JPS5854652A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To efficiently manufacture a semiconductor pellet having a solder layer on he back surface by forming a photoresist film along a line for cutting and isolating the back surface of a semiconductor wafer into semiconductor elements. CONSTITUTION:A through hole 3 which reaches from the front surface 1a to the back surface 1b of a semiconductor wafer 1 formed with semiconductor elements 2 is formed partly of a line to be cut and isolated. A photoresist film 4 is formed in a lattice shape along the line indexed from the hole 3. Subsequently, an ohmic metallic layer 5 is formed on the overall surface of the back surface 1b, and a solder paste layer 6 is formed on the overall upper surface of the layer 5. Thereafter, when the wafer 1 is heated by the melting temperature of the layer 6, the film 4 is burnt and lost, and the layer 5 is also vanished, thereby exposing the silicon base of the wafer 1. Accordingly, molten solder is agglomerated, and is cooled to form a solder layer 7 insularly on the layer 5. Thus, the wafer can be readily cut.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a semiconductor device having a solder layer on its back surface.

Generally, semiconductor devices such as transistors are manufactured by supplying solder pieces onto a heated stem or a heat sink such as a lead frame, melting the solder pieces, and applying semiconductor pellets having an ohmic metal layer on the back surface to the molten solder. The semiconductor pellet is placed on the heat dissipation plate and fixed to the heat sink via a solder layer. By the way, this method of melting solder pieces and then supplying semiconductor pellets may result in the formation of an oxide film, etc. on the surface of the melted solder layer. The adhesion between the pellet and the heat sink becomes incomplete.

For this reason, in the past, semiconductor pellets were placed on the molten solder layer, which was called scrubbing. The molten solder layer is rotated three times, and the surface of the molten solder layer is scratched with a scraper to remove oxide films and the like just before supplying the semiconductor pellets. However, in such a method, the process of fixing the semiconductor pellet takes time, which poses a problem in mass production.

Therefore, a preliminary solder layer has recently been formed on the back surface of a semiconductor pellet, and the semiconductor pellet is supplied onto a heated heat sink with the back surface facing downward, and the semiconductor pellet is used for scrubbing or pulling a J rod. A method has been proposed for fixing semiconductor pellets to a radiation plate without the scratching action.

When manufacturing semiconductor pellets having a solder layer on the back surface as described above, if a solder layer is previously formed on the entire back surface of the semiconductor wafer, it is not easy to cut and separate the solder layer into individual semiconductor pellets. This is because when attempting to completely cut a semiconductor wafer using a thin blade, if a solder layer is formed on the entire back surface of the semiconductor wafer, the solder layer is soft and is considerably thicker than the surface electrode. ,
This is because the blade becomes clogged, making cutting impossible or extremely difficult. On the other hand, when attempting to manufacture semiconductor pellets by applying bending force to the semiconductor wafer after forming grooves from the surface side of the semiconductor wafer to the middle of the thickness of the semiconductor wafer, it is difficult to produce semiconductor pellets that are soft and thick. The solder layer could not be cut properly, and the semiconductor pellets were connected to each other through the solder layer.

This is because so-called avec defects occur.

Therefore, the main object of the present invention is to provide a method for efficiently manufacturing semiconductor pellets having a solder layer on the back surface.

To summarize this invention, a photoresist film is formed on the back surface of a semiconductor wafer along the cutting and separating lines for each semiconductor element, and then an ohmic metal layer is formed on the entire back surface of the semiconductor wafer, including on the photoresist film. Then, a solder paste layer is formed on the ohmic metal layer, and the semiconductor wafer is heated to melt the solder paste layer to form a solder layer, and then the semiconductor wafer is cut and separated along the lines. The invention is characterized in that semiconductor pellets are obtained by

Hereinafter, an embodiment of the present invention will be explained with reference to the drawings. First, as shown in FIG. 1, a semiconductor wafer l having a large number of semiconductor elements 2 formed thereon is prepared, and a laser beam is irradiated onto a portion of the surface 1a of the cutting and separating machine between each semiconductor element 2. A through hole 3 is provided to reach the back surface 1b, and a cut plan on the back surface 1b4m is determined based on the through hole 3, and a photoresist film 4 is formed in a lattice shape along the cut plan line. This photoresist film 4 may be directly formed in a grid shape by screen printing or the like, or as is well known, a photoresist film is formed on the entire back surface 1b of the semiconductor wafer 8l, and then a grid pattern is formed by exposure and development processing. Alternatively, the photoresist film 4 may be formed in a manner similar to that shown in FIG. Next, as shown in FIG. 2, an ohmic metal layer 5 is formed on the entire back surface 1b of this semiconductor wafer 1. This ohmic metal layer 5 may be the same as the conventional one, and can be formed, for example, by sequentially depositing chromium, niracle+ml silver. Thereafter, as shown in FIG. 3, solder paste is applied to the entire back surface 1b of one semiconductor wafer l to a uniform thickness by screen printing or the like to form a solder paste layer 6.
form. Next, in step (2), this semiconductor wafer l is heated to the melting temperature of the solder paste layer 6.

For example, the solder paste layer 6 is heated at about 350° C. to melt the binder component and burn out the binder component. 1, a solder layer 7 is formed. At this time, the photoresist film is burnt out due to the heating temperature, and the ohmic metal layer 541 thereon disappears, exposing the silicon substrate of the semiconductor wafer 711, so that the molten solder does not touch or wet the silicon substrate. and ohmic metal layer 6
Due to the cohesive force of the molten solder above, the molten solder aggregates only on the ohmic metal layer 5, and as a result, when it is cooled,
The solder layer 7 is formed in an island shape only on the ohmic metal layer 5.

In other words, the wires in the shape of each semiconductor element 2 are formed independently, and the ohmic metal layer 5 and solder layer 7 are not present on the cutting line, so that a conductive wire can be observed. Finally, this semiconductor unit 11 is cut and separated from the center of the edge to be cut, that is, at the position shown by the dashed dotted line in FIG.
A semiconductor pellet 2a having a solder layer 7 on the back surface as shown in FIG. 5 is obtained.

At this time, the ohmic metal layer 5 and the solder layer 7 do not exist on the planned cutting line of the semiconductor wafer 1, so even if the semiconductor wafer 11 is completely cut with the dicing blade, when the solder layer 7 is cut, the ohmic metal layer 5 and the solder layer 7 are not present. - It can be cut very easily without causing the problem of clogging of the dicing blade, or after forming a groove halfway through the thickness of the semiconductor wafer l, a bending force is applied to the semiconductor wafer l to cut the groove. Even when cutting from the base, the semiconductor belenium 2a are connected to each other by the soft solder layer 7. There are no so-called Abec defects.

In the above embodiment, the solder paste layer 6 is formed entirely on the ohmic metal layer 5 on the back surface 1b of the semiconductor wafer 1 (see FIG. 3). There is an advantage that alignment work is not required when forming the . However, if necessary, align and apply the solder paste to the photoresist film 4.
Alternatively, the solder resist layer 6 may be coated except for the upper portion of the solder resist layer 6 to form one island-shaped solder resist layer 6.

The present invention includes the steps of forming a photoresist film along the lines L for cutting and separating each semiconductor element on the back surface of a semiconductor wafer 1 on which a large number of semiconductor elements are formed;
a step of forming an ohmic metal layer on the entire back surface of the semiconductor wafer including the photoresist film, and a step of forming a solder paste layer on the ohmic metal layer;
The method includes a step of heating the semiconductor wafer to melt the solder paste layer to form a solder layer, and a step of cutting and separating the semiconductor wafer 1 along the lines to obtain semiconductor pellets. It is possible to easily manufacture semiconductor pellets having the following properties.

[Brief explanation of drawings]

1(2) to 6 are cross-sectional views of the semiconductor wafer 1 to the semiconductor pellet at each stage for explaining an embodiment of the present invention. 1...Semiconductor wafer, 1b...Back surface, 2...Semiconductor element 1 4...Photoresist film, 5...Ohmic metal layer , 60.911. Solder paste layer, V...Solder layer. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 a

Claims (1)

[Claims] A step of forming a photoresist film on the back surface of a semiconductor wafer on which a large number of semiconductor devices are formed along the lines that cut and separate the semiconductor devices, and applying an ohmic metal to the back surface including the photoresist layer on the semiconductor wafer. a step of forming a solder paste layer on the ohmic metal layer; a step of heating a semiconductor wafer to melt the solder paste layer to form a solder layer; and a step of forming a solder layer on the semiconductor wafer. - A method for manufacturing a semiconductor device, including a step of cutting and separating along the m wiring and obtaining a semiconductor pellet.