Method of Producing Magnetosensitive Semiconductor Devices

This invention relates to a method of producing magnetosensitive semiconductor devices and more particularly to such a method by which devices with improved sensitivity can be assembled easily and their substrates are not cracked easily.

FIGS. 3-5 show conventional assembly methods of a semiconductor chip and a magnetic piece which are prepared separately to produce a magnetosensitive semiconductor device such as a Hall element with improved sensitivity. According to the method shown in FIG. 3, a magnetic piece 2 is bonded onto a leadframe 1 and a semiconductor chip 3 such as a Hall element is bonded onto this magnetic piece 2. According to the method shown in FIG. 4, a semiconductor chip 3 is bonded onto a leadframe 1 and a magnetic piece 6 is bonded onto this semiconductor chip 3. According to the method shown in FIG. 5, a magnetic piece 2 is bonded onto a leadframe 1, a semiconductor chip 3 is bonded onto this magnetic piece 2 and then another magnetic piece 6 is bonded onto this semiconductor chip 3. In FIGS. 3-5, numerals 31 each indicate a magnetosensitive part of the semiconductor chip 3, numerals 4 indicate a terminal wire, and numerals 5 indicate a package resin. These methods, however, involve complicated assembly processes and do not effectively improve device sensitivity.

In order to improve the device sensitivity by using a magnetic piece, it is necessary to make it thick or to place it near the magnetosensitive part 31 of the semiconductor chip 3, but the thickness of the magnetic piece is limited by the size of the package. As for the placing of the magnetic piece near the magnetosensitive part of the semiconductor chip 3, there is a limit imposed by the thickness of the semiconductor chip 3 if the magnetic piece 2 is disposed below the semiconductor chip 3 as shown in FIGS. 3 and 5. Since the semiconductor chip 3 must be thick enough such that the semiconductor substrate will not easily crack when processed to form the magnetosensitive part 31 of a Hall element or the like. For this reason, its thickness must be greater than 200 .mu.m. Even if the product is to be handled very carefully, a minimum of 150 .mu.m is required.

It is an object of the present invention to provide a method by which magnetosensitive semiconductor devices of complicated structure can be produced without adversely affecting their sensitivity.

The above and other objects of the present invention are achieved by providing a method characterized as comprising the steps of forming a magnetosensitive part on one surface of a semiconductor substrate, pasting the semiconductor substrate thus formed on a handling wafer lapping or etching the opposite surface of the semiconductor substrate, pasting a magnetic substrate on it with the jig pasted thereon, dividing the pasted substrates into individual unistructural elements each with a semiconductor chip and a magnetic piece, and die bonding, wire bonding and resin molding these individual elements.

The accompanying drawings, which are incorporated in and form a part of the specification, illustrate an embodiment of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:

FIG. 1 is a sectional view of an ion injection type GaAs Hall element produced by a method embodying the present invention,

FIGS. 2A-2F are sectional views of the element of FIG. 1 during its production, and

FIGS. 3-5 are sectional views of semiconductor elements produced by conventional methods.

In what follows, reference is made to FIG. 1 and FIGS. 2A through 2F to explain a method of the present invention for producing an ion injection type GaAs Hall element. FIG. 1 is a sectional view of a completed product and FIGS. 2A through 2F show sectional views during its production.

Numeral 13 indicates a semi-insulative GaAs substrate and Si ions are injected thereinto at a desired area to form an n-type area by a heat treatment, thereby creating the active layer of a Hall element. Ion injection into a desired region can be easily achieved by using a photoresist to cover the areas other than the desired area and removing it after the injection. Thereafter, an ohmic electrode is formed on this active layer to form a magnetosensitive part 14 of a Hall element on one of the surfaces of the GaAs substrate 13 as shown in FIG. 2A.

Next, a handling wafer (also simply referred to as a jig) 15 is pasted onto the surface of the GaAs substrate 13 on which the magnetosensitive part 14 has been formed (FIG. 2B) and the opposite surface of the GaAs substrate 13 away from the magnetosensitive part 14 is lapped (FIG. 2C). This step may be replaced by that of etching, chemical or otherwise. Numeral 11 indicates the GaAs substrate 13 after it has been made thinner by the lapping step or the like. The device sensitivity improves as the thickness of the GaAs substrate 13 is reduced. In the present example, the thickness is about 100 .mu.m after the lapping.

With the lapping jig 15 still pasted onto the GaAs substrate 11, an epoxy resin is used to paste a magnetic substrate (such as a Ni-Zn ferrite substrate) 12 on the GaAs substrate 11. The thicker the magnetic substrate, the more does the device sensitivity improve, but there is a limit to this thickness because the device must be sealed within a package. In this example, a ferrite substrate of thickness about 300 .mu.m is used (FIG. 2D).

GaAs substrates with thickness less than 100 .mu.m are easy to break and difficult to handle but since the lapping jig 15 is pasted onto the GaAs substrate 11 according to the present invention, the magnetic substrate 12 can be attached without difficulty. After the magnetic substrate 12 is pasted, the GaAs substrate 11 can also be handled easily even if the jig 15 is removed.

After the jig 15 is removed, the product is put upside-down such that the GaAs substrate 11 is above the magnetic substrate 12 and, after an adhesive tape 16 is attached onto the side of the magnetic substrate 12 (FIG. 2E), the substrates are divided by dicing into individual chips of 0.55 mm (FIG. 2F). Magnetosensitive semiconductor devices shown in FIG. 1 are obtained from these individual chips by the usual processes including die bonding, wire bonding and resin molding without any special process of attaching a magnetic piece. It was observed experimentally that a product thus obtained has sensitivity 1.47 times greater than one without the ferrite substrate.

The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Such modifications and variations that may be apparent to a person skilled in the art are intended to be included within the scope of this invention.