JPS5834914A - Mask for selective diffusion - Google Patents

Abstract

PURPOSE:To obtain a mask having good blocking capability to the diffusion of impurities and preventing composition elements from invading into host crystal by a method wherein multilayer structure is made by using three kinds or more of thin films such as an SiO2 film, a phosphorus glass film, an SiO2 film which are coated from the surface of Ge crystal. CONSTITUTION:An SiO2 film 2, a PSG film 3 and an SiO2 film 4 are provided as the first layer, the second layer and the third layer respectively. The first layer, SiO2 film 2 is for preventing phosphorus in the PSG film 3 from diffusing in Ge crystal. The second layer, PSG film 3 is also the film for preventing the diffusion of Zn. The third layer, SiO2 film 4 is provided with the purpose of a protective film to the moisture-proof PSG film 3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides semiconductor crystals such as Si, GaA, I
This relates to a diffusion mask used in the selective diffusion process of impurities such as ZP, Cd, B, etc. to nP, etc.
The object of the present invention is to provide a mask that has good S blocking ability against diffusion of impurities and prevents elements constituting the mask from penetrating into the host crystal during the diffusion process.

The basic function of a diffusion mask is to prevent impurities from being diffused to other than the intended location when diffusing into the host crystal.
Control of the diffusion depth should not be affected by unnecessary thermal stress or crystal imperfections at the interface between the host crystal and the diffusion mask, and impurities in the mask itself should not be diffused into the host crystal. etc.

Conventionally, for these purposes, 8i0n* 8i,N,
, +J Ngara! Single layer films such as x(P2O) are often used. However, several drawbacks have been pointed out in these single-layer films. As a typical example, a case will be described in which Zn is diffused as a P-type impurity into an n-type Ge single crystal, and the points improved by the present invention will be described in detail with reference to the drawings.

Figure 1 shows an nmGe single crystal (8b doped n~lX101an) with a thickness of 2000 cD formed by KCVD method.
The depthwise concentration profile of Zn in a sample in which Zn was diffused through an 8i0° film by heat treatment at 650° C. for 40 hours was measured using a secondary ion mass spectrometer (SIMS). As seen in the figure, Kanashi's Z passes through the Si pseudomembrane.
It can be seen that n is diffused into the Ge crystal.

This infiltration of Zn can also be reduced by increasing the thickness of sto and g; however, as the film thickness becomes thicker, thermal stress inevitably increases at the interface with the semiconductor), and the junction depth exceeds the design value. It becomes difficult to obtain the desired value. In addition, this imperfection at the interface is caused by the horizontal spread of impurities at the mask and semiconductor interface, which promotes the diffusion of impurities.
Furthermore, dislocations may occur, which is very inconvenient in terms of device reliability.

Figure 2 shows that Zn is passed through a double-layer film of n-type Ge single crystal formed by CVD and heat-treated for 650 to 40 hours.
Depth direction and concentration of za and P in the diffused material! The fill was measured using 8IM8. As seen in the figure, Zno diffusion is blocked by the P2O film, but it is clear that a large amount of phosphorus in the phosphorus glass film is diffused into the Ge crystal.

Therefore, since the donor yield within the Ge crystal varies widely, the subsequent process 1i! Therefore, even if a P-type impurity is introduced by diffusion or ion implantation, the junction position cannot be controlled as designed. From the above 1)
8i0. The stopping power of Zn is weak with only a film, 2) P2O
Although the stopping power of Zn is weak when used as a film alone, it was found that phosphorus in the P8G film diffuses into the GC crystal and disturbs the bonding position.

However, what should be noted in Figure 2 is the phosphorus in the PEG film.
Although it diffuses into the pGe crystal, 8i0 on the surface hardly diffuses into the film.

Therefore, based on the above properties and the experimental fact that the PSG film inhibits Zn diffusion, we fabricated the Ilt diffusion mask shown in FIG. 3. This is to prevent phosphorus in the first layer of SiO and PSG film 3 from diffusing into the Ge crystal. The second layer PEG film 3 is also a film for preventing Zn diffusion, and has a phosphorus content of 7%. The thirty-first 5in2 film 4 serves as a protective film for the hygroscopic PSG film 3. The selective diffusion window 5 was formed by photolithography. The thickness of each layer is 8i0
2 membranes 2. : 500AP S GI [3: 2000A
, Sin! Membrane 4: 100OA ◎Figure 4 shows
Using a diffusion mask with the above structure, 650'O=40
This is the depth profile of Zn and P in the sample when hOZn is diffused.

Zn is in the third layer 8i0. Although the width is considerably diffused, it can be seen that most of it is deposited within the second layer P8G film. This is due to the strong chemical getter action of PSG. It is also understood from this figure that phosphorus in the PSG film does not diffuse into the Ge crystal due to the action of the 8i01 film of the first layer. 1st rft! The thermal W* coefficient of the 8i0° film is quite different from that of the ae crystal (Ger 5.7
10 deg 8i02: 0.4XIT) @
deg'), so it is preferable that the first layer be as thin as possible, and as a result of experiments in which the thickness of the first layer was varied, it was found that a thickness of about 5,000 degrees has a sufficient blocking power against phosphorus. Note that it is also effective to use a material whose thermal expansion coefficient is close to υGe, such as Si, N, or a film.

The diffusion mask according to the structure of the present invention can diffuse not only Zn to Oe, but also impurity diffusion to 8i, GaAs, InP, etc., for example, P-type impurity 8e such as Cd, Mn, Mg, etc.
A similar effect is expected for n-type impurities such as Te.

Selective diffusion of impurities is an important technology for all semiconductor devices with localized active regions, and the effects of the present invention are extremely large.

[Brief explanation of the drawing]

Figure 1 shows 8i0. SIMS profile of Zn in the depth direction of a sample in which Zn was diffused into Ge through a single layer film. Figure 2 shows Z to Ge through PSO,5i022 layer
Depth profile of Zn and P obtained by SIMS of a sample subjected to n diffusion. FIG. 3 is a cross-sectional view of a selective diffusion mask composed of three layers of SiO, PSG, and Sin. FA LCh v> Te, 1 is ()e crystal, 2 is 5iO
JJ, 3 is PSG film, 4 is 8i0. The membrane 5 is a selective diffusion window. Figure 4 is 8i0. , P S G, S T of the sample in which Zn was diffused into Ge through the 3-layer 5in2 film.
Zn and pomg direction profiles according to is■S. Figure 1 rtc to Lng Deptk Raku 3 Figure 41 + Figure rtC to 1rLfDQ1yL

Claims (1)

[Claims] There is a surface layer 1 (8i0. film, a phosphorus glass film in the intermediate layer, and a Vc8i0. film at the interface with the semiconductor crystal. Selective diffusion characterized by having a thin film of at least 3111 m or more and having a multilayer structure. mask.