JPS6286770A - Semiconductor pressure sensor manufacturing method - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a conductive pressure sensor, particularly an ultra-small semiconductor pressure sensor that can be mounted at the tip of a catheter.

Use [0] It is rapidly increasing in fields such as industrial measurement. A silicon diaphragm type pressure cassette that utilizes the piezoresistive effect is attracting attention as the only one that can meet these requirements. The reason for this is due to the following advantages or possibilities: ■ Mass production possible ■ Low price ■ High precision ■ High reliability ■ Small size and light weight ■ Multifunctionality possible.

Among these, the ones that have recently attracted particular attention are (a) For medical use: ■ Catheter-tip blood pressure sensors that are small and lightweight. This device 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. 3 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 is extremely long and thin with a diameter of about 1.0 to 2.4 mx, and has a silicon diaphragm-type pressure sensor chip (1) fixed on a ceramic substrate (2) and a diaphragm Q3 (pressure sensitive part). Blood pressure, which is the pressure to be measured, is applied from the top, and the bottom is open to atmospheric pressure via an air hole (power conduction tube (3) made of nylon, etc.).Electrically, the pressure on the chip (1) The metal pad 9 and the bonding wire (8) are connected to the metal wiring (9) on the ceramic substrate, and are further connected to the external monitor by the soldered lead wire α.Also, the bonding wire is not damaged due to cutting. Areas of concern are reinforced with a hard resin (4), such as epoxy resin, while other areas are reinforced with a soft resin (4) to provide appropriate softness.
5) For example, it is made of urethane resin. Furthermore, there is a hole called lumen α2 used for blood collection and measurement of cardiac output, and an attached tube aυ made of polyethylene.
The outer wall (6) of the catheter, including the top thereof, is coated with urethane resin.

Now, Fig. 4 shows a cross-sectional view of the sensor chip attachment part of such a catheter tip type blood pressure sensor.As is clear from this figure, in order to reduce the diameter of the catheter, the size of the sensor chip (1) itself must be reduced. I have to. Generally, a sensor chip with side surfaces perpendicular to both the front and back surfaces as shown in Figure (C) is used [a), but a sensor chip with side surfaces that do not intersect perpendicularly to the front and back surfaces, which should be called slopes as shown in (bl). A method of effectively utilizing space has also been proposed. However, this method cannot be an essential solution when the diameter of the catheter becomes less than 2.0 mm. This is because the thickness of the sensor chip cannot be ignored.In order to prevent warping, cracking, etc., the substrate used in the manufacture of general semiconductor integrated circuits becomes thicker as the diameter increases.For example, a 2-inch substrate The thickness is approximately 300 μm, 400 μm for 3 inches, 500 μm for 4 inches, and 65 μm for 5 inches.
0 μm, etc.

If the substrate is made thinner by polishing or the like, warping and cracking inevitably occur, which significantly reduces the overall yield.

For this reason, when manufacturing very small sensors, a substrate with the smallest possible diameter is used and the thickness of the substrate is warped to make it as thin as possible without causing cracks. For example, a substrate with a thickness of about 180 μm and a diameter of 2 inches is used. However, this has limits on miniaturization and poor work efficiency (there is also a limit on lowering prices.Also, a method of polishing the sensor chip after cutting it out could be considered, but it is difficult to handle tiny chips and is impractical. .

To solve this problem, a method of manufacturing a semiconductor pressure sensor as shown in FIG. 2 has been proposed. Even if a thick substrate with a large diameter is used, this method can be applied by forming a sensor chip forming area (ICJ) of an arbitrary thickness as shown in Figure (b) before cutting out the sensor chip. By manufacturing an ultra-small semiconductor pressure sensor (1) as shown in FIG.

However, with this method, it is necessary to perform two unique three-dimensional machining processes that are not found in general planar machining techniques: forming the sensor chip forming region α9 in Figure (b) and forming the diaphragm αJ in Figure tc). This method requires complicated processing, and a simple and highly practical method has not yet been proposed.

The present invention uses a semiconductor crystal substrate that is sufficiently thick (and thick) compared to the shape and dimensions of the sensor chip itself, and a process of forming a thin plate portion serving as a sensor chip formation area in the substrate, and a step of forming a sensor chip on the thin plate portion. A semiconductor pressure sensor manufacturing method that includes a step of forming a diaphragm and a diffused resistor, etc., which are chip components, and a step of cutting out a sensor chip, includes a step of forming a layer with excellent alkaline liquid resistance, and epitaxial growth of a semiconductor crystal on the layer. After repeating the steps twice, the steps corresponding to the thin plate forming step, diaphragm forming step, and sensor chip cutting out step are performed once by anisotropic etching using an alkaline etching solution.
The purpose is to manufacture an ultra-small semiconductor pressure sensor that can be mounted in a very narrow space such as a catheter and perform safe, stable, and highly accurate measurements. It is to provide a method.

In the present invention, in the method of manufacturing a semiconductor pressure sensor according to the prior art as shown in FIG.
By integrating and arranging the three processes of the sensor chip cutting process in d) into one process, the manufacturing process is prevented from becoming complicated and is highly practical.

That is, the method of the present invention makes full use of the processing method of anisotropically etching a silicon single crystal substrate using an alkaline solution, which is most commonly used for forming a diaphragm, and etching an etching stop layer embedded in the substrate and etching both the front and back surfaces. In this method, the formed protective film is used as a mask to form a sensor chip forming region and a diaphragm and to cut out the sensor chip in one etching process.

(e) 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, and only necessary components are shown. The figures are shown in the order of the steps, so the explanation will be given accordingly.

[a) As shown in the figure, an etching stop layer Cυ for forming a sensor chip and an etching stop layer (1) for forming a diaphragm are embedded in a silicon single crystal substrate α having an n′″ type (9) plane as a surface. In practice, a high boron concentration layer (a layer with a boron concentration of 7. (hereinafter referred to as shrimp growth),
On top of that, a high boron concentration layer of about 2 μm is formed again, and a further n layer is grown to form a silicon substrate α.
A is in a state as shown in (a).

That is, the boron high concentration layer formed first becomes the etching stop layer Qυ for forming the sensor chip, and the layer formed next becomes the stop layer (A) for forming the diaphragm. The shape of the sensor chip to be finally manufactured is almost determined at this time. In other words, the thickness of the sensor chip is the thickness of two degrees of shrimp growth and the etching stop layer CD for forming the sensor chip.
The thickness of the diaphragm is determined by the sum of the thickness of the second shrimp growth and the thickness of the etching stop layer (20) for forming the diaphragm. Etching stop layer for chip formation 01)
It is determined by the ratio of the pattern of the shrimp and the thickness of the two shrimp growths.

On the other hand, the error factors for these design values include the control accuracy of shrimp growth, the error in estimating the diffusion of boron-rich layer,
Only errors in estimating the etching depth in the (111) plane direction of anisotropic etching can be considered, and since each of these is a very small value, highly accurate processing can be performed as a whole.

fb) In the process shown in the figure, the components of the semiconductor pressure sensor are built into the substrate. That is, a piezoresistor (I) as a pressure-sensitive element is formed on the surface of the silicon substrate (+4), which is electrically connected to an Al pad "a7) formed via a surface protective film Q8) by a diffusion lead part α0. state.

At this time, a protective film (24) is also formed on the back surface, but a thermal oxide film is generally used as the protective film on the front surface (similar to the protective film 24).

tc + In the process shown in the figure, the protective film α stage on the surface is patterned to form an etching region @ for cutting out the sensor chip,
The protective film C)4) on the back surface is patterned to form an etching region (23) for a sensor chip formation region. Also, although not shown in the figure, in reality, the top of Al Patubi (1η) is covered with a protective film such as 5102 film made by CVD (chemical vapor deposition).

The process shown in Fig.
A sensor chip forming region is virtually formed on the surface where the stop layer eυ exists, and etching progresses further in the area where the stop layer eυ does not exist, forming an etching stop layer for diaphragm formation (
By stopping at 2■, a diaphragm is formed and an etching area (2) for cutting out the sensor chip on the surface is formed.
The sensor chip is cut out by penetrating the etching hole 21 that has progressed.

As the etching solution used at this time, a solution whose main component is KOf (hydrazine (Nf(2, NH2), etc.) is also effective, but due to its selectivity with the boron high concentration layer (20, 21) used as an etching stop layer, etc. Ethylenediami7 (H2N, ・CH2, ・CH2, 'NH2) and pyrocatechol (06H4(OH)2) and water (H2O
) and mixed with a small amount of pyrazine (04H4N2) as a catalyst is most suitable.

In addition, after cutting out the sensor chip, the protective film on the AJ pad αη must be removed, but since it is very difficult to perform photo processing on the chip, a separate film that can withstand alkaline liquids must be patterned and formed in advance. The protective film is removed by etching using this film as a mask.

The present invention has made it possible for the first time to manufacture an ultra-small semiconductor pressure sensor that can be attached to a catheter with an outermost diameter of approximately 1.0 to 1.5 mm in a form that is compatible with mass production.

In terms of process, there are some additional processes required compared to the general semiconductor pressure sensor Q manufacturing method, but basically there is one boro/high concentration layer formation process and one epitaxial growth process.
Since the manufacturing method according to the present invention can be realized by only adding steps one by one, the increase in manufacturing costs can be suppressed to a small amount.

In terms of chip size, conventionally the limit was to manufacture sensor chips with a thickness of approximately 180 μm using a 2-inch substrate, but now it is possible to manufacture sensor chips with a thickness of 50 μm or less. The limit for chip miniaturization has shifted to the mounting technology rather than the sensor chip processing capability itself.

Also, in terms of mass production, it is no longer necessary to use substrates with a small diameter, and it has become possible to improve productivity by using substrates with a diameter of about 5 inches.

From the above, ultra-compact pressure sensors that can be used for multiple purposes can now be produced in large quantities at low cost.For example, when applied as a catheter tip-type blood pressure sensor, this sensor can be made disposable and can be used in a wide range of applications. This will dramatically expand the

[Brief explanation of drawings]

FIG. 1 is a diagram schematically explaining a method of manufacturing a semiconductor pressure sensor according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a method of manufacturing a semiconductor pressure sensor according to the prior art. Figure 3 is a diagram showing the structure of the catheter tip type blood pressure sensor (aJ is a sectional view, [bl is a schematic plan view). Figure 4 is a cross section of the sensor chip attachment part of the catheter tip type blood pressure sensor in Figure 3. It is a diagram. 1 Semiconductor pressure sensor 15 Piezoresistor 2 Ceramic substrate 16 Diffusion saw 1 part 3 Atmospheric pressure transmission tube 171J Pad 4 Hard resin
18 Surface protective film 5 Soft resin
19 Sensor chip type 6 Catheter outer wall
Formation area 7 Air hole 20 Guiaphram formation 8 Etching stop for bonding wire 9 Metal wiring layer 10 Lead wire 21 Sensor chips cedar formation 11 Lumen tube Etching stop layer 12 Lumen 22
Surface etching area 13 Diaphragm 23
Back side etching region 14 Silicon single crystal substrate 2
4 Back protective film patent applicant Sumitomo Electric Industries, Ltd. (5 others)

Claims (3)

[Claims] (1) Using a semiconductor crystal substrate that is sufficiently large and thick compared to the shape and dimensions of the sensor chip itself, forming a thin plate part that is the sensor chip forming area in the substrate, and a diaphragm and diffusion that are the constituent elements of the sensor chip in the thin plate part. In a method for manufacturing a semiconductor pressure sensor, which includes a step of forming a resistor, etc., and a step of cutting out a sensor chip, the step of forming a layer having excellent alkaline liquid resistance and the step of epitaxially growing a semiconductor crystal thereon are performed at least twice. After repeating the steps, the steps corresponding to the thin plate forming step, diaphragm forming step, and sensor chip cutting out step are realized in one step by anisotropic etching using an alkaline etching liquid. . (2) The semiconductor crystal plate is silicon single crystal (100)
The semiconductor pressure sensor manufacturing method according to claim 1, wherein the substrate is a substrate having a surface as a front image. (3) The alkaline liquid is a mixture of ethylenediamine, pyrocatechol, and water, or a mixture containing a small amount of catalyst, according to any one of claims 1 and 2. A method for manufacturing a semiconductor pressure sensor.