JPH0456356A - Semiconductor integrated circuit - Google Patents

Abstract

PURPOSE:To eliminate influence applied on electrical characteristics of a transistor by using a bonding agent of polyimide resin system almost not including metal ion to a bonding layer on which a silicon active layer of SOI device is placed directly in contact. CONSTITUTION:The rear surface of a silicon active layer of SOI device is directly in contact with a bonding agent of polyimide resin system almost not including metal ion. Therefore, positive charges which work as a factor of raising a substrate potential are reduced and influence to be applied on electrical characteristic of transistor can be eliminated Particularly, in the N channel MOSFET, a channel is not formed at the rear surface of active layer and thereby a leak current of channel is remarkably reduced. In order to obtain this device, it is enough to use a bonding agent 32 of the polyimide resin system for the second trial of bonding of a supporting substrate 2, but the bonding agent 31 of the polyimide resin system is forced to be used for the first trial of bonding of the supporting substrate 1. On the occasion of executing the bonding using a bonding agent of the polyimide resin system, the substrate must be heated up to about 350 deg.C to 400 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a semiconductor integrated circuit in which semiconductor elements (hereinafter referred to as devices) on a thin film are bonded to a substrate using an insulating adhesive. be.

(Prior Art) A semiconductor integrated circuit has a structure in which an insulating layer is present on a substrate and a thin film device is further present on the insulating layer [hereinafter referred to as 5
One of the manufacturing methods of the OI (S city con qn in5ulator) device is the Deno (Ice transfer method) using selective polishing (Tsuneo Hamaguchi, Nobune Endo Applied Physics No. 5).
Volume 6, No. 1.1 (1987) pp1480-1484
) has been known for a long time. S using device transfer method
The outline of the manufacturing method of the OI device is shown in Fig. 3(a) to (e).
Shown below. First, MO fabricated using a normal process
A support substrate 51 for thinning is bonded to the S device (FIG. 3(a)) via an epoxy resin adhesive layer 61 (FIG. 3(b)). Subsequently, a selective polishing method is used to reduce the film thickness (FIG. 3(C)), and the support substrate 52 is bonded via an epoxy resin adhesive layer 62 (FIG. 3(C)).
d)). Finally, the adhesive layer 61 is removed from the supporting substrate 51 and the upper layer (FIG. 3(e)). In FIG. 3(d), the adhesive used to bond the support substrate 52 is in direct contact with the silicon active layer and serves as an insulating layer. Conventionally, epoxy resin adhesives, which are polymerization reaction type, have been used for this adhesive because of their ease of handling.

(Problem to be Solved by the Invention) However, this epoxy resin adhesive 62 has a fourth
As shown in the figure, metal ions 72 such as sodium are included, which act as positive charges to increase the substrate potential and affect the transistor electrical characteristics. Particularly in the N-channel MO8FET, a channel 71 is formed on the back side of the p-silicon active layer 21 due to positive charges (FIG. 4). Figure 5 is a diagram showing the change in drain current ID with respect to gate voltage VG of this N-channel MO8FET, and as is clear from this diagram, the leakage current increases by about 8 orders of magnitude compared to before thinning. (Figure 5) [Soji Takahashi, Yoshihiro Hayashi, Shigenobu Wada, Takemitsu Kunio, 37th Applied Physics Association Lecture, Lecture Proceedings Volume 2 pp, 64230p-Z
C-101° The presence of metal ions contained in the adhesive layer that directly contacts the silicon active layer has been an important problem in deteriorating the characteristics of SOI devices using the device transfer method.

The present invention aims to eliminate the influence of conventional epoxy resin adhesives on transistor electrical characteristics in SOI devices using a device transfer method.

(Means for Solving the Problems) The present invention uses a polyimide resin adhesive containing almost no metal ions for the adhesive layer in direct contact with the silicon active layer of the SOI device, thereby reducing the effect on transistor electrical characteristics. It is characterized by removing.

(Function) In the present invention, the adhesive used for adhering the support substrate 2 shown in FIG. 2(d) contains almost no metal ions (l
ppm or less) By using a polyimide resin adhesive, the positive charge, which is a factor that increases the substrate potential, is reduced,
The effect on transistor electrical characteristics is suppressed. In particular, in N-channel MO8FETs, the formation of a channel on the back side of the p-type silicon active layer due to a decrease in positive charge is suppressed, and leakage current can be significantly reduced compared to when using an epoxy resin adhesive. (Figure 6).

(Example) Next, an example of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view of an N-channel MO8FET. S
The back surface of the silicon active layer of the OI device is in direct contact with a polyimide resin adhesive that contains almost no metal ions (lppm or less). Therefore, the positive charges that are a factor in increasing the substrate potential are reduced, and their influence on the transistor electrical characteristics is eliminated.

Particularly in the N-channel MO8FET, no channel is formed on the back surface of the active layer, so channel leakage current is significantly reduced.

FIGS. 2(a) to 2(e) show a method for manufacturing an SOI device by a device transfer method using a polyimide resin adhesive. In this method, it is sufficient to simply replace the epoxy resin adhesive used in FIG. 3 with a polyimide resin adhesive. Here, in order to obtain a device with the above-described structure, it is sufficient to use the polyimide resin adhesive 32 for the second bonding of the support substrate 2 (FIG. 2(d)). Adhesion of support substrate 1 for the second time (Fig. 2(b)
)) It should be noted that the polyimide resin adhesive 31 is also used. When bonding using a polyimide resin adhesive, the substrate should be heated at approximately 350°C to 400°C.
It is necessary to heat it to C. In order to use a polyimide resin adhesive to bond the support substrate 2, the adhesive used to bond the support substrate 1 must have a heat resistance temperature of approximately 350° C. or higher. Conventionally used epoxy resin adhesives have a heat resistance temperature of about 2006C at most, so they cannot be used, but polyimide resin adhesives have a heat resistance temperature of about 5C.
Since the temperature is 50° C., a polyimide resin adhesive is also used for adhering the supporting substrate 1. However, the adhesive used to bond this support substrate 1 has a heat resistance temperature of 350°C.
Since the adhesive above is sufficient, it does not need to be a polyimide resin adhesive as long as it satisfies the above conditions.

In this embodiment, a MOSFET is used as a device, but other types of devices such as a bipolar transistor may also be used.

(Effects of the Invention) As explained above, the present invention makes it possible to eliminate the influence of conventional epoxy resin adhesives on transistor electrical characteristics in an SOI device using a device transfer method.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an SOI device according to an embodiment of the present invention;
Figures 2(a) to (e) are schematic diagrams for explaining the manufacturing method of the SOI device shown in Figure 1, and Figures 3(a) to (e) are diagrams for explaining the manufacturing method of the SOI device shown in Figure 1. FIG. 4 is a diagram for explaining the method for manufacturing an SOI device; FIG. 4 is a diagram for explaining the relationship between channel formation by metal ions in the adhesive layer and leakage current in an SOI device using an epoxy resin adhesive; Figure 5 shows the N-channel MO of the device before thinning and the SOI device using epoxy resin adhesive.
Figure 6 shows a comparison of the electrical characteristics of an N-channel MO8FET between an SOI 7' vise using an epoxy resin adhesive and an SOI device using a polyimide resin adhesive. It is a diagram. In the figure, 11...gate, 12...source, 1
3...Drain, 21...Silicon active layer, 31.3
2...Polyimide resin adhesive, 41...LOCO
8 Oxide film, 51.52...Support substrate, 61.62...
・Epoxy resin adhesive 1.71...Channel, 72
...Sodium ion, 81...Leakage current.

Claims (1)

[Claims] A semiconductor integrated circuit in which a thin film semiconductor element is bonded to a substrate by an insulating adhesive layer, characterized in that a polyimide resin adhesive is used as the adhesive layer.