JPH10312987A - Micromachining method for wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform etching of a wafer without requiring any fixture while preventing corrosion of a metallic material by immersing the wafer into a second etching liquid noncorrosive to a second passivation film along with a first noncorrosive etching liquid. SOLUTION: A passivation film 27 adheres to a protective film 24 including electrode terminals 25, 26. After the surface of the passivation film 27 is planarized, a passivation film 28 is stuck to the surface of the passivation film 27. A mask film 29 is then provided on the surface of the passivation film 28 at the part of the electrode terminals 25 and a mask film 30 is stuck to the other side of a silicon wafer 21. The part being stuck with no mask film 30 is then subjected to etching using an alkaline etching liquid (first etching liquid). Finally, one side of the silicon wafer 21 is etched using a mixed liquid of acetic acid and hydrofluoric acid as an etching liquid (second etching liquid).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a micromachining wafer processing method for subjecting a wafer to mechanical processing for micromachining.

[0002]

2. Description of the Related Art Sensors such as an acceleration sensor and a pressure sensor are mounted on a silicon wafer using LSI technology.
r) Micromachining, a technique of forming on top, is known. In micromachining, after a circuit is formed on one surface of a silicon wafer, etching is performed on a surface opposite to the circuit formation surface to form, for example, a sensor diaphragm utilizing a piezo effect. In the etching step, anisotropic etching of silicon is performed with an etching solution such as KOH or TMAH (tetramethylammonium hydride) while protecting the circuit formation surface using a jig called a fixture.

FIGS. 1A to 1E sequentially show such a conventional wafer processing method. In the step shown in FIG. 1A, diffusion layers 2 and 3 are formed on one surface of a single-crystal silicon wafer 1, and a protective film 4 made of SiO ₂ (silicon oxide) is attached to the surface. You. The protective films 4 in the diffusion layers 2 and 3 are removed, and the electrode terminals 5 and 6 made of aluminum are connected to the diffusion layers 2 and 3. Electrode terminal 5,
Reference numeral 6 denotes an electrode terminal for wire bonding. The protective film 4 including the electrode terminals 5 and 6 is further provided with PSG (phosphor glass).
A protective film 7 which is a passivation film made of In FIG. 1B, a hole 8 is formed in the protective film 7 on the electrode terminal 5 to form a pad to which a bonding wire is connected. In the step of FIG. 1C, a mask film 9 is adhered to the other surface of the silicon wafer 1, and the square portion where the mask film 9 is not adhered is etched in the next step of FIG. During this etching, the fixture 10 covers one surface of the silicon wafer 1. The fixture 10 is for preventing one surface of the silicon wafer 1, that is, the circuit forming surface, from being etched, and has a concave disk shape as shown in FIG. 2, for example. In etching, trapezoidal hole 1 as shown in cross section
1 is formed, and the wafer processing is completed in a state where a thin portion of the silicon wafer 1 can be used as a diaphragm between the diffusion layers 2 and 3 as shown in FIG.

[0004]

In such a conventional micromachining wafer processing method, the number of wafers that can be processed at one time in an etching process requiring a long time is limited because a fixture is used. This has been an obstacle to cost reduction of devices such as sensors using micromachining. In addition, the mounting and removal of the fixture is necessary, which causes a complicated process.

If the etching process is performed without using this fixture, the etchant will also enter the surface of the silicon wafer on the circuit formation side. As shown in FIG. 3, steps A, B, and C are formed in the protective film 15 attached so as to cover the electrode terminals 14 provided on the silicon wafer 13. The etching solution penetrates through the protective film due to the prolonged etching from the portion, and erodes the metal wiring material such as the electrode terminal. Therefore, the conventional wafer processing method for micromachining cannot eliminate the use of the fixture.

Further, it is conceivable to perform other processing such as forming a circuit on one surface of the silicon wafer after etching the silicon wafer first, but if the silicon wafer is formed first, Another problem is that the reduction in mechanical strength of the wafer places great restrictions during other processing. Accordingly, an object of the present invention is to provide a wafer processing method for micromachining, which can perform a wafer etching process without using a fixture and can prevent erosion of a metal wiring material.

[0007]

A micromachining wafer processing method according to the present invention is a processing method for performing micromachining processing on a wafer, comprising forming a circuit on one surface side of the wafer, Attaching a first passivation film to a surface including a circuit on one surface of the wafer, planarizing the surface of the first passivation film, and applying a second passivation film to the planarized surface of the first passivation film. Attaching a first mask film to the surface of the second passivation film to set portions for etching and removing the first and second passivation films, and setting a portion for etching and removing the wafer. Attaching a second mask film to the wafer, and attaching the wafer after the first and second masks are attached to the second mask film. A first etching step of immersing the wafer after the first etching step in a first etchant that is non-erosive to the oxidation film, and a second etching step of immersing the wafer after the first etching step in a second etchant that is non-erosive to the wafer. It is characterized by becoming.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.
This will be described in detail with reference to FIG. 4A to 4G show the present invention.
Of Wafer Processing Method for Micromachining by MIC
Is shown. First, in the process shown in FIG.
For example, single-crystal silicon with a thickness of 400 to 600 microns
Wiring and element shapes required on one side of wafer 21
And passivation film adheres after its formation
Is done. That is, one side of the silicon wafer 21
Are formed with diffusion layers 22 and 23, and SiO 2_TwoOr
A protective film 24 is attached. Diffusion layers 22, 23
Part of the protective film 4 is removed and an electrode made of aluminum is formed.
Terminals 25 and 26 are coupled to diffusion layers 22 and 23.
Electrode terminals 25 and 26 are electrode terminals for wire bonding
It is. The protective film 24 including the electrode terminals 25 and 26 is
Has a passivation film 27 attached thereto. Passive
The film 27 is made of CVD (Chemical Vapor Depositio).
n) TEOS (tetraethoxy silane) using the method
By thermal division of SiO _TwoObtained by forming a film
You.

In the step shown in FIG. 4B, the surface of the passivation film 27 is flattened. In the step of simply attaching the passivation film 27, since the step is large as shown in FIG. 3, flattening is performed to reduce the step. As a method of the planarization, an etch back method in which the surface of the passivation film 27 is etched with a photoresist, and a CMP (Chemical mechanical) method in which the surface of the passivation film 27 is polished chemically and mechanically.
l polishing) method and coating of liquid glass with SiO ₂
There is an SOG method for forming a layer. FIG. 4 after the flattening
In the step shown in (c), a passivation film 28 is further formed on the planarized surface of the passivation film 27 by CVD.
Is deposited using a method. Thereby, the surface is further flattened. The passivation films 27 and 28 are alkali-resistant films such as SiO ₂ .

In the step shown in FIG.
Mask film 29 for forming a pad pattern in a portion
Is formed on the surface of the passivation film 28. The mask film 29 is made of an alkali-resistant material.
Consists of nitride and tungsten. In the step shown in FIG. 4E, a mask film 30 for forming a diaphragm of the sensor is attached to the other surface of the silicon wafer 21. FIG. 4 shows a portion where the mask film 30 is not attached.
In step (f), KOH, TMAH, hydrazine, EPP
(Ethylenediamine pyrocathicol) or the like is etched with an alkaline etchant. In this etching, the entire silicon wafer 21 is immersed in an etching solution (first etching solution). However, since the passivation film 28 exposed from the mask film 29 on the circuit formation side of the silicon wafer 21 is an alkali-resistant film, the etching is performed. It will not be done. The hole 31 formed on the other surface side of the silicon wafer 21 by this etching is shown in FIG.
The cross-section shown in FIG.
Looking at the other side of the square has a square shape as shown in FIG.
The thin portion of the silicon wafer 21 becomes a diaphragm of a sensor utilizing the piezo effect.

When etching of the other surface of the silicon wafer 21 is completed, in the next step shown in FIG. 4 (g), one of the silicon wafers 21 is treated with a mixed solution of acetic acid and hydrofluoric acid as an etching solution (second etching solution). Is etched. As a result, the portion of the passivation film 28 exposed from the mask film 29 and the portion of the passivation film 27 thereunder are etched without etching the silicon wafer 21 to form holes 32, thereby forming pads for wire bonding.

In the above embodiment, silicon is used as the wafer. However, the present invention can be applied to micromachining of a wafer made of another material such as germanium. Further, in the above-described embodiment, etching was performed on the other surface of the silicon wafer 21 to form a hole for the diaphragm of the sensor. However, one surface of the silicon wafer 21 was also used for micromachining such as a diaphragm. Etching may be performed for the mechanical processing of. Further, the present invention can be applied to an apparatus using another micromachining technology such as an actuator.

In the above embodiment, the second etching solution is a mixture of acetic acid and hydrofluoric acid.
Any etchant that does not attack the wafer by eroding the passivation film may be used.

[0014]

As described above, according to the present invention, the wafer can be etched without using the fixture, and the erosion of the metal wiring material of the circuit can be prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view of a wafer showing a procedure of a conventional wafer processing method for micromachining.

FIG. 2 is a diagram showing an appearance of a fixture.

FIG. 3 is a diagram showing a step portion of a protective film.

FIG. 4 is a wafer cross-sectional view showing a procedure of a micromachining wafer processing method according to an embodiment of the present invention.

FIG. 5 is a diagram showing a hole for a diaphragm as seen from the other surface of a silicon wafer.

[Description of Signs of Main Parts]

 1,21 silicon wafer 2,3,22,23 diffusion layer 5,6,25,26 electrode terminal 9,29,30 mask film 10 fixture 27,28 passivation film

Claims (4)

[Claims] 1. A processing method for performing micromachining processing on a wafer, comprising: forming a circuit on one surface side of the wafer; and first forming a circuit on one surface of the wafer including the circuit. Attaching a passivation film; planarizing the surface of the first passivation film; and depositing a second surface on the planarized first passivation film.
Depositing a passivation film, depositing a first mask film on the surface of the second passivation film to set a portion where the first and second passivation films are etched away, and etching away the wafer. Depositing a second mask film on the wafer to set a portion; and a first etchant that is non-erosive to the second passivation film on the wafer after the first and second masks are deposited. A first etching step of immersing the wafer after the first etching step, and a second etching step of immersing the wafer after the first etching step in a second etchant that is non-erosive to the wafer. Wafer processing method. 2. The method according to claim 1, wherein the first etchant is KOH or TM.
2. The wafer processing method for micromachining according to claim 1, wherein the second etching solution is AH, and the second etching solution is a mixture of acetic acid and hydrofluoric acid. 3. The wafer processing method for micromachining according to claim 1, wherein in the first etching step, a diaphragm of a sensor utilizing a piezo effect is formed. 4. The micromachining wafer processing method according to claim 1, wherein in the second etching step, a pad hole for wire bonding is formed in the first and second passivation films.