JPH07245382A - Manufacture of composite element and lamination substrate - Google Patents

Abstract

PURPOSE:To acquire a composite element wherein a power element of high breakdown strength and an element of fast operation are formed on the same substrate by making a thickness of an insulation film irregular by thickening a part wherein an application voltage of an insulation film rises between a semiconductor substrate and a supporting substrate wherein a high breakdown strength element is formed. CONSTITUTION:Impurities are selectively introduced from a surface to an SOI substrate 1 whose conductivity type is n-type, a diode structure is formed by providing a p<+>-anode region 22 and an n<+>-cathode region 23 having an n<->-layer 21 therebetween and a field oxide film 24, an anode electrode 25 and a cathode electrode 26 are arranged on a surface like usual. Furthermore, an oxide film 2 is made thick below the p<+>-region 22. Thereby, breakdown strength is improved. For example, even if t=1mum, element withstand voltage attains 400V by making T=4mum. According to this constitution, not only a diode but also a power element such as IGBT and a logic circuit can be manufactured in the same process simultaneously.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite element including a high breakdown voltage element and a high speed element and a method for manufacturing a bonded substrate used for the composite element.

[0002]

2. Description of the Related Art In order to combine a power semiconductor element with a control circuit or a drive circuit on the same semiconductor substrate, a dielectric isolation structure using an SOI (Silicon on Insulatar) substrate having sufficient electric insulation is adopted. As a general SOI substrate, a bonded substrate in which a silicon wafer is bonded via an oxide film is known. Such a bonded substrate is also used for a high breakdown voltage IGBT or the like.

FIGS. 2A to 2C show a conventional method for manufacturing a bonded substrate, in which the surface of the silicon wafer 10 is
A uniform thermal oxide film 2 is formed by heat treatment in an oxygen or water vapor atmosphere [FIG. The film thickness of the thermal oxide film 2 is determined in accordance with the specifications of the SOI substrate, and the heat treatment conditions at that time may be general conditions and may be efficient conditions. Even after thermal oxidation, the mirror surface condition is sufficiently maintained, and even if the mirror surfaces of the wafers are piled up as they are, the adhesion is high. For example, Furukawa, Shinho, Applied Physics Vol. 60.
As described in (1991) p. 790, when the washing activation treatment is performed and the layers are superposed, the uniformity of the adhesion by the subsequent heat treatment is caused by the function of the hydroxyl group (OH group) bonded to the surface of the wafer. Is good. The two wafers 10 stacked as shown in FIG. 7B are heat-treated in an electric furnace. The temperature is 200 to 900 ° C., the time is 1 to 10 hours, and the atmosphere is not a particularly important factor. Considering that the coefficient of thermal expansion of silicon and that of silicon oxide film are different, it is better to process at a relatively low temperature, but there are no voids that are unbonded parts after heat treatment, and the bonding surface has sufficient strength. You have to consider what you are doing. In the bonding by such a method, the bonding surface is a mirror surface, and the surface activation treatment is a point for bonding a uniform and large area. After that, the silicon wafer 10 on the element forming side is polished to form the SOI substrate 1 having a thickness necessary for forming the element. The thickness is generally 5 to 50 μm. , Because it is extremely thin, one silicon wafer 10
Serves as a supporting substrate [(c) in the figure]. The total thickness is 400 to 700 μm, and is passed to the subsequent LSI forming process. In order to suppress dust generation in the element forming process, the outer peripheral portion of the SOI substrate 1 is etched so that the area is slightly smaller than that of the supporting substrate 10.

[0004]

The SOI substrate 1 manufactured by the above process has a uniform thickness, and has the supporting substrate 10
Are insulated by an oxide film 2 having a uniform thickness. However, when a power semiconductor element and a logic circuit are formed on the same substrate, the power element requires a high breakdown voltage and a thick semiconductor substrate, and the logic circuit is preferably as thin as possible in order to achieve high-speed operation. We cannot meet the requirements of both parties. It is difficult to manufacture a bonded substrate having an SOI substrate having such a different thickness and having a common flat surface because of mirror-polishing before bonding. As a measure for forming a high breakdown voltage element on a thin semiconductor substrate, it may be possible to adopt a lateral semiconductor element.
However, in that case, there is a problem shown in FIG. FIG. 3 shows a lateral diode, which is a p ⁺ anode region 22 on one side of the n ⁻ layer 21 and an n ⁺ cathode region 23 on the other side of the SOI substrate 1 bonded to the silicon supporting substrate 10 through the oxide film 2. Is formed, and the anode electrode 25 and the cathode electrode 26 are in contact with each other through the contact holes formed in the field oxide film 24. The + pole of the power source is connected to the cathode electrode 26 via the K terminal, and the − pole of the power source is connected to the anode electrode 25 via the A terminal, and a reverse bias is applied to the diode. The equipotential lines 27 shown by dotted lines are the field oxide film 24, the anode electrode 25, and the cathode electrode 2 on the surface portion of the n ⁻ layer 21.
Although the gap can be widened by the optimized breakdown voltage design of 6, the equipotential lines 27 do not spread in the supporting substrate 10, and therefore become dense in the oxide film 2. As a result, S on the thin oxide film 2 is similar to the SOI substrate for the high speed device.
Even if the lateral diode is formed on the OI substrate, the electric field strength becomes strong in the oxide film 2, so that dielectric breakdown occurs and a high element breakdown voltage cannot be obtained.

An object of the present invention is to solve the above problems and to provide a composite element in which a high breakdown voltage power element and a high-speed operation element are formed on the same substrate, and a method for manufacturing a bonded substrate which can be used for the composite element. To provide.

[0006]

In order to achieve the above object, the present invention according to claim 1 is formed on a semiconductor substrate formed on the same supporting substrate and a semiconductor substrate insulated by an insulating film. In a composite element including a high breakdown voltage element and a high speed element, the thickness of the insulating film is not uniform, and the thickness is increased in a portion where the applied voltage of the insulating film between the semiconductor substrate on which the high breakdown voltage element is formed and the supporting substrate is high. It has been done. The manufacturing method of the present invention according to claim 2, wherein the manufacturing method of the present invention is a bonded substrate comprising a semiconductor substrate on which an element is formed and a supporting semiconductor substrate that can be used for such a composite element. After forming a recess on one surface by processing, this surface is covered with an oxide film having a thick portion filling the recess, and the oxide film and the oxide film covering one surface of the element semiconductor substrate are overlapped and bonded by heat treatment. I shall.
Before stacking, it is effective to bond a hydrogen group to the surface of the oxide film on the one surface of the supporting semiconductor substrate and bond a hydroxyl group to the surface of the oxide film on the one surface of the device semiconductor substrate. It is a good method to dry-etch the surface of the oxide film on one surface of the supporting semiconductor substrate and then bring hydrogen activated by photoexcitation into contact therewith to bond hydrogen groups to the surface of the oxide film.

[0007]

Since the electric field strength is relaxed by increasing the thickness of the insulating film in the portion of the high breakdown voltage element where the voltage applied to the insulating film between the supporting substrate and the substrate is high, the semiconductor substrate on the same supporting substrate is not affected. High breakdown voltage elements can be combined. Such a thick portion of the insulating film must be formed by processing the surface of the supporting substrate to form a recess, and the processed surface is considerably roughened. Therefore, the surface of the oxide film formed in that portion is considerably roughened. However, when a hydrogen group is bonded to the surface, the oxide film on the surface of the supporting substrate having the hydrogen group and the oxygen group is oxidized on the surface of the semiconductor substrate for a device to which a hydroxyl group is bonded as in the conventional technique. Good adhesion by film and heat treatment.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows one embodiment of the present invention formed on an SOI substrate.
The horizontal diode of the embodiment is shown, and the same parts as those in FIGS.
Minutes are given the same reference numerals. N type conductivity SO
N is obtained by selectively introducing impurities into the I substrate 1 from the surface.^-layer
P sandwiching 21⁺Anode region 22, n⁺Cathode area
Create a diode structure by providing 23, and feel on the surface
The oxide film 24, the anode electrode 25, and the cathode electrode 26.
Placement is similar to the diode of FIG. 3, but p⁺
The oxide film 2 is thickened below the region 22. This
It is shown from the data shown in FIG. 4 that the breakdown voltage is improved. This
The data in the diode of FIG. 5 having the same structure as that of FIG.
And the thickness t ₀Thin oxide film 2 under 5 μm SOI substrate
The thickness t of the uncoated part is 1 μm, 2 μm, 3 μm,
It is the element breakdown voltage when the thickness T of the open portion is changed. Oxide film
If the thickness t of 2 is increased, the withstand voltage of the element increases, but
Substrate distortion easily occurs due to the thermal history of the child making process,
A fine logic circuit cannot be formed on the same semiconductor substrate. Only
However, for example, even if t = 1 μm, by setting T = 4 μm,
Therefore, the device breakdown voltage reaches 400 V, and such a structure is adopted.
As a result, not only for diodes but also for power such as IGBT
Devices and logic circuits can be manufactured simultaneously in the same process
It

Next, an embodiment of manufacturing a laminated substrate capable of forming such a power element of the present invention according to claim 2 will be described with reference to the drawings. In the manufacturing process shown in FIGS. 6A to 6E, the silicon wafer 1 is manufactured in the same manner as in FIG.
0 is thermally oxidized to form an oxide film 2 [(a) in the same figure]. Next, a pattern of the resist 3 is formed on the surface of at least one of such wafers, and the oxide film and silicon are etched to form the groove 4 [FIG. 6 (b)]. This groove is formed in the portion of the oxide film 2 where a high voltage is applied, as in the lateral diode described above. Next, after removing the resist 3 and washing, the oxide film 2 by the thermal CVD method is deposited until the groove 4 is sufficiently filled, and then flattened by dry etching [FIG. 6 (c)]. The detection of the end point of the dry etching may be performed by a method of managing it by time, or a method of forming a thermal nitride film having a different etching rate to a desired thickness before using the CVD film 2 as a stopper. At this stage, it is necessary to pay close attention to prevent uneven etching, but the steps up to this point can be handled by the already developed LSI process technology.

Next, the step of cleaning treatment before bonding is performed. In the case of the conventional method, the Si—O—Si bond on the surface of the oxide film is broken during the cleaning treatment in the liquid, resulting in a surface terminated with a Si—OH bond. Various cleaning methods have been studied, but essentially, it can be replaced with a hydroxyl (OH) group, and a general hydrochloric acid / hydrogen peroxide mixture (mixture of hydrochloric acid and hydrogen peroxide).
And ammonia hydrogen peroxide (a mixture of ammonia and hydrogen peroxide)
Washing with was sufficient. However, FIG. 6 (c)
In the case where one of the surfaces shown in (1) was processed, it was difficult to make a bonded substrate without voids (unbonded parts) over a wide surface. Therefore, for the processed wafer, after washing with hydrochloric acid / hydrogen peroxide, in a photoexcited H ₂ atmosphere,
A step of treating for several minutes was added. After the treatment, the raw wafer 10 is immediately brought into close contact with the unprocessed wafer 10 only through the step of FIG. 6 (a), and a bonding heat treatment is carried out [FIG. 6 (d)]. Heat treatment is performed at a relatively low temperature (200-400 ° C) for 1-2 hours and at a relatively high temperature (700-900 ° C) for 2-4 hours.
It is desirable to perform stepwise treatment.

The wafers shown in FIG. 6 (d) bonded in this way were examined for the occurrence of voids by the method utilizing the difference in infrared transmission intensity. As a result, the results were comparable to those when the unprocessed comrades were bonded. It was confirmed that it was not good. Finally, the SOI substrate 1 is polished and finished as usual, and the bonding S in which the thickness of the insulating film 2 is partially different is performed.
An OI substrate was obtained [Fig. 6 (e)].

The process up to this point will be described. Initially, it was thought that the reason why the bonding was not successful was that, as is generally considered, the surface on which the groove 4 had been processed was considerably roughened, and the adhesion was poor, and an attempt was made to perform mechanical polishing. It has been found that polishing of the silicon oxide film 2, that is, glass requires a considerably high technique, is not practical in terms of yield and cost.

Among various trials and errors, defects are caused by dry process steps such as planarization and resist ashing, and the damage layer formed by these steps is not improved even if removed by dilute hydrofluoric acid. It was also found that even with the thermal oxide film on the mirror surface, the unevenness of the surface became remarkable by etching with dilute hydrofluoric acid, and voids were easily generated. On the other hand, it was also found that even with the wafer that has undergone the above processing, voids do not occur if the other side is a mirror-finished silicon surface.

From such experimental facts, extreme flatness is not always necessary, and by increasing the reaction of the boundary surface,
It was found that a good bonded wafer can be formed. The essential points of the bonding method according to the present invention will be described with reference to the drawings. First, the flattening step by dry etching is usually performed by glow plasma discharge or ECR plasma. At that time, as shown in FIG. 7, a strong electric field layer called a sheath 31 is formed in the boundary layer with the oxide film 2, and the positive ions 32 accelerated by the space act to damage the surface of the oxide film 2 to the damaged layer 5. To form. This damage layer 5 is
Although it is extremely thin, its presence can be confirmed from the fact that the surface roughening state after cleaning with ammonia-hydrogen peroxide is clearly different compared to that without the dry process step. The damaged layer 5 is considered to be a metastable glass layer, and the Si-O-Si bond is considered to be weaker than usual.

The wafer 10 processed as described above is only washed with hydrochloric acid / hydrogen peroxide mixture and subjected to hydrogen radical treatment by photoexcitation. In this process, a wafer is installed in a vacuum chamber, an ultraviolet lamp is irradiated while H ₂ gas is adjusted to a pressure of 10 to 500 Pa, and the wafer is held for about 5 to 10 minutes. The UV irradiation activates the H ₂ gas, and various types of active hydrogen groups 33 are generated as shown in FIG.
This hydrogen group 33 is an unstable Si on the surface of the damage layer 5.
The —O—Si bond is broken, and many Si—H bonds are formed on the surface of the oxide film 2. Unlike the previous dry process, there is no ionization of gas, so the reaction proceeds slowly without damage. Normal glow plasma discharge and E
Similar effects can be obtained by modifying the CR plasma device so that only neutral radicals reach the wafer.

The mating of the wafer on the other side is performed before the Si--H bond reacts with the moisture in the air, and the heat treatment step is started. As shown in FIG. 9, first, at low temperature, Si—O—Si bond is formed by the reaction of Si—O and hydroxyl group, and adhesion proceeds.
The generated water is temporarily stored in the oxide film 2. Next, the high temperature treatment is performed. Here, water diffuses and escapes, but at this time, it assists the recovery and fluidity of the damage layer 5, and also supplies oxygen to the Si—H bond portion. By such a function, the void portion is filled, and a good bonded substrate can be obtained.

By applying this technique, good bonding can be similarly performed over a wide area even on a SiC substrate or quartz glass, which has been difficult to be mirror-finished. In the above embodiments, as a method of manufacturing a bonded substrate having a partially thick oxide film, a method of processing a silicon substrate by etching and embedding an oxide film by CVD has been described. However, according to the specifications of an applied device, the LOCOS technique is used. It is also possible to reduce the manufacturing cost by using accelerated oxidation.

[0018]

According to the present invention of claim 1, when a composite element including a high breakdown voltage element is formed on an SOI substrate bonded to a supporting substrate, an intermediate insulating film is thickened only in a portion to which a high voltage is applied. By doing so, it has become possible to combine a logic circuit such as a control circuit including a high-speed element on the same substrate. According to the present invention of claim 2, in manufacturing an SOI bonded substrate that can be used for such a composite element, hydrogen is used for activation of an oxide film on a supporting semiconductor substrate in which a concave portion provided with a thick oxide film is processed. By using the base, it becomes possible to perform the bonding while suppressing the generation of voids, and it is possible to improve the manufacturing yield and reduce the cost.

[Brief description of drawings]

FIG. 1 is a sectional view of a diode portion of a composite element according to an embodiment of the present invention according to claim 1.

FIG. 2 shows a manufacturing process of a conventional SOI bonded substrate
Sectional drawing shown in order of (a)-(c)

FIG. 3 is a sectional view of a diode portion of a conventional composite element.

FIG. 4 is a diagram showing the relationship between the breakdown voltage of a diode element and the thickness of a thick oxide film with the thickness of the oxide film of the SOI substrate as a parameter.

5 is a cross-sectional view of a diode for obtaining the data of FIG.

FIG. 6 shows a manufacturing process of an embodiment of the present invention according to claim 2.
Sectional views shown in the order of (a) to (e)

FIG. 7 is a cross-sectional view for explaining a dry process step of an embodiment of the present invention of claim 2;

FIG. 8 is a sectional view for explaining a hydrogen treatment process of an embodiment of the present invention according to claim 2;

FIG. 9 is a sectional view for explaining a heat treatment process of an embodiment of the present invention according to claim 2;

[Explanation of symbols]

1 SOI Substrate 2 Oxide Film 3 Resist 4 Groove 10 Supporting Substrate 21 n ^- Layer 22 p ⁺ Anode Region 23 n ⁺ Cathode Region 25 Anode Electrode 26 Cathode Electrode

Claims (4)

[Claims] 1. A high withstand voltage element formed on a semiconductor substrate insulated by the same supporting substrate and an insulating film, wherein the high withstand voltage element is not uniform and the high withstand voltage element is formed. A composite element characterized in that an insulating film between a semiconductor substrate and a supporting substrate is thickened in a portion where an applied voltage is high. 2. A method for manufacturing a bonded substrate comprising a semiconductor substrate on which elements are formed and a supporting semiconductor substrate,
After forming a recess on one surface of the supporting semiconductor substrate by processing, cover this surface with an oxide film having a thick portion filling the recess, and superimpose the oxide film and the oxide film covering one surface of the device semiconductor substrate. A method for manufacturing a bonded substrate, which comprises bonding by heat treatment. 3. Prior to stacking, a hydrogen group is bonded to the surface of the oxide film on the one surface of the supporting semiconductor substrate, and a hydroxyl group is bonded to the surface of the oxide film on the one surface of the device semiconductor substrate.
A method for manufacturing the bonded substrate as described. 4. The surface of an oxide film on one surface of a supporting semiconductor substrate is dry-etched, and then hydrogen activated by photoexcitation is brought into contact with the surface of the oxide film to bond a hydrogen group. Manufacturing method of bonded substrate.