JPH0546099B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a semiconductor substrate in which a modified layer such as a dielectric layer or a layer doped with a different impurity is formed.

[Technical background of the invention and its problems]

In semiconductor devices, semiconductor substrate crystals are modified by techniques such as oxidation and impurity diffusion for the purpose of forming pn junctions, insulating, and the like. Additionally, metals, dielectrics, semiconductors, etc. are deposited and grown using various film formation techniques. However, all of these techniques involve diffusion from the surface of the semiconductor substrate into the interior and stacking on top, and it is extremely difficult to embed an independent modified layer inside the semiconductor substrate. In particular, it is difficult to embed a dielectric material inside a semiconductor substrate.

For example, a technique is known in which an oxide layer is formed inside a silicon semiconductor substrate by implanting oxygen ions into the substrate and subjecting it to heat treatment. However, with this method, if an attempt is made to form an oxide film deep inside the semiconductor substrate, the semiconductor substrate will be significantly damaged. Furthermore, the degree of freedom in controlling the amount and depth of ion implantation is small, and it is almost impossible to bury an oxide film of a predetermined thickness at a predetermined depth with good controllability.

In addition, as a technique for embedding a high concentration impurity layer inside a semiconductor substrate, as is well known for bipolar ICs, a diffusion layer is formed on the surface of the semiconductor substrate, and then a semiconductor layer is formed on it using an epitaxial growth method. There is a way to do it. However, this method also has the problem that it takes a long time to obtain a thick epitaxial layer, during which time impurities in the buried layer are largely re-diffused.

For the reasons mentioned above, semiconductor element structures are naturally limited, and many efforts have been made to reflect requirements for element characteristics in element design. For this reason, there has been a desire for a technique for forming a modified 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 a modified layer such as a dielectric material to be embedded therein simply 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. 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 takes advantage of this new technology.

That is, the present invention is a method for manufacturing a semiconductor substrate in which a metamorphic layer is formed, which includes the steps of forming a groove opening to the end surface of the substrate in the surface of a mirror-polished first semiconductor substrate; A step of forming a bonded substrate by bringing the polished surfaces of mirror-polished second semiconductor substrates into close contact with each other in a clean atmosphere, and heating the bonded substrate without applying any external force to the bonded substrate. A process of increasing bonding strength,
This method of manufacturing a semiconductor substrate includes the step of exposing the bonded substrate to a gas atmosphere to form a metamorphic layer inside the bonded substrate along the groove.

For example, JP-A-56-13773 discloses a technique for bonding semiconductor substrates, but this technique requires mechanical pressing and heating during bonding and is accompanied by plastic deformation. In contrast, in the present invention, the adhesion itself is performed by itself, and no external pressure is required. Furthermore, no pressure is required during heat treatment to improve bonding strength, and no plastic deformation occurs, which is a completely different bonding technology. For example, if a gas atmosphere containing oxygen is used as the gas atmosphere, an oxide film can be formed as the modified layer. Furthermore, if a gas atmosphere containing impurities is used, an impurity-doped layer can be formed as the modified layer.

〔Effect of the invention〕

According to the present invention, when forming a bonded substrate in which two semiconductor substrates are bonded together, there is no need for a mechanism to apply pressure, and the mirror surfaces of the two mirror-polished substrates are held together in a clean atmosphere. All you need to do is face them and place them in close contact. Therefore, a bonded substrate can be easily formed, and mass productivity can be improved. Moreover, since the modified layer is selectively formed only on the exposed surface of the groove located at the joint portion of the bonded substrate, the modified layer can be formed with good controllability.
That is, a modified layer buried inside a semiconductor substrate can be easily realized with good controllability. The semiconductor substrate obtained in this way can be used, for example, as a conventional semiconductor substrate for IC manufacturing in which the modified layer serves as an element isolation layer, as well as a multilayer structure in which the upper and lower parts of the semiconductor substrate are separated by the modified layer.
It is used as a semiconductor substrate for ICs and for a variety of other uses.

In the present invention, providing a groove on the surface of the first semiconductor substrate is essential for forming a modified layer after forming a bonded substrate, but this groove is used to bond two semiconductor substrates. It also has the purpose of preventing air bubbles from remaining in between. The present inventors have experimentally confirmed that a strong bond cannot be obtained if air bubbles remain on the bonding surface, and this is important.

[Embodiments of the Invention] Examples of the present invention will be described below with reference to the drawings. FIGS. 1a and 1b are a plan view of the first silicon substrate 11 and a cross-sectional view thereof taken along line A-A'. This board 21
The surface is mirror-polished to a surface roughness of 500 Å or less, and there are grooves 12 that open at the edge of the substrate.
is formed. FIGS. 2a and 2b show a second silicon substrate 21, whose surface is also mirror-polished to a surface roughness of 500 Å or less. Further, holes 22 are formed on the surface of this substrate 21. These substrates 1
After thoroughly washing and drying 1 and 21, floating dust 20
As shown in FIG. ³ , the polished surfaces are brought into close contact with each other and bonded in a clean atmosphere with a particle density of less than 1.0 mm/m 3 . This bonded substrate is preferably heat-treated at 200° C. or higher, preferably at about 1000° C., in order to increase the bonding strength, but in this example, this heat treatment is also used in the next heat step. That is, the bonded substrate was heated for 1200 min in an oxygen-containing gas atmosphere.
By heating at .degree. C., an oxide film 31 is formed on the walls of the trenches 12 and holes 22, as shown in FIG.

In this manner, according to this embodiment, a silicon substrate with the oxide film 31 embedded therein can be easily formed. This substrate can be used as a normal IC substrate with the oxide film 31 as an element isolation layer. Furthermore, if the oxide film 31 completely electrically isolates the substrates 11 and 21, it can also be used as a multilayer IC substrate. Furthermore, when this substrate is used as a high-power semiconductor device substrate, the device can be cooled by flowing a cooling medium through the grooves 22.

Note that in the above embodiment, the hole 22 in the second substrate 21 does not necessarily need to be provided. Further, grooves may be formed in the second substrate 21 in a pattern similar to that of the first substrate 11.

In the above embodiments, an oxide film is formed as the modified layer, but the present invention is also effective, for example, when an impurity-doped layer is formed along the groove using a gas atmosphere containing impurities. Furthermore, an oxide film or the like may be formed as a modified layer.

[Brief explanation of the drawing]

1 to 4 are diagrams for explaining one embodiment of the present invention, in which FIGS. 1a and 1b are a plan view of a first silicon substrate and its A-A' cross-sectional view, and FIG. a,
b is a plan view of the second silicon substrate and its B-
3 is a sectional view showing a state in which these substrates are bonded together, and FIG. 4 is a sectional view showing a state in which an oxide film is formed inside the bonded substrate. 11...first silicon substrate, 12...groove, 2
1... Second silicon substrate, 22... Hole, 31...
...Oxide film (denatured layer).

Claims (1)

[Scope of Claims] 1. A method for manufacturing a semiconductor substrate in which a metamorphic layer is formed, which comprises the steps of: forming a groove opening to an end surface of the substrate in a mirror-polished first semiconductor substrate; A step of forming a bonded substrate by bringing the polished surfaces of the substrate and a mirror-polished second semiconductor substrate into close contact with each other in a clean atmosphere, and heating the bonded substrate without applying any external force to form the bonded substrate. A method for manufacturing a semiconductor substrate, comprising: increasing the bonding strength of the substrate; and exposing the bonded substrate to a gas atmosphere to form a metamorphic layer inside the bonded substrate along the groove. 2. The method of manufacturing a semiconductor substrate according to claim 1, wherein the heat treatment during the formation of the metamorphic layer and the heat treatment during the step of increasing the bonding strength of the bonded substrate are used. 3. The method of manufacturing a semiconductor substrate according to claim 1, wherein the gas atmosphere is a reactive gas atmosphere containing oxygen, and an oxide film is formed as the metamorphic layer. 4. The method of manufacturing a semiconductor substrate according to claim 1, wherein the gas atmosphere is a reactive gas atmosphere containing impurities, and an impurity-doped layer is formed as the metamorphic layer. 5. The method of manufacturing a semiconductor substrate according to claim 1, wherein the heat treatment in the step of increasing the bonding strength of the bonded substrate is performed at a temperature of 200°C to 1200°C.