JPH0494150A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To form an oxide film in a cavity by charging high-purity oxidizing gas into the cavity formed by the recess of the first semiconductor substrate and the second semiconductor substrate, and then heat-treating it. CONSTITUTION:One part of the mirror face 1a of an N<->-type first semiconductor substrate 1, which is polished into a mirror face, is etched selectively, and a recess 2, 0.2-2mum in thickness is made, and a groove 3, which opens at the end of the substrate, is made. The fellow mirror faces 1a and 5a of the first semiconductor substrate 1 and the second N<+>-type semiconductor substrate 5, which is also polished into a mirror face, are stuck together. The recess 2 is not joined, and by the recess 2 and the mirror face 5a of the second semiconductor substrate 5, a cavity 4 is formed. The joined substrate 10 is arranged in a vacuum vessel 6, and it is maintained for thirty minutes or more after a vacuum system becomes 10Pa or less. After the inside of the cavity 4 is vacuumized, O2 gas is supplied into the vessel 6, and immediately it is put in a heat treatment vessel 7 so as to do heat-treat the joined substrate 10 in oxidizing atmosphere, thus an oxide film 11 is made at the surface of the groove 3 and inside the cavity 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a semiconductor device with element isolation, and more particularly to a method for manufacturing a semiconductor device having a high breakdown voltage element isolation structure.

``Prior art'' Conventionally, isolation methods using PN junctions and isolation methods using insulators have been used to isolate elements with special high voltage resistance, such as when a high voltage power element and a logic circuit are mounted on one chip. ing.

In the isolation method using a PN junction, an N-type epitaxial layer is formed on a P-type semiconductor substrate, and a P layer extending from the surface of the epitaxial layer to the P-type substrate is formed by diffusion to separate the power element part and the logic circuit part. It is something to do. As a result, a PN junction is formed by surrounding the logic circuit section with the P layer, and by applying a reverse bias to this PN junction, a depletion layer is created to electrically isolate the logic circuit section from other regions. This method can be carried out at low cost, but in order to form a power device of 300 μm or more, the diffusion depth must be 40 μm or more, which requires a long time to separate the devices, and the lateral diffusion width increases, so the device The accumulation density is low.

On the other hand, in the isolation method using an insulator, a predetermined region of an N-type semiconductor substrate is selectively etched to form a ridge, a thermal oxide film is formed on the surface, and polycrystalline silicon is further deposited. There is a method of insulating and separating the N-type layer by polishing from the back side of the substrate until it reaches the groove, or a method of bonding two semiconductor substrates through an insulating film and selectively etching one side of the bonded substrate to form an insulating film. There is a method of forming an isolation trench that reaches up to 100 cm, forming a thermal oxide film, depositing polycrystalline silicon to fill the trench, and then removing the polycrystalline silicon layer on the surface.

Although these methods achieve a high isolation voltage, they all have the problem that one main surface of the substrate is insulated, making them unsuitable for vertical power devices with a current path on the back surface.

Therefore, in recent years, using direct bonding technology of silicon substrates,
A method of selectively embedding a thermal oxide film inside a substrate is attracting attention. As an example, Japanese Patent Application Laid-Open No. 61-42154 discloses that a hole for introducing oxygen is formed on the surface of a mirror-polished first semiconductor substrate, and a shallow recess communicating with the groove is formed. There is a method of directly bonding a mirror-polished second semiconductor substrate to form a cavity therein, and then supplying an oxidizing gas to the interior cavity along the groove to form a buried thermal oxide film. Proposed. According to this method, an oxide film of any shape can be embedded in any location.

Problems to be Solved by the Invention] However, in the method of JP-A-61-42154, the depth of the cavity in which the thermal oxide film is buried is at most 1.5 μm.
m, the groove for oxygen introduction must be extremely narrow, with a width and depth of at most 100 μm. On the other hand, since bonding of substrates is usually performed in the atmosphere, there is air (nitrogen:
Oxygen (4:1) remains, and the accumulation of nitrogen further inhibits the supply of oxygen, making it difficult to grow a uniform oxide film and requiring time for embedding. Moreover, this tendency becomes stronger as the wafer diameter becomes larger.

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to grow an oxide film uniformly and in a short time to easily form a high voltage isolation region.

[Means for Solving the Problems] A method for manufacturing a semiconductor device of the present invention includes forming a recess in the mirror surface of a first semiconductor substrate having at least one surface mirror-polished, and forming recesses along the side edges of the recess. a step of forming a deeper groove for introducing an oxidizing gas, and a step of directly bonding the mirror surface of the first semiconductor substrate to the mirror surface of a second semiconductor substrate having at least one surface mirror-polished; After the bonded substrate is evacuated, a cavity formed by the recessed portion of the first semiconductor substrate and the second semiconductor substrate,
The method includes a step of filling a high-purity oxidizing gas through the groove, and a step of embedding an oxide film in the cavity by heat-treating the bonded substrate in an oxidizing gas atmosphere.

Alternatively, a first semiconductor substrate having a recess and a groove formed therein and a second semiconductor substrate are placed in a high-purity oxidizing gas atmosphere, and their mirror surfaces are brought into close contact with each other and directly bonded to form a bonded substrate. , by filling the cavity formed by the recess of the first semiconductor substrate and the second semiconductor substrate with a high-purity oxidizing gas, and then heat-treating the obtained bonded substrate in an oxidizing gas atmosphere. , an oxide film may be formed within the cavity.

[Operation] When semiconductor substrates are directly bonded in the atmosphere, the cavity formed in the bonded substrate is filled with air. By evacuating this bonded substrate, the air inside the cavity is removed, and then, by supplying high-purity oxidizing gas into the vacuum system, the inside of the cavity is filled with oxidizing gas through the groove. . Alternatively, the cavity can be filled with oxidizing gas by performing the bonding in an oxidizing gas atmosphere.

When this bonded substrate is heat-treated, since the inside of the cavity is filled only with oxidizing gas, the oxidation reaction proceeds smoothly and an oxide film grows on the surface of the cavity. Further, since unreacted gas such as nitrogen does not remain and oxidizing gas is sequentially supplied from the outside, the oxidation rate increases and the oxide film can be embedded in a short time.

[First Embodiment] Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1st
The figure is a cross-sectional view showing the manufacturing process of the semiconductor device of this example.

First, as shown in FIG. 1(a), a part of the mirror surface 1a of an N-type first semiconductor substrate 1 whose at least one surface is mirror-polished is selected by chemical etching or reactive ion etching (hereinafter referred to as RIE). etching, depth 0
．． A recess 2 of 2 to 2 μm is formed.

Next, as shown in FIG. 1(b), a groove 3 opening at the edge of the substrate is formed along the side edge 2a of the recess 2 (FIG. 1(a)) by chemical etching, RIE, or dicing. At this time, it is desirable that the groove 3 is deeper than the recess 2, and specifically, the width is 2 μm or more and the depth is 2 μm or more.

This first semiconductor substrate 1 and an N+ type second semiconductor substrate 5 whose at least one surface is mirror-polished are subjected to, for example, trichlene boiling, acetone ultrasonic cleaning, NH3:H2O2:H2
Removal of organic matter with a mixture of 0=1:1:4, H
C, I! :H2O2:H20=1:1:4 mixture to remove metal contamination and clean with pure water in order to thoroughly clean. After that, more HF:
After removing the natural oxide film on the surface with a mixture of H20=1:50, for example)! 2 SO2: H2O2=3
: 1.1) Form an oxide film of 15A or less on the surface of the substrate to make it hydrophilic, and wash it with pure water.

Next, after drying with dry nitrogen or the like to control the amount of moisture adsorbed on the substrate surface, the mirror surfaces 1a and 5a of the two substrates 1.5 are brought into close contact with each other as shown in FIG. 1(c). As a result, the two substrates 1.5 are bonded together by hydrogen bonding between the silanol groups formed on the surfaces and the water molecules adsorbed on the surfaces. Furthermore, this bonded substrate 1.5
Dry in vacuum below. At this time, in order to compensate for the warpage of the substrate 1.5, a load of 30 g/weight may be applied.

Thereafter, the substrate 1.5 is heat-treated at 1100°C or higher for 1 hour or more in an inert gas atmosphere such as nitrogen or argon, so that a dehydration condensation reaction occurs on the adhesive surface and forms silicon (Si). Oxygen (0) (7) bond (Si-
0-3i) is formed, and further oxygen diffuses into the substrate to form bonds between Si atoms, (Si-3i) - two substrates 1
．． A bonded substrate 10 is formed by directly bonding the substrates 5 and 5. At this time, the recess 2 is not joined, and a cavity 4 is formed between the recess 2 and the mirror surface 5a of the second semiconductor substrate 5.

Note that in this step, high-temperature heat treatment at 1100° C. or higher is performed in an inert gas atmosphere, so oxygen in the cavity 4 is consumed during the heat treatment, and the cavity 4 is infiltrated and filled with inert gas from the outside. It turns out.

In this embodiment, in order to remove the inert gas that inhibits the growth of the oxide film from inside the cavity 4, the bonded substrate 10 is placed in the vacuum container 6 in the step shown in FIG. 61
The inside of the vacuum container 6 is evacuated. At this time, the vacuum pump 6
The vacuum valve 62 communicating with the oxidizing atmosphere gas 1 is open, and the vacuum valve 63 communicating with the oxidizing atmosphere gas is closed. Further, regarding the degree of vacuum attainment, it is necessary to almost completely remove the gas in the cavity in order to eliminate the inhibition caused by the expansion of the residual inert gas during the next step of growing an oxide film. Specifically, it is desirable that the degree of vacuum attainment is 10 Pa or less. Vacuuming time is at most 1μ
Since it is necessary to evacuate the cavity 4 which has a gap of only about m, it is necessary to wait as long as possible in order to completely remove the pressure loss or the gas adsorbed on the surface of the substrate facing the cavity 4.

Specifically, it is desirable to wait for 30 minutes or more after the vacuum system of the vacuum container 6 becomes 10 Pa or less. Furthermore, during this evacuation, the bonded substrate 10 may be heated by the heater 64 to promote exhaustion of the gas adsorbed on the substrate surface. The heating temperature at this time is preferably 100° C. or higher.

After evacuating the inside of the cavity 4 in this way, the valve 6
2 and open valve 63 to supply 02 gas or 02.
H2 mixed gas is supplied into the container 6. At this time 02,8
If an inert gas other than a secondary oxidizing gas gets mixed in, the cavity 4
It is desirable that the gas used be a high-purity oxidizing gas with an inert gas content of 1% or less. In this way, oxidizing gas is supplied to the vacuum container 6 until the pressure reaches atmospheric pressure or higher. Since the interior of the cavity 4 is a very narrow area as described above, it is desirable to maintain the pressure for at least one minute after reaching the atmospheric pressure or higher, taking pressure loss into consideration.

Immediately after filling the cavity 4 with the oxidizing gas, the bonded substrate 10 is placed in a heat treatment container 7 having a heater 71 capable of heating to 800° C. or higher (FIG. 1(e)).

Next, the bonding substrate 10 is subjected to, for example, dry O2, wet O2
2. 800 in an oxidizing atmosphere such as H2,,02 mixed gas
Heat treatment is performed at ℃ or higher for 1 hour or longer. As a result, groove 3
An oxidizing gas is supplied into the cavity 4 through the tube 3 to form an oxide film 11 on the surface of the tube 3 and inside the cavity 4. However, this oxidation step is continued until the cavity 4 is completely buried and filled with the growing oxide film 11.

In order to increase the oxidation rate of the cavity 4, oxygen ions may be implanted to promote oxidation before bonding, that is, in the step shown in FIG. 1 (a> or (b)).Ion implantation conditions are as follows. , for example, using 02 and increasing the dose to 5X1014
/-, and if it is implanted into either or both of the mirror surface 1a of the first semiconductor substrate and the mirror surface 5a of the second semiconductor substrate, the wafer surface becomes amorphous, and in this state, the above (,C)
If the above bonding step is carried out, solid phase growth will occur at the Si-8i junction, making it possible to obtain an Si-3i bonding state with better crystallinity.

Also, when moving from step (d) to step (e), the cavity 4
In order to avoid mixing of outside air into the interior, it is necessary to perform the treatment in as short a time as possible, and it is desirable that the time of exposure to the atmosphere be within one hour. Furthermore, it is more desirable if the processes (d) and (e) can be carried out in the same apparatus, since exposure to the atmosphere can be avoided. Further, if the atmosphere in the heat treatment container 7 can maintain a pressure higher than atmospheric pressure, the oxidizing gas can be more easily supplied into the cavity 4.

In this way, if the process is performed with the cavity 4 filled with high-purity oxidizing gas, all the gas in the cavity is used to form the oxide film 11, so the pressure between the outside air and the inside of the cavity 4 is reduced. Due to the difference, the oxidizing gas in the heat treatment container 7 is easily supplied through the groove 3, and the oxide film 11 on the surface of the cavity is quickly removed.
growth and burial becomes possible.

In this embodiment, as described above, since the heat treatment is performed in an inert gas atmosphere after the substrates are bonded, the oxygen in the cavity 4 is consumed and the cavity 4 is filled with inert gas. This cavity 4 has a gap of about 1 μm at most, so if it is simply left in the outside air, it will take a considerable amount of time for the inert gas inside the cavity to mix with the outside air and completely replace it. Even leaving it for 24 hours is not enough. Suppose that the heat treatment container 7 is opened in a state where the inert gas remains in the cavity 4 in this way.
When the oxidation treatment in step (e) is performed, the oxidation treatment step is usually performed at a high temperature of 1000° C. or higher, so the inert gas remaining in the cavity 4 expands thermally and becomes oxidized at room temperature. 3 times), the inside of the cavity 4 is filled with inert gas. In this case, oxidizing gas cannot easily enter the inside, which significantly reduces the growth rate of the oxide film.

Figure 2 shows a 3-inch wafer with a width of 30 μm and a depth of 3
These are the results of measuring how the buried state of the cavity changes when a 0 μm groove is formed and the cavity is filled with oxidizing gas (this example) and when it is filled with air (comparative example). . As is clear from the figure, in the method of the present example, the filling rate of the cavity reaches almost 100% by heat treatment for a short time of 2 hours. On the other hand, in the comparative example, the reaction rate was slow and it was impossible to embed the entire surface of the wafer even after heat treatment for a long time of 10 hours, proving that the method of the present invention is very effective.

Next, as shown in FIG. 1 (f), the entire surface of the first semiconductor substrate 1 is polished or etched until a groove 3 is opened. Then, as shown in FIG.
For example, polycrystalline silicon 13 is deposited by a method to fill the groove 3. However, the filling material in this case may be an insulating material such as oxide or silicon nitride, and the filling method may also be sputtering, vapor deposition, S
It may be OG etc. Further, the groove 3 does not necessarily have to be completely filled with polycrystalline silicon 13 as long as the opening on the surface is closed, and a cavity may remain.

Then, by removing deposits on the surface and flattening it by lap polishing or etching back, for example, the semiconductor has a region 12 that is completely electrically isolated from other regions by the polycrystalline silicon 13 and the oxide film 11. A substrate 10 is obtained. , a desired semiconductor device can be obtained by forming predetermined elements on the second semiconductor substrate 10.

FIG. 3 shows a vertical power transistor 8 and a logic circuit 9 that controls the transistor 8 on a single-chip semiconductor substrate 1.
This is an example installed in 0.

Here, the semiconductor substrate 10 is an N-type first semiconductor substrate with a low impurity concentration.
The semiconductor substrate 1 and the N-type second semiconductor substrate 5 are directly bonded, and have an insulating isolation region 12 produced by the process shown in FIG. 1 above. In the vertical power transistor 8, a source electrode 81 and a gate electrode 82 are formed on the end surface of the substrate 1, and a drain electrode 83 is formed on the end surface of the second semiconductor substrate 5.
is formed. In the logic circuit 9, source, train, and gate electrodes are formed in a region 12 of the substrate 1, and are insulated and separated from other parts of the substrate by a silicon oxide film 11 and polycrystalline silicon 13.

In this embodiment, since the isolation region 12 is formed of a single crystal substrate, the device characteristics are good, and since it is insulated from the transistor 8 by oxidation 11all, the isolation region 12 has a high isolation voltage and has good heat resistance. is also excellent.

Furthermore, since the separation groove 3 is exposed on the surface, the separation region 12
This makes it easy to align the elements formed on the surface.

[Second Embodiment] FIG. 4 shows the manufacturing process of a second embodiment of the present invention. In this embodiment, the steps in FIG. 4 (a>(b)) are the same as in the first embodiment, and a recess 2 with a depth of 0.2 to 2 μm is formed on the mirror-polished surface of the N-type first semiconductor substrate 1. A groove 3 is formed along the side edge 2a of the recess 2 and opens at the end of the substrate.

Next, in the step (C), this first semiconductor substrate 1 and an N-type second semiconductor substrate 5 whose at least one surface has been mirror-polished
After washing and surface treating the same in the same manner as in the first embodiment, they were placed in a vacuum container 6 without being bonded, and the vacuum pump 6
1, the inside of the vacuum container 6 is evacuated. The vacuum valve 62 is open and the vacuum valve 63 is closed. The ultimate degree of vacuum is desirably <10 Pa or less as described above. Thereafter, the vacuum valve 62 is closed, the vacuum valve 63 is opened, and the container is filled with high purity 02 gas or H2,0,2 mixed gas. At this time, the pressure inside the container 6 is preferably at least atmospheric pressure.

In this state, the mirror surfaces 1a and 5a of the two substrates 1.5 are brought into close contact with each other. As a result, the two substrates 1.5 are bonded together by hydrogen bonds between the silanol groups formed on the surfaces and the water molecules adsorbed on the surfaces, and the recesses 2 of the first semiconductor substrate 1 and the second substrate 1.5 are bonded together.
The cavity formed by the surface 5a of the semiconductor substrate 5 is filled with highly pure oxidizing gas.

Then, in FIG. 4(d), this bonded substrate 1 is immediately
For example, dry O2, wet O2,
82.02 800° in an oxidizing atmosphere such as mixed combustion gas
A heat treatment is performed for one hour or more at a temperature of C or more to oxidize the surface of the groove 3 and the inside of the cavity 4 to form an oxide film 11. In this case, as in the first embodiment, the process is continued until the cavity 4 is completely buried and filled with the oxide film 11.

Subsequently, in the step shown in FIG. 4(e), grooves 3 are formed on the surface 1b of the substrate 1.
In FIG. 1(f), the polycrystalline silicon 13 is opened.
deposit.

In this embodiment as well, since the heat treatment is performed in a state filled with high-purity oxidizing gas, it is possible to embed the oxide film 11 in the cavity 4 in an extremely short time, as in the first embodiment.

In the first and second embodiments described above, the combination of the substrates 1.5 is an N- type substrate and an N+ type substrate, but the concentration of these substrates can be arbitrary, and even if they are of different conductivity types. good.

Furthermore, it is also possible to use a substrate in which impurities are diffused in a part or the entire surface of these substrates, or a substrate in which two or more substrates are bonded together. Therefore, since it can be formed on any substrate, it is possible to form a thick, low-concentration layer with a low impurity concentration that cannot be obtained by conventional epitaxial methods, and it can easily correspond to higher breakdown voltages of devices.

Further, although the element formed in the first embodiment is an insulated gate type element, the present invention is not limited to this, and may be, for example, a diode, a bipolar element, a silice, or the like.

[Effects of the Invention] As described above, according to the method of the present invention, by filling the cavity of the bonded substrate with an oxidizing gas, the oxidation reaction in the subsequent oxidation treatment proceeds smoothly, and the process of filling the cavity in the cavity as in the conventional method Growth of the thermal oxide film is not inhibited due to accumulation of unreacted gas. Therefore, the oxide film grows uniformly and in a short time,
Since an insulating isolation region with high breakdown voltage can be easily formed, it is fully applicable to large-diameter wafers. Moreover, since the embedding time is extremely short, the heat load on the semiconductor substrate is small, the occurrence of defects in the substrate is reduced, and the defect rate can be significantly reduced.

[Brief explanation of drawings]

1 to 3 show an embodiment of the present invention, and FIG.
) to (g> are cross-sectional views showing the manufacturing process of the semiconductor device, the second
The figure shows the relationship between heat treatment time and cavity filling rate, FIG. 3 is a cross-sectional view of a semiconductor device manufactured by the process of this example, and FIGS. It is a cross-sectional view showing the manufacturing process of the second example. 1... First semiconductor substrate 1a... Mirror surface 2... Concavity 4... Cavity Part 5...Second semiconductor substrate 5a...Mirror surface 6...Vacuum container 7...Heat treatment container 10...Bonded substrate Fig. 1 (a) (b) (C) (d) Fig. 1 (e) (f) Fig. 2 Heat treatment time of this example (hr) Fig. 4 (a) (b) (C) a

Claims (2)

[Claims] (1) forming a recess in the mirror surface of a first semiconductor substrate, at least one surface of which has been mirror-polished, and forming a groove for introducing an oxidizing gas deeper than the recess along the side edge of the recess; a step of directly bonding the mirror surface of the semiconductor substrate to the mirror surface of a second semiconductor substrate whose at least one surface has been mirror-polished; In the cavity formed by the two semiconductor substrates,
The method comprises the steps of filling a high-purity oxidizing gas through the groove, and embedding an oxide film in the cavity by heat-treating the bonded substrate in an oxidizing gas atmosphere. A method for manufacturing a semiconductor device. (2) forming a recess in the mirror surface of the first semiconductor substrate, at least one surface of which has been mirror-polished, and forming a groove for introducing an oxidizing gas deeper than the recess along the side edge of the recess; A first semiconductor substrate and a second semiconductor substrate whose at least one surface is mirror-polished are placed in a high-purity oxidizing gas atmosphere, and the mirror surfaces are brought into close contact with each other and directly bonded. and a step of filling a high-purity oxidizing gas into a cavity formed by the first semiconductor substrate and the second semiconductor substrate, and embedding an oxide film in the cavity by heat-treating the obtained bonded substrate in an oxidizing gas atmosphere. A method for manufacturing a semiconductor device, comprising the steps of: