JP3160966B2 - Method for manufacturing SOI substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a silicon-on-insulator (SOI) substrate, and more particularly to a method for forming a silicon layer on an insulating substrate on a uniform surface.

[0002]

2. Description of the Related Art SOI technology for forming a silicon single crystal thin film on an insulating film has been widely studied in order to exceed the limit of a VLSI using silicon. As one of the SOI techniques, there is a technique of forming a single crystal silicon thin film by bonding silicon wafers. In this bonding method, after bonding the wafers, one of the wafers is thinned. Techniques such as grinding and polishing are used as techniques for thinning wafers, but ultra-fine MO
In the manufacture of S transistors, there is a limit in the current mechanical polishing, and techniques such as selective polishing for polishing only a silicon oxide film have been introduced.

[0003] Here, SOI by general bonding is used.
A method of manufacturing a substrate will be briefly described with reference to FIG. A step according to the pattern to be formed is formed on the surface of the silicon wafer 61, and the silicon wafer is covered with the silicon oxide film 62. Next, the polysilicon film 63
The silicon wafer 61 having the step formed thereon and another silicon wafer 64 are bonded together. Then, as shown in FIG. 6, the thickness y is reduced by grinding and polishing from the back surface 61b side of the silicon wafer 61, and when the silicon oxide film 62 is exposed, the polishing is completed and a single-crystal silicon thin film having a required pattern is formed. Is formed.

[0004]

However, the above-mentioned SO
In the method of manufacturing the I-substrate, since the film thickness y in FIG. 6 varies within the wafer surface, the thickness of the island-shaped single-crystal silicon thin film formed in a required pattern also varies.

In order to form a single crystal silicon thin film into a required pattern, selective polishing is performed until an interface 61a between the silicon wafer 61 and the silicon oxide film 62 is exposed. Over-polishing is required, which causes the silicon surface to be exposed to an alkaline polishing solution for a long time, resulting in roughening of the silicon surface. In the case where a TFT (thin film transistor) is formed on a rough silicon surface, the reliability of the gate insulating film is lowered, and the device does not have good characteristics.

In view of the above technical problems, an object of the present invention is to provide a method of manufacturing an SOI substrate that improves the uniformity of the surface of a polished silicon layer.

[0007]

In order to achieve the above object, the present invention provides a method of manufacturing an SOI substrate, wherein an epitaxial silicon layer in an island region of a thin film is formed on an insulating film by bonding the substrates. Forming an etching stop layer on the surface of the silicon substrate, forming an epitaxial silicon layer epitaxially grown on the etching stop layer, and forming a step in the epitaxial silicon layer along a pattern of island regions Forming an insulating film constituting the insulating substrate over the entire surface of the epitaxial silicon layer having the step formed thereon, bonding the silicon substrate having the insulating film formed to another substrate, and stopping the etching. Grinding the silicon substrate from the back side so that the layer is not exposed; Selectively etching the silicon substrate until the stop layer is exposed, and selectively polishing the etch stop layer and the epitaxial silicon layer until the insulating substrate is exposed, and removing the epitaxial silicon layer in the thin island region from the insulating substrate. Steps to be left above are sequentially provided.

In the present invention, before the bonding step, a step is formed in the silicon layer along the pattern of the island region to be formed, that is, a step of the negative pattern of the island region. Next, an insulating film constituting an insulating base is formed on the entire surface of the silicon layer having the step formed thereon. This insulating film serves as a polishing stop layer when the epitaxially grown silicon layer is polished and thinned in a later step, and also determines and separates the epitaxially grown silicon layer into island-like regions. It becomes a body separation membrane.

As the etching stop layer, a material layer having a high etching selectivity with respect to a silicon layer formed by epitaxial growth is used. For example, chemical etching due to a difference in impurity concentration is used for the etching. As an example where the difference in etching rate is large, a mixed solution of ethylenediamine-pyrocatechol-pure water can be used.
A speed ratio of 0/1 or more can be obtained.

[0010]

When a silicon layer is formed on a silicon substrate by epitaxial growth, the silicon layer becomes monocrystalline. Also, in general, when an etching stop layer is formed in advance on the surface of a silicon substrate that has been mirror-finished, the etching stop layer becomes a layer with small variation, and when the silicon substrate is polished and selectively etched from the back surface with the etching stop layer. , The etching stops in a state of small variation. Therefore, even if selective polishing is performed after the etching is stopped, polishing starts from a stage with good in-plane uniformity, and when the insulating film is exposed, this becomes a polishing stop layer. Therefore, the thickness of the silicon layer finally obtained is excellent in uniformity.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described with reference to the drawings.

The present embodiment relates to a method of manufacturing an SOI substrate manufactured by bonding a pair of silicon wafers, and particularly to a method of forming ap ⁺ -type impurity layer as an etching stop layer. Hereinafter, this embodiment will be described with reference to FIGS.

First, ap ⁺ -type impurity layer 2 having a thickness x is formed on the surface of the (100) plane of a p ^-- type single crystal silicon substrate 1. This p ⁺ -type impurity layer 2 functions as an etching stop layer. The p ⁺ -type impurity layer 2 is formed by introducing impurities such as boron into the surface of the silicon substrate 1 by, for example, ion implantation or thermal diffusion. p ⁺ -type impurity layer 2
Is about 10 ²⁰ cm ⁻³ , and the impurity concentration of the p ⁻ type silicon substrate 1 is about 10 ¹⁴ cm ⁻³ . Since the silicon substrate 1 is initially mirror-finished, the thickness x of the p ⁺ -type impurity layer 2 is also small.

Next, as shown in FIG. 1, ap ⁻ type silicon layer 3 is formed on the surface of the silicon substrate 1 on which the p ⁺ type impurity layer 2 is formed by an epitaxial growth method.
Because of the epitaxial growth method, the silicon layer 3 is a single crystal reflecting the crystallinity of the substrate.

Silicon layer 3 which is an epitaxial growth layer
Is formed, a step 4 is formed on the surface 3a of the silicon layer 3 along the pattern of the island region to be formed. The height of the step 4 corresponds to the thickness of the single crystal silicon thin film to be formed. After the formation of the step 4, as shown in FIG. 2, an insulating film constituting the insulating base 5, that is, a silicon oxide film 5 is deposited on the entire surface.

Here, another silicon substrate 6 is prepared, and as shown in FIG. 3, the silicon substrate 1 on which the silicon oxide film 5 is adhered via the polysilicon layer 7 is bonded to the silicon substrate 1 in accordance with a normal bonding method. to paste together. It is preferable to set the thickness of the silicon layer 3 so that the impurities of the p ⁺ -type impurity layer 2 do not diffuse to the bottom 4 a of the step 4 in the heat treatment up to the bonding stage.

Next, grinding is performed from the back side of the silicon substrate 1 so that the p ⁺ -type impurity layer 2 serving as an etching stop layer is not exposed, so that the thickness of the silicon substrate 1 is reduced.
After the grinding, the silicon substrate 1 is etched until the p ⁺ -type impurity layer 2 appears by etching using the impurity concentration difference.
Shaving. This etching is an etching using a mixed solution of ethylenediamine-pyrocatechol-pure water as an etchant. Assuming that the etching rate of the p ⁺ -type impurity layer is 1 with respect to the silicon of (100) plane, p ^-- type silicon The etching rate of the substrate 1 becomes 400, and etching with an extremely high selectivity is performed. Using a mirror-finished silicon substrate 1, a highly uniform p ⁺ -type impurity layer 2
Is formed, the etching is stopped in a state where the deviation of the film thickness is extremely small, as shown in FIG. 4, reflecting the p ⁺ -type impurity layer 2.

Since the etching rate ratio is 400 to 1, the thickness x of the p ⁺ -type impurity layer 2 is at least p
^It suffices if the distance z from the surface of the ⁺ -type impurity layer 2 to the bottom 4a of the step 4 is 1/400 or more.

[0019] After the good uniformity etched in the p ⁺ -type surface of the impurity layer 2 is stopped, to polish the silicon layer 3 formed by p ⁺ -type impurity layer 2 and the epitaxial growth by selective polishing of the silicon oxide film 5 . At this time, p ⁺
Since the in-plane variation is suppressed on the surface of the impurity layer 2 of the mold, overpolishing in the selective polishing can be performed in a short time, and the exposed surface 3b of the obtained silicon layer 3 can be prevented from being roughened. In addition, polishing starts at a stage where the in-plane uniformity is good, and when the insulating film is exposed, the silicon oxide film 5 functions as a polishing stop layer. Therefore, the film thickness distribution of the silicon layer 3 formed separately in the island region is also extremely excellent in uniformity.

As described above, in the method of manufacturing an SOI substrate of this embodiment, since etching is stopped on a uniform surface by the p ⁺ -type impurity layer 2, even if selective polishing is performed, single-crystal silicon in the island region is obtained. Variations in the thickness of the thin film are suppressed. In addition, since the polishing is excellent in uniformity, excessive polishing is not required, and the silicon layer 3 is exposed to an alkaline polishing liquid for a long time.
The exposed surface 3b is not exposed. Therefore, S
The reliability of the OI device is also improved.

[0021]

According to the method for manufacturing an SOI substrate of the present invention, the etching stop layer is formed uniformly on the surface of the silicon substrate, and the etching from the back surface of the bonded silicon substrate is stopped reflecting the uniformity. be able to. Therefore, the uniformity of the thickness of the single crystal silicon thin film is excellent, and the selective polishing can be completed in a short time. Therefore, surface roughness of the obtained silicon layer can be prevented, and the uniformity of the film thickness can be improved. Further, by forming a step along the island region in the silicon layer, it is possible to provide an SOI substrate which is dielectrically isolated even in the in-plane direction of the silicon layer epitaxially grown.

Therefore, by using the method of the present invention, the reliability of a device formed on an SOI substrate is greatly improved.

[Brief description of the drawings]

FIG. 1 is a process cross-sectional view up to a step of epitaxially growing a silicon layer in an example of a method for manufacturing an SOI substrate of the present invention.

FIG. 2 is a process cross-sectional view up to the step of forming a silicon oxide film in one example of the method for manufacturing an SOI substrate of the present invention.

FIG. 3 is a process cross-sectional view up to a step of bonding silicon substrates to each other in an example of the method for manufacturing an SOI substrate according to the present invention.

FIG. 4 is a process cross-sectional view up to an etching process using an impurity concentration difference in an example of the method for manufacturing an SOI substrate of the present invention.

FIG. 5 is a process sectional view up to a selective polishing step in an example of the method for manufacturing an SOI substrate according to the present invention;

FIG. 6 is a process sectional view showing an example of a conventional method of manufacturing an SOI substrate before a selective polishing step.

[Explanation of symbols]

Reference Signs List 1 silicon substrate, 2 p ⁺ type impurity layer, 3 silicon layer, 4 step 5 silicon oxide film, 6 silicon substrate, 7 polysilicon layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21 / 304,21 / 306,21 / 308 H01L 21 / 02,27 / 12

Claims (1)

(57) [Claims] 1. A method of forming an epitaxial silicon layer in an island region of a thin film on an insulating film by bonding substrates.
In the manufacturing method of OI substrate was forming an etching stop layer on the surface of the silicon substrate, it is epitaxially grown on the etch stop layer d
Forming a pita key interstitial silicon layer to form a step along the pattern of island regions in the epitaxial silicon layer, an insulating film of the insulating substrate on the entire surface of the epitaxial silicon layer in which the step is formed Forming, bonding the silicon substrate on which the insulating film is formed to another substrate , and grinding the silicon substrate from the back surface thereof so that the etching stop layer is not exposed. a step of the etch stop layer is selectively etched the silicon substrate to expose until said insulating substrate is exposed to selective polishing said etch stop layer and the epitaxial silicon layer, the epitaxial silicon layer of the island-shaped region of the thin film And step of leaving on the insulating substrate.