JPS6281774A - Semiconductor pressure sensor manufacturing method - Google Patents

Abstract

PURPOSE:To carry out production in large quantity at a low cost, by forming a slant surface by anisotropic etching using alkali liquid. CONSTITUTION:Etching regions 23 and 24 for cutting out a sensor chip at an upper and lower surfaces and a silicon single-crystal (100) surface, where an etching region 25 for forming a diaphragm is exposed, are etched with alkali liquid. At this time, the other part is all protected with SiO2 films 17, 18 and 20 and an SiN film 19. As the etching liquid, a liquid, whose main components are KOH, hydrazine NH2NH2 and the like can be used. In consideration of selectivity with respect to a high concentration boron layer 21 used as a etching stopping layer, however, the following liquid is best suited: a small amount of pyrazine C4N4N2 as a catalyst is mixed into the mixed liquid of ethylene diamine H2N.CH2.CH2.NH2, pyrocatechol C6H4(OH)2 and water H2O.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor pressure sensor that utilizes the piezoresistance effect of a semiconductor, and particularly to an ultra-small semiconductor pressure sensor that can be mounted at the tip of a catheter.

Conventional technology and its problems The demand for pressure sensors has increased in recent years (a) for medical use) for automobiles (C).
) It is rapidly increasing in fields such as industrial measurement. Silicon diaphragm pressure sensors that utilize piezoresistance effects are attracting attention as the only type of pressure sensor that can handle these problems. The reason for this is due to the following many advantages or possibilities. In other words, ■ Mass production possible ■ Low price ■ High precision ■ High reliability ■ Compact and lightweight ■ Possible to have multiple functions.

Among these, the one that has recently attracted particular attention is the small and lightweight catheter-tip blood pressure sensor for medical use. This is intended to be inserted into the body of a critically ill patient such as an ICU (intensive care unit) to accurately measure blood pressure at local sites within the heart or blood vessels.

FIG. 2 shows an example of a catheter tip type blood pressure sensor. (
(a) is a cross-sectional structural diagram thereof, and (1)) is a schematic plan view.

Such a catheter (6) is very long and slender with a diameter of about 1.5 to 2.4 plates, and a silicon diaphragm type pressure sensor chip (1) is fixed on a ceramic substrate (2) and serves as a pressure sensing part. Blood pressure, which is the pressure to be measured, is applied to the diaphragm α from the upper part, and the lower part is open to atmospheric pressure from the air hole (7) through the conduction tube (3) made of nylon or the like. Electrically, the metal pad on the chip (1) is connected to the metal wiring (9) on the ceramic substrate by the bonding wire (8), and is further connected to the external monitor by the lead wire α0 attached. There is. In addition, parts such as bonding wires that are likely to be damaged by cutting are reinforced with hard resin (4), such as epoxy resin, and other parts are reinforced with soft resin (5), such as urethane resin, to provide appropriate flexibility. It is formed. Furthermore, there is a hole called the lumen (6) used for blood collection and measurement of cardiac output, etc., and an attached tube αυ made of polyethylene, etc., which covers the outer wall of the catheter, including above the diaphragm part α of the sensor chip (1). (6) is coated with urethane resin.

As is clear from the cross-sectional view of the tip of the catheter shown in FIG. 3, the shape of the semiconductor pressure sensor chip (1) that has been commonly used in the past is a rectangular parallelepiped except for the concave portion of the diaphragm portion α. This is because the chips are cut out from the silicon wafer using a dicing saw using general semiconductor integrated circuit manufacturing technology.

However, this causes the following problems.

(I) Since a rectangular parallelepiped sensor chip is attached to a catheter with a circular cross section, space cannot be used effectively. To put this in detail, ■The diaphragm area cannot be increased.
■It is not possible to increase the bonding area between the chip and the ceramic substrate, and it is not possible to respond to ■higher sensitivity and stabilization of characteristics.

(n) Since the corner of the tip approaches the catheter outer wall (6) at an acute angle ζ, the catheter outer wall is easily torn at this portion, resulting in problems such as (1) low yield and (2) lack of safety.

It is clear that in order to solve these problems, ideally the cross-sectional shape of the sensor chip should be made circular to match the shape of the outer wall of the catheter, except for the portion bonded to the heptadramic substrate. However, in reality it is 1, OX8. It is extremely difficult to process a very small sensor chip of OXo, 4- or so into a circular shape, and even more so, it is almost impossible to fabricate a uniform diaphragm of several tens of degrees from Wtp- into it.

For this reason, by forming a plane or near-plane surface that forms an angle other than a right angle with both the front and back surfaces of the substrate, which should be called a slope, as shown in Figure 4, the angles of the outer wall of the catheter and the adjacent sensor chip can be made obtuse. It has been proposed to solve the above problems. However, a practical manufacturing method that can easily manufacture a sensor chip having such a slope has not yet been proposed.

Purpose of the Invention The purpose of the present invention is to propose a method for inexpensively and mass-producing a semiconductor pressure sensor that can be mounted in a very narrow space such as a catheter and perform safe, stable, and highly accurate measurements. do.

Means for Solving the Problems The present invention solves the above problems by directly utilizing anisotropic etching, which has been conventionally used in the diaphragm forming process, to form surfaces that form angles other than right angles to both the front and back surfaces of the substrate. It's resolved.

In other words, to create a uniform diaphragm of several μm to several tens of μm in the chip of a semiconductor pressure sensor (I
If an etching stop layer is formed in advance in a silicon single crystal substrate with the UO) plane as the surface and then etched with an alkaline solution, the etching speed of the (111) plane is extremely slow compared to the (100) plane. 111) surface remains as an etched surface, and its shape can be determined geometrically. This (111)
It uses a plane, and the angle it makes with the (100) plane is 54.7°
It is.

Effects and Examples The present invention will be explained below based on specific examples.

FIG. 1 is a diagram schematically explaining a method of manufacturing a semiconductor pressure sensor according to an embodiment of the present invention. In this embodiment, not only the slope is formed by anisotropic etching for forming the diaphragm, but also the process of cutting out the sensor chip is completed in this process.

The explanation will be given below according to the figures.

(a) A high concentration boron layer tpn as an etching stop layer is formed in a silicon single crystal substrate (c) whose surface is an n-type (100) plane, and a silicon substrate (a) is formed as an etching stop layer.
A piezoresistor α→ which is a pressure-sensitive element is formed on the surface of the Al pad (
26) is electrically connected to the diffusion lead part αQ, and the entire surface of this surface except for the etching area for cutting out the sensor chip is covered with a 5iOz film 08) formed by CVD 1 sputtering or the like.
Plasma CVD was applied to the top of the film, except for the lead extraction part (■).

It is covered with a SiN film a (g) formed by sputtering or the like.

At this time, a 5i02 film ω used as a mask when patterning the SiN film may be formed on the SiN film aω. This is SiN in dry etching.
This is because the selectivity between the film and Sing PA is not sufficient, so patterning is often performed by wet etching using hot phosphoric acid. Further, a thermal oxide film σ is formed on the entire back surface of the substrate (1).

(b) In the step shown in the figure, an example of an etching region for cutting out a sensor chip and an etching region (c) for forming a diaphragm of the thermal oxide film α on the back surface are removed by etching.

Next, in the process shown in Figure (C), the exposed silicon single crystal (100) surface of the sensor chip cutting out etching areas (23, 24) on the front and back sides and the diaphragm forming etching area (A) is etched with an alkaline solution. Etching. At this time, all other parts are 5i02 films (17, 18, 20)
Alternatively, it is protected by a SiN film opening 9). As an etching solution, a solution mainly composed of KOH, hydrazine loincloth, 'NH2), etc. is also effective, but a high concentration layer of boron (ethylenediamine [F]2N- CH2・CH2・NI(2
) and pyrocatechol (CaH4■I(), ) and water [F
]20), pyrazine (C4H4N
A solution containing a small amount of 2) is optimal. Etching is α
11) The surface completely appears and a high boron concentration layer (211
The machining accuracy is very high, considering that reaching ζ is almost automatically completed. Also, a high concentration layer of boron (2
It is desirable for B to form a layer with a boron concentration of 7 x 10" ions/cm3 or more to a thickness of about 2 μm. In this step, the silicon substrate is cut out into a sensor chip, and its side surfaces are (111) planes. , (100
) is composed of slopes forming an angle of 54° and 7°. At this time, in order to keep the etching rate constant within the substrate and prevent variations in the characteristics of the sensor chip, it is desirable that the step of cutting out the sensor chip be slow, so the etching area for cutting out the sensor chip on the back side should be as small as possible.

Finally, in the process shown in (d), the lead extraction part (7)
) Sing film Q81 Etching is performed using the S iN film (1 g) as a mask. The base of this etching is A.
For the β pad (26), a combination of wet etching and dry etching using an HF solution or only dry etching is performed. Although this work must be carried out in the chip state, since the SiN film 0ω is used as a mask, photo processing is unnecessary and it is relatively easy.

In addition, by controlling the film thickness by taking into account the characteristics of the film, the thermal oxide film aη on the back surface and the SiN film 0 are removed during this process.
It is also possible to automatically remove the i02 film on the film 9.

Effects of the Invention According to the present invention, space can be used effectively even when mounted in a very narrow and circular place like a catheter.
For the first time, it has become possible to manufacture semiconductor pressure sensors at low cost and in large quantities that can measure stably and safely, 1) have high precision, and 2) be compatible with multifunctional catheters that incorporate sensors with other functions at the same time.

That is, the process is simple because the following three steps can be performed in one anisotropic etching process: (1) diaphragm forming process, (2) slope forming process to effectively utilize space, and (2) sensor chip cutting process. Etching after cutting out the sensor chip is also relatively easy since no photo processing is required.

This makes it possible to mass-produce inexpensive catheter-tip type blood pressure sensors, thereby making the sensors disposable and dramatically expanding the scope of their use.

[Brief explanation of drawings]

FIGS. 1A, 1C, and 1D are diagrams schematically illustrating a method for manufacturing a semiconductor pressure sensor according to an embodiment of the present invention. FIG. 2 is a diagram showing the structure of a catheter tip type blood pressure sensor, in which (a) is a sectional view and (b) is a schematic plan view. Figure 3 is a cross-sectional view of a conventional semiconductor pressure sensor attached to the tip of a catheter, and Figure 4 (,)
(b) is a sectional view when the semiconductor pressure sensor manufactured by the manufacturing method of the present invention is mounted. 1. Semiconductor pressure sensor 2, ceramic substrate 3, atmospheric pressure transmission tube 4, hard resin (ex epoxy) 5, soft resin (ex urethane) 6, catheter outer wall 7, air hole 8, bonding wire 9, metal wiring 10, Lead wire 11, Lumen tube 12, Lumen 13, Diaphragm ■4. Piezo resistor 15, diffusion lead part 16, front thermal oxide film 17, back thermal oxide film 18, 5ing film 19, SiN film 20, SiN film etching mask film (exsi
OJ21, boron high concentration layer 22, lead extraction part 23, etching area for sensor chip cutting out (
Front surface] 24, Etching area for sensor chip cutting (back side) 25, Etching area for diaphragm formation 26, Ag pad 27, N-type silicon single crystal substrate

Claims (3)

[Claims] (1) A crystal in which a diaphragm that deforms depending on the atmosphere to be measured is provided in the center of a semiconductor crystal plate, a diffused resistor as a pressure-sensitive element is formed in the diaphragm, and a pair of parallel surfaces are formed on the side surfaces of the crystal plate. A method of manufacturing a semiconductor pressure sensor comprising forming at least one slope that does not intersect perpendicularly to both the front and back sides of a plate, characterized in that the slope is formed by anisotropic etching using an alkaline solution. A semiconductor pressure sensor manufacturing method. (2) The semiconductor crystal plate is silicon single crystal (100)
2. The method of manufacturing a semiconductor pressure sensor according to claim 1, wherein the substrate has a flat surface. (3) Claims 1 and 2, characterized in that the alkaline liquid is a mixture of ethylenediamine, pyrocatechol, and water, or a mixture containing a small amount of catalyst. A method for manufacturing a semiconductor pressure sensor.