacturing a micro unit for use in a microscope. The method comprises the steps of providing 200 a planar substrate supporting structure, creating 210 a chamber in the supporting structure for receiving a fluid containing a specimen to be inspected, coating 220 an inner surface of the chamber with a thin layer, and locally removing 230 material from the exterior of the supporting structure until the thin layer is reached for forming a window segment that is at least partially transparent to a beam of radiation generated by the microscope.

During the process of manufacturing the micro unit, a planar substrate, such as a semiconductor or glass wafer, is provided typically having a thickness of circa 0.5 mm. By using micro electro mechanical system

(MEMS) surface micromachining techniques and/or semiconductor fabricating techniques, such as a photolithographic wafer stepper technique, e.g. a sacrificial etching process, the chamber 3 may be created serving as a room that may receive a fluid including a specimen such as a chemically reacting substance. In this way a chamber 3 might be realized that is integrally formed with the supporting structure 1. In a first stage of the manufacturing process, the chamber 3 may include one or a multiple number of apertures, also called access holes 9, so that a region near window segments 13 to be realized is easily accessible from outside. The access holes 9 might also have been used for creating the chamber 3 in the supporting structure 1. Via the at least one access hole 9 at least a part of the chamber's inner surface is coated with a thin layer 11. Optionally, said chamber's inner surface is deposited with a stop layer 12 prior to coating the surface with the thin layer 11. Typically, the thin layer comprises SiN and the stop layer 12 typically contains Siθ2. The thin layer is e.g. 10 nm thick. Further, the stop layer 12 has e.g. a typical thickness of circa 150 nm. However, also other thicknesses may be chosen. After applying the coating process(es), the access holes 9 may be sealed, e.g. by inserting plugs 10 a-c.

The thin layer 11 and the stop layer 12 can be deposited using a conformal technique such as low-pressure chemical vapour deposition

(LPCVD) or atomic layer deposition (ALD). Any fluid required for coating may enter the chamber 3 interior through the access holes 9 that have typically been used in a surface machining step to etch away a sacrificial layer. The plugs 10 might be made by a combination of nonconformal thin film deposition technique such as plasma enhanced chemical vapour deposition (PECVD), by photolithography and by etching.

It is noted that instead of using at least one access hole 9 for coating the chamber's inner surface, in principle, also other holes providing access to the chamber 3 can be used, e.g. the inlet 6 and/or the outlet 7 that enable a fluid to flow into and from the chamber 3, respectively, during normal use of the micro unit 100.

Further, after application of the coating process(es), material is locally removed from outside the supporting structure 1, thus obtaining a blind hole 25a,b, until the thin layer 11 is reached. Preferably, opposite areas of the floor and the ceiling are removed, including the stop layer, thereby exposing the window segments 13. After the removal process, the blind hole 25a,b extends to the thin layer 11 and the thin layer 11 locally forms a window segment 13 separating the blind hole 25 and the chamber 3. The window segments are typically circular in shape and may have a diameter ranging e.g. from circa 1 to circa 10 microns. The window segment 13 is at least partially transparent to a beam of radiation generated by a microscope. When a stop layer 12 has been coated, said stop layer 12 might assist in the process of removing the material from the supporting structure 1. The removal process can be performed using a micromachining process or a lithographic process followed by an etching step.

The invention is not restricted to the embodiments described herein. It will be understood that many variants are possible.

It is noted that the micro unit according to the invention can be applied for inspecting, via a microscope, a specimen that is present in the chamber. As an example, the specimen to be inspected includes a fluid containing a chemically reacting substance. However, the micro unit might also find application in other fields, e.g. in the field of micro electron sources.

It is further noted that other materials can be used for realizing structure elements indicated above. As an example, other thin film material components can be used for forming the thin layer that is integrally formed with the window segment and extends along an inner surface of the chamber beyond the window segment.

The thin layer coated inside the chamber can not only be used for creating a window segment. The thin layer may also serve as a surface modification for further functionalities, such as a catalytic function for accelerating a chemical process. As a further example, a hydrophobic functionality might thus be realized. As such, the thin layer may also have the function of protecting the reactor interior from an attack by chemical substance, promoting chemical reactions in the interior, e.g. by catalytic action and/or attracting or repelling specific substance, e.g. for promoting

hydrophobicity. Also, the thin layer may serve as a protection layer. In addition, a further coating layer, e.g. a second thin layer, might be deposited in the chamber at least partially covering the thin layer. Here, the same technique can be used as employed for depositing the thin layer. The further coating layer may include a desired physical and/or chemical functionality, e.g. for fulfilling one or more of the above-mentioned functions. Other such variants will be obvious for the person skilled in the art and are considered to lie within the scope of the invention as formulated in the following claims.

Claims

1. A method of manufacturing a micro unit for use in a microscope, comprising the steps of:

- providing a planar substrate supporting structure;

- creating a chamber in the supporting structure for receiving a fluid containing a specimen to be inspected, the chamber including a pair of mutually facing wall sections;

- coating an inner surface of the chamber with a thin layer; and

- locally removing material from the exterior of the supporting structure until the thin layer is reached for forming a window segment in a first wall section of the pair of mutually facing wall sections, the window segment being is at least partially transparent to a beam of radiation generated by the microscope.

2. A method according to claim 1, wherein the step of creating a chamber includes providing a chamber including a multiple number of interconnecting members extending through the chamber and interconnecting said facing wall sections.

3. A method according to claim 1 or 2, wherein the creating step includes the use of a sacrificial etching process.

4. A method according to any of the preceding claims 1-3, wherein the thin layer includes SiN, SiC, Siθ2 and/or polycrystalline Si material.

5. A method according to any of the preceding claims 1-4, further comprising the step of coating the inner surface of the chamber with a stop layer prior to coating with a thin layer.

6. A method according to any of the preceding claims 1-5, wherein the coating process is performed using an aperture of the chamber that is sealed after the coating step.

7. A micro unit for use in a microscope, comprising a planar substrate supporting structure including a chamber for receiving a specimen to be inspected, wherein the chamber comprises a window segment that is at least partially transparent to a beam of radiation generated by the microscope, wherein the chamber includes a pair of mutually facing wall sections, the window segment being comprised in a first wall section of the pair of mutually facing wall section, and wherein the micro unit further comprises a thin layer integrally formed with the window segment and extending along an inner surface of the chamber beyond the window segment.

8. A micro unit according to claim 7, wherein the chamber includes a multiple number of interconnecting members extending through the chamber and interconnecting said facing wall sections.

9. A micro unit according to claim 7 or 8, wherein mainly the entire inner surface of the chamber is covered by the thin layer.

10. A micro unit according to any of the preceding claims 7-9, wherein the supporting structure including the chamber is integrally formed.

11. A micro unit according to any of the preceding claims 7-10, formed as a microreactor for use in a microscope, wherein the specimen to be inspected includes a fluid containing a chemically reacting substance.

12. A micro unit according to any of the preceding claims 7-11, wherein the chamber includes a pair of mutually facing wall sections and a multiple number of interconnecting members extending through the chamber and interconnecting said facing wall sections.

13. A micro unit according to any of the preceding claims 7-12, wherein the multiple number of interconnecting members are substantially evenly distributed over the inner surfaces of the mutually facing wall sections.

14. A micro unit according to any of the preceding claims 7-13, wherein the interconnecting members are designed to resist a pull force.

15. A micro unit according to any of the preceding claims 7-14, wherein the window segment is comprised in a first wall section of the pair of mutually facing wall sections.

16. A micro unit according to any of the preceding claims 7-15, comprising a second window segment that is comprised in a second wall section of the pair of mutually facing wall sections.

17. A micro unit according to any of the preceding claims 7-16, wherein the chamber includes an input port and an output port for flowing the fluid into and from the chamber, respectively.

18. A micro unit according to any of the preceding claims 7-17, wherein the window segment is at least partially transparent to a beam of radiation generated by the microscope.

19. A micro unit according to any of the preceding claims 7-18, wherein the chamber has a substantial elongated form.