Integrated chemical microreactor with separated channels for confining liquids inside the channels and manufacturing process thereof

0001The present invention refers to an integrated chemical microreactor with separated channels for confining liquids inside the channels and to the manufacturing process for making same. The chemical microreactors are advantageously used for biological tests.

0002Typical procedures for analyzing biological materials, such as nucleic acid, involve a variety of operations starting from raw material. These operations may include various degrees of cell purification, lysis, amplification or purification, and analysis of the resulting amplified or purified product.

0003As an example, in DNA-based blood tests the samples are often purified by filtration, centrifugation or by electrophoresis so as to eliminate all the non-nucleated cells. Then, the remaining white blood cells are lysed using chemical, thermal or biochemical means in order to liberate the DNA to be analyzed.

0004Next, the DNA is denatured by thermal, biochemical or chemical processes and amplified by an amplification reaction, such as PCR (polymerase chain reaction), LCR (ligase chain reaction), SDA (strand displacement amplification), TMA (transcription-mediated amplification), RCA (rolling circle amplification), and the like. The amplification step allows the operator to avoid purification of the DNA being studied because the amplified product greatly exceeds the starting DNA in the sample.

0005The procedures are similar if RNA is to be analyzed, but more emphasis is placed on purification or other means to protect the labile RNA molecule. RNA is usually copied into DNA (cDNA) and then the analysis proceeds as described for DNA.

0006Finally, the amplification product undergoes some type of analysis, usually based on sequence or size or some combination thereof. In an analysis by hybridization, for example, the amplified DNA is passed over a plurality of detectors made up of individual oligonucleotide probe fragments that are anchored, for example, on electrodes. If the amplified DNA strands are complementary to the probes, stable bonds will be formed between them and the hybridized probes can be read by observation by a wide variety of means, including optical, electrical, mechanical, magnetic or thermal means.

0007Other biological molecules are analyzed in a similar way, but typically molecule purification is substituted for amplification and detection methods vary according to the molecule being detected. For example, a common diagnostic involves the detection of a specific protein by binding to its antibody or by a specific enzymatic reaction. Lipids, carbohydrates, drugs and small molecules from biological fluids are processed in similar ways.

0008The discussion herein has been simplified by focusing on nucleic acid analysis, in particular DNA amplification, as an example of a biological molecule that can be analyzed using the devices of the invention. However, as described above, the invention can be used for any chemical or biological test.

0009The steps of nucleic acid analysis described above are currently performed using different devices, each of which presides over one part of the process. The use of separate devices decreases efficiency and increases cost, in part because of the required sample transfer between the devices. Another contributor to inefficiencies are the large sample sizes, required due to accommodate sample loss between devices and instrument limitations. Most importantly, expensive, qualified operators are required to perform the analysis. For these reasons a fully integrated micro-device would be preferred.

0010Integrated microreactors of semiconductor material are already known. For example, EP-A-1 161 985 (corresponding to US 2002 017 660) describes a microreactor and the respective manufacturing process suitable for making an integrated DNA-amplification microreactor.

0011According to this process, a substrate of monocrystalline silicon is etched in TMAH to form a plurality of thin channels; then an epitaxial layer is grown on top of the substrate and of the channels. The epitaxial layer closes at the top the buried channels and forms, together with the substrate, a semiconductor body.

0012The surface of the semiconductor body is then covered with an insulating layer; heating and sensing elements are formed on the insulating layer; inlet and outlet apertures are formed through the insulating layer and the semiconductor body and connect the surface of the structure so obtained with the buried channels. Then, a covering structure accommodating an inlet and an outlet reservoir is formed or bonded on the structure accommodating the buried channels.

0013The above solution has proven satisfactory, but does not allow separation of the samples because the channels are connected in parallel through the common input and outlet reservoirs. However, in some applications there is need for separating the channels from each other and from the outside environment, both for preventing evaporation and for preventing cross-contamination between channels.

0014Therefore, the aim of the present invention is to provide a microreactor and a manufacturing process overcoming the drawbacks of the known solution.

0015According to the present invention, there are provided a chemical microreactor and its manufacturing process, as defined, respectively, in claim 1 and claim 9.

0016For a better understanding of the present invention, two preferred embodiments thereof are now described, simply as non-limiting examples, with reference to the attached drawings, wherein: <ul id="ul0001" list-style="dash" compact="compact"><li>Figures 1 and 2 show respectively a cross-section and a top view of a first wafer incorporating a part of a microreactor during a manufacturing step;</li><li>Figures 3 and 4 are a cross-section and a top view of a second wafer of the microreactor according to a first embodiment of the present microreactor;</li><li>Figure 5 is a cross-section of the second wafer during a subsequent manufacturing step;</li><li>Figure 6 is a cross-section through a composite wafer obtained by bonding the first and second wafers in a final manufacturing step;</li><li>Figure 7 is a cross-section of the microreactor in use;</li><li>Figures 8 and 9 are cross-sections of a first wafer incorporating a part of a microreactor according to a second embodiment; and</li><li>Figures 10 and 11 are respectively a top view and a cross-section through a composite wafer obtained by bonding the first with a second wafer in a final manufacturing step according to the second embodiment.</li></ul>

0017Hereinbelow, a first embodiment of the invention will be described with reference to Figures 1 to 7. The various layers and regions are not in scale, for better representation.

0018Initially, process steps are carried out similar to those above described for the known process. Accordingly, Figure 1, a first wafer 1 of monocrystalline silicon is etched in TMAH to form a plurality of channels 3. To this end, a grid-like mask is used, e.g. as disclosed in EP-A-1 193 214 (corresponding to US 2002 045 244) or as disclosed in copending patent application "Integrated chemical microreactor with large area channels and manufacturing process thereof" filed on the same date.

0019Then, a structural layer is grown on top of the channels. The structural layer closes the top the channels 3 and forms a substrate 2 of semiconductor material with buried channels. The surface 4 of the substrate 2 is then covered with a first oxide layer; heating elements 10 of polycrystalline silicon are formed thereon; a second oxide layer is deposited and forms, with the first oxide layer, a first insulating layer 5; contact regions 11 (and related metal lines) are formed in contact with the heating elements 10; a second insulating layer 13 is deposited, for example of TEOS, defining an upper surface 12 of the first wafer 1.

0020Then, inlet apertures 14a and outlet apertures 14b are etched. The apertures 14a and 14b extend from the upper surface 12 through the second insulating layer 13, the first insulating layer 5 and the substrate 2 as far as the channels 3 and are substantially aligned with the longitudinal ends thereof. This is visible in Figure 2, wherein channels 3 are drawn with dashed lines. In the shown example, one inlet aperture 14a and one outlet aperture 14b is formed for each channel 3. In the alternative, two or more channels 3 may share the same inlet and outlet apertures 14a, 14b, if parallel processing in a part of channels 3 is desired.

0021In the meantime, beforehand or subsequently, a second wafer 15 of glass is treated to form reservoirs (Figures 3 and 4). In detail, the second wafer 15, formed by a glass sheet 18 having a surface 19, is subjected to a lithographic process, in a per se known manner, to define an inlet opening 16a and an outlet opening 16b intended to be aligned with the inlet and outlet apertures 14a, 14b and to form inlet/outlet reservoirs.

0022Then, Figure 5, a bonding layer 20 is applied on surface 19 of the glass sheet 18. For example, the bonding layer 20 is made of dry resist, with a thickness of 10-30 µm, and may be the product known by the commercial name "Riston® YieldMaster®" by Du Pont, that can be laminated in thin layers, or the resist sold by the firm Tokyo Ohka Kogyo Co., Ltd.

0023Subsequently, Figure 6, the second wafer 15 is turned upside down and put on the first wafer 1, with the bonding layer 20 in contact with the surface 12 of the first layer; then the sandwich including the first wafer 1, the bonding layer 20 and the second wafer 15 is treated to cause bonding of the bonding layer 20 to the first wafer 1, thereby obtaining multiple wafer 21.

0024For example, bonding may be carried out at a temperature of 140-180°C, preferably 160°C; at a force of 5-9 kN, preferably 7 kN (for wafers having a diameter of 6") and in a vacuum or low pressure condition of 5x10^-7 to 5x10^-6 bar, preferably 10^-6 bar.

0025In this way, the channels 3 are not connected to the inlet and outlet openings 16a, 16b forming inlet and outlet reservoirs, but are separated therefrom and from the outside environment by the bonding layer 20 that now acts as a sealing layer; thereby the channels are kept at the low pressure condition that existed during bonding.

0026After dicing the multiple wafer 21 into single microreactors 22, Figure 7, the inlet opening 16a is closed by a plug 25.

0027The plug 25 is e.g. formed by applying a drop of liquid thermosetting material that is subsequently hardened by heat.

0028In the alternative, the plug 25 may be applied only when the microreactor 22 is used, and may comprise a preformed plug 25 already connected to a syringe 26 of the retractable type. Preferably, the plug 25 is of a resilient material that is able to be punctured by the syringe 26 and to close the puncture passage after removal of the syringe, without forming shavings. For example, the plug 25 may be made of PVC including a softener, of the type used for biomedical applications.

0029In use, when liquid is to be inserted in a specific channel 3, a syringe 26 is inserted through the plug 25, perforates the bonding layer 20 and injects the mixture or mixtures to be treated in the selected channel (or channels) 3. Injection of the liquid to be treated is favored by the presence of low pressure (vacuum).

0030The syringe 26 is then removed and the plug 25 closes to as to ensure a complete isolation of the channel(s) 3 containing the injected liquid with respect to the environment during thermal cycling or other provided treatment.

0031At the completion of the treatment, the liquid is extracted by perforating the bonding layer 20 at the outlet reservoir 16b; for example, another syringe may be used to aspirate the liquid, or a plunger may brake the bonding layer 20 at the outlet reservoir 16b and a pressure be exerted from the inlet reservoir 16a.

0032According to a different embodiment, the bonding/sealing layer is applied to the semiconductor wafer and an auxiliary hole is provided to create the vacuum inside the channels during bonding, as shown in Figures 8-10, wherein the first wafer has been represented in a very schematic way.

0033In detail, Figure 8, a first wafer 1 is subjected to the same manufacturing steps described above with reference to Figure 1. Thus, the first wafer 1 is etched to form channels 3; a structural layer is grown to form a substrate 2 of semiconductor material; insulating layers 5, 13, and heating elements 10 and contacts 11 (none shown, please refer to Figure 1) are formed.

0034Then the inlet and outlet apertures 14a, 14b are etched. According to the second embodiment, simultaneously with the inlet and outlet apertures 14a, 14b, at least one hole 30 is formed for each channel 3, intermediate to the inlet and outlet apertures 14a, 14b. In case of more channels 3 connected to same inlet/outlet apertures 14a, 14b, a single hole 30 may be sufficient.

0035Then, Figure 9, a bonding layer 31 is formed on a surface 32 of wafer 1. Preferably, the bonding layer 31 is dry resist which is laminated onto the surface 32. For example, the bonding layer 31 may be of the same material as bonding layer 20 of figures 5-7 and have the same thickness (10-30 µm).

0036Thereafter, the bonding layer 31 is lithographically defined to form connection openings 33 over the holes 30 (see also Figure 10). Preferably, one connection opening 33 is formed for each hole 30, as shown in the drawings; in case of parallel connected channels 3, a connection opening 33 is in common to more holes 30 and/or more channels 3.

0037Thereby, the inlet/outlet apertures 14a, 14b are upwardly closed by the bonding layer 31, but the channels 3 are connected to the outside environment by the holes 30 and the connection openings 33.

0038Then, Figure 11, the first wafer 1 is bonded to a second wafer 15 formed by a glass sheet 18 wherein, previously, an inlet opening 16a and an outlet opening 16b have been formed, analogously to what has been described with reference to Figures 3 and 4. Also here, the input and output openings 16a, 16b are designed so as to be aligned to the inlet and outlet apertures 14a, 14b.

0039Bonding may be carried out as before described, that is at a temperature of 140-180°C, preferably 160°C; at a force of 5-9 kN, preferably 7 kN and in a vacuum or low pressure condition of 5x10^-7 to 5x10^-6 bar, preferably 10^-6 bar. Thus, during bonding, the channels 3 are maintained at low pressure by virtue of the holes 30 and the connection openings 33.

0040Thereby, a multiple wafer 35 is obtained, wherein the input and output openings 16a, 16b are closed upwardly by the bonding layer 31 and the holes 30 are upwardly closed by the glass sheet 18. However, the channels are buried inside the monolithic structure of the first wafer. As used herein "buried channel" is defined as a channel or chamber that is buried inside of a single monolithic support, as opposed to a channel or chamber that is made by welding or otherwise bonding two supports with a channel or two half channels together. Of course, other components may be welded or otherwise attached to the monolithic support, as required for the complete integrated device.

0041Therefore, also here, the channels 3 are sealed from the outside environment by the bonding layer 31 and are kept at the low pressure condition existing during bonding.

0042In use, analogously to the above, the mixture or mixtures is inserted in the selected channel (or channels) 3 in a very simple way, by virtue of the vacuum condition in the channel(s) 3 by simply perforating the bonding layer 31 with a syringe at the input opening 16a. Furthermore, a plug 25 may be provided to seal the channel(s) 3 after perforation.

0043By virtue of the described reactor and process, the finished microreactor 22 has channels 3 sealed from the outside, and allows separation of the material accommodated in the channels from the external environment. Furthermore the microreactor 22 is able to avoid any interference and contamination by the environment as well as by adjacent channels.

0044The manufacturing process is straightforward and employs steps that are common the manufacture of microreactors of this type; thus the resulting device is simple and cheap.

0045The separated channels described herein may be combined in an integrated device with any other components required for the application of interest. For example, the separated channels may be combined with one or more of the following: micropump, pretreatment channel, lysis chamber, detection chamber including detection means, capillary electrophoresis channel, and the like (see especially, Italian patent application TO 2002A 000808 filed on 17.9.02 and EP 03 103 421.8 filed on 17.09.2003 in the name of the same applicant). The heaters may be integral, or may be provided by the platform into which the disposable microreactor wafer is inserted. The overall design of the complete device will be dictated by the application, and need not be detailed herein.

0046It is clear that numerous variations and modifications may be made to the process and to the microreactor described and illustrated herein, all falling within the scope of the invention, as defined in the attached claims.