JPH01213523A - Micro-valve mass flow controller - Google Patents

Abstract

PURPOSE:To control a very small quantity of a gas with high sensitivity and high responsiveness with an ultra-small constitution by detecting the very small flow of a flow passage having a completely airtight structure through a micro- heater and deforming a diaphragm forming a valve of a required constitution by means of an actuator. CONSTITUTION:An ultra-small flow passage 5 which has a completely airtight structure and is provided with a gas leading-in and gas leading-out ports 2 and 3 is formed of a glass substrate 1 and silicon substrate 4. The very small gas flow of the passage 5 is detected by means of a thermal-type flow sensor provided inside the flow passage 5 and containing a micro-heater as a change in electric current corresponding to a change in temperature produced by the flow rate and a piezo-actuator 8 is controlled. Therefore, a very small micro- valve/mass flow controller which can control a very small quantity of a gas in the process of CVD, etc., with high sensitivity and high responsiveness through a diaphragm 7 constituting a micro-valve together with a mesa 6 provided on the substrate 4 is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a microvalve mass flow controller useful for detecting and controlling trace gases used in semiconductor processes and the like. In particular, this invention
and MOMBE (organometallic molecular beam epitaxial growth)
In the process of 5. The present invention relates to a trace gas controller useful for precisely controlling crystal growth by introducing a trace gas.

[Background technology] In recent years, with the improvement in performance of LSI and semiconductor lasers, MO
Ultra-thin film growth techniques such as CVD and MOMBE are becoming important. For example, superlattice devices and HEMT (
In high-mobility boundary transistors), HETs (hot electron transistors), phase-matched semiconductor lasers, and the like, it is necessary to control the thickness of multilayer GaAs layers and AjGaAs layers with an accuracy of several amps. In such film thickness control, precision control of trace gases is required because the accuracy largely depends on the flow rate of the reactant gas.

Several types of controllers have been known in the past, but for example, conventional mass flow controllers using needle valves and pressure sensors have large mechanical parts and piping systems, and flow control is performed through mechanical contact. Therefore, the gas could only be controlled to a few tens of cc at most, and this level was the limit of control. Furthermore, since the reactor and the mass flow controller must be installed apart from each other, there are problems in that the piping system becomes long and residual gas makes it difficult to control the amount of gas.

[Object of the Invention] This invention has been made in view of the above-mentioned problems, and by incorporating a flow sensor with high sensitivity and high speed response and arranging an actuator that gives minute displacement, The purpose of this invention is to provide a mass flow controller that is ultra-compact and capable of controlling extremely small amounts of gas.

[Disclosure of the Invention] In order to achieve the above object, the present invention is directed to bonding a glass or silicon substrate having a gas inlet and an outlet, and a silicon substrate having a gas flow path, a mesa, and a diaphragm. Forming a completely airtight structure, disposing a valve consisting of a mesa and a diaphragm at the lower part of the gas inlet or outlet, and; disposing an actuator for deforming the diaphragm at the lower part of the diaphragm to form a microvalve; A microvalve characterized in that it functions as a thermal type flow sensor that detects the flow rate based on changes in heater current due to flow rate by arranging a micro heater in the gas flow path.
Provide mass flow controllers.

The present invention will be described in detail below with reference to the attached drawings.

FIG. 1 illustrates the structure of the microvalve mass flow controller of the present invention.

FIG. 1(a) shows a plan view, and FIG. 1(b) shows a sectional view taken along the line AA'.

In this example, a gas introduction port (2) and a gas outlet (3) are provided on the Pyrex glass substrate (1), and a gas flow path (5) and a mesa (6) are provided on the silicon substrate (4) using micromachining technology. A diaphragm (7) is provided, and the glass substrate (1) and silicon substrate (4) are bonded to form a completely airtight structure. The mesa (6) and the diaphragm (7) at the bottom of the gas outlet (3) constitute a valve.

A piezo actuator (8) disposed at the bottom of the diaphragm (7) pushes up the diaphragm (7), brings the mesa (6) into contact with the glass substrate (1), controls the gas flow rate, and controls the gas flow path (5). ) The flow rate is detected by a thermal type flow sensor (9) disposed inside. Figure 1 shows
Although a normally open type structure is illustrated in which gas flows when no voltage is applied to the piezo actuator (8), a normally closed type structure is also possible.

The above micromachining technology that can be used in this invention utilizes the fact that the etching rate differs depending on the crystal axis and doping amount, and EPW (
By using ethylenediamine-pyrocatechol-water (ethylenediamine-pyrocatechol-water) or a KOH solution as an etchant, the (100) plane can be etched more efficiently than the (111) plane. Further, since the P''- layer formed by doping with boron or the like is not etched, a diaphragm of a desired thickness can be formed by forming the P+ layer.

Thermal type flow sensor (9) used in this example
consists of a microheater (10) provided in the gas flow path (5) and a signal processing circuit consisting of an operational amplifier mounted externally. The temperature that changes according to the gas flow rate of the micro heater (10) provided in the gas flow path (5) is
Detects the heater current supplied to keep this constant,
This measures the gas flow rate.

Figure 2 shows the micro heater (10) used in this example.
This is an example of the detailed structure of the section.

As is clear from this plan view (a) and cross-sectional view (b), Ni wire is used as the micro-heater (10), and the micro-heater (10) has a bent structure in order to increase the temperature of the heater. The Ni wire of the micro heater (10) is, for example,
Length 250μm, width 20μmn, thickness 0.4μm and va
Since it is formed thin, the heat capacity and thermal time constant are extremely small, and a flow sensor with high sensitivity and high speed response can be realized. #JChirunNi is not limited to Ni, and other metal wires may be used. Also, the micro heater (10) is coated with a SiO2 film to provide good thermal insulation and prevent direct exposure to gas. It has the characteristics that it can be applied to various gases.

Lead 1 (11) is a Pyrex glass substrate (1)
Since the structure is such that it is fixed with a conductive adhesive (12) such as a conductive epoxy resin and connected to the outside through a hole drilled in the hole, airtightness can be maintained sufficiently.

Although the above example has a structure in which the signal processing circuit is externally attached, the signal processing circuit may also be integrated on the silicon substrate (4).

FIG. 3 is a diagram showing a silicon substrate processing process and a microheater manufacturing process using micromachining technology.

The process will be explained step by step.

(a) n type (100) with a thickness of 400 μm
The S1 substrate is scribed to 20820++ m2, cleaned, and wet oxidized. Thereafter, a mask pattern for Si etching is formed by photolithography.

(b) Etching Si with 35 wt% KOH solution (80°C) using the 5102 film as a mask.

(c) 5i, which is the base of the nitride wire and wiring made of Ni.
02WA is deposited to a thickness of 2 μm by CVD.

A CVD5iOz film of 250 OA is deposited on the back surface of the substrate.

(d) Deposit 400 OA of Ni by electron beam evaporation. Thereafter, heater wire and wiring patterns are formed by photolithography. FeCj for etching:
A HO=1:15 solution was used.

(e) A 5i02 film was deposited at 2μIn by plasma CVD to protect the Ni-based interconnection pattern.
5ly2II by depositing and then photolithography
Etching I.

(f) A 3000A 5X mask is used to form valves and gas flow grooves by etching Si.
02WA is deposited by plasma CVD and photoetched. Thereafter, the Sl layer is etched by approximately 310 μm using hydrazine to form valves and gas flow grooves.

Here, the structure of the heater bridge is designed so that the Si under the heater wire is etched due to the property of hydrorazine as an anisotropic etching liquid.

The silicon substrate (4) having the mesa (6), diaphragm (7), and micro-heater (10) manufactured by the above process is made of Vilex glass having a gas inlet (2) and a gas outlet (3). It is bonded to the substrate (1) so as to form an airtight structure.

As this airtight bonding method, conventionally known techniques can be used, but preferably an anodic bonding method can be used.

After aligning the glass substrate (1) and the silicon substrate (4), perform anodic bonding by applying a constant voltage while heating so that the glass substrate (1) becomes negative.Heating temperature and applied voltage For example, 200-600℃, 300℃
It can be in the range of ~100OV, but 350
It is preferable to set the temperature to about 400°C and 500V.

Although various actuators can be used in this invention, a piezo actuator (8) as shown in FIG. 1 is preferable. This piezo actuator (8) has a cross section of, for example, 1.4 x 3 me2,
The length is 9 mm, and the displacement can be approximately 8 μm when a maximum DC voltage of 150 V is applied. Therefore, in this example, the distance between the valve formed by the mesa (6) and the Pyrex glass substrate (1) is designed to be 6 μm.

FIG. 4 illustrates the flow control results obtained with the present invention. We have realized a microvalve mass flow controller that can control gases with an extremely small tint of several CG11 or less. In addition, the micro valve of this invention
It has also been confirmed that the mass flow controller has a high-speed response of 10 to 20 is.

FIG. 5 is a diagram showing another embodiment, and is an example of a normally closed type. FIG. 5 (a> is a plan view,
FIG. 5(b) is a sectional view taken along line A-A', and FIG. 5(c)
) is a diagram explaining the basic operation.

Silicon substrates are used as the two bonded substrates (13) and (14) because a mesa (15) is formed on the two bonded substrates (13) and (14) to block the flow of gas. The basic structure is the same as the example shown in Fig. 1, but as mentioned above, the valve is formed by using a gasket formed by the contact of two mesas (15), and the gas outlet (16) A V clear (17) is formed at the bottom of the Figure 5 (C
) is used to connect the diaphragm (1) with the actuator (18) shown in
By pushing up 9), the gasket part B opens.
Gas is allowed to flow in.

In this example, for air-tight bonding between silicon and silicon substrates, a low-melting glass (200 g)
1) is formed using an RF sputtering method, and then anodic bonding is performed.

[Effects of the Invention] As described above, the present invention achieves high sensitivity, high-speed response, and high sensitivity by using a microvalve manufactured by micromachining technology and a thermal flow sensor using a microheater. , realized an ultra-compact microvalve mass flow controller that can control trace gases.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are a plan view and a sectional view showing an example of the present invention. FIGS. 2(a) and 2(b) are an enlarged plan view and a sectional view of the microheater section of this example. FIGS. 3(a), (b), (c), (d), (e), and (f) are cross-sectional views sequentially showing a part of the manufacturing process of this example. FIG. 4 is a flow chart showing the correlation with applied voltage. FIGS. 5(a), 5(b), and 5(c) are a plan view and a sectional view showing still another example. 1... Glass substrate 2... Gas inlet 3... Gas outlet 4... Silicon substrate 5... Gas flow path 6... Mesa 7... Diaphragm 8... Piezo actuator 9 ...Flow sensor 10...Micro heater 11...Lead wire 12...Conductive adhesive 13.14...Substrate 15...Mesa 16...Gas inlet 17...V tank 18...Actuator 19...Diaphragm 20...Gas inlet 21...Low melting point glass Representative Patent attorney Toshio Nishi Figure 1 (a) Figure 2 (a) Section 3

Claims (6)

[Claims] (1) A completely airtight structure is formed by bonding a glass or silicon substrate having a gas inlet and an outlet, a silicon substrate having a gas flow path, a mesa, and a diaphragm, and a gas inlet or outlet A valve consisting of a mesa and a diaphragm is placed at the bottom of the diaphragm, and an actuator for deforming the diaphragm is placed at the bottom of the diaphragm to form a microvalve.A microheater is placed in the gas flow path to generate a heater based on the flow rate. A microvalve mass flow controller that functions as a thermal flow sensor that detects flow rate based on changes in current. (2) The microvalve mass flow controller according to claim (1), which uses a piezo actuator. (3) A gas on-off valve is formed by a groove formed in the silicon substrate that contacts the lower part of the gas inlet or outlet, a gasket formed by local contact between the upper and lower substrates in the gas flow path, and a diaphragm. The microvalve according to claim 1, wherein the microvalve is of a normally closed type, in which gas is completely cut off when no voltage is applied to the actuator, and gas flows only when voltage is applied.・Mass flow controller. (4) The method for manufacturing a microvalve mass flow controller according to item (1), wherein the glass substrate and the silicon substrate are bonded by an anodic bonding method. (5) The microvalve according to item (1), wherein the silicon substrate and the silicon substrate are bonded by forming a film of low melting point glass on the bonding surface of the silicon substrate having a gas introduction outlet, and then performing anodic bonding.・Manufacturing method for mass flow controllers. (6) The method for manufacturing a microvalve mass flow controller according to item (1), wherein a SiO_2 layer is provided below the microheater for thermal insulation.