The present invention relates to a method for manufacturing a dynamic quantity detection device that is formed by bonding a semiconductor chip that includes a detection element for detecting a dynamic quantity to a stand using a bonding layer.
The publication JP-A-2000-241273 discloses such a method in the manufacturing process of a discrete pressure detection device 100 shown in FIGS. 3A and 3B.
As shown in FIGS. 3A and 3B, the discrete pressure detection device 100 includes a metal stem 20, a discrete semiconductor chip 30, and a glass layer 40. The metal stem 20 includes a disk-like diaphragm 10. The semiconductor chip 30 is bonded to the diaphragm 10 with the glass layer 40. The discrete semiconductor chip 30 is in contact with the glass layer 40 at a first surface 31 of the discrete semiconductor chip 30. The diaphragm 10 is in contact with the glass layer 40 at a first surface 11 of the diaphragm 10. The discrete semiconductor chip 30 includes four gauges (detection elements) 51, 52, 53, 54, or four piezo resistors 51, 52, 53, 54. The gauges 51, 52, 53, 54 are located in a second surface 32 of the chip 30, which is opposite to the first surface 31. The glass layer 40 is, for example, made of a low melting point glass.
When a medium that transmits pressure to be detected is introduced into the stem 20 to apply the pressure to a second surface 12 of the diaphragm 10, which is opposite to the first surface 11, the diaphragm 10 strains and the discrete semiconductor chip 30 also strains synchronously to change the resistances of the gauges 51, 52, 53, 54. The resistance changes are processed by a processing circuit, which is not shown in the figure, in order to detect the pressure. The processing circuit is provided in another chip outside the discrete semiconductor chip 30 and includes processing circuit elements such as a bipolar transistor and a trimming resistor.
Because the processing circuit is located in another chip, the system that includes the discrete pressure detection device 100 and the chip including the processing circuit is relatively bulky. To address the issue of the bulkiness of the system, the inventors of the present invention attempted to integrate gauges 51, 52, 53, 54 and processing circuit elements for making up a processing circuit equivalent to the foregoing processing circuit in an intelligent semiconductor chip 33 and to form an intelligent pressure detection device 101, which is shown in FIGS. 4A and 4B. The processing circuit elements are included in a processing circuit area 70.
However, it turned out that the following issue was caused when the intelligent pressure detection device 101 was manufactured using the intelligent semiconductor chip 33. When the discrete pressure detection device 100 of FIGS. 3A and 3B is manufactured, the discrete semiconductor chip 30 is normally bonded to the metal stem 20 by sintering the glass layer 40 at a temperature of approximately 500° C. However, when the glass layer 40 was sintered at a temperature of approximately 500° C. the characteristics of a bipolar transistor, which is included in the processing circuit area 70 as a processing circuit element, changed.
The characteristics change of the bipolar transistor may be caused by the following mechanism. Although not shown in the figure, the intelligent semiconductor chip 33 includes a substrate, which is made of silicon. Wiring lines, which electrically interconnect elements such as a bipolar transistor located in a surface of the substrate, an oxide film, which insulates the wiring lines, and a passivation film, which protects the wiring lines and the oxide film, are located on the surface of the substrate. The oxide film and the passivation film are formed in the atmosphere that contains hydrogen in the wafer manufacturing process, in which a wafer is processed for manufacturing the intelligent semiconductor chip 33.
When the oxide film and the passivation film are formed, the hydrogen in the atmosphere is absorbed into the oxide film and the passivation film as hydrogen ions. The dangling bonds of the silicon atoms located at the interface between the surface of the substrate and the oxide film are terminated by the hydrogen ions. At a subsequent step in the wafer manufacturing process, the wafer is heated at a high temperature in the atmosphere that contains hydrogen. During the step, the amount of hydrogen ions in the oxide film and the passivation film can increase as hydrogen in the atmosphere is absorbed, and the bonds between the hydrogen-terminated silicon atoms and the terminating hydrogen atoms at the interface between the surface of the substrate and the oxide film may be broken due to the high temperature.
At a later step, the wafer is diced to form the intelligent semiconductor chip 33. Because no heat is applied to the intelligent semiconductor chip 33 during the dicing step, the characteristics of the bi-polar transistor such as current amplification factor in the wafer manufacturing process is substantially determined by the concentration of the hydrogen ions resulting from the above high temperature treatment.
However, when the glass layer 40 is sintered for bonding the intelligent semiconductor chip 33 to the metal stem 20, the processing circuit area 70 is heated. As a result, the hydrogen atoms bonded to the silicon atoms at the interface between the surface of the substrate and the oxide film move away from the silicon atoms, and the hydrogen ions absorbed in the oxide film migrate toward the passivation film or get outgassed into the atmosphere.
As a result, electrons trapped by the hydrogen atoms included in the oxide film are released above the surface of the bipolar transistor located in the processing circuit area 70, and the transistor injection efficiency increases. Consequently, the base current increases, and the collector current also increases among the currents that flow through the base, the emitter, and the collector of the bipolar transistor. Thus, the current amplification factor, which is one of the characteristics of the bipolar transistor, increases.