JPS5931431A - semiconductor pressure sensor - Google Patents

Abstract

(57) [Summary] 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 semiconductor pressure sensor, and particularly to a semiconductor pressure sensor suitable for use in a high temperature and high humidity environment.

As an example of a semiconductor pressure sensor, one having a cross-sectional structure shown in FIG. 1 has been devised.

In FIG. 1, a gauge chip 1 as a diaphragm
is formed from a silicon semiconductor, and as shown in the figure, the center part of the lower surface is thin and the peripheral part is thick. This gauge chip 1 is fixed on a glass die 2 made of pirate glass. The thick part of the gauge chip 1 and the glass die 2 are fixed together in a high temperature atmosphere.
As shown in FIG. 1, a so-called anodic bonding method is used, in which a DC high voltage is applied using the gauge chip 1 as the positive electrode and the glass die 2 as the negative electrode, and a bonding layer is formed at the boundary layer between them.

However, when the semiconductor pressure sensor formed by the above-mentioned anodic bonding method is used in a high temperature and high humidity environment, there is a drawback that the gauge zero output shifts in the positive direction (so-called upshift), which causes the measurement value to change. There was a huge problem with reliability.

An object of the present invention is to provide a semiconductor pressure sensor that can reduce upshifts and improve reliability in high-temperature, high-humidity environments.

The present invention is based on the results of conducting various experiments to investigate the cause of upshift under high temperature and high humidity conditions, and finding that the cause is mainly due to the hygroscopicity of the bonding layer formed by the anodic bonding method. This is an attempt to reduce the upshift under high temperature and high humidity by controlling the junction current and setting the thickness of the bonding layer to 3 to 6 μm.

Hereinafter, the reason why the above object is achieved by the present invention will be explained.

First, the principle of the anodic bonding method applied to the present invention will be explained. A gauge chip 1 and a glass die 2 having the shapes shown in FIG. 1 are assembled, fixed with a jig, and housed in a chamber 3. Install this chamber 3 in an electric furnace 17
Then, a high DC voltage of about 800 to 1500'V is applied, with the gauge chip 1 being positive and the glass die 2 being negative. At this time, NaO, which is the alkaline component of the glass die 2, is polarized, and oxygen ions are released from the bonding interface of the glass die 2 as shown in the following equation (1) and move to the gauge chip l side, which is the anode side. I can pass.

Nap-+2Na"+O"-...-(1) Also, silicon (Si) on the gauge chip is also ionized and becomes Sl 4
+, and is moved to the glass die 2 side, which is the cathode side.

Due to the diffusion of these ions, the following equation (2) is formed at the junction boundary:
It is thought that a bonding layer of S'02 is formed by this reaction, and the gauge chip 1 and the glass die 2 are bonded by this layer.

202-10 Si4+→8102...(
2) Due to this reaction, a junction current Ip flows between the gauge chip 1 and the glass die 2. Therefore, it is considered that this junction current Ip influences the formation of the junction layer.

On the other hand, the cause of upshift in a high temperature and high humidity environment is thought to be due to moisture absorption by the glass die and moisture absorption by the bonding layer. In other words, their absorption of moisture causes a difference in the coefficient of thermal expansion between the gauge chip and the glass die or bonding layer, which causes an upshift. Moreover, it was found that the upshift due to moisture absorption in the bonding layer was much larger.

Therefore, as mentioned above, to form the bonding layer, the junction current I
Since p is involved, a high temperature and high humidity durability test of 85r-85% I (H) was conducted using the junction current Ip as a parameter, and changes in the gauge zero point output were measured experimentally.

The results of this durability test are shown in FIGS. 2(a) to (C).

In the 21st lines 1(a) to (C>), time (h) is shown on the horizontal axis and zero point output change (mV) is shown on the vertical axis, and the junction current Ip is shown attached to the curve in the figure. As is clear from these figures, it can be seen that the zero point output change is greatly influenced by the junction current Tp.However, since the conventional anodic junction was an application type and a method that controlled the pressure to be constant, ,
The flowing bonding current Ip was not constant due to fluctuations in bonding temperature, variations in glass die dimensions, lot-to-lot variations in NaO content in the glass die, etc. Therefore, the bonding layer formed was also constant17. It turns out that it did not become a thing.

Next, as mentioned above, the reason why the output is upshifted is due to the effect of moisture absorption, and this causes the diaphragm to become concave downward in Figure 1. confirmed. An example of this result is shown in Figure 3 (
Shown in a) to (d).

FIGS. 3(a) to 3(d) show the measurement of the unevenness on the surface of the gauge chip using a surface roughness meter and a laser interferometer in each manufacturing process of the semiconductor pressure sensor. The same figure (a) shows the gauge chip before formation of the diaphragm 3, and as shown in the figure, it had a convexity of Δh=O,j of 5 to 0.20 μm. When this gauge chip is used to form a thin part by etching at the center of the lower surface, it becomes more convex upward as shown in Figure (b), and Δh=0.32μ~0.6
It became μm. When this is anodically bonded onto a glass die,
As shown in Figure (C), it is deformed in the opposite direction, and during Δh -
It became a dent of 0.1 μm. When a humidity test (100 hours) was conducted using the semiconductor pressure sensor formed in this way, as shown in FIG. 0.15~-0.2μm
It became. That is, it was confirmed that the diaphragm part was deformed into a concave shape due to moisture absorption, and was thereby upshifted.

In other words, since the coefficient of thermal expansion αS of the gauge chip 1 is smaller than the coefficient of thermal expansion αG of the glass die 2, the thermal expansion coefficient αS of the gauge chip 1 is smaller than the coefficient of thermal expansion αG of the glass die 2. There is a difference, and after joining, as shown in FIG. 6(b), a moment is generated in the diaphragm portion as indicated by the arrow in the figure, causing it to become concave downward.

When the structure formed in this way is placed in a high temperature and high humidity environment, the bonding layer 4 absorbs moisture and expands, and when it is taken out to room temperature, the bonding layer 4 forms as shown in FIG. 4(C). I? A compressive force is applied to the gauge tip 44, and a tensile force is applied to the gauge tip 1, thereby causing the diaphragm portion to concave further downward. Incidentally, when the joint portion was obliquely polished and 5I02 was analyzed by XMA, it was found that the joint 1i4 was an 8 1 Q 2 thin layer formed at the gauge tip (+111).

Moreover, 1q of this bonding layer and the anodic bonding current Ip have the correlation shown in FIG.
From the characteristics of the zero point output change and the anodic junction current shown in C), it can be seen that an optimum junction layer thickness exists.

That is, when the bonding layer has a thickness of 6 μm or more, the moisture absorption becomes large and the upshift of the zero point becomes large. However, when the IP is 10 μA, a bonding layer of about 2.5 μm can be obtained, but some voids remain that are not bonded, and moisture infiltrates into those areas, so the apparent water absorption increases. However, this increases the amount of upshift.

Moreover, it cannot be said that the bonding strength is sufficient.

From these reasons, the anode junction current Ip is set to 15 to 25 μA.
By controlling the bonding layer to have a thickness of 3 to 6 μm, upshift can be significantly reduced.

As explained above, according to the present invention, even when formed by an anodic bonding method, upshifts in high temperature and high humidity environments can be significantly reduced and high reliability can be obtained. .

[Brief explanation of drawings]

Claims (1)

[Claims] 1. A semiconductor pressure sensor in which a gauge chip consisting of a diaphragm having a thick portion on the periphery is placed on a support made of a glass die, and the thick portion of the gauge chip is fixed to the support by an anodic bonding method. . A semiconductor pressure sensor, characterized in that the thickness of the lip mating layer formed between the thick portion and the support base by an anodic bonding method is set to 3 to 6 μm by controlling the bonding current.