Conventionally, electrostatic pressure sensors for detecting, as a change in electrostatic capacitance, a change in a pressure sensitive diaphragm that flexes when it bears the pressure of a fluid being measured have been widely known. For example, electrostatic pressure sensors are used for measuring the state of vacuum in a manufacturing process such as in semiconductor manufacturing equipment, where the electrostatic pressure sensor for measuring the vacuum state is known as a vacuum gauge.
This vacuum gauge has a housing that has an inlet portion for the fluid that is to be measured, and the change in the pressure-sensitive diaphragm that flexes when it bears the pressure of the fluid being measured that has been introduced through the inlet portion of the housing is detected as a change in electrostatic capacitance. In the vacuum gauge, a baffle for preventing the accumulation, on the diaphragm, of substances that are included in the fluid being measured and that are unnecessary and that are an impediment (where these substances shall be known as “contaminating substances”) is provided between the inlet portion and the pressure-sensitive diaphragm, with a plate face thereof perpendicular to the direction through which the fluid being measured flows.
FIG. 5 illustrates the critical portions of a vacuum gauge shown in Japanese Unexamined Patent Application Publication No. 2006-3234 (“the JP '234”). In this figure, 100 is a sensor chip, and is supported on the center portion of the top face of a pedestal plate 101. The pedestal plate 101 is made from a first pedestal plate 102 and a second pedestal plate 103, which are bonded to the top and bottom faces of a supporting diaphragm 104, where the peripheral portion of the supporting diaphragm 104 is bonded held between a lower housing 105 and an upper housing 106. That is, only the peripheral portion of the supporting diaphragm 104 is bonded between the lower housing 105 and the upper housing 106 in a state wherein the supporting diaphragm 104 is held between the first pedestal plate 102 and the second pedestal plate 103.
The sensor chip 100 has a spacer 107, a sensor diaphragm (a pressure-sensitive diaphragm) 108 that is bonded to the spacer 107, and wherein a strain is produced in response to the application of a pressure, and a sensor pedestal 109 that is bonded to the sensor diaphragm 108, and that forms a vacuum capacitance chamber (a reference chamber) 109A. Note that the vacuum capacitance chamber 109A maintains the same pressure level together with the internal space (the reference vacuum chamber) 106A of the upper housing 106, through a connecting hole, not shown, that is provided at an appropriate location of the sensor pedestal 109. Moreover, although omitted from the drawings, a movable electrode is provided on the back face (on the capacitance chamber 109A side) of the sensor diaphragm 108, and a stationary electrode is provided on the inner face of the sensor pedestal 109, facing the movable electrode.
An inlet portion 105A for the fluid to be measured is provided in the lower housing 105. Moreover, a baffle 105B is provided at the outlet, for the fluid being measured, from the inlet portion 105A of the lower housing 105 with the plate face thereof perpendicular to the direction of flow F of the fluid being measured. An inlet hole 105B1 for the fluid being measured is formed by a specific gap in the periphery of the baffle 105B. Moreover, an inlet hole 110, for directing the fluid to be measured to the sensor chip 100, is formed in the center parts of the pedestal plate 101 (102, 103) and the supporting diaphragm 104.
In this vacuum gauge, the fluid being measured (a gas) arrives at the sensor diaphragm 108 from the inlet portion 105A, and the sensor diaphragm 108 flexes due to the differential pressure between the pressure of the fluid being measured and the capacitance chamber 109A of the vacuum, changing the gap between the stationary electrode and the movable electrode that is provided between the back face of the sensor diaphragm 108 and the inner face of the sensor pedestal 109, so as to produce a change in the capacitance value (electrostatic capacitance) of the capacitor that is formed by the stationary electrode and the movable electrode. The pressure of the fluid being measured (the gas) is measured by reading out, on the outside of the vacuum gauge, the change in the electrostatic capacitance.
Moreover, when measuring the pressure, the fluid being measured (the gas) from the inlet portion 105A strikes the plate face at the center of the baffle 105B and goes around it, and passes through the inlet hole 105B1 at the periphery of the baffle 105B, to be sent to the sensor diaphragm 108 through the inlet hole 110 in the center portions of the pedestal plate 101 (102 and 103) and the supporting diaphragm 104. As a result, the fluid being measured does not strike the sensor diaphragm 108 directly, thus preventing the accumulation, on the sensor diaphragm 108, of the contaminating substances that are included in the fluid being measured.
However, while the baffle 105B is provided in the vacuum gauge, if the contaminating substance for which incursion is to be prevented is in a gaseous state at the point wherein the baffle 105B is provided, it will not be possible to completely prevent the incursion into the inside. For example, the contaminating substance incurs in a gaseous state in the thin film deposition process known as ALD (Atomic Layer Deposition), which is based on a surface adsorption reaction.
That is, the inlet hole 110 that is provided in the center portions of the pedestal plate 101 (102, 103) and the supporting diaphragm 104 is a single through hole, and there is no special structure for preventing the contaminating substance that passes through the baffle 105B in a gaseous state from arriving at the sensor diaphragm 108 within the sensor chip 100, and thus the contaminating substance easily arrives through the inlet hole 110 at the most sensitive part at the center portion of the surface of the sensor diaphragm 108. When the contaminating substance is deposited and accumulates at this part, this may cause a zero-point shift of the vacuum gauge, which would compromise the measurement accuracy.
The present invention is to solve problems such as set forth above, and an aspect thereof is to provide an electrostatic pressure sensor wherein it is possible to reduce the amount of the contaminating substances that accumulate on the pressure-sensitive diaphragm.