JPH0546100B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method of manufacturing a semiconductor substrate having a dielectric buried layer formed therein.

[Technical background of the invention and its problems]

In semiconductor integrated circuits, elements are generally separated by pn junctions. However, this element isolation method poses a problem when high voltage elements are included. In power semiconductor integrated circuits, it is necessary to reliably electrically separate the parts that handle high voltages and large currents from the signal processing circuits and drive circuit parts that handle small signals, but pn junction isolation is insufficient. many. A dielectric isolation method is preferable as an element isolation method in such a case.

However, in the dielectric isolation method, it is not easy to wrap a part of the element with a dielectric. In particular, a dielectric embedding layer is required to separate the element region from the substrate region, but conventional dielectric embedding methods have various drawbacks.

One method is to form elements on the surface of a semiconductor substrate, perform lateral element isolation, wrap the semiconductor substrate from the back side to expose the lower part of the element area, and then apply a dielectric film such as an oxide film to this area. Then, a polycrystalline silicon layer, etc., which is to serve as a support again is formed. This method has many process constraints and also makes it difficult to use the substrate area under the device area as a current path or other active device.

Another method for forming a buried dielectric layer is to form a dielectric layer on a single crystal substrate, deposit a polycrystalline silicon layer on top of it, and turn it into a single crystal by heat treatment or laser light irradiation. . However, this method also has problems such as limitations on the size, quality, shape, etc. of the single crystal that is formed.

For the above-mentioned reasons, many efforts have been necessary to reflect requirements regarding device characteristics in device design, especially in power integrated circuits. For this reason, there has been a desire for a technique for forming a dielectric buried layer inside a semiconductor substrate through a simple process and with good controllability.

[Purpose of the invention]

The present invention has been made in view of the above points, and
It is an object of the present invention to provide a method for manufacturing a semiconductor substrate that allows an oxide film to be embedded therein easily and with good controllability.

[Summary of the invention]

The present inventors have discovered that a strong bonded substrate can be obtained by bringing the polished surfaces of two mirror-polished semiconductor substrates into close contact with each other in a sufficiently clean atmosphere without intervening foreign substances such as dust. Furthermore this
It has been found that heat treatment at a temperature of 200°C or higher increases the bonding strength. In other words, the surface roughness
If semiconductor substrates that have been mirror-polished to a thickness of 500 Å or less are brought into contact with each other in a clean state, a strong bonded substrate can be obtained without using any adhesive or requiring mechanical pressing force. be. Although the details of this bonding mechanism are still unclear, it has been speculated that the natural oxide film formed on the mirror-polished surface seems to play an important role. The present invention uses this technique, which is different from the technique that involves plastic deformation under high temperature and pressurized conditions, as described in, for example, Japanese Patent Application Laid-open No. 13733/1983.

That is, the present invention includes a step of forming a groove opening to an end surface of the first semiconductor substrate on the surface of the first semiconductor substrate that has been mirror-polished to a surface roughness of 500A or less, and a step of forming a groove that opens to the end surface of the first semiconductor substrate; the groove that communicates with the groove when the mirror-polished surfaces of the first and second semiconductor substrates are bonded to the mirror-polished surface of at least one of the second semiconductor substrate and the first semiconductor substrate having a surface; a step of forming a shallower recess, and bringing the mirror-polished surfaces of the first and second semiconductor substrates into close contact with each other in a clean atmosphere,
forming a bonded substrate directly bonded without plastic deformation; and filling the recess with an oxide film by exposing the bonded substrate to an oxidizing gas atmosphere and supplying the oxidizing gas along the groove. A method of manufacturing a semiconductor substrate is characterized in that a dielectric buried layer is formed inside a directly bonded bonded substrate.

In this case, by forming the recess to be shallower than the groove, the groove for supplying the oxidizing gas will not be closed until the recess is completely filled with the oxide film.

In addition, by introducing impurities or damaging the recesses in advance to speed up the oxidation rate in these areas, oxidizing gas can be applied until the recesses are filled with an oxide film without having to make the recesses shallower than the grooves. can be supplied.

〔Effect of the invention〕

According to the present invention, a semiconductor substrate on which a buried oxide film is formed can be obtained very easily. This buried oxide film depends on the thickness of the semiconductor substrate and the depth of the recess.
The embedding position and shape can be set arbitrarily depending on the shape, and it is useful when applied to power integrated circuits and multilayer structure integrated circuits.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

Figures 1a-d illustrate the manufacturing process according to one embodiment. The first silicon substrate 1 ₁ and the second silicon semiconductor substrate 1 ₂ have opposing surfaces to be bonded that have surface roughness.
Mirror polished to 500Å or less. If the unevenness is larger than this, it becomes difficult to achieve good adhesion. 1st
The polished surface of the silicon semiconductor substrate ₁₁ is shown in Figure 1a.
As shown in FIG. 2, a groove 2 opening at the end of the substrate is formed, and a recess 3 is formed in a predetermined pattern so as to partially overlap the groove 2. As shown in FIG. FIG. 2 is a perspective view showing how grooves 2 and recesses 3 are formed in this first silicon substrate. The recess 3 is a position where an oxide film is buried, and its depth is shallower than the trench 2, and is approximately 0.7 times as deep as the required oxide film thickness. There is no particular limit to the pitch of the grooves 2, but it is convenient if it matches the sheaving line of the element. After thoroughly cleaning and drying these substrates 1 ₁ and 1 ₂ , floating dust 20
The polished surfaces are brought into close contact with each other and bonded as shown in ^FIG . This bonded substrate 1 is heated at temperatures above 200°C to increase bonding strength.
Preferably, the heat treatment is performed at about 1000°C. However, this heat treatment can also be used in the next heat step. The thus formed bonded substrate 1 is heated at about 1200° C. in an oxygen gas atmosphere and gas is supplied along the grooves 2 to the recesses 3, thereby forming the recesses 3 as shown in FIG. 1c. is filled with an oxide film 4.
Thereafter, the bonded substrate 1 is ground by polishing or the like to the position shown by the dashed line in FIG. 1c to obtain the substrate shown in FIG. 1d.

Desired elements are formed on the substrate in which the oxide film 4 is embedded in this manner, and the elements are separated in the lateral direction according to a conventional method to obtain an integrated circuit.

Thus, according to this embodiment, it is possible to easily form a silicon substrate in which the oxide film 4 is embedded. This substrate can not only be used as a normal IC substrate with the oxide film 4 as an element isolation layer, but also as a multilayer IC substrate if the oxide film 4 completely electrically isolates the upper and lower parts of the substrate. It will be done.

Figures 3a-d illustrate the manufacturing process of another embodiment of the invention. As shown in FIG. 3a, grooves 2 are formed in the first silicon substrate ₁₁ in the same manner as in the previous embodiment,
A recess 3 is formed in the second silicon substrate ₁₂ .
A high impurity concentration layer 5 is formed in the recess 3 by ion implantation. Thereafter, a bonded substrate is formed as shown in FIG. 3b in the same manner as in the previous embodiment, and heat treated in an oxidizing gas atmosphere. Since the oxidation rate of the recess 3 is about twice as fast as that of other parts, this part is first filled with the oxide film 4 as shown in FIG. It will be done. FIG. 3d shows the case where the oxidation treatment is further continued so that almost all of the grooves 2 are filled with an oxide film.

This embodiment also provides the same effects as the previous embodiment.

Note that the groove and the recess may be formed in either semiconductor substrate as long as they communicate with each other when the two semiconductor substrates are bonded.

[Brief explanation of drawings]

Figures 1 a to d are process sectional views for explaining one embodiment of the present invention, Figure 2 is a perspective view of the first substrate, and Figures 3 a to d are for explaining other embodiments. FIG. 1 ₁ ... first silicon substrate, 1 ₂ ... second silicon substrate, 2 ... groove, 3 ... recess, 4 ... buried oxide film, 5 ... high impurity concentration layer.

Claims (1)

[Claims] 1. A step of forming a groove opening to the end face of the first semiconductor substrate on the mirror-polished surface of the first semiconductor substrate to a surface roughness of 500A or less, and mirror polishing to a surface roughness of 500A or less. When the mirror-polished surfaces of the first and second semiconductor substrates are bonded to the mirror-polished surfaces of at least one of the second semiconductor substrate and the first semiconductor substrate, which have a polished surface, the mirror-polished surfaces of the first and second semiconductor substrates communicate with the groove. forming a recess shallower than the groove; and forming a bonded substrate in which the mirror-polished surfaces of the first and second semiconductor substrates are brought into close contact with each other facing each other in a clean atmosphere, and are directly bonded without plastic deformation. and a step of filling the concave portion with an oxide film by exposing the bonded substrate to an oxidizing gas atmosphere and supplying the oxidizing gas along the groove, and filling the inside of the bonded substrate directly. A method of manufacturing a semiconductor substrate, comprising forming a dielectric buried layer. 2. Forming a groove opening to the end face of the first semiconductor substrate on the mirror-polished surface of the first semiconductor substrate to a surface roughness of 500A or less; A recess shallower than the groove that communicates with the groove when the mirror-polished surfaces of the first and second semiconductor substrates are bonded to each other is formed in the mirror-polished surface of at least one of the second semiconductor substrate and the first semiconductor substrate. a process of introducing impurities into the recess or damaging the recess to make the oxidation rate of that part faster than other parts; and a process of cleaning the mirror-polished surfaces of the first and second semiconductor substrates. A step of forming bonded substrates that are directly bonded to each other by facing each other in close contact with each other without plastic deformation in an atmosphere, and exposing the bonded substrates to an oxidizing gas atmosphere and supplying an oxidizing gas along the grooves. A method of manufacturing a semiconductor substrate, comprising: filling the recess with an oxide film, and forming a dielectric buried layer inside the directly bonded assembly substrate.