Method of producing semiconductor substrate

Abstract

There is provided a method for suppressing the occurrence of defects such as voids or blisters even in the laminated wafer having an oxide film of a thickness thinner than the conventional one, wherein hydrogen ions are implanted into a wafer for active layer having an oxide film of not more than 50 nm in thickness to form a hydrogen ion implanted layer, and ions other than hydrogen are implanted up to a position that a depth from the surface side the hydrogen ion implantation is shallower than the hydrogen ion implanted layer, and the wafer for active layer is laminated onto a wafer for support substrate through the oxide film, and then the wafer for active layer is exfoliated at the hydrogen ion implanted layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart showing procedures of producing a semiconductor substrate by the conventional lamination process;

FIG. 2 is a graph showing a hydrogen dose and a thickness range of an oxide film for obtaining a good product;

FIG. 3 a flow chart showing procedures of producing a semiconductor substrate according to the invention;

FIG. 4 is a graph showing a relation between atomic mass of each element and a ratio of oxygen atom recoiled to the each element ion in the element implantation;

FIG. 5 is a graph showing adequate implantation doses of argon ions and oxygen ions; and

FIG. 6 is a flow chart showing procedures of producing a semiconductor substrate according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention lies in that when a semiconductor substrate is produced by directly silicon wafers to each other through the oxide film having a thickness thinner than the conventional one or without forming the oxide film, in addition to hydrogen ions for exfoliating the wafer for the active layer, ions other than hydrogen ions are implanted to sputter a necessary quantity of oxygen from the oxide film and implant oxygen into the active layer, and concrete methods therefor are explained individually.

In the method according to the first invention shown in FIG. 3, a wafer 1 for an active layer and a wafer 2 for a support substrate are previously provided (step (a)), and an oxide film 3 is formed on the wafer 1 for the active layer (step (b)), and then hydrogen ions are implanted into the wafer 1 for the active layer to form an ion implanted layer 4 in the interior of the wafer 1 for the active layer (step (c)).

Thereafter, ions other than hydrogen such as oxygen ions or argon ions are implanted to a position that a depth from the surface side the hydrogen ion implantation is shallower than the hydrogen ion implanted layer 4 (step (d)). When the implantation of oxygen ions or argon ions is carried out together with the implantation of hydrogen ions, these ions sputter oxygen from the oxide film to implant oxygen required for suppressing void or blister defects into the active layer.

Then, the wafer 1 for the active layer is laminated through the oxide film 3 at the ion implanted side to the wafer 2 for the support substrate (step (e)), and the exfoliation heat treatment is conducted to partly exfoliate the wafer 1 for the active layer at the ion implanted layer 4 as a cleavage plane (exfoliation face) (step (f)), and thereafter re-oxidation treatment (step (g)), removal of oxide film (step (h)) and planarization treatment (step (i)) are carried out to produce a semiconductor substrate 7 in which a silicon layer 6 is formed on a buried oxide film 5.

As the planarization treatment is suitable a treatment in Ar or H₂ atmosphere at a high temperature above 1100° C.

In the above method, the ions other than hydrogen are particularly implanted at the step (d) in addition to the implantation of hydrogen ions at the precedent step, so that the diffusion of hydrogen into the laminated interface at the exfoliation heat treatment of the step (f) is suppressed by oxygen sufficiently sputtered at these steps to suppress the occurrence of voids or blisters, whereby there is obtained the semiconductor substrate having a thin thickness of the oxide film.

The condition for implanting oxygen required for the suppression of void or blister defects in the active layer by conducting the implantation of oxygen ions or argon ions in addition to the implantation of hydrogen ions to sputter oxygen from the oxide film with these ions is explained in detail below.

In order that N_D defined in the above equation (I) satisfies N_D>4.2×10¹⁴ atoms/cm² through the implantation of ions other than hydrogen, it is necessary that a shortage of N_HO (oxygen introduced into the active layer by hydrogen ion implantation) is made up by N_IO (oxygen introduced into the active layer by element(s) other than hydrogen) and N_ID (defects introduced into the active layer by implanting ions other than hydrogen).

There are B, P and As as an element generally implanted into the wafer. In Table 1 is shown a dose of oxygen introduced by a recoil phenomenon in the implantation of such an element ion. In FIG. 4 are shown results arranged as a relation between atomic mass of each element and a ratio of oxygen atom recoiled in the implantation of the element to the element ion (recoil ratio). The recoil phenomenon means a phenomenon that when the element ion is implanted through the oxide film, oxygen atom is sputtered from the oxide film by the implanted ion to strike into Si crystal.

From the results of FIG. 4, a recoil ratio R_Z of a certain element can be represented by the following equation (III):

R _Z=0.0007×q_Z^1.325  (III)

where q_Z is an atomic mass.

TABLE 1
Thickness of oxide film: 1 nm, Ion dose: 1.00 × 1013 atoms/cm2
		Recoiled oxygen	Oxygen concentration
	Atomic	atom/implanted	introduced by recoil
Element	mass	element ion	phenomenon
B	11	0.0150	1.50 × 1018
P	31	0.0680	6.80 × 1018
As	75	0.1900	1.90 × 1018

Each recoil ratio of hydrogen, oxygen and argon is determined according to the equation (III) as follows:

Hydrogen: R_H=0.0007 (q_H=1)

Oxygen: R_O=0.0277 (q_O=16)

Argon: R_Ar=0.0934 (q_Ar=40)

When argon ions are implanted after the hydrogen ion implantation at hydrogen dose: 6×10¹⁶ atoms/cm² and implantation energy: 50 keV, a relation between implantation dose of argon ions and thickness of oxide film is determined in order that N_D defined in the equation (I) satisfies N_D>4.2×10¹⁴ atoms/cm².

At first, the equation (I) in the implantation of argon ions is represented as follows:

N _D =N _HO +N _ArO +N _ArD  (I)

When N_HO, N_ArO and N_ArD are

N _HO =D _H(hydrogen dose)×t_box(thickness of oxide film)×k_HO(coefficient)  (II)

(where D_H=6×10¹⁶ atoms/cm² and k_HO=4.76×102 8/cm)),

N_ArO=D_Ar(argon dose)×t_box(thickness of oxide film)×k_HO(coefficient) (where k_ArO=R_Ar/R_H×k_HO=0.0934/0.0007×4.67×10²=6.23×10⁴) and

N_ArD=D_Ar, the above equation (I) is

N_D=N_HO+N_ArO+N_ArD=D_H×t_box×k_HO+D_Ar×t_box×k_ArO+D_Ar=4.2×10¹⁴ atoms/cm², from which the implantation dose of argon ions is D_Ar=(4.2×10¹⁴-6.0×10¹⁶×t_box×4.67×10²)/(t_box×6.23×10⁴+1).

Similarly, when oxygen ions are implanted after the hydrogen ion implantation at hydrogen dose: 6×10¹⁶ atoms/cm² and implantation energy: 50 keV, a relation between implantation dose of oxygen ions and thickness of oxide film is determined in order that N_D defined in the equation (I) satisfies N_D>4.2×10¹⁴ atoms/cm².

At first, the equation (I) in the implantation of oxygen ions is represented as follows:

N _D =N _HO +N _OO +N _OD  (I)

When N_HO, N_OO and N_OD are

N _HO =D _H(hydrogen dose)×t_box(thickness of oxide film)×k_HO(coefficient)  (II)

(where D_H=6×10¹⁶ atoms/cm² and k_HO=4.76×10² (/cm)),

N_OO=D_O (oxygen dose)×t_box (thickness of oxide film)×k_OO (coefficient) (where k_OO=R_O/R_H×k_HO=0.0277/0.0007×4.67×10²=1.85×10⁴) and

N_OD=D_O, the above equation (I) is

N_D=N_HO+N_OO+N_OD=D_H×t_box×k_HO+D_O×t_box×k_OO+D_O=4.2×10¹⁴ atoms/cm², from which the implantation dose of oxygen ions is D_O=(4.2×10¹⁴-6.0×10¹⁶×t_box×4.67×10²)/(t_box×1.85×10⁴+1).

In FIG. 5 are shown results obtained by arranging the above adequate implantation doses of argon ions and oxygen ions by the thickness of the oxide film. Although defects are introduced into the active layer by implanting the argon ions or oxygen ions, if the implantation dose is too large, the crystallinity of the active layer is broken and the good active layer is not obtained. From such a viewpoint, there is the upper limit on the implantation doses of argon ions and oxygen ions in FIG. 5. The upper limit is experimentally 1×10¹⁶ atoms/cm² in case of the argon ions and 2×10¹⁶ atoms/cm² in case of the oxygen ions, respectively.

In the method according to the second invention shown in FIG. 6, a wafer 1 for an active layer and a wafer 2 for a support substrate are previously provided (step (a)). Firstly, an oxide film 3 is formed on the wafer 1 for the active layer (step (b)), and ions other than hydrogen such as oxygen ions or argon ions are implanted into the wafer 1 for the active layer up to a position shallower than an exfoliation region of the wafer 1 for the active layer (step (c)). Thereafter, hydrogen ions are implanted into the exfoliation region to form a hydrogen ion implanted layer 4 (step (d)).

Since the implantation of oxygen ions or argon ions is carried out in addition to the implantation of hydrogen ions, oxygen is sputtered from the oxide film by these ions to implant oxygen required for the suppression of void or blister defects into the active layer.

Then, the wafer 1 for the active layer is laminated through the oxide film 3 at the ion implanted side to the wafer 2 for the support substrate (step (e)), and an exfoliation heat treatment is applied to partly exfoliate the wafer 1 for the active layer at the ion implanted layer 4 as a cleavage plane (exfoliation face) (step (f)), and thereafter re-oxidation treatment (step (g)), removal of oxide film (step (h)) and planarization treatment (step (i)) are carried out to produce a semiconductor substrate 7 in which a silicon layer 6 is formed on a buried oxide film 5.

In the above method, the ions other than hydrogen are particularly implanted at the step (c) in addition to the hydrogen ion implantation at the subsequent step, so that the diffusion of hydrogen into the laminated interface at the exfoliation heat treatment of the step (f) is suppressed by oxygen sufficiently sputtered at these steps to suppress the occurrence of voids or blisters, whereby there is obtained the semiconductor substrate having a thin thickness of the oxide film.

Even in the method of FIG. 6, it is preferable to conduct the implantation of argon ions or oxygen ions within the preferable range shown in FIG. 5.

In any methods shown in FIGS. 3 and 6, it is preferable to conduct a plasma treatment for increasing the adhesion strength at the laminated interface prior to the lamination between the wafer 1 for the active layer and the wafer 2 for the support substrate. Since the plasma treatment has effects of activating the laminated surface and removing organic substance adhered to the surface, the adhesion strength of the laminated interface is improved to bring about the decrease of voids or blisters. Moreover, the conditions of the plasma treatment are not particularly limited, but the similar effects can be typically developed by treating the wafers in a gas atmosphere of oxygen, nitrogen, hydrogen or the like for several tens seconds.

COMPARATIVE EXAMPLE 1

According to the method shown in FIG. 1, a laminated semiconductor substrate is prepared by forming an oxide film of 150 nm in thickness on the surface of the wafer for the active layer, implanting hydrogen ions so as to come a peak of the implantation dose (ion implanted layer) to a depth position of 500 nm from the surface of the wafer for the active layer, and then laminating the wafer for the active layer to the wafer for the support substrate and conducting the exfoliation heat treatment to exfoliate the wafer for the active layer at the hydrogen ion implanted peak region (ion implanted layer), and thereafter conducting an oxidation treatment and removing the oxide film and conducting the planarization treatment.

COMPARATIVE EXAMPLE 2

According to the method shown in FIG. 1, a laminated semiconductor substrate is prepared by forming an oxide film of 20 nm in thickness on the surface of the wafer for the active layer, implanting hydrogen ions so as to come a peak of the implantation dose (ion implanted layer) to a depth position of 500 nm from the surface of the wafer for the active layer, and laminating the wafer for the active layer to the wafer for the support substrate and conducting the exfoliation heat treatment to exfoliate the wafer for the active layer at the hydrogen ion implanted peak region (ion implanted layer), and thereafter conducting an oxidation treatment and removing the oxide film and conducting the planarization treatment.

COMPARATIVE EXAMPLE 3

According to the method shown in FIG. 1, a laminated semiconductor substrate is prepared by forming an oxide film of 20 nm in thickness on the surface of the wafer for the active layer, implanting hydrogen ions so as to come a peak of the implantation dose (ion implanted layer) to a depth position of 500 nm from the surface of the wafer for the active layer, and then subjecting the surfaces of the wafer for the active layer and the wafer for the support substrate to an oxygen plasma treatment and laminating the wafer for the active layer to the wafer for the support substrate and conducting the exfoliation heat treatment to exfoliate the wafer for the active layer at the hydrogen ion implanted peak region (ion implanted layer), and thereafter conducting an oxidation treatment and removing the oxide film and conducting the planarization treatment.

INVENTION EXAMPLE 1 (FIRST INVENTION)

According to the method shown in FIG. 3, a laminated semiconductor substrate is prepared by forming an oxide film of 20 nm in thickness on the surface of the wafer for the active layer, implanting hydrogen ions so as to come a peak of the implantation dose (ion implanted layer) to a depth position of 500 nm from the surface of the wafer for the active layer, and further implanting oxygen ions so as to come a peak of the implantation dose to a depth position of 50 nm from the surface of the wafer for the active layer, and laminating the wafer for the active layer at its ion implanted side to the wafer for the support substrate after both the ion implantations, and conducting the exfoliation heat treatment to exfoliate the wafer for the active layer at the hydrogen ion implanted peak region (ion implanted layer), and thereafter conducting an oxidation treatment and removing the oxide film and conducting the planarization treatment.

INVENTION EXAMPLE 2 (FIRST INVENTION)

According to the method shown in FIG. 3, a laminated semiconductor substrate is prepared by forming an oxide film of 20 nm in thickness on the surface of the wafer for the active layer, implanting hydrogen ions so as to come a peak of the implantation dose (ion implanted layer) to a depth position of 500 nm from the surface of the wafer for the active layer, and further implanting argon ions so as to come a peak of the implantation dose to a depth position of 50 nm from the surface of the wafer for the active layer, and laminating the wafer for the active layer at its ion implanted side to the wafer for the support substrate after both the ion implantations, and conducting the exfoliation heat treatment to exfoliate the wafer for the active layer at the hydrogen ion implanted peak region (ion implanted layer), and thereafter conducting an oxidation treatment and removing the oxide film and conducting the planarization treatment.

INVENTION EXAMPLE 3 (SECOND INVENTION)

According to the method shown in FIG. 6, a laminated semiconductor substrate is prepared by forming an oxide film of 20 nm in thickness on the surface of the wafer for the active layer, implanting oxygen ions so as to come a peak of the implantation dose to a depth position of 50 nm from the surface of the wafer for the active layer, and further implanting hydrogen ions so as to come a peak of the implantation dose (ion implanted layer) to a depth position of 500 nm from the surface of the wafer for the active layer, and laminating the wafer for the active layer at its ion implanted side to the wafer for the support substrate after the implantation of both the ions, and conducting the exfoliation heat treatment to exfoliate the wafer for the active layer at the hydrogen ion implanted peak region (ion implanted layer), and thereafter conducting an oxidation treatment and removing the oxide film and conducting the planarization treatment.

INVENTION EXAMPLE 4 (SECOND INVENTION)

According to the method shown in FIG. 6, a laminated semiconductor substrate is prepared by forming an oxide film of 20 nm in thickness on the surface of the wafer for the active layer, implanting argon ions so as to come a peak of the implantation dose to a depth position of 50 nm from the surface of the wafer for the active layer, and further implanting hydrogen ions so as to come a peak of the implantation dose (ion implanted layer) to a depth position of 500 nm from the surface of the wafer for the active layer, and laminating the wafer for the active layer at its ion implanted side to the wafer for the support substrate after the implantation of both the ions, and conducting the exfoliation heat treatment to exfoliate the wafer for the active layer at the hydrogen ion implanted peak region (ion implanted layer), and thereafter conducting an oxidation treatment and removing the oxide film and conducting the planarization treatment.

INVENTION EXAMPLES 5-8

In these examples, the same procedures as in Invention Examples 1-4 are repeated, respectively, except that the surfaces of the wafer for the active layer and the wafer for the support substrate are subjected to an oxygen plasma treatment prior to the lamination between the wafer for the active layer and the wafer for the support substrate. Moreover, the plasma treatment is carried out under condition that the wafers are kept for 20 seconds after the interior of the reaction chamber replaced with oxygen gas is rendered into a vacuum state.

With respect to the thus obtained semiconductor substrates, the defect number is visually measured under a high-intensity light-gathering lamp or a fluorescent lamp. The results are shown in Table 2. As seen from Table 2, the occurrence of defects is suppressed in the semiconductor substrates according to the invention even when the buried oxide film is thin or the oxide film is not existent. Moreover, it is preferable to previously implant ions other than hydrogen because when hydrogen ions are previously implanted, the organic substance existing on the surface of the wafer is liable to be fixed on the wafer to fear the occurrence of the blisters. More preferably, the wafer after the implantation of ions other than hydrogen is cleaned to conduct the hydrogen ion implantation.

	TABLE 2
					Defect
	Thickness				number
	of oxide	Ion	Ion	Plasma	(defects/300 mm
	film (nm)	implantation 1	implantation 2	treatment	wafer)
Comparative	150	H	—	—	not more
Example 1					than 2
Comparative	20	H	—	—	50
Example 2
Comparative	20	H	—	◯	30
Example 3
Invention	20	H	O	—	not more
Example 1					than 10
Invention	20	O	H	—	not more
Example 2					than 2
Invention	20	H	Ar	—	not more
Example 3					than 10
Invention	20	Ar	H	—	not more
Example 4					than 2
Invention	20	H	O	◯	not more
Example 5					than 5
Invention	20	O	H	◯	not more
Example 6					than 1
Invention	20	H	Ar	◯	not more
Example 7					than 5
Invention	20	Ar	H	◯	not more
Example 8					than 1

Claims

1. A method of producing a semiconductor substrate, which comprises the steps of forming an oxide film having a thickness of not more than 50 nm on a wafer for an active layer forming a silicon layer, implanting hydrogen ions into the wafer for the active layer to form a hydrogen ion implanted layer, implanting ions other than hydrogen to a position that a depth from the surface side the hydrogen ion implantation is shallower than the hydrogen ion implanted layer, laminating the wafer for the active layer through the oxide film to a wafer for a support substrate, and then exfoliating the wafer for the active layer at the hydrogen ion implanted layer (first invention).

2. A method of producing a semiconductor substrate, which comprises forming an oxide film having a thickness of not more than 50 nm on a wafer for an active layer forming a silicon layer, implanting ions other than hydrogen into the wafer for the active layer to a position shallower than an exfoliation region of the wafer for the active layer, implanting hydrogen ions into the exfoliation region to form a hydrogen ion implanted layer, laminating the wafer for the active layer through oxide film to a wafer for a support substrate, and then exfoliating the wafer for the active layer at the hydrogen ion implanted layer (second invention).

3. A method of producing a semiconductor substrate according to claim 1 or 2, wherein a plasma treatment is carried out prior to the lamination of the wafer for the active layer and the wafer for the support substrate.