JPH0620144B2 - Method for manufacturing semiconductor pressure transducer - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor pressure converter, and more particularly to a method for manufacturing a semiconductor pressure converter using an ion implantation method for forming an element.

<Prior Art> FIG. 3 is a configuration diagram showing a configuration of a conventional semiconductor pressure converter. (A) is a plan view and (B) is a vertical sectional view.

The silicon substrate 10 is composed of a sensor section 10A and a circuit section 10B. The silicon substrate 10 is, for example, a p-type silicon single crystal, has a cylindrical recess 11 in a part of the sensor portion 10A, and is formed in a portion where the thickness of the silicon single crystal is thinned by forming the recess 11. The strained portion 12 is formed. Strain element 12
A pressure P to be measured is applied to.

An n-type epitaxial layer is formed on the strain-flexing part 12 and a horizontal crystal axis <1 passing through the center of the n-type epitaxial layer as shown in FIG.
10> Shear stress gauge G _S functioning as a pressure gauge having a longitudinal direction at 45 ° with respect to this crystal axis
Are formed by diffusion of p-type conductivity type impurities.

The shear stress gauge G _S has a power source end formed in the longitudinal direction, and a low resistance lead wire 14a from the conversion circuit 13 of the circuit section 10B,
For example, a constant voltage is applied via 14b. Lead wire 14
a and 14b are formed by diffusing a p-type semiconductor. On the other hand, a voltage corresponding to the shear stress τ _S generated by applying the pressure P to the strain-flexing portion 12 causes a low resistance lead wire to be formed from the output end formed substantially at the center of the shear stress gauge G _{S in} the longitudinal direction. It is input to the conversion circuit 13 via 15a and 15b. The lead wires 15a and 15b are also formed by diffusing a p-type semiconductor.

Circuit elements inside the conversion circuit 13 are also formed by diffusion of impurities in the same manner as the shear stress gauge.

FIG. 4 is a partially enlarged sectional view showing the vicinity of the shear stress gauge portion in an enlarged manner.

n-type epitaxial layer 16 on p-type silicon substrate 12
Is formed, and the shear stress gauge G _S and the lead wires 14a and 14b connected thereto are formed therein. Further, a thin film 17 of silicon dioxide (SiO ₂ ) is formed on this, and the thin film 17 is covered with silicon nitride (Si ₃ N ₄ ) as a protective film 18.

The shear stress gauge G _S can be formed by the thermal diffusion method as described above. However, the shear stress gauge can also be formed by the ion implantation method shown in FIG.

FIG. 5 is a sectional view showing the structure of the ion implantation gauge.
A mask 19 is first formed on a part of the n-type epitaxial layer 16 formed on the p-type silicon substrate 12, and then p-type impurity ions are implanted to form an ion implantation gauge G _i. A shear stress gauge is completed through a passivation process. Lead wires 14a, 14b, 15a,
The portion 15b is formed in the same manner.

The characteristics of the element formed by the ion implantation method as described above have the following advantages as compared with the characteristics of the element formed by the diffusion method.

(A) The sheet resistance R _S or the junction depth x _j can be easily controlled.

(B) The element formation time is short.

(C) Since the surface of the silicon layer after forming the element is flat, uneven surface stress is less likely to occur.

(D) A sheet having a high sheet resistance R _S can be easily obtained.

<Problems to be Solved by the Invention> However, the conventional method for manufacturing a semiconductor pressure converter for forming an element by one-time ion implantation has the following problems.

For sheet resistance R _S of elements such as gauges and lead wires, where C (X) is the impurity concentration and is the average impurity concentration up to the junction depth x _j , (X is the depth from the surface of the silicon layer).

Therefore, in order to reduce the sheet resistance R _S , there can be two methods (a) increasing the dose Q and increasing it, and (b) increasing the junction depth x _j .

When the method (a) is used, as shown in Fig. 6 (a), the amount of implanted ions is increased up to the solid solubility limit C _{M of} impurities, and lattice defects are generated, and finally crystallinity is recognized. It can even go into an amorphous state that cannot be achieved. For this reason, the damage may not be recovered even by the subsequent annealing, resulting in deterioration of the element characteristics (drift or the like).

In order to realize (b) with one ion implantation, the implantation energy E (keV) may be increased. However, Fig. 6 (b)
As shown in, the average impurity concentration decreases and the sheet resistance
R _S cannot be made too small.

Further, when the element is formed by one-time ion implantation, the junction depth x _j of the element is shallow and it is easily affected by the electric field effect on the surface. If the implantation energy E is increased for deep implantation, the collision of ions with the silicon surface causes damage to the crystal structure such as lattice defects, and this damage may not be recovered even by annealing.

<Means for Solving Problems> Therefore, it is possible to freely select the junction depth without damaging the crystal structure over a wide range of the sheet resistance of an element such as a gauge or a lead wire. ,
Mainly, in a method of manufacturing a piezoresistive semiconductor pressure transducer in which elements are formed by ion implantation, a small dose amount and a low first stroke are first provided in a predetermined region on a silicon substrate where a piezoresistive element for pressure detection is formed. Ions are implanted with an implantation energy, then ions are implanted into a predetermined region at a second implantation energy higher than the first implantation energy, and the implantation energy is increased as the implantation process proceeds. After the post-annealing process, the piezoresistive element is formed so that the impurities are distributed in a strip shape over a predetermined range of the junction depth.

<Examples> Examples of the present invention will be described below with reference to the drawings.
Incidentally, the portions having the same functions as those of the conventional technique are appropriately designated by the same reference numerals and the description thereof will be omitted.

FIG. 1 is a process drawing showing a manufacturing process for manufacturing a gauge according to the present invention.

first forming a mask 19 on the n-type epitaxial layer 16 (step), after the first round of ion implantation is performed while (step) to form a gauge G _'i. The distribution of the impurities in this case is as shown in FIG. 6 (a) as shown in FIG. 1 (c), but the dose Q is larger than that shown in FIG. 6 (a). Selected small. Further, in this step, the implantation energy E ₁ is small and the impurity distribution is distributed from the surface of the epitaxial layer 16.

Next, in the process, the second ion implantation is performed to form a gauge G ″ _i . Implantation energy E _{2 in} this case
Is selected larger than in the case of the process, and the junction depth x _j is deeper. Therefore, as can be seen from the impurity distribution shown in FIG. 1C, the distribution is slightly band-shaped, and the gauge G ″ _i is thicker than the gauge G ′ _i .

Further, in the process, the third ion implantation is performed to form the gauge G _i . Ion implantation energy in this case
E ₃ was selected to be larger than in the case of the process, and the junction depth x _{j was} larger. Therefore, as can be seen from the distribution of impurities in FIG.

After that, this ion implantation process is repeated as many times as necessary,
Go to the process and anneal. In such a multi-stage ion implantation method, since the element is formed by several times of ion implantation with the implantation energy E lower than the small dose amount Q, the damage to the crystal structure is small, and these damages are almost eliminated in the annealing process. A gauge is obtained that is fully recovered and exhibits stable properties.

After that, the process moves to the step of removing the mask 19 and performing passivation (step) to complete the process.

Further, according to the multi-step ion implantation method described above, even when the low resistance lead wires 14a, 14b, 15a, 15b are formed, the implantation energy E _{1 is set} for each ion implantation with a small dose Q. , E ₂ , and E ₃ are increased little by little for ion implantation, the epitaxial layer 16 can be formed even if the junction depth x _j is increased.
Impurities are almost evenly distributed from the surface to the junction depth x _j ,
The sheet resistance R _S of this portion can be reduced. Also, the dose Q is small and the damage given to the crystal structure is small, and the damage is recovered by annealing, and a stable element is obtained.

Further, as shown in FIG. 2, by performing annealing every time ion implantation is performed, a stable element can be obtained with almost no damage to the crystal structure.

Although the ion implantation is separately performed in the above description, the ion implantation may be continuously performed while changing the junction depth x _j (changing the implantation energy E).

Although the above embodiments have mainly described the sensor unit,
The same can be applied to circuit elements such as diodes and transistors.

<Effects of the Invention> As described above in detail with reference to the embodiments, according to the present invention, the amount of impurities per unit volume can be kept low, the thickness of the element layer can be increased, and a multi-step process can be performed to obtain a required resistance value. Since the ion implantation method of (1) is adopted, (a) it is possible to form a device with few defects in the crystal structure, and a highly reliable and highly accurate semiconductor pressure converter can be realized.

(B) Good sheet characteristics and a wide range of sheet resistance values can be obtained, which facilitates the design of the semiconductor pressure transducer.

(C) The junction depth can be made large, and it is not easily affected by the surface charge effect, and stable characteristics can be obtained.

And so on.

[Brief description of drawings]

FIG. 1 is a process drawing showing an embodiment of the manufacturing method of the present invention, FIG. 2 is a process drawing showing another embodiment of the manufacturing method of the present invention, and FIG. 3 shows the structure of a conventional semiconductor pressure converter. FIG. 4 is a partially enlarged cross-sectional view showing the vicinity of the shear stress gauge portion in FIG. 3 in an enlarged manner, and FIG. 5 is a gauge cross-section when the gauge shown in FIG. 4 is formed by an ion implantation method. FIG. 6 is an explanatory view for explaining the problems of the ion implantation method in FIG. 10 ... Silicon substrate, 10A ... Sensor part, 10B ... Circuit part, 12 ... Strain element, 13 ... Conversion circuit, 14a, 14b, 15
a, 15b ... Lead wire, 16 ... Epitaxial layer, 18 ...
… Protective film, G _S …… Shear stress gauge, C …… Impurity concentration, x _j …… Junction depth, Q …… Dose amount, E …… Implant energy.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Aga 2-932 Nakamachi, Musashino-shi, Tokyo Inside Yokogawa Hokushin Electric Co., Ltd. (56) Reference JP-A-54-129889 (JP, A) JP 50-161156 (JP, A)

Claims (2)

[Claims] 1. A method for manufacturing a piezoresistive semiconductor pressure transducer in which an element is formed by ion implantation, in which a small dose amount and a low dose are first provided in a predetermined region on a silicon substrate where a piezoresistive element for pressure detection is formed. Ions are implanted with a first implantation energy, then ions are implanted into the predetermined region with a second implantation energy larger than the first implantation energy, and the implantation energy is increased as the implantation process proceeds. Then, after that, an anneal process is performed to form the piezoresistive element so that the impurities are distributed in a band shape over a predetermined range of the junction depth. 2. The method of manufacturing a semiconductor pressure converter according to claim 1, wherein the ion implantation step is continuously performed.